Inverse-beta-decay reaction in the antineutrino flux from the fragments of <Superscript>232</Superscript>Th and <Superscript>233</Superscript>U fission

The energy spectra of antineutrinos produced in the beta decay of fragments originating from ²³³U and ²³²Th fission induced by neutrons are calculated. The relevant cross sections and the spectra of positrons produced in inverse beta decay are found. This study was motivated by the hypothesis (discussed over the past decade)t hat a self-sustained chain reaction proceeds at the center of the Earth (“georeactor”). According to the author of this hypothesis, the georeactor provides energy necessary for maintaining the Earth’s magnetic field. It is ²³⁵U and, probably, ²³²Th and ²³³U that serve as a nuclear fuel in this reactor. Data obtained in the present study can be guidelines in future experiments aimed at testing the hypothesis of the georeactor and at estimating the composition of its nuclear fuel within the development of geophysical and astrophysical investigations based on the observation of antineutrino fluxes in nature.     

Neutrino geophysics and astronomy at Baksan Neutrino Observatory: Potential of the spectroscopy of natural antineutrino sources

Prospects for studying, at the Baksan Neutrino Observatory, geoneutrinos, as well as neutrinos from supernovae, by means of a scintillation spectrometer having a target mass of 5000 t are considered. It is shown that the geographical location, a deep position (4800 mwe), and a modest background of antineutrinos from nuclear reactors makes the Baksan Neutrino Observatory one of the best places for performing such investigations. Particular attention is given to the derivation of information about the nature of neutrinos, the possibility of detecting relic neutrinos from supernovae, and the discovery of a hypothetical georeactor.     

Industrial Reactor Power Monitoring Using Antineutrino Counts in the DANSS Detector

Detection of antineutrino by the reaction of the inverse β-decay can be used for an independent monitoring of a nuclear reactor power. DANSS detector is located directly under a commercial WWER-1000 reactor and counts up to 5000 antineutrino per day, providing the accuracy of 1.5% in 2 days of the flux measurement. A powerful system of the passive and active shielding in combination with the fine spatial segmentation of the detector allows to diminish the contribution of the background processes to a level, negligible in comparison to the statistical error. The influence of the nuclear fuel composition on the neutrino flux can be accounted for based on the input from the NPP staff.

     

Search for neutrino oscillations at the palo verde nuclear reactors

We report on the initial results from a measurement of the antineutrino flux and spectrum at a distance of about 800 m from the three reactors of the Palo Verde Nuclear Generating Station using a segmented gadolinium-loaded scintillation detector. We find that the antineutrino flux agrees with that predicted in the absence of oscillations excluding at 90% C.L. nu;(e)-nu;(x) oscillations with Deltam(2)>1.12x10(-3) eV(2) for maximal mixing and sin (2)2straight theta>0.21 for large Deltam(2). Our results support the conclusion that the atmospheric neutrino oscillations observed by Super-Kamiokande do not involve nu(e).     

Indication of reactor ν(e) disappearance in the Double Chooz experiment

The Double Chooz experiment presents an indication of reactor electron antineutrino disappearance consistent with neutrino oscillations. An observed-to-predicted ratio of events of 0.944±0.016(stat)±0.040(syst) was obtained in 101 days of running at the Chooz nuclear power plant in France, with two 4.25 GW(th) reactors. The results were obtained from a single 10 m(3) fiducial volume detector located 1050 m from the two reactor cores. The reactor antineutrino flux prediction used the Bugey4 flux measurement after correction for differences in core composition. The deficit can be interpreted as an indication of a nonzero value of the still unmeasured neutrino mixing parameter sin(2)2θ(13). Analyzing both the rate of the prompt positrons and their energy spectrum, we find sin(2)2θ(13)=0.086±0.041(stat)±0.030(syst), or, at 90% C.L., 0.017相似文献   

Neutrons in extensive air showers

The first results of measurements of the thermal-neutron flux in extensive air showers (EASs) using an unshielded scintillation thermal-neutron detector in the Multicom prototype array at the Baksan Neutrino Observatory of the Institute for Nuclear Research are reported. The operating capacity of the new method for studying the EAS hadron component via detection of thermal neutrons and good prospects of this method are demonstrated.     

