Measurement of LET distribution and absorbed dose from secondary particles on board the spacecraft

The role of nuclear fragmentations in high energy transfers to a micro-object exposed to primary space radiation

This paper describes events of anomalously high energy transfer to a micro-object by fragments of nuclei generated in nuclear interactions in the environment on board a spacecraft in flight in low-Earth orbit. An algorithm has been developed that allows for the calculation of the absorbed energy from one or more fragments - products of nuclear interaction. With this algorithm the energy distributions for a spherical micro-volume in an aqueous medium were calculated. And the resulting absorbed energy spectra from nuclear fragments and from primary cosmic rays were compared. The role of nuclear interactions in events of large energy transfers in micro-objects in the field of primary cosmic radiation has been evaluated. The calculations performed in this study showed that the energy in a micro-volume from nuclear events can be several times higher compared to the energy imparted by primary space radiation.

Distributions of energy imparted to a micro-volume by secondary charged fragments of nuclear interactions in space radiation field

The field of cosmic radiation at low-Earth orbit (LEO) has a complex composition. It always contains a component of secondary charged particles, formed by the products of nuclear interactions of the primary high-energy radiation with the nuclei of spacecraft's shielding material, electronic components and biological matter on board. Generation of this secondary radiation can be observed in some track detectors in the form of "stars" formed by tracks-fragments with a common vertex. The energy absorbed by the medium in the region adjacent to the interaction vertex can reach abnormally high values because of its intersection by several particle fragments. In the present paper, a methodology is considered to calculate the energy imparted by such fragments to a spherical sensitive volume in an aqueous medium. The energy distributions for three fragment events were calculated for different positions of the vertex relative to the spherical volume. The obtained data were analyzed and were compared with the distribution for a uniform fluence of secondary particles. It was shown that as the fragmentation vertex approaches the boundary of the sensitive micro-volume, the probability of events with anomalously high energy transfers, higher than the energies from single fragments, increases. The method can be applied to calculate absorbed energy distributions from secondary radiation in media of different elemental composition than that used in the present work. In the future, it is of interest to apply the method for example to study the energy imparted from secondary fragments to a silicon medium, to quantify the number of single event upsets in electronic components.

MEASUREMENT OF DIFFERENT COMPONENTS OF SECONDARY RADIATION ONBOARD INTERNATIONAL SPACE STATION BY MEANS OF PASSIVE DETECTORS

The evaluation of different components of secondary radiation (charged fragments and neutrons) onboard ISS is described. Solid-state nuclear track detectors CR-39™ were applied for the measurements of short-range nuclear fragments, while the measurements of neutrons were carried out by means of thermo-luminescent dosimeters with various concentrations of 6Li and 7Li. The flux of charged secondaries and the gamma-equivalent neutron dose are presented in function of the low-LET dose in various modules of the Russian segment of ISS.