Radiation risks to humans in space will be better understood if ground-based mixed field irradiations are developed and used to measure the overall effectiveness of proposed space radiation shielding. The space environment is composed of wide range of particles containing various energies. Existing measurements illustrate the properties of galactic cosmic rays (GCR) in particle fluence and species. However, it is nearly impossible to simulate a radiation environment corresponding to both properties at once. Since the final objective of this thesis research is to understand radiation risks, and radiation risks are more directly related to the energy deposited in the human tissue than to fluence and charge, the more likely goal would be reproducing the linear energy transfer (LET) spectrum found in the GCR. The purpose of this thesis research is to use a Monte Carlo transport code to study the fragmentation of a combined iron and proton beam source using a multi-depth moderator block to reproduce the LET component of the GCR. To study mixed-field radiation exposures, the Monte Carlo transport code - Particle and Heavy Ion Transport code System (PHITS) will be used. Calculations showed it is necessary to design a moderator block that contains two different thicknesses - one with a length less than 23 cm and one with a length greater than 23 cm. The thinner moderator will allow high-Z particles to pass through and produce heavy-ion fragments that contribute mostly in the high-LET range. The thicker moderator will stop most of fragments and only allow lighter ions to penetrate and contribute to the mid-range and low-LET portion of the GCR spectrum. Since iron beams along will not produce enough low-LET particles, proton beams were employed to increase the abundance of the low-LET portion of the GCR spectrum. After series of studies, it was concluded that a 17 cm and 49 cm thickness will be most effective. The initial conclusion of this project was that it is possible to produce the GCR environment using a multi-depth moderator block and a combined iron and proton beam.

This thesis presents an analysis of the radiation environment on board the Russian section of the International Space Station (ISS) using data from the SilEye-3/Alteino experiment. As part of the analysis the efficiency and response of the SilEye-3/Alteino detector was studied. The relative nuclear abundance is generally in agreement with expected results. The presence of odd Z nuclei is significantly increased when compared with measurements outside the ISS. However, in ISS-y (Starboard-Ports) and z (Nadir-Zenith) directions an underabundance of carbon and oxygen nuclei is seen, whereasin x (Forward-Aft) there seemes to be an overabundance. One possible explanation is the absence of high-Z material in the ISS module wall for y and z . Whereas in x, most of the main body of the ISS is in front of the detector and the amount of high-Z material (i.e. aluminium) is large. The nalysis of fragmentation of iron into a range of secondary nuclei (15≤Z ≤25) indicates an aluminium hull equivalent thickness of 8-9 cm in y- and z-directions. For x the aluminium hull equivalence amounts to about 17 cm. Flux, LET, dose and dose equivalent rates present a clear anisotropy in the different orthogonal directions of the ISS, with rates consistently lower in x. This effect is more pronounced for the heavy-ion component (LET &gt;50 keV/μm). Measureddose rates vary from 25 μGy/day to 75 μGy/day, depending on location, orientationand configuration of the detector. The dose equivalent varies from 50 μSv/day toalmost 470 μSv/day.The shielding effect of the polyethylene amounts to 25-37% dependent on loca-tion and orientation inside the ISS. The majority of the reduction occurs duringpassages through the SAA. A Geant4 comparison with the Phits simulations code have been preformed as an initial survey into the treatment of hadronic physics for heavy ions in Geant4. / <p>QC 20140521</p>

Space travelling within the solar system is expected to expand within the upcoming years, with the Moon and Mars as main targets. These longer space flights results in longer time periods within a complex radiation environment for the astronauts. Dose limits therefore have to be established by space agencies for their respective space workers, to secure maximum safety and as low risks as possible. A radiation model is constructed by many building blocks, ranging from radiobiology to physics. The state of the art of the current models are described in this paper, followed by the uncertainties and knowledge gaps related to the respective space agency’s approach. These mainly include more extensive research of the available data for exposed populations, adapting the inputs to the relevant population, and the choice of risk quantity and track structure models. By focusing on the largest uncertainty contributors, Europe can add importance to this essential research and form a European space radiation model for European space workers.

