Detection of neutrons, at high total efficiency, with greater resolution in kinetic energy, time and/or real-space position, is fundamental to the advance of subfields within nuclear medicine, high-energy physics, non-proliferation of special nuclear materials, astrophysics, structural biology and chemistry, magnetism and nuclear energy. Clever indirect-conversion geometries, interaction/transport calculations and modern processing methods for silicon and gallium arsenide allow for the realization of moderate- to high-efficiency neutron detectors as a result of low defect concentrations, tuned reaction product ranges, enhanced effective omnidirectional cross sections and reduced electron–hole pair recombination from more physically abrupt and electronically engineered interfaces. Conversely, semiconductors with high neutron cross sections and unique transduction mechanisms capable of achieving very high total efficiency are gaining greater recognition despite the relative immaturity of their growth, lithographic processing and electronic structure understanding. This review focuses on advances and challenges in charged-particle-based device geometries, materials and associated mechanisms for direct and indirect transduction of thermal to fast neutrons within the context of application. Calorimetry- and radioluminescence-based intermediate processes in the solid state are not included.

https://iopscience.iop.org/article/10.1088/0953-8984/22/44/443201/pdf

The physics of solid-state neutron detector materials and geometries

Chapter 1 Magnetism of ternary intermetallic compounds of uranium

We present results of magnetic, transport and calorimetric measurements on U 3 T 3 X 4 with T=Ni, Cu, Pd, Pt and Au and X=Sn and Sb. A heavy-fermion behavior manifests itself in U 3 T 3 Sn 4 , where the electronic specific-heat coefficient increases from 90 mJ/K 2 mol U for T=Ni and Pt to about 300 mJ/K 2 mol U for T=Cu and Au. We ascribe the mass enhancement to the dehybridization of 5 f electrons with the d electrons derived from the T atom. On the other hand, U 3 T 3 Sb 4 with T=Ni, Pd and Pt shows a semiconducting behavior with a band gap of about 0.2 eV, whereas U 3 Cu 3 Sb 4 is a metallic ferromagnet with T c =91 K. In these antimonides, 5 f electrons are localized because of the weak hybridization with the 5 p electrons from the Sb atom. These results indicate that the number of 5 p electrons in the present system determines whether the system shows heavy-fermion or semiconducting behavior.

Heavy-fermion and semiconducting properties of the ternary uranium compounds u3t3sn4 and u3t3sb4 (t=ni, cu, pd, pt and au)

We grew high-quality single crystals of NpTGa 5 (T = Fe, Rh, and Ni) with a tetragonal structure by the Ga-flux method and measured their electrical resistivity, specific heat, magnetic susceptibility, and magnetization. All the investigated compounds undergo magnetic ordering. NpFeGa 5 orders antiferromagnetically at T N =118 K and shows another magnetic transition at T * =78 K. A relatively large electrical resistivity indicates that NpFeGa 5 might be a low-carrier compound. NpRhGa 5 also orders antiferromagnetically at T N1 =36 K. Below another magnetic transition at T N2 =32 K, the antiferromagnetic easy-axis is most likely changed from [001] to the (001) plane. On the other hand, NpNiGa 5 undergoes ferromagnetic ordering at T C =30 K, where the magnetic moment of Np is directed along the [001] direction. Furthermore, below another magnetic transition at T * =18 K, the ordered moment is discontinuously enlarged and a change of the magnetic structure occurs. The electronic specific heat coefficients ar...

Magnetic and Electrical Properties of NpTGa5 (T=Fe, Rh and Ni)

The magnetic susceptibility and the Cu and Si Knight shifts have been measured in CeCu 2 Si 2 . The transferred hyperfine couplings at both the sites are strongly temperature-dependent and noticeably anisotropic at low temperatures. The negative hyperfine couplings observed for the magnetic field along the c -axis at the low temperatures are anomalous as in Ce intermetallic compounds. It is pointed out that the transferred hyperfine coupling due to the hybridization of the f electrons with the ligand s electrons can be anisotropic and also can reverse its sign at the lower temperatures than the crystal-field splitting energy. It is concluded that this hybridization is the dominant mechanism of the transferred hyperfine coupling and responsible for the anomaly.

