Effective Shielding Multi-layered Boron Containing Aromatic Polymer Materials for High Energy Radiations

doi:10.21203/rs.3.rs-2003002/v1

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Effective Shielding Multi-layered Boron Containing Aromatic Polymer Materials for High Energy Radiations

https://doi.org/10.21203/rs.3.rs-2003002/v1

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It is always of extreme significance to research materials that can shield astronauts from radiation during space missions. In this study, hydrogen-rich aromatic polymer composites are used as radiation shielding materials, which diminish radiation exposures from solar particle events (SPE) and galactic cosmic radiation (GCR). We used three aromatic materials namely polyetherimide, polysulfone, and polyimide polymers as our shielding materials. Each material will have boron powder added in amounts ranging from 5 to 20 percent by weight. High Charge and Energy TRaNsport (HZETRN) is used to simulate the dose equivalent by particle kinds, Linear Energy Transfer (LET), and Flux analysis for each shielding material for the 2010 solar minimum GCR. For Dose Equivalent by neutrons and alphas particles, Boron-11 containing Polysulfone is more effective than boron-11 Polyetherimide, and Polyimide whereas for protons, Boron-11 Polyetherimide is performance better than boron-11 Polyimide, and Polysulfone. We found that boron-11 isotopes containing polymers performed improved shielding effectiveness. In pure and boron-containing Multi-layered Polymers, Al+Polysulfone strongly shields neutrons and alpha particles. Using a multi-layered method, we found that Polysulfone shields high LET particles more efficiently than Polyetherimide and Polyimide. At Optimal LET, Pure and Al+Polysulfone shield neutrons and alphas particles. In Flux analysis, a significant variation of neutrons flux was observed at 40 g/cm2 in Multi-layered analysis. In addition, boron added multi-layered Polyetherimide reduced the neutrons flux at 100 g/cm2.

Dose Equivalent

Linear Energy Transfer

HZETRN

shielding materials

Transport Codes

Radiation

Space radiation changes dramatically and causes dangerous biological effects on humans and also damages the electronics components. Electrons and Protons, Solar Energetic Particles (SEP), Galactic Cosmic Rays (GCR), and trapped radiations make up the majority of space radiation. SEPs particles are transmitted from several types of solar activities namely solar flares and coronal mass injection. Alpha particles and high atomic number and energy particle (HZE) ions with energies ranging from 10 to 100 MeV constitute the majority of SEPs (Kim et al. 1989). The GCR contains heavy ions spanning from protons to iron ions and is comparable to the radiation environment in space. Strong effectiveness of the GCRs particles was observed in the solar minimum event when the sunspots and solar flare activity reduces. Within 1 AU of the sun, GCRs are composed of high particles with energies ranging from 10³ to 10¹² MeV. These particles can easily enter the spacecraft and produce secondary particles since they travel at almost the speed of light (Yang and Bayazitoglu 2020). The mean radiation dose rate received by humans on Earth is 2–3 mSv/year, with maxima of 6–7 mSv/year in areas with the greatest radiation background (Henriksen and Maillie 2002). Straume et al. 2017 show that the lightest elements (H and He) in GCR have among the highest flux and thus traversal rates in biological targets, but heavy nuclides make a significant contribution to the mean dose and dose equivalent behind thin shielding, resulting in large energy transfer in small biological targets such as cell nuclei, is extremely interesting. The impact of High Z and E Particles (HZE) particles generates around 16 percent of the neutron flux behind the shield, despite the fact that GCR contains just 1% of HZE particles. Alpha particles, on the other hand, produce less than 10% of the secondary neutron flux behind the shield in GCR but account for 15% of it. Protons generate more than 90% of the GCR's constituents, yet only 69 percent of the secondary neutron flux behind the shield is generated by them (Wilson et al. 1997).

