RADIATION SHIELDING MATERIAL

Abstract

The present invention provides a radiation shielding material, particularly for shielding of particle radiation, comprising a fibre material and a radiation damping filler, wherein the amount of the radiation damping filler is 40 to 95 wt. % based on the dry weight of the radiation shielding material. The present invention further provides a radiation shielding structure, particularly for shielding of particle radiation, comprising a bottom layer and a top layer, wherein a hollow structure is sandwiched between the bottom layer and the top layer, wherein the hollow structure is filled with a radiation damping filler.

Claims

1. Radiation shielding material, particularly for shielding of particle radiation, comprising a fibre material and a radiation damping filler, characterized in that the amount of the radiation damping filler is 40 to 95 wt. % based on the dry weight of the radiation shielding material.

2. Radiation shielding material according to claim 1, wherein the fibre material is conventional in papermaking, preferably consisting of organic fibres, particularly preferably cellulose fibres, wherein preferably the cellulose fibres consist of a chemical pulp mixture of long fibre cellulose and short fibre cellulose, preferably a 40:60 mixture.

3. Radiation shielding material according to claim 1, wherein the radiation damping filler is present from 60-90 wt % based on the dry weight of the radiation shielding material, even more preferably from 80-90 wt %.

4. Radiation shielding material according to claim 1, wherein the radiation damping filler is selected from the group of boron and/or boron compounds and/or alkali metal hydrides, or mixtures thereof.

5. Radiation shielding material according to claim 1, wherein the radiation damping filler is selected from Lithium borohydride (LiBH4), Ammonia borane (H3NBH3), Boron (B), preferably 10B, hexagonal Boron nitrate (h-BN), Boron carbide (B4C) or Lithium hydride (LiH), or mixtures thereof.

6. Radiation shielding material according to claim 1, wherein the radiation damping filler is present in a particle size (d50) from 0.4-30 μm, preferably from 0.6-10 μm.

7. Radiation shielding material according to claim 1, wherein Boron is present in a particle size (d50) from 1-2 μm and/or Boron carbide is present in a particle size (d50) from 1-2 μm and/or hexagonal Boron nitrate is present in a particle size (d50) from 4-6 μm.

8. Radiation shielding material according to claim 1, wherein the purity of the radiation damping filler is 85-100%, preferably 95-99%.

9. Radiation shielding material according to claim 1, comprising at least one binding agent, wherein the binding agent preferably is a starch and/or a latex, particularly preferably a cationic starch and/or a negatively charged latex.

10. Radiation shielding material according to claim 1, comprising at least one retention agent, wherein the retention agent preferably is a cationic polymer, particularly preferably a cationic polyacrylamide.

11. Radiation shielding material according to any of claims claim 1, comprising a cationic starch, a cationic polyacrylamide and styrene butadiene latex.

12. Radiation shielding material according to claim 1 comprising or consisting of: fibre material, preferably cellulose fibres: 6.5-7.5 wt % cationic starch, preferably maize starch: 0.5-1 wt % cationic polymer, preferably polyacrylamide: 0.05-0.1 wt % latex, preferably styrene butadiene latex: 2-3% radiation damping filler, particularly preferably boron carbide: 80-90 wt %

13. Radiation shielding material according to claim 1, wherein the radiation shielding material is a flat paper with a thickness of 0.2-4 mm, preferably 0.4-3 mm, particularly preferably 1-2 mm.

14. Radiation shielding material according to claim 1, wherein the radiation shielding material has a grammage of 40-1400 g/m.sup.2, preferably 300-800 g/m.sup.2, particularly preferably of 400-600 g/m.sup.2.

15. Radiation shielding material according to claim 1, wherein the radiation shielding material has a density of 0.5-1.7 g/cm.sup.3, preferably of 0.95-1.5 g/cm.sup.3.

16. Radiation shielding material according to claim 1, wherein the radiation shielding material has a tensile strength of 1800-2000 N/m.

17. Radiation shielding material according to claim 1, wherein the radiation shielding material has a bending stiffness of 10-20 Nmm, preferably of 12-18 Nmm.

