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Register a new userObservation of annual modulation induced by $gamma$ rays from ($alpha$, $gamma$) reactions at the Soudan Underground Laboratory
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Annual modulation of $gamma$ rays from ($alpha$, $gamma$) reactions in the Soudan Underground Lab has been 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-$beta$ decay experiments. The measured annual modulation of the event rate from ($alpha$, $gamma$) reactions is strongly correlated with the time-varying radon concentration observed independently in the Lab. The $alpha$ flux from radon decay is simulated starting from the measured radon concentration, and the $gamma$-ray flux is determined using the convolution of the $alpha$ flux and the cross sections for ($alpha$, $gamma$) reactions. The calculated $gamma$-ray flux is sufficient to generate the measured event rate that exhibits an annual modulation.
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Tiwari {it et al.} have identified an annual modulation of the $gamma$-ray flux at the Soudan Underground Laboratory which is strongly correlated to the radon concentration. The $gamma$-ray flux results from ($alpha$,$gamma$) reactions which are induced by the $alpha$ activity of radon and its daughters. Unfortunately, the quantitative analysis of the $gamma$-ray flux is based on unrealistic ($alpha$,$gamma$) cross sections, and thus the calculated $gamma$-ray fluxes are not reliable.
The relevant interaction energies for astrophysical radiative capture reactions are very low, much below the repulsive Coulomb barrier. This leads to low cross sections, low counting rates in $gamma$-ray detectors, and therefore the need to perform such experiments at ion accelerators placed in underground settings, shielded from cosmic rays. Here, the feasibility of such experiments in the new shallow-underground accelerator laboratory in tunnels VIII and IX of the Felsenkeller site in Dresden, Germany, is evaluated. To this end, the no-beam background in three different types of germanium detectors, i.e. a Euroball/Miniball triple cluster and two large monolithic detectors, is measured over periods of 26-66 days. The cosmic-ray induced background is found to be reduced by a factor of 500-2400, by the combined effects of, first, the 140 meters water equivalent overburden attenuating the cosmic muon flux by a factor of 40, and second, scintillation veto detectors gating out most of the remaining muon-induced effects. The new background data are compared to spectra taken with the same detectors at the Earths surface and at other underground sites. Subsequently, the beam intensity from the cesium sputter ion source installed in Felsenkeller has been studied over periods of several hours. Based on the background and beam intensity data reported here, for the example of the $^{12}$C($alpha$,$gamma$)$^{16}$O reaction it is shown that highly sensitive experiments will be possible.
A correlation term ${{ sigma}_{n} }cdot ({ k_{n}times k_gamma}) $ in the ${}^{139}{rm La}(vec{n},gamma)$ reaction has been studied utilizing epithermal polarized neutrons and germanium detectors. The transverse asymmetry for single $gamma$-ray transition was measured to be $0.60pm0.19$ in the $p$-wave resonance.
The China Jinping Underground Laboratory, inaugurated in 2010, is an underground research facility with the deepest rock overburden and largest space by volume in the world. The first-generation science programs include dark matter searches conducted by the CDEX and PandaX experiments. These activities are complemented by measurements of ambient radioactivity and installation of low-background counting systems. Phase II of the facility is being constructed, and its potential research projects are being formulated. In this review, we discuss the history, key features, results, and status of this facility and its experimental programs, as well as their future evolution and plans.
We report results of a search for light Dark Matter WIMPs with CDEX-1 experiment at the China Jinping Underground Laboratory, based on 53.9 kg-days of data from a p-type point-contact germanium detector enclosed by a NaI(Tl) crystal scintillator as anti-Compton detector. The event rate and spectrum above the analysis threshold of 475 eVee are consistent with the understood background model. Part of the allowed regions for WIMP-nucleus coherent elastic scattering at WIMP mass of 6-20 GeV are probed and excluded. Independent of interaction channels, this result contradicts the interpretation that the anomalous excesses of the CoGeNT experiment are induced by Dark Matter, since identical detector techniques are used in both experiments.
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