Neutrino geophysics at baksan: On searches for antineutrinos and radiogenic-heat sources in the interior of the earth

Antineutrinos produced in the Earth (geoneutrinos) carry information that is of crucial importance for the understanding of the origin and evolution of our planet. It is shown that the Baksan Neutrino Observatory of the Institute for Nuclear Research (Moscow, Russian Academy of Sciences) may become one of the best laboratories for studying geoneutrinos with the aid of a large scintillation spectrometer. The article also presents a brief history of the development of concepts of the Earth as a source of antineutrinos—it dates back to 1960, spanning a period of nearly 45 years (1960–2004).     

Search for sterile neutrinos in the neutrino-4 experiment

An experimental search for sterile neutrinos has been carried out at a neutrino facility based on the SM-3 nuclear reactor in Dimitrovgrad, Russia. The movable detector with passive shielding against the external radiation may be positioned at a distance varying between 6 and 12 m from the center of the reactor. The antineutrino flux has for the first time been measured using a movable detector placed close to the antineutrino source. The accuracy of the measurements is largely restricted by the cosmic background. The results of the measurements performed at small and large distances are analyzed in terms of the sterile-neutrino model parameters Δm ₁₄ ² and sin²2θ₁₄.     

Secondary X-Ray Environment in the Lower Atmosphere of the Earth during Monsoon Season over Udaipur City （India） in July-September 2006

We present a study on the secondary x-rays of energy band 2-100 keV emitted by the intruded principal pollutant components （gases and minerals） brought up in the lower atmosphere by dust storms, monsoon drift and the gravitational pull on meteoritic showers. On the ground we employed a 1.5 × 1 inch^2 NaI crystal in a scintillation detector, suitable for the energy range 2-100 keV of secondary x-rays, providing better energy resolution than a larger sized crystal. In order to eliminate the radioactive background of the Earth, the detector was well shielded on all sides with the help of the lead （Pb） container, except with a.small open window at the top to permit only vertically incident secondary radiation. The results from the data analysis obtained during the monsoon over Udaipur city （India） during the period from July to September （2006） have revealed a linear correlation between dust storm cure monsoon clouds and observed luminosities of secondary x-ray radiation from intruded pollutants. We found intense flux of secondary x-rays from the intruded pollutants when heavy dust and monsoon clouds were brought up by dust storms and monsoon drift in the lower atmosphere over Udaipur city as compared to normal days. Thus, secondary x-rays in the environment provide a tool for investigation of local intrusive pollutant components in the lower atmosphere.     

Can radiogenic heat sources inside the Earth be located by their antineutrino incoming directions?

Antineutrinos born in the U and Th decay chains inside the Earth (geoneutrinos) carry information on the amount and distribution of radiogenic heat sources, which is of fundamental importance for geophysics. Models of the Earth distribute U and Th masses mainly between the continental crust and the lower mantle. It has been much discussed recently that a number of detectors stationed at appropriate geographical sites can separate the crust and mantle contributions. We analyze directional separation of signals arriving from the crust and the lower mantle with only one detector. We find that, with an ∼ 30-kt liquid scintillation antineutrino spectrometer using the + p → e ⁺ + n detection reaction and positron and neutron coordinate reconstruction techniques, the U and Th distribution model can roughly be tested. We also consider detector calibration using an ∼ 1-MCi commercially available ⁹⁰Sr-⁹⁰Y beta source which emits (E _ν,max = 2.28 MeV) in the geoneutrino energy range. The text was submitted by the authors in English. Also at CEA/Saclay.     

Experiment for search for sterile neutrino at SM-3 reactor

In connection with the question of possible existence of sterile neutrino the laboratory on the basis of SM-3 reactor was created to search for oscillations of reactor antineutrino. A prototype of a neutrino detector with scintillator volume of 400 l can be moved at the distance of 6–11 m from the reactor core. The measurements of background conditions have been made. It is shown that the main experimental problem is associated with cosmic radiation background. Test measurements of dependence of a reactor antineutrino flux on the distance from a reactor core have been made. The prospects of search for oscillations of reactor antineutrino at short distances are discussed.     

