Proton spectroscopy of 105Ag from the (3He, d) reaction

Nuclear Pkysics AZ41 (1975) 189-203; Not

PROTON

@ Nurr~-~ol~a~ P~i~hin~

Co., Amsterdam

to be reproduced by photoprint or microfibn without written permission from the publisher

SPECTROSCOPY

OF

lo5Ag FROM

THE

(3He,d)

REACTION

R. E. ANDERSON and 3. J. KRAUSHAAR Nuclear Physics Laboratory, Depurttnent of Physics and Astrophysics, University of ColoradoS Boulder, Colorado 80302, USA t Received 12 November

1974

Ah&act: The lo4PdCHe, d)to5Ag reaction has been studied at a bombarding energy of 33.3 MeV. Angular distributions were taken for the emergent deuterons from 2.5” to 55” with a typical resolution of 25 keV. Orbital angular momentum transfers and spectroscopic factors were deduced from comparisons with DWBA calctdations. Only the ground state and 54 keV state were found to be suitable candidates for qua&rotational bandheads. The level structure of ‘=Ag, ‘O’Ag, and losAg as seen with the (%e, d) reaction are compared.

E

NUCLEAR REACTIONS 104Pd(aHe, d), E = 33.3 MeV; measured a(&, 8). losAg deduced levels, J, n, L, S, spectroscopic factors, quasirotational bandhead states. Enriched targets, magnetic spectrograph.

Quasirotational bands built on 3’, gi, and ystates have been reported “) recently in each of the nuclei lolPd, lo3Pd, and “‘Pd. Although the doubly even cores of these nuclei display similar quasirotational structure 2), the well-developed 3” band in lolPd is not observed in lo3Pd and lo 5Pd. Subsequent study “) of the single-particle nature of the bandhead states with the (d, p) and (d, t) reactions showed that a close correlation exists between the existence of a q~sirotational band and the single-particle purity of the bandhead. Those states which contained essentially all of the available single-particle strength (of a particular JR) acted as bandheads while fragmentation of the single-particle strength implied an analogous breakup of the quasirotational band. The neutron deficient Ag isotopes 1OiAg, l 03Ag, and l OsAg represent situations analogous to lolPd , lo3Pd, and lo ‘Pd since they involve the same cores but a different valence particle, in this case a proton instead of a neutron. At present, experiments to identify the quasirotational band structure of these nuclei are underway elsewhere 4), while the experiment discussed here attempts to study the single-particle nature of the proton excitations in ’ “Ag . A similar experiment is planned to study the proton excitations in r 03Ag. When completed the Pd and Ag work should provide much information about the weak coupling of the valence particle to excited states of the core not only for the low-lying excitations of core normally studied in the weak 7 Research supported in part by the US Atomic Energy Commission. 189 April 1975

190

R. E. ANDERSON

AND J. J. KRAUSHAAR

coupling model (e.g., O’, 2+, 4+ states) but also for higher-lying excitations including 6+, 8+, and 10’ core states. In addition, little is known at present about the excited states of losAg although recent Nuclear Data Sheets “) include a level scheme based “) upon a study of the iieca y of lo 5Cd by Starke et al. In this reference “) the authors state that the numerical relationships displayed are not intended to establish the existence of excited states in losAg at the excitation energies shown. Thus it seems that a study of the lo4Pd t3He, d)lo5Ag reaction would be useful in order to firmly establish excitation energies for some states in losAg and to shed some light on the single proton character of these states. 2. Experiment and procedure The 3He beam used in this experiment was accelerated to an energy of 33.28 MeV using the University of Colorado 13’2cm AVF cyclotron. The beam energy was determined to an accuracy of about 0.5 % by standard NMR frequency techniques. The beam was then directed by a system of quadrupole magnets and 1” steering magnets into the 5 mm entrance aperture of the magnetic spectrograph system ‘) described in detail elsewhere. The soEd angle for the spectrometer was about 0.3 msr and typical (average) beam currents on target ranged from 3 to 4 PA. The position of the reaction products along the focal plane was obtained with a helical cathode proportional chamber with delay line position sensing, The position signals were gated into the MCA by the output of a plastic scintiliator which backed up the proportional chamber. In this experiment the deuteron signature in the scintillator was unambiguous and complete separation from background was achieved. The targets used consisted of 90 % enriched 104Pd supplied by Oak Ridge National Laboratory evaporated on a 50 fig/cm2 carbon backing. The major contaminants were ‘*‘Pd which was present in the target material and 13C which was present due to the carbon backing. Because of the Q-value for the 12C(3He, d)13N reaction, the “C in the backing was seen only at the extreme forward angles. The 1*‘Pd contaminant presented no problem since the ’ ofPd(3He, d)’ 06Ag reaction was studied *) in TABLE 1

