- Email: [email protected]
136Xe(13C, 4nγ) reaction study of 145Nd
Nuclear Physics A456 (1986) 317-336 @ North-Holland, Amsterdam
‘36Xe(‘3C, 4ny)
REACTION
STUDY
OF 14%d*
P. TARAS Dgpartement de Physique, Universite’ de Montreal, Montreal, Canada A. LARABEE’ Tandem Accelerator Laboratory, M&faster
University, Hamilton,
Received 4 February (Revised 3 Fabian
Ontnrin, Canada
1985 19863
y-ray spectroscopy with Abstract: Yrast and close to yrast states in 145Nd are studied by in-beam f f G?) level (%‘, 4n-y) reaction on enriched, solid ‘36Xe targets. A part of the rich medium-spun structure observed can be characterized to befong to shell mode! muitiplets vf:,,, vhs/zf3,1 and uf& x 3-. The vfq12 multiplct in N = 85 odd isotones from Nd to Er is calculated within the de-Shalit scheme using empirical two nucleon interactions. The energies are not well reproduced, but the deviations from experimental values behave regularly from isotone to isotone. The energy systematics of the vh9,2f:,2 and vf:/, x 3- multiplets in the N = 85 odd isotones is compared in details to that of the vf;,, multiple& in the corresponding even N = 84 isotones and of the uf:,2 multiple& of the N = 85 odd isotanes, respectively. -. ..- .._‘36Xe(‘3C, 4ny), E = 49-60 MeV; measured E,, r,(E), Nd deduced levels, J, 71: Pulsed beam, enriched solid
I,( ff ),
1, Introduction The quality
of the phenomenological shell model ‘) in the vicinity of the closed ‘46Gd has been extensively tested by several authors after the of Kleinheinz et al. “). The model is able to reproduce well both spin properties of the nuclei one and two nucleons apart from the the N = 85 odd isotones from 14’Sm to ‘%r studied recently 4-9)
shell ‘) nucleus pioneering work low and medium 14%d core. Even
* Financial support provided by the Natural Sciences and Engineering Research Council of Canada. ’ At present employed by the Academy of ~j~l~n~. Present address: ~nst~tut fiir Theoretisc~e Physik, ~~~versit~t T~binge~, T~~inge~, FRG. ’ permanent address: repayment of Physics, Simon Frazer university, Burn&y, BC, Canada. 3 Present address: Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA. 0375-9474/86/$03.50 @ Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
318
display
E. Hammare’n et al. / 14XNd
at least qualitatively
the characteristic
features
of the main particle
multiplets
expected to appear. The lowest shell model multiplets vf:,,, Vhgl,f:,2 and vf:,, x 3have been identified from Sm to Er with a surprisingly stable behaviour of relative energies inside a given multiplet. The only N = 85 isotone in the proton holes side with respect to the 146Gd core, where the above mentioned multiplets have been observed 4,5) is 14’Sm. In addition the experiments show ‘) for r4’Sm a group of medium spin levels, which are not seen in the heavier isotones and are consequently believed ‘) to have a two proton holes origin. The two additional proton holes of ‘45Nd could be expected to enhance possibilities to observe such excitations close to the yrast states. It has also been argued lately lo) that the polarizing effect of the neutrons added to the 146Gd core should be particularly pronounced in the proton holes side of the region in question. Excitations more collective in nature could be expected to appear in ‘45Nd at medium spins already. A study of the medium spin properties of ‘45Nd would be needed to find out whether the shell model type neutron multiplets still appear systematically here, quite apart from the ‘46Gd core, or whether the four proton holes dominate the structure in terms of particle multiplets or in appearance of (quasi) collective excitations. Unfortunately, the interesting medium and higher spin states of neutron rich nuclei, such like ‘45Nd, have conventionally remained experimentally untouched because of the lack of suitable, easily available target beam combinations. The amount of low spin data known previously for ‘45Nd (see sect. 3) is typical for such nuclei. We report here of the in beam y-ray study of ‘45Nd observed in bombardment of 136Xe target with “C ions. Depending on the bombarding energy one would expect to populate in such an experiment preferentially medium and high spin states. At the same experiment we have also acquired reported elsewhere. In sect. 2 we describe the method into a solid target together with other more standard will be dedicated
to discuss
in details
data for 146Nd, results being used to freeze the 136Xe gas experimental details. Sect. 3
some crucial
level scheme. The shell model content apparent together with systematics found for the heavier
2. Experimental
details
points in the construction of the in ‘45Nd will be discussed in sect. 4 N = 85 isotones.
and results
The high spin excitations in ‘45Nd were populated with 13C bombardment of a solid Xe target. The target was prepared by freezing enriched ‘36Xe gas on Pb backing (0.033 g/cm*) held at low temperatures. The Pb beam stopper was mounted on a copper gold finger (0.445 g/cm*). A commercial, small liquid-helium compressor was used to maintain temperature low enough to reduce the partial vapour pressure of Xe well below typical pressures used in beam lines. As a result of a 2h precooling time the 5 mg of ‘36Xe gas frozen on the Pb backing formed a 5 mg/cm’ thick in the beam. It is well to note that the (0.4 cm’) target of ‘36Xe ice fluorescent
E. Hammar&
1
I
1
el; al. / ‘45Nd
I 1800
I
1600
CHANNEL Fig. 1. y-ray
singles
spectrum
observed
during
,
I 2000
N~M~~~
~omba~drn~~~
of ‘j6Xe with 50 MeV 13C beam.
320
(4
4 163.5
23/2*
. 2112'
318.8
519.2
I.--
._
52
56
21/z% --m.1912-
637.9
19/Z- --- 1712"
9L6 3
19/2-
- Is/z-
657.7
11/z-
+ 712-.--1
I
60
E 13c (MeVI
598.7
52
Fig. 2. Relative
excitation
56
~~n~t~ons for y-rags
657.7
II/ 2- --* ?f2_
7OL.L 262.6
IUP-11/2(" 11/2++9/2-
3533
11/21+'-11/2-
60
decaying
through
~a~icu~~r
cascades
in 14*Nd.
r-(
P-
2o
Y t2
522.6
21/2-- 17/2-
380.3
2512--2112-
699.2 769.9
13&r91213/2---11/z11/2-- 9/2-
1.5
k!
1.0 52
56
60
/
LlJ
/ ,/’ -i I’ ,,>.”
3
tQ
E 13c
(MN
299.1. 33/z'--+ 31~’
g 5.0 -
--I
I.0 -
I
101jfJ.531/2*-w 271’2% 380.3 25/2---r2112+ 659.7 11/2---c9/2I
1
52
56
60
Fig. 2-continued
E,3c (MN
E. Hammart+~ et al. / I45Nd
322
TABLE y
transitions Angular
E, (keV)
Iy”) (0 = 125”)
distribution coeff. “)
‘4, 72.5 90.6 163.5 186.6 246.8 255.9 262.6
279.4 290.1 308.5 318.8 353.3 380.3 385.2 445.5
in 14sNd observed
Assignment s E, (keV)
A,
-0.10 -0.29
(3) (5)
-0.01 (3) 0.02 (7)
9
-0.21
(2)
0.00 (2)
5 5 19 6 5 12
-0.28 -0.21 -0.29 0.06 0.13 0.35
(7) (3) (2) (3) (5) (4)
0.05 0.02 0.00 0.01 -0.01 -0.13
(9) (4) (2) (3) (5) (4)
4847.6 1401.3 1709.9 3349.1 1011.0 2914.7
-0.10
(5)
-0.70
(30)
2866.8
0.15 (24) -0.03 (1) -0.24(11)
-0.70 (30) -0.02 (1) 0.04 (13)
1111.2 2866.8
8 16
-0.10 (4) 0.34 (2)
0.03 (5) -0.11 (3)
8 26 13
0.23 (5) 0.26 (2) -0.21 (3)
-0.03 -0.08 -0.00
$2 1 S30 3
610.5 632.1 631.9 657.7
15
Comment
r:+1;
72.5 748.3 3030.3 2534.4 3517.2 4211.4 1011.0
11 2
448.2 453.5 458.6 498.4 519.2 522.6 568.9 584.1 598.7 603.0 609.2
+0.05 -0.07
-0.11
-0.03 -0.05 -0.12 f0.19 -0.23
seen only in coinc’s seen only in coinc’s 162.2 keV in ‘44Nd 185.6 keV in ‘“Nd; d, seen only in coinc’s seen only in coinc’s mainly due to this = 262 keV assignment; also in ‘46Nd; ‘) 280.5 keV in ‘46Nd d, *) ‘) 379.2 keV in ‘43Nd; d, c.d) mainly due to 445.2 keV in ‘46Nd y53.9 keV in ‘46Nd
-0.03 ‘)
4 100
(6) (2) (3)
+0.07 d, seen only in coinc’s *I d, 0.0 resolved from 610.5 keV by coinc’s
-0.00
(3)
2011.8
-0.11
-0.25 (5) 0.26 (1)
-0.01 -0.08
(6) (1)
2347.6 657.7
0.0
-O.Ol(ll)
-0.11(13)
2
679.2 691.1 704.4 711.2
5
0.34 (4)
-0.11
(5)
5 21
0.20 (8) 0.24 (2)
-0.03 -0.09
3 47
2866.8 2534.4 6081.4 2011.8 1709.9 3517.7 3030.3
(3)
-0.28
664.9 675.7
715.3 132.6 743.6
1
in the ‘36Xe(‘3C, 4n) reaction
0.25 (5) 0.26 (1)
-0.15 -0.08
d, ‘) less than 1% belongs to luNd or to ‘43Nd
5512.5 148.3
resolved by coinc’s from 676.0 keV in ‘46Nd d, seen only in coinc’s
(10) (2)
1427.6 3961.5 1715.4 2421.1
(7) (1)
1726.3 4081.7 1401.3
seen only in coinc’s 732.6 keV also in ‘46Nd
d,e d)’
(f)+y y-+ +-
*)
Angular E, (keV1
Jya) (8 = 125”)
distribution coeff. b,
s
8 7
0.64 (5) -0.23 (3)
16 7
0.27 t 3) 0.20 (4)
-0.07 -0.10
(3) (Sf
4
0.18 (51
-0.05
(61
748.3 1427.6 2546.8 3270.4 2347.6 24082
-0.08 (6) 0.05 (3)
4568.2
+?,&2 3 UC+, ,&+ ZZ” ,I!$> 19’11 +1_zz +27 4. 2
f‘u2
“) Relative intensities measured at 56 MeV bombarding energy. resolved peaks <30/u. h, Errors indicated for the last figures are pure fit errors only. but not placed ‘) Transition assigned to ‘45Nd by coincidences, d, The parity of the parent state is assigned by assuming that the is an electric one. “) The parity of the parent state is assigned tentatively based on
the experiment by releasing the He-~oo~~~g and down with lilted nitr~g~o. The experiment consisted of a standard set of ‘%Z beam from the MP Tandem of Chalk River tion functions were measured at beam energies coaxial Ge(Li) detectors (50 cm3 with 1.8 keV 90” angles to the beam.
