Neutron deficient platinum and osmium isotopes produced in theS32+Sm144fusion reaction

Abstract

A recoil-mass selector has been used to detect evaporation residues formed by neutron emission from the compound nucleus $^{176}\mathrm{Pt}$ produced by bombarding $^{144}\mathrm{Sm}$ with 139.5- to 201-MeV $^{32}\mathrm{S}$. The neutron-deficient platinum isotopes $^{172}\mathrm{Pt}$ ($4n$ emission) and $^{171}\mathrm{Pt}$ ($5n$ emission) were identified, among others, as well as their alpha daughters, $^{168}\mathrm{Os}$ and $^{167}\mathrm{Os}$. The alpha-decay energies and half-lives are $^{172}\mathrm{Pt}$: 6.09 MeV, 0.09 sec; $^{171}\mathrm{Pt}$: 6.450 MeV, 0.02 sec, $^{168}\mathrm{Os}$: 5.670 MeV, 2.2 sec; and $^{167}\mathrm{Os}$: 5.843 MeV, 0.8 sec. Alpha branching ratios of these and other daughters were also measured. An alpha line at 6.547, observed at beam energies above 190 MeV, was tentatively assigned to $^{170}\mathrm{Pt}$ ($6n$ emission) and at energies around 140 MeV indications of $1n$ emission were observed. The optimum cross sections for $1n$, $2n$, $3n$, $4n$, $5n$, and $6n$ emissions in that order are approximately 0.003, 0.09, 1.5, 0.15, 0.02, and 0.002 millibarns. Formation of iridium isotopes by $2n$ $1p$ evaporation, etc., was also observed, but is not discussed in detail in this paper.NUCLEAR REACTIONS, RADIOACTIVITY Complete fusion, $^{32}\mathrm{S}$ + $^{144}\mathrm{Sm}$, $E=139.5 \mathrm{to} 201$ MeV laboratory, measured $\ensuremath{\sigma}(E)$, ${E}_{\ensuremath{\alpha}}$, and ${t}_{\frac{1}{2}}$ for evaporation residues.