Search

We reanalyze the dataset collected during the years 1998--2003 by the deep underwater neutrino telescope NT200 in the lake Baikal with the low energy threshold (10 GeV) in searches for neutrino signal from dark matter annihilations near the center of the Milky Way. Two different approaches are used in the present analysis: counting events in the cones around the direction towards the Galactic Center and the maximum likelihood method. We assume that the dark matter particles annihilate dominantly over one of the annihilation channels $b\bar{b}$, $W^+W^-$, $\tau^+\tau^-$, $\mu^+\mu^-$ or $\nu\bar{\nu}$. No significant excess of events towards the Galactic Center over expected neutrino background of atmospheric origin is found and we derive 90% CL upper limits on the annihilation cross section of dark matter., Comment: 15 pages, 14 figures, published version

The MAJORANA Collaboration is constructing the MAJORANA Demonstrator, an ultra-low background, 44-kg modular high-purity Ge (HPGe) detector array to search for neutrinoless double-beta decay in Ge-76. The phenomenon of surface micro-discharge induced by high-voltage has been studied in the context of the MAJORANA Demonstrator. This effect can damage the front-end electronics or mimic detector signals. To ensure the correct performance, every high-voltage cable and feedthrough must be capable of supplying HPGe detector operating voltages as high as 5 kV without exhibiting discharge. R&D measurements were carried out to understand the testing system and determine the optimum design configuration of the high-voltage path, including different improvements of the cable layout and feedthrough flange model selection. Every cable and feedthrough to be used at the MAJORANA Demonstrator was characterized and the micro-discharge effects during the MAJORANA Demonstrator commissioning phase were studied. A stable configuration has been achieved, and the cables and connectors can supply HPGe detector operating voltages without exhibiting discharge., 9 pages, 12 figures, 8 tables, submitted to NIM A

The second-stage neutrino telescope BAIKAL-GVD in Lake Baikal will be a research infrastructure aimed mainly at studying astrophysical neutrino fluxes by recording the Cherenkov radiation of the secondary muons and showers generated in neutrino interactions. The prototyping/early construction phase of the BAIKAL-GVD project which is directed towards deployment and operation of the first demonstration cluster has been started in April 2011. An important step on realization of the GVD project was made in 2014 by the deployment of the second stage of the demonstration cluster which contains 112 OMs arranged on five strings, as well as equipment of an acoustic positioning system and instrumentation string with an array calibration and environment monitoring equipment. Deployment of the demonstration cluster will be completed in 2015.

The Majorana Demonstrator is an array of point-contact Ge detectors fabricated from Ge isotopically enriched to 88% in 76 Ge to search for neutrinoless double beta decay. The processing of Ge for germanium detectors is a well-known technology. However, because of the high cost of Ge enriched in 76 Ge special procedures were required to maximize the yield of detector mass and to minimize exposure to cosmic rays. These procedures include careful accounting for the material; shielding it to reduce cosmogenic generation of radioactive isotopes; and development of special reprocessing techniques for contaminated solid germanium, shavings, grindings, acid etchant and cutting fluids from detector fabrication. Processing procedures were developed that resulted in a total yield in detector mass of 70%. However, none of the acid-etch solution and only 50% of the cutting fluids from detector fabrication were reprocessed. Had they been processed, the projections for the recovery yield would be between 80% and 85%. Maximizing yield is critical to justify a possible future ton-scale experiment. A process for recovery of germanium from the acid-etch solution was developed with yield of about 90%. All material was shielded or stored underground whenever possible to minimize the formation of 68 Ge by cosmic rays, which contributes background in the double-beta decay region of interest and cannot be removed by zone refinement and crystal growth. Formation of 68 Ge was reduced by a significant factor over that in natural abundance detectors not protected from cosmic rays.

