Measuring of fissile isotope partial antineutrino spectra in direct experiment at nuclear reactor

The direct measuring method is considered to get nuclear reactor antineutrino spectrum. We suppose to isolate partial spectra of the fissile isotopes by using the method of antineutrino spectrum extraction from the inverse beta-decay reaction positron spectrum applied at Rovno experiment. This admits to increase the accuracy of partial antineutrino spectra forming the total nuclear reactor spectrum. It is important for the analysis of the reactor core fuel composition and could be applied for non-proliferation purposes.     

Experimental spectrum of reactor antineutrinos and spectra of main fissile isotopes

Within the period between the years 1988 and 1990, the spectrum of positrons from the inverse-beta-decay reaction on a proton was measured at the Rovno atomic power plant in the course of experiments conducted there. The measured spectrum has the vastest statistics in relation to other neutrino experiments at nuclear reactors and the lowest threshold for positron detection. An experimental reactor-antineutrino spectrum was obtained on the basis of this positron spectrum and was recommended as a reference spectrum. The spectra of individual fissile isotopes were singled out from the measured antineutrino spectrum. These spectra can be used to analyze neutrino experiments performed at nuclear reactors for various compositions of the fuel in the reactor core.     

A study of antineutrino spectra from spent nuclear fuel at Daya Bay

The Daya Bay Reactor Antineutrino Experiment is designed to determine the as yet unknown neutrino mixing angle, θ₁₃, by measuring the disappearance of electron antineutrinos from several nuclear reactor cores. The projected sensitivity in sin²(2θ₁₃) of better than 0.01 at a 90% CL should be achieved after three years of data-taking. Antineutrinos emitted from spent nuclear fuel (SNF) distort the soft part of the energy spectrum. In this article, a calculation of the antineutrino spectra from the long-life isotopes in SNF is performed. A non-equilibrium generation of long half-life isotopes during the running time of the reactor is also analyzed. Finally, we show that the antineutrino event rate contribution from SNF, which has been stored in the SNF pool for several years, may be non-negligible.     

Measurement of the neutron spectrum of a Pu-C source with a liquid scintillator

The neutron response function for a BC501A liquid scintillator (LS) has been measured using a series of monoenergetic neutrons produced by the p-T reaction. The proton energies were chosen such as to produce neutrons in the energy range of 1 to 20 MeV. The principles of the technique of unfolding a neutron energy spectrum by using the measured neutron response function and the measured Pulse Height (PH) spectrum is briefly described. The PH spectrum of neutrons from the Pu-C source, which will be used for the calibration of the reactor antineutrino detectors for the Daya Bay neutrino experiment, was measured and analyzed to get the neutron energy spectrum. Simultaneously the neutron energy spectrum of an Am-Be source was measured and compared with other measurements as a check of the result for the Pu-C source. Finally, an error analysis and a discussion of the results are given.     

Components of antineutrino emission in nuclear reactor

New ?_ee scattering experiments aimed at sensitive searches for the ν_e magnetic moment and projects to explore small mixing angle neutrino oscillations at reactors require a better understanding of the reactor antineutrino spectrum. Six components which contribute to the total ?_e spectrum generated in a nuclear reactor are considered. They are beta decays of the fission fragments of ²³⁵U, ²³⁹Pu, ²³⁸U, and ²⁴¹Pu and decays of beta emitters produced as a result of neutron capture in ²³⁸U and in accumulated fission fragments which perturb the spectrum. For antineutrino energies of less than 3.5 MeV and for each of the four fissile isotopes, the time evolution of ?_e spectra is given during fuel irradiation and after the irradiation is stopped. The relevant uncertainties are estimated. Small corrections to the ILL spectra are considered.     

TEXONO反应堆中微子能谱的计算

在低能反应堆中微子物理实验中,无论是研究中微子振荡、中微子反应还是测量中微子反常磁矩,都必须准确地知道反应堆中微子的通量和能谱.本文详细讨论了反应堆中微子能谱的计算方法,依据TEXONO实验所用的NP2反应堆的实际情况及探测器的安排,计算并得到中微子的通量和能谱.     

