Present Status of Operational Dosimetry of Pulsed Photon Radiation

Introduction: With the increasing use of pulsed photon radiation in medical , industrial and security sectors in recent years, it has become necessary to reevaluate the properties of the radiation protection equipment in-use for measuring the operational quantities of external dosimetry. This work will elaborate on the limitations of various measuring equipment when measuring pulsed X-ray beams of the order of milliseconds down to a few femtoseconds, coupled with high dose rates produced by the pulsed source. Analysis of the current methods and equipment utilized in the inspection and survey of pulsed radiation facilities present a poor picture of deficiency and lack in measurement accuracy. This study will focus on the current problems and challenges in the measurement of pulsed fields and will put in question the effectiveness of dose rate measurements for this modality of photon radiation.

Methods: A thorough literature review that includes comparison and performance evaluation of various types of dosimeters will be presented. Specifically, the review will focus on different electronic dosemeters and available ionization chamber based survey meters from different vendors. In addition, this study will present results obtained using the Ram Ion (Rotem Industries) ionization chamber survey meter, when exposed to different X-ray flash generators with reference to the passive thermoluminescence dosimeters (TLD-100H).

Results: The measurements showed good agreement (deviation lies within 10%), with the TLD used as a reference. The calculated average dose per pulse is in good agreement with the X-ray flash generators manufacturer declared data. No energy compensation was needed, as the Ram Ion has relatively flat energy response. Thus, the dose per pulse remains accurate for different energies of the X-ray source.

Conclusion: An extension of the present work is being planned, to assess the response of the various detectors in use when surveying interventional radiology rooms and medical linear accelerators in Israel, and , if necessary, to propose a proper modification of the traditional ways of performing radiation surveys. The need of calibration in reference pulsed fields in standard accredited laboratories will be emphasized.

Reference:

Schmidt, C. et al. Current problems in the field of radiation protection technique - Use of Active Personal Dosimeters (APD) in pulsed radiation fields. Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU) (2009).
Klammer, J., Roth, J. and Hupe, O. Novel reference radiation field for pulsed photon radiation installed at PTB. Radiat. Prot. Dosim. 151(3), 478-482 (2012).
Ginzburg, D. Ionisation Chamber for Measurement of Pulsed Photon Radiation Fields, Radiat. Prot. Dosim. 174(3):297-301.
International Electrotechnical Commission. Radiation protection instrumentation—Electronic counting dosemeters for pulsed fields of ionizing radiation. Technical specification IEC 62743, Geneva (2012).