Anomalous Transferred Hyperfine Coupling in CeCu2Si2

New ternary uranium compounds of UNi 2 Sn and UNi 2 In have been prepared and found to crystallize in the MgCu 2 Al-type structure. On these compounds and UNi 4 Sn, UNi 4 In and U 3 Ni 3 Sn 4 with cubic structures, we report the results of electrical resistivity, thermoelectric power, magnetic susceptibility and specific heat measurements. Of the five compounds, only U 3 Ni 3 Sn 4 exhibits a moderately heavy-fermion behavior at low temperatures. The other four compounds, where the distance between the U atom and the nearest-neighboring Ni atom is almost the same as in U 3 Ni 3 Sn 4 , are, however, enhanced Pauli paramagnets. No compounds show magnetic or superconducting transition down to 1.6 K.

Physical and Structural Properties of Ternary Uranium Compounds in the U-Ni-Sn and U-Ni-In Systems

Synthesis and results of transport, magnetic and calorimetric measurements are reported on U 3 T 3 X 4 (T = Ni,Cu,Pd,Pt,Au and X = Sn,Sb). The resistivities of U 3 T 3 Sb 4 (T = Ni,Pd) are unusually high and show semiconducting behavior at temperatures above 200 K, whereas those of U 3 T 3 Sn 4 (T= Ni,Pt) are metallic and follow a T 2 law below 10 K. The low-temperature coefficients of specific heat of U 3 T 3 Sn 4 (T=Cu,Au) are much enhanced compared to that of U 3 Ni 3 Sn 4 . The results indicate that the 5f-sp hybridization governs transport properties, whereas the degree of 5f-d hybridization is a crucial parameter for the develpoment of heavy-fermion state.

Semiconducting and heavy-fermion behavior in new class of materials of U3T3X4

Specific heat, resistivity and ac- and dc-magnetic susceptibility measurements revealed that Th 3 Ni 3 Sn 4 is a new superconductor with the transition temperature T c =138 K The electronic specific heat coefficient γ is 311 mJ/K 2 mol-fu, the Debye temperature Θ D is 255 K and the electron-phonon coupling constant λ ep is 043 The upper critical field H c2 determined by ac-susceptibility in magnetic fields follows the temperature dependence calculated by Helfand and Werthamer We conclude that Th 3 Ni 3 Sn 4 is a BCS-superconductor of type-II with the GL parameter κ=10 Both susceptibility enhancement probably due to spin fluctuation and anomalous temperature dependence of the resistivity suggest that the conduction electrons with d -character play an essential role in the superconductivity

Superconductivity in Th3Ni3Sn4

The 119 Sn Knight shift K and nuclear spin-lattice relaxation time T 1 in a heavy fermion compound U 3 Ni 3 Sn 4 have been measured between 1.5 and 270 K. The K vs the susceptibility plot is linear and yields a hyperfine field of 53.2 kOe/µ B . The nuclear relaxation rate due to U 5f moments (1/ T 1 ) f decreases markedly below about 20 K and is proportional to temperature below about 4 K, where the system is in the Fermi liquid state. The relaxation rate of 5f moments obtained from (1/ T 1 ) f increases linearly with temperature above about 120 K, indicating that the Korringa mechanism is dominant in the fluctuation of localized 5f moments.

Shun-ichi Miyata

Papers

Heavy-fermion and semiconducting properties of the ternary uranium compounds u3t3sn4 and u3t3sb4 (t=ni, cu, pd, pt and au)

Physical and Structural Properties of Ternary Uranium Compounds in the U-Ni-Sn and U-Ni-In Systems

Semiconducting and heavy-fermion behavior in new class of materials of U3T3X4

Superconductivity in Th3Ni3Sn4

119Sn NMR Study of Heavy Fermion Compound U3Ni3Sn4