Calculation of the antineutrino spectrum from thermal fission of 235U

The electron and antineutrino spectrum of the products of thermal fission of ²³⁵U have been calculated. The uncertainty in the shape of the spectra is <5% in the range 2.5 ? E ? 7.5 MeV, as a result of a microscopic calculation of the beta decay schemes of neutron-rich fission products. Calculations of this type should give, as in the case of ²³⁵U investigated here, for arbitrary reactor fuel compositions a reliable basis for the interpretation of reactor $\text{ν}$ oscillation experiments.     

Accurate reconstruction of soft X-ray energy spectrum in detector response matrix

In this paper, we report the design of a Monte Carlo simulation for the energy spectrum measurement system based on the ladderabsorption method. Herein, the detector response matrix can be calculated using the detector responses to several monochromatic X-ray beams. A novel soft X-ray spectrum unfolding method based on the two-step reverse iteration(TSRI) algorithm is applied to acquire the primary spectrum. This paper provides examples of the use of TSRI, and the unfolded energy spectra for the soft Xray beams show excellent agreement with the references. The unfolded energy spectra obtained using the TSRI exhibit better accuracy than those obtained from the commonly used unfolding code GRAVEL.     

Unfolding the fast neutron spectra of a BC501A liquid scintillation detector using GRAVEL method

Accurate knowledge of the neutron energy spectra is useful in basic research and applications. The overall procedure of measuring and unfolding the fast neutron energy spectra with BC501A liquid scintillation detector is described. The recoil proton spectrum of 241Am-Be neutrons was obtained experimentally. With the NRESP7 code, the response matrix of detector was simulated. Combining the recoil proton spectrum and response matrix, the unfolding of neutron spectra was performed by GRAVEL iterative algorithm. A MatLab program based on the GRAVEL method was developed. The continuous neutron spectrum of ²⁴¹Am-Be source and monoenergetic neutron spectrum of D-T source have been unfolded successfully and are in good agreement with their standard reference spectra. The unfolded ²⁴¹Am-Be spectrum are more accurate than the spectra unfolded by artificial neural networks in recent years.     

行波堆深燃耗的计算特点

行波堆属于新概念堆型,卸料燃耗深度可达400 GWd/tHM,是现有快堆的3~4倍、压水堆的6~8倍,较高的卸料燃耗深度对堆芯物理分析工具计算正确性提出挑战。基于此,以KYLIN-1程序为基础,从能谱、裂变产物核素重要性、燃耗计算误差累积等方面探究行波堆深燃耗计算特点。对典型行波堆六角形组件分析结果表明:低富集度铀组件寿期初、末能谱差别较大,采用单一权重谱制备的多群截面库用于其燃耗计算时,无限增殖系数偏差较大;为保证行波堆深燃耗计算的正确性,燃耗链应包含重要的70种裂变产物核素;行波堆深燃耗计算时,由于燃耗步增多累积的误差较小,无限增殖系数偏差每燃耗步约为0.001%。     

Antineutrino background from spent-fuel storage in sensitive searches for θ 13 at reactors

Sensitive searches for antineutrino oscillations in the atmospheric mass-parameter region much discussed in recent years are based on accurate comparison of the inverse-beta-decay positron spectra measured in two (or more) detectors, far and near, stationed, e.g., at about 1000 and about 100 m from the reactor(s). We show that antineutrinos emitted from the stored irradiated fuel can distort in a different way the soft part of positron spectra measured in the far and near detectors and thus mimic (or hide) the oscillation signal. The text was submitted by the authors in English.     

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.     

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   

Monte Carlo simulation of the Neutrino-4 experiment

Monte Carlo simulation of the two-section reactor antineutrino detector of the Neutrino-4 experiment is carried out. The scintillation-type detector is based on the inverse beta-decay reaction. The antineutrino is recorded by two successive signals from the positron and the neutron. The simulation of the detector sections and the active shielding is performed. As a result of the simulation, the distributions of photomultiplier signals from the positron and the neutron are obtained. The efficiency of the detector depending on the signal recording thresholds is calculated.     

