Wi-Ho Ha

Retrospective biodosimetry using translocation frequency in a stable cell of occupationally exposed to ionizing radiation

Two cases of hematological malignancies were reported in an industrial radiography company over a year, which were reasonably suspected of being consequences of prolonged exposure to ionizing radiation because of the higher incidence than expected in the general population. We analyzed chromosomal aberrations in the peripheral blood lymphocytes from the other workers who had been working under similar circumstances as the patients in the company. Among the subjects tested, 10 workers who belonged to the highest band were followed up periodically for 1.5 years since the first analysis. The aim of this study was to clarify pertinence of translocation analysis to an industrial set-up where chronic exposure was commonly expected. To be a useful tool for a retrospective biodosimetry, the aberrations need to be persistent for a decade or longer. Therefore we calculated the decline rates and half-lives of frequency for both a reciprocal translocation and a dicentric chromosome and compared them. In this study, while the frequency of reciprocal translocations was maintained at the initial level, dicentric chromosomes were decreased to 46.9% (31.0–76.5) of the initial frequency over the follow-up period. Our results support the long-term stability of reciprocal translocation through the cell cycle and validate the usefulness of translocation analysis as a retrospective biodosimetry for cases of occupational exposure.

Tritium analysis of urine samples from the general Korean public.

The tritium concentrations of urine samples and the effective dose of the general Korean public were evaluated. To achieve accurate HTO analysis of urine samples, we established the optimal conditions for measuring the HTO content of urine samples. Urine samples from 50 Koreans who do not work at a nuclear facility were analyzed on the basis of the results. The average urine analysis result was 2.8 ±1 .4 Bq/L, and the range was 1.8-5.6 Bq/L. The measured values were lower than those reported for other countries. These results show that environmental factors and lifestyle differences are the main factors affecting the tritium level of the general public.

Feasibility study for the assessment of the exposed dose with TENORM added in consumer products

Consumer products including naturally occurring radioactive material have been distributed widely in human life. The potential hazard of the excessively added technically enhanced naturally occurring radioactive material (TENORM) in consumer products should be assessed. The aim of this study is to evaluate the organ equivalent dose and the annual effective dose with the usage of the TENORM added in paints. The activities of gammas emitted from natural radionuclides in the five types of paints were measured with the high-purity germanium detector, and the annual effective dose was assessed with the computational human phantom and the Monte Carlo method. The results show that uranium and thorium series were mainly measured over the five paints. Based on the exposure scenario of the paints in the room, the highest effective dose was evaluated as <1 mSv y(-1) of the public dose limit.

Estimation of counting efficiencies of a portable NaI detector using Monte Carlo simulation for thyroid measurement following nuclear accidents

Radioiodine can be released in nuclear accidents and can cause internal contamination of the thyroid gland in members of the public. For population monitoring in radiation emergencies, measurement of counting efficiency is very important to accurately determine thyroid activity. Here, we estimate the counting efficiencies of a portable NaI detector using Monte Carlo simulations. Two different types of neck phantoms and a 7.62 cm long by 7.62 cm diameter NaI detector were modeled and the counting efficiencies were calculated depending on the thyroid size and distance from the neck phantom to the detector. We found that distance is a more important parameter than thyroid size. The optimal distance of the NaI detector from the neck surface was determined to be greater than 12 cm, beyond which the counting efficiency was not affected by thyroid size.

Development of a minipig physical phantom from CT data

ABSTRACT Quantification of pathological progression of radiation-induced injury is essential in development of treatment methods, and a proper animal model is necessary for relevant radiological and medical studies. A minipig is a current animal model selected because of its similarities to humans in anatomy and pathology. In the present study, a minipig physical phantom was developed using computed tomography (CT) data. For dosimetry purposes, the minipig physical phantom was constructed on a slice-by-slice basis, with an array of holes to accommodate dosimeters. The phantom is constituted of three major organs, i.e. bone, lung, and remaining soft tissue, and the organs are clearly distinguishable on each 20-mm-thick axial slice. The quality of the tissue-equivalent (TE) substitutes was analyzed in terms of the atomic compositions and Hounsfield units (HUs). The density (in g/cm3) and effective atomic number of TE substitutes for the bone, lung, and soft tissue are 1.4 and 7.9, 0.5 and 10.0, and 1.0 and 5.9, respectively. Although the TE substitutes have slightly different physical properties, we think the phantom is acceptable because the HU values of the TE substitutes lie in the HU range of real tissues.

