Passage of Radiation Throught Matter: Radiation Damage

 

 

Radiation includes alpha, beta, and gamma rays; X rays; and protons, neutrons, pions, and other particles.

 

All these forms of radiation are called ionizing radiation, because they ionize material that they go through.

 

This ionization can cause damage to materials, including biological tissue.

 

Radiation damages biological tissue, but it can also be used to treat cancer and other diseases.

 

It is important to be able to measure the amount, or dose, of radiation received. The source activity is the number of disintegrations per second, often measured in curies, Ci.

 

 

The SI unit for source activity is the becquerel (Bq):

 

Another measurement is the absorbed dose – the effect the radiation has on the absorbing material.

The rad, a unit of dosage, is the amount of radiation that deposits energy at a rate of 1.00 x 10-2 J/kg in any material.

The SI unit for dose is the gray, Gy:

 

1 Gy = 1 J/kg = 100 rad

 

The effect on tissue of different types of radiation varies, alpha rays being the most damaging. To get the effective dose, the dose is multiplied by a quality factor.

 

If the dose is measured in rad, the effective dose is in rem; if the dose is grays, the effective dose is in sieverts, Sv.

Natural background radiation is about 0.3 rem per year. The maximum for radiation workers is 5 rem in any one year, and below 2 rem per year averaged over 5 years.

A short dose of 1000 rem is almost always fatal; a short dose of 400 rem has about a 50% fatality rate.