A renewed interest in experimental research on Accelerator-Driven Systems (ADS) has been initiated by the global attempt to produce energy from thorium as a safe(r), clean(er) and (more) proliferation-resistant alternative to the uranium-fuelled thermal nuclear reactors. The ADS research has been actively pursued at the Joint Institute for Nuclear Research (JINR), Dubna, since decades. Most recently, the emission of fast neutrons was experimentally investigated at the massive (m = 512 kg) natural uranium spallation target QUINTA. The target has been irradiated with the relativistic deuteron beams of energy from 0.5 AGeV up to 4 AGeV at the JINR Nuclotron accelerator in numerous experiments since 2011. Neutron production inside the target was studied through the gamma-ray spectrometry measurement of natural uranium activation detectors. Experimental reaction rates for (n,γ), (n,f) and (n,2n) reactions in uranium have provided valuable information about the neutron distribution over a wide range of energies up to some GeV. The experimental data were compared to the predictions of Monte Carlo simulations using the MCNPX 2.7.0 code. The results are presented and potential sources of partial disagreement are discussed later in this work.

The Majorana Collaboration is constructing a system containing 40kg of HPGe detectors to demonstrate the feasibility and potential of a future tonne-scale experiment capable of probing the neutrino mass scale in the inverted-hierarchy region. To realize this, a major goal of the Majorana Demonstrator is to demonstrate a path forward to achieving a background rate at or below 1 cnt/(ROI-t-y) in the 4 keV region of interest around the Q-value at 2039 keV. This goal is pursued through a combination of a significant reduction of radioactive impurities in construction materials with analytical methods for background rejection, for example using powerful pulse shape analysis techniques profiting from the p-type point contact HPGe detectors technology. The effectiveness of these methods is assessed using simulations of the different background components whose purity levels are constrained from radioassay measurements.

The MAJORANA DEMONSTRATOR will search for the neutrinoless double beta decay (ββ(0ν)) of the isotope 76Ge with a mixed array of enriched and natural germanium detectors. In view of the next generation of tonne-scale germanium-based ββ(0ν)-decay searches, a major goal of the MAJORANA DEMONSTRATOR is to demonstrate a path forward to achieving a background rate at or below 1 cnt/(ROI-t-y) in the 4 keV region of interest (ROI) around the 2039-keV Q-value of the 76Ge ββ(0ν)-decay. Such a requirement on the background level significantly constrains the design of the readout electronics, which is further driven by noise and energy resolution performances. We present here the low-noise low- background front-end electronics developed for the low-capacitance p-type point contact (P-PC) germanium detectors of the MAJORANA DEMONSTRATOR. This resistive-feedback front-end, specifically designed to have low mass, is fabricated on a radioassayed fused-silica substrate where the feedback resistor consists of a sputtered thin film of high purity amorphous germanium and the feedback capacitor is based on the capacitance between gold conductive traces.

The Prototyping phase of the BAIKAL-GVD project has been started in April 2011 with the deployment of a three string engineering array which comprises all basic elements and systems of the Gigaton Volume Detector (GVD) in Lake Baikal. In April 2012 the version of engineering array which comprises the first full-scale string of the GVD demonstration cluster has been deployed and operated during 2012. The first stage of the GVD demonstration cluster which consists of three strings is deployed in April 2013. We review the Prototyping phase of the BAIKAL-GVD project and describe the configuration and design of the 2013 engineering array., Proceedings of the RICAP 2013 Conference, Rome, Italy, May 22-24, 2013, 7 pages, 12 figures

The Majorana Collaboration is constructing the Majorana Demonstrator , an ultra-low background, 40-kg modular high purity Ge detector array to search for neutrinoless double-beta decay in 76Ge. In view of the next generation of tonne-scale Ge-based neutrinoless double-beta decay searches that will probe the neutrino mass scale in the inverted-hierarchy region, a major goal of the Demonstrator is to demonstrate a path forward to achieving a background rate at or below 1 count/tonne/year in the 4 keV region of interest around the Q-value at 2039 keV. The current status of the Demonstrator is discussed, as are plans for its completion.

We present a status of the Baikal-GVD Project. The objective of this project is a construction of a km3-scale neutrino telescope in the Lake Baikal. As an important milestone, the first GVD engineering array has been deployed and ran in April, 2011. Application of a completely new technology gave us an opportunity to study all the basic elements of the future full detector and to finalize the GVD technical design. We discuss the configuration and the design of the engineering array as well as data performance with the preliminary results.

