Explaining the anomalous abundance of 84Sr with gamma-ray and mass spectroscopy at TRIUMF-ISAC.

Synopsis

TRIUMF-ISAC was built to explain the production of the elements in stellar nucleosynthesis environments.  The TIGRESS and EMMA programs utilize gamma-ray spectroscopy and mass spectroscopy to address this and other topics in fundamental nuclear science.  Atoms and molecules of exotic isotopes are produced at the Isotope Separatior and ACcelerator facility at TRIUMF on the UBC campus.  They are ionized, extracted, mass analyzed, and accelerated to up to 10% the speed of light, high enough energy to overcome electric repulsion between atomic nuclei.  Nuclear reactions may be induced this way, resulting in, amongst other processes, the emission of photons (gamma rays) from the product nuclei themselves.  The reaction product and the photons emitted during a single reaction are measured simultaneously in the ElectroMagnetic Mass Analyzer and the TRIUMF-ISAC Gamma-Ray Escape Suppressed Spectrometer respectively.  The first measurement performed with TIGRESS and EMMA together used an accelerated radioactive rubidium beam to measure the luminescence cross section 83Rb+1H®84Sr+hn.    The results indicate a lower rate for the inverse photolysis reaction than is predicted by statistical models, which in turn partially explains the anomalously high abundance of the lightest stable Sr isotope that is observed in meteorite materials originating from outside our solar system.