Polymers are substances that have numerous structural units connected by a common structure. The low atomic number and density of polymers make them lightweight (More et al. 2021). Polymers are robust and have a long life expectancy. They are also cost-effective, low-maintenance, and temperature-stable throughout a wide range of temperatures (Alavian and Tavakoli-Anbaran 2019). In space, polymers such as Polyethylene, Epoxy resin, Polyetherimide, Polyimide, Polysulfone, and Poly (methyl methacrylate) (PMMA) are widely applied (Cucinotta et al. 2006). Aromatic polymers have higher mechanical strength, better radiation tolerance, and higher thermal stability than aliphatic polymers (Bate 2009). Polyetherimide is a high-strength amorphous polymer with excellent flame and heat resistance. It's also resistant to hydrolysis and acidic solutions, along with repeated autoclaving cycles. Polyetherimide has a density of 1.27 g/cm³. It has a tensile strength of about 113.8 MPa and a deflection temperature of 200 ̊C (Tripathi et al. 2008). Polypropylene and polyethylene, which have significant hydrogen content, are the most effective known polymer shields for GCR (Schiavone 2013). Polyimides, particularly Kapton and Ultem 1000, have been employed in NASA missions due to their wide range of thermal stability, dominantly as insulation for spacecraft and electronics. Because of the great stiffness of the rings, the aromatic structure of polyimides strengthens their mechanical capabilities significantly (Schiavone 2013). Lithium hydride significantly reduced the GCR and secondary radiations than Polyethylene and boron nitride composite against the recent 2010 solar minimum GCR event (Gohel et al. 2022). Al + Polysulfone had superior shielding performance than Al + Polyetherimide during the 2010 solar minimum GCR in the multi-layered strategy that included hydrogen-containing polyetherimide and polysulfone materials (Gohel and Makwana 2022). Borggräfe et al. 2009 simulated several polymers, including polyetherimide and polysulfone, while accounting for radiation for a manned Mars expedition. At a total slab thickness of 50g/cm², the relative location and ordering of the Kapton polyimide and polypropylene layers in the shield were changed. For a given thickness of the polypropylene, the shielding efficacy is significantly better when the Kapton polyimide layer is the front layer (Schiavone 2013). Kraus et al. 1993 showed that the inclusion of boron changes up to 20% wt to the polymer's efficiency as a barrier against high-energy heavy ions only a little.

The main goal of this paper is to explore and simulate the shielding efficacy of hydrogen-rich aromatic polymer composite materials against galactic cosmic radiation, as well as to reduce the number of secondary neutrons created during the shielding process. To restrict the low energy secondary radiation created by the collision of the space radiation with the spaceship, we primarily consider the aromatic type's materials, specifically Polyetherimide, Polysulfone, and Polyimide in pure form and boron powder containing between 5% and 20% by weight. We performed simulations of the fraction of dose equivalent for various particle types, LET analyses at various material thicknesses, and neutron flux calculations at various thicknesses also in the context of the 2010 solar minimum GCR condition.

In present simulations, we have used the BO-2014 GCR model for the 2010 solar minimum GCR event, the GCR was expected to occur at 1 AU in free space for all analyses. Fraction of dose equivalent, LET, and Flux are simulated for aromatic materials in mSv/year at various thicknesses using HZETRN 2015 (Slaba 2013; Slaba et al. 2013, 2015; Norman et al. 2013; Wilson et al. 2014, 2015b, 2015a).

The maximum energy loss from charged particles transfer to the target material and being accumulated during interactions between ions and shielding. The accumulated energy in shielding is calculated using linear energy transfer (LET),

$$S= \frac{dE}{dx}$$

Where dE is energy accumulated in the target material, and dx is the length of the path travelled by the particle in the material.

Materials

In this analysis, we consider three High Hydrogen containing aromatic materials namely Polyetherimide, Polysulfone, and Polyimide. The selection of these shielding materials are based on their high amount of hydrogen atoms and low density. The ultimate goal is to make a light weight and effective shield and therefore material should have these properties.

The different concentration of boron powder between 5% and 20% by weight containing each polymers to absorb the low energy secondary neutrons. Atomic parameters displayed in Table 1 (Kim et al. 1994). In the following Table 1, the details of each materials is given.

