Assessing the Effect of Laboratory Environment on Sample Contamination for I-129 Accelerator Mass Spectrometry.

Environmental contaminations of I were continuously monitored in various sample preparation rooms for accelerator mass spectrometry at the University of Tsukuba. Monitoring of I was performed in the rooms used for the treatment of samples in the past, in order to compare with the results obtained in the sample preparation rooms. Ambient levels of atmospheric I in each room were estimated from the measured concentrations in the alkali trap solutions. This article reports the results of one year of monitoring the temporal changes of stable iodine (I) and I contamination rates in the alkali trap solutions. It was found that I contamination rates were lower than approximately 10 atoms cm day in the rooms where ether no samples or only samples with environmental background levels of I were handled. Values from 10 to 10 atoms cm day were recorded in another room where environmental samples, such as the samples derived from nuclear power plant accidents, were treated. Higher levels of I, ranging from 10 to 10 atoms cm day, were recorded in rooms used for treating neutron-activated iodine. The experimental results show that the I level depended on the I sample-preparation histories for the respective rooms. It is possible to estimate the I contamination risk from the atmosphere to the samples by knowing the I level in the preparation room.