Radiobioassay performance evaluation of urine and faeces samples for radiation emergency preparedness

ABSTRACT In the event of a radiation emergency, it is necessary to assess intake and radiation dose for the internally contaminated casualties. This paper provides relatively rapid and simple procedures of bioassay. Faeces samples were ashed to improve sample homogeneity. Gamma spectrometry was used for radioactivity measurement. The measured results, including activity of the biosamples and associated uncertainty, were evaluated for traceability based on ANSI N42.22 and bias and precision based on ANIS/HPS N13.30. For all urine customary exercise samples, measurement results of 60Co and 137Cs were in good agreement with NIST values within 5% and satisfied ANSI N42.22 and ANIS/HPS N13.30 acceptance criteria. In contrast, the uncertainty of 57Co was quite large and the activity differed from the NIST value by 18%. For the urine emergency preparedness exercise, all measured results agreed well with NIST values, with less than 10% difference. Synthetic faeces samples included 54Mn, 60Co, and 134Cs. The activity of 60Co was different from the NIST value by 9%, whereas the results for 54Mn and 134Cs were within 3.2%. The measurement procedures given in this study can be applied to assess intake of radionuclides and resulting radiation dose to casualties.

Screening of alpha- and beta-emitting radionuclides using liquid scintillation counting and monitoring procedures in radiation emergencies.

Abstract Urine gross alpha and beta activity analysis was conducted, and an internal contamination screening method was adopted to monitor visitors to Japan after the Fukushima accident. In particular, spot urine samples were used to evaluate internal contamination for 16 mo, and a total of 90 people participated in gross alpha and beta emitter screening. An ultra-low-background liquid scintillation counter was used for measurement, and optimal pulse shape analysis values were determined by measuring alpha- and beta-emitting certified reference materials. Moreover, linearity and reproducibility were assessed to validate the adopted methods, and international intercomparison was conducted using synthetic urine samples by measuring alpha- and beta-emitting radionuclides in multi-contaminated samples. Here, the measurement results of visitors to Japan are discussed, and a screening procedure is established for gross alpha and beta activity analysis during radiation emergencies.

Radioactive contamination monitoring for the Korean public following Fukushima nuclear accident

On March 11, 2011, as a result of the Great East Japan Earthquake, severe damage to the Fukushima nuclear power plant caused the release of radioactive materials. We conducted radioactive contamination monitoring for Korean residents in Japan and Korean travelers to East Japan after the accident. More than 800 members of the Korean public were surveyed for personal monitoring. Measured levels of external and internal contamination were within the screening levels for each monitoring method.

Evaluation of sodium activation distribution in the PMMA water phantom after fast neutron irradiation.

(24)Na produced by the neutron activation of stable sodium in the body is commonly used to assess neutron doses after criticality accidents. However, the (24)Na distribution is not uniform owing to the interaction with the human body. In this study, we experimentally evaluated the (24)Na distribution in a PMMA water phantom and 60 polyethylene vials. The vials were analyzed to evaluate the sodium activation distribution in the PMMA water phantom by employing a correction factor.

RAPID MONITORING OF INTERNAL CONTAMINATION USING A MOBILE RADIOBIOASSAY LABORATORY FOLLOWING RADIATION EMERGENCIES

In any radiation emergency, it may be necessary to monitor large numbers of people for internal contamination resulting from inhalation/ingestion of radionuclides released from the accident. The National Radiation Emergency Medical Center of the Korea Institute of Radiological and Medical Sciences constructed a mobile radiobioassay laboratory for rapid field-based monitoring of internal contamination. The main features of the mobile laboratory were designed and the results of performance were tested for rapid monitoring in this paper. We found that maximum throughput for internal contamination monitoring using the whole body counter installed in the laboratory was about 200 people per day. The minimum detectable activities were estimated for the in-vivo and in-vivo radiobioassay systems in the mobile unit. This mobile unit will improve the population monitoring capabilities for internal contamination of individuals affected following nuclear or radiological emergencies.