Reactor Neutrino Flux Uncertainty Suppression on Multiple Detector Experiments

This publication provides a coherent treatment for the reactor neutrino flux uncertainties suppression, specially focussed on the latest $\theta_{13}$ measurement. The treatment starts with single detector in single reactor site, most relevant for all reactor experiments beyond $\theta_{13}$. We demonstrate there is no trivial error cancellation, thus the flux systematic error can remain dominant even after the adoption of multi-detector configurations. However, three mechanisms for flux error suppression have been identified and calculated in the context of Double Chooz, Daya Bay and RENO sites. Our analysis computes the error {\it suppression fraction} using simplified scenarios to maximise relative comparison among experiments. We have validated the only mechanism exploited so far by experiments to improve the precision of the published $\theta_{13}$. The other two newly identified mechanisms could lead to total error flux cancellation under specific conditions and are expected to have major implications on the global $\theta_{13}$ knowledge today. First, Double Chooz, in its final configuration, is the only experiment benefiting from a negligible reactor flux error due to a $\sim$90\% geometrical suppression. Second, Daya Bay and RENO could benefit from their partial geometrical cancellation, yielding a potential $\sim$50\% error suppression, thus significantly improving the global $\theta_{13}$ precision today. And third, we illustrate the rationale behind further error suppression upon the exploitation of the inter-reactor error correlations, so far neglected. So, our publication is a key step forward in the context of high precision neutrino reactor experiments providing insight on the suppression of their intrinsic flux error uncertainty, thus affecting past and current experimental results, as well as the design of future experiments

Mass predictions of exotic nuclei within a macro-microscopic model

International audienceDifferent Liquid Drop Model mass formulae have been studied. They include a Coulomb diffuseness correction Z2/A term and pairing and shell energies of the Thomas-Fermi model. The influence of the selected charge radius, the curvature energy and different forms of the Wigner term has been investigated. Their coefficients have been determined by a least square fitting procedure to 2027 experimental atomic masses. The different fits lead to a surface energy coefficient of 17-18 MeV. A large equivalent rms radius (r0 = 1.22 − 1.24 fm) or a shorter central radius may be used. A rms deviation of 0.54 MeV can be reached between the experimental and theoretical masses. The remaining differences come from the determination of the shell and pairing energies. Mass predictions are given for exotic nuclei

On the liquid drop model mass formulas and alpha decay of the heaviest nuclei

International audienceThe coefficients of different macro-microscopic Liquid Drop Model mass formulas have been determined by a least square fitting procedure to 2027 experimental atomic masses. A rms deviation of 0.54 MeV can be reached. The remaining differences come mainly from the determination of the shell and pairing energies. Extrapolations are compared to 161 new experimental masses and to 656 mass evaluations. The different fits lead to a surface energy coefficient of around 17-18 MeV. Finally, alpha decay potential barriers are revisited and predictions of alpha decay half-lives of still unknown superheavy elements are given from previously proposed analytical formulas and from extrapolated Qalpha values

On the liquid drop model mass formulas and decay of the heaviest nuclei

The coefficients of different macro-microscopic Liquid Drop Model mass formulas have been determined by a least square fitting procedure to 2027 experimental atomic masses. A rms deviation of 0.54 MeV can be reached. The remaining differences come mainly from the determination of the shell and pairing energies. Extrapolations are compared to 161 new experimental masses and to 656 mass evaluations. The different fits lead to a surface energy coefficient of around 17-18 MeV. Finally, decay potential barriers are revisited and predictions of decay half-lives of still unknown superheavy elements are given from previously proposed analytical formulas and from extrapolated Q values

Macro-microscopic mass formulae and nuclear mass predictions

Different mass formulae derived from the liquid drop model and the pairing and shell energies of the Thomas-Fermi model have been studied and compared. They include or not the diffuseness correction to the Coulomb energy, the charge exchange correction term, the curvature energy, different forms of the Wigner term and powers of the relative neutron excess I = (N − Z)/A. Their coefficients have been determined by a least square fitting procedure to 2027 experimental atomic masses [1]. The Coulomb diffuseness correction Z2/A term or the charge exchange correction Z4/3/A1/3 term plays the main role to improve the accuracy of the mass formula. The Wigner term and the curvature energy can also be used separately but their coefficients are very unstable. The different fits lead to a surface energy coefficient of around 17-18 MeV. A large equivalent rms radius (r0 = 1.22−1.24 fm) or a shorter central radius may be used. A rms deviation of 0.54 MeV can be reached between the experimental and theoretical masses. The remaining differences come probably mainly from the determination of the shell and pairing energies. Mass predictions of selected expressions have been compared to 161 new experimental masses and the correct agreement allows to provide extrapolations to masses of 656 selected exotic nuclei

