z. Physik 223, 145--149 (1969)

Excitation Functions for *SCa(d, p) * Ca (0) in the Range Ed= 3.0-- 5.5 MeV H. LACEK, W. BAKOWSKY, and U. STROHBUSCH Physikalisches Institut der Universit~it Freiburg, Freiburg i. Br., Germany Received March 4, 1969 Excitation curves for 4SCa(d, p) 49Ca(0) have been measured at 12 angles in the energy region from 3.0--5.5 MeV with the aim to investigate the charge exchange effect expected at the analogous (at, n) threshold opening at 4.3 MeV. A broad flat minimum is seen in the 165~ excitation curve around this threshold which is however much less significant than the charge exchange cusps observed in the A ~ 90 mass region. More significant structure is seen at Ea~ 5 MeV which possibly may be connected with 48Ca(4.611) core excitation or due to an intermediate state in S~

Introduction Several recent papers have been concerned with the behaviour of (d, p) excitation functions at energies near the threshold of the (d, n) channel leading to the analogue of the investigated state in the (d,p) reaction 1. A t this threshold an anomalous behaviour which could not be described by standard D W B A has been observed in the (d, p) excitation curves. This a n o m a l y has been attributed to charge exchange coupling. It has been stated that it should occur for nuclei for which either the s- or p-wave neutron strength function is large 2. The threshold effect has been studied especially in the A ~ 90 region where the p-wave neutron strength function has a peak value. In this paper the reaction 48Ca(d, p) 49Ca(0) is discussed, for which the s-wave neutron strength function has a large m a x i m u m 3. The only other (d, p) reaction on A ~ 5 0 studied in this connection is, as far as we know, 52Cr(d,p)4. But discussion is complicated by strong fluctuations appearing t h r o u g h o u t the energy range studied. It is hoped that in our case because of the double closed 48Ca-core the stripping mechanism is d o m i n a n t and that therefore fluctuations arising f r o m the c o m p o u n d mechanism are suppressed. 1. MOORE,C.F., C.E. WATSON, S.A.A. ZAIDI, J.J. KENT, and J.G. KULLECK: Phys. Rev. Letters 17, 926 (1966). -- HEFFNER,R., C. LING, N. CUE, and P. RICHARD:Phys. Letters 26B, 150 (1968). -- (JOKER,W. R., and C. F. MOORE:Phys. Letters 25B, 271 (1967). -- WILHJELM,P., G.A. KEYWORTH, G. C. KYKERJR., D. L. SELLIN, N. R. ROBERSON, and E. G. BILPUcI-I:Phys. Rev. Letters 18, 130 (1967). 2. TAMURA,T., and C. E. WATSON:Phys. Letters 25B, 186 (1967). 3. GOOD,W. i . , D. PAYA,R. WAGNER,and T. TAMURA:Phys. Rev. 151, 912 (1966). 4. CORER,W. R.: Private communication.

146

H. LACEK,W. ]3AKOWSKYand U. STROHBUSCH: 5.15 T=9/2 11.52

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Fig. 1. Level diagram for the 4SCa(d,p) and (d, n) reaction. The 11.52 MeV state in 49Scis the analogue of 49Ca(0). The analogous (d, n) channel of 4SCa(d,p) 49Ca(0) opens at Ea, ~ab=4.30 MeV

The energetic situation is illustrated in Fig. 1. The analogue of 49Ca(0) is 49Sc(11.52) 5. The threshold of the analogous (d, n) channel opens at Ed =4.30 MeV. This is well below the Coulomb barrier, what is necessary for the charge exchange effect to be observed 2. 5. ENDT,P. M., and C. VANDER LEUN:Nucl. Phys. A105, 417 (1967).

Excitation Functions for 4SCa(d, p) 49Ca(0)

147

Experimental Procedure The experiment was performed with a multi-detector scattering chamber on the Van de Graaff accelerator of the Physikalisches Institut Freiburg. Calcium targets were prepared by reducing CaCO 3 enriched to 97.16 % 4SCa to the metal and evaporating onto carbon backing foils. The target was mounted at 45 ~ to the incident deuteron beam. The effective thickness of the 4SCa target was < 10 keV in the energy region studied. The beam limited to a current of about 40 nA was collected in a Faraday cup. Excitation functions have been measured at 12 angles from 0 = 2 0 to 165 ~ with solid-state detectors. The bombarding energy was varied from 3.0 to 5.5 MeV in steps of 20 keV.