Table 1

Materials Names, Density, Chemical Formula, and Atomic parameters for Boron containing polymers from (Kim et al. 1994)
Materials	Atomic Parameters			Atom Density, 10²² atoms/g
Materials	Elements	Z	A	5% B (ρ = 1.30 g/cm³)	10% B (ρ = 1.33 g/cm³)	15% B (ρ = 1.36 g/cm³)	20% B (ρ = 1.40 g/cm³)
Pure Polyetherimide (C₃₇H₂₄O₆N₂) (ρ = 1.27 g/cm³)	H	1	1	23.2	22.0	20.7	19.5
	C	6	12	35.8	33.8	32.0	30.1
	N	7	14	1.93	1.83	1.73	1.63
	O	8	16	5.80	5.49	5.18	4.88
	B	5	11	2.23	4.46	6.69	8.93
	B	5	10	0.558	1.11	1.67	2.23
	Elements	Z	A	5% B (ρ = 1.27 g/cm³)	10% B (ρ = 1.30 g/cm³)	15% B (ρ = 1.34 g/cm³)	20% B (ρ = 1.37 g/cm³)
Pure Polysulfone (C₂₇H₂₆O₆S) (ρ = 1.24 g/cm³)	H	1	1	28.6	27.0	25.5	24.1
	C	6	12	35.0	33.1	31.3	29.6
	O	8	16	5.19	4.90	4.63	4.38
	S	16	32	1.30	1.22	1.16	1.10
	B	5	11	2.11	4.46	6.66	8.76
	B	5	10	0.527	1.12	1.66	2.20
	Elements	Z	A	5% B (ρ = 1.45 g/cm³)	10% B (ρ = 1.48 g/cm³)	15% B (ρ = 1.51 g/cm³)	20% B (ρ = 1.54 g/cm³)
Pure Polyimide (C₃₅H₂₈N₂O₇) (ρ = 1.42 g/cm³)	H	1	1	15.0	14.2	13.4	12.6
	C	6	12	33.0	31.2	29.4	27.7
	N	7	14	3.0	2.84	2.67	2.52
	O	8	16	7.52	7.10	6.69	6.31
	B	5	11	2.15	4.46	6.82	8.9
	B	5	10	0.538	1.12	1.7	2.23

GCR Model

One of the best ways to shield humans from high-energy radiation is to use material barriers. Transport codes may be used to measure the performance of various materials such as shields. The NASA Langley Research Center researchers have developed HZETRN, a typical deterministic method for solving the Boltzmann Transport Equation (Wilson et al. 2006). It uses a one-dimensional method to compute the interaction of both main and secondary particles. This differential equation is solved directly using a straight-ahead approximation, which implies that the primary ions' initial paths are still followed by the secondary particles created in the collision (Yang and Bayazitoglu 2020). As mentioned above the selected BO-2014 GCR model for 2010 solar minimum GCR event, which is occur at 1 AU in deep space.

To generate the nuclear data from the code, it requires some data inputs, which need to be generated. The execution mode, material name, density (g/cm3), number of atomic species, mass, charge, and number density (atoms/g) of the material are all defined in the input file for HZETRN. As a result, cross-section databases are created and stored in the cross section databases directory for a variety of shielding materials. Using this generated database it calculates the different parameters in output file. The output file contains a material definition file, the material's atomic cross-section database, a heavy ion nuclear cross-section database, a light particle nuclear cross-section database, isotropic source cross-section database using slab/3D transport for the same radiation environments, and databases for heavy ion, light particle, and isotropic source nuclear cross-sections. Flux as a function of energy at each depth, linear energy transfer (LET), dose, boundary condition, dose equivalent using ICRP 26 and ICRP 60 conversion coefficients, and dose equivalent using NASA quality factor for leukaemia and solid cancer all the response functions are simulated using HZETRN. In this work, we used the ICRP 60 conversion coefficients to simulate Dose Equivalent, LET, and Fluxes.

