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Storage characteristics of RBP[O.sub.5] (R: Ca, Sr)-based phosphors have been investigated for neutron detection. To increase the photostimulated luminescence (PSL) yields of CaBP[O.sub.5]:[Ce.sup.3+] and SrBP[O.sub.5]:[Ce.sup.3+] phosphors, fluorine atoms were introduced and the molar ratio of the fluorine atoms was optimized for the PSL yields. In addition, the authors found that the PSL yields of SrBP[O.sub.5]:[Eu.sup.2+] phosphors were significantly increased by adding [Li.sub.2][B.sub.4]O.sub.7], though introducing fluorine and bromine atoms in the phosphor was not effective for the PSL yields. These phosphors will be usable as new neutron storage phosphors with low gamma-ray sensitivity because they consist of light materials. Index Terms--CaBP[O.sub.5], gamma-ray sensitivity, neutron storage phosphor, SrBP[O.sub.5].

Neutron storage characteristics of CaBP[O.sub.5] : [Ce.sup.3+] based phosphors have been investigated. The authors found that the CaBP[O.sub.5] : [Ce.sup.3+] phosphor shows photostimulated luminescence (PSL) by illumination with 635 nm laser light after neutron irradiation. The PSL yields of CaBP[O.sub.5] : [Ce.sup.3+] phosphor were increased by adding Ca[F.sub.2]. The green laser (532 nm) seemed to be more efficient to produce PSL signal. The phosphor might be usable in a high gamma-ray field. The fading characteristics were similar to those of a commercially available neutron imaging plate. Using a disk-like sample, a collimated neutron beam image was clearly obtained by scanning focused laser light on it. Index Terms--CaBP[O.sub.5] : [Ce.sup.3+], Ca[F.sub.2], gamma-ray sensitivity, neutron sensitivity, neutron storage phosphor.

A capillary plate (CP) comprising an assembly of fine glass tubes was applied as a pre-gas-amplification device for a microstrip gas chamber (MSGC) operating under a gas pressure of 3 atm of helium-3 for use in neutron detection. The collection efficiency of the electrons between the CP and MSGC was maximally 17% using neutrons. The effective gas gain of the detector system was ~600 at a gas pressure of 3 atm with a 10% mixture of ethane with helium-3, confirming the feasibility of the CP as a pre-gas-amplification device. Moreover, we demonstrated that the coincidence measurement of the signals between the CP and the anodes of MSGC decreased the background levels of electronics noise, electronic discharges, and gamma-rays, indicating that a detector system with a low background can be constructed using the CP. Index Terms--Capillary plate (CP), gas gain, microstrip gas chamber, neutron detector.

In-situ radiation monitoring in the outside region of a reactor core has been experimentally demonstrated using radiation-resistant optical fibers with scintillators. To avoid influences of luminescence (400-450 nm) from the fibers by radiation, [Y.sub.3][A.sub.15][O.sub.12]: Ce scintillators were adopted because the luminescence has its peak around 550 nm. In this method, low radiation field was monitored with a pulse counting method, while high field with an integral method. The demonstration experiments shows that radiation intensity outside a reactor core can be well monitored with the system from the reactor power of 1 kW to 3.5 MW. The vertical radiation intensity distribution around the reactor core was also measured at 3.5 MW. Index Terms--Optical fiber, radiation monitoring, reactor, scintillator, YAG.

Characteristics of a SrBP[O.sub.5] : [Eu.sup.2+] material have been investigated as a neutron storage phosphor. The authors found that this phosphor shows photostimulated luminescence (PSL) by illumination with 635 nm laser light after neutron irradiation. The light with shorter wavelength than 635 nm seemed to be more efficient to produce PSL signal. The optimal concentration of Eu was 2% (mol %). The phosphor might be usable in a high gamma-ray field. The fading characteristics were similar to those of a commercially available neutron imaging plate. Using a disk-like sample, a collimated neutron beam image was clearly obtained by scanning focused laser light on it. The spatial resolution of 0.4 mm was obtained from the Edge Spread Function measurement. Index Terms--Gamma-ray sensitivity, neutron imaging plate, neutron sensitivity, SrBP[O.sub.5] : [Eu.sup.2+].

A fast readout method for an imaging plate is proposed using wavelength shifting fibers and line-shaped laser. This method adopts wavelength shifting fiber for signal transmission and line-shaped laser for reading out all pixels of the imaging plate in one axis at the same time, which results in reduction of readout time. To validate the method, the authors have fabricated an experimental system with a rotating mirror and carried out demonstration experiments using CAMAC readout system. In the experiments, two measuring method such as a photon counting method and a charge integral method were used. The experimental results show that an alpha particle image of 5 x 5 mm can be taken within 10 ms in both methods. The spatial resolution of 0.5 mm in the photon counting method was obtained in scanning direction, although the resolution perpendicular to scanning direction was more than 1 mm, which greatly depends on the diameter of the wavelength shifting fibers. Index Terms--Fast readout, imaging plate, line-shaped laser, wavelength shifting fibers.

Since the Nuclear Pumped Laser technique can be applied to optical detection of neutrons, numerical simulation and demonstration experiments have been carried out for He-Ne-Ar mixtures. Test cells filled with 3He gas (1140 torr), Ne gas (540 torr) and Ar gas (208 torr) were irradiated with thermal neutron fluxes up to about [10.sup.12] n/[cm.sup.2]/s at the JRR-4 reactor, JAERI. In these experiments, optical output of 585.3 nm from Ne 3p-3s transitions was clearly observed. Its intensity was almost proportional to the thermal neutron flux, and these results agree with those of numerical simulation. This system can be applied to optical neutron detection. The simulation results show that the population inversion between the 3p[prime][[1/2].sub.0] and 3s[prime][[[1/2].sub.0].sup.1]] levels of neon atoms for the cell can be achieved at the thermal neutron flux of much higher than [10.sup.12] n/[cm.sup.2]/s. It is also estimated that the threshold thermal neutron flux for the population inversion is about 3 x [10.sup.12] n/ [cm.sup.2]/s for the gas cell filled with optimized gas mixtures.