Prediction analysis of dose equivalent responses of neutron dosemeters used at a MOX fuel facility.

To predict how accurately neutron dosemeters can measure the neutron dose equivalent (rate) in MOX fuel fabrication facility work environments, the dose equivalent responses of neutron dosemeters were calculated by the spectral folding method. The dosemeters selected included two types of personal dosemeter, namely a thermoluminescent albedo neutron dosemeter and an electronic neutron dosemeter, three moderator-based neutron survey meters, and one special instrument called an H(p)(10) monitor. The calculations revealed the energy dependences of the responses expected within the entire range of neutron spectral variations observed in neutron fields at workplaces.

Development of a hand-held fast neutron survey meter.

A neutron survey meter with a ZnS(Ag) scintillator to measure recoil protons was built. The detection probe weighs ~2 kg, therefore providing us with true portability. Performance tests exhibited satisfactory neutron dosimetry characteristics in unmoderated or lightly moderated fission neutron fields and in particular work environments at a mixed oxide fuel facility. This new survey meter will augment a routine of neutron monitoring that is inconveniently being carried out by moderator-based neutron survey meters.

Recalibration of indium foil for personnel screening in criticality accidents.

At the Nuclear Fuel Cycle Engineering Laboratories of the Japan Atomic Energy Agency (JAEA), small pieces of indium foil incorporated into personal dosemeters have been used for personnel screening in criticality accidents. Irradiation tests of the badges were performed using the SILENE reactor to verify the calibration of the indium activation that had been made in the 1980s and to recalibrate them for simulated criticalities that would be the most likely to occur in the solution process line. In addition, Monte Carlo calculations of the indium activation using the badge model were also made to complement the spectral dependence. The results lead to a screening level of 15 kcpm being determined that corresponds to a total dose of 0.25 Gy, which is also applicable in posterior-anterior exposure. The recalibration based on the latest study will provide a sounder basis for the screening procedure in the event of a criticality accident.

Calculations of anisotropy factors for radionuclide neutron sources due to scattering from source encapsulation and support structures.

A model has been developed for calculating the angular neutron fluence distributions for radionuclide neutron sources that are heavily encapsulated or surrounded by source support structures as a source holder and a source movement system. These structures may cause an anisotropic neutron fluence distribution. This should be taken into account in the neutron-measuring instruments calibration procedure. The calculations were made for two types of widely used neutron sources, (241)Am-Be and (252)Cf, by combining an in-house code simulating the (9)Be(alpha,n) reactions and the Monte Carlo code MCNP-4C. As a result, anisotropy factors in the direction perpendicular to the source capsule axis for bare neutron sources were evaluated to be 1.012, 1.030 and 1.039 for (252)Cf in a standard Amersham X1 capsule, (241)Am-Be in a X3 capsule and (241)Am-Be in a X4 capsule, respectively. These values are in reasonable agreement with the published data. If the support structures are included in the MCNP simulation, the anisotropy factors for these neutron sources increase by approximately 10%.

Development of a neutron personal dose equivalent detector.

A new neutron-measuring instrument that is intended to measure a neutron personal dose equivalent, H(p)(10) was developed. This instrument is composed of two parts: (1) a conventional moderator-based neutron dose equivalent meter and (2) a neutron shield made of borated polyethylene, which covers a backward hemisphere to adjust the angular dependence. The whole design was determined on the basis of MCNP calculations so as to have response characteristics that would generally match both the energy and angular dependencies of H(p)(10). This new instrument will be a great help in assessing the reference values of neutron H(p)(10) during field testing of personal neutron dosemeters in workplaces and also in interpreting their readings.

Operational comparison of TLD albedo dosemeters and solid state nuclear tracks detectors in fuel fabrication facilities.

The authors carried out an operational study that compared the use of TLD albedo dosemeters and solid state nuclear tracks detector in plutonium environments of Japan Nuclear Cycle Development Institute, Tokai Works. A selected group of workers engaged in the fabrication process of MOX (Plutonium-Uranium mixed oxide) fuel wore both TLD albedo dosemeters and solid state nuclear tracks detectors. The TL readings were generally proportional to the counted etch-pits, and thus the dose equivalent results obtained from TLD albedo dosemeter agreed with those from solid state nuclear tracks detector within a factor of 1.5. This result indicates that, in the workplaces of the MOX fuel plants, the neutron spectrum remained almost constant in terms of time and space, and the appropriate range of field-specific correction with spectrum variations was small in albedo dosimetry.

RCA/IAEA third external dosimetry intercomparisons in East Asia region.

Several intercomparison exercises were organised by the International Atomic Energy Agency (IAEA) on the determination of operational quantities at the regional or interregional basis. In East Asia region, a third phase of the intercomparison finished in mid 2004. It was organised within the frame of the Regional Cooperation Agreement (RCA) as a follow-up to previous exercises carried out during 1990-1992 and 1995-1996. The results of this intercomparison for the determination of operational quantities were satisfactory for all Member States. The laboratories demonstrated a good performance in quantities tested. The purpose of this paper is to present the results of the RCA/IAEA intercomparison and the future of RCA activities in support of assessment of occupational exposure by organising intercomparison runs.

