The inclusive and exclusive measurements were carried out for 7Li projectile breakup on 27Al target at 48 MeV. In the inclusive data we have observed a broad peak around the beam velocity for alphas and tritons. The exclusive data for alpha-triton coincidences show good agreement with the post-form DWBA theory of breakup reactions

Avasthi, D.K.

Datta, S.K.

Madhusoodhanan, T.

Mandal, S.

Manual, A.

Mudhole, T.S.

Puttaswamy, N.G.

Ramania, .

Sathyavathiamma, M.P.

Shyam, R.

Pramana : Journal of Physics

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PRAMANA c Indian Academy of Sciences Vol. 53, No. 3— journal of September 1999physics pp. 541–544Inclusive and exclusive measurements in the projectilebreakup of 7LiT MADHUSOODHANAN1, SAMIT MANDAL2, M P SATHYAVATHIAMMA1,RAMANI1, N G PUTTASWAMY1, T S MUDHOLE3, A MANDAL2, D K AVASTHI2,R SHYAM4 and S K DATTA21Department of Physics, Bangalore University, Bangalore 560 056, India2Nuclear Science Centre, P.B. No 10502, New Delhi 110 067, India3Department of Physics, Karnatak University, Dharwad 580 003, India4Saha Institute of Nuclear Physics, Calcutta 700 064, IndiaAbstract. The inclusive and exclusive measurements were carried out for7Li projectile breakup on27Al target at 48 MeV. In the inclusive data we have observed a broad peak around the beam velocityfor alphas and tritons. The exclusive data for alpha–triton coincidences show good agreement withthe post-form DWBA theory of breakup reactions.Keywords. Direct reactions; projectile breakup; post-form DWBA.PACS Nos 25.10+s; 24.50+g; 25.70+z1. IntroductionThere has been considerable interest in the study of the emission of charged particles ina reaction between two complex nuclei. It is characterized by large cross-sections andunusual shapes of the energy spectra. In addition to the compound nucleus formationand emission of charged particles from the equilibrated system, the direct breakup of theprojectile in the field of the target nucleus is found to be a dominant reaction channel[1–3]. A broad peak centered around the beam velocity is characteristic of the projectilebreakup. The inclusive spectra are basically interpreted to originate from fragments in aspectator role, reflecting the momentum distribution of the clusters in the projectile beforecollision. Various simple models describe the shapes of the breakup spectra fairly well [4].However these models account for only the elastic breakup mode and neglect the inelasticmode. Experimentally it is found that the inelastic channel contributes predominantly tothe inclusive cross-section. A realistic approach is the DWBA breakup theory developedby Baur and coworkers. The theory is based on a one-step breakup mechanism and enablescalculations of contributions from both the elastic and inelastic breakup modes [5].A kinematically complete study of the 7Li breakup is of considerable importance as itmay lead to a better understanding of the breakup of the neutron rich 11Li isotope and541T Madhusoodhanan et alother isotopes which have a ‘halo’ structure [6]. Our motivation in this study is mainly toinvestigate the nuclear and Coulomb part of the breakup cross section.2. Experimental detailsA beam of 48 MeV 7Li obtained from the Nuclear Science Centre, New Delhi was usedin the experiment. A self supporting 27Al foil of thickness 190 g/cm2 was used as target.The particle identification was achieved by usingE   E detector telescope. The exper-iment was carried out in the 1.5 m diameter general purpose scattering chamber (GPSC).Two telescopes were kept on each arm of the GPSC and one telescope was moved to differ-ent angles with the other fixed at 10Æ. The solid angle subtended by the solid state detectorwas 0.3 msr. The beam current on the target was around 10 pnA. A monitor detector waskept at 10Æ to view the beam. The data were also acquired using both solid state detectors(SSD) and a combination of a gas ionization chamber and a position sensitive strip detec-tor (PSSD). The SSDs used were 100 m Si for E detector and 5 mm Si(Li) for the Edetector. The 1 mm thick silicon PSSD with an active area of 50 mm 50 mm was used asE detector. An ionization chamber with an active length of 10 cm, and operated at a fieldof 1 V/Torr/cm, was used as a E detector for alpha particles. The coincidences betweenalpha particles and tritons were also recorded.Figure 1. Experimental alpha energy (shown as histogram) spectrum obtained at 10Æin the reaction 