Fission hindrance studies inPb200: Evaporation residue cross section and spin distribution measurements

Abstract

Evaporation residue cross sections and spin distributions have been measured for 200 Pb compound nucleus formed in 16 O+ 184 W reaction at the laboratory beam energies of 84, 92, 100, 108, 116, and 120 MeV. The evaporation residues have been selected using the recoil mass spectrometer, HIRA and detected using a 2D position sensitive silicon detector. The evaporation residue spin distributions have been measured by detecting gamma rays with 14 element BGO multiplicity filter. Measured evaporation residue cross sections and spin distributions are compared with the values predicted by a standard statistical model code. Comparison shows that, in the energy region studied, the nuclear viscosity parameter γ = 3 is required to explain total evaporation residue cross sections and evaporation residue spin distributions.

A Monte Carlo C-code for calculating transmission efficiency of recoil separators and viewing residue trajectories

“…Here we show an example of transmission efficiency calculation for the complete fusion reaction 16 O + 184 W, studied in HIRA, at E beam = 100 MeV leading to the compound nucleus 200 Pb * [12]. We consider 5 neutron evaporation in the exit channel and 10 5 events.…”

ER cross section measurement in16O+194Pt reaction using gas-filled mode of HYRA

“…Conventional γ-ray method to determine transmission efficiency was not very effective in the present measurement due to the intense γ-ray background originating from fission fragments as well as the nickel window foil, used for separating the gas medium from the high vacuum of the beam line. Hence we used 16 O+ 184 W as the calibration reaction, for which ER cross sections were already reported [6], for determining transmission efficiency of the HYRA for 16 O+ 194 Pt reaction. Isotopically enriched 184 W target [7] was bombarded by 16 O beam at 96.0 MeV beam energy.…”

“…ǫ MWPC HYRA for this reaction was then calculated, using the ER cross section from Ref. [6], which was found to be 2.48±0.40% when the ER yields were taken from the MWPC detector. ǫ SSBD HYRA obtained with the ER counts from the silicon detector for the 16011-p.2 FUSION11 same reaction was 1.78±0.27%.…”

“…This result provides further evidence of onset of nuclear dissipation in mass ∼200 region. Shidling et al [6] reported that a dissipative strength of β = 3 is required to explain ER excitation function in 16 O+ 184 W reaction. Similar results were reported in Ref.…”

A Monte Carlo code to calculate transmission efficiency of HIRA

“…Transmission efficiency for a system can be measured by g-ray method [3] in which g-rays from the ERs are measured in singles and in coincidence with the ERs, detected at the focal plane of the separator. The ratio of counts of a specific g-line, corresponding to a particular ER, in coincidence spectrum to that in the singles spectrum gives the absolute transmission efficiency of the separator.…”