Level structure of 99Tc by inelastic scattering and proton stripping

ri--1 B:24

Neckar Phygo A290 (1977) 155-172 ; @ North-Holland Pubfiahim Co., Amawdom peradmion hvm Ow publisher Not to be reviroduced by pbotoprint or microfibn widwat wd

INELASTIC LEVEL STRUCTURE OF 99 rc BY SCATTERING AM PRCVWN STRIPPING t R. J. PETERSON, R. A. EMIGH and R. E. ANDERSON Nuclear Phydcs Laboratory, Departnwnt of Physics and Astrophysics, University of Colorado, Boulder, Colorado 80309, USA Received 22 February 1977 (Revised I June 1977) levels of Abohict: The "MoeHc, d) 99 Tc and "Tc(d, d) reactions all have been used to study the of 99 rc. SPin-parity assignments are made fornearly states below 1.5 MeV excitation. Strong J-depandence is noted for I = I transitions in the proton stripping reaction, irnakin possible several now spin assignments. The inelastic scattering data on 99Tc are compared to simila data on 9 OMo, and are found to be in agreement with a coupling sclieme based on a shell model with good seniority. E

NUCLEAR REACTIONS 9O Mo, 9OTc(d. d) E - 17 .2 MeV; measured a(Ft ,, 0). 9OMo("He, d), E = 33 .3 MeV; measured a(&, 0). 9117c levels deduced AL, 4 C2 Sti.

i. Inft9~n The properties of nuclear levels are revealed diflerently be reactions specific to particular modes of nuclear excitations. Inelastic scattering is wen known to be sensitive to collective motion, such as rotations and vibrations. Single-nucleon transfer reactions, on the other band, show yields determined by the single-nucleon parentages of the final states . Information obtained by use of both types of reactions provides a stringent test of nuclear models . The nuclei most important for studies of the applicability of the shell model are those near closed shells. It would be expected in the simplest picture that 112r, with N - 56 and Z = 40, would be such a closed shell. Weed, reactions on a "'Zr target that transfer a neutron or a proton show the validity of this model '- "). As nucleons are added to the supposed core of "Zr, simple derivations provide level schemes for nearby nuclei. A sequence of spins 0', 2', 4', 6', 8', is expected and found based on the (g.1)' proton configuration in "Mo W. ')]. The low-lying level scheme of "ff Tc is found to be much as expected for a valence gt proton and a valence d# neutron hole '). The low-lying levels of "Tc could then be expected to be due to seniority one and three arrangements of the (gf)' proton configuration. Studies have been done for t Work supported In part by the US Energy Research and Deveknnnent Administration. 155

156

t

-

R. I PETERSON et at.

th0 (f.,)3 configuration levels of ~IV assuming that the 48 Ca nucleus forms a closed core . In this case the level sequence and electromagnetic transition rates calculated from a simple shell model are in good agreement with the numsured properties of the levels of `V [ref. ")]. The spectrum of low-spin states of "Tc is known from fl-7 decay ") and the strong quadrupole electromagnetic transitions are known from Coulomb excitation 'I). Due to the large ground-state spin of 19'Tc Q'), the latter work notes p4marily states of higher spins. In addition, while the present work was under analysis, another study of the single-proton states of "I'Tc became available 10). These data were taken at 18 MeV. In the present work, inelastic scattering of deuterons is used to compare transition rates in ""Mo and "Irc. This complements the existing Coulomb excitation data by determining the shapes of differential cross sections as weHl as their magnitudes. The inelastic scattering is also somewhat sensitive to transitions of higher multipolarity. The ('He, . d) reaction was also used in order to , study the single-particle properties of levels in "Tc. At the higher incident energy used in the present work, the (-'He, d) reaction spedfies the I-transfer more clearly than does the work of ref. 10). There also appears to be a definite j4ppendence for I --,! I transfers to .or J- states at the higher beam energy. Some indication of j-depandence is also noted for I = 2 transfers. 2. The exputment The University of Colorado AVF . cyclotron was used to produce beams of 17.2 MeV deuterons and 33.3 MeV 3 He ions. The energy-loss spectrograph 11) allowed resolution of 15 keV (FWHM) to be obtained for the deuteron scattering and 30 keV for the proton stripping. Particle identification was performed by measuring the energy loss of the particles in a plastic scintillator located behind a position-sensitive helical-cathode proportional counter 11) positioned in the focal plane of the Spectrograph. Additional particle identification for the VHe, d) reaction was obtained by measuring the time of Right of the reaction product relative to the radio-frequency of the cyclotron. Sample spectra for the (d, d') and OHe, d) reactions are shown in fig.. 1. Note that only a few states are strongly excited by both reactions, indicating the specific sensitivity of each of the reactions. The "'Mo target was in the form of the highly enriched oxide evaporated onto a thin carbon foil and was about 50 jig/cm'. in thickness. A monitor counter located at a fixed angle provided the relative normalizations for the (3 He, d) and (d, d) data, even at small angles where the charge collection was not possible . The "'Tc target, also approximately 50 jig/cm' thick, was in the form of the pure radioactive isotope evaporated onto a carbon foil. Due to the refractory nature of the "Tc target, a high powered electron gun was needed to evaporate the material, with concomitant

