Monitoring of crew exposures has been a normal part of the space programme since the dawn of human space exploration. Over the last decades, a broad variety of detector systems has been developed and applied on board different spacecraft, either in the form of passive integrating devices or as active real-time radiation monitors. The effective dose essentially depends on altitude and inclination of the orbit. The highest doses were observed during the high-altitude Shuttle flights at low inclinations with up to 4 mSv per day and during the Apollo programme with ~3 mSv per day. For the purpose of comparison, the mean daily dose on Earth from natural sources of radiation (including radon) is ~7 µSv.

Following the recommendations of NRCP Report No. 142, operational radiation monitoring on board the ISS consisting of area monitors and personal dosimeters shall provide experimental data of sufficient accuracy for:

• Determination of field quantities and organ or tissue doses to be used for normalizing radiation transport calculations;
• Dose assessment and record keeping purposes;
• Real-time or near real-time estimates of dose rates for purposes of immediate dose management or ALARA.

The active area radiation monitoring systems are based on the concepts of microdosimetry, silicon detector technology and ionization chamber principles. As a semi-active device, the Hungarian PILLE system comprises an automated on-board reader for passive thermoluminescence detectors (TLDs) and is applied on a regular base for dose assessment of cosmonauts on extravehicular activity (EVA). The main advantage of active radiation monitors are their real-time data viewing capabilities and built-in ‘radiation alarm functions’.

The dosimetric area monitoring data have mostly been achieved by passive devices which do not need a power supply. Such equipment includes TLDs and plastic nuclear track detectors (PNTDs) to assess absorbed dose, ionization density spectra and dose equivalent in space.

References and Notes

• T. Berger, Radiation dosimetry onboard the International Space Station ISS. Zeitschrift für Medizinische Physik 18, 265-275 (2008).
• National Council on Radiation Protection and Measurements. Operational radiation safety program for astronauts in low Earth orbit: a basic framework. NCRP Report 142 (2002).
• E. R. Benton, E. V. Benton, Space radiation dosimetry in low-Earth orbit and beyond. Nuclear Instruments and Methods in Physics Research B 184, 255-294 (2001).