Decays of New Nuclides 169Au, 170Hg, 165Pt and the Ground State of 165Ir Discovered Using MARA

Abstract

<p>New nuclides&nbsp;¹⁶⁹Au,&nbsp;¹⁶⁵Pt and&nbsp;¹⁷⁰Hg and new ground state&nbsp;¹⁶⁵Irg&nbsp;were produced using reactions of&nbsp;⁹⁶Ru(⁷⁸Kr,XpXn) at bombarding energies of 390 MeV and 418 MeV and&nbsp;⁹²Mo(⁷⁸Kr,XpYn) at a bombarding energy of 418 MeV. The MARA vacuum mode recoil mass separator was used to separate the new nuclei and implant them into a DSSD instrumented with digital readout electronics to measure their decay properties. The proton-emitting nuclei were identified using digitised preamplifier output `traces', and the method used is discussed in depth.</p> <p>Fifteen proton-decay chains of&nbsp;¹⁶⁹Au^<i>m</i> were measured with proton-emission energy&nbsp;E_<i>p</i>&nbsp;= 2182(28) keV and half-life&nbsp;T_1/2&nbsp;= 1.27⁺⁰^.⁶¹_–0_.₅₇_&nbsp;ms. One&nbsp;&alpha;-decay chain of&nbsp;¹⁶⁹Aum&nbsp;was also identified with&nbsp;&alpha;-particle energy&nbsp;<em>E</em><em>_&nbsp;</em>_&alpha; = 7333(27) keV, which occurred 1.3&nbsp;&mu;s after the recoil ion was implanted. Combining the data for both decay branches yielded a half-life of 1.16⁺⁰^.⁵⁰_–0_.₄₇ &mu;s and an estimated production cross section of 5 nb for this state in&nbsp;¹⁶⁹Au.</p> <p>Seven proton-decay chains of&nbsp;¹⁶⁵Ir^g were measured with proton emission energy&nbsp;E_<i>p</i>&nbsp;= 1454(38) keV and&nbsp;T_1/2&nbsp;= 1.20⁺⁰^:⁸²_–₀_:₇₄ &mu;s.</p> <p>The results are compared withWentzel-Kramers-Brillouin (WKB) calculations.The prospects of observing proton emission from even lighter gold and iridium isotopes are discussed.</p> <p>Four&nbsp; &alpha;-decay chains of&nbsp;¹⁶⁵Pt were measured with&nbsp;_-particle energy&nbsp;E_&alpha;&nbsp;= 7272(14) keV and&nbsp;T_1/2&nbsp;= 0.26⁺⁰^:²⁶ _–₀_:₀₉ ms, with an assumed&nbsp;a&nbsp;branching ratio of&nbsp; &asymp; 100%.</p> <p>One&nbsp;&alpha;-decay chain of&nbsp;¹⁷⁰Hg was measured with&nbsp;E_&alpha; = 7590(30) keV and&nbsp;T_1/2&nbsp;= 0.08⁺⁰^:⁴⁰_–₀_:₀₄ ms, with an assumed&nbsp; &alpha; &nbsp;branching ratio of&nbsp;&asymp;100%. Reduced&nbsp;&alpha;-decay widths were compared with systematic data in the region, indicating that both&nbsp;&alpha;&nbsp;decays are unhindered. Combining the&nbsp;&alpha;-decay&nbsp;<i>Q</i>&nbsp;values measured with extrapolated masses indicates that the new nuclides are both unbound to 2-proton emission by&nbsp;&gt;1 MeV. However, this decay mode does not compete as their&nbsp;&alpha;-decay half-lives are too short. Improved data were obtained for the&nbsp;a&nbsp;emitters&nbsp;¹⁶⁶^;¹⁶⁷Pt, produced via the&nbsp;⁹⁶Ru(⁷⁸Kr,&nbsp;&alpha;4n) and&nbsp;⁹⁶Ru(⁷⁸Kr,&nbsp;&alpha;3n) reactions at bombarding energies of 390 MeV and 418 MeV, respectively.</p> <p>The results of this thesis are presented in 2 refereed publications [1, 2].</p>