A sample
spectrum
Comment
I: -, ry
E, (keV)
A,
A2 748.3 769.9 831.4 849.3 946.3 1~7~~ 10~~.5
Assignment
training
1.2 0.0
d,
seen only in coinc’s d, dl seen only in coinc’s
Typical
errors
in intensities
to the level scheme. depopulating quadrupole systematic
arguments
of well
transition
only.
Xe into a container
cooled
in-beam measurements using pulsed Nuclear Laboratories. y-ray excitaof 49, 52, 56 and 60 MeV with two FWHM for 6oCo) placed at 0” and
is shown in fig. 1 and the results
for the
excitation functions are summarized in figs. 2a-d. The bombarding energies were chosen to cover both 3n and 4n reaction channels populating 146Nd and 14’Nd, respectively, The analysis indicates that one extra value at lower and two more values
at higher
beam
energy
would
have been
desirable
for a more
convincing
result, especially for high spin states of ‘45Nd. Angular distributions of y rays were measured in 15” steps from 0” to 90” using 56 MeV 13C beam. The normalization of the spectra measured at seven angles was done by photo-peak areas of primary y rays measured with a detector placed at 55” to the beam. The areas of the photo-peaks recorded with the movable detector were carefulty corrected for absorption effects caused by the Pb backing and the Cu gold finger. The normalized intensities were analyzed as customary with second order Legendre polynomials and the resulting coefficients A, and A4 are given in table 1. The angular distribution data was also used to define the relative intensities of y transitia~s of table 1. Thus each intensity indicated corresponds to a value
E. Hammarin
324
et al. / L45Nd 2
TABLE
The y-y coincidences
for ‘45Nd at 60 MeV bombarding
observed
Gate [keV]
Coincident
y-transitions
energy
“) [keV]
262.6, 675.7
13 163.5
308.5,318.8,426.7 657.7, (1180.9)
185.6 b, +186.6
b),445.5,453.5,458.6,476.7
696.5 b), 711.2,
732.4,
743.6,
b). (498.4),
(754.0)
519.2, (598.7),617.8
b), (769.9),
796.9’),
946.3,
b), (637.9), (1007.9)
‘),
b,
(162.2) b), (246.8),
308.5, 314.6 b), 327.1 ‘), 372.4 b), 380.3,
426.8 b), 476.8 b), (504.5) ‘),
514.4 b). 617.8 b), 657.7,
696.5 b), 711.2”),
743.6,
753.9 b),
849.3 ‘), 946.3, 997.6 ‘) 246.8
(308.5),
453.5,
262.6
(380.3),
(453.9)‘),
(598.7),
279.4
380.3,
453.5,
(769.9),
522.6,
(817.6)
290.1
308.5, (380.3),
308.5
(163.5),
657.7.
711.2,
(474.7)‘), 568.9,
‘), 849.0 453.5,
(290.1),
849.3,
(657.7), (584.1),
(946.3)
675.7,
704.4,
(711.2),
748.3,
(598.7),
603.0,
(610.5),
657.7,
831.4 664.9,
711.2,
743.6,
1050.5
(4+6x657.7>->
318.8, (426.2)‘),
711.2, 849.3, (946.3)
(453.5),
(476.9) ‘), 657.7,
(664.9),
691.1, 711.2, 743.6,
849.3 318.8
163.5,
(279.4),
743.6
946.3
(308.5),
(453.5),
(458.6).
(444.4)
380.3
(186.6),
385.2 d,
610.5 3-I 657.7 664.9, 679.2, (711.2) ,A> 743 6 769.9, 950.2 ‘), 1050.5 598.7, (609.2), 657.7, (711.2). 743.6
445.2 ‘)
(163.3),
448.2 d, 453.5
280.5 ‘), (308.5).
(453.5),
598.7, 623.6’),
295.2 ‘), 380.3,
(473.5) “), (522.6),
249.5 ‘), (255.9),
318.8,334.0 (637.9),
676.4e),
(711.2),
(280.5)
‘), 290.1, (308.5)
743.6
(474.7) ‘), 511.8 ‘), (519.2),
(699.0) ‘), 711.2,
163.5, (308.5), 163.5, 318.8,
519.2
318 8 (425.7) ‘), 453.5, 637.9, 657.7, 732.6, 743.6, 946.3 -,163.5 ____L_, (279.4), (318.8), 380.3, 584.1, 603.0, 610.5, 640.4’), 657.7, 679.2, (691.1),
568.9
(163.5), (279.4),
589.6’),
598.7,
657.7, 743.6,
1007.0
(425.7) ‘), 453.5, 522.6, 657.7, 743.6 743.6, (748.3),
1050.5 (318.8),
657.7, 664.9, 584.1
(598.7),
(522.6),
(732.7) ‘), 736.7 ‘), 849.3
458.6
769.9,
(453.5),
603.0,
743.6, (791.0) ‘)
498.4 d, 522.6
318.8,
(691.1),
657.7, 711.2, 736.7’),
657.7,
(445.5),
568.9, 584.1, (598.7),
474.7 ‘), 511.8 “)
649.4’),
(279.4).
‘), 380.3, (385.2),
657.7,
(514.2) ‘), 522.3,
380.3 ‘), 453.8’),
we),
(163.5), “)
704.4, (831.4)
279.4, (295.5) “), (308.5),
(522.6)‘),
+445.5
711.2 1;)732 6
519.2, 598.7, 609.2 1-, 657.7
353.3
+453.9
‘), 657.7,
425.9’),
(341.0)‘),
(711.2),
380.3,
743.6,
3JO.3, (458.6),
(385.2),
(519.2),
(522.6),
(598.7),
(603.0),
(610.5),
1050.5
522.6,
(568.9),
603.0, 657.7, (664.9),
679.2, 711.2 ‘), 748.3, 769.9,
(1050.5) 598.7
(163.5),
603.0
279.4,
(279.4), (330.0)
(318.8),
‘),
(341.0) ‘), 380.3 1-1-F 453.5 657.7 (691.1), 711.2, (743.6) ‘), 849.3 (360.5) ‘), 380.3, 453.5, 522.6, 568.9, 584.1, 610.5, 657.7,
(341.0) ‘),
664.9, 679.2, 743.6, (748.3), 610.5 +609.2
(163.5), 522.6
(279.4), (568.9),
(308.5),
770.2’),
(318.8),
(1035.9)
‘),
1050.5
(360.3) ‘), 380.3,
(583.5) ‘), (598.7),
453.5
603.0, (610.5) ‘), 657.7,
(664.9),
711.2, (732.7),
743.6,
(1050.5) 632.1 d,
(453.5),
657.7,
(711.2),
(743.6),
631.9
(163.5),
308.5,
(318.8),
453.5, 519.2, 657.7, 743.6
657.7
163.5,
(279.4),
(290.1),
(295.5) ‘),
(466.4) ‘), 519.2, 522.6, (568.9), (691.1),
711.2,
(732.6),
(849.3)
743.6,
308.5
318.8,
(584x:89.6) 769.9, (795.7)
380.3,
‘), 849.3, 946.3,
664.9
163.5, 279.4, 380.3, 453.5, (522.6),
568.9, (603.0),
679.2
(380.3),
(522.6),
(584.1),
(748.3)
691.1
(255.9),
(308.5),
453.5, (598.7),
704.4
262.6, 353.3, (476.9)
(675.7),
353.3,
‘),598.7,603.0,610.5,
425.9 ‘) 2-7 453.5 (458.6), (616.9) ‘), (664.9),
(1007.0),
657.7, 711.2, 743.6, 849.3
‘), 657.7, (675.7).
(748.3),
(1050.5)
(616.2) “), 657.7, (704.4),
(790.7) ‘), (831.4)
743.6, 1050.5
E. ~a~~ar~n TABLE
711.2 715.3 743.6 748.3 769.9 849.3 946.3 1050.5
325
2-continued
Coincident
Gate [keV]
et al. / ‘05Nd
y-transitions
“) [keVj
(163.5), m, 318.8, 329.5”), (353.3), (380.3), (445.5), 453.5, 598.7, (609.2), 657.7, 691.1, 743.6, 849.3 262.6, 353.3, (657.7), (675.7), (748.3) 163.5, (279.4), m, 318.8, 380.3, (38X?), (458.6), 519.2, 522.6, (568.9), 603.0, 610.5, (637.9), 657.7 (664.9), (691.1), 711.2, (74X9)‘), (849.3), 946.3, (1007.0), 1050.5 262.6, 380.3,;84.1~ (704.4), (83 1.4) 380.3, 522.6, 584.1, 603.0, 64X4”), 657.7 (255.9) ,&I 308 5 329-5 ‘f, 340.5 =),453.5,598.7,637.7 “),657.7,691.1,711.2. (716.4) “), 743.6 163.5, 318.8, rrso.3), 519.2, 657.7, 743.6, (1050.5) 279.4, 380.3, 522.6, 568.9, 603.0, 610.5, 657.7, 743.6
“) Coincidences are classified to three categories: weak (in ~a~~~tb~ses), clear (bare number) and strong (underlined); compare with examples in fig. 3. b, Transition in ““%Jd. ‘) Coincidence cannot be explained due to the present assignment in 145Nd or due to known contaminant transitions, d, Transition belongs to 14’Nd but is not located in the level scheme. ‘) Transition in ‘46Nd. ‘) Transition in *43Nd.
averaged over seven independent measurements with proper account of the variation of the intensity with angle as observed experimentally at 56 MeV of beam energy. The angular distributions measured for the entire period of 90” make the values of the A, coefficients reliable. A smaller ~~~e~a~~ty of a A4 coefficient in turn allows a more reliable prediction for the multipole mixing ratios, preferentially S( E2JMl). Thus we have extended the analysis of some angular distributions to predict these ratios as well; results are given in table 1. These fits have also been used to determine spins of levels involved. We carried out two coincidence experiments, both with four parameters (E,E,, tYY, t,beam), at beam energies of 52 and 60 MeV primarily for 146Nd and 14’Nd, respectively.