Antineutrino energy spectrum unfolding based on the Daya Bay measurement and its applications

The prediction of reactor antineutrino spectra will play a crucial role as reactor experiments enter the precision era.The positron energy spectrum of 3.5 million antineutrino inverse beta decay reactions observed by the Day a Bay experiment,in combination with the fission rates of fissile isotopes in the reactor,is used to extract the positron energy spectra resulting from the fission of specific isotopes.This information can be used to produce a precise,data-based prediction of the antineutrino energy spectrum in other reactor antineutrino experiments with different fission fractions than Day a Bay.The positron energy spectra are unfolded to obtain the antineutrino energy spectra by removing the contribution from detector response with the Wiener-SVD unfolding method.Consistent results are obtained with other unfolding methods.A technique to construct a data-based prediction of the reactor antineutrino energy spectrum is proposed and investigated.Given the reactor fission fractions,the technique can predict the energy spectrum to a 2% precision.In addition,we illustrate how to perform a rigorous comparison between the unfolded antineutrino spectrum and a theoretical model prediction that avoids the input model bias of the unfolding method.     

Prospects of the search for neutrino bursts from supernovae with Baksan large volume scintillation detector

Observing a high-statistics neutrino signal from the supernova explosions in the Galaxy is a major goal of low-energy neutrino astronomy. The prospects for detecting all flavors of neutrinos and antineutrinos from the core-collapse supernova (ccSN) in operating and forthcoming large liquid scintillation detectors (LLSD) are widely discussed now. One of proposed LLSD is Baksan Large Volume Scintillation Detector (BLVSD). This detector will be installed at the Baksan Neutrino Observatory (BNO) of the Institute for Nuclear Research, Russian Academy of Sciences, at a depth of 4800 m.w.e. Low-energy neutrino astronomy is one of the main lines of research of the BLVSD.     

KamLAND and solar antineutrino spectrum

We use the recent KamLAND observations to predict the solar antineutrino spectrum at some confidence limits. We find a scaling of the antineutrino probability with respect to the magnetic field profile—in the sense that the same probability function can be reproduced by any profile with a suitable peak field value—that can be utilized to obtain the general shape ofthe solar antineutrino spectrum. This scaling and the upper bound on the solar antineutrino event rate, which can be derived from the data, lead to: 1) an upper bound on the solar antineutrino flux and 2) the prediction of their energy spectrum. We get \(\phi _{\bar \nu } < 3.8 \times 10^{ - 3} \phi (^8 B)\) or \(\phi _{\bar \nu } < 5.5 \times 10^{ - 3} \phi (^8 B)\) at 95% C.L., assuming Gaussian or Poissonian statistics, respectively. For 90% C.L., these become \(\phi _{\bar \nu } < 3.4 \times 10^{ - 3} \phi (^8 B)\) and \(\phi _{\bar \nu } < 4.9 \times 10^{ - 3} \phi (^8 B)\). This provides an improvement by a factor of 3–5 with respect to the existing bounds. These limits are quite general and independent of the detailed structure of the magnetic field in the solar interior.     

Be(d,n)反应中子源能谱测量及应用

 利用中子飞行时间技术和BC501A液体闪烁探测器的粒子分辨特性,测量了0°方向、20 MeV氘束轰击厚金属铍靶反应产生的中子源能谱,测量的中子能谱范围为0.7～25.0 MeV。在60°方向放置芪晶体闪烁探测器,由刻度好的BC501A液体闪烁探测器归一校正后,用于中子源强度监测。利用Be(d, n) 反应中子源,采用单粒子灵敏度标定方法,实验标定了0.75~15.75 MeV能量范围内的薄膜闪烁探测器中子能量响应曲线,实验结果与蒙特卡罗模拟计算结果在8%的不确定度范围内一致。     

土卫六探测器高超声速化学非平衡特性数值计算

为了研究土卫六探测器在地球大气和土卫六大气中飞行时气动热环境的差异,采用数值模拟的方法分别对地球大气成分和土卫六大气成分下探测器前方流场内气动热环境进行了研究,得到如下结论:与地球大气条件相比,土卫六大气条件下探测器表面的热流密度较高,其峰值可达到地球大气条件的1倍以上.探测器表面的热流密度先随着高度的减小而增加,而后...     

