Makoto Maeda

Synchronization of reproductive period among the two male forms and female of the damselflyMnais pruinosa selys (Zygoptera: Calopterygidae)

Ecological parameters in a population ofMnais pruinosa were investigated in a mountain stream. In the study area, there were two forms of male with regard to wing color, the orange-winged male (esakii) and the hyaline-winged male (strigata), and only one female form with hyaline wings. Emergence of adults began in late April, and the flying season ended in late June. The time after emergence was spent in maturation, and the insects began to mate when they reached maturity. Longevity of adults was 17.6 days foresakii males, 18.4 days forstrigata males and 21.9 days for females. There was little difference in emergence time, maturation period, survivorship curve and longevity among the two male forms and female. In other words, the period for reproductive activities was perfectly coincident among them. The factors influencing the synchronization of emergence were discussed.

Study of the neutron multiplication effect in an active neutron method

ABSTRACT The neutron multiplication effect appears when an item contains large amounts of nuclear material. The neutron multiplication effect in this paper means the effect of subsequent fission reactions which are caused by fission neutrons produced by interrogation neutrons from a neutron generator. The previous active neutron method could not distinguish between first-fission and subsequent-fission neutrons and might overestimate the amount of nuclear material. However, the neutron multiplication effect in the active neutron method has not been adequately investigated. We discuss the evaluation method of the multiplication effect in the fast neutron direct interrogation method, one of the active neutron methods, using simulations with the Monte Carlo code MVP and experiments involving uranium waste drums. The first-generation neutrons from an external neutron source generate fission neutrons called second-generation neutrons, the second-generation neutrons generate third-generation neutrons, and so on. This study supposes that the neutron multiplication effect is mainly caused by the third-generation neutrons under the condition that the fourth-generation neutrons are much fewer. This paper proposes a correction method for the neutron multiplication effect in the measured data.

Peak identification of L X-ray spectra of elemental Np and U

The L X-ray photons emitted by transuranic (TRU) elements are expected to be useful for developing nondestructive TRU monitors. Energy spectra of L X-rays emitted by 241Am, 238Pu and 239Pu sources were measured by a transition edge sensor (TES) microcalorimeter, which allowed precise peak identification with high energy resolution. In the measurements using the TES microcalorimeter, the full width at half-maximum energy resolution was 62.6 eV at 17.222 keV for 239Pu source, 62.5 eV at 17.222 keV for 238Pu source and 60.9 eV at 17.751 keV for 241Am source. This study demonstrates the separation of 241Am and plutonium isotopes by L X-ray spectroscopy using a TES microcalorimeter.

Design study on differential die-away technique in an integrated active neutron NDA system for non-nuclear proliferation

A specific Differential Die-away Analysis (DDA) system in an advanced non-destructive analysis (NDA) system using a compact pulsed neutron generator has been studied and designed for non-nuclear proliferation in the Japan Atomic Energy Agency (JAEA). The NDA system is composed mainly of combination of four active neutron analysis techniques, DDA, PGA (Prompt Gamma-ray Analysis), NRTA (Neutron Resonance Transmission Analysis) and DGS (Delayed Gamma Spectroscopy). The design study on the DDA section in the system has been performed with Monte Carlo simulation code (MCNP) to evaluate the performance of the DDA system. The simulation result shows that the 239Pu mass (contained in MOX fuel) of as low as 0.01 g is detectable. The dependence of the performance on the type of the inner wall material in the DDA section and the thickness of the cylindrical moderator placed to circumscribe the measurement sample are presented.

X-Ray Response of a Transition Edge Sensor Microcalorimeter With a Mushroom-Shaped Absorber

Superconducting transition edge sensor (TES) microcalorimeters are excellent energy-resolving devices for X-ray detection. We fabricated two types of TES microcalorimeter using different mushroom-shaped absorber thicknesses (0.5 and 5μm). Both types of TES microcalorimeter were irradiated with X-ray photons emitted by an 55Fe source. X-ray detection signal pulses were collected to examine the effects of absorber thickness on performance. The values of the thermal conductance G were obtained by analyzing the current-voltage characteristics of the TES. By comparing the experimental G for both types of TES microcalorimeter, the absorber thickness was found to not affect the thermal properties of either type of TES microcalorimeter. The sensitivity α values for both TES microcalorimeters were obtained by analyzing the decay time constant of the X-ray detection signal pulses. The experimental ratio of the full-width at half-maximum value for the energy peaks of the Mn-Kα X-ray between both types of TES microcalorimeter was similar to theoretical estimations based on the different absorber thicknesses.

Development of a microcalorimeter for measurement of L X-rays emitted from transuranium elements

We fabricated a transition-edge sensor (TES) microcalorimeter for spectroscopic measurements of L X-rays emitted by transuranium (TRU) elements. A Pu L X-ray energy spectrum was obtained by irradiation with L X-rays emitted by a 244Cm source to the TES microcalorimeter. The energy resolution was evaluated to be 64 eV at the full width at half maximum (FWHM) for L X-rays at 14.28 keV. The obtained L X-ray spectrum indicated that the TES microcalorimeter made it possible to distinguish between the L X-ray lines of TRU elements.

Development of a microcalorimeter with transition edge sensor for detection of LX rays emitted by transuranium elements.

A transition edge sensor (TES) microcalorimeter has been developed for use as an energy dispersive X-ray spectrometer. The TES microcalorimeter is a thermal detector that enables one to determine the energy of an incident photon by measuring the resultant increase in temperature. In this work, a Ti/Au TES microcalorimeter was developed to measure LX rays emitted by transuranium elements. The phase transition temperature was set at ~200 mK by using a bilayer structure composed of a 110-nm-thick Au layer and a 40-nm-thick Ti layer. An Au of 5 µm thickness was deposited on the Ti/Au bilayer to achieve an absorption efficiency of 35-80 % for the energy range of LX rays (10-25 keV). The developed TES microcalorimeter was irradiated with LX rays emitted by an (241)Am source at an operating temperature of 140 mK. An energy resolution of ~80 eV (full width at the half maximum) was obtained for L(β1)X ray of 17.75 keV.