"Tc LEVEL STRUCrURE ChowAR Nwimm

10 3 . . . . . . . . . I . . . . 111111 . . . . . . . . . I I . . . . . . . . 1 . 1 . 1 ..

157

, I . . . . . . gill . . . . . . . . . I'll . . . . . . IM

Chw" NwrAw reactions Fi& 1 . Sanz& spectra for the 98 Mo(sHc, d)99Tc and "Tc(d~ d)99Tc am shown on ft energy same amaW scab. The resolutionthe is 30 IwV (FWHM) for the stripping qmctrmn and IS keV for scattering spectrum.

contamination of the target with a variety of light elements. These were easily idontified in the deuteron spectra. The absolute normalization of the scattering data was obtained by comparing the elastic scattering data to the predictions of an optical model calculation at small angles . These comparisons are shown in fig. 2, where the predicted curve was obtained using set I of ref. 13) for the deuteron potential-The fit to the 9OMo data The is fine, but 11 spin of the ""Tc data are notably higher than the "Mo data at back angles. the 9"Tc target was not included in the calculation and is probably the cause of the discrepancy through some sort of spin-dependent interaction with the deuteron pro-

158

IL J. PETERSON et aL

jectile. Small angle data for 'He elastic scattering were also obtained during the proton stripping experiment. A comparison of thew data to the optical model calculation was used to provide the absolute normalization for the ('He, d) reaction. All optical model parameters are fisted in table 1. In order to provide consistent spectroscopic factors, the ('He, d) data were analyzed with the same optical model parameters as were used for nearby nuclei ") studied in using the same incident beam energy. Finite range and non-local corrections the incident and exit channels were included in the DWBA code DWUCK "). The spin-orbit potentials provided the J-dependence as found in the data for known and I - states . The energy calibration for the I`Mo(- He, d)"Tc reaction was provided by proton stripping on "Ni to the well-known ") levels of "Cu. The resulting uncertainties are estimated to be ±4 keV for strong states below 2.5 MeV, and ± 8 keV for the others . The Q-value for the ground state of Y9 Tc was found to agree with the tabulated value to within ±5 keV Where comparisons can be made the excitation energies found in the present work are in good agreement with those known 91 17) and with those noted in the previous proton stripping experiment 10 ) . 3. Inelude dwteron scathnft The deuteron beam was chosen to provide a moderate momentum trander without the large Coulomb scattering found for He beams. Since the first excited state of 9 9Tc is located at only 140 kaV excitation, any experimental tail on the elastic peak tends to obscure this transition. . TAKE I Opecal nw" parametm used for douteron scatterinS and proton stripping Particle

17 MOV A 9

33 MOV "He *)

su 30 MeV d 1)

-110 1 .05 0.86

-170 1 .140 0.723 -20 1 .60 0 .81

-101 1 .150 0.81 0

V(MOV) r (fin) a (fin) W. (MOV) r. (fin) a. (fin) 4W' (Mffl r, (fin) a, (fin) V.... (MêV) r.s. (fin) a.,.. (fin)

a)

R,£ 7) .

40 1 .45 0.80 0

20 1 .60 0.81 0

Bound p

lm

0.65

66.5 1 .34 0 .68 -24 1 .13

25 h) Re£ 14 ).

