The level structure of 90Mo

Nuclear Physics A388 (1982) 303-316 © North-Holland Publishing Company

THE LEVEL STRUCTURE OF "Mo F. W. N. DE BOER ", C. A. FIELDS and L. E. SAMUELSON "" Nuclear Physics Laboratory f, University oJColorado, Boulder, CO 80309, USA

and J. SAU Institut de Physique Nucléaire, Université Claude Bernard, Lyon-I, 69422 Yilleurbanne Cedex, F}ance

Received 3 February 1982 (Revised 10 May 1982) Abstract : High-spin states of the N = 48 nucleus 9 °Mo have been studied using the 33 MeV 9 oZr('He, any) reaction . A previously unknown level structure above the 8 + isomer and several new lower-lying levels have been identified . The results are discussed in terms of shell-model calculations which allow four protons in the 2p r~~ and lgvi~ subshells and two neutron holes in the lf,~~, 2p3 ~=, 2p,i~, or 1g9~= orbitals .

E

NUCLEAR REACTIONS 9°Zr('He, 3ny~ E = 333 MeV ; measured E,, h(B,, t), yy(t). nycoin. 9° Mo deduced levels, Trn, J, n. Enriched target, Ge(Li) and hyper pure Ge detectors. Shell-model analysis.

1. Introdaction The Sr, Zr and Mo isotopes near A = 90 are of great interest due to the existence of possible subshell closures at N = 50 and Z = 38 or 40. In thelast few years a numberof nuclei in this mass region have been studied at this laboratory ; in the present work we extend this investigation to the N = 48 nucleus 9°Mo. Until now only a few investigations ofthe level structure of°Mo have been performed. In addition to the low-spin states observed in the 92Mo(p, t) reaction r~ the ground-state band was found up to spin 8 + in the 93Nb(p, 4ny) reaction s~ As in other N = 48 nuclei, the 8 + member ofthe ground-state band is isomeric ; in'°Mo the haV life is 1 .05 f 0.10 ps [ref. 2)]. The 2+ and 4+ levels ofthe ground-state band have also been identified') in the ß+ decay of 9°Tc. " Present address : Univ . of Fribourg, c/o SIN, CH-5234 Villigen, Switzerland.

"" Present address : Princeton Plasma Physics Lab, Princeton University Princeton, NJ 08540, USA. t

Work supported in part by the US Departrnent of Energy . 303

F. W. N. de Bcer et al.

304

/

9°Mo

One would naively expect the low-lying positive-parity states in 9 °Mo to consist of some mixture of two neutron hole v(g~) -Z excitations and either two or four proton particle n(g~Y' excitations, the latter depending on whether Z = 38 or Z = 40 represents the better shell closure. The negative-parity states would arise from the coupling of g>1" particles or holes to particle-hole pairs involving a hole in one of the negativeparity subshells (lft, 2p t, or 2pß). This type of structure is indeed found in the N = 48 isomer eBZr [ref. 4)1. The structure of 9°Mo has previously been calculated using empirical el%ctive interactions and a 2p ßlg~ model space for both protons and neutrons s ). While the low-spin level scheme of 9 °Mo was reproduced reasonably well by these calculations, the low-lying 3- and 5- levels could not be accounted for. The present study was undertaken in order to extend the level scheme of 9°Mo to higher spin values . In addition, further shell-model calculations were performed using an extended basis which includes the 2pß and lf~ subshells. 2. Experimental techniques 2.1 . TARGET AND REACTIONS

