Title: Meaning of the Confidence Index displayed on Radionuclide Identification Devices and Spectrometric Personal Radiation Detectors
Language: English
Authors: Siebenhofer, Bernhard 
Qualification level: Diploma
Keywords: RID - SPRD - Nucleare Sicherheit - Konfidenz Index
RID - SPRD - Nuclear Security - Confidence Index
Advisor: Böck, Helmuth 
Assisting Advisor: Arlt, Rolf 
Issue Date: 2009
Number of Pages: 86
Qualification level: Diploma
Um adäquate Gegenmaßnahmen bei einem Strahlungsalarm an einem Grenzübergang treffen zu können werden von den Grenzbeamten unter anderem Messungen mit einem Radionuclide Identification Device (RID) durchgeführt. Nach einer voreingestellten Messdauer zeigen diese Geräte das gemessene Radioisotop, seine Kategorie und ein Maß für die Genauigkeit der Messung, den Confidence Index (CI), an. Dieser CI wird vom Messgerät berechnet und hängt in einer komplexen Weise von Statistik, Detektor Parametern, Art der Quelle, Messgeometrie, Abschirmung und von der Methode der Identifikation ab. Der CI erreicht Werte zwischen '0' und '10',

To decide on the adequate response after a radiation alarm at a border crossing point, the frontline officer (FLO), amongst other, performs a measurement with an radionuclide identification device (RID).
These devices show after a preset measurement time the isotope, its category and a confidence index (CI), which is calculated by the instrument software. Its value depends in a complex manner on statistics, detector parameters, type of source, measurement geometry, shielding, and last not least the method used for radionuclide identification.
The CI reaches values from '0' to '10', 0 to 100% or low-medium-high and is the only indicator the user has, with respect to the weight to give to the indication of the RID.
On the other hand, the only reliable measure of the correctness of a radionuclide identification result is the hitrate of a series of many repeated measurements, made under the same conditions. The hitrate (HR) is defined as the percentage of correct indications of the series of measurements. If, for instance, 100 measurements are made and 90 times the correct radionuclide is indicated, the hitrate equals 90%. This hitrate can not be seen by the user in the field, but only determined in automated measurement series in a test laboratory. To be a valid indicator of the correctness of an identification result, the CI must correlate with the hitrate. In this work, this is investigated for two instruments, a Radionuclide Identification Device (RID) and a Spectrometric Personal Radiation Detector (SPRD). This interrelation of the confidence index and the hitrate is needed to understand, how reliable the conclusions which are drawn from the value of the CI are.
URI: https://resolver.obvsg.at/urn:nbn:at:at-ubtuw:1-30582
Library ID: AC07452372
Organisation: E141 - Atominstitut 
Publication Type: Thesis
Appears in Collections:Thesis

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