18. Radiation shielding material according to claim 1, wherein the radiation shielding material is impregnated, preferably with an epoxy resin.

19. A method for production of a radiation shielding material, comprising the steps of: mixing at least one fibre material conventional in papermaking, preferably containing cellulose fibres, and at least one radiation damping filler, in a liquid medium, preferably water, to form a slurry, wherein the dry content in the slurry is preferably 15-35 wt %, adding at least one additive to the slurry to produce a bound slurry, processing the bound slurry to a paper, wherein the radiation damping filler is present from 40-95 wt % based on the dry weight of the paper, preferably calendering of the paper.

20. A radiation shielding structure, particularly for shielding of particle radiation, comprising a bottom layer and a top layer, wherein a hollow structure is sandwiched between the bottom layer and the top layer, characterised in that the hollow structure is filled with a radiation damping filler.

21. Radiation shielding structure according to claim 20, wherein the bottom layer and the top layer are essentially parallel to each other.

22. Radiation shielding structure according to claim 20, wherein the hollow structure is made of a plurality of open ended cells, particularly with walls perpendicular to the bottom and/or top layer.

23. Radiation shielding structure according to claim 22, wherein the cross-section of the cells is hexagonal or circular or oval or rectangular or triangular and/or the walls of the cells are corrugated.

24. Radiation shielding structure according to claim 20, wherein the hollow structure is a honeycomb structure, preferably with a cell size of 2.5-5 mm, preferably 3-4 mm, particularly preferably 3.2 mm.

25. Radiation shielding structure according to claim 20, wherein each cell has a volume of 0.05-1.00 ml, preferably 0.075-0.45 ml, particularly preferably 0.100-0.150 ml and/or wherein each cell is filled with the filler to at least 70 vol %.

26. Radiation shielding structure according to claim 20, wherein the hollow structure has a height of 4-100 mm, preferably 10-50 mm, particularly preferably 10-20 mm.

27. Radiation shielding structure according to claim 20, wherein the hollow structure has a density of 25-60 kg/m.sup.3, preferably 35-55 kg/m.sup.3, particularly preferably 48 kg/m.sup.3.

28. Radiation shielding structure according to claim 20, wherein the hollow structure is made of an aramid-paper, preferably coated with a phenolic resin.

29. Radiation shielding structure according to claim 20, wherein the weight of the radiation damping filler is 55-75% of the total weight, preferably 60-70%.

30. Radiation shielding structure according to claim 20, wherein the radiation damping filler is compacted, preferably to at least 60% of its close-packing of spheres volume, particularly preferably to 80%.

31. Radiation shielding structure according to claim 20, wherein the radiation damping filler is selected from the group of boron and/or boron compounds and/or alkali metal hydrides, or mixtures thereof.

32. Radiation shielding structure according to claim 20, wherein the radiation damping filler is selected from Lithium borohydride (LiBH4), Ammonia borane (H3NBH3), Boron (B), preferably 10B, hexagonal Boron nitrate (h-BN), Boron carbide (B4C) and/or Lithium hydride (LiH), or mixtures thereof.

33. Radiation shielding structure according to claim 20, wherein the radiation damping filler is present in a particle size (d50) from 0.4-30 μm, preferably from 0.6-10 μm.

34. Radiation shielding structure according to claim 20, wherein Boron is present in a particle size (d50) from 1-2 μm and/or Boron carbide is present in a particle size (d50) from 1-2 μm and/or hexagonal Boron nitrate is present in a particle size (d50) from 4-6 μm.

35. Radiation shielding structure according to claim 20, wherein the purity of the radiation damping filler is 85-100%, preferably 95-99%.

36. Radiation shielding structure according to claim 20, wherein the radiation shielding structure has a thickness of 5 to 50 mm, preferably 10 to 30 mm, particularly preferably 10 to 20 mm.

37. (canceled)

38. Radiation shielding structure according to claim 20, wherein the radiation shielding material contains boron carbide as radiation damping filler and the hollow structure is are filled with Boron as radiation damping filler.