An enriched 9 °Zr target was bombarded with 3He ions from the University of Colorado AVF cyclotron. The target was a self-supporting foil approximately 2 mg/cmz thick. The 9°Zr(3He, 3ny)9°Mo reaction was measured at 33, 38 and 43 MeVin order to obtain y-ray excitation functions. The (3He, any) cross section is largest at 33 MeV, in agreement with statistical-model calculations carried out using the code ALICE 6 ). Excitation functions were also determined by measuring the 9°Mo ~ 9°Nb ß+ decay') (t~ = 5.7 h) immediately following the in-beam measurements. The cross section for 9 °Zr( 3He, p2ny)9°Nb is nearly the same as a function ofbeam energy as that of (3He, 3ny). In order to coal-um assignment of y-rays to 9 °Mo, n-y coincidences were measured and compared with systematics presented in ref. a). This technique hasthe advantage that y-rays from radioactivity and background sources are almost completely eliminated. The y-ray spectra were calibrated for energy and detector efficiency with 1 s2Eu and 'SSe sources. A singles spectrum measured at 33 MeV is shown in fig. 1. 2.2 . GAMMA-RAY ANGULAR DISTRIBUTIONS

Details of the angular distribution measurements are presented in a companion study of the 9°Zr(3He, p2ny)9°Nb reaction 9). Relative y-ray intensities and angular distribution coefficients obtained by fitting the data with the usual expansion W(9)

= A°(1 +aZPz(cosB)+a 4P4(cosB))

are presented in table 1 . The a4 values are only significant for the strongest transitions.

F. W. N. de Boer et al. / 9°Mo 10

10

6

9 °Zr( 3He,Xy)

33 MeV

5 C

10

4

'10

3

I

1000

0 'J

305

55°

Singles

594 Nh 607 Nh Mo

2000

Channel Number

Fig. 1. Singles y-ray spectrum of the 33 MeV 9°Zr( 3 He, 3n) reaction . The labels Zr, Nb, and Mo indicate transitions in the A = 90 isotopes of these elements. C = contaminant .

Values of the alignment coefficient aZ were calculated for the pure quadrupole transitions. These az values increase fairly smoothly with spin, as can be expected for the (3He, 3n) reaction ; below J = 8iß the alignment is significantly decreased due to the isomeric 8 + level. The angular distributions ofsome prominent transitions in 9°Mo are shown in fig. 2. 2.3 . y-y COINCIDENCE MEASUREMENTS

Standard fast-slow coincidence systems 9) were used to meastue both prompt and delayed (by at least 100 ns) y-y coincidences. The data were written on tape in an event mode and analyzed o&line using both random andCompton background subtraction. Prompt and delayed y-y coincidence spectra are shown in figs . 3 and 4 respectively .

306

F. W. N. de Boer et nl. / 9°Mo T~sLe 1

Energies, intensities, and angular distribution coefficients of transitions in ' °Mo observed in the 33 MeV 9 °Zr( 3 He, any) reaction E~ ") (keV) 62 .9 105 .9 113 .3 135 .3 231 .E 262 .9 292 .2 297 .1 310 .3 364 .0 468 .9 477 .0 482 .4 490 .1 536 .E 544.4 649.4 809 .9 818 .5 821 .1 `) 857 .3 897 .7 930 .1 945 .2 948 .3 951 .2 973 .0 1054 .4 1317 .9

n) Is (rel) (57) °) (79)') (58) (23) 123 21 12 11 46 21 (527) 302 (19) 37) 21 52 24 456 146 (13) (10) 79 43 =1000 (550) 68 844 83

C1~

0.417(42) 0.046(63) 0.404(114) 0.389(142) 0.465(38) 0.375(90) 0 .494(26)

O4

0 .400(33) 0.154(105) 0.166(10) 0.379(84) 0.209(11) 0.363(53)

1' 6+ 11 (10 + ) 6+ 8+

1 .22(6)

8+ (13 - ) (10 + ) (6 + ) 8+ 6+ (7 - ) (9 - ) 5(12 + ) (4") (12 + )

0.68(16)

(11 ") 3" " (11 )

57(9 - ) 5(10 + ) 5(10 + ) 6+ (9 - ) 2+ (9' )

(11 ) 6+ 7" (12 + ) 5" (5") (9 - ) (6 + ) 2+ 2+ (10+ ) 4+

(10 + ) 4+ 5(12 + ) 4+ 57" 4+ 0+ 2+ 8+ 2+

-0 .010(48) -0 .091(200) 0 .93(22) 0 .037(31)

