Environmental Engineering FOURTH EDITION

Radioactive Waste 321

Table 16-4. Average Annual Dose Equivalent of Ionizing Radiation to a Member

of the U.S. Populationa

Source of radiation

Dose equivalent, Effective dose

mSv equivalent, mSv

Natural

Radon

Cosmic radiation

Terrestrial

Internal

24 (2400) 2.0

0.27 (27) 0.27

0.28 (28) 0.28

0.39 (39) 0.39

Total 24.94 3.0

Medical: diagnostic X-ray 0.39 (39) 0.39

Medical: nuclear medicine 0.14 (14) 0.14

Anthropogenic

Medical: consumer products 0.10 (10) 0.1

Occupational 0.009 (0.9) to.1

Nuclear fuel cycle tO.O1 ((1.0) to. 1

Fallout <0.01 (t1.0) <o. 1

Miscellaneous <0.01 ((1.0) to. 1

Total 0.67 0.67

‘From A. Upton et al. (Eds.), National Academy of Sciences, Health Effects of Exposure to Luw Levels

of Ionizing Radiation: BEIR V, National Academy Press, Washington, DC, 1990.

Ionization chambers consist of a pair of charged electrodes that collect ions formed

within their respective electric fields. Ionization chambers can measure dose or dose

rate because they provide an indirect representation of the energy deposited in the

chamber.

Photographicjlm darkens on exposure to ionizing radiation and is an indicator of

the presence of radioactivity. Film is often used for determining personnel exposure

and making other dose measurements for which a record of dose accumulated over a

period of time is necessary, or for which a permanent record is required.

Thermoluminescent detectors (TLD) are crystals, such as NaI, that can be excited

to high electronic energy levels by ionizing radiation. The excitation energy is then

released as a short burst or flash of light, which can be detected by a photocell or

photomultiplier. TLD systems are replacing photographic film because they are more

sensitive arid consistent. Liquid scintillators, organic phosphors operating on the same

principle as TLDs, are used in biochemical applications.

HEALTH EFFECTS

When a? and ,3 particles, and y radiation, interact with living tissue they transfer
energy to the receiving material through a series of collisions with its atoms or nuclei.