Since the beginning of space exploration in last century, several kinds of devices from passive and active dosimeters to radiation environment monitors have been used to measure radiation levels onboard different space crafts and shuttles allowing the space community to identify and quantify space radiation. The recent construction of several laboratories on the International Space Station (ISS) has confirmed that prolonged duration space missions are now becoming standard practice and as such, the need to better understand the potential risk of space radiation to Astronaut’s health, has become a priority for long mission planner. The complex internal radiation environment created within the ISS is due to high-energy particle interactions within the ISS shielded environment. As a result, a large number of secondary particles, that pose specific health risks, are created. Neutrons are one important component of this mixed radiation field due to their high LET. Therefore, the assessment of the neutron dose contribution has become an important part of the safety and monitoring program onboard the ISS. The need to determine whether neutron dose measured externally to the human body give an accurate and conservative estimate of the dose received internally is of paramount importance for long term manned space missions. This thesis presents a part of an ongoing large research program on radiation monitoring on ISS called Matroshka-R Project that was established to analyze the radiation exposure levels onboard the ISS using different radiation instruments and a spherical phantom to simulate human body. Monte Carlo transport code was used to simulate the interaction of high energy protons and neutrons with the spherical phantom currently onboard ISS. A Monte Carlo model of the phantom has been built, and it consists of seven spherical layers presenting different depths of the simulated tissue. The phantom has been exposed to individual proton energies and to a spectrum of neutrons. The flux of the created neutrons inside the phantom has been calculated. The internal to external neutron flux ratio was calculated and compared to the experimental data, recently, measured on three separate expeditions of the ISS. The results from the calculations showed that the value of the neutron fluxes inside and outside the phantom is different from the data recently measured with bubble detectors. / UOIT

Tissue equivalent proportional counters (TEPC) are used for medical and space activities whenever a combination of high and low LET (lineal energy transfer) radiations are present. With the frequency and duration of space activities increasing, exposure to fast heavy ions from galactic cosmic radiation and solar events is a major concern. The optimum detector geometry is spherical; to obtain an isotropic response, but simple spherical detectors have the disadvantage of a non-uniform electric field. In order to achieve a uniform electric field along the detector axis, spherical tissue equivalent proportional counters have been designed with different structures to modify the electric field. Some detectors use a cylindrical coil that is coaxial with the anode, but they are not reliable because of their sensitivity to microphonic noise and insufficient mechanical strength. In this work a new spherical TEPC was developed. The approach used was to divide the cathode in several rings with different thicknesses, and adjust the potential difference between each ring and the anode to produce an electric field that is nearly constant along the length of the anode. A-150 tissue equivalent plastic is used for the detector walls, the insulator material between the cathode rings is low density polyethylene, and the gas inside the detector is propane. The detector, along with the charge sensitive preamplifier, is encased in a stainless steel vacuum chamber. The gas gain was found to be 497.5 at 782 volts and the response to neutrons as a function of angle was constant ±7%. This spherical tissue equivalent proportional counter detector system will improve the accuracy of dosimetry in space, and as a result improve radiation safety for astronauts.

Human exposure to reduced weightbearing results in bone loss. The rate of bone loss during microgravity exposure is similar to that of a post-menopausal women. In fact, the maintenance of bone mass is intimately dependent on exercise. Therefore, exercise associated mechanical loads to bone tissue are an important countermeasure to prevent disuse-induced bone loss. However, the types of exercise modalities required to prevent such bone loss are unclear. Moreover, how mechanical loading to bone translates into molecular osteogenic signals in bone cells is unknown. Radiation exposure is another potent inducer of bone loss, namely observed on Earth in the clinical setting following radiotherapy procedures. It is expected that long duration space missions outside the protection of Earth’s magnetosphere will result in significant galactic cosmic radiation exposure. However, the magnitude of bone loss resulting from this galactic cosmic radiation exposure is unclear. Moreover, it is unknown if radiation exposure will exacerbate disuse-induced bone loss. Therefore, a series of experiments were designed to determine: 1) Will simulated galactic cosmic radiation exacerbate reduced weightbearing-induced bone loss? 2) Will pharmacological activation of the putative mechanosensing Wnt pathway enhance exercise-induced bone mass gain? To address these questions the experimental study series employed two animal models of reduced weightbearing, hindlimb unloading and partial weightbearing. These model test-beds enabled the evaluation of two novel countermeasures (simulated resistance exercise and glycogen synthase kinase-3 (GSK-3) therapeutic) and simulated exposure to space radiation environments. To test the impact of simulated space radiation (28Si) one study of the series was conducted at Brookhaven National Laboratory. To quantify the impact of the abovementioned countermeasures and space radiation on bone, mechanical testing, peripheral quantitative computed tomography, micro-computed tomography, histomorphometry, and immunohistochemistry served as primary outcome measures. The primary findings are: 1) Low-dose high-LET radiation negativity impacts maintenance of bone mass by lowering bone formation and increasing bone resorption. This impaired bone formation response is in part due to sclerostin induced suppression of Wnt signaling. 2) Combining GSK-3 inhibition with high intensity exercise mitigates cancellous bone loss and restores cortical periosteal growth during disuse.