39. (canceled)

40. (canceled)

Description

[0125] The invention is described in greater detail below based on exemplary embodiments by way of example only and without limitation.

[0126] FIG. 1 shows a radiation shielding structure (RSS) according to the invention.

[0127] FIG. 2 shows a cross-section of the radiation shielding structure of FIG. 1.

[0128] FIG. 3 shows a comparison of Microdosimetric Spectra: RSS vs. Aluminium at 100 MeV before the Bragg Peak.

[0129] FIG. 4 shows a comparison of Microdosimetric Spectra: RSS vs. Aluminium at 100 MeV after the Bragg Peak.

[0130] FIG. 5 shows a comparison of Microdosimetric Spectra: Measurement vs. Simulation at 75 MeV.

[0131] FIG. 6 shows a comparison of Microdosimetric Spectra: Measurement vs. Simulation at 100 MeV.

[0132] FIG. 7 shows the Dose Equivalent, H TEPC behind Shielding Layers vs. Shielding Depth with incident 100 MeV protons.

[0133] FIG. 8 shows the Depth Dose Profile of Effective Dose Equivalent, H.sub.E, using the ICRP 60 quality factor with incident 100 MeV protons.

[0134] FIG. 9 shows the Depth Dose Profile of Effective Dose Equivalent, H.sub.E, using the ICRP 60 quality factor with the radiation environment spectrum from the mission scenario.

[0135] FIG. 10 shows the Depth Dose Profile of Effective Dose Equivalent, H.sub.E, using the NASA quality factor with the radiation environment spectrum from the mission scenario.

[0136] FIG. 11 shows the Effective Dose Equivalent, H.sub.E, contribution of protons and neutrons compared to the total, behind RSS shielding using ICRP 60 quality factor and radiation environment spectrum from the mission scenario vs. shielding depths.

[0137] FIG. 12 shows the Effective Dose Equivalent, H.sub.E, contribution of protons and neutrons compared to the total, behind Aluminium reference shielding using ICRP 60 quality factor and radiation environment spectrum from the mission scenario vs. shielding depths.

[0138] FIG. 1 shows a radiation shielding structure (RSS) according to the invention. The RSS has a bottom layer (2) and a top layer (1) that are parallel to each other. In an advantageous embodiment the bottom layer (2) and/or the top layer (1) can be made of a radiation damping material, e.g. produced according to Example 1. The radiation damping material may consist of a paper highly filled with BaC.

[0139] In the present embodiment of FIG. 1 a hollow structure (3) is sandwiched between the bottom layer (2) and the top layer (1). The hollow structure (3) is made of a plurality of open ended cells with walls perpendicular to the bottom and top layer (1.2). In the present embodiment the hollow structure (3) is a honeycomb structure.

[0140] The honeycomb structure is filled with a particle radiation damping filler (4). In the present embodiment the radiation damping filler is amorphous Boron.

[0141] FIG. 2 shows a cross-section of the radiation shielding structure of FIG. 1.

[0142] The radiation shielding structure of FIG. 1 can be produced according to Example 4.

EXAMPLE 4

Production of an Exemplary Radiation Shielding Structure (RSS)

[0143] In a first step, pre-trials were carried out to be able to define the process conditions for impregnation and gluing:

[0144] a) Materials

[0145] The following materials were used: [0146] Laboratory sheets highly filled with B.sub.4C (see Examples 1 and 2), [0147] Hexagonal honeycomb material (Schütz Composites: CORMASTER® C1-3.2-48T, thickness: 14.3 mm; Nomex T412 (Poly(m-phenylen-isophthalamid) paper coated with a phenolic resin), pre-cut to round core material with a diameter of 200 mm. [0148] Epoxide resin type L and curing agent type L (R&G Faserverbundwerkstoffe GmbH) were prepared according to the specifications of the manufacturer and used immediately. [0149] Filling material: elemental Boron (powder; amorphous, Grade I, H.C, Starck). The specifications of the filler material are listed in detail hi Tab. 2. [0150] WiPAK PET-A foil was used as a drying support.

