Low-background Laboratory Research Articles

Production and decay of the 73Ge*(1/2−) metastable state in a low-background germanium detector

The 73Ge*(1/2−) metastable state decays with a very characteristic signature which allows it to be tagged event-by-event. Studies were performed using data taken with a high-purity germanium detector in a low-background laboratory near a nuclear power reactor core where the -flux was . The measured average and equilibrium production rates of 73Ge*(1/2−) were (8.7 ± 0.4) and (6.7 ± 0.3) kg−1 day−1, respectively. The production channels were studied and identified. By studying the difference in the production of 73Ge*(1/2−) between the reactor ON and OFF spectra, limiting sensitivities in the range of for the cross sections of neutrino-induced nuclear transitions were derived. The dominant backgrounds are due to β− decays of cosmic-ray-induced 73Ga. The prospects of enhancing the sensitivities at underground locations are discussed.

Reconstructing the velocity distribution of weakly interacting massive particles from directdark matter detection data

Weakly interacting massive particles (WIMPs) are among the leading dark mattercandidates. Currently, the most promising method for detecting many differentWIMP candidates is the direct detection of the recoil energy deposited in a lowbackground laboratory detector due to elastic WIMP–nucleus scattering. So far theusual procedure has been to predict the event rate of direct detection of WIMPsbased on some model(s) of the galactic halo. The aim of our work is to invert thisprocess. That is, we study what future direct detection experiments can teachus about the WIMP halo. As the first step we consider a time-averaged recoilspectrum, assuming that no directional information exists. We develop a method forconstructing the (time-averaged) one-dimensional velocity distribution function fromthis spectrum. Moments of this function, such as the mean velocity and velocitydispersion of WIMPs, can also be obtained directly from the recoil spectrum. Theonly input needed in addition to a measured recoil spectrum is the mass of theWIMP; no information about the scattering cross section or WIMP density isrequired.

Comparative analysis of the in and ex situ determination of environmental radiation and dosimetry levels

A method is proposed to determine the activities of natural and artificial gamma-emitting radionuclides in soils using in situ spectrometry that is validated with conventional low-background laboratory gamma spectrometry. From the two sets of results, the dose-equivalent rate levels in the environment were reproduced and we are thus able to determine the principal components of those levels.

Status of the experiment on the measurement of the neutrino magnetic moment with the spectrometer GEMMA

The investigation of the background structure of the spectrometer GEMMA was carried out in a low-background laboratory in ITEP. GEMMA is destined for measurement of the neutrino magnetic moment near the core of a nuclear power plant (NPP) reactor. The results of the investigation in ITEP and measurement of the background in the experimental hall at the Kalininskaya NPP proved that GEMMA is ready for the start of the experiment at the reactor. Now the preparation of the experimental hall for the measurement is completed and an assembling of the setup is in progress.

Ion-pulse ionization chamber for direct measurement of radon concentration in the air

A large-volume (24.8l in total volume, 16.8l in fiducial volume) multiwire pulse ion collection ionization chamber was examined as a detector of α particles from radon decays in the air inside the chamber. The possibility of obtaining spectrometric information from slow ion pulses was tested. An energy resolution of 3.9% for 5.49-MeV α particles was obtained in preliminary measurements. It was shown that a detector of this kind could be used for direct measurements of radon activities in flowing air at a level less than 1 Bq/m3. A radon concentration at a level of 10 Bq/m3 can be measured with an accuracy better than 10 % for a counting time of 103 s. The detector will be used for continuous accurate monitoring of the 222Rn concentration in the air of low-background laboratories.

Double-Beta Decay of 150Nd and 76Ge to Excited States

New results of experimental search for double beta decay of 76Ge (2νββ) and 150Nd (0ν + 2ν) to excited states of the daughter nuclei are presented. Data from 228 days of measurements performed with four HPGe detectors in the low background laboratory of Baksan neutrino observatory yield new limits on life-times T1/2(0+→ 0+1)≥6.2×1021} yr at 90% C.L. for transition of 76Ge to 0+1 level of 76Se and T1/2(0+→ 0+1)≥1.5×1020 yr at 90% C.L. for transition of 150Nd to 0+1 level of 150Sm.

New bound to the probability of 76Ge ββ decay to the 0 1 + 76Se level

Measurements were carried out at the underground low-background laboratory of the Baksan Neutrino Observatory using a detection system involving four ultrapure germanium detectors made from enriched 76Ge. The sensitivity of the experiment to the detection of a 76Ge double beta decay to the excited levels of the 76Se nucleus was determined. As a result of 228-day measurements, the new bound to the time of 76Ge half-decay to the 76Se 01+ excited level is found to be T1/2(2ν2β)≥6.2×1021 years (90% confidence level).

