Minimum detection limit of the Sodium Iodide (NaI) field gamma spectrometer instrument in thyroid radioactivity intake measurement

Abstract

Radioisotopes have a wide range application in industry, research and medicine but they can cause a large scale disaster. The latest incident is the Tohoku earthquake and tsunami on March 11, 2011. The Fukushima Daiichi Nuclear Power Plant suffered a series of equipment failure, nuclear meltdown and release of radioactive materials in the environment. Considering the effects of nuclear accident, released radionuclides once ingested by a person may pose health risks. This study assess NaI Inspector 1000 as portable thyroid counter to measure the radioactivity of a person's thyroid. The fabricated gel samples to represent thyroid were prepared by the used of Cs -137 and I – 131 in liquid form as the main material and the superabsorbent polymer. The controlled variables are the amount of volume of Cs – 137 and I -131 used which is 30ml, 35ml and 40ml with slush powder and the distance between the detector. The actual activity of the samples was compared to the detection of the NaI Detector to determine the efficiency of the detector in every activity varying in distance. The minimum detection limit of NaI detector was determined by varying in distance. Results showed that the samples namely Cs-137 and I-131 didn’t reach the contamination limit set by the Philippine Nuclear Research Institute (PNRI) but the performance of the fabricated samples are comparable to the limit for the screening and field measurement.