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By using the recoil-fission correlation technique, the exotic process of beta-delayed fission (βDF) was unambiguously identified in the very neutron-deficient nuclei 192,194At in experiments at the velocity filter SHIP at Gesellschaft f¨ur Schwerionenforschung (GSI). The upper limits for the total kinetic energy release in fission of 192,194Po, being the daughter products of 192,194At after β+/EC decay, were estimated. The possibility of an unusually high βDF probability for 192At is discussed. ispartof: Physical Review C, Nuclear Physics vol:87 issue:1 status: published

NESTER; The new neutron-deficient isotope 187Po has been identified in the complete fusion reaction 46Ti+144Sm-->187Po+3n at the velocity filter SHIP. Striking features of the 187Po alpha decay are the strongly-hindered decay to the spherical ground state and unhindered decay to a surprisingly low-lying deformed excited state at 286 keV in the daughter nucleus 183Pb. Based on the potential energy surface calculations, the 187Po ground state and the 286 keV excited state in 183Pb were interpreted as being of prolate origin. The systematic deviation of the alpha-decay properties in the lightest odd-A Po isotopes relative to the smooth behavior in the even-A neighbors is discussed. Improved data for the decay of 187Bim,g were also obtained.

The Doppler-shift attenuation method was applied to measure the lifetime of the 4.03 MeV state in 19Ne. Utilizing a 3He-implanted Au foil as a target, the state was populated using the 20Ne(3He,alpha)19Ne reaction in inverse kinematics at a 20Ne beam energy of 34 MeV. De-excitation gamma rays were detected in coincidence with alpha particles. At the 1 sigma level, the lifetime was determined to be 11 +4, -3 fs and at the 95.45% confidence level the lifetime is 11 +8, -7 fs., Comment: 6 pages, submitted to Phys. Rev. C

NESTER; The new neutron-deficient isotopes 193,194Rn have been identified in the complete fusion reaction 52Cr+144Sm-->196Rn* at the velocity filter SHIP. The alpha-decay energy and half-life value of 194Rn were determined to be Ealpha=7700(10) keV and T1/2=0.78(16) ms, respectively. For 193Rn the half-life of T1/2=1.15(27) ms and two alpha lines at Ealpha1=7685(15) keV, Ialpha1=74(20)% and Ealpha2=7875(20) keV, Ialpha2=26(12)% were found. The decay pattern of 193Rn, which is substantially different from that of the heavier odd-A Rn isotopes, provides first experimental evidence for the long-predicted deformation in the very neutron-deficient Rn nuclei.

Multiple band structures in 179Au are established from γ-ray spectroscopic measurements with Gammasphere at the Argonne Fragment Mass Analyzer. The yrast band, based on the 13/2+ proton, confirms the predicted drop in excitation energy of the prolate deformed band head as compared to the heavier isotopes. The implications for the prolate energy minimum in odd-mass Au nuclei beyond the neutron i13/2 midshell (N

High-spin states in 174Pt were populated via the 92Mo(84Sr, 2p) and 92Mo(84Sr, 2p2n) reactions. The ground-state band has been extended from I= 14 to 24 (tentatively 26) and a new side band is observed up to a spin of 21 (tentatively 23). A low-frequency crossing is observed in the latter band at a rotational frequency that is similar to that seen in the ground-state band. The first and second i13/2 neutron alignments are also observed in 174Pt. Surprisingly, these crossings occur at approximately the same frequency. Total Routhian surface and cranked shell model calculations are used in an attempt to understand this behavior.

The decays of the very neutron rich Sn isotopes $^{135-137}$Sn were studied at CERN/ISOLDE using isotopic and isobaric selectivity achieved by the use of a resonance ionization laser ion source and mass spectroscopy, respectively. Neutron decay rates, $\gamma$-ray singles, and $\gamma\gamma$-coincidence data were collected as a function of time. The half-life ( T$\scriptstyle_{1/2}$ ) and delayed neutron emission probability ( $p_{n}$ ) values of $^{135}$Sn were measured to be 530(20) ms and 21(3)%, respectively. For $^{136}$Sn, a T$\scriptstyle_{1 /2}$ of 250(30) ms was determined along with a $p_{n}\,$ value of 30(5) %. For $\,^{137}$Sn, a T$\scriptstyle_{1/2}$ of 190(60) ms and a $p_{n}$ value of 58(15)% were deduced. Identification of low-energy transitions in $^{135}$Sb was made possible by comparison of laser-on and laser-off $\gamma$-ray spectra. Those data combined with $\gamma\gamma$-coincidence spectra were used to construct a level scheme for $^{135}$Sb that includes an unexpectedly low first excited state at 282 keV. A ground state $\beta$-branch of 33.2% was measured by following the growth and decay of the $^{135}$Sb daughter. Shell-model calculations are consistent with the observed $^{135}$Sb level structure and can account for a lowered first excited state.