Supersymmetric dark matter

When combined with the wealth of observational evidence for a nonrelativistic matter density Ω 0≳0.3 , the big-bang-nucleosynthesis constraint on the baryon density, Ω b ≲0.1 indicates the existence of a significant amount of nonbaryonic dark matter. Several lines of reasoning suggest that the dark matter consists of some new, as yet undiscovered, weakly interacting massive particle (WIMP). Of the WIMP candidates that have been considered, perhaps the best-motivated and certainly the most theoretically developed is the neutralino, the lightest supersymmetric particle (LSP) in many supersymmetric theories. There is now a vast experimental effort being mounted to detect these particles in the Galactic halo. Techniques include direct detection in low-background laboratory detectors, indirect detection through observation of energetic neutrinos from annihilation of WIMPs that have accumulated in the Sun and/or the Earth, and observation of anomalous cosmic-ray antiprotons, positrons, and gamma rays.

Neutrinoless double-β decayof76Ge: First results from the International Germanium Experiment (IGEX) with six isotopically enriched detectors

The International Germanium Experiment (IGEX) has six HPGe detectors, isotopically enriched to 86% in 76Ge, containing approximately 90 active moles of 76Ge. Three detectors of 2 kg each operate in the Canfranc Underground Laboratory (Spain) with pulse-shape analysis electronics. One detector (∼0.7 kg active volume) has been operating in the Baksan Low-Background Laboratory for several years, and two additional similar detectors will operate in Baksan. A maximum likelihood analysis of 74.84 active mole years of data yields a lower bound T1/20ν>~0.8×1025yr (90% C.L.), corresponding to 〈mν〉<(0.5–1.5)eV, depending on the theoretical nuclear matrix elements used to extract the neutrino mass parameter.Received 25 June 1998DOI:https://doi.org/10.1103/PhysRevC.59.2108©1999 American Physical Society

Achieving ultralow background in a germanium spectrometer

A germanium diode gamma-ray spectrometer has been constructed that exhibits background levels three orders of magnitude lower than conventional low-background laboratory spectrometers in the energy region around 100 keV and five orders of magnitude lower in the energy region above 3 MeV. The steps necessary to achieve this reduction are described, and the application of this technology to construction of ultralow background laboratory based germanium diode gamma-ray spectrometers is discussed.

The LBL/UCSB 76Ge Double Beta Decay Experiment: First Results

A paper given at the IEEE Nuclear Science Symposium last year presented the scientific justification for this experiment and discussed the design of the detector system. At the present time two of the dual detector systems (i.e., four out of a final total of eight detectors) are operating in the complete active/ passive shield in the low background laboratory at LBL. Early results (1620 hrs) of an experiment using two detectors yield a limit of 4 × 1022 years (68% confidence) for the half life of the neutrinoless double beta decay (sso?) of 76Ge. Although this experiment was carried out above ground, the result approaches those achieved by other groups in deep underground laboratories. Based on studies of the origins of background in our system, we hope to reach a limit of 3 × 1023 years (or more) in a two month/ four detector experiment to be carried out soon in an underground facility.

A low-background laboratory

Consideration of the design, cost and construction of a low-background laboratory for the measurement of low specific activity samples leads to the choice of demineralized water as the main shielding material. Background figures and spectra obtained for a range of proportional and scintillation counters in the completed laboratory, show that the shielding is slightly better than 12 in. of steel. It is deduced from energy and intensity measurements that the gamma-ray peaks occurring in the background spectrum arise mainly from ThC″ present in the counter construction materials.

Iodine-131 in human thyroids following the Windsclae reactor accident.

Following the Windscale reactor accident of October 1957, measurements were made of iodine-131 levels in the thyroid gland of persons from various sections of the country. The measurements were made in a lowbackground laboratory using a crystal detector coupled to a photomultiplier tube. The measurements were repeated over a four-month period. Data are tabulated. An attempt is made to correlate the findings with the milk consumption of the subjects, the location of the dairies supplying the milk, and the passage of the atomic cloud over Britain. (C.H.)

Increase in γ-Radiation from Powdered Milk and Beef, 1953-56

Two apparatuses consisting of cylindrically arranged high-pressure ion chambers (diameter of sample container approximately 1 m., total volume approximately 3 m.3, 20 kgm. nitrogen and carbon dioxide) placed in a low-background laboratory in the rock near the city of Stockholm, and protected in all directions by 1 m. of water and more than 50 m. of granite, have been described in earlier communications1. In these, the results of measurements on 306 persons who have had no known contact with other than natural radioactive material of common concentration were also reported. The γ-radiation of human subjects is, in all probability, caused mainly by the potassium-40 content of the body, as has been shown by Burch and Spiers2.