Production and characterization of a ²²²Rn-emanating stainless steel source

Precise radon measurements are a requirement for various applications,ranging from radiation protection over environmental studies to materialscreening campaigns for rare-event searches. All of them ultimately depend onthe availability of calibration sources with a known and stable radon emanationrate. A new approach to produce clean and dry radon sources by implantation of$^{226}$Ra ions into stainless steel has been investigated. In a proof ofprinciple study, two stainless steel plates have been implanted incollaboration with the ISOLDE facility located at CERN. We present results froma complete characterization of the sources. Each sample provides a radonemanation rate of about 2 Bq, which has been measured using electrostatic radonmonitors as well as miniaturized proportional counters. Additional measurementsusing HPGe and alpha spectrometry as well as measurements of the radonemanation rate at low temperatures were carried out.<br

Search for the double-beta decay of 96Zr with the NEMO-3 detector and ultra-low radioactivity measurements for the SuperNEMO experiment using the BiPo-3 detector

The double-β decay of Zr-96 was studied with data from NEMO-3, a unique experiment combining tracking and calorimetry. A total isotope mass of 9.4 g and a runtime of 5.25 y were available for this work. The half-life of the two-neutrino double-β decay of Zr-96 was measured to be T1/2(2ν2β) = 2.41 ± 0.11 (stat.) −0.18 +0.21 × 1019 y. A lower limit on the neutrinoless double-beta decay half-life was set at T1/2 (0ν2β) > 1.29 × 1022 y @ 90% C.L. corresponding to a limit on the effective neutrino mass of |mββ | 5.85 × 1019 y @ 90% C.L.. SuperNEMO is the next-generation experiment based on NEMO-3 detection principle. The principle and the construction of the BiPo-3 detector for ultra-low contaminations are described. Developments of calibration procedures are exposed along with the validation of the Monte-Carlo simulations. The intrinsic background level has been proven acceptable for SuperNEMO isotopic source foils requirements. Measurements of the contamination of the first SuperNEMO source foils have been performed and the first results are very promising

Radon daughter removal from PTFE surfaces and its application in liquid xenon detectors

Long-lived radon daughters are a critical background source in experiments searching for low-energy rare events. Originating from radon in ambient air, radioactive polonium, bismuth and lead isotopes plate-out on materials that are later employed in the experiment. In this paper, we examine cleaning procedures for their capability to remove radon daughters from PTFE surfaces, a material often used in liquid xenon TPCs. We found a large difference between the removal efficiency obtained for the decay chains of $^{222}$Rn and $^{220}$Rn, respectively. This indicates that the plate-out mechanism has an effect on the cleaning success. While the long-lived $^{222}$Rn daughters could be reduced by a factor of ~2, the removal of $^{220}$Rn daughters was up to 10 times more efficient depending on the treatment. Furthermore, the impact of a nitric acid based PTFE cleaning on the liquid xenon purity is investigated in a small-scale liquid xenon TPC

Removing krypton from xenon by cryogenic distillation to the ppq level

The XENON1T experiment aims for the direct detection of dark matter in a cryostat filled with 3.3 tons of liquid xenon. In order to achieve the desired sensitivity, the background induced by radioactive decays inside the detector has to be sufficiently low. One major contributor is the $\beta$-emitter $^{85}$Kr which is an intrinsic contamination of the xenon. For the XENON1T experiment a concentration of natural krypton in xenon $\rm{^{nat}}$Kr/Xe < 200 ppq (parts per quadrillion, 1 ppq = 10$^{-15}$ mol/mol) is required. In this work, the design of a novel cryogenic distillation column using the common McCabe-Thiele approach is described. The system demonstrated a krypton reduction factor of 6.4$\cdot$10$^5$ with thermodynamic stability at process speeds above 3 kg/h. The resulting concentration of $\rm{^{nat}}$Kr/Xe < 26 ppq is the lowest ever achieved, almost one order of magnitude below the requirements for XENON1T and even sufficient for future dark matter experiments using liquid xenon, such as XENONnT and DARWIN

Analysis of test beam data taken with a prototype of TPC with resistive Micromegas for the T2K Near Detector upgrade