-0 .120(73) 0 .279(69) 0 .130(140) 0 .182(13) 0 .395(29)

Jx

az

-0.074(18) -0.146(40)

0.40(3) 0.90(7)

0.92(8) -0.132(15)

0 .23(1)

-0.124(16)

0 .41(2) 0 .88(13)

(10 + )

8+

') Errors in E~ : f 1 .0 keV below 800 keV, f 1 .5 keV above 800 keV. b) Values not in parentheses from angular distribution data, uncertainty f 10 ~ ;values in parentheses from 90° nsy coincidence or y-y coincidence . `) Unresolved from 818 .5 keV transition. ~ Corrected for electron conversion s`).

2.4 . LIFETIME MEASUREMENTS

The half-lives of9°Mo transitions were measured using the coincidence system. The 810 keV 6+ -. 4+ transition displays a 1.0 Ets half-life, consistent with earlier measurements. The 948 and 1054 keV transitions, however, also show a somewhat longer-lived component (t# . 1.8 f 0.2 ps~ Although we suspect that this second delayed component originates in the negative-parity cascade, its source could not be located.

F. W. N. de Boer et al. / 9°Mo

307

L0

231.6

O5 F 5444

0'

005

05 04

0

20

40

60

80

100

6,~ (deg)

Fig. 2. Angular distributions of prominent y-rays in °°Mo.

3. Reaalts sod shdl-model calculitlons

3.1 . THE 9 °Mo LEVEL SCHEME

The level scheme for 9°Mo deduced from the present results is shown in fig. 5. All of the levels shown were established by either the prompt or the delayed y-y coincidence measurements. The .T'~ assignments were based on the angular distribution measurements, the excitation functions, and the tendency of the (3He, 3n) reactïon to preferentially populate yrast or near yrast states. Previously observed t ) low-spin levels which were not observed in the present study are not included in the level scheme . No evidence was found for the proposed' ) (6+ )level at 2706 keV. 3.2. SHELIrMODEL CALCULATIONS

In order to examine the nature of the observed levels quantitatively, shell-model calculations using an extended basis have been performed. The 9 °Mo nucleus can be described as four protons and two neutron holes outside an BBSr core. Calculations in this mass region have already been performed'" '6" te) using eûective interactions and

F. W. N. de Boer et al. / 9°Mo

30 8

`c 0 U

1000

2000

3000

4000

Channel Number

Fig. 3 . Typical prompt coincidence spectra gated by transitions in'° Mo.

restricting both protons and neutron holes to the 2pß and lgt subshells. In the present calculations we have enlarged the neutron shell-model space to include the 2p ß and lf~ subshells, since the ~- and i - levels occur at rather low excitations in 9 t Mo. Moreover, the inclusion of these new neutron configurations can account for 3 - and 7- states observed at low excitation in 9 °Mo. Let us write the total hamiltonian in the form H = Hp+Ho+Hpo .

We have taken as Hp the hamiltonian of four protons in the 2p.t and lg} subshells with the parameters ofGloeckner and Serduke 16~ In the absence ofeffective interactions for all of the N = 22-50 shell, we have chosen to use as the neutron-neutron force a gaussian interaction with spin exchange, the parameters of which can be found in

F. W. N. de Boer et al. /'°Mo

30 9

N O

U

Channel

Number

Fig. 4. Delayed coincidence spectra gated by transitions in' ° Mo .

ref. t 9 ) . Finally the Vpo interaction is a Q ~ Q interaction of the form with

Vvo =

- X~t ' Qz"1~

Qzr = (~~~ k2YZ~Cr).

This kind ofinteraction has already been applied 2°~ s t ) in similar situations where one must deal with the coupling of neutron and proton systems. We then proceed in the following way : once the fotu-proton hamiltonian HP is diagonalized, which gives the nucleus 9ZMo, we fix theneutron single-hole energies and the parameter X of Vpn in order to satisfactorily reproduce the lower part of the 9t Mo spectrum (which is simply a single neutron hole coupled to 92Mo). The resultingvalues of these parameters are 8~-8~ = 0.80 MeV,

i~-g} = 1.35 MeV,

-8t = 1.80 MeV,

X = 0.20 MeV.

