32.2 Biological effects of ionizing radiation  (Page 3/19)

The RBEs given in [link] are approximate, but they yield certain insights. For example, the eyes are more sensitive to radiation, because the cells of the lens do not repair themselves. Neutrons cause more damage than $\gamma$ rays, although both are neutral and have large ranges, because neutrons often cause secondary radiation when they are captured. Note that the RBEs are 1 for higher-energy $\beta$ s, $\gamma$ s, and x-rays, three of the most common types of radiation. For those types of radiation, the numerical values of the dose in rem and rad are identical. For example, 1 rad of $\gamma$ radiation is also 1 rem. For that reason, rads are still widely quoted rather than rem. [link] summarizes the units that are used for radiation.

A high level of activity doesn’t mean much if a person is far away from the source. The activity $R$ of a source depends upon the quantity of material (kg) as well as the half-life. A short half-life will produce many more disintegrations per second. Recall that $R=\frac{\text{0.693}N}{t_{1/2}}$ . Also, the activity decreases exponentially, which is seen in the equation $R=R_0{e}^{-\mathrm{\lambda t}}$ .

The large-scale effects of radiation on humans can be divided into two categories: immediate effects and long-term effects. [link] gives the immediate effects of whole-body exposures received in less than one day. If the radiation exposure is spread out over more time, greater doses are needed to cause the effects listed. This is due to the body’s ability to partially repair the damage. Any dose less than 100 mSv (10 rem) is called a low dose    , 0.1 Sv to 1 Sv (10 to 100 rem) is called a moderate dose    , and anything greater than 1 Sv (100 rem) is called a high dose    . There is no known way to determine after the fact if a person has been exposed to less than 10 mSv.