Method of measuring hydrogen concentration of radioactive metallic material

A method of measuring a concentration of hydrogen contained in a radioactive test object of metallic material, said method comprising the steps of:

• positioning an electromagnetic acoustic transducer (EMAT) adjacent to the object, the EMAT including a magnet that creates a static magnetic field and a coil that creates a magnetic field variable with time;
• supplying a radio-frequency current to the coil of the EMAT, thereby generating an ultrasonic wave that is reflected for multiple reflections by opposite surfaces of the object;
• changing a frequency of the radio-frequency current, thereby finding a resonance frequency that makes the object exhibit electromagnetic acoustic resonance by means of a detector connected to the coil of the EMAT;
• and
• determining the concentration of hydrogen contained in the object on the basis of an experimentally determined relation between a numerical value and the hydrogen concentration of the object, the numerical value being calculated by using an expression including the resonance frequency as a variable,
• wherein the object is formed from a rolled material, and the numerical value is calculated by dividing a difference between ft and fr by a sum of ft and fr or an average of ft and fr, where fr is a resonance frequency when a direction of an amplitude of a transverse ultrasonic wave generated by the EMAT is the same as the rolling direction of the rolled material, and ft is a resonance frequency when a direction of an amplitude of a transverse ultrasonic wave generated by the EMAT is perpendicular to the rolling direction of the rolled material.