Meters Water Equivalent Research Articles

Development of a compact muon veto for the Nucleus experiment

The Nucleus experiment aims to measure coherent elastic neutrino nucleus scattering of reactor anti-neutrinos using cryogenic calorimeters. Operating at an overburden of 3 meters of water equivalent, muon-induced backgrounds are expected to be one of the dominant background contributions. Besides a high efficiency to identify muon events passing the experimental setup, the Nucleus muon veto has to fulfill tight spatial requirements to fit the constraints given by the experimental site and to minimize the induced detector dead-time. We developed highly efficient and compact muon veto modules based on plastic scintillators equipped with wavelength shifting fibers and silicon photo multipliers to collect and detect the scintillation light. In this paper, we present the full characterization of a prototype module with different light read-out configurations. We conclude that an efficient and compact muon veto system can be built for the Nucleus experiment from a cube assembly of the developed modules. Simulations show that an efficiency for muon identification of >99 % and an associated rate of 325 Hz is achievable, matching the requirements of the Nucleus experiment.

Solar neutrino detection in a large volume double-phase liquid argon experiment

Precision measurements of solar neutrinos emitted by specific nuclear reaction chains in the Sun are of great interest for developing an improved understanding of star formation and evolution. Given the expected neutrino fluxes and known detection reactions, such measurements require detectors capable of collecting neutrino-electron scattering data in exposures on the order of 1 ktonne-yr, with good energy resolution and extremely low background. Two-phase liquid argon time projection chambers (LAr TPCs) are under development for direct Dark Matter WIMP searches, which possess very large sensitive mass, high scintillation light yield, good energy resolution, and good spatial resolution in all three cartesian directions. While enabling Dark Matter searches with sensitivity extending to the ``neutrino floor'' (given by the rate of nuclear recoil events from solar neutrino coherent scattering), such detectors could also enable precision measurements of solar neutrino fluxes using the neutrino-electron elastic scattering events. Modeling results are presented for the cosmogenic and radiogenic backgrounds affecting solar neutrino detection in a 300 tonne (100 tonne fiducial) LAr TPC operating at LNGS depth (3,800 meters of water equivalent). The results show that such a detector could measure the CNO neutrino rate with ∼15% precision, and significantly improve the precision of the 7Be and pep neutrino rates compared to the currently available results from the Borexino organic liquid scintillator detector.

The Dortmund Low Background Facility — Low-background gamma ray spectrometry with an artificial overburden

The Dortmund Low Background Facility is an instrument for low-level gamma ray spectrometry with an artificial overburden of ten meters of water equivalent, an inner shielding, featuring a neutron absorber, and an active muon veto. An integral background count rate between 40keV and 2700keV of (2.528±0.004)counts/(kgmin) enables low-background gamma ray spectrometry with sensitivities in the range of some 10mBq/kg within a week of measurement time.

Measurement of the underground atmospheric muon charge ratio using the MINOS Near Detector

The magnetized MINOS Near Detector, at a depth of 225 meters of water equivalent (mwe), is used to measure the atmospheric muon charge ratio. The ratio of observed positive to negative atmospheric muon rates, using 301 days of data, is measured to be 1.266+/-0.001(stat.)+0.015/-0.014(syst.). This measurement is consistent with previous results from other shallow underground detectors, and is 0.108+/-0.019(stat. + syst.) lower than the measurement at the functionally identical MINOS Far Detector at a depth of 2070 mwe. This increase in charge ratio as a function of depth is consistent with an increase in the fraction of muons arising from kaon decay for increasing muon surface energies.

The new set-up in the Belgrade low-level and cosmic-ray laboratory

The Belgrade underground laboratory consists of two interconnected spaces, a ground level laboratory and a shallow underground one, at 25 meters of water equivalent. The laboratory hosts a low-background gamma spectroscopy system and cosmic-ray muon detectors. With the recently adopted digital data acquisition system it is possible to simultaneously study independent operations of the two detector systems, as well as processes induced by cosmic-ray muons in germanium spectrometers. Characteristics and potentials of the present experimental setup, together with some preliminary results for the flux of fast neutrons and stopped muons, are reported here.

A neutron multiplicity meter for deep underground muon-induced high-energy neutron measurements

We present, for the first time, the design of an instrument capable of measuring the high energy ( > 60 MeV ) muon-induced neutron flux deep underground. The instrument is based on applying the Gd-loaded liquid-scintillator technique to measure the rate of multiple low-energy neutron events produced in a Pb target and from this measurement to infer the rate of high energy neutron events. This unique signature allows both for efficient tagging of neutron multiplicity events as well as rejection of random gamma backgrounds so effectively that typical low-background techniques are not required. We present design studies based on Monte Carlo simulations that show that an apparatus consisting of a Pb target of 200 cm by 200 cm area by 60 cm thickness covered by a 60 cm thick Gd-loaded liquid scintillator (0.5% Gd content) detector could measure, at a depth of 2000 meters of water equivalent (m.w.e), a rate of 70 ± 8 (stat) events/year with a background of less than 10 events/year. We discuss the relevance of this technique to measuring the muon-induced neutron background in searches for dark matter in the form of Weakly Interacting Massive Particles (WIMP). Based on these studies, we also discuss the benefits of using a neutron multiplicity meter as a component of active shielding in such experiments.