Simulation Geometry

In this analysis, each slab's thickness was adjusted to 5 g/cm² for the 2010 solar minimum GCR condition, and all hydrogen-rich boron-containing polymer composite shielding materials were simulated using the slabs mode with a total shielding material thickness ranging from 0 to 100 g/cm². In addition, an Aluminium slab of 10 g/cm² followed by the various polymers composites materials slabs of 90 g/cm² in a Multi-layered approach. We simulated fraction of dose equivalent by various particle types, LET, and Flux of neutron particle using HZETRN for 2010 solar minimum GCR.

Fraction of Dose Equivalent by Particle Type

As the GCR mainly consists of higher concentrations of high-energy protons and alpha particles, it is imperative to study each particle's impact on shielding effect. In this study, we introduced the isotropic boron powder (isotopes ¹⁰B and ¹¹B separately), we study the effectiveness of both isotopes on each polymers materials respectively by the same incident particles (Fig. 1). The dose equivalent of each shielding material to study tendency in terms of length analysis in Fig. 2. In addition, an Aluminium slab of 10 g/cm² followed by a different combinations of polymers materials slabs of 90 g/cm² ware also analyzed to study the effectiveness of each material by particle types (Fig. 3). In Fig. 1, boron containing polymers by 5% and 20% plots was recently presented in ICFP-2022 (8th to 10th July 2022) conference organized by Mahatma Gandhi University, Kottayam, Kerala, India (Gohel and Makwana 2022). In Fig. 1, we calculated the dosage equivalent of polymers with boron power additions ranging from 5–20% by weight. In our observation, we found that polymers containing the boron-11 isotope drop more gradually, indicating a greater energy loss and increased shielding efficiency. We observed that Polysulfone (5% B-11) effectively reduced the neutrons (0.0015 mSv/year) and alphas (0.027 mSv/year) particles dose equivalent than Polysulfone (20% B-11) for neutrons (0.0018 mSv/year) and Alphas (0.032 mSv/year) at 100 g/cm². In addition, boron-containing polysulfone shows more effectiveness than the remaining materials. Increasing the concentration of the boron powder in each polymer, the effectiveness of the shielding materials decreases observed in Fig. 1. Figure 2 exemplifies a significant tendency in the units of length from the perspective of volume. The efficiency of shielding material appears to be proportional to its volume density. More shielding per unit length and more nuclei colliding with incoming particles are correlated with higher density. As shown in Fig. 2, for Polyetherimide (1.27 g/cm³), the material thickness at a length of 50 cm is 64 g/cm². For Polysulfone (1.24 g/cm³), the thickness at 50 cm is 62 g/cm². Similarly, for Polyimide (1.42 g/cm³), thickness is 71 g/cm² at 50 cm length. The dose equivalent for Polyetherimide at 64 g/cm² is 0.82 mSv/year, for Polysulfone at 62 g/cm² is 0.81 mSv/year, and for Polyimide at 71 g/cm² is 0.84 mSv/year. Therefore, for the same volume and difference in material density, Polysulfone has a lower dose equivalent than Polyetherimide and Polyimide. We also performed the Multi-layered approach to simulate the dose equivalent by particles type in which an Aluminium slab of 10 g/cm² was followed by each composite of polymers slab of 90 g/cm² in Fig. 3. In Multi-layered Al + Pure Polysulfone, we observed a decrease of significant dose equivalent of neutrons when the thickness is below 90 g/cm². In the case of protons, Al + Pure Polyimide has better shielding strength than Al + Pure Polyetherimide and Al + Pure Polysulfone at lower material thickness. Also in alphas, Al + Pure Polysulfone effectively reduced the dose equivalent to the remaining materials. In Al + Polymers (5% B11 and 20% B11), we observed the higher shielding of the neutrons performed by Al + Polyetherimide and Al + Polysulfone. For the shielding of protons and alphas, all the combinations of material's performance are nearly the same.

