• When a radioactive nucleus emits beta particles, these particles ionize the gas in the instrument, which registers the ionization by indicating that an electric current has passed between two electrodes. • Another measuring device, called a scintillation scintillation counter counter , has a phosphor that emits a unit of light when a beta particle or gamma ray strikes it. • Intensity is recorded in counts/min or counts/s. 17
Detecting Nuclear Radiation Ionizing radiation 18
Characteristics of Nuclear Radiation Figure 9-6 Penetration of radioactive emissions . 19
Radiation Dosimetry • Although alpha particles cause more damage than X-rays or gamma radiation, they have very low penetrating power and cannot pass through skin. • Consequently alpha particles are not harmful to humans or animals as long as they do not get into the body; if they do get into the body, they can be quite harmful. • Beta particles are less damaging to tissue than alpha particles but penetrate farther and so are generally more harmful. • Gamma rays, which can easily penetrate skin, are by far the most dangerous and harmful form of radiation. 20
Radiation Dosimetry Terms and units • 1 Becquerel (Bq): 1 Becquerel (Bq): 1 Bq is 1 dps. 1 Bq is 1 dps. • 1 Curie (Ci): 1 Curie (Ci): Ci = 3.7 x 10 10 dps. • Roentgen (R): Roentgen (R): The amount of radiation that produces ions having 2.58 x 10 -4 coulomb/kg; a measure of the energy delivered by a radiation source. • Radiation absorbed dose (Rad): Radiation absorbed dose (Rad): A measure of the ionizing radiation absorbed; the SI unit is the gray (Gy). gray (Gy). • 1 Gray (Gy): 1 Gray (Gy): Gy = 1 joule/kilogram (1 J/kg). • Roentgen-equivalent-man (Rem): Roentgen-equivalent-man (Rem): A measure of the effect of the radiation when one roentgen is absorbed by a person; the SI unit is the sievert (Sv) sievert (Sv) where one Sv = 1 J/kg. 21
Radiation Dosimetry • The relationship between delivered dose in roentgens (R) and the absorbed dose in rads; exposure to 1 R of high energy photons yields 0.97 rad in water, 0.96 rad in muscle, and 0.93 rad in bone. • For lower-energy photons such as soft x-rays, 1 R yields 3 rads of absorbed radiation in bone; soft tissue lets radiation pass, but bone absorbs it, giving an x-ray. 22
Radiation Dosimetry Table 9-4 Average exposure to radiation from common sources 23
Radiation Dosimetry • A single whole-body irradiation of 25 rem is noticeable in decreased white blood cell count.