ILL Reactor Research Articles

Search for a New Internucleon Interaction Using Neutron Powder Diffraction

The application of neutron powder diffraction to search for a new internucleon Yukawa-like interaction is considered. The essence of the method is in the investigation of dependency of the neutron scattering amplitude on the momentum transfer. The possible contributions to the scattering amplitude and to the integrated intensity of diffraction maxima were analyzed. The neutron diffraction experiment with silicon powder at D20 diffractometer of the ILL reactor (Grenoble, France) was performed. From the data obtained constraints on the coupling constant of the considered interaction were made. It is shown that in the interaction radius range of λ = 10–13–10—11 m they improve the values already existing in the literature. The result obtained is limited by imperfections of the experimental setup. Eliminating the instrumental contribution may allow increasing the sensitivity of the method by at least an order of magnitude.

The Stereo search for a sterile neutrino at the ILL reactor with full data sample

During the last decades, several parameters describing the neutrino oscillation phenomenon have been characterized thanks to reactor neutrino experiments, in particular the precise measurement of the last-to-be-measured mixing angle θ 13. Following a reactor antineutrino flux re-estimation in 2011, a 6% deficit between observed and predicted reactor antineutrino fluxes, known as the Reactor Antineutrino Anomaly, has been observed. The Reactor Antineutrino Anomaly could be explained by an oscillation toward an additional non-interacting, (thus “sterile”) neutrino. The parameters that best explain the RAA are a mixing angle value of sin2 (2θnew ) = 0.17 and a mass splitting value of . Additionally, a discrepancy between the measured and predicted antineutrino energy spectrum taking the form of an excess of events around 5 MeV has been observed by several reactor neutrino experiments. This discrepancy has yet to be fully understood but could be caused by incorrect predictions of the neutrino spectra. The STEREO experiment, located at Institut Laue-Langevin in Grenoble (France), was designed to test the above mentioned oscillation hypothesis independently of shape and rate predictions. The segmented detector, located at ∼10 m of a compact reactor core, allows for a measurement of the antineutrino energy spectrum at various baselines, sensitive to the oscillation toward a sterile neutrino that would distort the spectrum differently at each baseline. The experiment could also help to disentangle isotopic contributions to the neutrino energy spectrum by providing a measurement of the spectrum shape and rate originating from a core with highly enriched (93%)235U. The experiment took data between November 2016 and November 2020. This talk will present the latest limits set in the oscillation parameter space with the full data sample, amounting to 334 (544) days of reactor-on (off), as well as the updated rate and spectrum shape measurements.

Progress in neutron techniques: towards improved polymer electrolyte membranes for energy devices

Design and implementation of advanced membrane formulations for selective transport of ions and molecular species are critical for creating the next generations of fuel cells and separation devices. It is necessary to understand the detailed transport mechanisms over time- and length-scales relevant to the device operation, both in laboratory models and in working systems under realistic operational conditions. Neutron scattering techniques including quasi-elastic neutron scattering, reflectivity and imaging are implemented at beamline stations at reactor and spallation source facilities worldwide. With the advent of new and improved instrument design, detector methodology, source characteristics and data analysis protocols, these neutron scattering techniques are emerging as a primary tool for research to design, evaluate and implement advanced membrane technologies for fuel cell and separation devices. Here we describe these techniques and their development and implementation at the ILL reactor source (Institut Laue-Langevin, Grenoble, France) and ISIS Neutron and Muon Spallation source (Harwell Science and Technology Campus, UK) as examples. We also mention similar developments under way at other facilities worldwide, and describe approaches such as combining optical with neutron Raman scattering and x-ray absorption with neutron imaging and tomography, and carrying out such experiments in specialised fuel cells designed to mimic as closely possible actual operando conditions. These experiments and research projects will play a key role in enabling and testing new membrane formulations for efficient and sustainable energy production/conversion and separations technologies.

First antineutrino energy spectrum from 235U fissions with the STEREO detector at ILL * * Stereo Collaboration, http://www.stereo-experiment.org.

This article reports the measurement of the 235U-induced antineutrino spectrum shape by the Stereo experiment. 43 000 antineutrinos have been detected at about 10 m from the highly enriched core of the ILL reactor during 118 full days equivalent at nominal power. The measured inverse beta decay spectrum is unfolded to provide a pure 235U spectrum in antineutrino energy. A careful study of the unfolding procedure, including a cross-validation by an independent framework, has shown that no major biases are introduced by the method. A significant local distortion is found with respect to predictions around E ν ≃ 5.3 MeV. A Gaussian fit of this local excess leads to an amplitude of A = 12.1 ± 3.4% (3.5σ).