[0151] b) Manufacturing procedure

[0152] The following procedure was carried out for the manufacture of the radiation shielding structure: [0153] Impregnation of the bottom layer (2) with epoxide resin [0154] Positioning of the hollow structure (3) on the bottom layer (2) [0155] Drying semi-finished structure) [0156] Filling of the semi-finished structure with radiation damping filler (4) [0157] Impregnation of the top layer (1) [0158] Positioning of the top layer (1) on the semi-finished structure, subsequent drying process

[0159] c) Step 1: Impregnation of the paper layers:

[0160] A two-side metering bar coater type CHM was used for the impregnation of the highly filled paper layers. Each of the paper samples was saturated with epoxide resin for 3 minutes until complete deaeration, The excess resin was removed subsequently by two metering bars (one bar with smooth surface for the bottom layer, one 0.6 mm bar for the top side) with a traverse speed of 8 rpm.

[0161] d) Step 2: Positioning and drying process:

[0162] The highly filled papers were impregnated with the epoxide resin, dried and glued to the honeycomb structure using the epoxide resin as adhesive. The impregnated sheets were placed on a flat sheet with the side containing more resin pointing upwards. Then a pre-cut honeycomb core was placed centric on the sheet. The composite was dried at room temperature under surface pressure of 59 N. In an additional step, the outer groove was brushed with epoxide resin and dried for 24 hours to seal the surface, resulting in the semi-finished structure.

[0163] e) Step 3: Filling procedure:

[0164] The semi-finished structure was filled with elemental Boron. At first, 145 g Boron powder were deposited centrally on the honeycomb structure. The excess material was spread to the outside using a ruler and the filling material was densified as follows: two 22 cm×22 cm×1 cm medium density fibreboard plates were placed below and onto the RSS and 100 hits with a 70 g wooden hammer were applied to the upper plate.

[0165] Step 4: Impregnation and drying of the top layer:

[0166] The impregnation and drying of the top layer were carried out in analogy to the bottom layer, but here the side containing more resin was oriented downwards in the direction of the honeycomb core. In order to ensure a complete sealing, the side grooves were filled with some additional epoxy resin using a small paintbrush.

[0167] 20 sandwich structures filled with Boron and two empty reference structures without Boron filling were manufactured.

EXAMPLE 5

Specifications of the RSS of Example 4

[0168] Table 6 and 7 show the mean values for the weight-parameters of 20 manufactured RSS samples with a mean diameter of 200 mm, and mean thickness of 15.2 mm. The average total mass of one RSS is 232 g. A diameter of 20 cm yields an average shielding depth of 0.74 g/cm.sup.2 per RSS. Stacking of the RSSs allows achieving shielding depths ranging from 0.74 g/cm.sup.2 to 14.8 g/cm.sup.2. The average thickness of one RSS is 1.6 cm. The whole stack of 20 RSSs has a total length of 32 cm.