7Li on 27Al at 48 MeV.542 Pramana – J. Phys., Vol. 53, No. 3, September 1999Projectile breakup of 7Li3. Inclusive measurements and resultsThe differential energy spectra of the outgoing alphas and tritons were measured over arange of 8Æ to 38Æ in steps of 2Æ. A typical alpha spectrum at 10Æ is shown in figure 1. Thebroad bump corresponding to the beam velocity can be seen at the alpha energy of 27.4MeV.The breakup contribution was calculated in the framework of post-form DWBA theory.The inclusive breakup cross section for the reaction a+A! b+ x+B, with c = B + x,can be expressed asdincl=(2)4hvaXcTDWBAa;bc2Æ(E  Eb EBc)d3qb; (1)where vadenotes the projectile velocity [5]. In this calculation for the breakup of 7Li,a value of  100 MeV.fm3=2 has been used for D0. The prediction of the direct breakuptheory is shown in figure 1 as dashed line. In order to take into account the high energy tail,the pre-equilibrium contribution has been estimated in the frame work of the coalescencemodel using a coalescence radius of 248 MeV/fm for alpha particles [7]; this is shownas dotted line. The low energy part of the spectrum is accounted for by the equilibriumemission of the particles. The energy distribution of those particles is calculated usingthe PACE code and the result is shown as dash-dotted curve. The sum of all these threecontributions shown as solid line gives a reasonable fit to the experimental spectrum.4. Exclusive measurements and resultsFor coincidence measurements one telescope was fixed at 10Æ and the other moved todifferent angles. The E+Etspectrum showed a quasi-elastic peak around 45 MeV. Thispeak is used as a gate for extracting the exclusive spectra. It was noticed that there wereno prominent peaks arising from the resonant breakup of 7Li especially via the 4.63 MeVstate. The energy integrated triple differential cross sections for alpha particles extractedat each angle are shown in figure 2.These cross sections were compared with the direct fragmentation model (DFM) ofbreakup reactions formulated within the post-form DWBA [5]. In this model the incomingprojectile is assumed to breakup instantaneously in the Coulomb and nuclear fields of thetarget nucleus. The triple differential cross section is given byd3dbdxdEb= TDWBAfi2; (2)where  is the three-body density of states [5]. The optical potentials needed for the calcu-lations are taken from the literature. The value of D0used in the evaluation of the matrixelement is given in x3. In figure 2, the dashed (dotted) line represents the results of thecalculation preformed with pure nuclear (pure Coulomb) interactions while the solid lineis the full DWBA calculation. The theory is able to quantitatively describe the featuresof the data in the region where the angular seperation between the fragments is large. Asimilar agreement has been found for the case of energy integrated triton cross-sections.Pramana – J. Phys., Vol. 53, No. 3, September 1999 543T Madhusoodhanan et al-40 -20 0 20 4010-1100101102103Θt = 10o SSB telescope data Nuclear + Coulomb Nuclear Only Coulomb Only Strip detector telescope datad2 σ/dΩα dΩt (mb/sr2 )Θα (deg)Figure 2. Energy integrated triple differential cross sections for alpha particles in the7Li breakup on 27Al at 48 MeV. The triton detector was fixed at 10Æ.AcknowledgementThe authors wish to thank the Pelletron staff of NSC for smooth running of the machine.The project has been partially supported by a research grant from the University GrantsCommission.References[1] J Pampus, J Bisplinghoff, J Ernst, T Mayer-Kuckuk, J Rama Rao, G Baur, F Rosel and D Traut-mann, Nucl. Phys. A311, 141 (1978)[2] N Matsuoka, A Shimizu, K Hosono, T Saito, M Kondo, H Sakaguchi, A Goto and F Oklani,Nucl. Phys. A337, 269 (1980)[3] B Neumann, H Rebel, J Buschmann, H J Gils, H Klewe-Nebenius and S Zagromski, Nucl. Phys.A269, 113 (1980)[4] U Bechstedt, H Machner, G Baur, R Shyam, C Alderliesten, O Bousshid, A Djaloeis and P Jahn,Nucl. Phys. A343, 221 (1980)[5] G Baur, R Rosel, D Trautmann and R Shyam, Phys. Rep. 111, 333 (1984)[6] Isao Tanihata, J. Phys. G. Nucl. Part. Phys. 22, 157 (1996)[7] H Machner, Phys. Rep. 127, 309 (1985)544 Pramana – J. Phys., Vol. 53, No. 3, September 1999

Inclusive and exclusive measurements in the projectile breakup of 7Li

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Inclusive and exclusive measurements in the projectile breakup of 7Li

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