Double Beta Decay Of 48Ca Research Articles

Laser isotope separation to study for the neutrino-less double beta decay of 48Ca

The laser isotope separation (LIS) system is being developed for the study of neutrino-less double beta decay of 48Ca. A proof-of-principle experiment has been successfully conducted, and development of a mass production (∼1 mol/year) system is currently underway. For stable and efficient production, we are preparing an atomic beam system capable of producing a well-collimated beam with sufficient flux and a high-power semiconductor laser system with stable frequency over a long period of time.

Isotope separation by DC18C6 crown-ether for neutrinoless double beta decay of 48Ca

The isotope separation via liquid-liquid extraction (LLE) using crown-ether (DC18C6) was carried out in order to demonstrate the feasibility of calcium isotope enrichment, which aimed to find a cost-effective way to enrich calcium-48 (48Ca) for the study of neutrinoless double beta decay (0vββ) in the CANDLES project. The LLE results revealed that the extraction was solvent dependent in the presence of HCl and the distribution coefficient (D) increased approximately threefold (0.0546±0.0012) with 12 M HCl solvent under a 3.9 M CaCl2 (aq) (30% w/w) system. Furthermore, the HCl solvent maintained the calcium content attached to the crown-ether at lower feed concentrations. The reaction cell ICP-MS (Agilent 7900) with an additional H2 gas was used to analyze the isotopic composition. The single-stage separation factor of organic phase was found to be 0.992±0.003, 0.994±0.003, 0.996±0.004 for 48Ca/42Ca, 48Ca/43Ca, and 48Ca/44Ca, respectively in the extracted organic phase of 3.3 M CaCl2 (aq) (30% w/w) system. The obtained results were comparable with the HCl solvent system. As a result, without the addition of an acidity reagent, the production of the enriched 48Ca isotope via LLE was highly feasible. To improve the mass production of enriched 48Ca, filter separation was applied in order to shorten the time required and to study various volumes of the extraction system. The results indicated that the extraction efficiency of filter LLE was comparable to conventional LLE. Filter LLE resulted in more than threefold reduction in time required (approximately 10 minutes for a complete single-stage separation) in comparison with a conventional LLE, consequently implying great potential in the enrichment and mass production via filter LLE.

Development of the laser isotope separation method to study for the neutrino-less double beta decay of 48Ca

Search for the ultra-rare process, neutrino-less double beta decay, is a powerful tool to test the Majorana nature of neutrinos. Among the potential double beta decay nuclei, 48Ca has the largest Q-value, hence we can expect the measurement with least background. On the other hand, due to its low natural abundance, isotope enrichment is essential to achieve the sensitivity in the region of interest (inverted/normal mass hierarchy of neutrinos).We have been developing a laser isotope separation method using a tunable semiconductor laser that can excite only a specific isotope (48Ca). The laser is irradiated perpendicular to the collimated calcium vapor beam. Only 48Ca atoms are separated by deflecting them from the original atomic beam by momentum transfer due to multiple absorption and emission of laser photons. The isotope separation is confirmed by irradiating an ionization laser and time-of-flight measurement.Following the success of the proof-of-principle experiment, we are now developing the mass production system which include efficient generation of atomic beams, frequency-stabilized high-power laser, efficient laser irradiation method, and collection method of deflected isotope beams. In this paper, we report on the status and prospects of these developments.

Neutrino-less double beta decay of 48Ca studied by CaF2(pure) scintillators

We have studied the neutrino-less double beta decay(0νββ) of 48Ca by using CaF2(pure) scintillators. Analysis for rejection of backgrounds(212Bi→ 212Po events and 208Tl events) was effective to reduce backgrounds in Qββ-value region. No events are observed in the Qββ-value region for the data of 131 days × 86 kg. It gives a lower limit (90% confidence level) of (math) > 6.2 × 1022 year (preliminary) for the half-life of 0νββ of 48Ca.

The CANDLES experiment for the study of Ca-48 double beta decay

CANDLES studies the double beta decay of 48Ca through CaF2 scintillation crystals. The CANDLES III detector, located in Kamioka underground laboratory, is currently running. Here we describe recent status of data analysis which includes detector performance, detector stability, and background estimation. Current sensitivity for 0νββ half-life is also discussed in this paper.