We can now diagonalize the neutron hamiltonian, yielding neutron states ~ie.l~. In the

F. W . N. de Boer et al. / 9°Mo

310

5378 .3 g PP.P ~.? h h ~°' P~

113 - 1 111 - 1 III J

19 )

1 " P"O1 O " ^~~° A~

ti

112 " )

.y0~

499x,4 4

ô

~o

4789 .5 a °, 95 .5 4557,2

0

4298.4 4193,4 4090 .1 o,`LL

(7 - 1

j~

(5 7'

8+~ (6t1

\

(a"1~

-1

y

0~

o-0

~ p ^ih

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,y ,5 1 " 6L.°~

h7hL "oA ~_ -o6 6L ~O~

~h o,

~ 0h

8`

31 G' .1 294? .9

0 .

2905 .U 2875 .5 286C .G 2812 .E

~

eO

ti

lO

hP

6 .

,h6 h

2 5 49,7 o-

yb"

4+ 2+

366G.5 3447,a 336ß,3 3295,G

oh

2436,, 2002 .7 1899 .5

2`

U.~

9 ~Mo

48

Fig. 5. The level scheme of °Mo derived from the present work . Only levels established by coincidence relations are shown.

last step, the proton and neutron systems are coupled via the Vpo interaction. The final eigenfunctions of H are obtained using the expansion h~tMt> - ~bin ty[I t pJp~ ~b

® ItnJn~]~~+

where the bracket [ ],'~ includes the relevant angular momentum coupling . No truncation is made in any of the above three steps.

F. W. N. de Boer et al . /' ° Mo

5

4

~r

I2' nl

13' Il' Ih 9_ 12 "

12 " -I I" 12"

9" 10 " 10+

9' 9~IJ+

r

~o" - 6_

7'

m

6' 7_

S'_ 7 8+\

3

K

w

31 1

4

4

"

_ -4 ~ q"

5-

L "3-

~6+ 6+ 0+~

2

4" 2"

4"

2+

2"

2r

0

Theory

Exp.

90

Mo

48

Fig. 6. Comparison of experimental and calculated spectra of 9 °Mo. The calculations are described in sect. 4.

The resulting energy spectrum is compared with the experimental spectrum in fig. 6. Due to the high density of calculated levels above 2.5 MeV, we show only those (the high-spin states) which may be compared with the experimental data. The overall agreement is satisfactory, although the levels of intermediate spin are generally calculated to lie too low in energy . The calculated higher-spin states tend to agree well with the data The wave functions of the more interesting levels are given in tables 2 and 3. The basis

31 2

F. W. N. de Bcer et al. / °°Mo TABLE

2

The structure of the most interesting positive-parity states of q°Mo _ -0 .71121®Oi)+0 .66101®2i ) = 0.64101®21)+0 .60121®01) = 0.81101®4i)+0 .40121®2i)-0.32141®Oi) = 0.85141®Oi)+0 .39101®4i)-0.16121®2i ) = 0.92101®6i)+0 .29121®4i ) = 0.93161®Oi)+0 .25141®2i ) = 0.92101®8i)+0 .32121®Si ) = 0.94181®Oi)+0 .26181®2i ) 1101) = 0.93121®8i)+0 .25141®8i)+0 .22141®6i ) I102) = 0.85181®2i)+0 .31161®4i)+0.30181®4i ) 1121) = 0.79141®8i) - 0.34161®6i) -0.33161® 8 i)+0 .22181® 4 i) 1122) = 0.71181®4i)+0 .43181®6i)+0 .37141®8i)+0 .32181® 8 i ) 12i) 122) 14i) 142) 16i) 162) 18i) 182)

Only the main components are given. The basic vectors are the coupled

1(JP®Jo")J~ .

