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A hypothesis is proposed to explain the long-standing DAMA/LIBRA puzzle.Introduced into the DAMA/LIBRA shielding is a purge gas of nominallyhigh-purity nitrogen, which under this hypothesis contains argon impurities.Argon is introduced into the nitrogen purge gas either through leaks in thepurge gas plumbing, or through commercially-supplied bottled nitrogen, diffusesthrough materials in the detector housings, and then comes in direct contactwith the DAMA/LIBRA detectors. These argon impurities can then lead to amodulating 2.8 keV background under two scenarios. Scenario 1): Theseimpurities include the isotope 37Ar, which decays by electron capture, emittinga 2.8 keV x-ray. These decays appear as single-site, monoenergetic events inDAMA/LIBRA, and produce an annual modulation due to the variation of neutronflux in the atmosphere and at the Earth's surface, which in turn leads to aseasonal variation in 37Ar production from the reactions$^{40}\textrm{Ca}(\textrm{n,}\alpha)^{37}\textrm{Ar}$ and$^{36}\textrm{Ar}(\textrm{n,}\gamma)^{37}\textrm{Ar}$. Scenario 2): Radon isalso in the DAMA/LIBRA purge gas, modulating seasonally at a rate below thecurrent DAMA/LIBRA limits. When radon or its short-lived daughters decay, theresulting beta, gamma, and bremsstrahlung radiation cause stable 40Ar to beionized within the copper housings surrounding the NaI(Tl) detectors, resultingin characteristic 2.8 keV x-rays. Modulating backgrounds might also result fromradon-induced neutron or gamma-ray flux from the surrounding cavern, leading toa small modulating background enhanced at low energy by the presence of 40Arwithin the copper housings. These two scenarios are straightforward to testthrough assay of the purge gas as well as Monte Carlo and laboratory study ofthe DAMA/LIBRA copper housings when excited by ionizing radiation.

Is DAMA Bathing in a Sea of Radioactive Argon?