A flexible scintillation light apparatus for rare event searches

Compelling experimental evidences of neutrino oscillations and their implication that neutrinos are massive particles have given neutrinoless double beta decay a central role in astroparticle physics. In fact, the discovery of this elusive decay would be a major breakthrough, unveiling that neutrino and antineutrino are the same particle and that the lepton number is not conserved. It would also impact our efforts to establish the absolute neutrino mass scale and, ultimately, understand elementary particle interaction unification. All current experimental programs to search for neutrinoless double beta decay are facing with the technical and financial challenge of increasing the experimental mass while maintaining incredibly low levels of spurious background. The new concept described in this paper could be the answer which combines all the features of an ideal experiment: energy resolution, low cost mass scalability, isotope choice flexibility and many powerful handles to make the background negligible. The proposed technology is based on the use of arrays of silicon detectors cooled to 120 K to optimize the collection of the scintillation light emitted by ultra-pure crystals. It is shown that with a 54 kg array of natural CaMoO4 scintillation detectors of this type it is possible to yield a competitive sensitivity on the half-life of the neutrinoless double beta decay of 100Mo as high as ~10E24 years in only one year of data taking. The same array made of 40CaMoO4 scintillation detectors (to get rid of the continuous background coming from the two neutrino double beta decay of 48Ca) will instead be capable of achieving the remarkable sensitivity of ~10E25 years on the half-life of 100Mo neutrinoless double beta decay in only one year of measurement.

Study of 48Ca Double Beta Decay by CANDLES

CANDLES is a project to search for neutrinoless double beta decay of 48Ca using CaF2 scintillators. The observation of neutrinoless double beta decay would confirm the existence of massive Majorana neutrinos. Herein the expected performances and current status of the CANDLES system are described.

Influence of pairing in double beta decay of 48Ca

Two-neutrino ββ decay matrix elements and half-life of 48Ca are calculated after including neutron-proton pairing correlations in projected Hartree-Fock-Bogoliubov (PHFB) formalism. The GT matrix elements in 2νββ decay are reduced due to broader smearing of Fermi surfaces. Half-life results for 2νββ decay of 48Ca with np pairing are better than without pairing.

Ultra-violet wavelength shift for undoped [formula omitted] scintillation detector by two phase of liquid scintillator system in CANDLES

CANDLES is a project to search for neutrinoless double beta decay of 48Ca with CaF 2 scintillators. An effective 4 π active shield is achieved by placing the CaF 2 crystals in a liquid scintillator. Energy resolution is improved by converting the ultra-violet light of the CaF 2 scintillator into the visible region with a wavelength shifter dissolved in the liquid scintillator. The newly developed technique, “two phase system of liquid scintillator”, is presented. It will be used to exploit the unique features of the CANDLES system. Experiments to determine liquid scintillator composition will be described. Performance of CANDLES will be demonstrated with prototype detectors. Obtained results indicate that the proposed two phase technique is effective for CANDLES system which will utilize several tons of CaF 2 scintillators.

Study of 48Ca double beta decay with CANDLES

CANDLES is the project to search for double beta decay of 48Ca by using CaF2 scintillators. If neutrinos have Majorana mass they violate lepton number conservation and neutrino-less double beta decay (OvDBD) can then take place. Therefore the study of the 0 vDBD is one of the most fundamental researches to be carried out in a coming decade.We have been studying the DBD of 48Ca using CaF2 scintillators. The Q value of 48Ca is the highest (4.27 MeV) among potential DBD nuclei. It is far above energies of γ-rays from natural radio-activities (maximum 2.615 MeV from 208TI decay), therefore we can naturally expect small backgrounds in the energy region we are interested in.Required performances for the detector are radio-purity, good background rejection efficiency and good energy resolution. We have constructed CANDLES III detector in our laboratory at sea level, which consists of 60 CaF2 crystals with the total mass of 191 kg. We are studying the basic performances of the system, including the light collection, position reconstruction and background rejection. On the bases of experiences in CANDLES III, the CANDLES project will be scaled up to several tons of calcium to have the sensitivity to the mass region of interest.

Double beta decay of 48Ca studied by CaF2(Eu) scintillators

We report the new limit on the half-life of neutrino-less double beta decay(0νββ) of 48Ca. In order to achieve the background free measurement, measurement of pulse shape was essential. We have observed no event in the Qββ-value region. We set the new limit on 0νββ half-life as T0νββ1/2 > 40 × 1022 year.

Study of double beta decay of 48Ca with CANDLES

CANDLES system had proposed for the study of double beta decay of 48Ca by using of undoped CaF2 scintillator. We have constructed CANDLES III detector at sea level. The result of first performance check is described.

Study of the design for the CANDLES trigger system

We are searching for 0ν double beta decay of 48Ca with CANDLES detector. We have a plan to construct a more larger detector underground from next year and considering the deadtime, we have to reduce background events at online trigger. Because FPGA is useful high integrated module, we are experimenting for the performance evaluation with prototype detector now.