"Tc LEVEL SMUCTURE

159

""Tc (d.d') 10 0 0% 10-4

ELWIC

103

140 keV M* XI

2 10 111

.C

181 keV f t f 100

X10-1

625 keV 110-2

o

727 k*V 1112*

o

jor3

.0

10

20

30

40

50

60 70 80 S c. ft (DEG)

90

100

110

Fig. 2. The differential cross sections for 17 .2 MeVelastic deuteron scattering on 98 Mo and 9'qc are compared to the optical model prediction in the top curve. The five cqxcted quadrupole transitions in "Tc are compared to the DVIBA L - 2 prediction (the solid curve) and to the sW-tnodel prediction for the weighted sum of 98 Mo diffimmtial crow section (the broken curve) . In RX 2 and 4 maenitudes of the predictions based on the 9IMo data have not been renormalized to fit the data. The assumed spms are noted, although several are not known for certain, as discussed in the text .

In addition to the usual DWBA calculations, the angular distributions for "Tic are compared to the data obtained for the known states of "Mo. These data am shown in fig. 3, where the solid curves are DWBA predictions obtained using a collective deformation of the optical potential. The agreement is good for most states . The data for the 735 keV 0' first excited state of "'Mo are in rough agreement with this simple prediction only at small angles . It is unlikely that this is a two-phonon

160

R. L PETERSON et al.

state although the inadequacy of the one-step excitation is noted at back angles. Fortunately, the poorly understood transition to this level plays no role in the interpretation of the low-lying level structure of "91'b. The broken curves for the 787 koV 2 -1 *, 1510 k6V 4"' and 2019 keV 3 - states am and taken to be the empirical shapes magnitudes to which the "Tcdata arecompared. The L - 2 broken curve is also compared to the data for the weak 1432 keV 2 + state of 98 mo. The strengths A obtained from the comparison of the data to the DWBA are listed in table Z Thew are also compared to the results of Coulomb excitation I ') for the 2 + states by the expression of ref. 19 ). The PR values for the 787 and 2025 IwV states are similar to those found in inelasitc proton scattering 20). If integrated, rather than peak, differential cross sections are compared to the DWBA, the B(E2) value for the 797 keV state would be much nearer the Coulomb excitation results.

50 60 TO SO 90 100 8c. 9,(DEG) inelastic Fig. 3. Data from deuteron scattering on 1"IMo are compared to the collective DWBA prediction (the solid curves). The broken curves for the 797, 1510 and 2018 keV states are used as the comparisons to the "Tc data. The broken curve for the 1432 kzV state shows the shape of the differential cross sections for the first 2+ state at 787 keV. 0

10

20

30

40

"Tc LEVEL ErMUCrURE

16 1

Nonetheless, the deuteron scattering overestimates the B(E2) values for the higher 2' states, certainly indicating the role of some multiple excitation. The observed 2' and 4' cross sections for "Mo are interpreted as being due to the seniority two (gt)l J - 2 and 4 excitations. The 6+ and 8+ cross sections were too small to be observedL The senionty three (4)3 excitations in I Irc provide final spins J+ to -V-+, lacking only the *+ spin. Transitions from the ground states of "Mo and "Tc may then be computed by standard algebraic Methods 21). The 9'Tc predictions can be written in terms of the "Mo measured cross sections as: 0 .l22a(4)+0.0l8v(6), OW) or(j+) - 0.l25v(2)+0.049v(4)+0-09lv(6),

a(i+ ) - 0.315a(2)+0.047or(4)+0.00047a(6), u(j+) = 0.025v(2)+0.l79v(4)+0.l4(kr(6),

or(-V+) - 0.1244(2)+0 .198(r(4)+0.039or(6),

ty(-V+) - 0.3l8v(2)+0 .030a(4)+0 .l04ar(6),

0.089ar(4)+0.294
Ile cross sections for the 6+ state of 98Mo am included to indicate where they may be important Five states of "Tc an expected to have a quadrupole exctation. Including the known or suspected spins of levels in "'Tc and the above analyisis of the scattering data, the levels and assumed spins are shown in fig. 2. 11w broken curves are the predictions based on the "Mo data and the assumed shell modeL In most cases, the slightly 99Tc data are larger than predicted, but the relative strengths and shapes are well reproduced . Note that although the I' prediction is dominated by the v(4) term, the role of the cr(2) seem to be less than predicted. Once again, the solid curves are the DVIBA predictions for an L - 2 excitation. Comparison of the Coulomb excitation results from "Mo and gr'Tc is equivalent to a comparison of the v(2) terms alone. Using the value of B(F2) = 2M±90 TABU 2

Comparison of B(E2) values from Coulomb excitation on 98 Mo to the present results of denteron inelastic scattering F,

JW

787 1432 1510 1759 2018

2+ 2+

ff)

Ref. 0).

