Calculation and Application of the «Spectrum-Dose» Operator for a Scintillation Detection Unit Based on a Large-Volume Plastic Detector Used in Portal Radiation Installations

The article investigates the possibility of using the «spectrum-dose» operator to measure the ambient dose equivalent rate H(10) with a detection unit (DU) based on a plastic scintillator with an active volume of 11 liters, employed in various types of radiation portal systems. For this purpose, geometric and physical models of the DU were developed and validated in the FLUKA Monte Carlo simulation environment. Based on these models, a response matrix was calculated, representing a set of instrumental spectra obtained when the DU is irradiated with monoenergetic gamma radiation. Using the resulting response matrix, the «spectrum-dose» operator was calculated and implemented in an experimental DU prototype. The performance of the DU prototype incorporating the «spectrum-dose» operator was tested at the UDG-AT110 and UDG-AT130 gamma radiation reference dosimetry facilities (⁶⁰Co, ¹³⁷Cs, and ²⁴¹Am sources). Additionally, the DU was tested in a lowbackground chamber using a set of OSGIRT type reference point gamma sources (²²Na, ⁵⁴Mn, ⁶⁰Co, ⁸⁸Y, ¹⁰⁹Cd, ¹¹³Sn, ¹³⁷Cs, ¹³⁹Ce, ¹⁵²Eu, ²²⁸Th).
It was found that the difference between the ambient dose equivalent rate H(10) measured by the experimental DU prototype, based on the calculated «spectrum-dose» operator, and the reference values generated by the sources at the measurement point does not exceed 30%, provided that H(10) does not exceed 25 μSv/h. With minor hardware and software modifications to the DU, the upper measurement limit of H(10) can be extended to 40 μSv/h.