Neutron Background and Possibility for Shallow Experiments

As a possible design of a future geoneutrino detector, a KamLAND-type, monolithic, liquid scintillator detector with a thicker veto and a method for particle identification to reject neutron and 9Li background from cosmic-ray muon spallation is considered. Assuming such a detector, the possibility for geoneutrino observation at a depth of around 300 meters of water equivalent is investigated.

Mass balance and area changes of four high arctic plateau ice caps, 1959–2002

Small, stagnating ice caps at high latitudes are particularly sensitive to climatic fluctuations, especially with regard to changes in ablation season temperature. We conducted mass balance measurements and GPS area surveys on four small High Arctic plateau ice caps from 1999–2002. We compared these measurements with topographic maps and aerial photography from 1959, and with previously published data. Net mass balance (bn) of Murray Ice Cap was −0.49 (1999), −0.29 (2000), −0.47 (2001), and −0.29 (2002), all in meters of water equivalent (m w.eq.). The mass balance of nearby Simmons Ice Cap was also negative in 2000 (bn=−0.40 m w.eq.) and in 2001 (bn=−0.52 m w.eq.). All four ice caps experienced substantial marginal recession and area reductions of between 30 and 47% since 1959. Overall, these icecaps lost considerable mass since at least 1959, except for a period between the mid‐1960s and mid‐1970s characterized regionally by reduced summer melt, positive mass balance, and ice cap advance. The regional equilibrium line altitude (ELA) is located, on average, above the summits of the ice caps, indicating that they are remnants of past climatic conditions and out of equilibrium with present climate. The ice caps reached a Holocene maximum and were several times larger during the Little Ice Age (LIA) and their current recession reflects an adjustment to post‐LIA climatic conditions. At current downwasting rates the ice masses on the Hazen Plateau will completely disappear by, or soon after, the mid‐21st century.

Measurement of fast neutron background in SAGE

The spectrometer intended for direct measurements of ultra low fluxes of fast neutrons is described. It is sensitive to neutron fluxes of 10 −7 cm −2 s −1 and lower. The detection efficiency of fast neutrons with simultaneous energy measurement was determined from Monte-Carlo simulation to be equal to 0.11 ± 0.01. The background counting rate in the detector corresponds to a neutron flux of (6.5 ± 2.1) × 10 −7 cm −2 s −1 in the range 1.0–11.0 MeV. The natural neutron flux from the surrounding mine rock at the depth of 4700 meters of water equivalent was measured to be (7.3 ± 2.4) x 10 −7 cm −2 s −1 in the range 1.0–11.0 MeV. The flux of fast neutrons in the SAGE main room was measured to be < 2.3 × 10 −7 cm −2 s −1 in 1.0–11.0 MeV energy range.

Neutron production by cosmic-ray muons at shallow depth

The yield of neutrons produced by cosmic ray muons at a shallow depth of 32 meters of water equivalent has been measured. The Palo Verde neutrino detector, containing 11.3 tons of Gd loaded liquid scintillator and 3.5 tons of acrylic served as a target. The rate of one and two neutron captures was determined. Modeling the neutron capture efficiency allowed us to deduce the total yield of neutrons $ Y_{tot} = (3.60 \pm 0.09 \pm 0.31) \times 10^{-5}$ neutrons per muon and g/cm$^2$. This yield is consistent with previous measurements at similar depths.

Sarennes, un bassin versant de recherche et d'expérimentation nivo-glaciaire, cinquante années d'études

Click to increase image sizeClick to decrease image sizeThe basin of Sarennes is located in the French Alps, more precisely in the Grande Rousses range, 30 km east of Grenoble. The catchment area reaches some 30 square kilometers with a small glacier studied since 1948. Hydrologic studies started in 1991 with the installation of 3 gauging stations at 2720 m., 2050 m. and 1450 meters of altitude. An automatic snow gauge called "telenivometer"and a simplified meteorological station were installed close to the laboratory-hut at the altitude of 2700 m., nearby the glacier tongue. In 1991, the Sarennes basin was selected for the ERB club (European Research Basin). This paper provides a description of This basin unique in France due to its glacial and snowy components. Mass balance evolution for the last half century shows an annual loss of 0.6 meters of water equivalent and we present the first hydrologic results and the ultimate results of the field 1998-99 campaign.

Study of underground muons during the January 1991 radio flare of Cygnus X-3.

Muons recorded by the IMB proton decay detector during the radio outburst from Cygnus X-3 in January 1991 are studied. Data are examined for both aperiodic excesses and those phase modulated at the x-ray period of Cygnus X-3. No correlation between the muon data and Cygnus X-3 is found. Further, this observation provides flux limits of ${\ensuremath{\Phi}}_{90% \mathrm{C}.\mathrm{L}.}\ensuremath{\le}2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}10}$ \ensuremath{\mu}${\mathrm{cm}}^{\ensuremath{-}2}$${\mathrm{s}}^{\ensuremath{-}1}$ at 1570 meters of water equivalent on the 20th and 23rd, in contrast with other reported signals.

