Volume 87B, number 1,2 PHYSICS LETTERS 22 October 1979 LIGHT-PARTICLE SPECTRA OBSERVED IN CENTRAL AND PERIPHERAL COLLISIONS OF 160 + 238U AT 20 MeV/NUCLEON T C AWES and C K GELBKE Heavy Ion Laboratory, Mtchlgan State Unwerstty, East Lansing, MI 48824, USA and Lawrence Berkeley Laboratory, Umverstty of Cahforma, Berkeley, CA 94720, USA B B BACK, A C MIGNEREY and K L WOLF Chemistry Dtvtslon, Argonne Nattonal Laboratory, Argonne, IL 60439, USA P DYER Heavy Ion Laboratory, Mwhlgan State Umverstty, East Lansing, 114148824, USA and H BREUER and V E VIOLA Jr Department of Chemistry, Untverslty of Maryland, College Park, MD 20742, USA Receded 29 June 1979 Energetic light particles have been measured m coincidence with two outgoing fission fragments which result from the reactmn 16 O + 2as U at 315 MeV Central and peripheral colhsmns can be distinguished by the momentum transferred to the target residue as deduced from the angle between coincident fissmn fragments A remarkable similarity is observed m the forward angle hght particle spectra observed m peripheral and central eolhsmns The enusslon of energetic hght particles [1 ] in heavy- 1on reactions at non-relatlWStlC energies has attracted renewed interest both expenmentally [1-9] and theo- retically [10-14] At present, however, little is known about the relatwe importance of peripheral and central collisions for the production of these particles In this letter we address ourselves to this questmn by mea- suring the angle between two coincident fissmn frag- ments [ 15-16] to &scnmmate between central and peripheral colllsmns The experiment was performed at the 88 inch cyclotron of the Lawrence Berkeley Laboratory A 238UF4 target of 200 ttg/cm 2 thickness mounted on a 50/ag/cm 2 carbon backing was bombarded with 16 06+ runs of 315 MeV energy I_aght pamcles (p, d, t, a) were detected at 14 ° with a AE-E telescope consist- mg of a 350/lm thick sohd state AE-detector and a 1½ inch thick NaI E-detector An aluminum absorber of 1 mm thickness was placed m front of this telescope to stop heavy parhcles (Z > 3) In adchtlon, two sohd- state detector telescopes were installed to detect alpha particles at 30 ° and heavy ions (l_a, , O) at 15 ° A lower threshold of 40 MeV was placed on both alpha particle spectra m the final analysis Two fission frag- ments enutted m coincidence with hght particles were detected by two posltlon-sensltlVe sohd-state detectors, each subtending the angular range of 620-98 ° and mounted m a plane with the hght particle telescopes In addition to the measurements at 315 MeV a short cahbratlon run was also performed at 140 MeV beam energy The momentum transferred to the target residue can be written as PR =PA +PB , (1) where the radices R, A, and B denote the target resxdue 43