Quality control by autoradiography for the thin layer activation technique

Abstract

In measurements of wearing and corrosion based on the thin layer activation technique; a part is locally activated by charged particles and placed in its working context and wear/corrosion is calculated precisely and continuously by measuring the removed activity. It is essential in the method to know the exact position of the activated zone because the wearing ratio may vary up to 50% for a shift of only 2 mm. So we do need a control procedure after irradiation. Our quality control system of irradiated parts is based on autoradiography. The films are chosen according to the type of emission of the source: high resolution films as Structurix D4 are used with beta sources whereas pure gamma sources need more sensitive films as Structurix D7 with lead filters. The finite range of the rays generates blur which can be partly corrected by digitizing and deconvoluting the image using IRIS software. The exposure time is empirically determined for each radioisotope and linked to the activity, in order to optimise contrast and resolution. The position control is mainly based on a system of detailed marks and cuts made under inactinic light; we can obtain a basic precision of approximately one tenth of millimetre. Routine applications of this control methodology confirm its simplicity, precision, speed and its relative low cost.