Optical model anC used in the 10*Pd(3He, d: Particle (2) jHe d proton well

172.0 101.4

1.14 1.085 1.20

0.70 0.857 0.65

16.0 61.0 finite-rangt

“) Non-locality correction.

“) 1=

25 using the Thomas spin orbit form.

losAg

191

a separate experiment. In addition, the states seen in this reaction are very weak compared with most transitions seen in the ’ 04Pd(3He, d) reaction. Target thicknesses were not measured but were estimated to be of the order of 200 pg/cm2 for the thicker targets. Absolute normalization was accomplished by comparing the results of elastic scattering measurements to the optical model predictions using the parameters shown in table 1. This procedure should provide cross sections with an uncertainty of about f25 %. The relative normalization is much better, with an estimated uncertainty of about 5 %. The data were normalized in several ways. At angles further back than Oiab= 15” charge normalization was used by scaling the output of the Faraday cup. At angles below 15” the cup interfered with the exit deuterons by blocking a portion of the entrance aperture of the spectrograph, so a graphite plate mounted just to the side of the entrance aperture was used to collect the beam charge. At 2.5”, however, the beam would partially miss the plate and disappear into the spectrometer. For this angle a monitor detector which counted 3He elastically scattered from the target was used. Sufficient overlap points were taken to assure equivalence of these different procedures. A sample spectrum for the 104Pd(3He, d) lo ‘Ag reaction is presented in fig. 1, and the individual peaks are labeled according to their excitation energies in losAg. The states above 2769 keV are not labeled and are thought to be comprised of multiplets. The energy resolution obtained was about 25 keV FWHM, and this spectrum is representative of all the data collected except for a few runs taken on a much thinner target (Z 20 to 50 pg/cm2) in order to minimize the target thickness contribution to the resolution. In these runs a resolution of about 18 keV FWHM was achieved, and they will be discussed in more detail later. Peak areas and centroids were extracted from each spectrum using the least squares fitting routine SPECTR ‘). The centroids were then input to a standard relativistic kinematics program in order to determine the excitation energy for each peak. Calibration was achieved using the strong peaks seen in the ’ 06Pd(3He, d)” ‘Ag and 56Fe(3He 3d)“Co reactions. The excitation energies of the strongly populated levels

D WBA parameters 1 o 5Ag calculations

1.54 1.293 parameter

0.80 0.788 = 0.77

7.2 25 “)

1.085

0.788

1.40 1.30 1.25

0.25 0.54 0.85

R. E. ANDERSON

AND J. J. KRAXJSHAAR

I93

losAg

in ’ O’Ag are well known up to 1222 keV due to past lo) and present 11,12) work. The excitation energies of states seen in “Co were obtained 13) from other (3He, d) work. A non-linear least squares fit to a third-order polynomial of lab momentum versus channel number was made and the resulting parameters were used to calcufate the deuteron momenta of the lo5 Ag excited states. 3. Angular distributions Data were taken for the 104Pd(3He, d) losAg reaction over the angular range 2.56” 5 8.c m. 5 56.1”. The angular distributions obtained for the stronger states are shown in figs. 2-5. The solid curves shown are the results of DWBA calculations which, for the most part, describe the data very accurately. Only two slight deviations from this behavior are noted. First, the states at 1880 and 1922 keV appear to have some small amount of low &value contaminant (probably E = 2) along with the I

I

I

I

I

lo4Pdt3He,d)

I

‘05Ag

=33.4 MeV R=l

IO”

ZOO

30’ Bc.m.