Search for eV Neutrino Sterile: Status of STEREO Experiment

Reactor neutrinos have played a key role in understanding neutrino physics since their discovery. The so-called reactor-anti-neutrino-anomaly RAA, a ∼6.5% deficit of the mean observed neutrino flux compared to the prediction appeared recently. This anomaly could be interpreted by the existence of a fourth, sterile, neutrino and this hypothesis is currently being tested by the very short baseline experiment STEREO. The latter is installed at very short distance (9-11m) from the compact core of the ILL research reactor in Grenoble-France and collecting data since November 2016. The ILL core is highly enriched in 235U and releases a nominal thermal power of 58.3 MW. The geometry of the STEREO detector, segmented into six identical cells filled with Gd-loaded liquid scintillator, is designed for a direct test of a new oscillation pattern in the L/E range around 1 m/MeV, relevant for the RAA. First published results of STEREO have demonstrated the mitigation of the background induced by the reactor and the cosmic-rays and a good energy response. The data taking is now in progress with very stable conditions favorable for an improved accuracy. We will present an overview of the experiment and an update of the sterile neutrino analysis. A refined prediction of the neutrino spectrum emitted by the ILL reactor is also presented.

Crystal-Diffraction Method for Ultraprecision Neutron Spectrometry. Influence of the Temperature Stability and Vibration Level

A test setup for measuring the neutron electric charge using spin interferometry and the effect of the double-crystal focusing of neutrons upon Laue diffraction is described. It is shown that a considerable increase in the distance between the crystals (up to 1 m) is needed to improve the accuracy of neutron-charge measurements. This is a difficult task because the setup becomes sensitive to slight external influences (temperature, vibration, etc.). To determine the degree of these influences, temperature tests with combined (active and passive) thermal protection were carried out. It is shown that under conditions of the reactor hall with temperature fluctuations of several degrees, the experimental setup provides a temperature stability of the crystals no worse than 0.01 K and stability of the temperature differences for the crystals and between them at a level of ~0.005 K. Measurements of the vibration level in the area of the PF1b cold neutron beam at the ILL reactor (Grenoble, France) allow estimation of the rate of displacement of crystals relative to each other at a level of ~10–3 cm/s. As follows from the data obtained, the angular resolution of the setup, without taking into account the influence of the imperfection of real crystals, can be at the level of 10–3 of the Bragg-reflection width, which is ~0.001 arc-second.

Shape-coexistence Studies in the Ni Isotopic Chain by Using the Selectivity of Different Reaction Mechanisms

We report on the investigation of the shape coexistence phenomenon in the Ni isotopic chain, from A = 62 to A = 66, by using γ-ray spectroscopy techniques and different reaction mechanisms, such as sub-Coulomb barrier transfer reactions and thermal-neutron capture. Our aim is to understand, from the microscopic point of view, the appearance of nuclear deformation in Ni isotopes at low excitation energy. A series of experiments was performed at the Tandem Accelerator Laboratory in Bucharest, at ALTO IPN-Orsay and at the ILL reactor in Grenoble. Various mean-field theoretical approaches, as well as recent state-of-the-art Monte Carlo Shell Model (MCSM) calculations, predict in 66Ni a deep secondary prolate minimum in the nuclear potential energy surface at spin zero, resulting in a hindered electromagnetic decay towards the spherical ground state (i.e., with an E2 transition probability less than 1 W.u.). This has been confirmed in the first experiment performed in Bucharest. Less pronounced prolate minima, at higher excitation energies, are also expected in lighter neutron-rich Ni isotopes, from state-of-the-art Monte Carlo Shell Model (MCSM) calculations. Preliminary results are discussed for 62Ni and 64Ni, in comparison with theory predictions.

Кристалл-дифракционная тестовая установка для измерения заряда нейтрона: испытания тепловой защиты и измерения вибраций

AbstractA prototype system design for ultra-high-precision neutron spectrometry using diffraction in perfect crystals is described. Results of experimental verification of the temperature stability inside the setup are presented. Results of vibration spectrum measurements in working zone of the PF1b beam of ILL reactor (Grenoble, France), where the prototype setup will be arranged for experimental testing, are considered.