A Novel real-time dosimetry technique based on radiation-induced surface activation.

A novel real-time dosimetry technique based on radiation-induced surface activation (RISA) phenomenon has been proposed that is similar to ultraviolet surface activation known typically in anatase-type titanium dioxide. It has been found that the RISA phenomenon occurs on the surface of an oxidised semiconductor or oxidised metal film by radiation incidence. The RISA dosemeter has the following advantageous characteristics: (1) output of the RISA dosemeter is proportional to the dose equivalent rate in harsh environments, (2) fluctuation of output of the RISA dosemeter irradiated by (60)Co gamma-rays is <2.5% beyond the total dose equivalent of 1.8 MSv, (3) the transient current observed in simple insulators for a few seconds or more after onset of irradiation was not detected in the RISA dosemeter and (4) this dosemeter worked well even at high temperatures.

Characteristics of the simulated workplace neutron fields using a 252Cf source surrounded with cylindrical moderators.

The authors established the simulated workplace neutron fields using a 252Cf source surrounded with cylindrical moderators at the Japan Nuclear Cycle Development Institute (JNC), Tokai Works. The moderators are annular cylinders made of polymethyl methacrylate and steel. The neutron energy spectrum at the reference calibration point was evaluated from the calculations by MCNP-4B and the measurements by the Bonner multisphere spectrometer and the hydrogen-filled proportional counters. The calculated neutron spectra were in good agreements with the measured ones. These fields can provide the realistic neutron spectra similar to those encountered around the glove-boxes of the fabrication process of MOX (PuO2-UO2 mixed oxide) fuel.

Dose evaluation based on 24Na activity in the human body at the JCO criticality accident in Tokai-mura.

24Na in the human body, activated by neutrons emitted at the JCO criticality accident, was observed for 62 subjects, where 148 subjects were measured by the whole body counter of JNC Tokai Works. The 148 subjects, including JCO employees and the contractors, residents neighboring the site and emergency service officers, were measured by the whole-body counter. The neutron-energy spectrum around the facility was calculated using neutron transport codes (ANISN and MCNP), and the relation between an amount of activated sodium in human body and neutron dose was evaluated from the calculated neutron energy spectrum and theoretical neutron capture probability by the human body. The maximum 24Na activity in the body was 7.7 kBq (83 Bq(24Na)/g(23Na)) and the relevant effective dose equivalent was 47 mSv.

Cloning and characterization of a gene, mpsA, encoding a protein associated with intracellular magnetic particles from Magnetospirillum sp. strain AMB-1.

Proteins located within the lipid bilayer, surrounding the intracellular bacterial magnetic particles (BMP) from Magnetospirillum sp. AMB-1, were separated using SDS-PAGE. Several major proteins of approximate molecular weight 66.2, 35.6, and 24.8 kDa were identified. The N-terminal amino acid sequence of one of these proteins, designated MpsA, was determined and used to design a pair of PCR primers which amplified a 105 bp DNA fragment from AMB-1 genomic DNA. Gene-walking, using anchored PCR, was used to determine the complete nucleotide sequence (954 bp) of the mpsA gene. The mpsA encodes a 317 amino acid protein which does not have an N-terminal cytoplasmic transport signal sequence. Intracellular localization studies were carried out using an mpsA-luc gene fusion expressed in AMB-1 following gene transfer by conjugation. The gene fusion was constructed by cloning a 1.6 kb mpsA fragment upstream of luc in the conjugal plasmid pKLC. The MpsA-Luc fusion protein was preferentially located on the magnetic particle membrane. Although the function of MpsA remains unknown, homology searches suggest similarity with the alpha subunit of acetyl-CoA carboxylase and the CoA-binding motif.

Chemiluminescence enzyme immunoassay using bacterial magnetic particles.

A novel chemiluminescence enzyme immunoassay using bacterial magnetic particles (BMPs) has been developed for highly sensitive and rapid detection of immunoglobulin G. Antibody was immobilized onto BMPs using the heterobifunctional reagents sulfosuccinimidyl 6-[3'-(2-pyridyldithio) propionamido]hexanoate (sulfo-LC-SPDP) and sulfosuccinimidyl 4-(N-maleimidomethyl)cyclohexane-1-carboxylate (sulfo-SMCC). For the highly sensitive immunoassay method using these BMPs, a good relationship was obtained between the luminescence intensity and mouse IgG concentration in the range of 1-10(5) fg/mL. Furthermore, in order to reduce assay time and to simplify operations, a rapid chemiluminescence enzyme immunoassay method has been developed. The rapid method was completed in 10 min. A linear relationship was obtained between the luminescence and mouse IgG concentration in the range of 10-1000 ng/mL.