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Register a new userMeasurement of the ion fraction and mobility of $^{218}$Po produced in $^{222}$Rn decays in liquid argon
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We report measurements of the charged daughter fraction of $^{218}$Po as a result of the $^{222}$Rn alpha decay, and the mobility of $^{218}$Po$^+$ ions, using radon-polonium coincidences from the $^{238}$U chain identified in 532 live-days of DarkSide-50 WIMP-search data. The fraction of $^{218}$Po that is charged is found to be 0.37$pm$0.03 and the mobility of $^{218}$Po$^+$ is (8.6$pm$0.1)$times$10$^{-4}$$frac{text{cm}^2}{text{Vs}}$.
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Alpha decays in the EXO-200 detector are used to measure the fraction of charged $^{218}mathrm{Po}$ and $^{214}mathrm{Bi}$ daughters created from alpha and beta decays, respectively. $^{222}mathrm{Rn}$ alpha decays in liquid xenon (LXe) are found to produce $^{218}mathrm{Po}^{+}$ ions $50.3 pm 3.0%$ of the time, while the remainder of the $^{218}mathrm{Po}$ atoms are neutral. The fraction of $^{214}mathrm{Bi}^{+}$ from $^{214}mathrm{Pb}$ beta decays in LXe is found to be $76.4 pm 5.7%$, inferred from the relative rates of $^{218}mathrm{Po}$ and $^{214}mathrm{Po}$ alpha decays in the LXe. The average velocity of $^{218}mathrm{Po}$ ions is observed to decrease for longer drift times. Initially the ions have a mobility of $0.390 pm 0.006~mathrm{cm}^2/(mathrm{kV}~mathrm{s})$, and at long drift times the mobility is $0.219 pm 0.004~mathrm{cm}^2/(mathrm{kV}~mathrm{s})$. Time constants associated with the change in mobility during drift of the $^{218}mathrm{Po}^{+}$ ions are found to be proportional to the electron lifetime in the LXe.
For the development of liquid argon dark matter detectors we assembled a setup in the laboratory to scatter neutrons on a small liquid argon target. The neutrons are produced mono-energetically (E_kin=2.45 MeV) by nuclear fusion in a deuterium plasma and are collimated onto a 3 liquid argon cell operating in single-phase mode (zero electric field). Organic liquid scintillators are used to tag scattered neutrons and to provide a time-of-flight measurement. The setup is designed to study light pulse shapes and scintillation yields from nuclear and electronic recoils as well as from {alpha}-particles at working points relevant to dark matter searches. Liquid argon offers the possibility to scrutinise scintillation yields in noble liquids with respect to the populations of the two fundamental excimer states. Here we present experimental methods and first results from recent data towards such studies.
In this paper, we describe the XENON100 data analyses used to assess the target-intrinsic background sources radon ($^{222}$Rn), thoron ($^{220}$Rn) and krypton ($^{85}$Kr). We detail the event selections of high-energy alpha particles and decay-specific delayed coincidences. We derive distributions of the individual radionuclides inside the detector and quantify their abundances during the main three science runs of the experiment over a period of $sim$ 4 years, from January 2010 to January 2014. We compare our results to external measurements of radon emanation and krypton concentrations where we find good agreement. We report an observed reduction in concentrations of radon daughters that we attribute to the plating-out of charged ions on the negatively biased cathode.
The construction and characteristics of the cylindrical ion pulse ionization chamber (CIPIC) with a working volume of 3.2 L are described. The chamber is intended to register alpha-particles from the $^{222}$Rn and its daughters decays in the filled air sample. The detector is less sensitive to electromagnetic pick-ups and mechanical noises. The digital pulse processing method is proposed to improve the energy resolution of the ion pulse ionization chamber. An energy resolution of 1.6% has been achieved for the 5.49 MeV alpha-line. The dependence of the energy resolution on high voltage and working media pressure has been investigated and the results are presented.
Rare event physics demands very detailed background control, high-performance detectors, and custom analysis strategies. Cryogenic calorimeters combine all these ingredients very effectively, representing a promising tool for next-generation experiments. CUPID-0 is one of the most advanced examples of such a technique, having demonstrated its potential with several results obtained with limited exposure. In this paper, we present a further application. Exploiting the analysis of delayed coincidence, we can identify the signals caused by the $^{220}$Rn-$^{216}$Po decay sequence on an event-by-event basis. The analysis of these events allows us to extract the time differences between the two decays, leading to a new evaluation of $^{216}$ half-life, estimated as (143.3 $pm$ 2.8) ms.
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