Advances in Radioactive Isotope Science

Mass Measurements of Neutron-rich Rare-earth Isotopes

30 May 2017, 17:20

15m

Invited Presentation Breakout 1

Speaker

Rodney Orford (McGill University)

Description

The rapid neutron capture process (r process) is thought to be responsible for the production of roughly half of the heavy elements found in nature, however the site of the r process is unknown and remains one of the most active areas of research in nuclear astrophysics. Testing r-process predictions requires experimental nuclear data inputs including masses, beta-decay properties, and neutron-capture rates. A recent study [1] has posited a link between the formation of the rare-earth peak near N = 100 and an array of potential r-process sites, but there is currently little available nuclear data in this region. As current RIB facilities improve and next-generation facilities come online, the opportunity to test such r-process calculations and inspire others is quickly growing. One such facility is CARIBU, located at Argonne National Laboratory, where intense beams of neutron-rich isotopes are produced from the spontaneous fission of 252Cf. The recent commissioning of a MR-TOF at CARIBU provides highly mass-resolved (R>50,000) beams to the low-energy experimental area where the Canadian Penning Trap mass spectrometer (CPT) is housed. A major upgrade to the detector system at the CPT has been made in order to implement the contemporary Phase-Imaging Ion-Cyclotron-Resonance (PI-ICR) mass measurement technique [2], which has allowed us to probe further from stability than was previously possible. PI-ICR is intrinsically more efficient than other Penning trap mass measurement schemes and offers increased sensitivity to more weakly produced isotopes without loss in precision. Buoyed by the MR-TOF, this new technique has been used to determine the masses of a number of previously unmeasured rare-earth nuclides around A~160 in the past year. The benefits of PI-ICR and the astrophysical implications of the newly measured masses will be discussed. References: [1] M. Mumpower et al., ApJ, 833, 282, 2016 [2] S. Eliseev et al., Phys. Rev. Lett. 110, 082501, 2013 [3] T.Y. Hirsh et al., Nucl. Instr. Meth. Phys. Res. B, 376, 229, 2016 This work was supported by the following: NSERC SAPPJ-2015-034, NSF grants PHY-1419765 and PHY-14330152, and the U.S. Department of Energy, Office of Nuclear Physics, under Contract No. DE-AC02-06CH11357. This research used resources of ANL's ATLAS facility, which is a DOE Office of Science User Facility.