40”

50°

60”

(DEG)

Fig. 2. Angular distributions for the 104Pd(3He, d)lo5Ag reaction which involve an l-transfer of 1. In fig. 2 through fig. 5 the solid curves are the remits of DWBA calculations discussed in the text.

194

R. E. ANDERSON

AND J. J. KRAUSHAAR

-1

-Q

0.01

P \

*Q

I IO

I

20

I 30

/

1555

,>f

7

0

986 keV

1748

::

P 40

50

60

8 ,.ln.(DEG)

dist~butions

for the 104Pd(3He, d)losAg

reaction which involve an f-transfer of 2.

losAg

(JS/q'JJ)7JP/aP

-

196

R. E. ANDERSON

AND J. J. KRAUSHAAR

2 = 4 strength. Secondly, the data are consistently higher than the DWBA predictions between 20” and 25” for I = 0 transitions. The ~haviour was also seen I’) in the 106Pd(3He, d)’ 07Ag reaction and is not understood at present. The code 14) DWUCK was utilized in conjunction with the optical parameters ’ “) of Auble et al. listed in table 1. The parameters have been used over a wide range of target masses and have given satisfactory fits to reaction data. They do, however, constitute the major source of un~rtainty involved in the absolute normalization of the data. The calculations included both finite-range and non-locality corrections and spectroscopic factors (Slj) were obtained from the relation

Here (da/dG),,, is in mb/sr, (da/dSt)nw is in fm’lsr, C2 is the isospin coupling coefficient and the zero-range normalization constant is used. The Q-dependence of the DWBA calculations was investigated by computing do/dlR,w(Z) at three Q-values corresponding to the ground state Q-value, 1 MeV of excitation, and 2 MeV of excitation in ’ 05Ag. No significant change in shape was observed for any I-value and the change in the magnitude of the cross section for a particular Z-value and angle was described by an exponential dependence on the Q-value of the reaction. Having ascertained the Q-dependence of the DWBA calculations, the value of da/d&& 8) for an arbitrary excitation energy was then obtained by interpoIation. The spectroscopic factors for states for which an angular ~stribution could be obtained are listed in table 2 along with the excitation energies. Since the final state J-value was not determined in this experiment, two spectroscopic factors are listed for each assigned I-value. The J, column corresponds to J = Ifs while the J, column corresponds to J = I-s and s refers to the spin of the proton. One remark should be made about the ma~itudes of the spectroscopic strengths reported. While the shapes of the DWBA curves are insensitive to the various iiniterange and non-locality corrections, the magnitudes certainly are not. The widest variation is encountered in comparing the predictions of the local zero-range (LZR) approximation with those including the non-local finite-range (NLFR) corrections. The spectroscopic factors obtained using the NLFR corrections are about 45 % smaller than those obtained using the LZR approximation. Notice that, from table 2, the summed spectroscopic strength for the ground state, 54 keV state, 348 keV state, and 876 keV state is 2.3. In the LZR approximation this sum is 4.2, which is very close to the value of 4.0 predicted by the shell model for a 2 = 46 target. This dependence is identical to that seen 12) in the ro6Pd(3He, d)‘O’Ag reaction and also 15) in the 108Pd(3He, d)logAg reaction. This is in contrast 16) to the A w 88 region where the LZR approximation overestimates the spectroscopic factors while calculations using the NLFR corrections are more in agreement with the predictions of the shell model, However, a reduction of the bound state radius parameter from 1.20 to 1.10 brings down the predicted cross sections for both the LZR appro~mation and

losAg

197

TABLE2 Summary of level information for lo sAg Energy

1

Jr

(keV) ‘1

0.0 54&l 348&-l 433f4 802&5 876f2 986fl 104Of7 1096&4 1165&7 1295&3 1329&-2 b, 1385f4 1439*3 1555&6 1580&6 1635f4 1689&6 1748&6 1790&6 1880f6 1922&7 1982L-6 2093&-8 2166*8 2255&7 2332&6 b, 2420&-7 2534&14 2617&12 2719110 b, 2745&14 b, 2769+13 b, ‘) b, “) “)

w+

J< 1 4 1

!$- ‘) (8’) d,

1 2

0 2 2 2 2 0 2

3’