4+ 2+ 3-

IPLI2

0.0241

0.0021 0.0028 0.00083 0.023

B(EL)t

B(EL)t 11)

(e2 - finu)

(ez - finiz.)

5600

497

2860 129

192

<5

162

R. L PETERSON et at.

e - fm4 for 98 MO [ref. 18)], the predictions and observations 9) for 99're (agWn assuming the spins as given below, although some remain doubtful), we obtain the 9r9 : following B(E2) values (in e .. fM4) for the quadrupo le quintet in Tc calc obs 180 keV, j' : 358 270 140 keV, 625 keV,

il : 1' :

902 72

1080 -

727 keV, 9 1: 355 650 13 + : 910 762 keV, ~r 1200 This agreement of the deuteron scattering results with the Coulomb excitation results indicates that five dominant (gl)3 states have been found. Similar tests have been made for "Cr and 5'V [ref. 7)]. A number of other known states are weakly populated in the deuteron scattering in ' Ire. The data and suggested spin values are compared to the DWBA predictions in fig. 4. Several of these spin assignments are suggested from the stripping data in the next section. Arguments for these spin assignments are made in sect. 5, where the positive-parity spectrum is compared to the results of a simple shell-model calculation. A fairly strongly excited state at 1208 ±4 keV shows a good fit to both the DWBA and empirical L - 3 curves. The strength is 0.16 times that for the strong 3- state of YlMo at 2018 Lev. The stripping data below imply a 1"' assignment ot the 12M keV state. That the lowest spin member of the 3 - 0 gt multiplet is so strongly excited means that a sunple weak coupling model for those states is not feasible. If such a model were valid one would expect only about 5 % of the 3 - strength to be found in this level. 4. Tbc 0*Mo(311e, d)**Te rea~

The data for the known and newly observed states of "Tc are shown in figs. 5-7, collected by the Ptransfers . It is seen that very clean, distinctive I-assignments may be made for all cases. The worst fitis that to theground state, of secure I' assignment. A doublet of J- and I' states is known at 141 keV. The excitation of the I' state dominates the deuteron scattering, but the I - transition dominates the stripping Fig. 4 . Deuteron scanning data to several weak states of 99're are compared to collective DWBA preffictions (the solid curves) and to the shapes observed from the 98Mo data (the broken curves) .

The dot-dashed curves show alternative DVIBA predictions. If the 509 keV state has the suggaMA f- spin, both L - 3 and L - 5 transfers are possible in the scattering. The broken curve for the 534 keV data shows the shell-model prediction for tbo (g#)s 1 4, state, based on the 4 4* data ftom the OlMo. The suggested J- spin for the 672 kzV state requires an L - 5 DWBA prediction. In agmement with the fits shown . Only an L - 4 excitation is allowed to populate the 920 keV J+ state. 1110 data for the 1021 keV and 1208 keV states are seen to agree with either the DWBA or empirical L - 3 sluLpes. A I- assignment for the 1208 koV state is inferred from the stripping data. The sparse data for the 1129 keV state are compared to an L - 2 curve, but no assigiunent may be made.

99Tc LEVEL STRUCTURE

163

lop

167

IOf

103

472hv IUW J RS X103

1e

fio IW_ III , 1. " 4 RIO=

103

100

IO-2

10'3

10"

0

10

20

30

40

60 50 70 0,,, (DEG)

Fig. 4 .

