[Triumf-seminars] TRIUMF Nuclear Physics Seminar today at 15:30

[TRIUMF Seminars]

Date/Time: Mon 2015-11-02 at 15:30

Location:  Auditorium          

Speaker:   Cody Parker (Ohio University)

Title:     The 3H(d,gamma) 5He reaction at Ecm ~300 keV

Abstract: The 3H(d,gamma;)5He reaction has gained importance in the scientific community because of inertial confinement fusion (ICF) studies, particularly at the National Ignition Facility. One way to investigate the fusion burn in the deuterium-tritium fuel is by detecting gamma;'s above about 10 MeV, which is useful for diagnostic purposes because the gamma come out of the implosion nearly unscattered, as opposed to the neutrons. In addition to the ICF application, studying the reaction can lead to a better understanding of the properties of the unbound 5He nucleus, which has two low-lying states that are unbound with respect to 4He+n, leading to both states having significant width when compared to the 3/2+ resonance state. There are gamma-ray transitions from the resonance state to each lower state, however, the gamma-rays from these transitions are not monoenergetic, but rather have an energy distribution, with uncertainty in the overall lineshape. Due to its importance, the 3H(d,gamma)/3H(d,n) branching ratio has also been measured, however there is a discrepancy regarding the order of magnitude of the ratio when comparing experimental results for similar deuteron energies.
In order to investigate this branching ratio discrepancy and the lineshape uncertainty, the 3H(d,gamma)5He reaction has been measured using a 500-keV pulsed deuteron beam incident on a stopping titanium tritide target at Ohio University's Edwards Accelerator Laboratory. The time-of-flight (TOF) technique has been used to distinguish the gamma-rays from neutrons detected in the bismuth germinate (BGO) gamma-ray detector. A stilbene scintillator and an NE-213 scintillator have been used to detect the neutrons from the 3H(d,n)alpha; reaction using both the pulse-shape discrimination and TOF techniques. A newly-designed target holder with a silicon surface barrier detector to simultaneously measure alpha-particles to normalize the neutron count was incorporated for subsequent measurements. The gamma-rays have been measured at laboratory angles of 0°, 45°, 90°, and 135°. Information about the gamma-ray energy distribution for the unbound ground state and first excited state of 5He can be obtained experimentally by comparing the BGO data to Monte Carlo simulations. The 3H(d,gamma;)/3H(d,n) branching ratio has also been determined. Current analysis for data at each laboratory angle will also be presented.



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