4’

2 4 4 4 2

1Kx,

J>

0.46 0.21

1.57 0.16

0.19 0.69

0.14 0.52

0.16

0.17 0.86 0.06 0.03 0.09 0.04 0.12

0.11 0.45 1.21 0.67 0.07

0.08 0.23 0.61 0.34 0.05

1.14 0.08 0.04 0.12

The errors are quoted to the nearest keV. Multiplet. Ref. 5). Refs. 6*1s).

NLFR corrected treatment. In this case the expected spectroscopic sum of 4.0 for the g+ pt. and P+ levels is reproduced by the NLFR predictions while this sum is 45 % larger when the LZR approximation is used. This serves to illustrate the difficulties one encounters in attempting to obtain absolute spectroscopic strengths. 4. Discussion and conclusions Comparison of this work with other studies of losAg is not very revealing. As mentioned in the introduction, only one published study “) of ’ “Ag exists, and this

198

R. E. ANDERSON AND J. J. KRAUSHAAR

was a measurement of the intensities and energies of the y-rays from the decay of lo 5Cd. In this work the authors present a level scheme which is based only on energy sums and as such does not intend to imply definite evidence for the existence of specific levels in losAg . The fact that the y-ray intensities are not always balanced merely serves to point out the difficulties inherent in constructing reliable decay schemes for complex nuclei without the aid of coincidence data. The authors are, however, confident of the placement and spins of the two lowest excited states, the 3’ state at 25 keV and the 9’ state at 53 keV. The present work represents a partial confirmation of these results. The r7 + state was not excited in the (3He, d) reaction, but that state is believed l ‘) to be of a rather complex character. Calculations have been completed by Paar 18) for the wave functions for the low-lying positive parity states of “‘Ag and losAg using a model involving the three proton-hole cluster coupled to a quadrupole vibration field, In these calculations the I = J- 1 anomaly has been accounted for and the components of the wave functions for the 2’ and 8’ states in loTAg and losAg specified. The z’ state has seniority-3 components for the most part, with the seniority-l components involving admixtures of one- and twophonon core excitation. The 3’ state on the other hand has a major component with seniority 1 and no core excitation. It appears clear that the low-lying 3’ and Q’ states in losAg should show the same general features as ‘O’Ag and lo9Ag. If the ground state of ’ 04Pd is purely (g&” ( seniority 0) then no population of the +* state can be expected for simple one-proton transfer. It is only to the extent that the ground state has seniority-4 components like [(gf);2(g&2]o where I can be 2, 4, 6 or 8 that the t’ state can be reached. In the high resolution runs previously referred to, no indication of the 25 keV -z’ state was seen even though the ground and 54 keV states were almost completely separated at baseline. An upper limit on the strength of the transition to the 25 keV state may be set at 3 % of that for the 54 keV state. A state at 54 keV was seen in this experiment and an Z-value of 4 has been assigned to the transition. If one assumes that the broad predictions of the shell model are correct, then the spin-parity assignment for this state would be Sf since the gS orbital is expected to lie below the & orbital. This is quite consistent with the calculations of Paar 18) for 1°‘Ag and lo9Ag. Because of the large gap (e 1736 keV) which exists between the 54 keV state and the next I = 4 transition, it seems reasonable to assume that the 54 keV transition essentially exhausts the gs strength in 1OsAg and that the three I = 4 transitions with E, 2 1790 keV may be assigned as sf states. These assumptions are implicit in the discussion in the preceding section of the summed spectroscopic strengths of the lowest four states. The levels at 1295 keV and 1580 keV display I = 0 diffraction patterns and may unambiguously be assigned as $+ states. All other states, however, must be assigned J-values in a model dependent fashion, For this reason, two spectroscopic factors, corresponding to J = Ifs, are quoted in table 2 for each transition. However, one can postulate tentative assignments based on the broad predictions of the shell model.