However,
it turned
out that the complementary
information
of the two
experiments was crucial to distinguish between close doublets formed by y rays belonging bo the two deferent final nuclei. In these experiments the detectors were situated at 0” and 90” and they were shielder against mutually back scattered y rays. The results for ld5Nd are summarized in table 2, The ~o~n~~den~e data did not indicate any delayed ( TIi2 > 2 ns) transitions associated to 14’Nd. The coincidence relationships summarized in table 2 and examples shown in fig. 3 are obtained with timing conditions set over prompt events both with respect to the tybeamand to t,,. 3. Level scheme of ‘*‘Nd The low spin states of ‘45Nd have been recently studied in the P--decay of ‘4SPr by Jackson and Meyer ‘I). From transfer reaction investigations for ‘45Nd relevant for this work are the recent (“He, cy) pick-up experiment by ~0vh0~de~ et al. 12) and
325
m
GATE 522.6
z m -Qrn
keV
f-=
610.5+~609.2)
ke’
E. Hammarin
the (d, t) study
of Ardal
321
et al. / 14’Nd
et al. 13). The results
of these
experiments
useful
in the
present analysis are the energies, spin and parity assignments of the iP 0 keV, $72.5 keV, y- 657.7 keV, tP 748.3 keV, y- 1011 keV and 2’ 1110 keV states through which all the feeding
from the 25 new higher
spin states observed
decays.
The level scheme of ‘45Nd shown in fig. 4 is constructed first of all based on coincidence relationships of table 2 including the strengths of coincidences indicated roughly in table 2 as well. Two more natural ingredients have been the singles y-ray intensities of table 1 and the excitation functions of figures 2a-2d. The spins have been determined with a standard method by fitting theoretical angular distributions to experimental data looking at all possible spin combinations in cascades of two consecutive transitions. The multipole mixing ratios were determined by defining the nuclear alignment as a function of spin from known transitions in contaminant reaction products (mainly 143Nd and ‘44Nd). As a result of the rather high quality angular distribution data firm spin assignments could be made for a fairly large fraction of the observed levels. Since we did not measure the linear polarizations of the y-rays - a high quality conversion electron experiment using the present frozen target on a thick packing is not possible - parities were determined by assuming that clean quadrupole transitions are electric ones. This assumption, though supported by the short lifetimes ((2 ns) of the y-rays, should be taken with some caution bearing in mind the richness of possibilities associated with nuclei having noncollective, irregular (multi)particle excitations. The result of the analysis is summarized in table 1. In the following we will comment on few crucial and less straightforward cases met in the construction of the level scheme. The spin and negative parity of the y- 1011.0 keV level was in ref. I’) deduced from its y decay to lower spin negative parity states. Especially crucial for the parity assignment with intensity
is the preferentially
E2 transition
Z, (1011.0 keV) = 1.6 compared
262.9 and 353.5 keV transitions,
respectively.
to the $- ground to the intensities
state observed
I’)
I’) 13.2 and 7 of the
We have not observed
the 1011.0 keV
y ray with an upper limit of Z, < 0.2 for the intensity in the previous units. Consequently the parity of the 1011.0 keV level could be plus or minus. The present angular distribution data of the 262.6 and 353.3 keV transitions is unique with the analogue dipole transitions decaying from the 7’ 873.5 keV state in 149Gd [ref. “)I. Although we cannot exclude the negative parity with arguments based on intensity balance, similarly to ‘49Gd, we assign tentatively positive parity for the 1011.0 keV level. The pure quadrupole 704.4 keV transition defines further I” = y(+) for the 1715.4 keV state. The 83 1.4 keV transition in the same cascade is seen in coincidences only. In addition to the corresponding states in 149Gd this sequence of positive parity states is also in details similar to the recently newly interpreted ‘) y’+) 931.9 and y(+) 1762.3 keV states in 14’Sm. The parity of the 1111.2 keV state cannot be deduced from the present experiment, since the 453.5 keV y ray feeding the yP 657.7 keV state is within detection resolution
2
L
Fig. 4. Leveli scheme of ‘@Nd observed in the 136Xe(“3C,4x1~) reaction. Relative intensities of y-rays observed at 56 MeY are indicated by the thickness of the arrows. Clear quad~~ole (E2) transitions are supplemented with open squares (01. Shell modei co~~~o~t~~ns indicated are discussed in the text.
vh 9/2
E. Hammarth et ai. f “‘Nd
to the 453.9 keV E2 ground
state transition
339
of ‘46Nd present
with an equal intensity
at 56 MeV bombarding energy. The almost uniform angular distribution observed for the doublet is consequently in agreement with the y!’ assignment for the 1110 keV state observed in the C3He, LY)pick-up reaction study 12). Furthermore, in (jHe, cry) coincidence study 14) a 453.5 keV y ray was seen coincident I.1 10 keV cu-group. Thus the I” = y’ assignment for the 1111.2 keV state The stretched 593.7, 711.2 and $49*3 keV E2 transitions are used to define $I’ and ‘3” sequence on top of this l;’ excitation.
a recent with the is firm. the l?s7_+,
The spins of the ?‘I 2408.2 keV and y 2866.8 keV levels are based on the pure dipole nature of 519.2 keV and 458.6 keV y transitions. The 445.5 keV transition is too close in energy to be separated from the 445.2 keV transition in 146Nd, The tentative parity assignment for the I$!“’ state is in agreement with the life-time limit (T,,, < 2 ns) for the 2408.2 keV state preferring E2 for the 1007,O keV transition. The parities in the cascade above the 2866.8 keV level up to the F 408 1.7 keV state cannot be specified even tentatively. he spins and parities of the cascade starting from the z- 748.3 keV state are well defmed up to the yP 2914.7 keV state. The 603.0 keV trans~tjo~ is pure dipole and the 1050.5 keV one a pure quadr~pole fitting well to a cascade $t-+ F --, F”-.
4. ~~elI-rn~d~~ excitations
of N =85 odd-mass isotanes
We will discuss in the following the observed decay scheme of “‘Nd in fig. 3 mainly in the light of comparisons to the experimental systematics of the other N = 85 isotones. Because of the lack of reliable (microscopic) calculations the structure of these nuclei is customarily analyzed relying on the terminology of the phenomenological shell model. Qbviously one should keep in mind that collective phenomena can be expected to mix extensively with the single particle degrees of freedom as indurated e.g. by the article-cluster vibrational model calculations “) for ‘“‘Sm. Neve~he~ess~
we will restrict the comparisons
to the t ree lowest ( vf712)3,
in the N = 85 vh9/2f$z and yf$2 x 3- shell model rn~~t~p~ets appearing systematically odd-mass isotones. In each ease we first indicate the experimental facts used for the classification of the particular excitations in ‘45Nd into the multiplets and then proceed with the systematic analysis. It is well to note that in the following we discuss only the medium-spin close to yrast excitations. Several non-yrast low-spin states are known experimentally especially for the lighter nuclei. These states are problematic as usual, they are difficult to treat but would provide an even more critical test for nuclear models.
4.1. THE
vf_:,, STATES
although the empirical shell model “) was shown “> to be only moderately successful for 14’Gd, which a priori is the best case for the A! = 85 isotones, we apply it
330
E. Hammar&
et al. / ‘45Nd
here from Nd to Er to get a reference for studying the behaviour of the multiplet in some detail. We consider only excitation energies relative to ground states of each odd nucleus because of the lack of experimental values of ground needed to extract the absolute energies. The result of the calculation
state masses is compared
with experiment in figs. 5 and 6. The empirical energies of the vf:,? quartet of the N = 84 nuclei needed in the calculation are from refs. ‘5,4,3*3 and ‘) for Nd, Sm, Gd, Dy and Er, respectively. The members of the vf :I* multiplets from Sm to Er are identified as they appear in refs. 3-9). The vf7,2 origin of the $- ground state of ‘45Nd is clear from the characteristic, large spectroscopic amplitudes observed 12,13)for it in (3He, CY)and (d, t) reactions. The yrast vf:,, members, y- 657.7 and y- 1401.3 keV states, are obvious from their stretched E2 decay to the ground state. Moreover, they are not seen in particle transfer experiments supporting their few-particle nature. The most natural candidates for the low-spin members are the $- 67.2 and sP 72.5 keV states I’), from which the $- state only has an observable 13), but still small, spectroscopic amplitude. We have included in fig. 5 also the only candidate available experimentally for the zmember of the multiplet, the z- 920.7 keV state observed “) in the decay of 14’Pr but not seen in particle transfer experiments. Taken as such, this state would be the first observed one of the missing z- members of the vf:,* multiplets in N = 85 isotones. The calculation reproduces the experimental vf:,, states qualitatively only. From fig. 5 we can already see that the agreement is best for ‘49Gd as expected in view of the possibilities for mixing effects via the open proton core of the other isotones. Because of the normalization to the ground state energies, fig. 5 cannot be used to judge the quality of the calculation for the individual levels in one multiplet. In fact, the same calculation with absolute energies shows 6, that the agreement is best order of quality and that the result is for the y-, 2p and y- states in decreasing significantly worse for the $- and $- members. Whether this would be true for the other isotones cannot be argued without the empirical ground state masses. Despite of the approximative nature of the calculations it is instructive to see the smooth behaviour of the deviations shown in more details in fig. 6. This behaviour is a clear sign of the common origin of the states in question. The differences shown are related to the additional mixing effects available when protons are removed from or added to the 2 = 64 core. A striking feature is the symmetry with respect to the Z = 64 core, which would be worthwhile to verify for the g- and $- members, too.