in which the final eigenfunctions are expressed is particularly well suited to their physical interpretation . Electromagnetic transition rates have also been calculated using the following parameters. The effective charge is 1.5 for protons and 0.5 for neutrons for electric transitions. For magnetic transitions, g, = 1.0 for protons and 0.0for neutrons, and g, = 0.5 g, (free) for both neutrons and protons. 3.3 . THE POSITIVE-PARITY LEVELS

It is interesting to compare the low-lying levels of 9 °Mo with those of the N = 48 nucleus BSZr (Z = 40) and the N = 50 nucleus 92Mo (Z = 42). Such a comparison is shown in fig. 7. The similarity between the 8* ~ 6* ~ 4* -. 2* -" 0* sequences in TABLE

3

The structure of the most interesting negative-parity states of °Mo 13 ;) 132) I5~) 152) 17 ;) 172) 191) 192) I11~ ) 1112) 113i ) 14~ )

= 0.821 01®3i)+0 .45121®5,) -0.27121®3i ) = 0.87l31 ®01)+0 .29141 ®21) - 0.27131 ®21) = 0.871 01®Si ) -0.35121®5~)+0.22121®3,)-0 .22121®7i) = 0.921 Si ®Oi)-0.2214~ ®2i)-0.18171 ®2 i ) = 0.821 01®7~) - 0.42121®5,) - 0.35121®7 ;) = 0.781 7i ®Oi) - 0.53151 ®2i)-0.1719i ®2i) = 0.631 9-®0 *) -0 .4915-®4 *) -0.4717 - ®2 *) = U.801 2* ®7-) -0 .4814* ®5-) -0.2514* ®7 -) = 0.701 5-®8 *) +0 .4614* ®8 *) -0.3715- ®6 *) = 0.86111 - ®0 *) -0 .2919- ®2 *) +0.3715- ®6 *) = 0.891 5 ; ®8 *) -0 .3217-®6 *) -0.2516'®8 *) = 0.871 4i ®0 *) +0 .3014-®2 *) -0 .2716'®2 *)

Only the main components are given. The basic vectors are the coupled

1(Jô®Je`).1~.

F. W. N. de Boer et al. / 9°Mo

10+

6r 9-

lo+

9-

p+ 10+

4

T_ 7_

7"_ T

g+ 3

e+ 6+

ss-

5

g*

s-

3-

2

31 3

4+

3<+ 2+

2+

5-

a+ s+

s

4+

_

r z+

0

o+

z+

88 Z~ 40 4B

a

90 Mo 42 48

o"

92 Mo 42 50

Fig. 7. Comparison of partial level structures in the N = 48 nuclei "sZr and '°Mo and the N = 50 nucleus' = Mo . Only the lowest one or two levels of each spin are shown.

°Mo and ssZr [and s 6Sr-ref. 2)] is quite striking. Theselevels in saZr are known to be two neutron hole v(g } ) -2 excitations z " 4" to " t') ; the g-factor of the 2887 keV 8 + level has been measured to beg = -0.20 [refs. t t" t~)], consistent with this interpretation. It is quite natural to assume that the corresponding levels of 9 °Mo are also two-neutrôn excitations, as is suggested not only by their excitation energies but also by their decay properties s) and their population in the (p, t) reaction t ~ This assumption is corroborated by the shell-model calculations . One clearly observes in table 2 that the J~ = 4i, 6i and 8i states proceed mainly from the coupling ofthe neutron state 1~ to the proton ground state. The symmetrical situation is found in the 42, 62 and 82 levels (although not all of these are observed experimentally We note that while the two neutron 2 + , 4+, 6 + and 8 + states consist mainly of the (g t)j 2 configuration, the four proton 2 + , 4+, 6 + , and 8 + levels are mixttu~es of (p~)ô ® (lg~.)~ and seniority-two (g~.); configtuations. The foul-proton states share the same approximate structure 9

As in ssZr [refs. 4" s)], the second 8 + level, at 3107 keV, can naturally be interpreted as a proton state, though, as seen above, it cannot be interpreted as simply a R(g}~,

