210Pb Contamination Research Articles

Depth profile study of 210Pb in the surface of an NaI(Tl) crystal

The surface 210Pb is one of the main background sources for dark-matter-search experiments using NaI(Tl) crystals, and its spectral features associated with the beta-decay events for energies less than 60 keV depends on the depth distribution of 210Pb in the surface of an NaI(Tl) crystal. Therefore, we must understand the profile of surface 210Pb to precisely model the background measurement in the low-energy region for the low-background experiment using NaI(Tl) crystals. We estimate the depth profile of the surface 210Pb contamination by modeling the measured spectrum of the alpha emission from the decay of 210Po at the decay sequence of the surface 210Pb contamination that is obtained using an 222Rn-contaminated crystal. In order to describe the energy spectra of the surface contamination we perform a log-likelihood fit of the measured data to a sum of Geant4 Mote Carlo simulations, weighted by an exponential curve as a function of the surface depth. The low- and high-energy events from the beta decay of surface 210Pb are also modeled to improve the depth profile for shallow depths. We simulate the energy spectra from beta decays of 210Pb that are exponentially distributed in the surface by following two exponential functions where the mean-depth coefficients are free parameters in the data fitting; we observed that the energy spectra are in good agreement with the measured data.

Evaluation and mitigation of trace 210Pb contamination on copper surfaces

Clean materials are required to construct and operate many low-background physics experiments. High-purity copper has found broad use because of its physical properties and availability. In this paper, we describe methods to assay and mitigate 210Pb contamination on copper surfaces, such as from exposure to environmental radon or coming from bulk impurities. We evaluated the efficacy of wet etching on commercial samples and observed that 210Po contamination from the copper bulk does not readily pass into solution. During the etch, the polonium appears to trap at the copper–etchant boundary, such that it is effectively concentrated at the copper surface. We observed a different behavior for 210Pb; high-sensitivity measurements of the alpha emissivity versus time indicate the lowest level of 210Pb contamination ever reported for a commercial copper surface: 0±12nBq/cm2 (1σ). Additionally, we have demonstrated the effectiveness of mitigating trace 210Pb and 210Po surface backgrounds using custom, high-purity electroplating techniques. These approaches were evaluated utilizing assays performed with an XIA UltraLo-1800 alpha spectrometer.

Background analysis and reduction for the ECHo experiment

ECHo-lk is a new experiment which is designed to investigate the electron neutrino mass from the calorimetric measurement of the electron capture spectrum of 163Ho. In this presentation, we give an overview of our recent activities in the background analysis and reduction. Low background measurements of the radiopurity of the implanted Holmium in the ECHo detectors have been used to constrain the maximum activity of 166mHo in the sample to be less than ~ 0.4 mBq. On top of this, the background spectrum introduced by coimplanted 166Ho in the absorber of the ECHo detectors has been obtained with a GEANT4 simulation showing that if the projected reduction of coimplanted 166mHo to 163Ho of 10-10 can be achieved, the background contribution of 166mHo is negligible. Additional GEANT4 based Monte-Carlo simulations of test contaminations have been conducted. Simulations have been completed for internal 210Pb contamination in the absorber and 55Fe contaminations on the surface of the absorber.

ANAIS: Status and prospects

ANAIS (Annual modulation with NAI Scintillators) experiment aims to look for dark matter annual modulation with 250 kg of ultra-pure NaI(Tl) scintillators at the Canfranc Underground Laboratory (LSC), in order to confirm the DAMA/LIBRA positive signal in a model-independent way. The detector will consists in an array of close-packed single modules, each of them coupled to two high efficiency Hamamatsu photomultipliers. Two 12.5 kg each NaI(Tl) crystals provided by Alpha Spectra are currently taking data at the LSC. These modules have shown an outstanding light collection efficiency (12-16 phe/keV), about the double of that from DAMA/LIBRA phase 1 detectors, which could enable reducing the energy threshold down to 1 keVee. ANAIS crystal radiopurity goals are fulfilled for 232Th and 238U chains, assuming equilibrium, and in the case of 40K, present crystals activity (although not at the required 20 ppb level) could be acceptable. However, a 210Pb contamination out-of-equilibrium has been identified and its origin traced back, so we expect it will be avoided in next prototypes. Finally, current status and prospects of the experiment considering several exposure and background scenarios are presented.

