One way the Dosimetric Mapping system, or Dosmap, measures radiation is by using Nuclear Track Detector Packages. These packages contain three strips of plastic film, called CR39 plastic, on which high energy particles passing through it will leave a track which scientists can analyze. Each package contains three strips of a plastic film on which high energy particles passing through this film will leave a track. One strip will be used for each of three perpendicular axes. Several mobile dosimetry units will be used by crew members as personal dosimeters or placed throughout the Station.
Neutrons are uncharged atomic particles that have the ability to penetrate living tissues.
The TLDs are encased in Lexan plastic which responds to radiation by exciting long-lived electronic states in various lithium compounds. After exposure, the amount of this radiation can be revealed by applying heat and measuring the amount of visible light released as these excited states decay. The mobile dosimetry units will be recharged every five days, and the readout of the TLDs will be checked every 10 days. The Station crew will deactivate and stow the Dosmap at the end of Expedition Two, to prepare it for return to Earth on Space Shuttle mission STS 105, scheduled in July 2001. Since balloon launches in the 1940s, scientists have been measuring radiation in Earth's upper atmosphere and beyond.