TABLE-US-00006 TABLE 6 Specifications of the RSS Mass of Dry mass of Dry mass of Mass of empty Mass of Mass of Mass of bottom B.sub.4C top B.sub.4C empty structure + Mass of honeycomb epoxide Boron Total Sample paper layer paper layer structure filling B.sub.4C paper structure resin filling mass No. (g) (g) (g) (g) (g) (g) (g) (g) (g) Bor-1 15.6 15.3 46.2 195.7 30.8 21.5 39.0 149.5 219.3 Bor-2 15.7 17.4 48.2 199.5 33.1 21.4 45.0 151.2 229.3 Bor-3 16.1 15.5 49.0 191.5 31.5 21.6 45.0 142.5 219.0 Bor-4 16.0 15.9 48.0 191.9 32.0 21.2 42.9 143.9 218.8 Bor-5 16.3 15.8 51.1 208.9 32.1 23.5 47.4 157.8 237.3 Bor-6 16.3 16.1 51.1 208.0 32.4 23.8 45.6 156.8 234.8 Bor-7 16.0 16.1 52.4 211.2 32.2 23.8 48.6 158.8 239.5 Bor-8 16.1 15.9 52.2 204.3 32.1 23.9 47.7 152.1 231.8 Bor-9 16.3 16.3 51.1 208.1 32.6 24.0 45.5 156.9 235.0 Bor-10 16.0 16.4 51.0 205.8 32.4 23.7 46.6 154.8 233.8 Bor-11 16.3 15.4 51.1 204.0 31.7 22.8 45.2 152.9 229.8 Bor-12 15.3 16.0 48.8 204.3 31.3 23.0 45.3 155.5 232.1 Bor-13 15.8 16.7 47.9 209.6 32.5 21.4 44.8 161.8 239.0 Bor-14 15.9 16.5 49.5 207.0 32.4 21.4 46.4 157.6 236.3 Bor-15 15.9 16.6 48.2 202.7 32.5 21.3 43.9 154.6 230.9 Bor-16 15.6 16.4 48.6 203.6 32.0 21.7 45.1 154.9 232.0 Bor-17 16.0 15.0 47.8 206.5 31.1 21.1 43.6 158.7 233.3 Bor-18 15.7 16.1 48.2 204.1 31.7 20.9 44.9 155.8 232.5 Bor-19 16.2 15.7 48.3 206.3 31.9 21.2 43.6 158.0 233.6 Bor-20 16.6 15.3 49.8 207.4 31.8 21.4 46.3 157.6 235.8 Mean 16.0 16.0 49.4 204.0 32.0 22.2 45.1 154.6 231.7 Std. dev. 0.3 0.6 1.7 5.5 0.5 1.2 2.0 4.8 6.1 (abs.) Var. 2.0 3.6 3.4 2.7 1.7 5.2 4.5 3.1 2.6 coeff. (%)

TABLE-US-00007 TABLE 7 Specifications of reference structure Dry mass of Dry mass of Mass of Mass of bottom B.sub.4C top B.sub.4C Mass of honeycomb epoxide Total Sample paper layer paper layer B.sub.4C paper structure resin mass No. (g) (g) (g) (g) (g) (g) Ref-1 17.0 16.5 33.5 21.1 45.1 78.6 Ref-2 17.0 17.5 34.6 21.1 46.2 80.7

[0169] Table 8 shows the chemical composition of a RSS sample.

TABLE-US-00008 TABLE 8 Chemical Composition of the RSS Aramid- Epoxy paper hollow Paper Sheet resin structure Filler C.sub.12H.sub.20O.sub.10 + B.sub.4C C.sub.18 H.sub.19O.sub.3 C.sub.14H.sub.10N.sub.2O.sub.2 B Element wt. % wt. % wt. % wt. % C 24.0 76.3 70.6 — H 1.0  6.7 4.2 — N — — 11.8 — O 6.0 17.0 13.4 — B 69.0 — — 100.0 SUM 100.0 100.0  100.0 100.0

[0170] The paper sheets consist mainly of cellulose fibres and Boron carbide (the content of latex, cationic starch and cPAM used in the manufacturing process can be neglected). The Boron carbide content of the paper sheets (approx. 88 mass percent) was determined by ashing. The elemental composition of the paper sheets was calculated subsequently from the mass shares and the theoretical sum formulas of cellulose and Boron carbide. The elemental composition of the different components (epoxy, meta-aramid) was calculated from their theoretical sum formulas available in the manufacturer data sheets or in the chemical literature. The mass shares of the paper sheet, the meta-aramid honeycomb, the epoxy resin and the Boron filler were determined by weighing during the different steps of the RSS manufacturing process. Accordingly, the overall elemental composition of the RSS was calculated.

Example 6

Testing of RSS of Example 4

[0171] The following scenario was used for comparison of the materials: The Space Radiation Environment Prediction Models have been applied for the prediction and specification of the space radiation environment for a “Round-trip Earth-Mars-Stay on Mars—and return to earth” in the years 2033/2034. The scenario used for testing the RSS was a 300 days long flight from Mars to Earth from January 2034 to November 2034. This flight phase is the longest of all mission segments, and therefore, it is associated with the highest radiation absorption dose of the mission segments. Based upon the mission scenario for 2034, space radiation environmental data have been acquired from SPENVIS data base. The Space Environment Information System (SPENVIS) is an ESA operational software that provides a web-based interface for assessing the Space environment and its effects on spacecraft systems and crews. SPENVIS also includes extensive background information on the space environment and the environment models.

