Energy-resolved neutron imaging with glass gas electron multiplier and dynamic time-over-threshold method

Energy-resolved neutron imaging with pulsed neutron source provides quantitative neutron imaging techniques such as Bragg-edge imaging, resonance absorption imaging, and polarized neutron imaging. Micro-pattern gaseous detectors (MPGDs) such as gas electron multipliers (GEMs) are widely used in neutron detection. In this research, we will report on the first demonstration of energy-resolved neutron imaging with a glass gas electron multiplier (G-GEM) and the dynamic time-over-threshold (dToT) signal processing method. We successfully performed energy-resolved neutron imaging at J-PARC MLF by measuring incident position and the Time-of-Flight (TOF) of each neutron simultaneously.

Exploring nuclear photonics with laser driven neutron source

Neutron beams have been providing dispensable tools for wide range of fields in modern science and engineering. Recently, a new type of pulsed neutron source has been developed, known as Laser-Driven Neutron Source (LDNS). The LDNSs utilize the laser-accelerated ions, including protons and deuterons as a primary beam and generate neutrons from a secondary target (lithium, beryllium, etc.) via nuclear reaction. Applying an additional moderator part, LDNSs can provide a broad energy range of neutrons (meV∼MeV). This paper aims to introduce the current status of LDNS and the results of application-oriented experiments implemented at Institute of Laser Engineering (ILE) of Japan.

Polarization analysis for small-angle neutron scattering with a 3He spin filter at a pulsed neutron source

Neutron polarization analysis (NPA) for small-angle neutron scattering (SANS) experiments using a pulsed neutron source was successfully achieved by applying a 3He spin filter as a spin analyzer for the neutrons scattered from the sample. The cell of the 3He spin filter gives a weak small-angle scattering intensity (background) and covers a sufficient solid angle for performing SANS experiments. The relaxation time of the 3He polarization is sufficient for continuous use for approximately 2 days, thus reaching the typical duration required for a complete set of SANS experiments. Although accurate evaluation of the incoherent neutron scattering, which is predominantly attributable to the extremely large incoherent scattering cross section of hydrogen atoms in samples, is difficult using calculations based on the sample elemental composition, the developed NPA approach with consideration of the influence of multiple neutron scattering enabled reliable decomposition of the SANS intensity distribution into the coherent and incoherent scattering components. To date, NPA has not been well established as a standard technique for SANS experiments at pulsed neutron sources such as the Japan Proton Accelerator Research Complex (J-PARC) and the US Spallation Neutron Source. It is anticipated that this work will contribute significantly to the accurate determination of the coherent neutron scattering component for scatterers in various types of organic sample systems in SANS experiments at J-PARC, particularly for systems involving competition between the coherent and incoherent scattering intensity.

Effective Delayed Neutron Fraction

In kinetic analyses on ADS, although adjoint flux distribution is defined under the existence of an external neutron source, an issue of the proper determination of the weighting function still remains in the definition to obtain the kinetics parameters in the fixed-source calculations. Here, an alternative methodology is proposed with the combined use of the k-ratio method and the reaction rates obtained by the fixed-source calculations, when the subcriticality level or the spectrum of the external neutron source is varied. In ADS experiments, the measurement of βeff is expected to provide complementary verification of the calculation and reliability of nuclear data. Then, the formulation of the Rossi-α method in the pulsed-neutron source has been already available for application to the subcriticality measurement in the pulsed-neutron source (PNS) experiments. Accordingly, the methodology is applied uniquely to deduce the βeff value with the pulsed-neutron source (spallation neutrons), with the combined use of the results of experiments and calculations. Using parameters α and ρ$, the values of βeff/Λ are deduced at near-critical configurations through experimental analyses. To estimate the numerical precision of Λ, the value of βeff/Λ is used as an index of Λ evaluation that is defined by a ratio of Λ values in the super-critical and subcritical states.

Pulsed neutron imaging for differentiation of ice and liquid water towards fuel cell vehicle applications

Water/ice identification images throughout the thawing process of ice in a metal capillary by using a pulsed neutron source.