4.2. THE
vhs,Zf:,2
AND
vf;,,x3-
STATES
The lowest excited negative parity multiplet formed by three neutrons expected Since to appear in N = 85 nuclei is related to the vh912 single particle excitation. only one valence particle is occupying the vhgi2 shell, a nearly complete decoupling
E. Hamma&
et al. / ‘4sNd
E. Hammarh
332
AE
AE
CkeV)
et al. / ‘45Nd
= E :;'" -
E'eEPt
500
/‘5’*-
LOO -
300 200:
-
1;:;’ 312-v
11/2-
I
;;;:gp&;
is 7/2-
-
100 0 -
Fig. 6. Detailed
of this particle
comparison
I
I
I
I
I
Nd
Sm
Gd
Dy
Er
of the experimental and calculated odd-isotones.
results
of the vf:,,
states
in N = 85
from the vf:,,
Ot, 2+, 4+ and 6+ core should occur. Consequently and q- should appear well below the unfavoured members and have their energies closely related to the core excitations. In 14’Nd and 14’Sm the main components of the vh 9,2 states are firmly identified the favoured
states z-, y-,
q-
at 748 and 809 keV, respectively, by the single-nucleon transfer reactions 12,16).The higher spin members of the multiplet in these two nuclei (present work and refs. “) and ‘)) have almost identical y branchings to stretched E2’s inside the multiplet and to mixed E2/Ml’s decaying into the members of the vf:,2 multiplet. The identification of the aligned members of the vhg,2f:,2 multiplets in “‘Dy and 153Er is clear based on the strong, stretched E2 transitions in the cascade y- + y- + y- + z-. In “‘Dy and in 149Gd the vhg12 origin of the lowest ;- state at 527.3 and 795.9 keV, respectively, is experimentally supported by the P-decay characteristics, in is3Er at 299.4 keV by systematic considerations “) only. The more complicated situation of the higher spin members in ‘49Gd is discussed thoroughly in ref. “). The comparison of the energies of the analog, stretched E2 transitions inside the multiplets shown in fig. 7a is a sensitive criterion for the validity G/2 and vb2f:,2 of the classification discussed above. On the average the decreasing transition energies from lower to higher spin members of the core multiplets are repeated by the transitions in the odd multiplets. The sensitivity of the representation shows in finer details the smooth variation of the core multiplet within the isotonic chain and, furthermore, significant differences between the two multiplets. Roughly viewed, the differences increase with the spin of the levels and are larger in the proton particle’s side. The differences are naturally related to the additional particle (hole)
I
+ t Ncu
0
a
I
E. Hammath
et al. / ‘45Nd
8 00
z
I
333
I
I
z
z
W
G
I
I
N
I
2 s g
multiplets itself should
available
for mixing
contribute
via the vhg,Z neutron.
pronouncedly
to the higher
The uh9,2f,,r! interaction
by
spin states and thus lower their
energies, a feature present in fig. 7a. To interpret the information further details would call for a major theoretical work.
of fig. 7a for
As discussed in sect. 2 the lowest j?” state in I45Nd is firmly identified at 1111.2 keV. The stretched E2 cascade observed furthermore relates the favoured y’, q* and 9 states to the y’ state, which carries at least a fraction of the vi13,2 strength as indicated by the Textron transfer data 12*14). However, due to the Iow-Iying 3 octupole state at 15 10 keV in 144Nd the yi”’ state is expected to have a strong admixture from the VfS,z x 3- multiplet as wefl. This multiplet has spin members y+, y+, . . . , 9’ and the energies should resemble those of a vf;,, one. The unfavoured members of the octupole coupled ‘/f;,2 multiplet in 145Nd could be the tentative y(+) and ye-c) states at 1011.0 and 1715.4 keV, respectively. The prominent vf,,, octupole nature of the lowest 9’ excitations in N = 83 nuclei has been discussed in detail by Daly eF al. 18). The proton dominated shell model content of the 3- octupole excitations in nuclei in the vicinity of 14’6d is revealed in the same context 18). Similarly to the N = 83 nuclei the lob-Iyi~g y”” state and the related positive parity levels in ‘47Sm and ld9Gd have been argued “3”) to be dominated by the pf;,* x 2- nature. In both nuclei the states from spin y’ to 9” display a sequence ~haracteristi~ to a yf;,* multiplet instead of a r,+1312f;,Z, which would have level spacings typical to the 0’, 2+, 4’ and 6’ states of the N = 84 core. In order to demonstrate how well the newly observed positive parity states in 145Nd fit to the systematics we present analog transition energies of the vf:,, and z x 3multiplets in N = 85 isotones in fig. 7b. The favoured states, only, are uf:, considered, because the y’ to y-* transition is not known except tentatively for ‘45Nd and 14’Sm and, furthermore, because the analog $- to i- difference is available in sect. 4.1. The systematic behaviour of the two for 14’Nd, only, as discussed m~lt~plets is strikingly similar in contrast to the behaviour of the z~f;,:! multi~let shown in fig. 7a. However, it is well to note that quantitativeIy the $” to q’ separation is better reproduced by the y!- to yi?- separation in proton holes side only, from Gd to Er the 4’ to 2+ difference fits perfectly. This could indicate that the r&.,2f$L2 admixture is increasingly building up for higher spin members of the multiplet from Cd to Et-. The distance of the vf:,Z x 3- states to the 4’ state having “) predominantly r~i~~,~(vf;,&+ character supports this argument: the $’ to y” separation drops from about 900 keV for Nd to Gd to 530 keV for ‘53Er getting close to the 6+ to 4+ difference of 422 keV in ‘52Er, From the remaining levels of ld5Nd oniy two, the 9- 2347.6 keV and the p2914.7 keV levels have definite spin-parity assignments and could thus be given an x (3-j’ one discussed “) for the $- state interpretation possibly similar to the vf:j2 at 2384 keV in ‘49Gd. It is di~~~lt to make such conclusive interpretations for 145Nd, since we should have a possibility~ similar to 14’Sm [ref. 5)], to observe a rich structure of levels related to the unfilled proton core. On the other hand we do not find
E. Hammarch
striking
resemblance
between
the remaining
335
et al. / “‘Nd
states in 14’Nd and those
observed
5,
in 14’Sm.
5. Conclusions The frozen Xe-target technique in combination with the conventional 13C beam used to populate the medium spin states of the neutron rich Nd nuclei proved to be successful and technically easy to access. The technique opens a possibility for a number of fresh in-beam measurements for nuclei around the N = 82 neutron shell. The target with a massive backing prevents the use of (light) ion beams above the Coulomb barrier of the backing and does not allow conversion electron or light ion spectroscopy,
either.
The structure of the 25 newly observed medium spin states of 14’Nd is in detail similar to the one of the neighbouring heavier N = 85 isotones. The four proton holes character of 145Nd did not open major, new decay pathways in the present multiplets found in 14’Nd agree well reaction. The vf:,,, vh 9,2f5,2 and vf:,,x3with the systematics of the other N = 85 isotones. The phenomenological shell model calculations carried out for the vf:,, states fail to reproduce quantitatively the energies, but the deviations show systematic and symmetric behaviour to Z=64. of N = 85 and N = 84 nuclei, Comparisons of the vh9,zf:lz and vf:,, multiplets respectively, justify the assignments made, but indicate of additional configuration mixing increasingly present for the higher spin members in the odd multiplets. Similar comparisons of the vf:,2 x 3- and the vf37,2 multiplets show, that the vi,3,2 single-particle state coupled to the vf;,, core builds progressively from 149Gd to 153Er into the vf37,2~ 3- states of positive parity. It would be a challenge to (semi) microscopic nuclear theories to explain these systematic features, in the present way of comparisons of transition energies. Fruitful discussions edged. The assistance help.