31 4

F. W. N. de Boer et d. /'°Mo

state. A possible candidate for the proton 6+ state is the level at 2968 keV. If this is the case, since the 82 -~ 62 transition is not seen experimentally, one can conclude that, due to configuration mixing, the 82 -.8i transition is priveleged even if these states are not of the same structure. The calculated branching ratio (82 -. 8; )/ (82 -. 62 ) = 4, though not very high, reflects this situation. The proton 4+ state in asZr is most probably the one at 2606 keV [ref. 4)] ; if the corresponding (but unobserved) level in 9 °Mo is near this energy, the absence of an inband 62 ~ 42 decay is again understandable in terms of configuration mixing. Indeed we have calculated the branching ratio [(62 -" 4; )+(62 -" 6; )]/(62 -~ 42 ) = 37, a value which confirms this hypothesis. We have also calculated the branching ratio (62 -. 6; )/(62 -. 41 ) = 0.24, a value not far from the experimental value 0.53, and which shows the hindered character of the M1 transition. We also note that the antisymmetric 2+ state is lowest in excitation energy . Tlùs appears to be a general phenomenon in even particle-hole systems zZ ). The decay ofthe 22 level to the 2; level is calculated to be 22 times more probable than the (unobserved) decay to the ground state. The calculated l0i and 12i levels are mainly built from the coupling of the neutron 8i state with the proton 2i and 4i levels respectively, while the complementary coupling is responsible for the 102 and 122 levels . Since the calculated B(E2, 102 -" 82)/B(E2, 102 -. 8i ) = 103 and B(E2, loi -i 82)/B(E2, loi -~ 8i ) = 10 -3, we conclude that, on the basis ofdecay properties, the calculated 10+ levels are opposite to the experimental ones, i.e. we assign the mainly 2+(4p) ® 8+(2n) character to the experimental 102 level and 8+(4p) ® 2+(2n) to the experimental l0i level. Concerning now the 12+ levels, we have performed the calculation ofthe ratio B(E2, 12+ -" l0i )/B(E2,12+ -~ 102 ~ the indices 1 and 2 referring to the experimental order. With the hypothesis of 12+ being the calculated 12i level we find the ratio 0.3, while with 12 being the calculated 122 we find the ratio 3.7. Since the experimental value is 3.4, we conclude that the experimental 12i level is the calculated 12i level, i.e. with main component 8 + (4p) ® 4+ (2n). In fact these levels are fairly mixed, which is consistent with the non-observation of the E2 transitions 122 -. 102 and 122 -" l0i , and with the 122 level feeding the 12i. Indeed the calculated branching ratios (122 -" 12 i )/(122 --~ 102) and (122 -" 12i )/(12Z -" loi) are respectively 32 and 183, the 122 -" 12i decay being an M1 transition. 3.4 . THE NEGATIVE-PARITY LEVELS

The negative-parity levels of 9°Mo can be interpreted along the same lines as the positive-parity levels . However, due to the inability ofthe QZ ~ Qs proton-neutron force to mix the negative-parity levels, the theoretical results will show two separate sequences, with definite neutron and proton features (see table 3), and with almost no ydecay connections between levels belonging to different sequences. This does not reflect the experimental situation, where levels of equal J~ are connected by M 1 transitions

