Radioactivity measurement of the food imported from Japan after 4 years of Fukushima Daiichi disaster using high purity germanium (HPGe) detector

Abstract

After four years of Fukushima Daiichi Disaster, the potential risk of contaminated food imported from Japan is still existed, especially the concern of contaminated water released from the Fukushima nuclear power plant to the Pacific Ocean. The most significant radionuclides contained in contaminated food are; Iodine-131 (I-131), Caesium-134 (Cs-134), and Caesium-137 (Cs-137). According to the Codex Alimentarius Commission in the Guidelines Levels for Radionuclides in Foods, the limit of I-131 is 100 Bq/kg and 1000 Bq/kg for Cs-134 & Cs-137 for general food and infant food. However, the guidelines level of infant food should be adjusted to a stricter limit (e.g. 50 Bq/kg in Japan) since the high amount of infant food or milk powder will be consumed by the babies if they continued to use the food imported from Japan. The food imported from Japan to Hong Kong will be initially screened by Hand-held survey meters and samples will be taken from every consignment by NaI detector system. The sample will be tested by High Purity Germanium (HPGe) Detector only if the samples failed the previous screening or randomly checked. However, the radioactivity level in food is very low. Hence a high sensitivity and high resolution detector, HPGe detector, would be a better choice for food screening if the radiation level is very low, e.g. below 100 Bq/kg. In this study, several different food varieties which imported from Japan, with comparison to the local food or food imported from other country, are collected, processed and data on each sample analyzed using a HPGe Detector. The purpose is to establish whether these levels and subsequently their annual effective doses from the intake of these radionuclides were within the acceptable limits. The performance of HPGe detector would be reviewed and analyzed. This study concluded that the radionuclide activities of the food samples are all within acceptable radiation levels. However, the guideline level of infant food should be adjusted to a lower alert level because the babies may have chance to ingest contaminated milk powder or infant foods imported from Japan. Based on principal of “As Low As Reasonably Achievable”, the guideline level of infant food should be adjusted to 10 Bq/kg for I-131 and 190 Bq/kg for Cs-134 + Cs-137. Due to the long half-lives of Cs-137 (30.17 years), the risk of radioactive contaminated food is still existed and it should not be neglected in the future.published_or_final_versionDiagnostic RadiologyMasterMaster of Medical Science