[Triumf-seminars] TRIUMF Seminar today at 14:00

[TRIUMF Seminars]

Date/Time: Thu 2012-05-03 at 14:00

Location:  Auditorium          

Speaker:   Krzysztof  Rykaczewski (Oak Ridge National Laboratory)

Title:     Decay studies at the limits of neutron-rich nuclei

Abstract: The decay studies of radioactive nuclei are often offering the last verification points for nuclear theories and are helping to extrapolate nuclear properties into unknown territories.  The examples of such studies of 238U fission products  including ten most neutron-rich isotopes of Cu, Zn, Ga, Ge and As performed at the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge will be given. 

New beta half-life measurements of 81Zn [Padgett2010], 82Zn, 83Zn and 85Ga [Madurga 2012] inspired the refinement of theoretical description of beta decay process [Borzov 2012] and led to the re-analysis of r-process nucleosynthesis [Surman 2012].  
Further improvements in isobaric selectivity at the HRIBF were achieved by using charge exchange cell to remove Zn from separated beam to study Cu decays, molecular beams of GeS and AsS, laser ion source and new detection techniques. These enhancements of experimental techniques allowed us to measure the decay properties of 79Cu [Korgul2012, Miller2012], of 85Ge, 86Ge, 86As and 87As [Korgul2012a, Mazzocchi2012] and of 86Ga verifying further Borzov’s theoretical modeling.

The construction of 2200 pounds Modular Total Absorption Spectrometer and its 12,000 pounds shielding completed in December 2011 enabled the HRIBF measurements of over twenty fission products between 85Br and 142La. The studied decays included seven nuclei declared by Nuclear Energy Agency of IAEA to have the highest priority for the decay heat analysis in nuclear fuels [NEA2007]. MTAS total energy spectra compared to current nuclear data base references clearly demonstrated an excess of high energy gamma radiation release in practically all studied decays.  

The HRIBF measurements using mass-separated, post-accelerated and on-line analyzed fission product beams [Gross2005, Winger2009] pointed to the beta-delayed neutron branching ratios much higher than accepted values.  These results contributed to the triggering of new evaluation of beta-delayed neutron emission process under the auspices of IAEA.
The continuation of the HRIBF research program on fission product decays at TRIUMF will be discussed.

Stimulants available 15 minutes before the talk.

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