Master of Science / Department of Mechanical and Nuclear Engineering / J. Kenneth Shultis / A program which calculates the radiation dosage to a predetermined set of components inside of a kill vehicle as a result of natural or artificial radiation sources has been developed for use within the confines of a parent external simulation. This dose can then be used to determine if a critical component has malfunctioned or failed completely, thereby rendering the interceptor unable to finish its mission. Knowledge of system and component performance as a function of incident high-energy particles leads to better battle management planning, CONOPS, and potentially a more efficient shielding design to achieve a higher probability of mission success.

The energy deposition characteristics of heavy ions vary substantially compared to those of photons. Many radiation biology studies have compared the damaging effects of different types of radiation to establish relative biological effectiveness among them. These studies are dependent on cell type, biological endpoint, radiation type, dose, and dose rate. The radiation field found in space is much more complicated than that simulated in most experiments, both from a point of dose-rate as well as the highly mixed field of radiative particles encompassing a broad spectrum of energies. To establish better estimates for radiation risks on long-term, deep space missions, the damaging ability of heavy ions requires further understanding. Track structure studies provide significant details about the spatial distribution of energy deposition events in and around the sensitive targets of a mammalian cell. The damage imparted by one heavy ion relative to another can be established by modeling the track structures of ions that make up the galactic cosmic ray (GCR) spectrum and emphasizing biologically relevant target geometries. This research was undertaken to provide a better understanding of the damaging ability of GCR at the cellular level. By comparing ions with equal stopping power values, the differences in track structure will illuminate variations in cell particle traversals and ionization density within cell nuclei. For a cellular target, increased particle traversals, along with increased ionization density, are key identifiers for increased damaging ability. Performing Monte Carlo simulations with the computer code, FLUKA, this research will provide cellular dosimetry data and detail the track structure of the ions. As shown in radiobiology studies, increased ionizations within a cell nucleus generally lead to increased DNA breaks and increased free radical production, resulting in increased carcinogenesis and cell death. The spatial distribution of dose surrounding ions tracks are compared for inter- and intracellular regions. A comparison can be made for many different ions based upon dose and particle fluence across those different regions to predict relative damaging ability. This information can be used to improve estimates for radiation quality and dose equivalent from the space radiation environment.