A study of signals originating near the lithium-diffused n+ contact of p-type point contact (PPC) high purity germanium detectors (HPGe) is presented. The transition region between the active germanium and the fully dead layer of the n+ contact is examined. Energy depositions in this transition region are shown to result in partial charge collection. This provides a mechanism for events with a well defined energy to contribute to the continuum of the energy spectrum at lower energies. A novel technique to quantify the contribution from this source of background is introduced. Experiments that operate germanium detectors with a very low energy threshold may benefit from the methods presented herein.

The radioactivity levels in the air of the radionuclides released by the Fukushima accident were measured at the Laboratoire Souterrain de Modane, in the South-East of France, during the period 25 March–18 April 2011. Air-filters from the ventilation system exposed for one or two days were measured using low-background gamma-ray spectrometry. In this paper we present the activity concentrations obtained for the radionuclides 131 I, 132 Te, 134 Cs, 137 Cs, 95 Nb, 95 Zr, 106 Ru, 140 Ba/La and 103 Ru. The activity concentration of 131 I was of the order of 100 μBq/m 3 , more than 100 times higher than the activities of other fission products. The highest activities of 131 I were measured as a first peak on 30 March and a second peak on 3–4 April. The activity concentrations of 134 Cs and 137 Cs varied from 5 to 30 μBq/m 3 . The highest activity concentration recorded for Cs corresponded to the same period as for 131 I, with a peak on 2–3 April. The results of the radioactivity concentration levels in grass and mushrooms exposed to the air in the Modane region were also measured. Activity concentrations of 131 I of about 100 mBq/m 2 were found in grass.

The MAJORANA Collaboration is building the MAJORANA DEMONSTRATOR, a 60 kg array of high purity germanium detectors housed in an ultra-low background shield at the Sanford Underground Laboratory in Lead, SD. The MAJORANA DEMONSTRATOR will search for neutrinoless double-beta decay of 76Ge while demonstrating the feasibility of a tonne-scale experiment. It may also carry out a dark matter search in the 1-10 GeV/c^2 mass range. We have found that customized Broad Energy Germanium (BEGe) detectors produced by Canberra have several desirable features for a neutrinoless double-beta decay experiment, including low electronic noise, excellent pulse shape analysis capabilities, and simple fabrication. We have deployed a customized BEGe, the MAJORANA Low-Background BEGe at Kimballton (MALBEK), in a low-background cryostat and shield at the Kimballton Underground Research Facility in Virginia. This paper will focus on the detector characteristics and measurements that can be performed with such a radiation detector in a low-background environment., Comment: Submitted to NIMA Proceedings, SORMA XII. 9 pages, 4 figures

A cadmium tungstate crystal scintillator enriched in 106 Cd was developed for an experiment to search for double beta processes in 106 Cd. With this aim samples of cadmium with natural isotopic composition and enriched in 106 Cd were purified by vacuum distillation. Cadmium tungstate compounds were synthesized from solutions. The absolute isotopic composition of the enriched cadmium was accurately determined as 66.4% by thermal ionisation mass-spectrometry. A 106 CdWO 4 crystal boule was grown by the low-thermal-gradient Czochralski technique. The total irrecoverable loss of the enriched cadmium in all the stages of the crystal scintillator production does not exceed 2.3%. The produced 106 CdWO 4 crystal scintillator with mass of 216 g exhibits good optical and scintillation properties.

The time-differential perturbed angular correlations technique (TDPAC) has been employed for measuring the parameters of hyperfine interactions in earlier known RAl 3 compounds, synthesized at high pressure (8 GPa) and high temperature, where R = La, Ce, Sm, Gd, Tb, Dy, Ho, Er, Yb and Lu. The 111 Cd( 111 In) radioactive atom was used as a probe nucleus. The X-ray method has revealed that with the increase in the atomic number of a rare-earth element R, the obtained RAl 3 high-pressure phases crystallize, respectively, into orthorhombic, hexagonal and cubic structures. It has been found that in the compounds containing R=La, Ce, Sm and Gd, a deviation from earlier known structural types and the formation of new ones is observed, which is associated with the change of the stoichiometric composition of the said compounds. The results of the PAC measurements have confirmed the deviation from the predetermined stoichiometric composition 1R:3Al for the compounds LaAl 3 , CeAl 3 , SmAl 3 and GdAl 3 and have verified the RAl 3 stoichiometric structure for the other high-pressure phases obtained in this work.

