Alpha emission in coincidence with fission-like fragments from Cl+Ag reactions at 10 MeV/n

Abstract

Energy and angular correlations between alpha particles and fission-like fragments in the reaction of asCI+Ag at 10MeV/n have been measured. The coincident yield is dominated by two mechanisms: sequential emission from both fragments (M~=0.137 _+0.014) and alpha emission from the composite system prior to scission (M,=0.124 _+0.012). The observation of nuclear shadowing for sequential emission from the fragments allowed us to estimate the "lifetime" of the 218 MeV excited 143Gd composite system as (1-3)x10-2~It is argued that this rather long time reflects the slow evolution in shape of the composite system and might be termed "sticking time," since statistical-model lifetimes are typically an order of magnitude shorter. Observed also are small contributions of nonequilibrium emission in the forward direction (M~=0.005 _+0.001) and a component displaying the characteristics of emission from the neck (M s = 0.010 + 0.002).

Field emission of ? particles during scission of161Ho,169ta compound nuclei

“…This finding was also made in the experiment 3sc1 + natAg [5] where A = 5.5 and we speculate that this observation is not found in the experiments A and B, because of the small anisotropies there (A = 2.6 and A = 4.3).…”

“…This was accomplished by simply scaling down each component of the calculation (CNE, FE) in order to fit the experimental spectra. This finding of anisotropic particle emission is ascribed to the rotation of the supposedly deformed a-evaporating nucleus [3,5] and is regarded as an important clue to the determination of the shape of the nuclei [-5, 28]. The analysis of the data in terms of nuclear deformation will be published elsewhere [29].…”

“…From previous experiments [- 1,3,4,5,19] it is known that the spectra are dominated by sequential light particle emission from composite nucleus (CNE) and from fully accelerated fission fragments (FE). In a standard 3-source calculation [5,20,21] the reaction kinematics were defined by the measured velocity distribution of the fragments; the energy distribution of the primary fragments was parametrized by a Gaussian distribution, the mean and standard deviation of which were taken from the measured distributions. The latter was corrected for light particle evaporation by increasing the cm energy [22].…”

Ternary fission involving4He emission in the16O (144 MeV)+232Th and12C (108 MeV)+197Au reactions

“…This fact, together with the results of [12,13] implies that the probability of ternary fission increases with the excitation energy of the fissioning system.…”

“…The TFE multiplicities are considerably greater than those for the ternary fission of 252Cf(MTFE=0.0033__+0.0001 [26]) or for the p(42MeV)+23sU reaction [3]. On the other hand, in [13] for the ascl(350MeV)+"atAg reaction MTv E was found somewhat greater (MTvE=0.010 is shown in Fig. 8.…”