80

90

100

164

R. L PETERSON et at. 104 98 Mo (3He, d) 99 Tc %# - 1

10 3

102 %

142.6koV 1/2and 140.5 ksV 7/2 4 ' XI

--

1J3~

-5100 ci b

lo-,

10-2

10-3

10-4

0

i

L--L-

1

iô-20

1

1

1

1

a

1

30 40 50 Oc.m.(DEG)

1

1

60

1

0

I 10

20

30 40 50 Oc.w,.(DEG)

60

Fig. S. Data from the qsMo(sKe, d)"Tc reaction are compared to DVIBA predictions as described in the text . The I - I results on the left exhibit the J-dependence between f- and I- #Alto& The broken curve for the 140 keV ante shows the effixg of it small I- 4 contribution due to the P state. New assiginnents, based on the J-dependence near 40% are made for the 671, 1326 and 1435 IwV of "Tc. A states. The expected I - 4 shapes are observed for the ground state and 625 kcV state predictions "non-dripping" pattern Is noted for the 727 IwV stat . The data are compared, to for available for this state. A very weak I - 4 Q"') and I - 6 (4+), the spin assignments previously pattern state near 1090 keV h seen to exhibit an I - 4 stripping . Previous data limited the possible spins to J+ or it +. A doublet at 1210 kcV contains gates with I - 1 and I - 4stripping patterns . The sum is shown as the solid curve.

data. The fit to the stripping data allows only a rough estimate of the g4 singleproton strength, as show in E& 5, However, this small admixture is enough to allow an MI transition mte for electromagnetic decay which is large enough to account

99'rc LEVEL SrRUCrURE

165

10a

le lo~ 105 104 A

.5 103 ci ID

b «qlo

lot

lop

10

20

30

40

50

60

1

30

Oe.nL (DEG) te.«,(DEG) MS. 6. The stripping data for 99Tc are compared to I - 2 DWSA PredictionL TheJ-dePendOnCS at are shown for the 762 koV small angles is used to predict the assiglunOuts made . Both predictiozls angles state. In many cam the data seem to show a stronger effed at small Predicte& 110 VOrY thethan data are condstent with weak states at 181 keVand 534 keV have little single-proton strength, but the known #", spin for the 181 keV stat . A spin of 11 for the 534 keV state is preferred by the shellmodel prediction for the deuteron scattering.

for the observed lifetime t. An MI. transition is forbidden within the model of a strictly good seniority (Igt)-l configuration. t As quoted in ref. 17) .

166

PL

I PETMWN et at.

105

104

10 3

le C: MI è

102

lo, 10 0

Jo-I

10-2

0

10

20

30 40 50 Oc.«,(DEG)

60

0

10

20

30 40 50 Oc., . (DEG .)

60

ft 7. The striking i - 0 data are compared to the DWBA predictions. For several states, an un resolved doublet .of a J4- and a (1, J+) state is inferred. The DVVRA curve shown is the best fitted sum of the I - 0 and I - 2 (#+) predictions.

With the proper inclusion of projectile spin and spin-orbit potentials, a J-dependmce for I = I ftwWtions is predicted. A good fit to the predicted I - shape is found for the known J- state at 509 keV. Predictions for both I - and I - transfers are shown for the 672 keV state. The observed dip near 40" clearly prc&rs the I - fit. This is also true for the 1326 keV state, while the I - assignment is preferred for the 1435 keV state. The resulting spectroscopic factors, listed in table 2, are calculated using: dcrC'S,,4.42, dOm Wow where C2 is the isospin Clebsch-Gordan COOfficient, equal to 0.875 for the T~ states of 9'9'rc.

