Gamma-ray studies of A = 119-126 tin isomers formed in deep inelastic heavy ion collisions
Abstract
The purpose of the present study was to investigate the feasibility of using deep-inelastic heavy-ion collisions as spectroscopic tool to study yrast isomerism in A $>$ 120 tin nuclei which cannot be produced in conventional fusion-evaporation reactions. Enriched 1mg/cm$\sp2\ \sp{122}$Sn and $\sp{124}$Sn targets, backed with lead, were placed at the center of the Argonne-Notre Dame $\gamma$-ray Facility. In-beam and off-beam $\gamma$-ray singles and $\gamma\gamma$ coincidences were recorded following the collisions with pulsed $\rm\sp{76}Ge,\ \sp{80}Se\ and\ \sp{136}Xe$ beams at energies of ${\sim}{15}$% above the Coulomb barrier. Experimental results include the identification of new $I\sp\pi = 10\sp+$ isomers in even-A $\rm\sp{122}Sn,\ \sp{124}Sn,\ and \sp{126}Sn$ and first characterizations of isomeric $I\sp\pi = 27/2\sp-$ decays in odd-A $\rm\sp{119}Sn,\ \sp{121}Sn,\ and\ \sp{123}Sn$ nuclei. The obtained level schemes are discussed in terms of shell model configurations. For even-A tin isotopes, the $10\sp+$ isomers are interpreted as ($\nu h\sb{11/2})\sp{n}$ seniority v = 2 states. The measurement of their isomeric half-lives completes a series of B($E2;10\sp+\to8\sp+)$ determinations in $\rm\sp{116-130}Sn$ nuclei illustrating the predicted dependence of $E2$ transition rates between $j\sp{n}$ states on $h\sb{11/2}$ subshell occupation number. The results establish half-filling of the $h\sb{11/2}$ in tin isotopes to occur close to mass number A = 123. The 27/2$\sp-$ isomers identified in odd-A tin nuclei are interpreted as ($\nu h\sb{11/2})\sp{n}$ seniority v = 3 states. Observed level energies are found to be in excellent agreement with predictions from fractional parentage calculations. The $\gamma\gamma$ coincidence data have also provided yield distributions of even-even deep-inelastic reaction products in both projectile and target regions. General features of the observed yield patterns are discussed within the framework of N/Z equilibration of the dinuclear system. Such calculations can be used to predict the outcome of future experiments. The new method of populating high-spin states in neutron-rich isotopes may aid in experimentally accessing up to now unexplored regions of the nuclear chart.
Degree
Ph.D.
Advisors
Grabowski, Purdue University.
Subject Area
Nuclear physics
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