Radiation dosimeters containing thin KCl:Eu2+ storage phosphors for quantifying andor verifying the dose of radiation applied during radiation therapy. The interface 61 is designed and arranged with respect to the waveguide 60 such that as the ultrasonic wave propagates along the waveguide 60, each portion of the ultrasonic wave is transmitted into the propagation medium portion 3 through the interface 61 and then converged toward a predetermined convergence point. If the reception quality of the diversity reception is equivalent to the reception quality of the array antenna reception, then the calibration of the array receiving unit is carried out while implementing the diversity reception so as to obtain the correction amounts of the amplitude fluctuation and the phase shift of the array receiving unit.