Abstract
Upstream of the efficiency of proton or carbon ion beams in cancer therapy, and to optimize hadrontherapy results, we analysed the chemistry of Fricke solutions in track-end of 64-MeV ...protons and 1.14-GeV carbon ions. An original optical setup is designed to determine the primary track-segment yields along the last millimetres of the ion track with a sub-millimetre resolution. The Fe
3+
-yield falls in the Bragg peak to (4.9 ± 0.4) × 10
–7
mol/J and 1.9 × 10
–7
mol/J, under protons and carbon ions respectively. Beyond the Bragg peak, a yield recovery is observed over 1 mm for proton beams. It is attributed to the intermediate-LET of protons in this region where their energy decreases and energy distribution becomes broader, in relation with the longitudinal straggling of the beam. Consequently to this LET decrease in the distal part of the Bragg peak, Fe
3+
-yield increases. For the first time, this signature is highlighted at the chemical level under proton irradiation. Nevertheless, this phenomenon is not identified for carbon ion beams since their straggling is lower. It would need a greater spatial resolution to be observed.
The damaging effect of ionising radiation on cellular structure is one of the prime limiting factors on the survival of life in potential astrobiological habitats. Here we model the propagation of ...solar energetic protons and galactic cosmic ray particles through the Martian atmosphere and three different surface scenarios: dry regolith, water ice, and regolith with layered permafrost. Particle energy spectra and absorbed radiation dose are determined for the surface and at regular depths underground, allowing the calculation of microbial survival times. Bacteria or spores held dormant by freezing conditions cannot metabolise and become inactivated by accumulating radiation damage. We find that at 2 m depth, the reach of the ExoMars drill, a population of radioresistant cells would need to have reanimated within the last 450,000 years to still be viable. Recovery of viable cells cryopreserved within the putative Cerberus pack‐ice requires a drill depth of at least 7.5 m.
An overview is presented of basic results and recent developments in the field of cosmic ray induced ionisation in the atmosphere, including a general introduction to the mechanism of cosmic ray ...induced ion production. We summarize the results of direct and indirect measurements of the atmospheric ionisation with special emphasis to long-term variations. Models describing the ion production in the atmosphere are also overviewed together with detailed results of the full Monte-Carlo simulation of a cosmic ray induced atmospheric cascade. Finally, conclusions are drawn on the present state and further perspectives of measuring and modeling cosmic ray induced ionisation in the terrestrial atmosphere.
•We have modeled cosmic ray interaction with the venusian atmosphere.•We have computed the ionization rates for typical GCR and SEP conditions.•We provide a needed update to study of ionization in ...venusian atmosphere.•Sporadic SEP events may produce large enhancement in ionization rates.•Our study serves as important input to modeling of atmospheric physics, chemistry.
The atmospheres of the terrestrial planets are exposed to solar and galactic cosmic rays, the most energetic of which are capable of affecting deep atmospheric layers through extensive nuclear and electromagnetic particle cascades. In the venusian atmosphere, cosmic rays are expected to be the dominant ionization source below ∼100km altitude. While previous studies have considered the effect of cosmic ray ionization using approximate transport methods, we have for the first time performed full 3D Monte Carlo modeling of cosmic ray interaction with the venusian atmosphere, including the contribution of high-Z cosmic ray ions (Z=1–28). Our predictions are similar to those of previous studies at the ionization peak near 63km altitude, but are significantly different to these both above and below this altitude. The rate of atmospheric ionization is a fundamental atmospheric property and the results of this study have wide-reaching applications in topics including atmospheric electrical processes, cloud microphysics and atmospheric chemistry.
Currently a cosmic ray cloud connection (CRC) hypothesis is subject of an intense controversial debate. It postulates that galactic cosmic rays (GCR) intruding the Earth's atmosphere influence cloud ...cover. If correct it would have important consequences for our understanding of climate driving processes. Here we report on an alternative and stringent test of the CRC‐hypothesis by searching for a possible influence of sudden GCR decreases (so‐called Forbush decreases) on clouds. We find no response of global cloud cover to Forbush decreases at any altitude and latitude.
Target studies for surface muon production Berg, F.; Desorgher, L.; Fuchs, A. ...
Physical review. Accelerators and beams,
02/2016, Letnik:
19, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Meson factories are powerful drivers of diverse physics programs. With beam powers already in the MW-regime attention has to be turned to target and beam line design to further significantly increase ...surface muon rates available for experiments. For this reason we have explored the possibility of using a neutron spallation target as a source of surface muons by performing detailed Geant4 simulations with pion production cross sections based on a parametrization of existing data. While the spallation target outperforms standard targets in the backward direction by more than a factor 7 it is not more efficient than standard targets viewed under 90°. Not surprisingly, the geometry of the target plays a large role in the generation of surface muons. Through careful optimization, a gain in surface muon rate of between 30% and 60% over the standard “box-like” target used at the Paul Scherrer Institute could be achieved by employing a rotated slab target. An additional 10% gain could also be possible by utilizing novel target materials such as, e.g., boron carbide.
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