9 F. W. N. de Boer et al. / °Mo

31 5

(with the exception of the 11 - pair where the possible 53 keV M1 was not observed indicating that these levels are mixed. The in-band transitions between unfavoured states are at least an order of magnitude weaker than the coupling M 1 transitions. However, the calculated 11 ~, Z levels both proceed from the coupling of proton negative-parity states with neutron positive-parity levels . We have calculated the ratio B(E2,11 z -" 9~)/B(E2,11 i -" 9 ~) = 1.6, which agrees with the experimental value 1.2. Consequently we can assign proton character to the experimental 9 ~, 7~ and 5 ~ levels. This is in agreement with the BBZr case where the 5 - levels at 2550 keV and 2860 keV are the n(p~gt) and v(p.~ fg+l" f). The 2906 keV state is perhaps the calculated 4i state, which proceeds from the coupling of the proton 4i state to the 0+ and 2 + neutron states . 4. Cooclosioo In this study we have extended the level structure of 9°Mo to J; = 13 -. The highspin positive-parity levels can be qualitatively understood with simple weak-coupling arguments based on the systematics of neighboring nuclei. Shell-model calculations using an extended basis successfully provide a detailed quantitative description of the observed states of both parities. Overall, the calculations reproduce the experimental levels rather well, even though, as pointed out already by Gloeckner f' ), the Z = 38 core is not a good inert core. A qualitative explanation may be that, since the proton hamiltonian taken from ref. f 6 ) is fitted to experimental energy levels, it must contain the influence ofthe core in an efléctive way. As this work was beingcompleted, a new study ofthe 9°Tc ß~ecay was presented zs). The results. of this study are consistent with those of the present work for low-spin states. We would like to thank Dr. P. A. Smith, Dr. E. Sugarbaker and B. Diana for their assistance at various stages of this work . References E . J . Kapfein, H. P. Blok, L. Hulstman and J . Blok, Nucl. Phys . A260 (1976) 141 M. Ishihara, H . Kawakami, N. Yoshikawa, M . Salai and K . Ishü, Phyn. Left . 36B (1971) 398 R . Iafigliola, S. C. Gujrathi, B . L. Tracy and J . K . P . Lee, Can. J . Phys . 52 (1974) 96 T . Numao, H . Nahayama, T. Kobayashi, T. Shibata and Y. Kuno, J . Phys . Soc. Japan 46 (1979) 361 R . Gros and A. Fnenkel, Nucl . Phys. A267 (1976) 85 M . Blsnn and F . Plasil, USAEC Report C349410 (1973) D. C. Kocher, Nuel. Data Sheets 16 (197 SS C. A. Fields, F . W . N . de Haer, R . A . Ristinen, L . E . Samuelson and P. A. Smith, Nucl. Instr.169 (1980) 173 9) C . A . Fields, F. W. N. de Huer, J. J . Kraushaar, R . A. Ristincn, L . E. Samuelson and E. Sugarbarker, Nucl. Phys. A363 (1981) 311

1) 2) 3) 4) ~ 6) 7) 8)

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W. N. de Boer er a! . / 9°Mo

10) J. B. Ball, R. L. Auble and P. G. Roos, Phys. Rev. C4 (1971) 1% 11) J. E. Kitching, P. A. Batay-Csorba, C. A. Fields, R. A. Risdnen and B. L. Smith, Nucl. Phys. A302 (1978) 159 12) T. Faestermann, O. Hauler, T. K. Alexander, H. R. Andrews, D. Horn and D. Ward, Hyp. Int.4 (1978) 1% 13) V. Weisskopf, Phys . Rev. 83 (1951) 1073 14) W. P. Alford, R. E. Anderson, P. A. Batay-Csorba, D. A. Lind, H. H. Weimar and C. D. Zafiratos, Nucl. Phys. A293 (1977) 83 15) P. Luksch, Nucl . Data Sheets 30 (1980) 573 16) D. H. Gloeckner and F. J. Serduke, Nucl . Phys. A2211(1974) 477, and references therein 17) D. H. Gloeckner, Nucl. Phys . A253 (1975) 301 18) F. J. Serduke, R. D. Lawson and D. H. Gloeckner, Nucl. Phys . A256 (1976) 45 19) J. Sau and K. Heyde and R. Chery Phys . Rev. C21(1980) 409 20) J. Sau and K. Heyde, J. of Phys. GS (1979) 1643 21) J. Sau and K. Heyde, Phys. Rev. C73 (1981) 2315 22) K. Heyde, J. Sau and J. van Maldeghem, Pros . 4th Int. Conf. on nuclei far from stability (Helsing~r, Denmark, 1981) CERN 81-09, 519 23) K. Oxorn and S. K. Mark, Z. Phys. A303 (1981) 63 24) F. Rosel, H. M. Fries, K. Alder and H. C. Pauli, Atomic Data and Nucl . Data Tables 21 (1978) 92