An Example of Abnormal Glow Curves Identification in Personnel Thermoluminescent Dosimetry

Description

The personal Dosimetry Service Seibersdorf analyses monthly a large number of thermoluminescent dosemeters. The dosemeters consist of LiF chips and the readout is carried out with an automated Harshaw 8800 reader system. In rare cases the luminescent glow curves of the routine analyse do not have the expected form. They have an abnormal shape as a result of external chemical contamination, hardware problems, poor heat transfer, etc. It is therefore interesting to investigate the reasons for the irregularity of these curves. An algorithm for the investigation of the routine curves was developed. It is based on the fact that that the shape of an abnormal glow curve differs from the shape of a normal one. In order to avoid the influence of the magnitude of the dose, the glow curves are normalised with respect to the total area. Each measured curve is divided into four regions of interest (ROIs) and the relationships between these different ROIs are analysed. Only few criteria combining all four ROIs are necessary to distinguish between regular and irregular glow curves. This algorithm was tested for its effective application in the routine service. An interesting type of abnormal glow curves in the routine service was found. Some dosemeters of a certain client, a steel industry, exhibit a glow curve with an untypical form and very high signals. In those dosemeters were discovered a possible chemical contamination in form of a powder, that interferes in the dosimetric signal. A quantitative analyse of that powder was made with ICP-AES after Multiwave dissolution. Elements like Aluminium, Barium, Calcium and others were found. Such elements are used in different combinations as thermoluminescent materials. In order to avoid the influence of the powder in the signal, the dosemeters ought to be cleaned with methanol before the readout. The cleaning can not always keep away from the interference signal. Additionally investigation are carried out at the moment in order to identify the process of signal generation in detail.

Period	24 Jun 2001 → 27 Jun 2001
Event title	6th Symposium on Instrumental Analysis
Event type	Other
Degree of Recognition	International