A study on possible use of Urtica dioica (common nettle) plant as polonium (210)Po and lead (210)Pb contamination biomonitor in the area of phosphogypsum stockpile.

The aim of this study was to test a possible use of Urtica dioica (common nettle) plant as a biomonitor of polonium 210Po and lead 210Pb contamination near phosphogypsum stacks by determining concentrations of these radionuclides in samples collected from the area of phosphogypsum stockpile in Wiślinka (northern Poland). The 210Po and 210Pb contents in roots depended on their concentrations in soils. Bioconcentration factor values from soil to root of the plant did not depend on 210Po and 210Pb contents in soils that leads to the conclusion that different polonium and lead species have different affinities to U. dioica plants. The main sources of both analyzed radionuclides in green parts of plants are wet and dry air deposition and transportation from soil. The values of 210Po/210Pb activity ratio indicate natural origin of these radioisotopes in analyzed plants. 210Po and 210Pb concentration in U. dioica roots is negatively weakly correlated with distance from phosphogypsum stockpile.

Determination of Radionuclides in Chemical Reagents by Low-background .GAMMA.-Ray Spectrometry and Application of the Coprecipitation Method to Seawater Sample

Extremely low-background γ-ray spectrometry is applied to the determination of blank levels of nuclides (7Be, 60Co, 134Cs, 137Cs, 210Pb, 226Ra, 228Ra and 234Th) in various chemical reagents and carriers, including Ba and Pb chemicals, BaSO4 from natural barite, contrast media for medical use, and Pb in an old roof tile. Barite shows less contamination with 226Ra compared with the Ba chemicals (6 - 90 mBq/g-Ba in Ba reagents, 0.7 -1.5 mBq/g-Ba in barite) . 210Pb contamination is notable in all Pb reagents, but not in the roof tile. In CsCl reagent, 134Cs, 137Cs and 234Th (238U) are found to be negligible. Using the least-contaminated carrier reagents, the coprecipitation method is successfully employed to the simultaneous measurement of low-level activities of these nuclides in seawater sample.

Determination of strontium-90 in deer bones by liquid scintillation spectrometry after separation on Sr-specific ion exchange columns

The activity concentration of 90Sr was determined in several deer bones from Austria. Strontium specific ion exchange columns with 4′,4″(5″)-di-t-butylcyclohexane-18-crown-6 from Eichrom Industries, Inc. were used for separation. The yield of the chemical procedure was quantified with AAS. Directly after column separation, the solution containing 90Sr was mixed with the scintillation cocktail HiSafe III and measured by liquid scintillation counting. Prevention of 210Pb contamination and reusability of the separation columns was investigated as well as the activity distribution within the bones. Results were compared with pre-Chernobyl measurements in Austria; a correlation between activity concentration of 90Sr and site altitude was found.

The bolometers as nuclear recoil detectors

Our group is involved in experiments using bolometric detectors since ten years for rare event searches like double beta decay or Dark Matter interactions. During last year, to check the quenching factor of TeO2 bolometers, we have measured the nuclear recoils at energy as low as 15keV in our experimental apparatus at Laboratori Nazionali del Gran Sasso. Two 72g TeO2 detectors were exposed under vacuum to a 228Ra α source that implanted on them 224Ra nuclei. The nuclei emitted by the implanted source were detected in one bolometer in coincidence with the corresponding α particles in the other. The energy spectrum of the 103.4keV 224Ra nuclei has been obtained with an energy resolution of about 12keV. Furthermore an α measurement of Roman lead has exploited also the sensitivity of this technique to check for ultralow activity in matter, taking advantage of the source≡detector approach. A limit on the 210Pb contamination in roman lead as low as 4mBq/Kg has been obtained.

Identification and suppression of low-energy background from 210Pb contamination in lead

Identification and suppression of low-energy background from 210Pb contamination in lead

Alpha-particle emission from contaminants in counter materials

Energy spectra of surface activities from thorium and uranium contaminants have been investigated for typical counter materials. Soft-tempered stainless steel with a rate of 1.2 ± 0.1 α-particles emitted per 100 cm 2 in one hour was found better than other stainless steel and far better than brass and aluminum. Energy spectra provide information about the contaminating activity and about its depth profile. Thorium, uranium and 210Pb contamination was also observed for thin sources of other materials including isotopically enriched materials.