[Triumf-seminars] TRIUMF Nuclear Physics Seminar today at 15:15
TRIUMF Seminars
triumf-seminars at lists.triumf.ca
Wed Sep 25 05:00:00 PDT 2019
Date/Time: Wed 2019-09-25 at 15:15
Location: Auditorium
Speaker: Andrew Briscoe :: Jacob Heery (University of Liverpool)
Title: The Decay of the previously unobserved nucleus 160Os84 :: Developing the charge plunger technique for lifetime measurements in the heaviest nuclei
Abstract: Alpha radioactivity is the principal decay mode of the most neutron deficient isotopes of even-Z elements from plutonium (Z=94) down to osmium (Z=76). Qalpha-values increase steadily with increasing neutron deficiency down to N=84 and consequently half-lives decrease rapidly. Beyond N=84 a sudden drop in Qalpha-values is observed as a result of the neutron shell closure at N=82. For this reason the previously unobserved nucleus 160Os84 is expected to be the lightest osmium isotope for which alpha emission is the dominant ground-state decay mode.
Apart from alpha decay, there is the possibility of a competing two-proton (2p) emission decay branch from this nucleus, since the ground state of 160Os is predicted to be unbound with Q2p=0.64 MeV. Two-proton emission from the ground state is unlikely, but spin-gap isomers have been observed in the neighbouring even-even isotones.
The experiment aimed at the synthesis and investigation of the new isotope 160Os was performed at the Accelerator Laboratory of the University of Jyvaskyla. Nuclei were produced via fusion-evaporation by bombarding a 106Cd target with 58Ni ions, separated in flight using the newly commissioned MARA vacuum mode recoil-mass separator and implanted into a double-sided silicon
strip detector (DSSD). An array of four HPGe clover detectors surrounding the DSSD was present, allowing for spectroscopy of the charged-particle and gamma-ray radiation of implanted nuclei.
::
Lifetime information on nuclear states provides a crucial test for theoretical models predicting the structure of nuclei and the interplay between a single particle shell model description of the nucleus, and one involving more collective forms of excitation. However, there is little lifetime information for excited nuclear states in the heavy region of the chart where internal conversion coefficients (ICCs) for low energy transitions become large. The charge plunger technique aims to provide a way to use these large ICCs to measure lifetimes in heavy nuclei. One region where information on deformation parameters would be particularly insightful is the Z=100, N=152 deformed shell gap, lying at the boundary between the transactinide nuclei and the superheavy elements.
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