Non-contact Position Measuring Technique by Gamma-Ray Signals for a Moving Object with a Radioisotope Source Attached

Abstract

The position of a moving object can be measured with avoiding contact in real time by observing intensity from a gamma-ray source attached to the object. Experimental position measurements are carried out for linear (l-dimensional) and rotary (2-dimensional) motion, and the results obtained are compared with theoretically calculated ones. The position measurements in 3-dimensional motion are also theoretically deduced by the aid of computer simulation. On this occasion, the statistical characteristics of the gamma-ray count rate observed will be varied with time. The dynamic error in the position measurement increases with increasing velocity of the object. The statistical error increases in comparison with the stationary one when the object is closing up to a detector, and decreases in the opposite motion. The system with short time constant permits quick response for change of the object position, but increases statistical error. In the experimental 1-dimensional position measurement, use of a 3.4 MBq ²⁴¹Am gamma-ray source with a time constant of 94ms, an object velocity below 100mm/s and a detector-to-source distance below 500mm gave dynamic and statistical (1σ) errors less than ±10 and ±25mm, respectively.