The neutron instruments suite, installed at the spallation neutron source of the Materials and Life Science Experimental Facility (MLF) at the Japan Proton Accelerator Research Complex (J-PARC), is reviewed. MLF has 23 neutron beam ports and 21 instruments are in operation for user programs or are under commissioning. A unique and challenging instrumental suite in MLF has been realized via combination of a high-performance neutron source, optimized for neutron scattering, and unique instruments using cutting-edge technologies. All instruments are/will serve in world-leading investigations in a broad range of fields, from fundamental physics to industrial applications. In this review, overviews, characteristic features, and typical applications of the individual instruments are mentioned.

The ionomers distributed on carbon particles in the catalyst layer of polymer electrolyte fuel cells (PEFCs) govern electrical power via proton transport and oxygen permeation to active platinum. Thus, ionomer distribution is a key to PEFC performance. This distribution is characterized by ionomer adsorption and deposition onto carbon during the catalyst-ink coating process; however, the adsorbed and deposited ionomers cannot easily be distinguished in the catalyst layer. Therefore, we identified these two types of ionomers based on the positional correlation between the ionomer and carbon particles. The cross-correlation function for the catalyst layer was obtained by small-angle neutron scattering measurements with varying contrast. From fitting with a model for a fractal aggregate of polydisperse core–shell spheres, we determined the adsorbed-ionomer thickness on the carbon particle to be 51 Å and the deposited-ionomer amount for the total ionomer to be 50%. Our technique for ionomer differentiation can be used to optimally design PEFC catalyst layers.

The structure and conformation of methyl cellulose (MC) and hydroxypropyl methyl cellulose (HpMC) ether samples dissolved in dilute aqueous (D₂O) solutions at a temperature of 25 °C were reconsidered in detail based on the experimental results obtained using small- and wide-angle neutron scattering (S-WANS) techniques in a range of scattering vectors (q) from 0.05 to 100 nm⁻¹. MC samples exhibited an average degree of substitution (DS) by methyl groups per glucose unit of DS = 1.8 and the weight average molar mass of M_w = 37 × 10³ and 79 × 10³ g mol⁻¹. On the other hand, HpMC samples possessed the average molar substitution number (MS) by hydroxypropyl groups per glucose unit of MS = 0.25, DS = 1.9, and M_w = 50 × 10³ and 71 × 10³ g mol⁻¹. The concentration-reduced scattering intensity data gathered into a curve for the solutions of identical sample species clearly demonstrated the relationship I(q)c⁻¹ ∝ q⁻¹ in a q range from 0.05 to 2.0 nm⁻¹, and small interference peaks were found at q ∼ 7 and 17 nm⁻¹ for all examined sample solutions. These observations strongly revealed that form factors for both the MC and HpMC samples were perfectly described with that for long, rigid rod particles with average diameters of 0.8 and 0.9 nm, respectively, and with an inner structure with characteristic mean spacing distances of ca. 0.9 and 0.37 nm, respectively, regardless of the chemically modified conditions and molar masses. A rationally speculated structure model for the MC and HpMC samples dissolved in aqueous solution was proposed.