Man-Sievert

Another dose concept is that of the collective dose. It is based on the assumption that cancer is induced by a stochastic single process, independently of the dose rate and the dose fractionation, and it imphes that the detriment is the same whether one person receives 20 Sv or 20 000 persons receive 1 mSv each. In both cases the collective dose is 20 man sieverts (man Sv) and there should be a 100% probability of one disease of cancer. The collective dose concept is often apphed to assess the effect of the natural radiation background. At an average level of 3mSv/y, 0.015% of the population should die each year due to natural radiation. As the frequency of deaths by cancer is about 0.2% per year, it is not possible to confirm the collective dose concept by epidemiological investigations. 

The linear relationship between dose and effect, as illustrated by eqn. (18.4) and the line a in Figure 18.10, are based on the assumption that cancer induction is a stochastic single hit process independent of dose rate or dose fractionation. Thus the detriment to the population is die same whether one person receives 20 Sv, or 20 000 receive 1 mSv each. Using the dose-effect relation of (18.4) there will be a 100% chance of cancer in both cases. We can express this by saying that the collective (ffective dose is 20 man sieverts (manSv). The collective effective dose, is the sum of the effective doses to all n individuals ... 

For the whole of French NPPs the mean annual collective dose per unit has regularly decreased from 2.44 man. Sievert in 1991 to 1.59 man. Sievert in 1996. The objective for the next years is to continue this decrease to 1.2 man. Sievert in the year 2000. 

The former (non-SI) unit of dose equivalent was the roentgen equivalent man (rem), which was defined in the same way as the sievert but with the absorbed dose in rad thus, 1 rem = 10 2 Sv. 

Collective dose—The sum of the individual doses received in a given period of time by a specified population from exposure to a specified source of radiation. Collective dose is expressed in units such as man-rem and person-sievert. 

Roentgen equivalent man (rem) The amount of ionizing radiation of any type that produces the same damage to humans as 1 roentgen of radiation. One rem = 1 roentgen equivalent physical (rep)/relative biological effectiveness (RBE). In the latest nomenclature, 100 rem = 1 Sievert (Sv). 

S02(g) in the extraction of copper, rock-salt structure A crystal structure the same as that of a mineral form of sodium chloride, roentgen equivalent man rem The unit for reporting dose equivalent. See also sievert. root (of an equation) The solutions of the equation f(x) = 0. See also Appendix IE. root mean square speed c The square root of the average value of the squares of the speeds of the molecules in a sample. 

Two SI units refer to doses of radioactivity and these are used when calculating exposure levels for a particular source. The sievert (Sv) is the amount of radioactivity giving a dose in man equivalent to 1 gray (Gy) of v-rays 1 Gy = an energy absorption of 1 Jkg. The dose received in most biological experiments is a negligible fraction of the maximum permitted exposure limit. Conversion factors from older units are given in Table 35.3. 

Different types of radiation affect biological materials in different ways, so a different unit is needed to describe the dose necessary to produce an equivalent biological damage. Historically, this unit is the rem (roentgen-equivalent-man). The dose in rem is equal to the dose in rad multiplied by a quality factor, which varies with the type of radiation. For )3 -, y-, and X-ray radiation, the quality factor is 1 for neutrons, it is 2-11, depending upon the energy of the particle and for a-particles, the quality factor is 20. The SI unit for equivalent dose is the sievert (Sv), which is equivalent to 100 rem. 

Dj is the absorbed dose averaged over the tissue organ T, due to radiation R. Hj is measured in sieverts (Sv) 1 Sv = 1 J kg. The earlier, but similar concept was the rent (radiation equivalent man), where 1 Sv equaled 100 rem. Until 1990, Hj was called dose equivalent. Dj is measured in the units of gray (Gy). The summation is taken over all sources irradiating the target. 

Biological Effects and Dose Equivalence Radiation produces biological effects on the human body. Diffoent types of radiation produce effects at different rates. Dose equivalent or effective dose combines the amount of radiation absorbed and the medical effects for a type of radiation. Units of biological effect are Rems (roentgen equivalent man). The metric unit is sievert (Sv). For example, the effect produced by a dose of 1 R of X-rays is 1 rem. Some dose equivalents are much lower and measured in millirems (mrem). 

The rad is a unit of absorbed radiation dose in terms of energy actually deposited in the tissue. The rad is defined as an absorbed dose of 0.01 joules of energy per kilogram of tissue. The rem (radiation equivalent man) is the unit of human exposure and is a dose equivalent (DE). The international or SI unit for human exposure is the sievert, which is defined as equal to 100 rem [2]. It takes into account the biological effective of different types of radiation. The biologically effective dose in rems, is the radiation dose in rads multiplied by a quality factor, which is an assessment of the effectiveness of that particular type and energy of radiation. 

Roentgen equivalent man (Rem) is the dosage of any ionizing radiation that will cause biological injury to human tissue equal to the injury caused by one roentgen of x-ray or gamma ray dosage with one rem equivalent to 0.01 Sievert (Sv)... 

REM Derived from Roentgen Equivalent Man. This is the unit of dose equivalence, and is intended to equate the biological effectiveness of different types of radiation. Rem = RAD X QUALITY FACTOR. (See also SIEVERT)... 

Because absorbed radiation creates different degrees of damage in different tissues absorbed doses of radiation are often expressed in rem (rads equivalent man) to allow for such differences. The rem has now been replaced officially by the Sievert (100 rem = I Sievert). 

---