Neutrinoless double [formula omitted]-decay nuclear matrix elements within the SRQRPA

The nuclear matrix elements associated with the light Majorana neutrino mass mechanism of the neutrinoless double beta decay of 48Ca, 76Ge, 82Se, 96Zr, 100Mo, 116Cd, 128Te, 130Te, 136Xe, and 150Nd have been calculated within the self-consistent renormalized quasiparticle random phase approximation (SRQRPA). By following a recently proposed procedure, where data on the two-neutrino double β decay half-lives are used to derive appropriate value of the particle–particle strength of the nuclear Hamiltonian, we have found that the SQRPA results are comparable with those from the QRPA and the RQRPA approaches. This constitutes an additional argument in favor of the convergence of the QRPA-like results.

Search for neutrino-less double beta decay of 48Ca by CaF 2 scintillator

A CaF 2 scintillation detector system (ELEGANT VI) has been operating at Oto Cosmo Observatory to study double beta decays of 48Ca. No events were observed around the Q-value energy region after the analysis of 4.23 kg yr data. To derive the lower limit for the half-life of the neutrino-less double beta decay of 48Ca, the expected number of background events in that energy region was estimated by a Monte Carlo simulation using the measured activities of 214Bi and 220Rn inside CaF 2 crystals. A new lower limit is obtained to be 1.4×10 22 yr at the 90% C.L. An experimental sensitivity is 5.9×10 21 yr at the 90% C.L.

Distinguishing between electrons and γ-rays in experiment TGV using a pulse rise time

The TGV (Telescope Germanium Vertical) collaboration is interested in the measurement of double-beta decay of 48Ca (TGV I) and 106Cd (TGV II). The background in the experiment TGV I has been suppressed by several methods. One of them was based on distinguishing between electrons and γ-rays due to the different rise time of the signals obtained from semiconductor detector. Two experimental setups have been tested, the first one used a charge-sensitive analog-to-digital converter, while the second one utilized digital oscilloscope. The reduction of the background counting rate (due to γ-rays) in single HPGe detector by a factor of (1.4-3.8) was reached.

Search for double beta decay of 48Ca in the TGV experiment

This Letter describes a collaborative TGV (Telescope Germanium Vertical) study of the double beta decay of 48Ca with a low-background and high sensitivity Ge multi-detector spectrometer. The results of T 1/2 2 νββ =(4.2 +3.3 −1.3)×10 19 years and T 1/2 0 νββ >1.5×10 21 years (90% CL) for double beta decay of 48Ca were found after processing experimental data obtained after 8700 hours of measuring time, using approximately 1 gramme of 48Ca. The features of a TGV-2 experiment are also presented.

Double-beta decay of 48Ca in the TGV experiment

The low-background, high-sensitivity Ge multidetector spectrometer TGV is used to study the double-beta decay of 48Ca. Additional suppression of the recorded background is achieved with neutron shielding and a method for distinguishing β particles from γ rays by detector-pulse rise time. The estimates T 1/2 γγ2ν = (4.2 ± 2.4) × 1019 yr and T 1/2 γγ0ν > 1.5 × 1021 yr (at a 90% C.L.) for the double-beta decay of 48Ca are obtained.

Experiments TGV I (double-beta decay of 48Ca) and TGV II (double-beta decay of 106Cd and 48Ca)

Present status of experiments TGV I and TGV II is given. The TGV I collaboration has studied the double-beta decay of 48Ca with a low-background and high sensitivity Ge multi-detector spectrometer TGV (Telescope Germanium Vertical). The preliminary results of \({\text{T}}_{{\text{1/2}}}^{{\text{2}}\nu \beta \beta } = (4.2_{ - 1.3}^{ + 3.3} ) \times 10^{19} \) years and \({\text{T}}_{{\text{1/2}}}^{0\nu \beta \beta } >1.5 \times 10^{21} \) years (90% CL) for double-beta decay of 48 Ca has been found after the processing of experimental data obtained after 8700 hours of measuring time using approximately 1 gramme of 48Ca. The aim of the experiment TGV II is the development of the experimental methods, construction of spectrometers and measurement of the ββ decay (β+β+, β+/EC, EC/EC) of 106Cd particularly the 2νEC/EC mode. The theoretical description and performance of the TGV II spectrometer are also given.

Present status and future of the experiment TGV (measurement of double beta decay of 48 Ca)

A short description of experiment TGV (double beta decay of48Ca) is given. The measurement started in the Modane underground laboratory in August 1996. The first result ofT12/0ν ≥ 4.6 × 1020 years [90% CL] after 2545 hours is presented.