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An element may have several forms, or isotopes. A radioactive form of an
element is called a radioisotope or radionuclide. Each radionuclude has a half-
life, which is the time required for half of a quantity of the material to decay.
Measuring Radiation
Alpha, beta, gamma, and x-rays ionize material they strike or pass through.
The amount of radiation is generally measured by measuring the resulting
ionization.
The Geiger tube used in the Digilert 100 consists of an anode and a cathode
(positive and negative electrodes) separated with a mixture of argon, neon, and
either chlorine or bromine gases. The cathode is a thin-walled metallic cylinder
sealed at each end with an insulating disk to contain the gas. The anode is a
wire that extends into the cylinder. A high voltage is applied to the electrodes to
create an electrical field within the chamber. When radiation passes through the
chamber and ionizes the gas, it generates a pulse of current. The Digilert 100
electronically processes these pulses to display the radiation level.
Radiation Measurement Units
Several different units are used to measure radiation, exposure to radiation, and
dosage.
A roentgen is the amount of X-radiation or gamma radiation that produces one
electrostatic unit of charge in one cc of dry air at 0* C and 760 mm of
mercury atmospheric pressure. The Digilert 100 displays readings in
milliroentgens per hour (mR/hr). A milliroentgen is one one-thousandth of a
roentgen.
A rad is the unit of exposure to ionizing radiation equal to an energy of 100 ergs
per gram of irradiated material. This is approximately equal to 1.07 roentgen.
A rem is the dosage received from exposure to a rad. It is the number of rads
multiplied by the quality factor of the particular source of radiation. The rem and
millirem (one one-thousandth of a rem) are the most commonly-used
measurement units of radiation dose in the U.S. One rem is generally
considered to equal one rad.
