NSRL Time of Flight Study using Carbon Ions at 120 MeV/n

Abstract

angular distributions which are peaked strongly in the forward direction. For the Be/sup 9/(He/sup 3/ ,n)C/sup 15/ reaction resolved neutron groups were seen for the ground state and the flrst four excited states (1.99 4.26 4.75 and 6.50 Mev) in C/sup 11/ Excitation functions were measured at 0 and 90 deg for He/sup 3/ energies from 0.5 to 2.7 Mev and angular distributions measured at 2.l Mev. From the distorted wave calculations, the following spin and parity assignments were made; n/sub 0/ (1/2 /sup -/ yields 7/2/sup -/)n/sub 1/(1/2/sup -/ yields 7/2 /sup -/ ), n/.sub 2/(*1/2 /sup -/ yields 7/2 /sup -/ annd n/sub 4/ (3/2/sup -/). For the Li/sup 7/(He/sup 3/,n)B/sup 9/ reaction, neutrons from the ground state were clearly resolved from the unresolved second and third excited states. An excitation function was measured from 0.5 to 2.7 Mev at 0 deg and an angular distribution was taken at 2.1 Mev for the ground state group. Distorted wave calculations give a spin and parity assignment of resolved neutron groups were seen for the ground state and third excited state (6.15 Mev) in O.sup 15/. Excitation functions were measured from 1 to 2.7 Mev at 0 and 90 deg . The most outstanding feature of the excitation function is the resonance at a He/sup 3/ center of mass energy of l.55 Mev. This resonance corresponds to a new state in O/sup 16/ at an excitation of 24.04 Mev. This state has a laboratory width of plus or minus 100 kev. Angular distributions were measured for the ground and third excited states at 2.66 Mev. From the distorted wave calculations, the following spin and parity assignments were made; n/sub 0/(1/2/sup -/) and n/sub 3/ (5/2 /sup +/ yields 7/2 /sup +/. In a summary it might be said that the angular distributions from the (He/sup 3/,n) reactions studied, though complex in nature, can be fitted with distorted wave calculations, even at low energies. Furthermore it appears that the (He/sup 3/,n) reactions can be used to make spin and parity assignments to many of the proton-rich nuclides which are virtually inaccessible by other reactions. (auth)