"Tc LEVEL STRUCrURE

167

A weakJ-dependence is noted for the I - 2 calculations for angles less than 10". At the smallest angles, the 2df curves rise, while the 2c4 curves drop. The data for the weak I' state at 191 keV provide a poor test, but at higher excitation some clear cases of each shape are noted, but only for states of unknown spin. A very weak transition to the 534 keV state could sometimes be resolved . These sparse data are best fit by the d* prediction. For I = 0 transfers, the final state must be 1' . Fig. 7 shows the Striking rise in the data and predictions at small angles . In addition to the spin-parity information and indications of the weak singleproton strength in the (g4) -' states, the present results also allow a calculation of the strengths and centroids of the observed single-proton strength. These results are compared to the proton stripping results for the core nuclei I *Zr [ref. 23)] and 96Zr (ref. 21)] as well as the proton pickup results on 9'Mo [ref. 24)]. On both the 1OZr and 9r6 Zr, proton stripping into the S4 orbital provides a summed spectroscopic strength E(2j+ I)C2SIJ very near 9.0, while a sum near 0.8 is found for the 2p* transition. These are quite close to the expected values. Two fewer holes are available in the g4-p* shells for "Mo, and we observe spectroscopic strengths of 7.0 and 0.54, respectively, showing that the added protons in "Mo are not simply completing the p* closure. The 'OZr(3 He, d) work studied transitions up to 7 MeV in excitation 23 ), and found nearly all the I = 0 strength. The centroid was located 5.78 MeV above the ground state of 91Nb. The present work up to 3.2 MeV excitation in 99Tc finds about half the expected I = 0 strength with the centroid 2.12 MeV above the ground state. Essentially none of the 4 strength in 99Tc has been seen. The centroid in I'M is located at 5.56 MeV. The I = 2 strength in I'M was found to be distributed quite evenly up to 7 MeV, but with only one weak state below 3 MeV In 99'Tc, on the other band, much I = 2 strength is noted at or below 3.193 MeV. Using thepassignments of table 3, the spectroscopic sum is found to be 3.15 for the df orbital and 2.29 for the di orbital. If this strength were all d#, then the sum would be 4.86. Clearly, much of the I - 2 single-particle strength has come lower in 9"Tc. The centroid, if all the I = 2 strength is ascribed to the dj orbital, is 2.16 MeV above the ground state. Proton pickup from "Mo to the first four states of 17Nb yklds a spectroscopic Strength (2j+ I )C2 S of 2.2 for the I' ground state, 1.1 for the 2p* state, and 1.24 1j for the 2pt state. This indicates 0.9 and 2.8 holes in thew latter shells, respectively. The proton stripping data on YOMo indicate 0.49 holes in the 2p* shell and 0.21 holes in the 2p* shell. The remahiing 2p* and 2p* pickup strength must lie at higher excitations in 97M. 5. New s& usigomemb in 99Tc

Of greatest interest in 99Tc are the (g4)3 states of seniority three. The excitation energies may be calculated from the known levels of 'ehlo. Since'the 8" (gt )2 State of "Mo is not known, an average of the excitation energies in 9'Mo(2.76D MeV)

168

R. J. PETERSON et aL

POSITIVE PARITY STATES OF 99TC 1297-21/210

(7/2, 9/2)+-121o 3/t .5,001*

-1138 9/2+-1081 3/2+-1021

939-17/2 4* 920 - 15/2*

1/2" -921 13/2 "'-76 2 5/24'- 76 Z 11/2+-727

572-13/24' 527- 9/24* 469-11/2 4' 312 303

(912)4'~-- 625 M/W' -534

5/24'4, 3/2

[140]- 7/2+.

5W-181 7/2+-140 9/2* -CS

(9 9/2) 3 v a 3 THEORY

OBSERVED

Pis. 8. On the left is the spectrum of (403 states of seniority three. normalized to the 140 kvV *+ state, as predicted fivm the known states of "Ohlo. The deuteron. scattering data and the known or spectrum as due to this simple shell-model con suggested spin assignownts identify the middle fispure on . Further low-bft states of positive-parity identified in the ("T~ d) reaction are shown on the right.

and "Mo(1953 Mev) is tabn. lim calculated spectrum is shown in fis. 8 and is seen to be in fhir agreement with the ordering determined in secL I This comparison and the inclastic scattering (or Coulomb excitation) data prefer a spin of I' for the 534 keV state. This is also consistent with the proton stripping data and the j-decaY data 8). A spin of I' is suggested for the 625 kaV state, based on the I - 4 proton stripping, and the agreement between the magnitude of thedeuteron scattering data and the prediction for a I' state. A weak "non-strippijW' angular distribution is soon in proton stripping to the 727 keV state. Ifthis were a I' state, an I - 4 pattern would be expected. The data and OWBA predictionsfor I = 4 (J') and I - 6 are shown in fig. 5. . ,

169

"Te IJP#TL STRUCIVRE

Famay 0 140.5 143 181 509 534 625 671 727 761 .7 762.0 920.5 ION 1015 1073 1081 1138 1142 1210 (D) 1326 1435 1301 1562 1682 1779 1824 1913 1988 2106 2162 2200 2279 2«>8 (D) 2478 2521 2585 2659 (D) 2714

Jw (known)

P P

G. D*+ (1) + PIP it + *+

V G. W W. I-)

TAWX 3 Results of the present work C2S M) IU)

4(j) 1 (*) 2(j) I (#) (2)(1) 4(j) 1 G-)

?

