Masaki Katagiri

Design of neutron detector by using a novel superconductor MgB2

Abstract It is difficult to detect neutrons compared to charged particles. A novel metallic superconductor MgB 2 has a high T c of 40 K. It is well known that the 10 B has a huge cross-section for the nuclear reaction of 10 B( n , α ) 7 Li. It reaches 3800 barns for thermal neutrons. The Li particle has 0.84 MeV while α particle has 1.47 MeV. We propose to use the MgB 2 as a superconducting neutron detector. We design a prototype of a MgB 2 neutron detector from an MgB 2 film where the electron beam lithography is employed to fabricate a meandering MgB 2 stripe line of the 1-μm width. The hot spot caused by the nuclear reaction is responsible for detecting neutrons.

Diamond radiation detector using a synthetic IIa type mono-crystal

A diamond radiation detector using a synthetic IIa type mono-crystal was developed. An energy resolution of 0.81%, 45 keV, was achieved for 5.486 MeV α particles in a vacuum environment. The ionization energy, ∈Diamond, was estimated as 13.07 eV by calibration with a silicon surface barrier detector. On a preamplifier output signal, a trapping and detrapping effect on holes was observed.

Cryogenic InSb detector for radiation measurements

The energy spectra of 241Am alpha particles were measured by a detector employing the compound semiconductor InSb at an operating temperature below 4.2 K. The fabrication method and current–voltage curves are shown. Though the energy resolution of the detector is not discussed in this article, this is the first report on an InSb radiation detector.

Radiation measurements by a cryogenic pn junction InSb detector with operating temperatures up to 115 K

Pn junction-type radiation detectors were fabricated with an InSb substrate. The detectors had 1000 times higher resistances than those of previously reported Schottky-type detectors. The output pulses of the preamplifier were analyzed from the point of view of the contribution of electrons and holes. The energy spectra of 241Am alpha particles were measured at operating temperatures of up to 115 K. The inherent voltage of the detector was estimated.

Response function measurement of a synthetic diamond radiation detector for 14 MeV neutrons

The response function of a diamond radiation detector using a synthetic type IIa single diamond crystal for 14 MeV neutrons was measured. There was severe trapping of electrons in the synthetic diamond crystals used in this study. Accordingly, a prototype diamond radiation detector using the synthetic type IIa single diamond whose thickness was 0.1 mm was used with high bias voltage up to 1000 V, i.e., electric field of 100 kV/cm. The measurement resulted in the first observation of a 14 MeV neutron peak corresponding to 12C(n,α)9Be reactions by a synthetic diamond radiation detector. Energy resolution of the prototype detector for 14 MeV neutrons was 9%. Experimental detection efficiency of the detector was consistent with calculated detection efficiency. Synthetic diamond crystals which do not have trapping of charge carriers are indispensable in order to improve energy resolution for 14 MeV neutrons.

Experimental imaging diagnosis of superconducting tunnel junction x-ray detectors by low-temperature scanning synchrotron microscope

Imaging diagnosis of superconducting tunnel junction x-ray detectors has been performed by an apparatus called the low-temperature scanning synchrotron microscope (LTSSM) using an x-ray microbeam with a diameter of 5–10 μm originated from synchrotron radiation. Quasiparallel intense synchrotron radiation enables one to obtain the full two-dimensional images of junctions with dimensions of 200×200 μm2 in about 1 h. The LTSSM results indicate that the standard quasiparticle diffusion and edge loss model for the spatial distribution of the junction response to x rays is evidently inadequate for intermediate or large junctions (with respect to a Josephson penetration depth). On this basis, it is argued that the models proposed for the signal creation and loss mechanism should be reconsidered.

Source position effect in gamma-ray energy measurements with Ge(Li) detectors

Abstract The source position effect for gamma-ray pulse heights was investigated with two planar and three coaxial Ge(Li) detectors at the gamma-ray energies of 303 keV, 512 keV and 1275 keV. The peak shift in the pulse height spectrum was measured as a function of the source-to-detector distance and of the source angle from the detector axis. A clear shift of the peak center was observed for the planar detectors, and a smaller shift for the coaxial detectors. It was found that the shift was almost independent of the bias voltage. These experimental results are difficult to explain by the field increment effect and the charge trapping effect in the detector. The rise time effect was not observed in any of the planar detectors.

Fast response of InSb Schottky detector.

An InSb Schottky detector, fabricated from an undoped InSb wafer with Hall mobility which is higher than those of previously employed InSb wafers, was used for alpha particle detection. The output pulse of this InSb detector showed a very fast rise time, which was comparable with the output pulses of scintillation detectors.

Environmental Gamma-Ray Exposure Rates Measured by In-Situ Ge(Li) Spectrometer

A conversion function (G(E) function) was determined to obtain an exposure rate directly from a γ-rays spectrum measured by an in-situ Ge(Li) spectrometer. In order to verify the utility of the G(E) function method, three kinds of detector, namely, a portable Ge(Li) detector, a Nal(Tl) detector and an ionization chamber, were used to measure exposure rate due to environmental γ-rays at the same place, and the measured values of exposure rate were compared with each other. Two exposure rate values were obtained from a γ-ray spectrum measured by the Ge(Li) detector, using two different methods, namely, the G(E) function method and the HASL method. The average of exposure rates obtained by four different methods was 4.15 uR/h, and the deviation was 15% of the average. By applying both the G(E) function method and the HASL method to an environmental γ-ray spectrum, a total exposure rate can be determined directly without information on the distribution of the radionuclides in soil, and individual exposure rat...

Undoped InSb Schottky detector for gamma-ray measurements

For measuring X-rays and gamma-rays with better energy resolution and higher efficiency than conventional semiconductor detectors such as Si and Ge detectors, we are studying InSb radiation detectors. Previously, we fabricated p-InSb Schottky type, pn-junction type detectors, and undoped InSb Schottky type detectors with an electrode of 3 mm in diameter, and measured alpha particles of 241Am. For measuring gamma-rays, we fabricated undoped InSb Schottky type detectors with smaller electrode areas. Gamma-ray signals were clearly separated from the background, and differences between energy spectra of 241 Am and 133Ba gamma-rays were observed