There are three questions arise in radioactivity measurements: (1) Dose the measured value originate from the radioactivity being present in the sample? (2) Is the measurement procedure suitable for the intended measurement purpose with respect to the requirements? (3) What is a range of values fairly sure our true value lies in with a specified probability? These three questions are answered by determining characteristic limits (decision threshold, detection limit and limits of the coverage interval), which are widely used as part of quality assurance in radioactivity measurements. In the past, numerous papers have focused on the questions in different ways, and have drawn a variety of conclusions about the meaning of the different characteristic limits using various terms and symbols. In recent years, substantial efforts were made in order to obtain a systematic and unified way to calculate and express these limits. As a result, the ISO 11929 Series which specify a procedure for calculation of the characteristic limits have been developed. This paper is focused on the calculations of characteristic limits for noble gas monitor (NGM204 monitor) that offers the continuous measurements of radioactive noble gases discharged from the stacks of the HANARO reactor facility. The calculations are based on the standard ISO 11929 as well as the traditional formulas provided by NUREG 1576, ANSI N42-18, ANSI N42-17 and DIN 25482. A comparison is made among the results obtained from the formulas given in each literature.

The effects of noble gas (such as helium, neon, argon, krypton, and xenon) on the sonolytic decomposition of water and 2-methyl-2-propanol(t-butanol) with 200 kHz high power ultrasound were investigated. The physical properties of the noble gas have an effect on the formation rate of products (H2O2, H2, O2) and the decomposition rate on the sonolytic decomposition of water. The pyrolysis products, such as methane, ethane, ethylene, and acetylene are formed during the sonolytic decomposition of t-butanol. From the estimation of the ratio [C2H4 + C2H2] / [C2H6], the cavitation temperature would be varied by the used noble gas. In all cases for the sonolytic decomposition of water, t-butanol, and diethyl phthalate, the decomposition rates were xenon > krypton > argon > neon > helium with a significant difference and were closely correlated with the formation rate of OH radical and high temperature inside the cavitation bubble under each noble gas.