Radiation Basics

• Alpha radiation is present in airborne fallout and is breathed into the lungs where is causes internal damage and death. Beta radiation is present on the surface of items covered with radioactive dust and causes surface radiation burns. Gamma radiation penetrates the body and its organs; if enough is absorbed, severe radiation sickness or death can follow.
  
  Radiation detectors fall into two general subtypes. These are the dosimeter and the survey meter (more often referred to as a Geiger counter). They are designed to measure a person's exposure to ionizing radiation, specifically gamma radiation. Radiation dosages are expressed in terms of units like the Roentgen, the rem, the RAD (considered to be obsolete), the sievert or the grey. While these terms symbolize different ways of measuring radiation exposure, they can be considered somewhat equivalent.
  
  

Dosimeters Basics

• Dosimeters measure moderate to high levels of radiation. In their simplest form, they use a quartz fiber electroscope that detects and indicates the radiation level. These detectors can either measure radiation in milliRoentgens or Roentgens. These devices record cumulative doses, somewhat the way the trip meter on your odometer records how many miles you've driven.
  
  

Dosimeter Types

• They are available in the form of a pen-type detector, a badge or a digital readout.
  
  The pen or tube types record exposure and can be read by being inserted into a lighted socket on a charging unit. After the reading is taken and recorded, the pen is set to zero again for its next period of use.
  
  The badge types contain one or several rolls of photographic film that record the passage of ionizing radiation. The film must be removed and developed before the cumulative dose can be established.
  
  The digital readout dosimeters are usually handheld devices about the size of a pocket calculator. They constantly record radiation exposure and will sound an alarm if hazardous limits are reached.
  
  

Survey Meter Basics

• The radiation survey meters used by civilian emergency personnel work by means of an ionization chamber measuring the radiation rate in specific areas. While they indicate the level of radioactivity, they do not store this information like a dosimeter does. Rather, they alert the user to rising levels of radiation, usually by means of a clicking sound heard through earphones. Survey meters measure radiation in rems and usually indicate the presence of gamma radiation alone, but there are some kinds that also measure beta radiation.
  
  

Survey Meter Types

• Survey meters are most often encased in an aluminum shell approximately 5 inches by 8 inches by 7 inches and weigh a few pounds. Most are designed to be hand-carried and use a handheld wand that connects to the case. This is the familiar Geiger counter seen on TV shows.
  
  A variation of this design includes a remote probe device that can be placed outside a fallout shelter; the main portion of the meter stays inside the shelter. This configuration permits safe monitoring of radiation levels outside without making it necessary for someone to go outside the shelter to take a reading.
  
  Placing several survey meters around the interior of a fallout shelter will allow residents to identify any "hot spots" and take measures to reduce their risk of exposure.