Chernobyl Liquidators' Health
as a Psycho-Social Trauma
2.4.3. External gamma-irradiation
22.214.171.124. Units of irradiation dose
In the works about Chernobyl and its health impact, the irradiation doses of the affected are reported in different units: Roentgens R (the exposure dose), rads and Grays Gy (the absorbed dose), and Sieverts Sv and rems (the equivalent dose; it directly characterises probable medical-biological impact). Before starting to deal with the radiation circumstances of the Chernobyl Disaster, I want to discuss the ways of the dose (and, hence, its rate) representation, using (Murray 1993: 193195; Sivintsev 1991: 2127; Averyanova et al. 1992: 41, 4551), and to choose the one adequate to the purpose of this study.
From my experience and observations in the zone, I can say that the most widely spread instrument used to measure external gamma-irradiation dose of the liquidators (except for special teams of professionals) was Soviet military instrument DP-5 in several modifications. It measures the exposure dose rate (or RA-level, in military terms) in Roentgens per hour or milliRoentgens per hour. With this (or similar) instrument, the ideal procedure to obtain the personal irradiation dose consists of:
the measurement of the RA-level at the exact place where the person is staying/working (at the height of 0.81 m; this standard is defined, in particular, by location of the most sensitive part of the standing person abdominal and pelvic areas (Antonov 1987: 7));
the measurement of time of the stay/work at this place, and
defining by multiplying the two values the exposure dose E (in Roentgens or milliRoentgens).
If the person during this time had no external protection from gamma-irradiation, all the radiation the person had been exposed to, has penetrated into the body and absorbed by it. In this case the absorbed dose (A) in centiGy (or rad) is numerically equal to exposure dose in R. If the person during the exposure had external protection from gamma-irradiation (say, wore leaded overalls, or worked inside a light armoured vehicle (the vehicle's coefficient of external gamma-radiation reduction k=3), the absorbed dose of the person is equal to the exposure dose, reduced by the factor of k.
Biological effect of the absorbed dose upon the human system or its organs is assessed by value of the (biologically, or medically) equivalent dose B. It is a product of the absorbed dose on the quality factor f, which reflects the injuring ability of the given type of radiation. For gamma-radiation f=1. Further, if (1) the whole body was irradiated (2) uniformly then no further corrections for the relative risk of the separate organs and tissues should be made, and the factor r, reflecting this circumstance, is equal to 1: r=1 (Averyanova et al. 1992: 51). Upon these preconditions, numerical values of the (physically) absorbed dose (in cantiGy, or in rad) and those of the (biologically, or medically) equivalent dose (in cantiSv, or in rem) are equal.
Summing it up:
1 R of the exposure dose E >>> (if factor
of shielding k=1) >>>
0.01Gy = 1 cGy, or 1 rad of the (physically) absorbed dose A >>>
(if factors of (radiation type) quality f=1
and of (relative tissue/organ's) risk r=1) >>>
0.01 Sv = 1 cSv, or 1 rem of the (biologically, or medically)
equivalent dose B
This set of assumptions is typically implied (but, as a rule, not mentioned explicitly), when the degree of irradiation dose is characterised in medical and other Chernobyl-related studies. However, except for a few cases, whatever quantities and units are mentioned, the actual data refers to the exposure dose in Roentgens. Thus, in order to standardise the way of the dose representation, further in this paper I will (1) denote the units of the irradiation dose used in the study referred to, and (2) simultaneously write an equivalent quantity of Roentgens of the exposure dose they originate from (say, 25 cGy (25 R)).
Then, if the source of the exposure dose was so-called officially documented doses which proved to be extremely inaccurate and, moreover, heavily distorted12 (for details see (Mirnyi 1998 (Appendix 1)) I will use an asterisk (*25 R) to indicate that this figure, albeit reported, is not reliable and shall not be regarded as trustworthy.
Design by: M.Opalev
Studio ARWIS Kharkov, 2001