losAg

199

As discussed above, it is tempting to assign the 1790 keV, 1880 keV, and 1922 keV states as 3’ states since they are 1763 keV to 1868 keV higher in excitation than the 4” state at 54 keV. If these three states are indeed 3’ states, they represent about 9 of the total gr strength. Since the d, orbital is unbound in this region ‘l) this probably means that the strong, low-lying I = 2 transitions are 3’. Thus one would assign the 9X6 keV and 1326 keV states a spin-parity of 3’. These assignments are also consistent with the systematics of the assignments made i2) in lo ‘Ag. These states represent about 40 % of the total d, strength, and if all of the 1 = 2 transitions seen in this work are d, transitions, then about 55 % of the total d, strength is seen. Appreciable amounts of 2 = 2 and I = 4 strength together with some E = 0 strength appear in the unresolved multiplets above 2769 keV. The level density in this region makes the extraction of detailed spectroscopic information extremely difficult, however. An interesting progression may be noted in comparing the results “* *‘*’ “) of the 104,106,108Pd(3He,d)~05,10%109A g studies and tracking the excitation energies of analogous states, i.e. those states which are populated by the same Z-transfers (which probably have the same spin-parity) with comparable spectroscopic strength. The level structure of these three nuclei as observed with the (jHe, d) reaction is shown in figs. 6 and 7. Unless otherwise noted, all references to lo 5Ag, lo ‘Ag, and lo9Ag will refer to this work, ref. 12) and ref. ’ ‘), respectively. In comparing the various transitions for the three nuclei the sum of the spectroscopic strengths for the 2p+, 2~~ and 1% levels were normalized to 4.0. The lowest-lying state involving an I = 1 transition (other than the ground state) appears at 348 keV in lo 5Ag, 325 keV in lo ‘Ag and 3 11 keV in ’ 09Ag. For the next I = 1 transition, the progression is 876 keV, 786 keV, and unknown in lo9Ag. All of the above are most likely 3- states and it is possible that the known Q- state at 702 keV in lo9Ag would complete the second progression. The strong doublet at 706 keV and 731 keV in ‘09Ag might prevent observation of that transition. However, the expected strength of this transition is such that one should see an anomalous behavior in the angular distribution of the 706 keV state or the 73 1 keV state at about 10”. Such a behavior does not appear, however. The strong I = 2 transitions exhibit similar behavior. The lowest-lying state involving an 1 = 2 transition is found at 986 keV in lo5Ag, 922 keV in ’ “Ag, and 731 keV in lo9 Ag. The next strong I = 2 transition drops from 1329 keV in losAg to 1222 keV in t 07Ag and finally to 866 keV in lo 9Ag. Above this excitation range the f = 2 strength which is seen seems to fragment more drastically in losAg than in either i *‘Ag or lo9Ag although definite conclusions are somewhat difficult to draw due to the lack of observation of all the available d, and d, strength. The lowest-lying E = 0 transition appears at 1295 keV in lo 5Ag, 1142 keV in lo ‘Ag and 706 keV in 1’ 'Ag. The behavior of the next I = 0 transition is not uniform but it is possible that the transition is not identified properly in ali three nuclei due to its weak strength (C’S x 0.05).

200

R. E. ANDERSON

AND J. J. KRAUSHAAR

D8fd 13He, d) losAg

lo4 Pd (‘He, d) “‘A, E13Hef=33.3MeV

:(3He) = 2’7. 0 MeV .