A Crystal-Diffraction System Prototype for Measuring Neutron’s Charge: Thermal Protection Test and Vibration Measurements

A prototype system design for ultra-high-precision neutron spectrometry using diffraction in perfect crystals is described. Results of experimental verification of the temperature stability inside the setup are presented. Results of vibration spectrum measurements in working zone of the PF1b beam of ILL reactor (Grenoble, France), where the prototype setup will be arranged for experimental testing, are considered.

A new methodology for studying neutron absorber materials: First results with boron carbide

Abstract This paper presents a new methodology used to study transmutation damage in boron carbide (B4C). B4C samples were set in a specially designed sample holder and irradiated in a neutron thermal flux in the ILL reactor. After describing the sample holder and the irradiation conditions, this paper discusses the results of the first post-irradiation examinations by secondary-ion mass spectrometry (SIMS), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results obtained for a B4C disc with natural boron composition prove the efficiency of the methodology.

Measurement of the ROT effect in the neutron induced fission of 235U in the 0.3 eV resonance at a hot source of polarized neutrons

The TRI and ROT asymmetries in fission of heavy nuclei have been extensively studied during more than a decade. The effects were first discovered in the ternary fission in a series of experiments performed at the ILL reactor (Grenoble) by a collaboration of Russian and European institutes, and were carefully measured for a number of fissioning nuclei. Later on, the ROT effect has been observed in the emission of prompt gamma rays and neutrons in fission of 235U and 233U, although its value was an order of magnitude smaller than in the α-particle emission from ternary fission. All experiments performed so far are done with cold polarized neutrons, what assumes a mixture of several spin states, the weights of these states being not well known. The present paper describes the first attempt to get “clean” data by performing the measurement of gamma and neutron asymmetries in an isolated resonance of 235U at the POLI instrument of the FRM2 reactor in Garching.

Interplay Between Particle and Core Excitations in $^{133}$Sb

The decay of the one-proton valence nucleus 133Sb is studied using the cold-neutron induced fission of 235U and 241Pu targets. The experiment is performed at the ILL reactor in Grenoble, using a highly efficient HPGe array, also coupled to fast LaBr3(Ce) scintillators. High-spin excited states above the 16.6 s isomer are observed, and the lifetime of the 13/2+ and 15/2+ states is measured by fast-timing techniques, revealing a complex nature of the wave functions. The experimental results are well-interpreted by a newly developed microscopic model which takes into account the coupling between the valence proton and excitations (both collective and noncollective) of the doubly magic 132Sn core.

The mutable nature of particle-core excitations with spin in the one-valence-proton nucleus 133 Sb

The gamma-ray decay of excited states of the one-valence-proton nucleus 133Sb has been studied using cold-neutron induced fission of 235U and 241Pu targets, during the EXILL campaign at the ILL reactor in Grenoble. By using a highly efficient HPGe array, coincidences between gamma-rays prompt with the fission event and those delayed up to several tens of microseconds were investigated, allowing to observe, for the first time, high-spin excited states above the 16.6 micros isomer. Lifetimes analysis, performed by fast-timing techniques with LaBr3(Ce) scintillators, reveals a difference of almost two orders of magnitude in B(M1) strength for transitions between positive-parity medium-spin yrast states. The data are interpreted by a newly developed microscopic model which takes into account couplings between core excitations (both collective and non-collective) of the doubly magic nucleus 132Sn and the valence proton, using the Skyrme effective interaction in a consistent way. The results point to a fast change in the nature of particle-core excitations with increasing spin.

Analysis of prompt fission neutrons in235U(nth,f) and fission fragment distributions for the thermal neutron induced fission of234U

This paper presents the ongoing analysis of two fission experiments. Both projects are part of the collaboration between the nuclear reactions group at Uppsala and the JRC-IRMM. The first experiment deals with the prompt fission neutron multiplicity in the thermal neutron induced fission of 235 U(n,f). The second, on the fission fragment properties in the thermal fission of 234 U(n,f).The prompt fission neutron multiplicity has been measured at the JRC-IRMM using two liquid scintillators in coincidence with an ionization chamber. The first experimental campaign focused on 235 U(n th ,f) whereas a second experimental campaign is foreseen later for the same reaction at 5.5 MeV. The goal is to investigate how the so-called sawtooth shape changes as a function of fragment mass and excitation energy. Some harsh experimental conditions were experienced due to the large radiation background. The solution to this will be discussed along with preliminary results.In addition, the analysis of thermal neutron induced fission of 234 U(n,f) will be discussed. Currently analysis of data is ongoing, originally taken at the ILL reactor. The experiment is of particular interest since no measurement exist of the mass and energy distributions for this system at thermal energies. One main problem encountered during analysis was the huge background of 235 U(n th ,f). Despite the negligible isotopic traces in the sample, the cross section difference is enormous. Solution to this parasitic background will be highlighted.

