Discrete ?-rays in the reactions of 143 MeV32S with58Ni

Abstract

The reactions induced by 143 MeV 32S on 58Ni have been studied detecting discrete ?,-rays in coincidence with projectile-like fragments (PLF). Information on PLF excitation probability and sequential decay of target-like fragments (TLF) has been obtained. For the 28Si+ 62Zn outgoing channel at small energy loss (IQ[<20 MeV), both PLF and TLF data indicate that thermal equilibrium is not attained. The hypothesis of an equal excitation energy partition between the two reaction fragments does not describe properly experimental TLF data. A dependence of PLF excitation probability on the outgoing channel is found for the two final channels 32S+58Ni and 28Si+62Zn. The values of the spin alignment parameter Pzz, derived for PLF and TLF from measurements of ?,-rays anisotropy, are in disagreement with the expectations of the transport theory for dissipative collisions. PACS: 25.70.Lm.

Projectile-like fragments excitation and gamma-rays emission after the deep inelastic reaction of32S on58Ni

“…This supports the hypothesis that the dominant origin of gammas is from the PLF's in this energy region, in agreement with the PLF excitation probability [4] and with the interpretation of the My vs. Q data, as discussed in Sect. 3.…”

“…Coincidences between projectile-like fragments, discriminated in energy and nuclear charge Zplf, and v-rays in four shielded 10 cm x 10 cm NaI(TI) scintillators, up to energies E~ = 8 MeV have been studied. The details of the experimental set-up and the data analysis have been reported in previous works [4,5,6]. Figure 1 shows samples of the y-spectra in coincidence with Zpl f-14 for different Q-value windows.…”

“…As a result, it has been shown that, in a given reaction, the ratio W(90~ ~ for discrete E2 7-transitions is much higher than for integrated values [2]. For the 32S + 58Ni reaction, W(90~ ~ 2 has been measured for E2 transitions with Ge detectors [4]. The effect of lowering the y-ray anisotropy due to the integration over E~ in the scintillator experiment is shown in Fig.…”

“…Taking this observation alone, the constancy of M s may be interpreted as evidence for weak or negligible sequential decay of the reaction fragments by particle emission in that energy loss region. However, a completely different explanation follows if the data are interpreted in the light of the discrete line experiment [4]. From that work it is known that at ]Q I= 20 MeV one half of the target-like fragments (TLF) in coincidence with Zplf= 14 emits one particle in the sequential decay and this fraction increases with the energy loss.…”

“…We reported previously on the study of discrete y-rays in the reactions of 143 Mev 32S + 58Ni [4]. Correlations between gamma intensities, nuclear charge (Zp~f) of projectile-like fragment (PLF) and energy loss were studied.…”