A model of galactic cosmic rays for use in calculating linear energy transfer spectra

Investigation of HZE particle fluxes as a space radiation hazard for future Mars missions

Manned Mars missions planned in the near future of very low solar activity period and hence higher than acceptable radiation doses due mainly to the Galactic Cosmic Rays (GCR), would require special techniques and technological development for maintaining the good health of the astronauts. The present study is an attempt to make an assessment and characterise the coming years in terms of solar activity and space radiation environment especially due to the abundance of highly energetic heavy ions (known as HZE charged particles). These HZE particle fluxes constitute a major hazard to the astronauts and also to the critical electronic components of the spacecraft. Recent data on the HZE species (from B to Ni) obtained from ACE spacecraft shows a clear enhancement of the particle fluxes between the solar cycle 23 and solar cycle 24 (~between SSN peaks 2002 and 2014) due to the persisting low sunspot numbers of the latter cycle. The peak values of these cosmic ray fluxes occur with a time lag of about a year of the corresponding minimum value of the sunspots of a particular 11-year cycle which is pseudo-periodic in nature. This is demonstrated by the Fourier and Wavelet transform analyses of the long duration (1700-2018) yearly mean sunspot number data. The same time series data is also used to train a Hybrid Regression Neural Network (HRNN) model to generate the predicted yearly mean sunspot numbers for the solar cycle 25 (~2019-2031). The wavelet analysis of this new series of annual sunspot numbers including the predictions up to the end of 2031 shows a clear trend of continuation of the low solar activity and hence continuation of very high HZE fluxes prevailing in Solar cycle 24 into the solar cycle 25 and perhaps beyond.

RAD51 plays a crucial role in halting cell death program induced by ionizing radiation in bovine oocytes

Reproductive health of humans and animals exposed to daily irradiants from solar/cosmic particles remains largely understudied. We evaluated the sensitivities of bovine and mouse oocytes to bombardment by krypton-78 (1 Gy) or ultraviolet B (UV-B; 100 microjoules). Mouse oocytes responded to irradiation by undergoing massive activation of caspases, rapid loss of energy without cytochrome-c release, and subsequent necrotic death. In contrast, bovine oocytes became positive for annexin-V, exhibited cytochrome-c release, and displayed mild activation of caspases and downstream DNAses but with the absence of a complete cell death program; therefore, cytoplasmic fragmentation was never observed. However, massive cytoplasmic fragmentation and increased DNA damage were induced experimentally by both inhibiting RAD51 and increasing caspase 3 activity before irradiation. Microinjection of recombinant human RAD51 prior to irradiation markedly decreased both cytoplasmic fragmentation and DNA damage in both bovine and mouse oocytes. RAD51 response to damaged DNA occurred faster in bovine oocytes than in mouse oocytes. Therefore, we conclude that upon exposure to irradiation, bovine oocytes create a physiologically indeterminate state of partial cell death, attributed to rapid induction of DNA repair and low activation of caspases. The persistence of these damaged cells may represent an adaptive mechanism with potential implications for livestock productivity and long-term health risks associated with human activity in space.

An analysis of energy deposition in a tissue equivalent proportional counter onboard the space shuttle

An improved prediction for space radiations in the lower earth orbits measured by the shuttle TEPC is obtained when energy loss straggling and chord length distribution of the detector are considered. A generalized analytic model is used to describe the energy deposition of direct ion interaction events in a micron-size detector. The transport calculation accounting for the shuttle configuration is accomplished by using a new version of HZETRN that has been extensively verified with laboratory and flight data. The agreement of predicted and measured lineal energy spectra is within 70% for the region above 2 keV/micrometer but within a factor of 2.3 underpredicted for the region below this value. The inclusion of indirect delta ray events in the model is needed before possible causes for the underprediction below 2 keV/micrometer can be assessed.