An example of abnormal glow curves identification in personnel thermoluminescent dosimetry

The personal Dosimetry Service Seibersdorf analyses monthly a large number of thermoluminescent dosimeters (TLD). The dosimeters consist of LiF chips, and the readout is carried out with an automated Harshaw 8800 reader system. In some cases, the luminescent glow curves of the routine analysis do not have the expected form as a result of external chemical contamination, hardware problems, poor heat transfer, etc. It is therefore necessary 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 the shape of an abnormal glow curve differs from the shape of a normal one. An interesting type of abnormal glow curves in the routine service was found. Some dosimeters of a certain client, a steel industry, exhibit glow curves with an untypical shape and very high signals. In those dosimeters, a possible chemical contamination in the form of a powder was discovered, which interferes with the dosimetric signal. A quantitative analysis of that powder was made by means of inductively coupled plasma emission spectroscopy (ICP-OES) after microwave dissolution. Elements like aluminium, barium, calcium and others were found. Such elements are used in different combinations as thermoluminescent materials.