IosPd f3He, E t3He)

2600

~32.8

-

0

2400 2320

-

2,5 0

2220

-

2.4?

-

2,4?

-

1841 -

?

2

23281, 2310

2285”--2l972tO5- 21652095 2030 -

2

-

1658 1600

-

0

1656-4

1490 1430

-

2 0

1508-4 1471 -1,2

1310

-

1.2.41

1326 -2 1259-2

I?

1222

I .

-247

412-

3?

311-I

131-4 GS -

2617

-

2534

-

2420

-

2332

-

2t66---2

1962 1922 1880

----4,(i

1790-4 1748-2 t689’16331580-O 1555 -2 1439 1385 1329-2 1295-O

-2

2 4, (s

2

2 2

1165 ----

1147 -0

. . ._

1096 1040---686-2

-4

I

876802

----

423-3?

433

----

325-t

348-l

786-l

731-2 706-O

-

2093

922-2

910-4 866-2

2769 2745 2719

2255----

t917INO1820 -0

to59

Fig. 6. A comparison

-

1750

t2551200

C

MeV

-

2470

2130 2070 2030 -t970-- 2000

d) io7Ag

126-4 t

GS-

t

54-4 GS-

I

of the energy levels seen in the ro4*106*10sPd(3He, d)105-107*109Ag tions; I-values are labeled.

reac-

losAg

201

The I = 4 transitions provide the anomaly in this discussion. The low-lying $+ state rises from 54 keV in losAg to 126 keV in “‘Ag to 131 keV in logAg. The higher-lying I = 4 transitions all exhibit a systematic drop in excitation energy as the neutron number increases although there may be an inversion of the two lowest levels based on their spectroscopic strengths. The systematics observed suggest that a weak coupling approach to the understanding of the odd-A silver isotopes could be useful. In that case one would attempt to explain the systematic changes in excitation energy in terms of some systematic change in the core. In this case other data suggest that the onset of permanent deformation occurs as the neutron number increases. Coulomb excitation studies 1‘) show significant static quadrupole moments for the first 2+ states in 106Pd, 1°*Pd, and

Distribution of Spectroscopic Strengths Seen in the

104, l06,106,,d

2.

(3He,

d)

l05,i07,

lOgAg

Reactions li -

P

I. s r”

LIT

I.

0.

c=l

0

. . . . . . . . . . . . . . .

0.’

d 1

0

I

0.0

1.0

logAg

2.0

“Cl0

1.0

lo7Ag (2JtllC2S

2.0

--

0.0

1

I

I.0

1

2.0

“‘A g

Fig. 7. A comparison of the locations of the spectroscopic strengths seen in the lo** 106*10sPd f%e. d) 105~x07*109Ag reactions. The sum of the lgs, 2p+ and 2p* levels has been normalized to 4.0.

