An approach to evaluate the efficiency of γ-ray detectors to determine the radioactivity in environmental samples

This work provides an approach to determine the efficiency of γ-ray detectors with a good accuracy in order to determine the concentrations of either naturally occurring or artificially prepared radionuclides. This approach is based on the efficiency transfer formula (ET), the effective solid angles, the self- absorptions of the source matrix, the attenuation by the source container and the detector housing materials on the detector efficiency. The experimental calibration process was done using radioactive (Cylindrical & Marinelli) sources, in different dimensions, that contain aqueous ¹⁵²Eu radionuclide. The comparison point to a fine agreement between the experimental measured and calculated efficiencies for the (NaI & HPGe) detectors using volumetric radioactive sources.     

AMANDA observations constrain the ultrahigh energy neutrino flux

A number of experimental techniques are currently being deployed in an effort to make the first detection of ultrahigh energy cosmic neutrinos. To accomplish this goal, techniques using radio and acoustic detectors are being developed, which are optimally designed for studying neutrinos with energies in the PeV-EeV range and above. Data from the AMANDA experiment, in contrast, have been used to place limits on the cosmic neutrino flux at less extreme energies (up to approximately 10 PeV). In this Letter, we show that by adopting a different analysis strategy, optimized for much higher energy neutrinos, the same AMANDA data can be used to place a limit competitive with radio techniques at EeV energies. We also discuss the sensitivity of the IceCube experiment, in various stages of deployment, to ultrahigh energy neutrinos.     

High-energy astrophysics with neutrino telescopes

Neutrino astrophysics offers new perspectives on the Universe investigation: high-energy neutrinos, produced by the most energetic phenomena in our Galaxy and in the Universe, carry complementary (if not exclusive) information about the cosmos with respect to photons. While the small interaction cross section of neutrinos allows them to come from the core of astrophysical objects, it is also a drawback, as their detection requires a large target mass. This is why it is convenient to put huge cosmic neutrino detectors in natural locations, like deep underwater or under-ice sites. In order to supply for such extremely hostile environmental conditions, new frontier technologies are under development. The aim of this work is to review the motivations for high-energy neutrino astrophysics, the present status of experimental results and the technologies used in underwater/ice Cherenkov experiments, with a special focus on the efforts for the construction of a km³-scale detector in the Mediterranean Sea.     

Recording of ultrahigh-energy astrophysical neutrinos

This review is devoted to the problems of recording ultrahigh-energy neutrinos produced in distant astrophysical sources and during the decay of supermassive particles. Prospects for the detection of neutrino fluxes are considered based on peculiarities of the propagation and interaction of ultrahigh-energy neutrinos. The operating and planned facilities designed to investigate neutrinos from various sources are described: neutrino telescopes recording neutrino interactions in natural water and ice volumes; ground-based arrays of detectors and optical telescopes onboard orbital space stations capable of detecting neutrino-triggered horizontal air showers. Instruments based on new principles of recording neutrinos with extremely high energies are considered: radio telescopes designed to observe Cherenkov radio emission from neutrino cascades originating in such radio-transparent natural environments as the atmosphere, salt domes, ice packs, and lunar regolith; underwater acoustic detectors. It is shown that putting new facilities into operation will allow neutrinos from most of the known astrophysical sources with energies differing by more than ten orders of magnitude, from 10¹² to 10²²–10²⁴ eV, to be recorded.     

Hunting potassium geoneutrinos with liquid scintillator Cherenkov neutrino detectors

The research on geoneutrinos is a new interdisciplinary subject involving particle experiments and geo-science.Potassium-40(40K)decays contribute roughly to 1/3 of the radiogenic heat of the Earth,which is not yet accounted for by experimental observation.Solar neutrino experiments with liquid scintillators have observed uranium and thorium geoneutrinos and are the most promising experiments with regard to low-background neutrino detection.In this study,we present the new concept of using liquid-scintillator Cherenkov detectors to detect the neutrino-electron elastic scattering process of 40K geoneutrinos.Liquid-scintillator Cherenkov detectors using a slow liquid scintillator achieve this goal with both energy and direction measurements for charged particles.Given the directionality,we can significantly suppress the dominant intrinsic background originating from solar neutrinos in conventional liquid-scintillator detectors.We simulated the solar-and geo-neutrino scatterings in the slow liquid scintillator detector,and implemented energy and directional reconstructions for the recoiling electrons.We found that 40K geoneutrinos can be detected with three-standard-deviation accuracy in a kiloton-scale detector.     

