Resonances inC12+C

Abstract

1213 14 15 16 17 LAB ENERGY (MeV)Resonant structures at 9.4 and 10.3 MeV cm. energy have been observed in both the reaction 12 C( 13 C,«) 21 Ne and the elastic scattering of 13 C from 12 C. Unambiguous assignments ofl~7 for both of the resonances are made.Considerable effort has been devoted to the search for resonances in heavy-ion systems. Previously, such resonances had been found in the systems 12 C + 12 C 1,2 and i2 C+ i6 0 3.4, 5 but had been considered nonexistent in 12 C + 13 C. 6 ' 7 In the present paper, we report the observation of resonances in the system 12 C+ 13 C. To reexamine the system 12 C + 13 C, we measured the excitation function of the reaction 12 C( 13 C, a) 21 Ne at a lab angle of 10° over a range of lab bombarding energies, £( 13 C) = 12 to 22.5 MeV, in 100-keV steps. Elastic scattering was measured at eight lab angles over the same energy range. As a result two definite resonances were observed to be correlated in the two exit channels.The excitation function for the reaction 12 C( 13 C, a) 21 Ne at a lab angle of 10° is shown in Fig. 1(a); the yield has been summed over the lowest thirteen levels in 21 Ne. Statistical fluctuations in summed excitation functions are expected to be damped by a factor which is greater than or equal to the number of levels (13). 8 * 9 From examination of Fig. 1(a) it can be seen that variations in the yield considerably in excess of those allowed by the statistical model do occur. Most of the energy range has been measured at least twice with good reproducibility. Prominent structures in the summed a yield are observed near the lab energies £^ = 15, 16.2, 17.3, 19.5, and 21.5 MeV (£ , c#m . = 7.2, 7.8, 8.3, 9.4,and 10.3 MeV, respectively). Less prominent structures are observed near £ lab = 20.3 (£ c>m . =9.7 MeV).In order to investigate whether the observed structure in the 12 C( 13 C, a) 21 Ne excitation curves might be due to resonances, we examined a different exit channel, the elastic scattering. The elastic scattering excitation functions for three cm. angles-73.4, 89.6, and 100.5°-are shown in Fig. 1(b). Resonances at .F lab =19.5 and 21.5 MeV can be plainly seen.In order to determine the I values of these resonances, the background elastic scattering was fitted by using the elastic-transfer theory of von 15 16 17 18 19 20 ZT LAB ENERGY (MeV) FIG. 1. (a) Excitation function for the reaction l2 C( 13 C,a) 21 Ne a t 0lab =1 O o . Different symbols represent data taken on different days with different targets. The solid curve is intended to "guide the eye" only. (b) Excitation functions for the elastic scattering of 13 C from 12 C at three cm. angles. The solid curves are optical-model calculations of the background cross section as described in the text. No resonances were considered in these calculations.782

Observation of a Backward-Angle Anomaly in the ReactionC12(C13

“…21 Ne and in the elastic scattering of 13 C on 12 C by Crozier and Legg. 5 The uncorrected nature of the resonant structure observed in the 13 C + 12 C reactions suggests some form of odd-nucleon quenching of the molecular states observed for the 12 C + l2 C system. In this Letter we report additional information on the 12 C + 13 C system obtained with the reaction 12 C( 13 C, «) 24 Mg (Q = 8.984 MeV).…”

Study of the hindrance effect in sub-barrier fusion reactions

“…Within this energy range, our data do not show an obvious S-factor maximum but a plateau. The optical models (dotted curves) with Woods-Saxon type potential [9] reproduces the experimental data only at energies above 4 MeV. The Fowler's model (dashed curve) which employs a repulsive potential [7,10] explains the plateau (E c.m.…”