LIGHT ION REACTION MECHANISM

Transcription

1 Proceedigs of the 1983 RCNP Iteratioal Symposium o LIGHT ION REACTION MECHANISM MAY, 1983 Edited by H. Ogata, T. Kammuri ad I. Katayama RESEARCH CENTER FOR NUCLEAR PHYSICS OSAKA UNIVERSITY IBARAKI, OSAKA, JAPAN

2 ause excitatio at eergy lg cross sectio matterig at r the chage of that the ther tha the Nakao ad DEUTERON PROJECTILE BREAKUP ON 28Si AT E =17.85 MeV a C. A. Fields, R. J. Peterso, R. S. Raymod* ad J. L. Ullma Nuclear Physics Laboratory, Departmet of Physics, Uiversity of Colorado, ad Boulder CO USA R. J. demeijer ad E. H. L. Aarts ble discussios. Kerfysisch Verseller Istituut, Rijksuiversiteit Groige, 9747 AA Groige, The Netherlads ab 156 MeV ad M. B. Greefield Departmet of Physics, Florida A ad M Uiversity Tallahassee, FL USA ABSTRACT 28, Deutero breakup o ~ Si has bee studied at MeV usig both sigles ad p- coicidece techiques. Agular correlatio data were 40 SO i = obtaied betwee 144 ad -144 for protos ad betwee 120 ad -120 for eutros. These results allow the separatio of the breakup reactio ito elastic, ielastic, ad absorptive parts, ad the determiatio of the cotributio of each part to the reactio cross-sectio. r. Phys. to Prog. Letters

3 The first discovered ad most frequetly studied projectile breakup 1) 2) process is that of the deutero. At eergies of 190 ad 56 MeV the features of the breakup process are similar to those observed i the breakup 3 3-5) of He. The most commo techique used to study deutero breakup has bee the measuremet of the iclusive (d,p) reactio spectra. Kleifeller et al have recetly measured this reactio at low eergies. So far oly a few agular correlatio studies of the (d,p) reactio have bee made. 28 reactio I this paper we preset measuremets of the MeV Si(d,p) carried out at the AVF cyclotro at the Uiversity of Colorado. At oly 9 MeV per ucleo, this reactio is ear the low-eergy limit for the applicatio of direct reactio, ad therefore of direct breakup, models. The measuremets should therefore provide a strog test of such models. The Si target was chose because its groud ad first-excited states are easily separated eve with short pathlegth time of flight measuremets, ad because the log-rage Coulomb breakup mechaism is ot expected to be domiat i such a light ucleus. Fig. 1 shows the iclusive proto spectrum at 10. This spectrum exhibits a cotiuum structure as well as discrete states up to a excitatio of 15 MeV. The cotiuum structure may be divided ito a bump visible at forward agles ad a tail that is visible eve at 144. It is clear from this sigles spectrum that high resolutio i the proto detector is eeded i order to distiguish betwee the discrete states ad the cotiuum part of the spectrum. Fig. 2 shows the total kietic eergy (TKE) spectra at 8 =-12.5 ad 8 =+/-12.5 together with projected proto spectra i coicidece with both P eutros ad certai gates i the relevat TKE spectrum. It follows from the TKE spectra that the domiat reactios at forward agles are elastic ad ielastic breakup. The projected proto spectra clearly idicate the large cotributios to the TKE spectra of either (d,) trasitios to proto uboud states or (d,p) trasitios to eutro uboud states. Isufficiet proto eergy resolutio may easily result i a overestimate of the crosssectio of the projectile breakup process by a factor of two. Fig. 3 shows the agular correlatio for the elastic breakup process with 0 fixed at ad 8 variable. Similar agular correlatios have " P bee obtaied for ielastic breakup to the 1.78 MeV 2 state of Si. Correlatios were also measured with the proto detector fixed at ad

4 tile 2) breakup 6 MeV the the breakup breakup has Kleifel ler o far oly a V made. :olorado. Si(d,p) At imit for the up, models. models, The 3 are easily emets, ad?cted is up to be spectrum to a ito a bump '44c. It is o detector es ad the =-12.5cad j with both ollows from 3 re elastic idicate the s to proto sufficiet the crossup process it ios have, 28c. of Si e ad 7 50 i i i ' 111 i i Si (d,p) 10 deq. 638 i I I I I Jl I I I I I I I I I I I I I I II I I H I I I II I I I I I I I I I I I I I I I I I I I 0 Chael Fig. 1: Proto sigles spectrum at 10. TTTT 11 [ M M 4.93 HilifiiiJ.J the eutro detector variable. All of the direct breakup correlatios are similar i shape; they show a peak for detectors o opposite sides of the 1.27 G.S. 900 beam. I he correlatios with 8 fixed show a secod maximum at 6 =50c This p maximum is abset i the fixed-proto correlatios. This situatio i s similar to that of the p-d correlatios measured i the 52 MeV breakup of 3 28 He o Si. I this case i t was foud that the correlatio with 0 fixed d showed a secodary maximum at 6 =45, while the correlatio with 0 fixed 4,5) P 3 P showed o secod maximum. For He breakup the agular correlatios could be reproduced by calculatios usig the quasi-free breakup model (QFBM) with 4) the proto a spectator. Such calculatios are presetly beig used to determie which particle is the domiat spectator i the breakup of the deutero. A correlatio was also obtaied with the eutro couter fixed ad 28 gates set o the regio of the TKE spectrum above the 1.78 MeV state i Si excitatio. This correlatio has a sigle maximum at about 12, ad a FWHM of about 50c. Itegratig the agular correlatios over the agular rage allows a compariso with the iclusive breakup cross-sectio at The - 623

5 Fig. 2: TKE ad projected proto spectra. prelimiary results are listed i table 1. From table 1 it may be cocluded that the elastic ad ielastic breakup together cotribute about 20% of the cross-sectio, with the rest beig absorptive breakup. This work was fiaced i part by USDOE, NATO, FOM ad ZWO. preset address: Brookhave Natioal Lab, Upto, NY USA REFERENCES 1. R. Serber, Phys. Rev. 72. ( 1947) N. Matsuoka et aj_, Nucl. Phys. A391 (1983) E. H. L. Aarts et a]_, Phys. Lett. 105B (1981) E. H. L. Aarts et al_, Nucl. Phys. A380 ( 1982) E. H. L. Aarts et a], to be published 6. J. Kleifeller et a±, Nucl. Phys. A370 (1981) 205 ~ 624 -

6 28Si(d.p)28Si(g.».) E "17 85MeV 0 e_--12.5* tv p L A B < d e 9 ' Fig. 3: Proto agular correlatio. Table 1 Compariso of proto ad eutro breakup bump cross-sectios at 12.5 together with cross sectios obtaied from the agular correlatio measuremets. 6 =-12.5 : Elastic: 14+/-3 Ielastic: 11+/-3 Absorptive: 85+/-10 Total: 110+/-16 Sigles eutro cotiuum bump: 100+/ : Elastic: 17+/-4 Ielastic: 9+/-4 Absorptive: (umeasured) Total: 26+/-6 Sigles proto cotiuum bump: 148+/