基于虚拟刻度原理对放射性体源效率刻度方法的发展

采用蒙特卡罗模拟计算的方法,标定能够适用于不同HPGe探测器上的体源虚拟点源位置,需要对点源、体源的探测效率进行模拟计算。通过²⁴¹Am、¹³⁷Cs、⁶⁰Co点源和体源研究了HPGe晶体尺寸、类型对它们的虚拟点源位置的影响,模拟结果表明²⁴¹Am虚拟点源位置随着探测器尺寸、类型的不同呈现明显的差异性,说明虚拟刻度原理对于探测器表面的小体积样品测量在低能区间是不可取的,最后采用¹³⁷Cs、⁶⁰Co源得出体源高度与虚拟点源位置的半经验公式。通过实验室两台HPGe探测系统对尺寸Φ70 mm×65 mm标准土壤体源的探测效率进行计算,与模拟探测效率值、虚拟点源效率表征结果对比分析,验证了拟合一组表征虚拟点源位置的半经验公式是可行的。实验结果表明,对γ能量区间在300～2 000 keV进行体源的虚拟刻度时,选择可靠的定标源即可建立体源和虚拟点源位置的关系。这为解决监测工作中样品与探测器之间重复进行探测效率校准的问题提供了新的途径。     

A novel approach for modelling the cluster detector and the SPI spectrometer

A probabilistic approach has been presented in six recent papers (R Kshetri, J. Instrum. 2012 7 P04008; ibid., P07006; ibid., P07008; ibid., P08015; ibid., P12007; Appl. Radiat. Isotopes 2013 75 30) for modelling a general composite detector. In this paper, a simplistic view has been presented on the application of our formalism to composite detectors consisting of hexagonal closely packed encapsulated HPGe detector modules. We have presented modified calculations for the peak-to-total (PT) and peak-to-background (PB) ratios of the cluster and spectrometer for integral satellite (SPI) for the first time considering up to four-fold events. Instead of using an empirical method or simulation, we present a novel approach for calculating the peak-to-total ratio of the SPI spectrometer for high γ energies. Our work can provide guidance for designing new composite detectors and for performing experimental studies with the SPI spectrometer for high-energy γ-rays.     

Working group report: Neutrino and astroparticle physics

This is the report of neutrino and astroparticle physics working group at WHEPP-7. Discussions and work on CP violation in long baseline neutrino experiments, ultra high energy neutrinos, supernova neutrinos and water Cerenkov detectors are discussed.     

Testing neutrino magnetic moment in ionization of atoms by neutrino impact

The atomic ionization processes induced by scattering of neutrinos play key roles in the experimental searches for a neutrino magnetic moment. Current experiments with reactor (anti)neutrinos employ germanium detectors having energy threshold comparable to typical binding energies of atomic electrons, which fact must be taken into account in the interpretation of the data. Our theoretical analysis shows that the so-called stepping approximation to the neutrino-impact ionization is well applicable for the lowest bound Coulomb states, and it becomes exact in the semiclassical limit. Numerical evidence is presented using the Thomas-Fermi model for the germanium atom.     

Physics prospects of the Jinping neutrino experiment

The China Jinping Underground Laboratory(CJPL), which has the lowest cosmic-ray muon flux and the lowest reactor neutrino flux of any laboratory, is ideal to carry out low-energy neutrino experiments. With two detectors and a total fiducial mass of 2000 tons for solar neutrino physics(equivalently, 3000 tons for geo-neutrino and supernova neutrino physics), the Jinping neutrino experiment will have the potential to identify the neutrinos from the CNO fusion cycles of the Sun, to cover the transition phase for the solar neutrino oscillation from vacuum to matter mixing, and to measure the geo-neutrino flux, including the Th/U ratio. These goals can be fulfilled with mature existing techniques. Efforts on increasing the target mass with multi-modular neutrino detectors and on developing the slow liquid scintillator will increase the Jinping discovery potential in the study of solar neutrinos,geo-neutrinos, supernova neutrinos, and dark matter.     

Neutrino mass and mixing implied by underground deficit of low energy muon-neutrino events

Recent observations of a deficit of cosmic ray muon-neutrino interactions in underground detectors suggest that the muon neutrinos may have oscillated to another state. We examine possible neutrino mass and mixing patterns, and their implications for vacuum and matter effects on solar neutrinos, on neutrinos passing through the earth, and on terrastrial neutrino beams. By invoking the see-saw mechanism of neutrino mass generation, we draw inferences on closure of the universe with neutrino masses, on the number of generations, on t-quark and fourth generation masses, and on the Peccei-Quinn symmetry breaking scale. Testable predictions are suggested.     

Neutrino-nucleus reaction in supernovae

Neutrino reactions play an important role at various stages of core-collapse supernova. During infall, neutrinos are produced by electron capture mainly on nuclei and contribute significantly to the cooling of the collapsing core. After core bounce the nascent neutron star cools by neutrino emission. It is a major goal to observe such neutrinos from a future supernova by earthbound detectors and to establish their spectra. Recently it has been shown that the spectrum of electron neutrinos from the early neutrino burst is significantly altered if inelastic neutrino-nucleus scattering is considered in supernova simulations. Finally spallation reactions induced by neutrinos when passing through the outer burning shells can produce certain nuclides in what is called neutrino nucleosynthesis.     

Pulse shape analysis for γ-ray tracking (Part I): Pulse shape simulation with JASS

Next-generation g \gamma -ray spectrometers based on highly segmented HPGe detectors are using the recent technique of g \gamma -ray tracking to significantly improve on efficiency and Doppler correction capabilities. A precise reconstruction of the individual interaction locations within the active material is possible through the use of pulse shape analysis (PSA) which, in turn, demands an accurate knowledge of the detector response. We developed JASS, a Java-based simulation software package to generate pulse shapes for the AGATA detectors from physics constraints and basic material parameters. For verifying the simulation experimental data from a coincidence scan with known interaction locations was used. The achieved position resolution, in the order of a few millimeters, is within the requirements of the g \gamma -ray tracking array.     

