METHOD FOR MEASURING RADIOACTIVE MATTER OF AN INGOT UTILIZING A NAI GAMMA SCINTILLATOR

PURPOSE: A method using a Nal measuring device for measuring radioactive substances in an ingot is provided to measure gamma rays with respect to a U-235 among uranium isotopes by a gamma spectroscopy method with the Nal measuring device, thereby rapidly determining the existence of radioactivity radiated from whole uranium. CONSTITUTION: A method for measuring radioactive substances in an ingot is as follows. An ingot of 1 to 5cm thickness for metal wastes generated when treating or manufacturing a nuclear fuel is manufactured. The ingot is arranged in the inside an internal shielding portion surrounding a probe portion of a Nal measuring device. The lead of 50 mm thickness is installed on a wall surface and the upper part of the internal shielding portion. The lower part of the internal shielding portion is received in the inside of an outer shielding portion. Gamma rays emitted from the ingot with respect to a U-235 among uranium isotopes are measured by using a gamma spectroscopy method with the Nal measuring device(S10). A self-absorption correction depending on medium density using a MCNP(Monte Carlo N-Particle) computer code and a measuring device correction by a certified reference material are performed and the radioactivity and mass of the U-235 are quantized and a whole uranium weight is calculated depending on the enrichment of the U-235 determined by the source of the metal wastes(S30). [Reference numerals] (AA) Formula for calculating whole specific radioactivity of uranium; (S10) Measuring U-235(185.72keV); (S20) Quantizing amount of the U-235(Specific radioactivity = 80,000 Bq/g); (S30) Calculating whole uranium weight; (S40) Calculating whole radioactivity of the uranium