High sensitivity activation analysis using an underground laboratory for gamma spectrometry

The underground laboratory of the CINR with 125 metres water equivalent (mwe) is used mainly for activation analysis of pure materials. Background spectra of NaI(Tl) and Ge(Li) detectors are discussed in comparison with those of other underground laboratories. Detection limits are calculated as disintegration rates to about 15 mBq as well as masses detectable by neutron activation analysis for some 50 elements, most of them below pg.

A Medium Rigidity Muon Experiment for the South Pole Station

AbstractA proposal for a medium rigidity muon telescope system to be installed at the U.S. South Pole Station for observations of time variations of cosmic ray intensity is at present being prepared by Professor Pomerantz, Director of the Bartol Research Foundation, University of Delaware and Drs Jacklyn and Duldig of the Cosmic Ray Section, Antarctic Division, Department of Science. A novel approach to medium energy cosmic ray observations viewing in equatorial to mid-latitude directions is described. The absorber depth required for the proposed 50-1000 GV rigidity range would be achieved by locating the telescope system at a depth of approximately 7 metres water equivalent (MWE) in the ice and viewing at high zenith angles. Optimization techniques used in the telescope design are presented together with the unique advantages of the location. Justification for the experiment and comparison with important observatories in this rigidity range are also discussed.

Untergrundlaboratorium für Messungen geringer Radioaktivität

An underground laboratory has been installed under 47 m rock covering (125 metres water equivalent), where the cosmic radiation ist diminished more than 40-fold. The massive laboratory building, 6 × 3.5 m2 by 3.4 m height, was erected on a foundation of 0.8 m serpentinite with a framework of old steel, forming walls and ceiling with 0.7 m thickness, filled with serpentinite. A Ge(Li)-detector of 75 m3 and 9.1% efficiency ist shielded by lead of 10 cm thickness. The background spectra are comparable with those of anticoincidence devices described in the literature. Detection limits for small samples amount to 0.025 Bq; for natural radioactivities of 1000 g samples to 0.15 ppm Th, 0.03 ppm U and 0.011% K2O for 12 h-measurements.

Experimental Test of Baryon Conservation: A New Limit on Neutron-Antineutron Oscillations in Oxygen

This paper reports the result of a search for baryon-number-nonconserving neutron-antineutron transitions in oxygen using a 300-ton water Cherenkov detector located in the Homestake gold mine at a depth of 4200 meters of water equivalent. The 90%-confidence-level upper limit for the neutron partial lifetime for this process is found to be 1.4\ifmmode\times\else\texttimes\fi{}${10}^{30}$ yr. According to a recent calculation of neutron-antineutron oscillations in oxygen, this result corresponds to a lower limit on the free-neutron oscillation time of 2\ifmmode\times\else\texttimes\fi{}${10}^{7}$ sec.

Possible antineutrino pulse of extraterrestrial origin

WE report an unusual event observed during our search for electron antineutrino Ve bursts of extraterrestrial origin1. Our experiment uses a deep underground Ve burst-detector station, adjacent to the Brookhaven Solar Neutrino Observatory2 at a depth of 4,400 metres water equivalent (m.w.e.) in the Homestake Gold Mine in Lead, South Dakota. At this station we have placed a number of large water Cerenkov counters (Fig. 1) designed to detect Ve interactions by the Cerenkov radiation from positrons resulting from Ve + p →n + e+ (ref. 3).

Recent Evidence Concerning the Sidereal Anisotropy in the Charged Primary Cosmic Radiation

Significant evidence for a bi-directional sidereal anisotropy has been obtained from observations with meson telescopes at depths in the vicinity of 40 metres water equivalent (m.w.e.) underground. The anisotropy is of the type which should occur when charged particles which were formerly isotropic stream equally in both directions along a magnetic field, if there is a tendency for pitch angles to become reduced (the pitch angle being the angle between the particle trajectory and the direction of the field). If the magnetic moments of the particles are adiabatically invariant, changes in the magnetic field, both with position and time, could be responsible for the anisotropy.

Search for aluminum 26 induced by cosmic-ray muons in terrestrial rock

Terrestrial Al26 produced by cosmic-ray muons has been sought in silicate rock. Aluminum was isolated and purified from tens of kilograms of chert obtained from an area with a low erosion rate. Al26 was counted with a low-level gamma-gamma coincidence spectrometer. The specific activity for the present surface rock has been measured to be (0.02 ± 0.12) dpm/10 kg SiO2, and the specific activity for the rock at a depth of 24 meters of water equivalent, to be (0.00 ± 0.08) dpm/10 kg SiO2. The Al26 activity in terrestrial rocks has been limited to 0.01 dpm/kg SiO2.

Muon Solar Daily Variation at a Depth of 60 Metres Water Equivalent

THE solar daily variation of the underground secondary cosmic ray intensity has shown remarkable changes in phase and amplitude during the recent solar minimum.