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R. Hazama

Publications and source records attributed to R. Hazama.

47 records · Page 3Linked to original sources
arXiv2010

Astroparticle Physics with a Customized Low-Background Broad Energy Germanium Detector

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.

nucl-ex↗
arXiv2008

Neutrino-less Double Beta Decay of 48Ca studied by CaF2(Eu) Scintillators

We searched for the neutrino-less double beta decay(0nbb) of 48Ca by using CaF2(Eu) scintillators. Analysis of their pulse shapes was effective to reduce backgrounds. No events are observed in the Q-value region for the data of 3394 kg days. It gives a lower limit (90% confidence level) of T > 2.7 x 10^22 year for the half life of 0nbb of 48Ca. Combined with our previous data for 1553 kg days, we obtained more stringent limit of T > 5.8 x 10^22 year.

nucl-ex↗
arXiv2007

Challenge on Ca-48 enrichment for CANDLES double beta decay experiment

Chemical isotope effects of calcium were studied by liquid-liquid extraction using a crown ether of dicyclohexano-18-crown-6 for the purpose of finding a cost-effective and efficient way of enrichment of Ca-48 towards the study of the neutrinoless double beta decay of Ca-48. We evaluated each contribution ratio of the field shift effect and the hyperfine splitting shift effect to the mass effect of the calcium isotopes for the first time. The present preliminary result suggests the contribution of the field shift effect is small, especially for Ca-40-Ca-48 case, compared with the case of Chromium trichloride-crown in which the isotope enrichment factors are strongly affected by the field shifts. These indications are promising towards the mass producion of enriched Ca-48 by the chemical separation method.

nucl-ex↗
arXiv2007

An array of low-background $^3$He proportional counters for the Sudbury Neutrino Observatory

An array of Neutral-Current Detectors (NCDs) has been built in order to make a unique measurement of the total active flux of solar neutrinos in the Sudbury Neutrino Observatory (SNO). Data in the third phase of the SNO experiment were collected between November 2004 and November 2006, after the NCD array was added to improve the neutral-current sensitivity of the SNO detector. This array consisted of 36 strings of proportional counters filled with a mixture of $^3$He and CF$_4$ gas capable of detecting the neutrons liberated by the neutrino-deuteron neutral current reaction in the D$_2$O, and four strings filled with a mixture of $^4$He and CF$_4$ gas for background measurements. The proportional counter diameter is 5 cm. The total deployed array length was 398 m. The SNO NCD array is the lowest-radioactivity large array of proportional counters ever produced. This article describes the design, construction, deployment, and characterization of the NCD array, discusses the electronics and data acquisition system, and considers event signatures and backgrounds.

nucl-ex↗
arXiv2006

Multi-layer scintillation detector for the MOON double beta decay experiment: Scintillation photon responses studied by a prototype detector MOON-1

An ensemble of multi-layer scintillators is discussed as an option of the high-sensitivity detector Mo Observatory Of Neutrinos (MOON) for spectroscopic measurements of neutrino-less double beta decays. A prototype detector MOON-1, which consists of 6 layer plastic-scintillator plates, was built to study the sensitivity of the MOON-type detector. The scintillation photon collection and the energy resolution, which are key elements for the high-sensitivity experiments, are found to be 1835+/-30 photo-electrons for 976 keV electrons and sigma = 2.9+/-0.1% (dE/E = 6.8+/-0.3 % in FWHM) at the Qbb ~ 3 MeV region, respectively. The multi-layer plastic-scintillator structure with good energy resolution as well as good background suppression of beta-gamma rays is crucial for the MOON-type detector to achieve the inverted hierarchy neutrino mass sensitivity.

nucl-ex↗
arXiv2006

The performance of thin NaI(Tl) scintillator plate for dark matter search

A thin (0.05cm) and wide area (5cmX5cm) NaI(Tl) scintillator was developed. The performance of the thin NaI(Tl) plate, energy resolution, single photoelectron energy and position sensitivity were tested. An excellent energy resolution of 20% (FWHM) at 60keV was obtained. The single photoelectron energy was calculated to be approximately 0.42 0.02keV. Position information in the 5cmx5cm area of the detector was also obtained by analyzing the ratio of the number of photons collected at opposite ends of the detector. The position resolution was obtained to be 1cm (FWHM) in the 5cmx5cm area.

nucl-ex↗
arXiv2005

WIMPs search by means of the highly segmented scintillator

The highly sensitive method to search for WIMPs dark matter particles is proposed. An array of thin NaI(Tl) plate has the great selectivity for distinguishing the WIMPs events and background ones. The principle of signal selection for WIMPs is described. The high sensitivity for SD (spin-dependent) type WIMPs is expected by applying multi-layer system of NaI(Tl) detector.

astro-ph↗
arXiv2002

Comment on "Evidence for Neutrinoless Double Beta Decay"

We comment on the recent claim for the experimental observation of neutrinoless double-beta decay. We discuss several limitations in the analysis provided in that paper and conclude that there is no basis for the presented claim.

hep-ex↗
arXiv2001

Scintillation efficiency of nuclear recoils in a CaF-2(Eu) crystal for dark matter search

The scintillation efficiency (quenching factor) of fluorine and calcium nuclei recoiling in a CaF-2(Eu) crystal was measured in an energy region relevant to dark matter searches. The recoiling nuclei were obtained via the 19-F(n,n') and 40-Ca(n,n') reactions, where the neutron beam was provided via the d(d,n)3-He reaction. The quenching factor of F and Ca nuclei in the CaF-2(Eu) crystal was found to be 11 ~ 20 %, and 9 ~ 23 % relative to the electron equivalent energy for 53 ~ 192 keV and 25 ~ 91 keV recoil energies, respectively, and the energy dependence was observed. The quenching factor we measured here is a little larger than that of previous studies, which may depend on the Eu doping concentration of the crystal.

nucl-ex↗
arXiv2000

Spectroscopy of Double-Beta and Inverse-Beta Decays from 100Mo for Neutrinos

Spectroscopic studies of two beta-rays from 100Mo are shown to be of potential interest for investigating both the Majorana neutrino mass by neutrinoless double beta-decay and low energy solar neutrino's by inverse beta-decay. With a multi-ton 100Mo detector, coincidence studies of correlated beta-beta from neutrinoless double beta-decay, together with the large Q value, permit identification of the neutrino-mass term with a sensitivity of ~ 0.03 eV. Correlation studies of the inverse beta and the successive beta-decay of 100Tc, together with the large capture rates for low energy solar neutrino's, make it possible to detect in realtime individual low energy solar neutrino in the same detector.

nucl-ex↗