prominently
visible
with M. Piiparinen and P. Kleinheinz are gratefully acknowlof Miss P. Toivonen in analysis of the data has been of great
References 1) J. Blomqvist, unpublished; I. Bergstrom, Proc. XVI Int. Winter Meeting on Nuclear Physics, Bormio 1978, I. lori (ed.), vol. II, p. 636 and references therein 2) P. Kleinheinz, R. Broda, P.J. Daly, S. Lunardi, M. Ogawa, J. Blomqvist, Z. Physik A290 (1979) 295 3) P. Kleinheinz, Proc. Symp. on High Spin Phenomena in Nuclei, Argonne 1979, ANL/PHY-79-4, p. 125 and references therein 4) J. Kownacki, Z. Sujkowski, E. Hammaren, E. Liukkonen, M. Piiparinen, Th. Lindblad, H. Ryde and V. Paar, Nucl. Phys. A337 (1980) 464 5) M. Piiparinen, Y. Nagai, J. Styczen, P. Kleinheinz, Conf. on Nuclear Behaviour at High Angular Momentum, Strasbourg 1980, p. 53
336
E. Hammarch et al. / 14’Nd
6) M. Piiparinen, R. Pengo, Y. Nagai, E. Hammaren, P. Kleinheinz, N. Roy, L. Carl&r, H. Ryde, Th. Lindblad, A. Johnson, S.A. Hjort and J. Blomqvist, Z. Physik A300 (1981) 133 7) J.G. Fleissner, E.G. Funk and J.W. Mihelick, Phys. Rev. C20 (1979) 977 8) D. Horn, G.R. Young, C.J. Lister and C. Baktash, Phys. Rev. C23 (1981) 1047 9) L. Carlen, S. Jonsson, J. Krumlinde, J. Lyttkens, N. Roy, H. Ryde, S. Stromberg, W. Walus, G.B. Hagemann and B. Herskind, Nucl. Phys. A381 (1982) 155 10) R.F. Casten, D.D. Warner, D.S. Brenner and R.L. Gill, Phys. Rev. Lett. 47 (1981) 1433 11) S.V. Jackson and R.A. Meyer, Phys. Rev. Cl3 (1976) 339 12) G. Lovhoiden, J.R. Lien, S. El-Kazzaz, J. Rekstadt, C. Ellegaard, J.H. Bjerregaard, P. Knudsen and P. Kleinheinz, Nucl. Phys. A339 (1980) 477 13) J. Ardal, J.R. Lien, G. Levhoiden, D.G. Burke and J.C. Waddington, Can. J. Phys. 60 (1982) 1534 14) T. Ramsey, J. Rekstad, A. Henriquez, F. Ingebretsen, M. Guttormsen, E. Hammartn and T.F. Thorsteinsen, Nucl. Phys. A414 (1984) 269 15) L.E. De Geer, A. Kerek, Z. Haratym, J. Kownacki and J. Ludziejewski, Nucl. Phys. A259 (1976) 399 16) J. Rekstad, G. Levhoiden, J.R. Lien, S. El-Kazzaz, C. Ellegaard, J. Bjerregaard, P. Knudsen and P. Kleinheinz, Nucl. Phys. A348 (1980) 93 17) P. Kleinheinz, Conf. on Nuclei at Very High Spin, Lund 1980, Phys. Scripta 24 (1981) 236 18) P.J. Daly, P. Kleinheinz, R. Broda, S. Lunardi, H. Backe and J. Blomqvist, Z. Phys. A298 (1980) 173
‘36Xe(‘3C, 4ny)
REACTION
STUDY
OF 14%d*
P. TARAS Dgpartement de Physique, Universite’ de Montreal, Montreal, Canada A. LARABEE’ Tandem Accelerator Laboratory, M&faster
University, Hamilton,
Received 4 February (Revised 3 Fabian
Ontnrin, Canada
1985 19863
y-ray spectroscopy with Abstract: Yrast and close to yrast states in 145Nd are studied by in-beam f f G?) level (%‘, 4n-y) reaction on enriched, solid ‘36Xe targets. A part of the rich medium-spun structure observed can be characterized to befong to shell mode! muitiplets vf:,,, vhs/zf3,1 and uf& x 3-. The vfq12 multiplct in N = 85 odd isotones from Nd to Er is calculated within the de-Shalit scheme using empirical two nucleon interactions. The energies are not well reproduced, but the deviations from experimental values behave regularly from isotone to isotone. The energy systematics of the vh9,2f:,2 and vf:/, x 3- multiplets in the N = 85 odd isotones is compared in details to that of the vf;,, multiple& in the corresponding even N = 84 isotones and of the uf:,2 multiple& of the N = 85 odd isotanes, respectively. -. ..- .._‘36Xe(‘3C, 4ny), E = 49-60 MeV; measured E,, r,(E), Nd deduced levels, J, 71: Pulsed beam, enriched solid
I,( ff ),
1, Introduction The quality
of the phenomenological shell model ‘) in the vicinity of the closed ‘46Gd has been extensively tested by several authors after the of Kleinheinz et al. “). The model is able to reproduce well both spin properties of the nuclei one and two nucleons apart from the the N = 85 odd isotones from 14’Sm to ‘%r studied recently 4-9)
shell ‘) nucleus pioneering work low and medium 14%d core. Even
* Financial support provided by the Natural Sciences and Engineering Research Council of Canada. ’ At present employed by the Academy of ~j~l~n~. Present address: ~nst~tut fiir Theoretisc~e Physik, ~~~versit~t T~binge~, T~~inge~, FRG. ’ permanent address: repayment of Physics, Simon Frazer university, Burn&y, BC, Canada. 3 Present address: Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA. 0375-9474/86/$03.50 @ Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
318
display
E. Hammare’n et al. / 14XNd
at least qualitatively
the characteristic
features
of the main particle
multiplets
expected to appear. The lowest shell model multiplets vf:,,, Vhgl,f:,2 and vf:,, x 3have been identified from Sm to Er with a surprisingly stable behaviour of relative energies inside a given multiplet. The only N = 85 isotone in the proton holes side with respect to the 146Gd core, where the above mentioned multiplets have been observed 4,5) is 14’Sm. In addition the experiments show ‘) for r4’Sm a group of medium spin levels, which are not seen in the heavier isotones and are consequently believed ‘) to have a two proton holes origin. The two additional proton holes of ‘45Nd could be expected to enhance possibilities to observe such excitations close to the yrast states. It has also been argued lately lo) that the polarizing effect of the neutrons added to the 146Gd core should be particularly pronounced in the proton holes side of the region in question. Excitations more collective in nature could be expected to appear in ‘45Nd at medium spins already. A study of the medium spin properties of ‘45Nd would be needed to find out whether the shell model type neutron multiplets still appear systematically here, quite apart from the ‘46Gd core, or whether the four proton holes dominate the structure in terms of particle multiplets or in appearance of (quasi) collective excitations. Unfortunately, the interesting medium and higher spin states of neutron rich nuclei, such like ‘45Nd, have conventionally remained experimentally untouched because of the lack of suitable, easily available target beam combinations. The amount of low spin data known previously for ‘45Nd (see sect. 3) is typical for such nuclei. We report here of the in beam y-ray study of ‘45Nd observed in bombardment of 136Xe target with “C ions. Depending on the bombarding energy one would expect to populate in such an experiment preferentially medium and high spin states. At the same experiment we have also acquired reported elsewhere. In sect. 2 we describe the method into a solid target together with other more standard will be dedicated
to discuss
in details
data for 146Nd, results being used to freeze the 136Xe gas experimental details. Sect. 3
some crucial
level scheme. The shell model content apparent together with systematics found for the heavier
2. Experimental
details
points in the construction of the in ‘45Nd will be discussed in sect. 4 N = 85 isotones.
and results
The high spin excitations in ‘45Nd were populated with 13C bombardment of a solid Xe target. The target was prepared by freezing enriched ‘36Xe gas on Pb backing (0.033 g/cm*) held at low temperatures. The Pb beam stopper was mounted on a copper gold finger (0.445 g/cm*). A commercial, small liquid-helium compressor was used to maintain temperature low enough to reduce the partial vapour pressure of Xe well below typical pressures used in beam lines. As a result of a 2h precooling time the 5 mg of ‘36Xe gas frozen on the Pb backing formed a 5 mg/cm’ thick in the beam. It is well to note that the (0.4 cm’) target of ‘36Xe ice fluorescent
E. Hammar&
1
I
1
el; al. / ‘45Nd
I 1800
I
1600
CHANNEL Fig. 1. y-ray
singles
spectrum
observed
during
,
I 2000
N~M~~~
~omba~drn~~~
of ‘j6Xe with 50 MeV 13C beam.
320
(4
4 163.5
23/2*
. 2112'
318.8
519.2
I.--
._
52
56
21/z% --m.1912-
637.9
19/Z- --- 1712"
9L6 3
19/2-
- Is/z-
657.7
11/z-
+ 712-.--1
I
60
E 13c (MeVI
598.7
52
Fig. 2. Relative
excitation
56
~~n~t~ons for y-rags
657.7
II/ 2- --* ?f2_
7OL.L 262.6
IUP-11/2(" 11/2++9/2-
3533
11/21+'-11/2-
60
decaying
through
~a~icu~~r
cascades
in 14*Nd.
r-(
P-
2o
Y t2
522.6
21/2-- 17/2-
380.3
2512--2112-
699.2 769.9
13&r91213/2---11/z11/2-- 9/2-
1.5
k!
1.0 52
56
60
/
LlJ
/ ,/’ -i I’ ,,>.”
3
tQ
E 13c
(MN
299.1. 33/z'--+ 31~’
g 5.0 -
--I
I.0 -
I
101jfJ.531/2*-w 271’2% 380.3 25/2---r2112+ 659.7 11/2---c9/2I
1
52
56
60
Fig. 2-continued
E,3c (MN
E. Hammart+~ et al. / I45Nd
322
TABLE y
transitions Angular
E, (keV)
Iy”) (0 = 125”)
distribution coeff. “)
‘4, 72.5 90.6 163.5 186.6 246.8 255.9 262.6
279.4 290.1 308.5 318.8 353.3 380.3 385.2 445.5
in 14sNd observed
Assignment s E, (keV)
A,
-0.10 -0.29
(3) (5)
-0.01 (3) 0.02 (7)
9
-0.21
(2)
0.00 (2)
5 5 19 6 5 12
-0.28 -0.21 -0.29 0.06 0.13 0.35
(7) (3) (2) (3) (5) (4)
0.05 0.02 0.00 0.01 -0.01 -0.13
(9) (4) (2) (3) (5) (4)
4847.6 1401.3 1709.9 3349.1 1011.0 2914.7
-0.10
(5)
-0.70
(30)
2866.8
0.15 (24) -0.03 (1) -0.24(11)
-0.70 (30) -0.02 (1) 0.04 (13)
1111.2 2866.8
8 16
-0.10 (4) 0.34 (2)
0.03 (5) -0.11 (3)
8 26 13
0.23 (5) 0.26 (2) -0.21 (3)
-0.03 -0.08 -0.00
$2 1 S30 3
610.5 632.1 631.9 657.7
15
Comment
r:+1;
72.5 748.3 3030.3 2534.4 3517.2 4211.4 1011.0
11 2
448.2 453.5 458.6 498.4 519.2 522.6 568.9 584.1 598.7 603.0 609.2
+0.05 -0.07
-0.11
-0.03 -0.05 -0.12 f0.19 -0.23
seen only in coinc’s seen only in coinc’s 162.2 keV in ‘44Nd 185.6 keV in ‘“Nd; d, seen only in coinc’s seen only in coinc’s mainly due to this = 262 keV assignment; also in ‘46Nd; ‘) 280.5 keV in ‘46Nd d, *) ‘) 379.2 keV in ‘43Nd; d, c.d) mainly due to 445.2 keV in ‘46Nd y53.9 keV in ‘46Nd
-0.03 ‘)
4 100
(6) (2) (3)
+0.07 d, seen only in coinc’s *I d, 0.0 resolved from 610.5 keV by coinc’s
-0.00
(3)
2011.8
-0.11
-0.25 (5) 0.26 (1)
-0.01 -0.08
(6) (1)
2347.6 657.7
0.0
-O.Ol(ll)
-0.11(13)
2
679.2 691.1 704.4 711.2
5
0.34 (4)
-0.11
(5)
5 21
0.20 (8) 0.24 (2)
-0.03 -0.09
3 47
2866.8 2534.4 6081.4 2011.8 1709.9 3517.7 3030.3
(3)
-0.28
664.9 675.7
715.3 132.6 743.6
1
in the ‘36Xe(‘3C, 4n) reaction
0.25 (5) 0.26 (1)
-0.15 -0.08
d, ‘) less than 1% belongs to luNd or to ‘43Nd
5512.5 148.3
resolved by coinc’s from 676.0 keV in ‘46Nd d, seen only in coinc’s
(10) (2)
1427.6 3961.5 1715.4 2421.1
(7) (1)
1726.3 4081.7 1401.3
seen only in coinc’s 732.6 keV also in ‘46Nd
d,e d)’
(f)+y y-+ +-
*)
Angular E, (keV1
Jya) (8 = 125”)
distribution coeff. b,
s
8 7
0.64 (5) -0.23 (3)
16 7
0.27 t 3) 0.20 (4)
-0.07 -0.10
(3) (Sf
4
0.18 (51
-0.05
(61
748.3 1427.6 2546.8 3270.4 2347.6 24082
-0.08 (6) 0.05 (3)
4568.2
+?,&2 3 UC+, ,&+ ZZ” ,I!$> 19’11 +1_zz +27 4. 2
f‘u2
“) Relative intensities measured at 56 MeV bombarding energy. resolved peaks <30/u. h, Errors indicated for the last figures are pure fit errors only. but not placed ‘) Transition assigned to ‘45Nd by coincidences, d, The parity of the parent state is assigned by assuming that the is an electric one. “) The parity of the parent state is assigned tentatively based on
the experiment by releasing the He-~oo~~~g and down with lilted nitr~g~o. The experiment consisted of a standard set of ‘%Z beam from the MP Tandem of Chalk River tion functions were measured at beam energies coaxial Ge(Li) detectors (50 cm3 with 1.8 keV 90” angles to the beam.
