A3F-CNS Summer School 2023

ER cross-section and ER gated spin distribution measurements in the mass region A∼190

5 Aug 2023, 15:40

15m

Experimental Nuclear Physics Young Scientist Session I

Speaker

Mr Ranjan Sariyal (Department of Physics, Panjab University Chandigarh)

Description

Evaporation Residue (ER) cross-sections and ER gated $\gamma$-ray fold distributions were measured for the ${}^{32}$S + ${}^{154}$Sm nuclear reaction above the Coulomb barrier at six different beam energies from 148 to 191 MeV. $\gamma$-ray multiplicity and spin distributions were extracted from ER-gated fold distributions. The measured ER cross-sections are compared with the results of both the Statistical model calculations and the dynamic model calculations. Statistical model calculations have been performed to generate a range of parameter space for both the barrier height and Kramers' viscosity parameter over which ER cross-section data can be reproduced. The calculations performed by the dinuclear system model reproduce the data considering both complete and incomplete fusion processes. Comparison of the ER cross-sections measured in previous work using very different target-projectile combinations with much less mass asymmetry than the present measurement clearly demonstrates the effect of the entrance channel on ER production cross-section.

In the present case, ${}^{186}$Pt${}^{\ast }$ compound nucleus was popultaed to measure the ER cross-sections. These measurements were carried out using HYbrid Recoil Mass Analyser (HYRA) in gas mode coupled with TIFR 4$\pi$ spin-spectrometer. ${}^{32}$S pulsed beam from 15 UD Pelletron + LINAC accelerator facility at IUAC(Inter-University Accelerator Facility), New Delhi with an average current of ∼ 0.5 - 1 pnA was bombarded on ${}^{154}$Sm target of thickness 118µgm/cm${}^2$ with carbon capping and backing of 25µgm/cm${}^2$ and 10µgm/cm${}^2$ respectively.

Raw fold distributions were ER-gated to remove statistical and non-rotating $\gamma$ rays contributions. Realistic simulations of TIFR 4$\pi$ spectrometer, consisting of 32 NaI(Tl) detectors were carried out using Geant4, and fold distribution for different multiplicities were generated i.e. for a given gamma multiplicity M, distribution in fold k. Fold distribution P(k) probability can be given by:
$$P(k)=\sum _{M_{\gamma =0}}^{\mathrm{\infty }}R(k,M_{\gamma })P(M_{\gamma })$$
where R(k, M${}_{\gamma }$) is the response function, in other words, it is the probability of firing k detectors out of N detectors for M uncorrelated $\gamma$ rays and P(M${}_{\gamma }$) is the probability of multiplicity distribution. Experimental fold data is used to extract multiplicity as well as spin distribution of ${}^{186}$Pt${}^{\ast }$. Response function was generated using Geant4 simulations using the exact geometry of the spin-spectrometer. We have convoluted experimental fold data with R(M${}_{\gamma }$,k) to get the multiplicity distribution (with error bars). Theoretical calculations along with experimental results will be presented in the school.