In this paper we describe the performance of a prototype of the High Angle Time Projection Chambers (HA-TPCs) that are being produced for the Near Detector (ND280) upgrade of the T2K experiment. The two HA-TPCs of ND280 will be instrumented with eight Encapsulated Resistive Anode Micromegas (ERAM) on each endplate, thus constituting in total 32 ERAMs. This innovative technique allows the detection of the charge emitted by ionization electrons over several pads, improving the determination of the track position. The TPC prototype has been equipped with the first ERAM module produced for T2K and with the HA-TPC readout electronics chain and it has been exposed to the DESY Test Beam in order to measure spatial and dE/dx resolution. In this paper we characterize the performances of the ERAM and, for the first time, we compare them with a newly developed simulation of the detector response. Spatial resolution better than 800 ${\mu \rm m}$ and dE/dx resolution better than 10% are observed for all the incident angles and for all the drift distances of interest. All the main features of the data are correctly reproduced by the simulation and these performances fully fulfill the requirements for the HA-TPCs of T2K

Characterization of Charge Spreading and Gain of Encapsulated Resistive Micromegas Detectors for the Upgrade of the T2K Near Detector Time Projection Chambers

An upgrade of the near detector of the T2K long baseline neutrino oscillation experiment is currently being conducted. This upgrade will include two new Time Projection Chambers, each equipped with 16 charge readout resistive Micromegas modules. A procedure to validate the performance of the detectors at different stages of production has been developed and implemented to ensure a proper and reliable operation of the detectors once installed. A dedicated X-ray test bench is used to characterize the detectors by scanning each pad individually and to precisely measure the uniformity of the gain and the deposited energy resolution over the pad plane. An energy resolution of about 10% is obtained. A detailed physical model has been developed to describe the charge dispersion phenomena in the resistive Micromegas anode. The detailed physical description includes initial ionization, electron drift, diffusion effects and the readout electronics effects. The model provides an excellent characterization of the charge spreading of the experimental measurements and allowed the simultaneous extraction of gain and RC information of the modules

Measurement of the 2νββ decay half-life of 150Nd and a search for 0νββ decay processes with the full exposure from the NEMO-3 detector

We present results from a search for neutrinoless double-β (0νββ) decay using 36.6 g of the isotope 150Nd with data corresponding to a live time of 5.25 y recorded with the NEMO-3 detector. We construct a complete background model for this isotope, including a measurement of the two-neutrino double-β decay half-life of T2ν 1=2 ¼ ½9.34 0.22ðstatÞ þ0.62 −0.60 ðsystÞ × 1018 y for the ground state transition, which represents the most precise result to date for this isotope. We perform a multivariate analysis to search for 0νββ decays in order to improve the sensitivity and, in the case of observation, disentangle the possible underlying decay mechanisms. As no evidence for 0νββ decay is observed, we derive lower limits on half-lives for several mechanisms involving physics beyond the standard model. The observed lower limit, assuming light Majorana neutrino exchange mediates the decay, is T0ν 1=2 > 2.0 × 1022 y at the 90% C.L., corresponding to an upper limit on the effective neutrino mass of hmνi < 1.6–5.3 eV

Development of methods for the preparation of radiopure ⁸²Se sources for the SuperNEMO neutrinoless double-beta decay experiment

A radiochemical method for producing 82Se sources with an ultra-low level of contamination of natural radionuclides (40K, decay products of 232Th and 238U) has been developed based on cation-exchange chromatographic purification with reverse removal of impurities. It includes chromatographic separation (purification), reduction, conditioning (which includes decantation, centrifugation, washing, grinding, and drying), and 82Se foil production. The conditioning stage, during which highly dispersed elemental selenium is obtained by the reduction of purified selenious acid (H2SeO3) with sulfur dioxide (SO2) represents the crucial step in the preparation of radiopure 82Se samples. The natural selenium (600 g) was first produced in this procedure in order to refine the method. The technique developed was then used to produce 2.5 kg of radiopure enriched selenium (82Se). The produced 82Se samples were wrapped in polyethylene (12 μm thick) and radionuclides present in the sample were analyzed with the BiPo-3 detector. The radiopurity of the plastic materials (chromatographic column material and polypropylene chemical vessels), which were used at all stages, was determined by instrumental neutron activation analysis. The radiopurity of the 82Se foils was checked by measurements with the BiPo-3 spectrometer, which confirmed the high purity of the final product. The measured contamination level for 208Tl was 8-54 μBq/kg, and for 214Bi the detection limit of 600 μBq/kg has been reached.</p