202

R. E. ANDERSON

AND J. J. KRAUSHAAR

‘r*Pd. On the other hand, (heavy ion, xn) work “) indicates that the neutron deficient Pd isotopes, looPd and lo2Pd, are very nearly spherical. That is, the moments of inertia which one extracts foi the ground states in a VMI “) (variable moment of inertia) calculation are about two orders of magnitude smaller 2”) than one would extract for a permanently deformed nucleus such as 168Er. If the doubly even Pd nuclei do undergo a transition from spherical to deformed shapes, the excitation energies of analogous states in 1’ “Ag, lo7Ag, and lo ‘Ag should represent a sensitive test of any theoretical calculations which incorporate this feature. A discussion of the theoretical state of affairs regarding small deformations in the Pd isotopes may be found in ref. “). As stated in the introduction, the presence of a quasirotational band in ‘erPd, lo3Pd and lo5Pd was shown to depend on the strong single-particle nature of the bandhead state. That is, the state in question must carry a large fraction of the available single-particle strength. Thus in lo5Ag we may immediately eliminate all states populated by I = 0 and 1 = 2 transitions since the I = 0 and 1 = 2 strength appears to be severely fragmented. If, as seems likely, the 1790, 1880 and 1922 keV states are all 3’ states, then the g%orbital is likewise fragmented. From comparisons with known states in ’ 07Ag and logAg it is also likely that the 348 and 876 keV states are both +- states. The uniform distribution of p* strength observed in this work thus effectively precludes the existence of a quasirotational band based on a $- bandhead. The only states which meet the requisite condition of single-particle purity are the e+ state at 54 keV and $- ground state. Both of these two transitions appear to carry all of the available single-particle strength of that particular shell model orbital. In conclusion, this study has shown that only two states exist as candidates for quasirotational bandhead states in losAg. These are the ground state and the 54 keV state. In addition, much of the single proton particle structure of the excited states of 105Ag has been revealed, as well as their excitation energies. The excitation energies and spectroscopic factors determined should be sensitive tests for any theoretical calculations when they become available. This is especially true for the I = 1 transitions since they are forbidden in the simple shell model. Finally, a study of the ‘““Pd(3He, d)“‘Ag and l 02Pd(3Hc, d)’ 03Ag reactions would provide a more complete understanding of the level systematics and the latter reaction a more complete comparison of the,natures of the quasirotational bands built on single neutron and si ngle proton states in nuclei which have the same core. The authors are indebted to Professors P. D. Kunz and E. Rost for helpful cussions on some theoretical topics.

dis-

References 1) F. A. Rickey and P. C. Simms, Phys. Rev. Lett. 31 (1973) 404 2) G. Scharff-Goldha~r, M. McKeown, A. N. Lumpkin and W. F. Pi& Jr., Phys. Lett. 448 (1973) 416

losAg 3) 4) 5) 6) 7) 8) 9) 10) 11) 12) 13) 14) 15) 16) 17) 18) 19) 20) 21)

203

F. A. Rickey, R. E. Anderson and J. R. Tesmer, to be published F. A. Rickey, private communication F. E. Bertrand, Nucl. Data Sheets 11 (1974) 449 C. L. Starke, E. A. Phillips and E. H. Spejewski, Nucl. Phys. Al39 (1969) 33 B. W. Ridley, D. E. Prull, R. J. Peterson, E. W. Stoub and R. A. Emigh, to be published R. E. Anderson, R. L. Bunting, J. D. Burch, S. R. Chinn, J. J. Kraushaar, R. J. Peterson, D. E. Prull, B. W. Ridley and R. A. Ristinen, to be published Proc. DECUS, Fall Symp. (1970) p. 263 F. E. Bertrand, Nucl. Data Sheets B6 (1972) 1 A. W. Kuhfeld and N. M. Hintz, to be published R. E. Anderson, R. L. Bunting, J. D. Burch, S. R. Chinn, J. J. Kraushaar, R. J. Peterson, D. E. Prull, B. W. Ridley and R. A. Ristinen, to be published G. Hardie, T. H. Braid, L. Meyer-Schiitzmeister and J. W. Smith, Phys. Rev. C5 (1972) 1600; B. Rosner and C. H. Holbrow, Phys. Rev. 154 (1967) 1080 P. D. Kunz, to be published R. L. Auble, F. E. Bertrand, Y. A. Ellis and D. J. Horen, Phys. Rev. CS (1973) 2308 J. R. Comfort, J. R. Duray and W. J. Braithwaite, Phys. Rev. CS (1973) 1354; J. V. Maher, J. R. Comfort and G. C. Morrison, Phys. Rev. C3 (1971) 1162 P. K. Hopke, R. A. Naumamr, E. H. Spejewski and A. T. Strigachev, Phys. Rev. 187 (1969) 1704 V. Paar, Phys. Lett. 39B (1972) 587 W. R. Lutz, J. A. Thomson, R. P. Scharenberg and R. D. Larsen, Phys. Rev. C6 (1972) 1385 M. A. J. Mariscotti, G. Scharff-Goldhaber and B. Buck, Phys. Rev. 178 (1969) 1864 A. B. Volkov, Phys. Lett. 41B (1972) 1