2(j) 0 G) not resolved 2(j) not resolved 2 Q) not resolved 4(j) 1 1 1 2 Q) 0 2 2 2 Q) 0 (j) 2(j) 2(j) 0 G) 2(j) 0 G)

o G)

+2(j) 0 (j) 2(j) 2 (j) 0 (j) +2(j) 2(j)

0.62 < 0.09 0.36 0.0088 0.137 0.025 0.19 0.026 0.064 0.012 weak 0.019 weak O.OD12 0.018 weak 0.018 0.003 0.041 0.0" 0.012 0.15 0.038 0.018 0.100 0.016 0.091 0.17 0.073 0.059 0.086 0.010 0.031 0.0070 0.077 0.049 0.024 0.039 0.063

L

IPL I2

2

0.0078

2 3,5 (4) 2 5 2

0.0031

0.0045

4 + 6)

2 (4)

o.0094 0.00036

P

(2)

0.00047

P

2

0.0016

P

3

0.0032

Jw assigned

V P

0.00077 J+ it +

(P .

V)

V , #+

P , #+ p

P. V P. V P V. V PIP

170

R. J. PETERSON et al. TAWA 3 (continued)

Enerv 2765 28M 2916 (D) 2997 3066 3113 3186 3245

PI (known)

IU) 2(1) 2(1)

o (k)

+2(1) 2(1) 2(1)

o (è)

(2)(1) (0) G)

C2S .)

0.063 0.036 0.010 0.0084 0.0« 0.016 0.013 0.044 0.040

L

JPL12

J' assigned

1+ , 1+ 1+, 1+ ì+

1*. VI 1+ , 1+ 1+. 1+ ì+

G. D+ G+)

calculation uses the expression in the 1) The normalization of the finite-range non-local DVIBAUse text, with theD20 fi-om local, zero-range (LZR) calculations . of the same D02 in the LZR would provide spectroscopic factors 26 % greater than tided here for the ground state. Also, b) The 534 kev state demys only to the 143 keV i- state '), -Irin a spin of f-I' unlikely. a f-" state would have an allowed L - 2 deuteron scattering or Coulomb excitation Yield, not as observed. 0) The inelastic scattering or Coulomb excitation strength implies the spin assignment from the (4 )3 Mo del. Previously known excitation energies are used below I MeV, while those determined from this work are listed above that excitation . The I(/) and C2S2 results are from the DWBA fits shown in the figures for the (3 He, d) data. The L and Pr. are as determined from the deuteron scafterin& Previously known J* results an from rob. 9.17) . The last colurnin presents the spins inferred from previous results and the present worIL

Although most of our stripping results agree with those of Cheung et al. "), there are several discrepancies. Most important is the transition to the 672 bV state. At the lower beam energy, a transfer I = 3 was claimed, which implied a I - assignment since this state decays to the 142.6 keV I- state. With the higher beam energy of the present experiment, a clearw signature of the 1-trander is obtained and only I - I is admissible. The J-dependence further suggests a final spin of J-. Ether I - or I - spins are admissible for the 509 keV state from the earlier data. Thej-dependence in the ('He, d) data is quite clear for this case and a spin of I- is inferred. The 761 .7 keV state was known to be I' or 1' . The I = 2 stripping angular distribution requires the I' assignment. The 1081 keV state shows a very weak I - 4 angular distribution, which is enough to eliminate the previous possibility of an assignm nt, leaving only the 4'. In addition, a few other less important discrepancies are noted at higher excitation. Remaining I-assignments from the proton stripping are listed in table 3. The Jassignments are based on any hints ofj-dependence or, where none are available, df transfer is assumed for I - 2, pf for I - I and gt for I = 4. The ratios of DV~3A predictions forj - /+ I toj - I- I are 4.4 for I = 1, 1.9 for I - 2 and 2.5 for I - 4. in the assignments of As mentioned previously, there is reasonable agreement excitation energies, /-values and spectroscopic factors between the present (3 He, d)

4'

