Units radioactivity

The dose of radiation absorbed by a unit of mass per unit of time is called the absorbed dose rate in units of joules/kg. The rad (radiation absorbed dose) is 10 J/kg. A rad of a rays is more harmful than a rad of rays. Hence, the RBE (relative biological effectiveness) of radiation can normalize the damage to tissue by different types of radiation. This is illustrated by the equation 

The human body contains some naturally occurring radioactive isotopes besides These are all listed in Table 7.7. The energy of the radiation is very low, and the biological damage due to these isotopes is of minor importance. The normal exposure levels to man is given in Table 7.8. 

Source Amount of isotope (g) Number of atoms Total activity (Bq) Particle energy MeV y 

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Average internal dose from natural radioactivity, United States 0.25... 

Radiopharmaceuticals are prescribed according to units of radioactivity. A pharmacist practicing nuclear pharmacy may need to convert radio activity units from curies to SI unit, becquerel and its multiples, and vice versa. The following examples illustrate the interconversion of radioactive units. 

The basic unit of radioactivity is the curie, Ci. One curie is the amount of radioactive material that emits particles at a rate of 3.7 X 1010 disintegrations per second (dps), or 2.2 X 1012 min-1 (dpm). Amounts that large are seldom used in experimentation, so subdivisions are convenient. The milli-curie (mCi, 2.2 X 109 min-1) and microcurie (yu,Ci, 2.2 X 106 min-1) are standard units for radioactive measurements (see Table 6.2). The radioactivity unit of the meter-kilogram-seconds (MKS) system is the becquerel (Bq). A becquerel, named in honor of Antoine Becquerel, who studied uranium radiation, represents one disintegration per second. The two systems of measurement are related by the definition 1 curie = 3.70 X 1010 becquerels. Since the becquerel is such a small unit, radioactive units are sometimes reported in MBq (mega, 106) or TBq (tera, 1012). Both unit systems are in common use today, and radioisotopes received through commercial sources are labeled in curies and bequerels. 

Define the following terms related to radioactivity units. 

Plot the equation A curies (radioactivity unit) and X 25 years. 

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