arXiv subjects

A. Ilker Topuz

Publications and source records attributed to A. Ilker Topuz.

4 recordsLinked to original sources

arXiv2026

Contribution of cosmic alphas to generation of albedo neutrons and gammas in lunar regolith: A computational study based on GEANT4 simulations

The lunar surface is constantly and directly exposed to Galactic Cosmic Rays (GCRs) due to the lack of the atmosphere and the magnetic field around it. The high-energetic alpha particles subsequently contribute to the generation of the secondary neutrons through either the spallation reaction or the low-energetic $(α, n)$ process along with the cosmic protons. In this study, the contribution of the alpha particles to the production of the albedo neutrons as well as the albedo gamma rays in the lunar regolith is studied by using the Monte Carlo simulations based on the GEANT4 toolkit. The incident alpha particles are referenced from the PAMELA spectrometer over the interval between 0.14 and 52 GeV and executed as a probability-based primary particle source. The present simulations demonstrate the production of the albedo neutrons and gamma rays upon the process of cosmic alpha irradiation in the lunar regolith. The albedo neutron production is predominantly situated within the near-surface region of the lunar regolith and progressively diminishes with the increasing depth. The population of the secondary neutrons is primarily distributed over the low-energy region and reduces towards the high energies. These results imply that the cosmic alpha particles have also quantifiable contribution in the generation of the secondary radiation at the lunar surface together with the cosmic protons, and this study demonstrates a computational framework in the evaluation of the lunar albedo, the radiation transport, the surface composition, and the radiation environment for the further lunar exploration missions.

physics.ins-det↗

arXiv2026

Thermal/epithermal neutron detection via LiO$_{2}$-doped fiber bundles: A computational study through GEANT4 simulations

One of the neutron capture processes in lithium or lithium-doped materials leads to the production of secondary alpha-triton pairs. The counts of these secondary charged particle pairs in the presence of thermal/epithermal neutrons indirectly give access to detecting the primary incident neutrons with the aid of the plastic scintillators by reminding that both these secondary alphas and tritons deposit their entire kinetic energy within a short range. In this study, we modify the polystyrene fiber core of Kuraray Y11-200(M) by doping with 10 wt.$\%$ LiO$_{2}$. We investigate a fiber bundle system hinged on 10 wt.$\%$ LiO$_{2}$-doped Kuraray Y11-200(M) fibers via the GEANT4 simulations by targeting the detection of the incident thermal/epithermal neutrons through the generation of the secondary alpha-triton pairs. First, we estimate an optimal number of fiber arrays by using a monoenergetic beam of thermal neutrons with a kinetic energy of 0.025 eV and we count the number of secondary alpha-triton pairs. Subsequently, we insert a pixelated photo-sensor on both ends of the fiber bundle in order to collect the entrapped optical photons. In addition to the thermal neutrons, we also explore the detection of epithermal neutrons with a kinetic energy of 1 eV by utilizing a combination of the 10 wt.$\%$ LiO$_{2}$-doped Kuraray Y11-200(M) fiber bundles and the neutron absorption layers. We demonstrate that the LiO$_{2}$-doped plastic scintillating fiber bundles are instrumental for the detection of thermal/epithermal neutrons in diverse applications.

physics.ins-det↗

arXiv2026

Unveiling neutron and gamma spectrum at Martian surface in presence and absence of hydrogen: A computational study based on GEANT4 simulations

Motivated by the interactions of the GCR protons with the Martian atmosphere and regolith in the absence and presence of hydrogen, a series of GEANT4 simulations are employed in this study to reveal the influence of hydrogen on the energy spectra of secondary and albedo neutrons together with the associated gamma rays at the Martian surface. Following irradiation of the Martian atmosphere with a planar vertical PAMELA proton beam, the attenuation of the primary proton spectrum through the atmosphere and the range and energy deposition of protons within the regolith are first obtained. The depth profile of the generated neutrons and gamma rays, along with the kinetic energy spectra of the atmospherically produced neutrons and gammas reaching the surface, is then acquired in the absence and presence of 0.11 wt.% hydrogen by voxelizing the regolith into 100 cells of 2-cm thickness. Finally, a surface detector is placed atop the regolith, and the atmospherically produced neutron and gamma spectra are compared with the total neutron and gamma spectra recorded at the surface detector to assess the relative contribution of the atmosphere and the regolith to the overall radiation field reaching the Martian surface. The energy spectra of the albedo neutrons are also obtained in terms of thermal, epithermal, and fast neutrons. The GEANT4 simulations show that the Martian regolith, rather than the atmosphere alone, constitutes the dominant source of the neutron and gamma population arriving at the surface, and that the presence of 0.11 wt.% hydrogen is observable in each energy regime of the albedo neutrons at the Martian surface, while proton transport and the overall neutron and gamma production depth profile remain comparatively insensitive to hydrogen, thereby indicating the elemental variation of the Martian regolith.

physics.ins-det↗

arXiv2024

Implementation of atmospheric proton spectrum in GEANT4 simulations for space applications

A major part of cosmic rays consists of the primary protons, and this portion plays a crucial role in the space applications such as shielding of spacecrafts. In this study, the proton flux values measured at the top of the atmosphere through the BESS-TeV spectrometer in 2004 are introduced into the GEANT4 simulations by using a probability grid that generates the corresponding discrete kinetic energies with a certain discrete probability. The introduced scheme is tested over a set of the shielding materials such as aluminum, polypropylene, Kevlar, polyethylene, and water by computing the total absorbed dose, which is the measure of the cumulative energy deposited in the investigated target volumes by protons per unit mass in Gy. It is shown that the present recipe provides the opportunity to use the discrete energy values together with the experimental flux values, thereby demonstrating a beneficial capability in the GEANT4 simulations for diverse space applications.

physics.ins-det↗