Biological Effects of Ionization - hdbk110997

DOE-HDBK-1109-97

Radiological Safety Training for Radiation-Producing (X-Ray) Devices

Student's Guide

BIOLOGICAL EFFECTS OF IONIZATION

X-rays can penetrate into the human body and ionize atoms. This process creates radicals that

can break or modify chemical bonds within critical biological molecules. This can cause cell

injury, cell death, and may be the cause of radiation-induced cancer. The biological effect of

radiation depends on several factors (discussed below) including the dose and dose rate.

In some cases, altered cells are able to repair the damage. However, in other cases, the effects

are passed to daughter cells through cell division and after several divisions can result in a

group of cells with altered characteristics. These cells may result in tumor or cancer

development. If enough cells in a body organ are injured or altered, the functioning of the

organ can be impaired.

FACTORS THAT DETERMINE BIOLOGICAL EFFECTS

Several factors contribute to the biological effects of X-ray exposure, including:

Dose rate.

Total dose received.

Energy of the radiation.

Area of the body exposed.

Individual sensitivity.

Cell sensitivity.

Dose Rate.

The rate of dose delivery is commonly categorized as acute or chronic. An acute dose is

received in a short period (seconds to days); a chronic dose is received over a longer

period (months to years).

For the same total dose, an acute dose is more damaging than a chronic dose. It is

believed that this effect is due to the ability of cells to repair damage over time. With an

acute dose, a cell may receive many "hits" without sufficient time to repair damage.