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Register a new userThe energy calibration system for CANDLES using (n, gamma) reaction
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CAlcium fluoride for the study of Neutrinos and Dark matters by Low-energy Spectrometer (CANDLES) searches for neutrino-less double beta decay of $^{48}$Ca using a CaF$_2$ scintillator array. A high Q-value of $^{48}$Ca at 4,272 keV enabled us to achieve very low background condition, however, at the same it causes difficulties in calibrating the detectors Q-value region because of the absence of a standard high-energy $gamma$-ray source. Therefore, we have developed a novel calibration system based on $gamma$-ray emission by neutron capture on $^{28}$Si, $^{56}$Fe and $^{58}$Ni nuclei. In the paper, we report the development of the new calibration system as well as the results of energy calibration in CANDLES up to 9 MeV.
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In a neutrinoless double-beta decay ($0 ubetabeta$) experiment, energy resolution is important to distinguish between $0 ubetabeta$ and background events. CAlcium fluoride for studies of Neutrino and Dark matters by Low Energy Spectrometer (CANDLES) discerns the $0 ubetabeta$ of $^{48}$Ca using a CaF$_2$ scintillator as the detector and source. Photomultiplier tubes (PMTs) collect scintillation photons. At the Q-value of $^{48}$Ca, the current energy resolution (2.6%) exceeds the ideal statistical fluctuation of the number of photoelectrons (1.6%). Because of CaF$_2$s long decay constant of 1000 ns, a signal integration within 4000 ns is used to calculate the energy. The baseline fluctuation ($sigma_{baseline}$) is accumulated in the signal integration, thus degrading the energy resolution. This paper studies $sigma_{baseline}$ in the CANDLES detector, which severely degrades the resolution by 1% at the Q-value of $^{48}$Ca. To avoid $sigma_{rm baseline}$, photon counting can be used to obtain the number of photoelectrons in each PMT; however, a significant photoelectron signal overlapping probability in each PMT causes missing photoelectrons in counting and reduces the energy resolution. Partial photon counting reduces $sigma_{baseline}$ and minimizes photoelectron loss. We obtain improved energy resolutions of 4.5-4.0% at 1460.8 keV ($gamma$-ray of $^{40}$K), and 3.3-2.9% at 2614.5 keV ($gamma$-ray of $^{208}$Tl). The energy resolution at the Q-value is estimated to be improved from 2.6% to 2.2%, and the detector sensitivity for the $0 ubetabeta$ half-life of $^{48}$Ca can be improved by 1.09 times.
The newly built second experimental area EAR2 of the n_TOF spallation neutron source at CERN allows to perform (n, charged particles) experiments on short-lived highly radioactive targets. This paper describes a detection apparatus and the experimental procedure for the determination of the cross-section of the 7Be(n,{alpha}) reaction, which represents one of the focal points toward the solution of the cosmological Lithium abundance problem, and whose only measurement, at thermal energy, dates back to 1963. The apparently unsurmountable experimental difficulties stemming from the huge 7Be {gamma}-activity, along with the lack of a suitable neutron beam facility, had so far prevented further measurements. The detection system is subject to considerable radiation damage, but is capable of disentangling the rare reaction signals from the very high background. This newly developed setup could likely be useful also to study other challenging reactions requiring the detectors to be installed directly in the neutron beam.
Gamma sources are routinely used to calibrate the energy scale and resolution of liquid scintillator detectors. However, non-scintillating material surrounding the source introduces energy losses, which may bias the determination of the centroid and width of the full absorption peak. In this paper, we present a general method to determine the true gamma centroid and width to a relative precision of 0.03% and 0.50%, respectively, using energy losses predicted by the Monte Carlo simulation. In particular, the accuracy of the assumed source geometry is readily obtained from the fit. The method performs well with experimental data in the Daya Bay detector.
We derive the full expression for the shape of the charge spectrum that results from the illumination of a photo-multiplier tube. The derivation is for low intensity illumination with constant gain, a common condition for most nuclear and particle physics applications. Under these conditions, it is shown that an analytic expression can be formulated that describes details of the spectrum including the pedestal and dark noise with excellent fidelity to allow statistical fits to data. The derivation and full formula using either Gaussian or Poisson models for gain, and its limiting forms under various simplifying assumptions are presented with strategies on their use. The analytic description can be used to formulate data acquisition strategies to perform precise absolute calibration of photo-multipliers, the digitizers, and the data acquisition system.
We present the design, data and results from the NEXT prototype for Double Beta and Dark Matter (NEXT-DBDM) detector, a high-pressure gaseous natural xenon electroluminescent time projection chamber (TPC) that was built at the Lawrence Berkeley National Laboratory. It is a prototype of the planned NEXT-100 $^{136}$Xe neutrino-less double beta decay ($0 ubetabeta$) experiment with the main objectives of demonstrating near-intrinsic energy resolution at energies up to 662 keV and of optimizing the NEXT-100 detector design and operating parameters. Energy resolutions of $sim$1% FWHM for 662 keV gamma rays were obtained at 10 and 15 atm and $sim$5% FWHM for 30 keV fluorescence xenon X-rays. These results demonstrate that 0.5% FWHM resolutions for the 2,459 keV hypothetical neutrino-less double beta decay peak are realizable. This energy resolution is a factor 7 to 20 better than that of the current leading $0 ubetabeta$ experiments using liquid xenon and thus represents a significant advancement. We present also first results from a track imaging system consisting of 64 silicon photo-multipliers recently installed in NEXT-DBDM that, along with the excellent energy resolution, demonstrates the key functionalities required for the NEXT-100 $0 ubetabeta$ search.
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