Radiation 



Detector response affects the 

 accuracy with which the 

 radiation field is measured. 

 Each kind of detector is limited 

 by the type of radiation it can 

 measure and the amount of 

 detail concerning the categories 

 of radiation it can measure. As 

 our knowledge of the space 

 radiation environment has 

 grown, so have appropriate 

 detectors been designed, built, 

 and improved. Thermo- 

 luminescent detectors have 

 been developed that measure 

 low LET radiation well, but not 

 high LET Plastic track detectors 

 have been devised to identify 

 the HZE component of space 

 radiation. Experience in nuclear 

 physics is resulting in the 

 construction of detectors 

 capable of determining the 

 atomic number and energy of charged particles in radiation fields 



Vfhen the energy from solar particle events reaches the Earth, it can cause geomagnetic 

 storms that disrupt broadcast communications and can result in aurora such as the one 

 photographed bi/ astronaut Robert F. Overmyer during the Spacelab 3 mission. 



Although it is difficult to map radiation fields, much is now known about the 

 radiation surrounding Earth. Trapped electrons, occupying a much wider range of 

 altitudes— some extending many Earth radii away— are perhaps not quite so well 

 measured as the protons. The pronounced interaction of electrons with shielding 

 material resulting in the production of bremsstrahlung also complicates these 

 measurements. Fairly solid data exist for the spatial distribution of electrons as a 

 function of altitude and their spectral distributions at each altitude. It is known 

 that the particle fluence undergoes marked diurnal fluctuations, as well as strong 

 variations influenced by solar storms. This discussion perhaps can best be 

 summarized by the observation that current space radiation data and models can 

 predict the radiation measurements on the Space Shuttle only within a factor of 

 two (9). 



Measurement of SPE's is probably the most uncertain aspect in determining the 

 space radiation environment. The frequency of their occurrence is related to the 

 solar cycle, so that accurate characterization is to some extent determined by the 

 length of the solar cycle (11 years). As the name implies, this type of radiation is 

 not continuous but occurs in short bursts of several days. The timing of their 

 occurrence is of much interest to the humans in space program, but as yet, the 

 events cannot be predicted. The temporal evolution, spectral characteristics, and 

 particle species profile are all subject to variations and are functions of a number 

 of variables. So far, the ability to predict the magnitude of the events is very 

 limited. In an effort to establish an early warning system for astronauts, however, 



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