Search for direct detection of thorium-229m nuclear VUV photons

Journal Article · Mon Jan 14 00:00:00 EST 2019 · Journal of Physics. B, Atomic, Molecular and Optical Physics

DOI:https://doi.org/10.1088/1361-6455/ab53c3· OSTI ID:1595743

Knize, Randall J. ^[1]; Lindsay, Mark D. ^[1]; Bowen, James M. ^[2]; Rotondaro, Matthew D. ^[1]

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1. United States Air Force Academy (USAFA), USAF Academy, CO (United States). Laser and Optics Research Center (LORC)
2. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)

We used two methods to attempt to measure the lifetime and energy level of the ^229mTh low-lying nuclear state. Both methods used a ²³³U source to implant ²²⁹Th into a VUV transparent substrate. The uranium source had a low concentration of ²³²U (0.08 ppm) and was chemically purified one week prior to the start of the experiment. In the first method, the time decay method, sensitive to ^229mTh lifetimes from 10 min to 15 h, the VUV substrate was irradiated for 4–36 h to ensure a sufficient transfer of ^229mTh ions into the substrate. Then the signal from the substrate was observed using a PMT for 15 h. A bandpass filter was placed between the substrate and PMT to provide a means of measuring the ^229mTh photon energy. We used nine filters with center transmissions ranging from 140 to 244 nm. In the second method, direct detection, sensitive to lifetimes from zero to 10 min, the substrate was observed directly with the PMT and filter during the deposition process. For both methods our results were limited by the strong background fluorescence and phosphorescence due to the alphas and betas intrinsic to the decay of the ²³³U and its daughters. We did not see unambiguous signs of photons from ^229mTh. This may be due to one or more of the following: lifetime of ^229mTh too short or too long, branching ratio to produce ^229mTh from ²³³U is too small, energy of ^229mTh transition is outside of our observed range of 5.1–8.9 eV, and/or most likely, ^229mTh ions drop to a +1 or 0 charge state, and thus lose their nuclear excitation through non-radiative processes.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
• Sponsoring Organization: US Air Force Office of Scientific Research (AFOSR); USDOE Office of Science (SC), Nuclear Physics (NP) (SC-26)
• Grant/Contract Number: AC05-76RL01830
• OSTI ID: 1595743
• Alternate ID(s): OSTI ID: 23011767
• Report Number(s): PNNL-SA--142911
• Journal Information: Journal of Physics. B, Atomic, Molecular and Optical Physics, Journal Name: Journal of Physics. B, Atomic, Molecular and Optical Physics Journal Issue: 1 Vol. 53; ISSN 0953-4075
• Publisher: IOP Publishing
• Country of Publication: United States
• Language: English

Related Subjects

229Th
229mTh
73 NUCLEAR PHYSICS AND RADIATION PHYSICS
VUV
excitation
nuclear
optical
thorium-229m