Thesis submitted in partial fulfilment of the requirements for the degree Doctor of Technology: Electrical, Electronic and Computer Engineering in the Faculty of Engineering at the Cape Peninsula University of Technology / This research investigates the effects of sub-10 MeV protons on coatings obtained from the pulsed laser ablation of W2B5/B4C. This is in an attempt to extend the bullet proof applications of W2B5/B4C to space radiation shielding applications, offering low cost and low mass protection against radiation including X-rays, neutrons, gamma rays and protons in low Earth orbit. The focus in this research, however, is on low energy protons. The associated problems addressed in this work are solar cell degradation and Single Event Upsets in high density semiconductor devices caused by low energy protons. The relevant constraints considered are the necessity for low cost, low mass and high efficiency solutions. The work starts with a literature review of the space environment, the interaction of radiation with matter, and on pulsed laser deposition as a technique of choice for the coating synthesis. This paves the way for the pulsed laser ablation of W2B5/B4C. The resulting coating is a solid solution of the form WC1-xBx which contains crystalline and amorphous forms. Two proton irradiation experiments are carried out on this coating, and the resulting effects are analysed. The effects of 900 keV proton irradiation were the melting and subsequent growing of nanorods on the surface of the coating, the lateral transfer of the proton energy across the coating surface, and the lateral displacement of matter along the coating surface. These effects show that the coating is a promising cost effective and low mass radiation shield against low energy protons. The effects of 1 MeV protons on this coating are the three-stage melting of rods formed on the coating surface, and further evidence of lateral transfer of energy across the coating surface. Optical measurements of this coating show that it is about 73% transparent in the Ultraviolet, Visible and near Infrared range. This allows it to be used as radiation shielding for solar cells, in addition to high density semiconductor devices, against low energy protons in low Earth orbit. Simulations show that based on coulombic interactions alone, the same level of protection coverglass offers to solar cells can be achieved with about half the thickness of WC1-xBx or less.

Beyond the protective confines of Earth's atmosphere and magnetosphere, spacecraft are subject to constant bombardment by high-energy charged particles originating from our Sun in the form of Solar Particle Events (SPEs), and from outside the solar system in the form of Galactic Cosmic Rays (GCRs). The harm these particles do can be reduced or mitigated outright through radiation shielding. Because protons and other charged particles comprise most of these radiation particles, strong magnetic fields could be generated around spacecraft to deflect incoming charged radiation particles. This thesis investigates the performance of specific configurations of toroidal superconducting solenoids to generate magnetic fields that deflect incoming energetic protons via the Lorentz force. Bulk material shielding configurations using various thicknesses of liquid water are similarly investigated, as are combination shielding configurations combining the best-performing toroidal shielding configurations with a small bulk material shield surrounding the spacecraft. The water shielding configurations tested included shields of uniform thicknesses from 1 cm to 10 cm surrounding an Apollo CSM-sized cylindrical candidate spacecraft. Water shielding was found to be very effective at reducing the SPE dose, from a 86\% reduction at 1 cm of water to a 94\% reduction at 10 cm. However water shielding was found to be minimally effective against the much higher energy Galactic Cosmic Ray protons, with no dose reduction at 1 cm and a paltry 1\% reduction at 10 cm. The toroidal shielding geometric configurations tested consisted of either 5 or 10 primary toroidal shields surrounding the candidate spacecraft, as was the addition of smaller nested toroidal shields inside the primary toroids and of toroids on the spacecraft's endcaps. The magnetic field strengths tested were 1.7 Tesla, 8.5 Tesla, and 17 Tesla. The best geometric configurations of electrodynamic shielding consisted of 5 primary toroidal shields, 5 total nested shields placed inside the primary toroids, and 2 total shields on the spacecraft's endcaps. The second best geometric configuration consisted of 10 primary toroidal shields plus two total endcap shields. These configurations at 1.7 Tesla reduced the SPE dose by 87\% and 87\%, and reduced the GCR dose by 11\% and 10\%. At 17 Tesla, these configurations both reduced the SPE dose by 90\%, and reduced the GCR dose by 76\% and 61\%. Combining these two configurations with a 1 cm-thick shield of water improved performance against SPE protons to 95\% and 93\% at 1.7 Tesla, and a 97\% and 96\% reduction at 17 Tesla. GCR dose reductions decreased slightly. Passive material shielding was found capable of providing substantial protection against SPE protons, but was minimally effective against GCR protons without very thick shielding. Electrodynamic shielding, at magnetic field strengths of 1.7 Tesla, was found to be similarly effective against SPE protons, and marginally more effective against GCR protons. Combining the best toroidal shielding configurations, at magnetic field strengths of 1.7 Tesla, with water shielding yielded high protection against SPE protons, but still marginal protection against GCR protons. Increasing the magnetic field strength to 17 Tesla was found to provide very high protection against SPE protons, and to significantly reduce the radiation dose from GCR protons. Of all shielding configurations tested, only those electrodynamic configurations with magnetic fields of 17 Tesla were able to reduce the GCR dose by more than half.