Observation of annual modulation induced by γ rays from (α,γ) reactions at the Soudan Underground Laboratory

Ashok Tiwari, C. Zhang, D. M. Mei, P. Cushman

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Abstract

Annual modulation of γ rays from (α,γ) reactions in the Soudan Underground Laboratory was observed using a 12-liter scintillation detector. This significant annual modulation, measured over 4 years, can mimic the signature for dark matter and can also generate potential background events for neutrinoless double-β decay experiments. The measured annual modulation of the event rate from (α,γ) reactions is strongly correlated with the time-varying radon concentration observed independently in the laboratory. The α flux from radon decay is simulated starting from the measured radon concentration, and the γ-ray flux is determined using the convolution of the α flux and the cross sections for (α,γ) reactions. The calculated γ-ray flux is sufficient to generate the measured event rate that exhibits an annual modulation.

Original languageEnglish (US)
Article number044609
JournalPhysical Review C
Volume96
Issue number4
DOIs
StatePublished - Oct 12 2017

Bibliographical note

Funding Information:
The authors would like to thank the Soudan Underground Laboratory staff and technical team for their assistance in running the experiment. The authors appreciate the wonderful suggestions and comments from Jing Liu. This work was supported in part by NSF Grants No. PHY-0919278, No. PHY-1242640, and No. OIA 1434142, DOE Grant No. DE-FG02-10ER46709, and a governor's research center supported by the state of South Dakota.

Publisher Copyright:
© 2017 American Physical Society.

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