[0172] The following Space Radiation Environment Prediction Models have been applied for the prediction and specification of the space radiation environment for an assumed mission scenario: The ESP (Emission of Solar Protons) model, the PSYCHIC model (Prediction of Solar particle Yields for CHaracterizing Integrated Circuits), the CREME96 models, ISO-15390 model, i.e. GCR particle flux models.

[0173] The radiation environment for this scenario was calculated for selected particle types, i. e.

[0174] the fluence of Solar Protons and of Galactic Cosmic Radiation Fluxes composed of protons, helium, carbon and iron dependent as function of their particle energy.

[0175] Radiation hardness testing on Earth can only account for a limited segment of the complete radiation environment spectrum. Particle accelerators are limited in energy and may only accelerate one particle type at once. Compared to solar protons, GCR occur with small frequency. Furthermore, solar protons have energies that can be achieved in accelerator facilities with reasonable effort. Thus, protons were used for radiation testing of the RSS. The protons used for testing correspond to solar protons of the same energy.

[0176] For the experiments, monoenergetic protons with energies of 75 MeV, 100 MeV and 150 MeV were used, provided with a beam diameter of 12 cm FWHM.

[0177] The investigated RSS-Samples consist of sheets enriched with BaC and glued with epoxy to seal a Aramid-paper honeycomb core filled with elemental Boron. The sandwich structure provides stability and the lightweight materials used yield a low overall density of the shielding. The average volumetric density of a RSS is 0.46 g/cm.sup.3.

[0178] The reference material was Aluminium. Aluminium has a density of 2.7 g/cm.sup.3. Thus, a RSS of 16 mm thickness with 0.74 g/cm.sup.2 shielding depth has equal shielding depth to a 2.74 mm-thick aluminium sheet. Although both stacks have similar shielding depth (14.8 g/cm.sup.2 and 16.2 g/cm.sup.2) they differ by 26 cm in length (32 cm vs. 6 cm for RSS vs. aluminium).

[0179] Circular aluminum sheets with a diameter of 20 mm and a thickness of 3 mm served as a reference for the shielding performance investigations. With a thickness of 3 mm, one sheet has similar shielding depth to one RSS (Al: 0.81 g/cm.sup.2; RSS: 0.74 g/cm.sup.2). For the experiments, a total of 20 aluminium reference sheets were manufactured that allow shielding depths between 0.81 g/cm.sup.2 and 16.2 g/cm.sup.2.

[0180] The chemical composition of the reference material is shown in Tab. 9.

TABLE-US-00009 TABLE 9 Chemical composition of Aluminium - reference (Al99.5/AW-1050A/3.0255) Al Si Fe Cu Mn Mg Zn Ti others in % in % in % in % in % in % in % in % in % min max max max max max max max max 99.5 0.25 0.40 0.05 0.05 0.05 0.07 0.05 0.03

[0181] The measurements were performed by a tissue equivalent proportional counters (TEPC). TEPCs are used to determine microdosimetric energy deposition spectra. Due to their tissue equivalence, dose distributions derived from TEPC measurements allow for a dose estimation for humans. The microdosimetry approach investigates distribution of radiation energy deposition in micrometer-size volumes of tissue, on cell-level scale.

[0182] The TEPC instrument used is a HAWK type manufactured by Far West Technology Inc. The detector itself is a gas filled proportional counter of spherical shape with a lower threshold of 0.5 keV/μm and an upper threshold of 1024 keV/μm. The wall of the detector is made of conducting tissue equivalent plastic (A150). The inner diameter of the sphere is 125 mm. The gas cavity is filled with pure propane gas at low pressure (933.2 Pa) and represents a tissue site size of about 2.16 μm. The detector sphere and the required electronics are contained in a cylindrical structure made of stainless steel and aluminum.