A sample
spectrum
Comment
I: -, ry
E, (keV)
A,
A2 748.3 769.9 831.4 849.3 946.3 1~7~~ 10~~.5
Assignment
training
1.2 0.0
d,
seen only in coinc’s d, dl seen only in coinc’s
Typical
errors
in intensities
to the level scheme. depopulating quadrupole systematic
arguments
of well
transition
only.
Xe into a container
cooled
in-beam measurements using pulsed Nuclear Laboratories. y-ray excitaof 49, 52, 56 and 60 MeV with two FWHM for 6oCo) placed at 0” and
is shown in fig. 1 and the results
for the
excitation functions are summarized in figs. 2a-d. The bombarding energies were chosen to cover both 3n and 4n reaction channels populating 146Nd and 14’Nd, respectively, The analysis indicates that one extra value at lower and two more values
at higher
beam
energy
would
have been
desirable
for a more
convincing
result, especially for high spin states of ‘45Nd. Angular distributions of y rays were measured in 15” steps from 0” to 90” using 56 MeV 13C beam. The normalization of the spectra measured at seven angles was done by photo-peak areas of primary y rays measured with a detector placed at 55” to the beam. The areas of the photo-peaks recorded with the movable detector were carefulty corrected for absorption effects caused by the Pb backing and the Cu gold finger. The normalized intensities were analyzed as customary with second order Legendre polynomials and the resulting coefficients A, and A4 are given in table 1. The angular distribution data was also used to define the relative intensities of y transitia~s of table 1. Thus each intensity indicated corresponds to a value
E. Hammarin
324
et al. / L45Nd 2
TABLE
The y-y coincidences
for ‘45Nd at 60 MeV bombarding
observed
Gate [keV]
Coincident
y-transitions
energy
“) [keV]
262.6, 675.7
13 163.5
308.5,318.8,426.7 657.7, (1180.9)
185.6 b, +186.6
b),445.5,453.5,458.6,476.7
696.5 b), 711.2,
732.4,
743.6,
b). (498.4),
(754.0)
519.2, (598.7),617.8
b), (769.9),
796.9’),
946.3,
b), (637.9), (1007.9)
‘),
b,
(162.2) b), (246.8),
308.5, 314.6 b), 327.1 ‘), 372.4 b), 380.3,
426.8 b), 476.8 b), (504.5) ‘),
514.4 b). 617.8 b), 657.7,
696.5 b), 711.2”),
743.6,
753.9 b),
849.3 ‘), 946.3, 997.6 ‘) 246.8
(308.5),
453.5,
262.6
(380.3),
(453.9)‘),
(598.7),
279.4
380.3,
453.5,
(769.9),
522.6,
(817.6)
290.1
308.5, (380.3),
308.5
(163.5),
657.7.
711.2,
(474.7)‘), 568.9,
‘), 849.0 453.5,
(290.1),
849.3,
(657.7), (584.1),
(946.3)
675.7,
704.4,
(711.2),
748.3,
(598.7),
603.0,
(610.5),
657.7,
831.4 664.9,
711.2,
743.6,
1050.5
(4+6x657.7>->
318.8, (426.2)‘),
711.2, 849.3, (946.3)
(453.5),
(476.9) ‘), 657.7,
(664.9),
691.1, 711.2, 743.6,
849.3 318.8
163.5,
(279.4),
743.6
946.3
(308.5),
(453.5),
(458.6).
(444.4)
380.3
(186.6),
385.2 d,
610.5 3-I 657.7 664.9, 679.2, (711.2) ,A> 743 6 769.9, 950.2 ‘), 1050.5 598.7, (609.2), 657.7, (711.2). 743.6
445.2 ‘)
(163.3),
448.2 d, 453.5
280.5 ‘), (308.5).
(453.5),
598.7, 623.6’),
295.2 ‘), 380.3,
(473.5) “), (522.6),
249.5 ‘), (255.9),
318.8,334.0 (637.9),
676.4e),
(711.2),
(280.5)
‘), 290.1, (308.5)
743.6
(474.7) ‘), 511.8 ‘), (519.2),
(699.0) ‘), 711.2,
163.5, (308.5), 163.5, 318.8,
519.2
318 8 (425.7) ‘), 453.5, 637.9, 657.7, 732.6, 743.6, 946.3 -,163.5 ____L_, (279.4), (318.8), 380.3, 584.1, 603.0, 610.5, 640.4’), 657.7, 679.2, (691.1),
568.9
(163.5), (279.4),
589.6’),
598.7,
657.7, 743.6,
1007.0
(425.7) ‘), 453.5, 522.6, 657.7, 743.6 743.6, (748.3),
1050.5 (318.8),
657.7, 664.9, 584.1
(598.7),
(522.6),
(732.7) ‘), 736.7 ‘), 849.3
458.6
769.9,
(453.5),
603.0,
743.6, (791.0) ‘)
498.4 d, 522.6
318.8,
(691.1),
657.7, 711.2, 736.7’),
657.7,
(445.5),
568.9, 584.1, (598.7),
474.7 ‘), 511.8 “)
649.4’),
(279.4).
‘), 380.3, (385.2),
657.7,
(514.2) ‘), 522.3,
380.3 ‘), 453.8’),
we),
(163.5), “)
704.4, (831.4)
279.4, (295.5) “), (308.5),
(522.6)‘),
+445.5
711.2 1;)732 6
519.2, 598.7, 609.2 1-, 657.7
353.3
+453.9
‘), 657.7,
425.9’),
(341.0)‘),
(711.2),
380.3,
743.6,
3JO.3, (458.6),
(385.2),
(519.2),
(522.6),
(598.7),
(603.0),
(610.5),
1050.5
522.6,
(568.9),
603.0, 657.7, (664.9),
679.2, 711.2 ‘), 748.3, 769.9,
(1050.5) 598.7
(163.5),
603.0
279.4,
(279.4), (330.0)
(318.8),
‘),
(341.0) ‘), 380.3 1-1-F 453.5 657.7 (691.1), 711.2, (743.6) ‘), 849.3 (360.5) ‘), 380.3, 453.5, 522.6, 568.9, 584.1, 610.5, 657.7,
(341.0) ‘),
664.9, 679.2, 743.6, (748.3), 610.5 +609.2
(163.5), 522.6
(279.4), (568.9),
(308.5),
770.2’),
(318.8),
(1035.9)
‘),
1050.5
(360.3) ‘), 380.3,
(583.5) ‘), (598.7),
453.5
603.0, (610.5) ‘), 657.7,
(664.9),
711.2, (732.7),
743.6,
(1050.5) 632.1 d,
(453.5),
657.7,
(711.2),
(743.6),
631.9
(163.5),
308.5,
(318.8),
453.5, 519.2, 657.7, 743.6
657.7
163.5,
(279.4),
(290.1),
(295.5) ‘),
(466.4) ‘), 519.2, 522.6, (568.9), (691.1),
711.2,
(732.6),
(849.3)
743.6,
308.5
318.8,
(584x:89.6) 769.9, (795.7)
380.3,
‘), 849.3, 946.3,
664.9
163.5, 279.4, 380.3, 453.5, (522.6),
568.9, (603.0),
679.2
(380.3),
(522.6),
(584.1),
(748.3)
691.1
(255.9),
(308.5),
453.5, (598.7),
704.4
262.6, 353.3, (476.9)
(675.7),
353.3,
‘),598.7,603.0,610.5,
425.9 ‘) 2-7 453.5 (458.6), (616.9) ‘), (664.9),
(1007.0),
657.7, 711.2, 743.6, 849.3
‘), 657.7, (675.7).