Lead tungstate (PbWO4) crystal scintillators are discussed as an active shield and light guides in Cd-116 double-beta decay experiment with Cadmium tungstate (CdWO4) scintillators. Scintillation properties and radioactive contamination of PbWO4 scintillators were investigated. Energy resolution of CdWO4 detector, coupled to PbWO4 light guide, was tested. Efficiency of PbWO4-based active shield to suppress background from the internal contamination of PbWO4 crystals, as well as possible contribution from radioactivity of copper shield and phototubes were calculated. Using of lead tungstate crystal scintillators as high-efficiency 4 pi active shield could allow to build sensitive 2 beta experiment (T-1/2(0 nu 2 beta) similar to 10(26) yr) to search for 0 nu 2 beta decay of Cd-116 with (CdWO4)-Cd-116 crystal scintillators. (c) 2005 Elsevier B.V. All rights reserved.

Energy resolution, α / β ratio and the pulse-shape discrimination ability of the CaWO4 crystal scintillators were studied. The radioactive contamination and background of the crystals were measured in the Solotvina Underground Laboratory. Despite a rather high level of radioactive impurities, the background rate of the CaWO4 detector in the energy window of the 48Ca neutrinoless 2 β decay (3.6–5.4 MeV) was reduced to 0.07 counts/(yr keV kg). The indication for α decay of 180W (Phys. Rev. 67 (2003) 014310) was confirmed (the measured half-life is T 1 / 2 = 1 . 0 - 0.3 + 0.7 × 10 18yr).

A precision measurement of the 277 keV γ ray produced by capturing muons in gaseous oxygen was performed using high-resolution HPGe detectors. The Doppler-broadened shape of this line is sensitive to the possible admixture into muon capture of genuine scalar interaction. This experiment complements, in the muon sector, in principle, similar ones undertaken recently in nuclear β decay. Using a procedure discussed in earlier papers, a fit to the experimental line-shape allowed us to obtain for the recoil–gamma correlation coefficient the value of a 1 2 =0.096±0.041 (95% CL). The available evaluations of the contributing nuclear matrix elements, performed in the impulse approximation in the absence of scalar interaction, produce correlation coefficients in disagreement with our result. These evaluations are independent of the induced pseudoscalar coupling and so of the validity of the PCAC hypothesis, but their reliability and model dependence remain to be investigated.

We describe an improved follow-up of our previous spin-neutrino correlation experiment, where the 1229 and 2171 keV gamma-rays emitted after the 28 Si( μ , ν ) 28 Al(1 + , 2202 keV) reaction were observed by high-resolution HPGe detectors at different angles with respect to the muon spin. In the experiment described here, a magnetic field was used both to select events according to the spin-gamma angle and to measure the residual muon polarization by the muSR method. We further increase the precision of our result making use of new experimental and theoretical information. We obtain for the parameter x ≡ M (2)/ M (−1) the value of x =0.239±0.029, which can be compared to our previous result (Brudanin et al., Nucl. Phys. A 587 (1995) 577) x =0.254±0.034 and to the value x =0.315±0.080 obtained recently at TRIUMF with a different technique. The coupling-constant ratio g P / g A was deduced from the mean value x =0.247±0.027. Using renormalized transition operators calculated recently, we obtained for g P / g A the solution range of −1.0 to +1.3 to be compared to the value of 7 predicted by PCAC for the free nucleon. This result confirms the strong quenching of g P / g A reported earlier.

Spectra of photons emitting due to internal Compton effect in 203Tl have been measured in a coincidence experiment. It is found that the calculated theoretical values from the formula of Wang Chang and Falkoff fit the experimental ones fairly well within the accuracy of the measurement.