[0183] The following set-ups were tested: [0184] 1. a stack of RSS with shielding depths ranging from 0 g/cm.sup.2 to 14.8 g/cm.sup.2 in front of a TEPC [0185] 2. a stack of aluminium reference sheets with shielding depths ranging from 0 g/cm.sup.2 to 16.2 g/cm.sup.2 in front of a TEPC [0186] 3. the TEPC without shielding for background measurements with no proton beam

[0187] Further, a numerical simulation of the TEPC detector response behind the RSS and reference shielding being exposed to monoenergetic protons was carried out, as well as to protons having an energetic distribution representative for the assumed mission scenario. For all simulation-investigations, the Monte Carlo Code FLUKA was used.

[0188] The test set-up proton beam was modelled for the two nominal proton energies of 75 MeV and 100 MeV. The proton beam used at the facility has been characterised directly before the experiments by measuring beam profiles along the horizontal and vertical main axis of the radiation field. To assess the beam divergence the lateral characterisation of the beam profiles was performed in two planes that are separated 30 cm from each other. The first layer was positioned 5 cm from the last ionisation chamber being used for beam diagnostics, while the second plane was located another 30 cm downstream, thus in a distance of 35 cm from the last ionisation chamber.

[0189] For depth dose investigation the numerical source was modelled as a pencil beam that impinges in the centre of the front-side of the shielding set-up. Also, for these simulation the lateral extend of the RSS shielding set-up and also of the Aluminium reference set-up increased. The usage of a pencil beam and the lateral extension of the set-up was done to minimise border effects that might appear due to a limited lateral extend of the shielding set-up. After conduction of the numerical investigations, the results were renormalized properly in order to be presented correctly per unit incident proton fluence.

[0190] An overview on the simulations performed with respect to test set-up and depth dose profile modelling using a RSS model and an Aluminium reference model is presented in Table 10.

TABLE-US-00010 TABLE 10 Overview on the simulations performed with respect to Test set-up and depth dose profile modelling using a RSS model and an Aluminium reference model. Energy/Spectrum Shielding Model Set-Up Type Type Shielding Depth (g/cm.sup.2) Test  75 MeV RSS 4.44, 5.18, 5.92 set-up Aluminium 4.86, 5.67, 6.48, 16.20 Reference 100 MeV RSS 8.14, 8.88, 9.62, 10.36, 11.84, 14.80 Aluminium 8.91, 9.72, 10.53, 16.20 Reference Depth  75 MeV RSS 0.000, 0.703, 1.406, 2.109, 2.812, 3.515, 4.218, 4.921, Dose 5.624, 6.327, 7.030, 7.733, 8.436, 9.139, 9.842, 10.545, 11.248, 11.951, 12.654, 13.357, 14.060 Aluminium 0.000, 0.810, 1.619, 2.429, 3.239, 4.048, 4.858, 5.668, Reference 6.477, 7.287, 8.097, 8.906, 9.716, 10.526, 11.335, 12.145, 12.955, 13.764, 14.574, 15.384, 16.193 100 MeV RSS 0.000, 0.703, 1.406, 2.109, 2.812, 3.515, 4.218, 4.921, 5.624, 6.327, 7.030, 7.733, 8.436, 9.139, 9.842, 10.545, 11.248, 11.951, 12.654, 13.357, 14.060 Aluminium 0.000, 0.810, 1.619, 2.429, 3.239, 4.048, 4.858, 5.668, Reference 6.477, 7.287, 8.097, 8.906, 9.716, 10.526, 11.335, 12.145, 12.955, 13.764, 14.574, 15.384, 16.193 Mission RSS 0.000, 0.703, 1.406, 2.109, 2.812, 3.515, 4.218, 4.921, scenario 5.624, 6.327, 7.030, 7.733, 8.436, 9.139, 9.842, 10.545, 11.248, 11.951, 12.654, 13.357, 14.060 Aluminium 0.000, 0.810, 1.619, 2.429, 3.239, 4.048, 4.858, 5.668, Reference 6.477, 7.287, 8.097, 8.906, 9.716, 10.526, 11.335, 12.145, 12.955, 13.764, 14.574, 15.384, 16.193

[0191] Results for the absorbed dose D and dose equivalent H derived by the TEPC as well as the quality factor Q for background measurements, stacks of aluminium reference material and stacks of RSS for 75 MeV, 100 MeV and 150 MeV incident protons are shown in Tables 11 and Table 12.

