Proof of concept: Emergency dosimetry in a realistic irradiation scenario using fortuitous dosimeters.

In 2002 a radiological incident occurred in Cochabamba, Bolivia, in which 55 passengers were exposed to ionizing radiation due to a malfunction of an industrial Ir-192 γ-radiography source, which was incidentally transported for repairs as cargo on a passenger bus. The International Atomic Energy Agency (IAEA) reconstructed this incident with a field experiment using TLDs to estimate the personal dose of the bus passengers and workers who handled the source [1]. In the past decade new physical methods for emergency dosimetry have emerged, such as optically stimulated luminescence (OSL) and thermally stimulated luminescence (TL) of so-called fortuitous dosimeters, which can be applied to determine the absorbed dose. If no personal dosimeter is available, mobile phones or other ubiquitous personal belongings, which are carried on or close to the body, can be used as accident dosimeters. This has been investigated by different research groups [2-7]. So far, these investigations were only carried out under laboratory conditions. Within the framework of a European FP7 security research project CATO (CBRN Architecture, Technologies and Operational Procedures) a repetition of the field experiment with a similar bus was carried out, which simulates the Bolivian radiological incident. In this field test, physical methods of retrospective dosimetry were tested and verified in a realistic irradiation scenario using mobile phones as emergency dosimeters, attached to water canisters and anthropomorphic phantoms. The results were compared to measured dose values from dosimeters placed in the mobile phone, TLDs, OSLDs and readouts of electronic personal dosimeters (EPD) fixed close to the mobile phones. The proof of concept affirmed the usability of the tested emergency dosimeter but also demonstrated the limitation of the proposed method. In addition, the experimental values were compared to results of radiation transport calculations using a Monte Carlo code, which simulated the exposure conditions of the emergency dosimeters in the bus on a sufficiently detailed level

Evaluation of physical retrospective dosimetry methods in a realistic accident scenario: Results of a field test.

The radiological incident in Cochabamba (Bolivia, 2002), where members of the general public where exposed to an unshielded Ir-192 radiation source whilst traveling on a bus was replicated here in an attempt to asses and evaluate emerging retrospective dosimetry methodologies using objects of daily life, that are either carried on or close to the human body or can be found in the vicinity of an individual. For this purpose an accidental exposure was simulated under controlled conditions in a secured area and an unshielded radioactive source was placed in the cargo compartment of a bus resembling a Radiological Exposure Device (RED). Water canisters and anthropomorphic phantoms were placed at selected seats on the bus and equipped with personal objects (mobile phones, chip cards) that had reference dosimeters attached to them. At one seat position, additional salt dosimeters and dental ceramics in the phantom were also tested. Two types of 8 h exposures were conducted: one with a source activity similar to the one in Cochabamba (0.65 TBq) and one with a stronger source (1.5 TBq) in order to have more samples with absorbed doses above the detection limit of the different methods. For 43 out of 61 resistor and glass samples from mobile phones, measured doses agreed within error limits with reference doses, but for some materials more research is needed for a more reliable application. In 13 cases outliers with a significant dose over- or underestimation were observed, 10 of these could be identified by combining the results of at least three dose assays. The field test thus evaluated the potential and limitation of retrospective dosimetry using personal objects and demonstrated the importance of using a multi-dosimeter approach to increase robustness of the method