(748.3),
(1050.5)
(616.2) “), 657.7, (704.4),
(790.7) ‘), (831.4)
743.6, 1050.5
E. ~a~~ar~n TABLE
711.2 715.3 743.6 748.3 769.9 849.3 946.3 1050.5
325
2-continued
Coincident
Gate [keV]
et al. / ‘05Nd
y-transitions
“) [keVj
(163.5), m, 318.8, 329.5”), (353.3), (380.3), (445.5), 453.5, 598.7, (609.2), 657.7, 691.1, 743.6, 849.3 262.6, 353.3, (657.7), (675.7), (748.3) 163.5, (279.4), m, 318.8, 380.3, (38X?), (458.6), 519.2, 522.6, (568.9), 603.0, 610.5, (637.9), 657.7 (664.9), (691.1), 711.2, (74X9)‘), (849.3), 946.3, (1007.0), 1050.5 262.6, 380.3,;84.1~ (704.4), (83 1.4) 380.3, 522.6, 584.1, 603.0, 64X4”), 657.7 (255.9) ,&I 308 5 329-5 ‘f, 340.5 =),453.5,598.7,637.7 “),657.7,691.1,711.2. (716.4) “), 743.6 163.5, 318.8, rrso.3), 519.2, 657.7, 743.6, (1050.5) 279.4, 380.3, 522.6, 568.9, 603.0, 610.5, 657.7, 743.6
“) Coincidences are classified to three categories: weak (in ~a~~~tb~ses), clear (bare number) and strong (underlined); compare with examples in fig. 3. b, Transition in ““%Jd. ‘) Coincidence cannot be explained due to the present assignment in 145Nd or due to known contaminant transitions, d, Transition belongs to 14’Nd but is not located in the level scheme. ‘) Transition in ‘46Nd. ‘) Transition in *43Nd.
averaged over seven independent measurements with proper account of the variation of the intensity with angle as observed experimentally at 56 MeV of beam energy. The angular distributions measured for the entire period of 90” make the values of the A, coefficients reliable. A smaller ~~~e~a~~ty of a A4 coefficient in turn allows a more reliable prediction for the multipole mixing ratios, preferentially S( E2JMl). Thus we have extended the analysis of some angular distributions to predict these ratios as well; results are given in table 1. These fits have also been used to determine spins of levels involved. We carried out two coincidence experiments, both with four parameters (E,E,, tYY, t,beam), at beam energies of 52 and 60 MeV primarily for 146Nd and 14’Nd, respectively.
However,
it turned
out that the complementary
information
of the two
experiments was crucial to distinguish between close doublets formed by y rays belonging bo the two deferent final nuclei. In these experiments the detectors were situated at 0” and 90” and they were shielder against mutually back scattered y rays. The results for ld5Nd are summarized in table 2, The ~o~n~~den~e data did not indicate any delayed ( TIi2 > 2 ns) transitions associated to 14’Nd. The coincidence relationships summarized in table 2 and examples shown in fig. 3 are obtained with timing conditions set over prompt events both with respect to the tybeamand to t,,. 3. Level scheme of ‘*‘Nd The low spin states of ‘45Nd have been recently studied in the P--decay of ‘4SPr by Jackson and Meyer ‘I). From transfer reaction investigations for ‘45Nd relevant for this work are the recent (“He, cy) pick-up experiment by ~0vh0~de~ et al. 12) and
325
m
GATE 522.6
z m -Qrn
keV
f-=
610.5+~609.2)
ke’
E. Hammarin
the (d, t) study
of Ardal
321
et al. / 14’Nd
et al. 13). The results
of these
experiments
useful
in the
present analysis are the energies, spin and parity assignments of the iP 0 keV, $72.5 keV, y- 657.7 keV, tP 748.3 keV, y- 1011 keV and 2’ 1110 keV states through which all the feeding
from the 25 new higher
spin states observed
decays.
The level scheme of ‘45Nd shown in fig. 4 is constructed first of all based on coincidence relationships of table 2 including the strengths of coincidences indicated roughly in table 2 as well. Two more natural ingredients have been the singles y-ray intensities of table 1 and the excitation functions of figures 2a-2d. The spins have been determined with a standard method by fitting theoretical angular distributions to experimental data looking at all possible spin combinations in cascades of two consecutive transitions. The multipole mixing ratios were determined by defining the nuclear alignment as a function of spin from known transitions in contaminant reaction products (mainly 143Nd and ‘44Nd). As a result of the rather high quality angular distribution data firm spin assignments could be made for a fairly large fraction of the observed levels. Since we did not measure the linear polarizations of the y-rays - a high quality conversion electron experiment using the present frozen target on a thick packing is not possible - parities were determined by assuming that clean quadrupole transitions are electric ones. This assumption, though supported by the short lifetimes ((2 ns) of the y-rays, should be taken with some caution bearing in mind the richness of possibilities associated with nuclei having noncollective, irregular (multi)particle excitations. The result of the analysis is summarized in table 1. In the following we will comment on few crucial and less straightforward cases met in the construction of the level scheme. The spin and negative parity of the y- 1011.0 keV level was in ref. I’) deduced from its y decay to lower spin negative parity states. Especially crucial for the parity assignment with intensity
is the preferentially
E2 transition
Z, (1011.0 keV) = 1.6 compared
262.9 and 353.5 keV transitions,
respectively.
to the $- ground to the intensities
state observed
I’)
I’) 13.2 and 7 of the
We have not observed
the 1011.0 keV
y ray with an upper limit of Z, < 0.2 for the intensity in the previous units. Consequently the parity of the 1011.0 keV level could be plus or minus. The present angular distribution data of the 262.6 and 353.3 keV transitions is unique with the analogue dipole transitions decaying from the 7’ 873.5 keV state in 149Gd [ref. “)I. Although we cannot exclude the negative parity with arguments based on intensity balance, similarly to ‘49Gd, we assign tentatively positive parity for the 1011.0 keV level. The pure quadrupole 704.4 keV transition defines further I” = y(+) for the 1715.4 keV state. The 83 1.4 keV transition in the same cascade is seen in coincidences only. In addition to the corresponding states in 149Gd this sequence of positive parity states is also in details similar to the recently newly interpreted ‘) y’+) 931.9 and y(+) 1762.3 keV states in 14’Sm. The parity of the 1111.2 keV state cannot be deduced from the present experiment, since the 453.5 keV y ray feeding the yP 657.7 keV state is within detection resolution
2
L
Fig. 4. Leveli scheme of ‘@Nd observed in the 136Xe(“3C,4x1~) reaction. Relative intensities of y-rays observed at 56 MeY are indicated by the thickness of the arrows. Clear quad~~ole (E2) transitions are supplemented with open squares (01. Shell modei co~~~o~t~~ns indicated are discussed in the text.
vh 9/2
E. Hammarth et ai. f “‘Nd
to the 453.9 keV E2 ground
state transition
339
of ‘46Nd present
with an equal intensity
at 56 MeV bombarding energy. The almost uniform angular distribution observed for the doublet is consequently in agreement with the y!’ assignment for the 1110 keV state observed in the C3He, LY)pick-up reaction study 12). Furthermore, in (jHe, cry) coincidence study 14) a 453.5 keV y ray was seen coincident I.1 10 keV cu-group. Thus the I” = y’ assignment for the 1111.2 keV state The stretched 593.7, 711.2 and $49*3 keV E2 transitions are used to define $I’ and ‘3” sequence on top of this l;’ excitation.
a recent with the is firm. the l?s7_+,
The spins of the ?‘I 2408.2 keV and y 2866.8 keV levels are based on the pure dipole nature of 519.2 keV and 458.6 keV y transitions. The 445.5 keV transition is too close in energy to be separated from the 445.2 keV transition in 146Nd, The tentative parity assignment for the I$!“’ state is in agreement with the life-time limit (T,,, < 2 ns) for the 2408.2 keV state preferring E2 for the 1007,O keV transition. The parities in the cascade above the 2866.8 keV level up to the F 408 1.7 keV state cannot be specified even tentatively. he spins and parities of the cascade starting from the z- 748.3 keV state are well defmed up to the yP 2914.7 keV state. The 603.0 keV trans~tjo~ is pure dipole and the 1050.5 keV one a pure quadr~pole fitting well to a cascade $t-+ F --, F”-.
4. ~~elI-rn~d~~ excitations
of N =85 odd-mass isotanes
We will discuss in the following the observed decay scheme of “‘Nd in fig. 3 mainly in the light of comparisons to the experimental systematics of the other N = 85 isotones. Because of the lack of reliable (microscopic) calculations the structure of these nuclei is customarily analyzed relying on the terminology of the phenomenological shell model. Qbviously one should keep in mind that collective phenomena can be expected to mix extensively with the single particle degrees of freedom as indurated e.g. by the article-cluster vibrational model calculations “) for ‘“‘Sm. Neve~he~ess~
we will restrict the comparisons
to the t ree lowest ( vf712)3,
in the N = 85 vh9/2f$z and yf$2 x 3- shell model rn~~t~p~ets appearing systematically odd-mass isotones. In each ease we first indicate the experimental facts used for the classification of the particular excitations in ‘45Nd into the multiplets and then proceed with the systematic analysis. It is well to note that in the following we discuss only the medium-spin close to yrast excitations. Several non-yrast low-spin states are known experimentally especially for the lighter nuclei. These states are problematic as usual, they are difficult to treat but would provide an even more critical test for nuclear models.