99Tc LEVEL STRUCrURE

171

results and those of Cheung et al. "), who studied levels up to 2.5 MeV excitation. The most important descrepancies have been discussed above. Thus, the excitation above 1.0 MeY which are listed in table 3 are those determined in the present work. Finally, more sophisticated calculations could also be performed for "Tc. The most obvious would utilize the method of Paar 21), who calculates both positive and negative-parity spectra of nuclei with three protons removed from closed cores. Although the presence of stripping into the p* and p* orbitals indicates that the description of "'Tc must be more complicated than three protons plus a `IZr core, it is not obvious that such a description would be inadequate. The low-lying spectrum of "'Tc does not exhibit the strong, low-lying strength for orbitals with Z > 50 which are present in the Ag isotopes "), especially II 'Ag [ref. ")]. These intruder states which are not treated in the basis assumed by Paar ") provide the principle deviations from the predicted spectra for the Ag isotopes . 6. Conclusiow The low-lying states of "'Tc have been studied with the "Tc(d, d') and "Mo ('He, d) reactions. The spins and parities of most levels below 1 MeV have been established through identification of observed levels with excitation intensities in the (d, d) reaction anticipated on the basis of a simple shell-model calculation and with predictedj-dependence in the (- He, d) reaction. Reasonable agreement is noted in the latter reaction with another (- He, d) study undertaken at a lower bombarding energy . The high seniority states seen appear to be reasonably well described by the simple shell-model calculation performed. We wish to thank Dr. J. E. Kitching for communicating the results of the previous (-'He, d) experiment before publication. In addition, we would like to thanic J. G. Povelites of the Los Alamos Scientific Laboratory for preparation of the 99Tc target and D. Cooke for his aid in data reduction. Refermm 1) B. L. Cohen and 0. V. Chubinsky, Phys . Rev. IL31 (1963) 2184 2) C. R. lRingbam and 0. T. Fabian, Phys . Rev. C7 (1973) 1509 3) B. M. Freedom. E. Newman and J. C. Hiebert, Phys . Rav. 166 (1968) 1156 4) L. R. Medsker, Ph". Rev. CO (1973) 1906 5) L. R. Medsker, Nucl . Data 11 (1974) 157 6) R. A, Emigh and R. E. Anderson, Nucl . Phys . A, to appear 7) R. J. Peterson, Phys. Rev. 172 (1969) 1098 8) W. B. Cook, L. Schellenberg and M. W. Johns, Nucl. Phys. 139 (1969) 277 9) L. G. Svensson, D. G. Sarantites and A. BAcklin, Nuel . Phys . A267 (1976) 190 10) H. C. Cheung, S. 1. Hayakawa, J. F- Kitchia& J. K. P. lice~ S. K. Mark and J. C. Waddingon, Z. Phys., to be published 11) B. W. Ridley, D. E. Prull, R. J. Peterson, E. W. Stoub and R. A. Emigh, Nucl. Instr. 130 (1975) 79

172 12) 13) 14) 15) 16) 17) 18) 19) 20) 21) 22) 23) 24) 25) 26)

R. L PETERSON et aL IL W. Stoub, R. A. Ristinen and R. R. Sercely, Nuel . Instr. 127 (1975) 329 Y, K. Seth, X AL Buzard, J. C- Picard and 0. Bamani- Phy& Rev. CIO (1974) 1928 S. Harar and R. N. Horooltko. Nuel. Phys. A183 (1972) 161 P. D. Kunr, DWUCIC. a distortod wave born approximation program, Univ. of Colora", unpubIU" R. I~ Auble, Nuel . Data 14 (1975) 119 L. R. Nkdkker, Nucl . Data 12 (1974) 431 1. Barrette, M. Barrette, X Boutard, R. HaroUtWàM, 0. La ureux and S. Monaro, Phys . Rev. C6 (1972) 1339 A. M. Bernstein, Adv. NueL Phys. 3 (1968) 325 H. F. Lutg, D. W. Reikkinen and W. Bartolini, Phys . Rev. C4 (1971) 934 A. do .%qhalft and 1. Tabn4 Nuclear sheâ theory (Acadmic Press, NY~ 1963) R. IL Anderson, J. L Xmushau, R. AL P-ich P. AL Batay-Càorba and M. P. Blok, Nucl . Pbn A287 (1977) 265 Y, T. Knopile, M. Rone, C. hiaytt-Borklo, J. Pederseu and D. Burch, Nucl. Phys. A159 (1970)642 H. Ohnuma and L J. Yâtems, Pbys. Rev. 176 (1968) 1416 V. Peu, Phys. Lon. 39B (1972) 587; Nucl. Phys. AMI. (1973) 29 R. U Aublc~ P. B. Bertrand, Y. A. EM and D. 1. Horen, Phys. Rev. CO (1973) 2308