Antineutrino Energy Spectrum Research Articles

Present and future experiments in nonequilibrium reactor antineutrino energy spectrum

Considerable efforts that have been undertaken in recent years in low-energy antineutrino experiments require further systematic investigations in line of reactor antineutrino spectroscopy as a metrological basis of these experiments. We consider some effects associated with the nonequilibrium of reactor \(\bar \nu _e \) radiation and residual \(\bar \nu _e \) emission from spent reactor fuel in contemporary \(\bar \nu _e \) experiments.

Supernova neutrinos: production, propagation and oscillations

I shall review some of the recent results concerning the astrophysics of a core collapse supernova (SN) and neutrino oscillations. Neutrinos play an important role in the SN explosion, and they also carry most of the energy of the collapse. The energy spectra of neutrinos and antineutrinos arriving at the Earth incorporate information on the primary neutrino fluxes as well as the neutrino mixing scenario. The analysis of neutrino propagation through the matter of the supernova and the Earth, combined with the observation of a neutrino burst from a galactic SN, enables us to put limits on the mixing angle $\theta_{13}$ and identify whether the mass hierarchy is normal or inverted. The neutrino burst also acts as an early warning signal for the optical observation, and in addition allows us to have a peek at the shock wave while still inside the SN mantle.

Neutrino geophysics at Baksan I: Possible detection of georeactor antineutrinos

J.M. Herndon in the 1990s proposed a natural nuclear fission georeactor at the center of the Earth with a power output of 3–10 TW as an energy source to sustain the Earth magnetic field. R. S. Raghavan in 2002 pointed out that, under certain conditions, antineutrinos generated in such a georeactor can be detected using massive scintillation detectors. We consider the underground Baksan Neutrino Observatory (4800 m.w.e.) as a possible site for developments in geoneutrino physics. Here, the intrinsic background level of less than 1 event/yr in a liquid scintillation ∼1000-t target detector can be achieved and the main source of background is the antineutrino flux from power reactors. We find that this flux is ∼10 times lower than at the KamLAND detector site and two times lower than at the Gran Sasso laboratory and thus at Baksan the georeactor hypothesis can be conclusively tested. We also discuss possible searches for the composition of georeactor burning nuclear fuel by analysis of the antineutrino energy spectrum.

Inverse-beta-decay reaction in the antineutrino flux from the fragments of 232Th and 233U 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.

Simple Calculation of Reactor Antineutrino Energy Spectrum by the Use of Nuclear Data Libraries

We calculated the nuclear reactor antineutrino spectrum on the basis of nuclear data libraries (JENDL-3.2, JNDC-V2). The antineutrino spectrum was first calculated with neglecting energy dependence of matrix element, and the result had tendency to be larger than the experimental data in the high energy region. We introduced an adjustable parameter for correcting the spectrum calculation. The method gives a good agreement between calculated and experimental spectra.

Simple Calculation of Reactor Antineutrino Energy Spectrum by the Use of Nuclear Data Libraries.

Simple Calculation of Reactor Antineutrino Energy Spectrum by the Use of Nuclear Data Libraries.

The search for new physics in nonequilibrium reactor-antineutrino energy spectrum

The calculations of the time-dependent reactor antineutrino energy spectrum are presented. Some problems associated with sensitive searches for neutrino magnetic moment and neutrino oscillations in reactor antineutrino flux are considered.

Bounds on the solar antineutrino total flux and energy spectrum from the SK experiment

A search for inverse beta decay electron antineutrinos has been carried out using the 825 days sample of solar data obtained at SK. The absence of a significant signal, that is, contributions to the total SK background and their angular variations has set upper bounds on (a) the absolute flux of solar antineutrinos originated from 8B neutrinos Φ ν ̄ ( 8B)⩽1.8×10 5 cm −2 s −1 which is equivalent to an averaged conversion probability bound of P<3.5% (SSM-BP98 model) and (b) their differential energy spectrum, the conversion probability is smaller than 8% for all E e,vis >6.5 MeV going down the 5% level above E e,vis ≈10 MeV. It is shown that an antineutrino flux would have the net effect of enhancing the SK signal at hep neutrino energies. The magnitude of this enhancement would highly depend on the, otherwise rather uncertain at this moment, steepness of the solar neutrino spectrum at these energies.

Mixed handedness in familial and non-familial schizophrenia

The Daya Bay experiment was the first to report simultaneous measurements of reactor antineutrinos at multiple baselines leading to the discovery of ν¯e oscillations over km-baselines. Subsequent data has provided the world׳s most precise measurement of sin22θ13 and the effective mass splitting Δmee2. The experiment is located in Daya Bay, China where the cluster of six nuclear reactors is among the world׳s most prolific sources of electron antineutrinos. Multiple antineutrino detectors are deployed in three underground water pools at different distances from the reactor cores to search for deviations in the antineutrino rate and energy spectrum due to neutrino mixing. Instrumented with photomultiplier tubes, the water pools serve as shielding against natural radioactivity from the surrounding rock and provide efficient muon tagging. Arrays of resistive plate chambers over the top of each pool provide additional muon detection. The antineutrino detectors were specifically designed for measurements of the antineutrino flux with minimal systematic uncertainty. Relative detector efficiencies between the near and far detectors are known to better than 0.2%. With the unblinding of the final two detectors’ baselines and target masses, a complete description and comparison of the eight antineutrino detectors can now be presented. This paper describes the Daya Bay detector systems, consisting of eight antineutrino detectors in three instrumented water pools in three underground halls, and their operation through the first year of eight detector data-taking.

