Space dosimetry

Radiation in space

Radiation dosimetry on board of space crafts is necessary for different reasons. First, astronauts are subject to an operational radiation safety program, including a dosimetry system to estimate their cumulative equivalent doses from space flights.

Secondly different experiments and instruments on board of a spacecraft can be affected by the space radiation. Radiation dose rates can vary with a factor two within the space craft, dependent upon the shielding and orientation of the space craft. In addition, there is also the variation in time due to the solar cycle and solar particle events (SPE’s), so it is necessary to continuously have a monitoring program for radiation doses in operation.

Determination of radiation doses in space is not straightforward because the radiation spectrum is very complex and different from situations on earth. The quantities to use are also complex to define. The radiation effects are dependent on the density of energy deposition along the radiation track (the linear energy transfer LET, expressed in keV/µm), so radiation dosimetry for humans is expressed in dose equivalent (expressed in Sievert).

For the complex mixtures of high and low LET radiations experienced in space, one needs to obtain the absorbed dose D and calculate the dose equivalent H using the quality factor relationship as a function of LET (Q(L)). Such quality factor relationship is not known for electronics and non-human species.

As an example one can say that astronauts in low earth orbit (LEO), like the International Space Station (ISS), are receiving between 200 and 600 microsievert (µSv) per day, dependent on many factors. This can be compared to the natural background from external radiation on the earth surface between 2 and 3 µSv per day. During solar particle events (SPE) the dose to astronauts can be very high, even several millisieverts (mSv) or higher, dependent on the strength of the eruption.

SCK•CEN's contribution to space dosimtry

SCK•CEN has been active in space dosimetry measurements for several years. In collaboration with the European Space Agency (ESA ) and several international partners we have been running the DOBIES-project (Dosimetry for Biological Experiments in Space). With this project we try to develop a standard dosimetric method (as a combination of different techniques) to determine the absorbed doses in biological samples. We use different types of passive dosemeters, like thermoluminescent and optically stimulated luminescent detectors, to characterize the radiation field.

The response characteristics of all types of dosemeters should be determined prior to use. This is accomplished by experiments at the appropriate energy ranges: high energy protons (10 to 800 MeV), high Z high energy ions (He, C, Si, Fe), electrons (0.5 to 10 MeV) and high energy neutrons (1 to 180 MeV). For this we participate in an international series of common characterisation and calibration exercises called ICCHIBAN.

The last years we have participated in a whole series of space exposures in the ISS with our dosemeters: Expose-Eutef, YING B1/B2, DOSIS, SI (Space Intercomparison), YING,….

Contact: Vanhavere Filip