Grant: Subatomic Physics Envelope - Project

The atomic masses of nuclides far from stability provide information on the energy released in the decay and nuclear reactions involving these exotic, short-lived, nuclei. The results are an important ingredient in predicting the rates and pathways of nuclear reactions that power explosive astrophysical events thought to be responsible for the nucleosynthesis of the heavier elements (through the rp-, nu-p- and r-processes). The data also provides a view of nuclear structure in regions where the nuclei have extreme neutron to proton ratios and, provide an opportunity for tests of nuclear physics theories trying to explain the properties of nuclei.*The Canadian Penning Trap Mass Spectrometer (CPT) is being used to measure the masses of very neutron-rich isotopes on or near the expected the reaction path for the astrophysical r-process. The nuclides of interest are produced by the CARIBU (Californium Radioactive Ion Beam Upgrade) facility at the Argonne Tandem Linear Accelerator System (ATLAS) by the spontaneous fission of the atoms in a ~1 Ci, 252Cf fission source. Improvements to the system have allowed us to perform measurements with an accuracy of (delta-m/m) of 10-7 among nuclides approaching 10-5% of the fission production. The implementation of a new phase-imaging measurement technique has allowed us to gain a dramatic increase in resolving power while reducing the observation time simultaneously, a significant improvement for measuring nuclides with short half-lives. Our measurements have focussed on nuclei that have been identified in astrophysical calculations as having the most effect on the calculated abundances in the rare earth peak. A new facility called the N = 126 factory is being developed that will give the CPT access to similar nuclei that are thought to contribute to the last abundance peak for the r-process.*In a second ion-trap system, the ions can be trapped in a gas-filled, cryogenic, open-geometry, radio-frequency quadrupole, ion trap (RFQ) providing a unique opportunity to study the correlation between the beta particles and the neutrinos emitted during the decay of the trapped ions. We have been studying the A=8 system with this apparatus in tests particle physics theories of the weak interaction. The trap can also be used to observe the emission of beta-delayed neutrons from fission fragments during their decay. A dedicated trap system is being constructed for the beta-delayed neutron work.*The amount requested will cover the operation and maintenance costs of the CPT mass spectrometer (which is entirely Canadian owned). The costs of the Canadian part of the team include the stipends for two graduate students, the salary for a post-doctoral fellow and, travel costs to and from the facility.