Results and Discussion In Fig. 2 some of the excitation curves measured are shown. The lines following the experimental points indicate average curves (A E = 100 keV). Absolute cross sections were obtained by measuring the elastic proton scattering excitation functions and comparison with results of JoN]~s et al. 6. Ten units in Fig. 2 correspond to 1.45 mb/sr. The solid curves are D W B A calculations obtained with the code JULIE 7 using optical model parameters reported by MARINOV et al. s. No lower cutoff radius was used. The D W B A cross sections are normalized to the 30 ~ excitation curve. F r o m the relation

(do'/d~"~)exp

~-

O'calc1.5 (2 I f + 1)/(2 Ii + 1) S

the spectroscopic factor S=0.75 was extracted. A weak dip and a slightly steeper ascent is seen in the 20, 40, 50 and 60 ~ excitation curves. This behaviour, however, probably is not due to charge exchange coupling as a charge exchange cusp is expected to have a width of about 0.5 MeV 4; it may be connected with the compound mechanism. Furthermore for all reactions investigated till now, the effect only occured at backward angles. Therefore the flat broad minim u m in the 165 ~ excitation curve indicated by the average curve may be due to the charge exchange coupling. Compared with the anomaly observed for A ~ 90 this effect is weak but it significantly differs from the standard D W B A curve. In order to state whether a coupling effect really is observed, a coupled channel calculation would be of interest. 6. JONES,K. W., J. P. SCHIFF~R,L. L. L~E JR., A. MARINOV,and J. L. L~RNER: Phys. Rev. 145, 894 (1966). 7. BASSELL,R.H., R. M. DRISKO, and G.R. SATC~L~R: ORNL Report Nr. 3240 (1962) and supplement (1966). 8. MARINOV,A., L. L. LE~ JR., and J. P. SC~IrrER: Phys. Rev. 145, 852 (1966).

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Excitation Functions for 4SCa(d, p) 49Ca(0)

149

A more p r o n o u n c e d structure is seen a r o u n d 5 MeV which is m o s t striking in the 20 and 30 ~ excitation functions. These angles are near the stripping m a x i m u m and it is expected, therefore, that the excitation curves are well fitted by the D W B A curves as holds g o o d below this energy. In the 165 ~ excitation curve there is a steep slope at the same energy. We have no explanation for this behaviour. The vertical dashed line marks the threshold above which the excitation of 4SCa(4.611) becomes possible. It m a y be supposed, therefore, that the structure mentioned is due to a two step process, i.e. inelastic scattering of the deuteron and p r o t o n emission afterwards 9 A n o t h e r explanation could possibly be an intermediate state in S~ whose excitation energy would be ~ 19 MeV. Experiments to search for similar effects in 4~ p) are in progress. The authors are indepted to B. P. GOEL, G. SCnEKLINSrJ and W. SCHMIDTfor their assistance during this work and to H. WroTH (MPI, Heidelberg) for the preparation of the targets. We express our thanks to E. R6SSLE, W. R. COKER and C.F. MOOREfor helpful discussions. 9. PErCNV,S. K., and G. R. SATCHLER:Nucl. Phys. 53, 145 (1964). Dipl.-Phys. HEINZ LACEK Dr. U D O STROHBUSCH WERNER BAKOWSKY

Physikalisches Institut der Universit/it 7800 Freiburg Hermann-Herder-Str. 3

Fig. 2. Excitation functions for 4SCa(d,p)49Ca(0). 10 arbitrary units correspond to 1.45 rob/st. The solid curves following the experimental points have been obtained by averaging over A E = 100 keV. The smooth solid curves are DWBA results. The threshold of the analogous (d, n) channel is indicated by the vertical solid line. The vertical dashed line marks the position of the threshold for 4SCa(d, d')4SCa (4.611)