LET Analysis

Linear Energy Transfer (LET) is the average energy deposited in shielding per unit length. LET function that is dependent on type and energy of the particle, and the material. The high LET component of the radiation flow is shown to drop as the shield thickness increases in all the pure polymer materials in Fig. 4. The decrease in high LET flux may contribute to an increase in low LET particles. From the perspective of radiation biology, this is helpful because the biological effects of low LET radiation are better understood than those of high LET radiation. When the LET value is less than 2 KeV/m, the particle flux in the multi-layered boron-11 containing polymers is significantly affected. Al + Polysulfone (5% B-11) effectively reduced the flux at any thickness than Al + Polysulfone (20% B-11). We observed that boron-containing Al + Polysulfone has a better shielding to the GCR flux at higher LET than boron-containing Al + Polyetherimide and Al + Polyimide. A lower concentration of multi-layered boron-11 has better shielding than a higher concentration. In Fig. 5 Optimal LET at 100 KeV/ µm, pure polysulfone (0.46), boron-containing Polysulfone (0.20 for 5% B-11 and 0.24 for 20% B-11) and Al + Polysulfone (0.46 for pure, 0.35 for 5% B-11 and 0.41 for 20% B-11) significantly decreases the particles flux which decreases the biological effects than Polyetherimide and Polyimide (flux unit is particles/cm²-keV/µm-year).

Flux Analysis

Neutrons have no electric charge at all. When GCR particles penetrate shielding materials during nuclear fission, they produce secondary radiation. Neutrons, in general, can be a biological threat since they can easily transport matter without the constraint of Coulomb force. Flux analysis, along with a multi-layered method, enables us to determine the neutron production in each hydrogen-rich boron-containing polymer. In Multi-layered analysis, Al followed by the boron-11 containing polymers, a significant variation of neutron flux was observed between 10¹ to 10³ MeV/n at 40 g/cm². Al + Polyetherimide (5% B-11) significantly reduced the neutrons flux ((5.2 x 10^− 5 particles/ (cm²-MeV/n-year)) at 40g/cm² and (3.02 x 10^− 8 particles/ (cm²-MeV/n-year)) at 100g/cm²) than Al + Polyetherimide (20% B-11) ((5.56 x 10^− 5 particles/ (cm²-MeV/n-year)) at 40g/cm² and (3.64 x 10^− 8 particles/ (cm²-MeV/n-year)) at 100g/cm²) observed in Fig. 6. In addition, we found that boron containing Al + Polyetherimide shields more neutrons flux than boron containing Al + Polysulfone and Al + Polyimide.

The purpose of this work is to discuss the potential use of materials with a high hydrogen concentration as shielding materials. Based on preliminary research with HZETRN code, the GCR particle shielding effectiveness of several materials namely Polyetherimide, Polysulfone, and Polyimide Polymers was simulated for 2010 solar minimum GCR. We noticed that the fraction of dose equivalent by B-11 in boron-containing polymers decreases more rapidly than that by B-10 in the same polymers. Dose equivalent by neutrons and alphas particles effectively reduced by Polysulfone (5% B-11) than B-11 contained Polyetherimide and Polyimide. At 50 cm, Pure Polysulfone decreased dose equivalent (0.81 mSv/year) to the remaining materials. Dose equivalent in Multi-layered shielding observed that Al + Polysulfone and Al + Polysulfone (5% B-11) reduced the neutrons and alphas particle type than other materials. In LET analysis, boron contained, and Multi-layered with Polysulfone shields high LET particles more effectively. At Optimal LET (100 keV/µm), Al + Polysulfone and Al + Polyetherimide diminished high LET at higher thickness. In the case of Flux analysis, Shielding of the neutron flux increased by boron-containing Multi-layered Polyetherimide materials.

Acknowledgments

The authors are thankful to NASA to provide the HZETRN transport code.

Author Contributions: Ankit Gohel performed simulation analysis, prepared all the tables and figures and wrote the main manuscript text. Rajnikant Makwana reviewed and edited the manuscript. All authors reviewed the manuscript.

Funding: The authors received no specific funding for this work.

Compliance with ethical standards

Conflict of Interest: The authors declare that they have no conflict of interest.

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No competing interests reported.

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Effective Shielding Multi-layered Boron Containing Aromatic Polymer Materials for High Energy Radiations

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Abstract

Figures

Introduction

Materials And Methods

Results And Discussion

Fraction of Dose Equivalent by Particle Type

LET Analysis

Flux Analysis

Conclusion

Declarations

References

Additional Declarations

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