Dosimetry is the measurement of doses in matter and tissue from ionizing radiation, or radioactivity as it is popularly known.
Doses are measured in gray (Gy) for matter or Sievert (Sv) for biological tissue. The dose refers to the amount of energy or damage deposited in the matter, and should not be confused with the unit of radioactive activity (becquerel, Bq). Doses can be measured in places other than where the radioactive decay occurred.
The worldwide average background dose for a human being is about 3.5 mSv per year [1], mostly from cosmic radiation and natural isotopes in the earth.
There are several ways of measuring doses from ionizing radiation. Workers that come in contact with radioactive substances or use radioactivity routinely carry personal dosimeters. These dosimeters contain of materials that can be used in Thermo Luminescence Dosimetry (TLD) or Optically Stimulated Luminescence (OSL). In radiotherapy, patient dosimeters are used to monitor the doses given to the patient. The equipment used in radiotherapy (linear particle accelerator in external beam therapy) is routinely calibrated using ionization chambers.
Since the attack on the World Trade Center on September 11th 2001, there has been an increasing interest in the field of Emergency Preparedness within the field of detecting and monitoring ionizing radiation.