Kitchen salt as a target for supernova neutrinos

According to the model of rotating collapsar, the gravitational stellar collapse occurs in two stages. During the first stage, electron neutrinos with average energies from 30 to 40 MeV, formed in the neutronization reaction (p + e ^? → n + ν_e), are mainly emitted. Previously iron was considered as a target for detecting neutrinos of such energies. It is shown in this study that addition of kitchen salt to the structure of existing detectors can both significantly improve the neutrino type identification and increase the active mass of existing detectors.     

The status of the study of solar CNO neutrinos in the Borexino experiment

Although less than 1% of solar energy is generated in the CNO cycle, it plays a critical role in astrophysics, since this cycle is the primary source of energy in certain more massive stars and at later stages of evolution of solar-type stars. Electron neutrinos are produced in the CNO cycle reactions. These neutrinos may be detected by terrestrial neutrino detectors. Various solar models with different abundances of elements heavier than helium predict different CNO neutrino fluxes. A direct measurement of the CNO neutrino flux could help distinguish between these models and solve several other astrophysical problems. No CNO neutrinos have been detected directly thus far, and the best upper limit on their flux was set in the Borexino experiment. The work on reducing the background in the region of energies of CNO neutrinos (up to 1.74 MeV) and developing novel data analysis methods is presently under way. These efforts may help detect the CNO neutrino flux in the Borexino experiment at the level predicted by solar models.     

Simulated minimum detectable activity concentration (MDAC) for a real-time UAV airborne radioactivity monitoring system with HPGe and LaBr3 detectors

An automatic real-time UAV airborne radioactivity monitoring system with high-purity germanium (HPGe) and lanthanum bromide (LaBr₃) detectors (NH-UAV) was developed to precisely obtain small-scope nuclide information in major nuclear accidents. The specific minimum detectable activity concentration (MDAC) calculation method for NH-UAV in the atmospheric environment was deduced in this study for a priori evaluation and quantification of the suitability of NH-UAV in the Fukushima nuclear accident, where the MDAC values of this new equipment were calculated based on Monte Carlo simulation. The effects of radioactive source term size and activity concentration on the MDAC values were analyzed to assess the detection performance of NH-UAV in more realistic environments. Finally, the MDAC values were calculated at different shielding thicknesses of the HPGe detector to improve the detection capabilities of the HPGe detector, and the relationship between the MDAC and the acquisition time of the system was deduced. The MDAC calculation method and data results in this study may be used as a reference for in-situ radioactivity measurement of NH-UAV.     

Supernova 1987A, 30 Years Later

Most supernova theories state that this phenomenon lasts for a few seconds and ends with a big final explosion. However, these theories do not take into account several experimental results obtained with neutrino and gravitational wave detectors during the explosion of SN 1987A, the only supernova observed in a nearby galaxy in modern age. According to these experimental results the phenomenon is much more complex that envisaged by current theories, and has a duration of several hours. Since recent data of the X-ray NASA Satellite NuSTAR show a clear evidence of an asymmetric collapse, we have revisited the experimental data recorded by some underground and gravitational wave detectors running at the time of SN 1987A. New evidence is shown that confirms the previous results, namely that the data recorded by the gravitational wave detectors running in Rome and in Maryland are strongly correlated with the data of both the LSD (Mont Blanc) and the Kamiokande detectors, and that the correlation extends over a long period of time (one or two hours) centered at the Mont Blanc time. In addition, the signals of the GW detectors preceded the signals of the underground detectors by a time of order of one second. This result, obtained by comparing six independent files of data recorded by four different experiments located at intercontinental distances, indicates that also Kamiokande detected neutrinos at theMont Blanc time, but these interactions were not identified because not grouped in a burst. A similar correlation was also found in the data of the underground experiments in Mont Blanc and Baksan.     

Radiography of Earth's core and mantle with atmospheric neutrinos

A measurement of the absorption of neutrinos with energies in excess of 10 TeV when traversing the Earth is capable of revealing its density distribution. Unfortunately, the existence of beams with sufficient luminosity for the task has been ruled out by the AMANDA South Pole neutrino telescope. In this Letter we point out that, with the advent of second-generation kilometer-scale neutrino detectors, the idea of studying the internal structure of Earth may be revived using atmospheric neutrinos instead.     

Matrix formalism and singular-value decomposition for the location of gamma interactions in segmented HPGe detectors

Modern coaxial and planar HPGe detectors allow a precise determination of the energies and trajectories of the impinging gamma-rays. This entails the location of the gamma interactions inside the crystal from the shape of the delivered signals. This paper reviews the state of the art of the analysis of the HPGe response function and proposes methods that lead to optimum signal decomposition. The generic matrix method allows fast location of the interactions even when the induced signals strongly overlap.