Masaharu Nakazawa

Estimation of the latent track size of CR-39 using atomic force microscope

Abstract As a frame work of the study for the latent track size measurement using atomic force microscope, we have measured the minute etch pits and the extremely small amount of bulk etch of CR-39 at the beginning of chemical etching, and obtained its growth curves in nanometer dimensions. The pieces of CR-39 were exposed to 6 MeV / n C and Fe ions with normal incidence angle and were etched in 70°C 7 N NaOH solution for 0.5,1,2,3,5 min . The diameters of latent track were estimated to be ∼17 nm for Fe ions and ∼8 nm for C ions, respectively. These values are comparable to the experimental data on the average ‘track core diameters’ that have been obtained by various experimental techniques.

New radiation detector of plastic scintillation fiber

Fundamental characteristics of a new plastic scintillation fiber (PSF) has been studied for four kinds of radiations, and the possibility of using the PSF as a radiation detector has been discussed. Irradiation experiments of scintillation output characteristics have been made for γ rays, x rays, fast neutrons, and α particles. Various scintillation pulse height spectra have been obtained, depending on the variations of radiation types, energies, intensities, and scintillating positions on the PSF. Position detection experiments have been also made for γ rays and fast neutrons, and a new position sensitive detector of the PSF has been proposed.

Development of a new multi-grid-type microstrip gas chamber

Abstract A new multi-grid-type MSGC (M-MSGC) has been designed and fabricated. This new MSGC has very narrow gaps between neighboring electrodes which can considerably reduce a surface charge effect. Several types of test detectors have been fabricated and the maximum gas gain was found to be beyond 10 4 for a 10 μm gap M-MSGC. The observed amplitude of the cathode signal was almost the same as the anode signal. This MSGC can be a promizing detector for the field, where both the high gain and the stable operation are required.

Signal processing for CdTe detectors using a fast signal digitizing technique

Abstract To suppress the charge collection loss variation in CdTe detectors, a signal processing method has been developed using a fast signal digitizing technique. Signal pulse waveforms were described as a modeling function. Then a set of model waveform patterns has been calculated for reference patterns. The most probable waveform pattern was selected by the pattern matching method which assures a finite calculation time. Obtained residue values were used for the further selection in the correction method. An energy resolution of 8.9 keV was obtained after the correction and selection of measured pulse signals for the 137Cs 662 keV photopeak. This method can be applied to a detector having any electrode configuration if the signal pulses from that configuration are given.

A new pulse height analysis system based on fast ADC digitizing technique

A fast digitizing system was used as a pulse height analysis system in nuclear spectroscopy. Input signals were processed by a computerized data processing system consisting of a fast ADC (analog-to-digital converter) of 200 MHz/10 b and a UNIX workstation without any shaping circuit. Measurements have been made with a HPGe detector and a /sup 60/Co gamma -ray source. An energy resolution of 1.7 keV was obtained in this system whereas it was 2.0 keV in the conventional system with a shaping circuit with a 6- mu s time constant. A digital analysis of the pulse waveform has been performed. The selection of convex waveform gives an improved peak to Compton ratio. This technique has the potential to analyze individual signals with required accuracies and to be used as an advanced signal processing method. >

Consequences of radiation effects on pure-silica-core optical fibers used for Raman-scattering-based temperature measurements

Two types of pure-silica-core fibers (one low-OH, Al-jacketed, one medium-OH, polyimide jacketed) suitable for use as sensing fibers for Raman-scattering-based temperature measurements in nuclear environments have been subjected to gamma and fission reactor irradiation tests. Spectral attenuation measurements were performed between 500 and 1500 nm with samples kept at room temperature, 80 and 300/spl deg/C. The Al-jacketed fiber was developed for use under ionizing radiation and showed lower loss compared with the polyimide-jacketed fiber at room temperature under gamma irradiation. Both fiber types showed similar spectra at room temperature with the main part of the loss originating from a band tail extending from the ultraviolet. Thermal bleaching of the radiation-induced defects was found to be effective in both fiber types. At 80/spl deg/C the loss in both fibers was compounded of a band at 625 nm together with the band tail from the ultraviolet, which now had a strength several times lower compared with room-temperature irradiations. At 300/spl deg/C, both fibers exhibited similar low-loss spectra, except for the band at 625 nm which reached levels of approximately /spl sim/2000 dB/km at an accumulated dose of 2.8/spl times/10/sup 4/ Gy(SiO/sub 2/). In light of the experimental spectral findings, selection of suitable Raman-distributed temperature sensors for nuclear plants can be made.

Digital signal processing for 3He proportional counters

Abstract Numerical analysis of individual pulses from 3 He proportional counters has been performed. A parametric approach has been used for the identification of a charge particle track direction. Using area parameters, a clear separation of events was observed for the wall effect on a triton and a proton, respectively.

Soft X-ray imaging using CR-39 plastics with AFM readout

Abstract Soft X-ray microscopy using CR-39 plastic track detectors was demonstrated with an atomic force microscope (AFM) readout for the first time. A transmission X-ray image of the biological cells was recorded on the CR-39 surface, and revealed as relief after etching process. The resolution of the X-ray imaging is expected to be 100 nm or less, therefore imaging of biological cells is possible at an intracellular structure level. Using this technique, the high resolution image of both biological cells and charged particle tracks can be obtained simultaneously on a CR-39 with the AFM. In boron neutron capture therapy, this new technique provides the information on the distribution of boron compounds and radiation dose by charged particles mapping inside a cell.

Fast neutron detector using PIN-type silicon photodiode

Abstract A new fast neutron detector has been developed using a PIN-type windowless photodiode with a polyethylene radiator of 45 μm thickness and a low noise charge sensitive preamplifier for the photodiode. The detection efficiency was 7.8 × 10−5 for fast neutrons and the detector was sensitive to neutrons with an energy higher than 1.2 MeV. Additionally the thickness of the depletion layer in the photodiode can be estimated using the saturated range of recoil proton pulses. A charge sensitive preamplifier with lower noise is described for the photodiode radiation detection systems. The input stage of this preamplifier consists of four FETs. The equivalent noise charge was obtained as 1.1 × 10−16 C (FWHM) when connected to the photodiode. It can be concluded that this new system can be successfully used as a simple fast neutron detector.

Radiation distribution sensor with optical fibers for high radiation fields

Radiation distribution sensors with their feasibilities have been described in earlier works. However, due to large radiation induced transmission losses in optical fibers, especially in the visible wavelength region, it has been difficult to apply these techniques to high radiation fields. In this study, we proposed a new concept of optical fiber based radiation distribution measurements with near infrared (IR) emission. Near IR scintillators were attached to the ends of optical fibers, where the fibers were bundled and connected to an N-MOS line sensor or a cooled CCD camera. From the measurements of each area density, the radiation levels at the positions of the scintillators can be known. The linearity between the gamma dose rate at each scintillator and the registered counts has been examined. For correcting the radiation induced loss effects, we applied the Optical Time Domain Reflectometry technique to measure the loss distribution and from the results, a possibility for correction of the loss effe...