G. Wakabayashi

Applicability of self-activation of an NaI scintillator for measurement of photo-neutrons around a high-energy X-ray radiotherapy machine

The applicability of the activation of an NaI scintillator for neutron monitoring at a clinical linac was investigated experimentally. Thermal neutron fluence rates are derived by measurement of the I-128 activity generated in an NaI scintillator irradiated by neutrons; β-rays from I-128 are detected efficiently by the NaI scintillator. In order to verify the validity of this method for neutron measurement, we irradiated an NaI scintillator at a research reactor, and the neutron fluence rate was estimated. The method was then applied to neutron measurement at a 10-MV linac (Varian Clinac 21EX), and the neutron fluence rate was estimated at the isocenter and at 30xa0cm from the isocenter. When the scintillator was irradiated directly by high-energy X-rays, the production of I-126 was observed due to photo-nuclear reactions, in addition to the generation of I-128 and Na-24. From the results obtained by these measurements, it was found that the neutron measurement by activation of an NaI scintillator has a great advantage in estimates of a low neutron fluence rate by use of a quick measurement following a short-time irradiation. Also, the future application of this method to quasi real-time monitoring of neutrons during patient treatments at a radiotherapy facility is discussed, as well as the method of evaluation of the neutron dose.

Light output response of GSO(Ce) and NaI(Tl) to protons up to 160 MeV

An experimental study on GSO(Ce) scintillation crystals was made in terms of the light output response to proton in an energy range up to 161 MeV. The experiment was carried out for cubic crystals of 43 mm edge length by using a 392 MeV proton beam. A good linearity was observed between 30 and 161 MeV, and a slight non-linearity below 30 MeV. A relation of dLdE versus E was determined with stopping protons. A calculation using the relation has agreed with measured pulse heights of protons penetrating the crystal, as well as those of stopping protons. Similar measurements were made for NaI(Tl) crystals of 2 in. cubic. Rather large non-linearity was observed in the proton energy range 0–122 MeV.

Absolute efficiency of a stacked GSO(Ce) spectrometer for intermediate energy protons

Abstract A spectrometer which consists of plastic plates and cerium-doped gadolinium orthosilicate, Gd 2 SiO 5 (Ce)–GSO(Ce), crystals has been developed. The absolute efficiency of the spectrometer for protons up to 310xa0MeV was investigated by an experiment at the Research Center for Nuclear Physics (RCNP) of Osaka University using a proton beam of 392xa0MeV. The efficiency of the spectrometer for protons is in good agreement with the simple Monte Carlo calculation.

Measurement of subcritical reactivity in unsteady state with Digital Time-Series Data Acquisition System using difference filter technique

The Digital Time-Series Data Acquisition System using first-in-first-out (FIFO) memory module has been developed for the monitoring of subcritical reactivity. The system records arriving time of the signal from a neutron detector, and time-series data are saved in a personal computer (PC). Using this system, the measurement of time-series data is carried out more efficiently than that using a conventional multichannel scaler (MCS) system, and it has been applied for the monitoring of subcritical reactivity of the reactor in a steady state using the conventional Feynman-/spl alpha/ technique. In the present work, this system was applied for the monitoring of subcritical reactivity in an unsteady state using the difference filter technique. The test experiment was carried out with the research reactor of Atomic Energy Institute of Kinki University, Japan. From the experimental results, it was shown that the present system was useful for the continuous monitoring of varying subcritical reactivity by application of the difference filter technique.

A ray-trace-type counter telescope for neutron spectrometry

A compact recoil proton counter telescope with two position sensitive proportional counters (PSPCs) for neutron spectrometry has been developed. This counter telescope consists of a radiator (a thin polyethylene film), two PSPCs used as /spl Delta/E detector and a Si-SSD used as E detector. Using the position information extracted from two PSPCs, the three-dimensional trajectory of the recoil proton and the recoil angle can be determined event by event. The performance of this counter telescope was tested by the measurement of 7.2 MeV neutrons produced from D-D reactions, and it was shown that the energy spectra of neutrons could be obtained by determining the energy of each incident neutron using a recoil angle.

Application of high-energy photon CT system with laser-compton scattering to nondestructive test

A CT system using high-energy monochromatic photons is one of the best choices for nondestructive test of industrial products. We have developed a CT system for nondestructive test of industrial products using the laser-Compton photons, which were generated with an electron accelerator and conventional commercial laser system. We measured the profile, and found that they were a 0.8 - 1.5 mm in diameter. We also applied the CT system to the nondestructive test of the concrete specimen, and successfully obtained the CT image.

Low-Level Radiation Measurement System With Magnetically Levitated Electrode Ionization Chamber Detector

An automatic system was developed for the measurement of radiation using a magnetically levitated electrode ionization chamber. The system was used to measure background and 40K gamma ray dose rates. The background dose rate measurement demonstrated high sensitivity and reliability of the system, and a low-level 40K gamma ray dose rate was successfully measured. For the case of a 30-minute measurement, the detection limit of the system is 13 nGy/h. This measurement system will be useful as an area monitor to measure space dose rates

100Mo(p→,d)99Mo reaction at 21 MeV and direct reaction analysis of the low-lying continuum spectrum

The 100 Mo( � p, d) 99 Mo reaction has been studied with 21 MeV polarized protons. Momentum spectra of the emitted deuterons corresponding to the excitation energy region up to 5.75 MeV in 99 Mo have been measured. Theoretical analysis based on the standard distorted-wave Born approximation (DWBA) provides the lj -angular momentum transfers and spectroscopic factors of neutron hole states for 27 levels from the ground state up to EX = 2.921 MeV. The polarization data gave a more affirmative information in assigning the spins and parities. Spectrum regions from discrete levels to continuum were treated with a global analysis using the direct reaction model and continuous strength functions. The double differential cross section-energy spectra were reproduced fairly well using the DWBA-based cross sections and the asymmetrical Lorentzian form strength response function having energy-dependent spreading widths. uf6d9 2002 Elsevier Science B.V. All rights reserved.

Continuum spectra in one-nucleon transfer reactions —(p→, d) reactions at medium energy region—

The continuum spectra up to about 20 MeV of the (p→, d) reactions induced by 65 and 21 MeV polarized protons have been analyzed using such an approach as proposed by Lewis. An asymmetry Lorentzian form strength function was employed in the analysis, in set with empirical spreading widths. The cross sections were estimated as an incoherent sum of many shell-orbits constituents based on the distorted-wave Bom approximation (DWBA). The comparisons between the theoretical and experimental results of cross section angular distribution indicate a systematic relation between the distribution of strength and the target mass number, in isotopes.

Measurement of varying sub-critical reactivity with digital time-series data acquisition system using difference filter technique

A digital time-series data acquisition system has been developed for the monitoring of sub-critical reactivity. The system registers arriving time of the signal from a neutron detector as digital data in a FIFO (First In First Out) memory module, and the time data is read and stored by PC (personal computer). This system can measure time series data more efficiently than conventional a Multi Channel Scaler (MCS) system, and it has been applied for the monitoring of steady or slowly varying sub-critical reactivity using a conventional Feynman-/spl alpha/ method. In the present work, this system was applied for the monitoring of rapidly varying sub-critical reactivity using the difference filter technique. The test experiment was carried out with a research reactor of the Atomic Energy Institute in Kinki University. From the result, it was shown that the present system is useful for the monitoring of rapidly varying sub-critical reactivity by application of the difference filter technique.