Radioactivity

Defintion: The number of atoms undergoing radioactive decay in one second is known as RADIOACTIVITY.

When radioactive materials decay, particles are released with great speed. Three types of radiation are likely to result. ALPHA Particles are heavy and propagate only a few inches in the air and only a few fractions of an inch into the human body. BETA Radiation propagates for a few meters in air and penetrates a few millimeters into the human skin. Layers of clothing or glasses are effective protection against ALPHA and BETA radiation.

During the decay of Alpha and Beta rays, GAMMA Radiation is frequently released, which can be dangerous to human beings. This electromagnetic radiation includes also X-Rays and the UV(ultra violet) rays of sunlight or a sun lamp.

Depending on its energy, Gamma radiation can be highly penetrating and is attenuated only very gradually. At high energies, it can penetrate hundreds of meters of atmosphere and about one meter of human tissue. No total protection is guaranteed, not even through one meter of concrete or 20 centimeter thick lead.

The prospecting for radioactivity minerals using a geiger counter or scintillation counter. These counters measure the natural background radioactivity of earth minerals. Commonly used for finding uranium deposits.

Measurement Units and Permissible Dosages

MEASUREMENT UNITS:

RADIOACTIVITY is measured in Becquerel (Bq) units.
1 Bq = 1 decay per second. Curie (Ci) was used earlier and
might still be around: 1 Ci = 37 billion Bq or 37 Bq = 1 nano-Ci.

To measure the health risk through ionization, in the US the most
commonly used unit is rem or mrem (milli-rem). Sometimes
the units Roentgen (R) or mR (milli-Roentgen) are used.
In Europe the most commonly used measuring unit for this purpose is
Sv (Sievers) or mSv (milli-Sv).

Conversion rem to Sieverts:

1 rem = 0.01 Sv = 10 mSv

1 mrem = 0.01 mSv

100 mrem = 1 mSv

PERMISSIBLE DOSAGES:

A normal "background" dosage in the US is appr. 0.005mrem/h to 0.012mrem/h, depending the location.

When is the Dose Rate considered dangerous?

Short term increases of Dose Rates up to 0.2mrem/hr have been experienced quite often. Although this value is higher than usual and would amount over 1 year to appr. 1800mrem, no danger is indicated.

Cumulated Dose is the continious registration of radiation exposure over the period of 1 year. A normal "background" dose in the US is 360mrem, depending the location you spent the last 12 months.

When is the Cumulated Dose dangerous?

For the general public, the permissible limit of radiation exposure from man-generated sources is 500mrem to 100mrem.