Neutron electric dipole moment and possibilities of increasing accuracy of experiments

The paper reports the results of an experiment on searching for the neutron electric dipole moment (EDM), performed on the ILL reactor (Grenoble, France). The double-chamber magnetic resonance spectrometer (Petersburg Nuclear Physics Institute (PNPI)) with prolonged holding of ultra cold neutrons has been used. Sources of possible systematic errors are analyzed, and their influence on the measurement results is estimated. The ways and prospects of increasing accuracy of the experiment are discussed.

PNPI differential EDM spectrometer and latest results of measurements of the neutron electric dipole moment

In this work, the double chamber magnetic resonance spectrometer of the Petersburg Nuclear Physics Institute (PNPI) designed to measure the neutron electric dipole moment (EDM) is briefly described. A method for long storage of polarized ultracold neutrons in a resonance space with a superposed electric field collinear to the leading magnetic field is used. The results of the measurements carried out on the ILL reactor (Grenoble, France) are interpreted as the upper limit of the value of neutron EDM |dn| < 5.5 × 10–26e cm at the 90% confidence level.

Total Absorption Spectroscopy Study of (92)Rb Decay: A Major Contributor to Reactor Antineutrino Spectrum Shape.

The antineutrino spectra measured in recent experiments at reactors are inconsistent with calculations based on the conversion of integral beta spectra recorded at the ILL reactor. (92)Rb makes the dominant contribution to the reactor antineutrino spectrum in the 5-8 MeV range but its decay properties are in question. We have studied (92)Rb decay with total absorption spectroscopy. Previously unobserved beta feeding was seen in the 4.5-5.5 region and the GS to GS feeding was found to be 87.5(25)%. The impact on the reactor antineutrino spectra calculated with the summation method is shown and discussed.

Wave Effect Neutron Radiographic Imaging Origins in WCNR and Prospects for Low Cost Systems

The origins of wave effect neutron test methods for advanced neutron radiography as published in World Conference on Neutron Radiography (WCNR) series has been reviewed. They include Neutron Holography demonstrated at the Dido reactor, Harwell, UK; Neutron Refraction and Small Angle Scattering demonstrated at the IR-8 reactor, Kurchatov Institute, Moscow, Russia; and Neutron Interferometry demonstrated at the ILL reactor, Grenoble, France. Each case presents encouraging evidence that the advanced techniques currently practiced at the most advanced shared-user facilities could be built upon at some lower cost, single-user facilities if the lessons of the original low cost experiments are studied.

UCN Source at an External Beam of Thermal Neutrons

We propose a new method for production of ultracold neutrons (UCNs) in superfluid helium. The principal idea consists in installing a helium UCN source into an external beam of thermal or cold neutrons and in surrounding this source with a solid methane moderator/reflector cooled down to ~4 K. The moderator plays the role of an external source of cold neutrons needed to produce UCNs. The flux of accumulated neutrons could exceed the flux of incident neutrons due to their numerous reflections from methane; also the source size could be significantly larger than the incident beam diameter. We provide preliminary calculations of cooling of neutrons. These calculations show that such a source being installed at an intense source of thermal or cold neutrons like the ILL or PIK reactor or the ESS spallation source could provide the UCN density 105 cm−3, the production rate 107 UCN/s−1. Main advantages of such an UCN source include its low radiative and thermal load, relatively low cost, and convenient accessibility for any maintenance. We have carried out an experiment on cooling of thermal neutrons in a methane cavity. The data confirm the results of our calculations of the spectrum and flux of neutrons in the methane cavity.

Ultracold neutron cooling upon reflection from a moving wall

The process of neutron cooling upon adiabatic increase in the storage volume has been studied on an ultracold neutron beam of the ILL reactor. The cooling of neutrons in the course of magnetic trap filling allows the number of stored neutrons to be significantly increased and, hence, the statistical accuracy of determination of their lifetimes to be improved.