Physics Letters B 283 ( 1992) 27-31 North-Holland PHYSICS LETTERS B The Coulomb break-up of 9Be E.W. Macdonald, A.C. Shotter, D. Branford, J. Rahighi 1, T. Davinson and N.J. Davis Department of Physics, Universityof Edinburgh, Edinburgh EH9 3JZ, UK Received 14 January 1992 Kinematically complete data is presented on the break-up reaction t Z°Sn(gBe, 8B%.,. + n ) 12OSng.s. at Eb~a,~ = 90 MeV for several scattering angles inside the grazing angle. These data are compared with the predictions of a Coulomb break-up model. It is shown that the data can be understood in terms of the Coulomb model provided some account is taken of the interactions of the break- up fragments with the target. Analysisof the 9Be break-up data, using radio-isotope measurements of the 9Be (~', n) cross-section, indicates that for this photo-disintegration reaction there is probably a significant direct component to the threshold cross-section, in addition to a threshold resonance at 1.69 MeV. It has now been well established that there exists a non-sequential break-up mechanism for VLi projec- tiles scattered off heavy targets such as 96Zr, 12°Sn and 2°Spb [ 1-4]. The original discovery of the non-se- quential mechanism was made by Shorter et al. [ 1 ] while studying the reaction 2°Spb(TLi, tt+t). This discovery stimulated much interest and further work [4-6], such that there now exists an extensive data- set on the 7Li non-sequential reaction. Shorter et al. proposed an explanation of the non-sequential yield in terms of a Coulomb direct break-up model [2 ]. The central feature of this model is that the 7Li pro- jectile is excited directly from its ground state into continuum a+t states by the projectile-target Cou- lomb interaction. At forward scattering angles, the direct Coulomb break-up model is very successful at reproducing both the shape and magnitude of the ex- perimental energy spectra [2]. Recent calculations [ 7 ] have extended the Coulomb model to include, in a simplifed fashion, the effect of nuclear final state interactions (FSIs) between the break-up fragments and the target. These new calculations have demon- strated that the Coulomb model can explain the mag- nitude of the non-sequential yield for all measured angles up to the grazing angle. (Beyond the grazing Permanent address: Esfahan Nuclear Technology Centre, Esfahan, Iran. angle, the assumptions of the Coulomb model are not valid. ) Interest in break-up reactions has recently grown due to the possibility of using such reactions to ex- tract radiative capture cross-sections. Clearly, if break-up reactions are to be used in this manner, it is important to test the Coulomb model on other break- up reactions and in particular to explore the new ideas regarding the role of final state interactions in the break-up process. The break-up of 9Be into the 8Be + n channel is a good reaction to study because this reaction has a high predicted Coulomb break-up cross-section due to its low Q-value (-1.666 MeV) and high E1 effective charge (ZsBe/A,Be -- Z,/An = 0.5). Furthermore, there exists high-quality 9Be(•, n) photo-neutron data [8,9], which means that Coulomb break-up cross-sections can be accurately calculated for the 9Be--,8Be+n reaction and that the Coulomb model can therefore be stringently tested by an experimen- tal measurement of this reaction. In this letter, we shall present the results of an experimental study of the break-up reaction ~2°Sn(gBe, 8Be+n). The mea- sured break-up cross-sections will be compared with the predictions of the Coulomb model and the effect of final state interactions on the 9Be break-up process will be investigated. The experimental work discussed here was under- taken at the nuclear structure facility (NSF) of Dar- 0370-2693/92/$ 05.00 © 1992 Elsevier Science Publishers B.V. All rights reserved. 27