New antineutrino energy spectra predictions from the summation of beta decay branches of the fission products

In this paper, we study the impact of the inclusion of the recently measured beta decay properties of the $^{102;104;105;106;107}$Tc, $^{105}$Mo, and $^{101}$Nb nuclei in an updated calculation of the antineutrino energy spectra of the four fissible isotopes $^{235, 238}$U, and $^{239,241}$Pu. These actinides are the main contributors to the fission processes in Pressurized Water Reactors. The beta feeding probabilities of the above-mentioned Tc, Mo and Nb isotopes have been found to play a major role in the $\gamma$ component of the decay heat of $^{239}$Pu, solving a large part of the $\gamma$ discrepancy in the 4 to 3000\,s range. They have been measured using the Total Absorption Technique (TAS), avoiding the Pandemonium effect. The calculations are performed using the information available nowadays in the nuclear databases, summing all the contributions of the beta decay branches of the fission products. Our results provide a new prediction of the antineutrino energy spectra of $^{235}$U, $^{239,241}$Pu and in particular of $^{238}$U for which no measurement has been published yet. We conclude that new TAS measurements are mandatory to improve the reliability of the predicted spectra.Comment: 10 pages, 2 figure

Antineutrino emission and gamma background characteristics from a thermal research reactor

The detailed understanding of the antineutrino emission from research reactors is mandatory for any high sensitivity experiments either for fundamental or applied neutrino physics, as well as a good control of the gamma and neutron backgrounds induced by the reactor operation. In this article, the antineutrino emission associated to a thermal research reactor: the OSIRIS reactor located in Saclay, France, is computed in a first part. The calculation is performed with the summation method, which sums all the contributions of the beta decay branches of the fission products, coupled for the first time with a complete core model of the OSIRIS reactor core. The MCNP Utility for Reactor Evolution code was used, allowing to take into account the contributions of all beta decayers in-core. This calculation is representative of the isotopic contributions to the antineutrino flux which can be found at research reactors with a standard 19.75\% enrichment in $^{235}$U. In addition, the required off-equilibrium corrections to be applied to converted antineutrino energy spectra of uranium and plutonium isotopes are provided. In a second part, the gamma energy spectrum emitted at the core level is provided and could be used as an input in the simulation of any reactor antineutrino detector installed at such research facilities. Furthermore, a simulation of the core surrounded by the pool and the concrete shielding of the reactor has been developed in order to propagate the emitted gamma rays and neutrons from the core. The origin of these gamma rays and neutrons is discussed and the associated energy spectrum of the photons transported after the concrete walls is displayed.Comment: 14 pages, 11 figures, Data in Appendix A and B (13 pages

Exploring CEvNS with NUCLEUS at the Chooz Nuclear Power Plant

Coherent elastic neutrino-nucleus scattering (CE$\nu$NS) offers a unique way to study neutrino properties and to search for new physics beyond the Standard Model. Nuclear reactors are promising sources to explore this process at low energies since they deliver large fluxes of (anti-)neutrinos with typical energies of a few MeV. In this paper, a new-generation experiment to study CE$\nu$NS is described. The NUCLEUS experiment will use cryogenic detectors which feature an unprecedentedly low energy threshold and a time response fast enough to be operated in above-ground conditions. Both sensitivity to low-energy nuclear recoils and a high event rate tolerance are stringent requirements to measure CE$\nu$NS of reactor antineutrinos. A new experimental site, denoted the Very-Near-Site (VNS) at the Chooz nuclear power plant in France is described. The VNS is located between the two 4.25 GW$_{\mathrm{th}}$ reactor cores and matches the requirements of NUCLEUS. First results of on-site measurements of neutron and muon backgrounds, the expected dominant background contributions, are given. In this paper a preliminary experimental setup with dedicated active and passive background reduction techniques is presented. Furthermore, the feasibility to operate the NUCLEUS detectors in coincidence with an active muon-veto at shallow overburden is studied. The paper concludes with a sensitivity study pointing out the promising physics potential of NUCLEUS at the Chooz nuclear power plant