The Influence of Nuclear Composition on the Electron Fraction in the Post–Core Bounce Supernova Environment

We study the early evolution of the electron fraction (or, alternatively, the neutron-to-proton ratio) in the region above the hot proto-neutron star formed after a supernova explosion. We study the way in which the electron fraction in this environment is set by a competition between lepton (electron, positron, neutrino, and antineutrino) capture processes on free neutrons and protons and nuclei. Our calculations take explicit account of the effect of nuclear composition changes, such as formation of particles (the alpha effect) and the shifting of nuclear abundances in nuclear statistical equilibrium associated with cooling in near-adiabatic outFLow. We take detailed account of the process of weak interaction freezeout in conjunction with these nuclear composition changes. Our detailed treatment shows that the effect can cause significant increases in the electron fraction, while neutrino and anti-neutrino capture on heavy nuclei tends to have a buffering effect on this quantity. We also examine the effect on weak rates and the electron fraction of fluctuations in time in the neutrino and antineutrino energy spectra arising from hydrodynamic waves. Our analysis is guided by the Wilson and Mayle supernova code numerical results for the neutrino energy spectra and density and velocity profiles.

Indication for neutrino oscillation from a high statistics experiment at the bugey reactor

The energy spectrum of electron antineutrinos has been measured at two distances, 13.6 and 18.3. meters, from the core of a PWR power reactor at Bugey (France). About 63 000 antineutrino events have been recorded using the inverse β-decay reaction ν e+p→n+e +. We observe a difference in the counting rates between the two positions. The compatibility of the results with solutions in a two-neutrino oscillations analysis is discussed.

The Energy Distribution of Antineutrinos Originating from the Decay of Fission Products in a Nuclear Reactor

The energy spectrum of antineutrinos around a nuclear reactor has been derived by summing contributions from individual fission products. The resulting spectrum is weaker at energies above approx. 8 MeV than earlier published antineutrino spectra. The reason may be connected to the strong feeding of high-lying daughter states in the beta decay of fission products with high disintegration energies.

Fission antineutrino-induced reactions

The cross sections for nu e-e- scattering, inverse beta decay of the proton and deuteron and also deuteron disintegration due to weak neutral currents were obtained using recently recalculated energy spectra of electron antineutrinos from 235U and 239Pu fission products in secular equilibrium. A comparison was made with previous theoretical results and experimental data.

Interpretation ofν¯-e−scattering with reactor antineutrinos

Numerically evaluated integrals of the theoretical cross section averaged over the energy spectrum of antineutrinos from $^{235}\mathrm{U}$ in secular equilibrium are presented. The three terms of the cross section were integrated separately to preserve the explicit dependence on ${C}_{A}$ and ${C}_{V}$. An updated version of the antineutrino spectrum was used resulting in some noticeable differences from earlier versions. A re-interpretation of the 1976 experimental results of Reines and his co-workers is given.

V−AElastic Scattering of Electrons by Fission Antineutrinos

The energy spectrum of electron antineutrinos from $^{235}\mathrm{U}$ fission products in secular equilibrium has been recalculated. Assuming the validity of $V\ensuremath{-}A$ theory, cross sections for the elastic scattering reaction ${\overline{\ensuremath{\nu}}}_{e}+{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\overline{\ensuremath{\nu}}}_{e}+{e}^{\ensuremath{-}}$, integrated over recoil electron energy for this antineutrino spectrum, are given for several values of minimum electron energy from 1 to 5.5 MeV. Theoretical error bars, which reflect the uncertainties in the input data, are given for the antineutrino spectrum and the cross sections.

Theoretical Fission-Antineutrino Spectrum and Cross Section of the ReactionHe3(ν¯e,e+)H3

The energy spectrum of antineutrinos emitted by binary fission fragments of uranium-235 in secular equilibrium was calculated. The primary fission yields used in this work were calculated, using the primary fission product charge distributions due to A. C. Wahl. The total number of antineutrinos per fission predicted with the calculated spectrum is 6.06. The antineutrino spectrum derived in this work was used to calculate the average cross section for the reaction $p({\overline{\ensuremath{\nu}}}_{e},{e}^{+})n$ and $^{3}\mathrm{He}({\overline{\ensuremath{\nu}}}_{e},{e}^{+})^{3}\mathrm{H}$. The cross sections are 1.09\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}43}$ $\frac{{\mathrm{cm}}^{2}}{(\mathrm{fission} \overline{\ensuremath{\nu}})}$ and 2.46\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}43}$ $\frac{{\mathrm{cm}}^{2}}{(\mathrm{fission} \overline{\ensuremath{\nu}})}$, respectively.

Energy spectrum of neutrinos produced in e+, e− pair annihilation

A calculation is made of the energy spectrum of neutrinos and antineutrinos produced in stars by electron-positron pair annihilation, on the basis of Feynman and Gell-Mann’s theory of weak interactions, in the electron density range from 1.6·103 to 1.6·106 g/cm3 and temperature range from 5·108 to 1010 °K. It is seen that the maximum of the neutrino spectrum ranges from 1.5 to 15 MeV.