Abstract
The paper investigates the characteristics of the chemical Fricke dosimeter (with the standard composition (D1), without NaCl addition to the solution (D2), without NaCl but with a tenfold increased concentration of Fe2+ (D3)) under continuous and pulsed irradiation with an ultra-high dose rate of the BARS-6 reactor with unshielded metallic cores. The dosimeter radiosensitivity had a linear dependence on the gamma neutron radiation dose in a range of 25 to 750 Gy and was respectively 1.96 ± 0.05 μGy–1 (D1), 2.04 ± 0.05 μGy–1 (D2), and 2.08 ± 0.5 μGy–1 (D3) in the continuous irradiation mode, and 1.24 ± 0.05 μGy–1, 2.00 ± 0.05 μGy–1, and 1.94 ± 0.05 μGy–1 in the pulsed irradiation mode. This makes ≈ 60% of their sensitivity to the 60Со gamma radiation (3.40 ± 0.02 μGy–1), and 36%, 1.6 times as less, for a standard Fricke dosimeter irradiated in the pulsed mode. The experimental value of the radiation chemical yield, Gn(Fe3+), for all solution modifications and both irradiation modes varied slightly and was 0.84 ± 0.11 μM/J on the average, except for the standard solution in the pulsed mode (0.66 ± 0.07 μM/J). The neutron doses determined by chemical and activation dosimeters coincided within the error limits, but the chemical dosimeter readings were systematically higher, by about 20%. Therefore, in the fission spectrum neutron dose rate range of 0.4 to 7×108 Gy/min, there is no dose rate effect both in the standard Fricke dosimeter version (without NaCl) and in the modified version, which makes it possible to use modified Fricke dosimeters to assess the physical and dosimetry characteristics of mixed gamma neutron radiation beams.
Highlights
At the present time, practically all types of electromagnetic and ionizing radiation are used in medicine, in oncology
This leads to new dosimetry tasks which are addressed, along with ionization techniques, with the extensive use of methods based on using liquid and solid scintillators, semi-conductors, and luminescent and chemical dosimeters. The latter use chemical radiation-induced changes taking place in certain substances. One of such dosimeters is the Fricke chemical dosimeter used in gamma radiation and electron dosimetry in a dose range of 0.05 to 2000 Gy and a dose rate range of up to 250 Gy/min (Sokolova 1972, Pikaev 1975)
A standard solution without NaCl addition was prepared for the BARS-6 pulsed reactor irradiation, since its presence can reduce the Fe3+ ion yield, G(Fe3+) (Pikaev et al 1963, Pikaev 1975, Klassen et al 1999), and a modified Fricke dosimeter was used for the dosimetry of radiation with an ultrahigh dose rate (~ 1×106 Gy/min), in which, apart from excluding NaCl from the composition, the Fe2+ iron concentration was increased tenfold, to 1×10–2 M
Summary
Practically all types of electromagnetic and ionizing radiation are used in medicine, in oncology. There is a growing interest in investigating pulse neutron impacts explained both by fundamental aspects and by certain practical tasks of current concern In fundamental terms, this is exploration of fast biological and radiobiological processes and determination of the RBE for radiations with a high and ultrahigh dose rate (Vazhenin et al 2007, Koryakina 2014). The practical use of radiations with an ultrahigh dose rate, including pulse radiations, to increase the efficiency of beam therapy, the so-called flash therapy, is considered theoretically (Symonds and Jones 2019, Jin et al 2020, Marlen et al 2020) This leads to new dosimetry tasks which are addressed, along with ionization techniques, with the extensive use of methods based on using liquid and solid scintillators, semi-conductors, and luminescent and chemical dosimeters. One of such dosimeters is the Fricke chemical dosimeter used in gamma radiation and electron dosimetry in a dose range of 0.05 to 2000 Gy and a dose rate range of up to 250 Gy/min (Sokolova 1972, Pikaev 1975)
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