13-19 June 2015
University of Alberta
America/Edmonton timezone
Welcome to the 2015 CAP Congress! / Bienvenue au congrès de l'ACP 2015!

The first GRIFFIN Experiment: An investigation of the $s$-process yields for $^{116}$Cd

16 Jun 2015, 16:15
15m
CCIS L1-140 (University of Alberta)

CCIS L1-140

University of Alberta

Oral (Student, In Competition) / Orale (Étudiant(e), inscrit à la compétition) Nuclear Physics / Physique nucléaire (DNP-DPN) T3-6 Nuclear Structure III (DNP) / Structures nucléaires III (DPN)

Speaker

Mr Ryan Dunlop (University of Guelph)

Description

In adopted models for the $s$-process, it is assumed that helium shell flashes give rise to two neutron bursts at two different thermal energies $(kT\sim10$ keV and $kT\sim25$ keV). The contribution to the isotopic abundance of $^{116}$Cd from the higher temperature neutron bursts are calculated assuming thermal equilibrium between the ground state and the long-lived isomeric state of $^{115}$Cd. However, it is unknown if the thermal equilibrium between these states is present at the low temperature of the first burst. The presence of thermal equilibrium at low temperatures would significantly decrease the calculated $s$-process yields of $^{116}$Cd. To answer this question, we are searching for gateway levels at slightly higher excitation energy than the isomer in $^{115}$Cd that could be populated from the isomeric state via $(\gamma,\gamma^\prime)$ reactions within stars. Currently, the lowest potential gateway level at an excitation energy of 394 keV has only been observed to decay directly to the isomeric state in $^{115}$Cd. Nonetheless, the observation of this state decaying to the previously known 361 keV level via a weak 33 keV transition would provide a $\gamma$-ray cascade which would bypass the isomeric state. Thus, the observation of this decay would be a direct signature for the presence of thermal equilibrium during the lower temperature neutron burst. However, the direct measurement of a 33 keV transition is difficult due to the large low-energy $\gamma$-ray backgrounds observed in $\beta$-decay experiments. We therefore require high-efficiency $\gamma$-ray detection to indirectly observe this transition via $\gamma$-$\gamma$ coincidences of $\gamma$-rays cascading through this transition. In November 2014, the high-efficiency GRIFFIN HPGe spectrometer was commissioned at TRIUMF's Isotope Separator and Accelerator (ISAC). GRIFFIN is a state-of-the-art array consisting of 16 HPGe clovers, and boasts a large $\gamma$-ray efficiency of roughly 17% at 1 MeV. GRIFFIN also hosts a large suite of auxiliary detectors such as SCEPTAR, which is an array of 20 plastic scintillators designed for $\beta$-particle detection. In this first experiment, beams of $^{115}$Ag and $^{115}$Ag$^{\text{m}}$ were delivered to the GRIFFIN spectrometer equipped with SCEPTAR in order to search for these very-low-intensity $\gamma$-$\gamma$ coincidences following the $\beta$ decay of $^{115}$Ag into $^{115}$Cd. In this talk, results from this first GRIFFIN experiment will be presented.

Primary author

Mr Ryan Dunlop (University of Guelph)

Co-authors

Dr Adam Garnsworthy (TRIUMF) Ms Alejandra Diaz Varela (University of Guelph) Mr Alex Laffoley (University of Guelph) Ms Allison Radich (University of Guelph) Mr Andrew MacLean (University of Guelph) Mr Badamsambuu Jigmeddorj (University of Guelph) Dr Baharak Hadinia (University of Guelph) Dr Bruno Olaizola Mampaso (University of Guelph) Dr Carl Svensson (University of Guelph) Ms Christina Burbadge (University of Guelph) Dr Corina Andreoiu (Simon Fraser University) Mr David Cross (Simon Fraser University) Dr David Miller (TRIUMF) Mr Evan Rand (University of Guelph) Dr Gordon Ball (TRIUMF) Dr Jenna Smith (TRIUMF) Dr Kyle Leach (TRIUMF) Mr Lee Evitts (TRIUMF) Ms Lisa Morrison (TRIUMF) Mrs Michelle Dunlop (University of Guelph) Dr Mohamad Moukaddam (TRIUMF) Ms Nikita Bernier (TRIUMF) Dr Paul Finlay (Katholieke Universiteit Leuven) Dr Paul Garrett (University of Guelph) Dr Peter Bender (TRIUMF) Dr Smarajit Triambak (University of Western Cape) Mr Southall Dan (TRIUMF) Mr Usman Rizwan (Simon Fraser University) Dr Vinzenz Bildstein (University of Guelph)

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