Status of an experiment aimed at laboratory searches for the electron-antineutrino magnetic moment at a level of μ ν ≤3±10− μ B

An experiment aimed at directly detecting antineutrino-electron scattering by using a 40-MCi tritium β-active source will make it possible to lower the present-day laboratory limit on the neutrino magnetic moment by two orders of magnitude. The experiment brings together novel unique technologies in studying rare processes of neutrino-electron scattering: (i) an artificial source of antineutrinos from tritium decay of 40-MCi activity with the antineutrino flux density of about 6×10¹⁴ cm^?2 s^?1 and (ii) new types of detectors capable of detecting electrons of energy down to about 10 eV, namely, a silicon cryogenic detector based on the ionization-into-heat conversion effect and a high-pure germanium detector with an internal signal amplification in the electric field. A compact installation located at a specially equipped underground laboratory (≤100 mwe) will provide favorable background conditions for running the experiment. With a background level of about 0.1 event/(kg keV d) and detector assembly masses of 3 and 5 kg for the silicon and germanium ones, respectively, a limit of μ _ν ≤3±10^? μ _B on the electron-antineutrino magnetic moment will be obtained within 1 to 2 years of data acquisition. The status of the experiment and the state of the art are presented.     

Determination of the direction to a source of antineutrinos via inverse beta decay in Double Chooz

To determine the direction to a source of neutrinos (and antineutrinos) is an important problem for the physics of supernovae and of the Earth. The direction to a source of antineutrinos can be estimated through the reaction of inverse beta decay. We show that the reactor neutrino experiment Double Chooz has unique capabilities to study antineutrino signal from point-like sources. Contemporary experimental data on antineutrino directionality is given. A rigorous mathematical approach for neutrino direction studies has been developed. Exact expressions for the precision of the simple mean estimator of neutrinos’ direction for normal and exponential distributions for a finite sample and for the limiting case of many events have been obtained.     

Employing low-power reactors in studying the mixing parameter sin<Superscript>2</Superscript>(2<Emphasis Type="Italic">θ</Emphasis><Subscript>13</Subscript>)

Measurement of the mixing parameter sin²(2θ₁₃) is one of the pressing problems in neutrino physics. Projects of reactor experiments characterized by a sensitivity of sin²(2θ₁₃)≈0.01 are being presently discussed. Almost all of them are based on the one reactor-two detectors scheme. Within this methodological approach, one employs an NPP reactor of power about a few GW for an antineutrino source and two detectors of identical configurations that are arranged at different distances from the reactor. In such experiments, the systematic error may be about 1%, which ensures a precision of about 0.01. In the present study, it is proposed to use, in a measurement of sin²(2θ₁₃), the existing SuperKamiokande (SK) detector combined with its own antineutrino source, a nuclear reactor of low thermal power, about 300 MW (low-power reactor, or LPR). Such an experiment can be performed within a rather short time. An analysis that studied various detection mechanisms revealed that the LPR-SK combination would make it possible to attain a sensitivity of sin²(2θ₁₃)≈0.002.     

中国散裂中子源反角白光中子束流参数的初步测量

中国散裂中子源(CSNS)已于2018年5月建设完工,随后进行了试运行.其中的反角白光中子束线(Back-n)可用于中子核数据测量、中子物理研究和核技术应用等多方面的实验.本文报道对该中子束的品质参数测量实验过程以及最终实验结果.实验主要采用中子飞行时间法,利用~(235)U,~(238)U裂变室和~6Li-Si探测器测量了中子能谱和中子注量率,又利用闪烁体-互补金属氧化物半导体探测系统测量了中子束斑的剖面,得到了该束线的初步实验测量结果.其中白光中子的全能谱测量范围eV—100 MeV,给出了不确定度分析;给出了中子注量率两个实验厅位置的满功率值;给出了白光中子在直径60 mm情况下的全能区束斑.通过与模拟结果的比较探讨了以上结果的合理性,并提出了改进计划.这些实验结果为以后该束线的核数据测量和探测器标定实验奠定了基础.