4.1. THE
vf_:,, STATES
although the empirical shell model “) was shown “> to be only moderately successful for 14’Gd, which a priori is the best case for the A! = 85 isotones, we apply it
330
E. Hammar&
et al. / ‘45Nd
here from Nd to Er to get a reference for studying the behaviour of the multiplet in some detail. We consider only excitation energies relative to ground states of each odd nucleus because of the lack of experimental values of ground needed to extract the absolute energies. The result of the calculation
state masses is compared
with experiment in figs. 5 and 6. The empirical energies of the vf:,? quartet of the N = 84 nuclei needed in the calculation are from refs. ‘5,4,3*3 and ‘) for Nd, Sm, Gd, Dy and Er, respectively. The members of the vf :I* multiplets from Sm to Er are identified as they appear in refs. 3-9). The vf7,2 origin of the $- ground state of ‘45Nd is clear from the characteristic, large spectroscopic amplitudes observed 12,13)for it in (3He, CY)and (d, t) reactions. The yrast vf:,, members, y- 657.7 and y- 1401.3 keV states, are obvious from their stretched E2 decay to the ground state. Moreover, they are not seen in particle transfer experiments supporting their few-particle nature. The most natural candidates for the low-spin members are the $- 67.2 and sP 72.5 keV states I’), from which the $- state only has an observable 13), but still small, spectroscopic amplitude. We have included in fig. 5 also the only candidate available experimentally for the zmember of the multiplet, the z- 920.7 keV state observed “) in the decay of 14’Pr but not seen in particle transfer experiments. Taken as such, this state would be the first observed one of the missing z- members of the vf:,* multiplets in N = 85 isotones. The calculation reproduces the experimental vf:,, states qualitatively only. From fig. 5 we can already see that the agreement is best for ‘49Gd as expected in view of the possibilities for mixing effects via the open proton core of the other isotones. Because of the normalization to the ground state energies, fig. 5 cannot be used to judge the quality of the calculation for the individual levels in one multiplet. In fact, the same calculation with absolute energies shows 6, that the agreement is best order of quality and that the result is for the y-, 2p and y- states in decreasing significantly worse for the $- and $- members. Whether this would be true for the other isotones cannot be argued without the empirical ground state masses. Despite of the approximative nature of the calculations it is instructive to see the smooth behaviour of the deviations shown in more details in fig. 6. This behaviour is a clear sign of the common origin of the states in question. The differences shown are related to the additional mixing effects available when protons are removed from or added to the 2 = 64 core. A striking feature is the symmetry with respect to the Z = 64 core, which would be worthwhile to verify for the g- and $- members, too.
4.2. THE
vhs,Zf:,2
AND
vf;,,x3-
STATES
The lowest excited negative parity multiplet formed by three neutrons expected Since to appear in N = 85 nuclei is related to the vh912 single particle excitation. only one valence particle is occupying the vhgi2 shell, a nearly complete decoupling
E. Hamma&
et al. / ‘4sNd
E. Hammarh
332
AE
AE
CkeV)
et al. / ‘45Nd
= E :;'" -
E'eEPt
500
/‘5’*-
LOO -
300 200:
-
1;:;’ 312-v
11/2-
I
;;;:gp&;
is 7/2-
-
100 0 -
Fig. 6. Detailed
of this particle
comparison
I
I
I
I
I
Nd
Sm
Gd
Dy
Er
of the experimental and calculated odd-isotones.
results
of the vf:,,
states
in N = 85
from the vf:,,
Ot, 2+, 4+ and 6+ core should occur. Consequently and q- should appear well below the unfavoured members and have their energies closely related to the core excitations. In 14’Nd and 14’Sm the main components of the vh 9,2 states are firmly identified the favoured
states z-, y-,
q-
at 748 and 809 keV, respectively, by the single-nucleon transfer reactions 12,16).The higher spin members of the multiplet in these two nuclei (present work and refs. “) and ‘)) have almost identical y branchings to stretched E2’s inside the multiplet and to mixed E2/Ml’s decaying into the members of the vf:,2 multiplet. The identification of the aligned members of the vhg,2f:,2 multiplets in “‘Dy and 153Er is clear based on the strong, stretched E2 transitions in the cascade y- + y- + y- + z-. In “‘Dy and in 149Gd the vhg12 origin of the lowest ;- state at 527.3 and 795.9 keV, respectively, is experimentally supported by the P-decay characteristics, in is3Er at 299.4 keV by systematic considerations “) only. The more complicated situation of the higher spin members in ‘49Gd is discussed thoroughly in ref. “). The comparison of the energies of the analog, stretched E2 transitions inside the multiplets shown in fig. 7a is a sensitive criterion for the validity G/2 and vb2f:,2 of the classification discussed above. On the average the decreasing transition energies from lower to higher spin members of the core multiplets are repeated by the transitions in the odd multiplets. The sensitivity of the representation shows in finer details the smooth variation of the core multiplet within the isotonic chain and, furthermore, significant differences between the two multiplets. Roughly viewed, the differences increase with the spin of the levels and are larger in the proton particle’s side. The differences are naturally related to the additional particle (hole)
I
+ t Ncu
0
a
I
E. Hammath
et al. / ‘45Nd
8 00
z
I
333
I
I
z
z
W
G
I
I
N
I
2 s g
multiplets itself should
available
for mixing
contribute
via the vhg,Z neutron.
pronouncedly
to the higher
The uh9,2f,,r! interaction
by
spin states and thus lower their
energies, a feature present in fig. 7a. To interpret the information further details would call for a major theoretical work.
of fig. 7a for
As discussed in sect. 2 the lowest j?” state in I45Nd is firmly identified at 1111.2 keV. The stretched E2 cascade observed furthermore relates the favoured y’, q* and 9 states to the y’ state, which carries at least a fraction of the vi13,2 strength as indicated by the Textron transfer data 12*14). However, due to the Iow-Iying 3 octupole state at 15 10 keV in 144Nd the yi”’ state is expected to have a strong admixture from the VfS,z x 3- multiplet as wefl. This multiplet has spin members y+, y+, . . . , 9’ and the energies should resemble those of a vf;,, one. The unfavoured members of the octupole coupled ‘/f;,2 multiplet in 145Nd could be the tentative y(+) and ye-c) states at 1011.0 and 1715.4 keV, respectively. The prominent vf,,, octupole nature of the lowest 9’ excitations in N = 83 nuclei has been discussed in detail by Daly eF al. 18). The proton dominated shell model content of the 3- octupole excitations in nuclei in the vicinity of 14’6d is revealed in the same context 18). Similarly to the N = 83 nuclei the lob-Iyi~g y”” state and the related positive parity levels in ‘47Sm and ld9Gd have been argued “3”) to be dominated by the pf;,* x 2- nature. In both nuclei the states from spin y’ to 9” display a sequence ~haracteristi~ to a yf;,* multiplet instead of a r,+1312f;,Z, which would have level spacings typical to the 0’, 2+, 4’ and 6’ states of the N = 84 core. In order to demonstrate how well the newly observed positive parity states in 145Nd fit to the systematics we present analog transition energies of the vf:,, and z x 3multiplets in N = 85 isotones in fig. 7b. The favoured states, only, are uf:, considered, because the y’ to y-* transition is not known except tentatively for ‘45Nd and 14’Sm and, furthermore, because the analog $- to i- difference is available in sect. 4.1. The systematic behaviour of the two for 14’Nd, only, as discussed m~lt~plets is strikingly similar in contrast to the behaviour of the z~f;,:! multi~let shown in fig. 7a. However, it is well to note that quantitativeIy the $” to q’ separation is better reproduced by the y!- to yi?- separation in proton holes side only, from Gd to Er the 4’ to 2+ difference fits perfectly. This could indicate that the r&.,2f$L2 admixture is increasingly building up for higher spin members of the multiplet from Cd to Et-. The distance of the vf:,Z x 3- states to the 4’ state having “) predominantly r~i~~,~(vf;,&+ character supports this argument: the $’ to y” separation drops from about 900 keV for Nd to Gd to 530 keV for ‘53Er getting close to the 6+ to 4+ difference of 422 keV in ‘52Er, From the remaining levels of ld5Nd oniy two, the 9- 2347.6 keV and the p2914.7 keV levels have definite spin-parity assignments and could thus be given an x (3-j’ one discussed “) for the $- state interpretation possibly similar to the vf:j2 at 2384 keV in ‘49Gd. It is di~~~lt to make such conclusive interpretations for 145Nd, since we should have a possibility~ similar to 14’Sm [ref. 5)], to observe a rich structure of levels related to the unfilled proton core. On the other hand we do not find
E. Hammarch
striking
resemblance
between
the remaining
335
et al. / “‘Nd
states in 14’Nd and those
observed
5,
in 14’Sm.
5. Conclusions The frozen Xe-target technique in combination with the conventional 13C beam used to populate the medium spin states of the neutron rich Nd nuclei proved to be successful and technically easy to access. The technique opens a possibility for a number of fresh in-beam measurements for nuclei around the N = 82 neutron shell. The target with a massive backing prevents the use of (light) ion beams above the Coulomb barrier of the backing and does not allow conversion electron or light ion spectroscopy,
either.
The structure of the 25 newly observed medium spin states of 14’Nd is in detail similar to the one of the neighbouring heavier N = 85 isotones. The four proton holes character of 145Nd did not open major, new decay pathways in the present multiplets found in 14’Nd agree well reaction. The vf:,,, vh 9,2f5,2 and vf:,,x3with the systematics of the other N = 85 isotones. The phenomenological shell model calculations carried out for the vf:,, states fail to reproduce quantitatively the energies, but the deviations show systematic and symmetric behaviour to Z=64. of N = 85 and N = 84 nuclei, Comparisons of the vh9,zf:lz and vf:,, multiplets respectively, justify the assignments made, but indicate of additional configuration mixing increasingly present for the higher spin members in the odd multiplets. Similar comparisons of the vf:,2 x 3- and the vf37,2 multiplets show, that the vi,3,2 single-particle state coupled to the vf;,, core builds progressively from 149Gd to 153Er into the vf37,2~ 3- states of positive parity. It would be a challenge to (semi) microscopic nuclear theories to explain these systematic features, in the present way of comparisons of transition energies. Fruitful discussions edged. The assistance help.
prominently
visible
with M. Piiparinen and P. Kleinheinz are gratefully acknowlof Miss P. Toivonen in analysis of the data has been of great
References 1) J. Blomqvist, unpublished; I. Bergstrom, Proc. XVI Int. Winter Meeting on Nuclear Physics, Bormio 1978, I. lori (ed.), vol. II, p. 636 and references therein 2) P. Kleinheinz, R. Broda, P.J. Daly, S. Lunardi, M. Ogawa, J. Blomqvist, Z. Physik A290 (1979) 295 3) P. Kleinheinz, Proc. Symp. on High Spin Phenomena in Nuclei, Argonne 1979, ANL/PHY-79-4, p. 125 and references therein 4) J. Kownacki, Z. Sujkowski, E. Hammaren, E. Liukkonen, M. Piiparinen, Th. Lindblad, H. Ryde and V. Paar, Nucl. Phys. A337 (1980) 464 5) M. Piiparinen, Y. Nagai, J. Styczen, P. Kleinheinz, Conf. on Nuclear Behaviour at High Angular Momentum, Strasbourg 1980, p. 53
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