软X光Dante谱仪的平滑解谱算法及其在Z箍缩诊断中的应用

 针对自行研制的8通道Dante谱仪,提出了一种使用B样条曲线进行平滑解谱的算法,并用黑体谱对其进行了验证。计算结果表明：新算法与使用矩形函数解谱的算法相比,对能谱轮廓与总辐射强度的反演精度均有明显提高。给出了“阳”加速器氩气喷气Z箍缩实验的测量波形,由8通道Dante谱仪的测量结果解谱得到的软X光峰值辐射功率和总能量分别为40.5 GW和851 J,与软X光功率计经修正后的测量结果相一致。     

The thermal-neutron-induced alpha-accompanied fission of235U investigation of the low energy part of the alpha spectrum

The energy spectrum of the α-particles emitted in the thermal-neutron induced fission of²³⁵U was measured from 11.5 MeV down to 2 MeV using the parabola mass spectrometer Lohengrin at the I.L.L. high flux reactor. This low energy part of the energy spectrum presents a smooth connection with the energy spectra which have been recently reported above 7 MeV. The overall energy spectrum, which is known to be quasi-gaussian above 12 MeV, is slightly asymmetric at low energy, where the observed particles are 6% more than expected from a gaussian shape. As a consequence, all the values reported for²³⁵U for the rate of α-accompanied fission compared to binary fission have to be multiplied by 1.06. This asymmetry is about 2 times less important than the one reported for²⁵²Cf. No evidence was seen for any intense low energy component as reported before. The possible reasons for the existence of this asymmetry are discussed.     

Are there sterile neutrinos at the eV scale?

New predictions for the antineutrino flux from nuclear reactors suggest that reactor experiments may have measured a deficit in this flux, which can be interpreted in terms of oscillations between the known active neutrinos and new sterile states. We perform a reanalysis of global short-baseline neutrino oscillation data in a framework with one or two sterile neutrinos. While one sterile neutrino is still not sufficient to reconcile the signals suggested by reactor experiments and by the LSND and MiniBooNE experiments with null results from other searches, we find that, with the new reactor flux prediction, the global fit improves considerably when two sterile neutrinos are introduced.     

Special features of the inverse-beta-decay reaction proceeding on a proton in a reactor-antineutrino flux

The evolution of the reactor-antineutrino spectrum and the evolution of the spectrum of positrons from the inverse-beta-decay reaction in the course of reactor operation and after reactor shutdown are considered. The present-day status in determining the initial reactor-antineutrino spectrum on the basis of spectra of beta particles from mixtures of products originating from uranium and plutonium fission is described. A local rise of the experimental spectrum of reactor antineutrinos with respect to the expected spectrum is studied.     

Potential reduction interior point algorithm unfolding of neutron energy spectrum measured by recoil proton method

A reconstruction algorithm for unfolding neutron energy spectra has been developed, based for the first time on the potential reduction interior point algorithm. This algorithm can be easily applied to neutron energy spectrum reconstruction in the recoil proton method. We transform the neutron energy spectrum unfolding problem into a typical nonnegative linear complementarity problem. The recoil proton energy spectrum and response matrix at angles of 0^o and 30^o are generated by the Geant4 simulation toolkit. Several different neutron energy test spectra are also employed. It is found that this unfolding algorithm is stable and provides efficient, accurate results.     

Ternary fission yields of 241Pu(nth,f)

Ternary events in the thermal neutron induced fission of ²⁴¹Pu(n,f) were studied with the recoil separator LOHENGRIN at the high-flux reactor of the Institut Laue Langevin in Grenoble. Yields and energy distributions could be determined for most isotopes of the elements hydrogen to oxygen. Also several heavier nuclei up to ³⁰Mg could be observed. Yields were measured for 42 isotopes, for further 17 isotopes upper limits could be deduced. For the first time the halo nuclei ¹¹Li, ¹⁴Be and ¹⁹C were found in neutron induced fission with yields of some 10⁻¹⁰ per fission.