[0192] Table 11 summarizes the results for the absorbed dose D and the dose equivalent H derived from measurements with the TEPC as well as the quality factor, Q for aluminium reference shielding.

TABLE-US-00011 TABLE 11 Results: Summary on Aluminium Reference Shielding Irradiation Proton Mean Total Shielding Time Energy Flux Fluence Depth D.sub.TEPC/UF H.sub.TEPC/UF ID Material min MeV p/cm.sup.2/s p/cm.sup.2 g/cm.sup.2 Layers pGy .Math. cm.sup.2 pSv .Math. cm.sup.2 Q A01 Al99.5 10 75 1 181 7.1E+05 16.20 20 2.37 6.38 2.69 A02 Al99.5 10 100 1 354 8.1E+05 16.20 20 2.79 8.45 3.03 A03 Al99.5 10 150 1 839 1.1E+06 16.20 20 199.70 288.83 1.45 A04 Al99.5 10 100 1 354 8.1E+05 9.72 12 254.74 866.16 3.40 A05 Al99.5 10 100 1 347 8.1E+05 10.53 13 18.67 64.63 3.46 A06 Al99.5 10 100 1 649 9.9E+05 8.91 11 375.81 980.78 2.61 A07 Al99.5 10 75 1 161 7.0E+05 5.67 7 134.08 484.08 3.61 A08 Al99.5 10 75 1 151 6.9E+05 6.48 8 10.55 27.86 2.64 A09 Al99.5 10 75 1 155 6.9E+05 4.86 6 445.47 1141.25 2.56

[0193] Table 12 summarizes the results for the absorbed dose D and the dose equivalent H derived from measurements with the TEPC as well as the quality factor, Q for RSS shielding.

TABLE-US-00012 TABLE 12 Results: Summary on Aluminium Reference Shielding Irradiation Proton Mean Total Shielding Time Energy Flux Fluence Depth D.sub.TEPC/UF H.sub.TEPC/UF ID Material min MeV p/cm.sup.2/s p/cm.sup.2 g/cm.sup.2 Layers pGy .Math. cm.sup.2 pSv .Math. cm.sup.2 Q M01 RSS 10 75 1 401 8.4E+05 14.80 20 2.50 6.14 2.46 M02 RSS 10 100 1 707 1.0E+06 14.80 20 2.12 5.17 2.44 M03 RSS 10 150 1 939 1.2E+06 14.80 20 212.23 303.28 1.43 M04 RSS 10 150 1 801 1.1E+06 14.06 19 202.08 288.70 1.43 M05 RSS 10 100 1 245 7.5E+05 14.06 19 2.75 7.30 2.65 M07 RSS 10 150 1 527 9.2E+05 13.32 18 208.25 297.10 1.43 M08 RSS 10 100 1 223 7.3E+05 11.84 16 7.05 14.52 2.06 M09 RSS 10 100 1 285 7.7E+05 8.14 11 361.80 966.26 2.67 M10 RSS 10 100 1 172 7.0E+05 8.88 12 90.20 304.78 3.38 M11 RSS 10 75 1 146 6.9E+05 8.88 12 4.34 10.82 2.50 M12 RSS 10 100 1 245 7.5E+05 9.62 13 9.26 22.70 2.45 M13 RSS 10 100 1 256 7.5E+05 10.36 14 7.06 13.24 1.87 M14 RSS 10 75 1 264 7.6E+05 5.18 7 70.88 248.55 3.51 M15 RSS 10 75 1 288 7.7E+05 5.92 8 9.16 20.05 2.19 M16 RSS 10 75 1 194 7.2E+05 4.44 6 359.83 978.38 2.72

[0194] Massive particles like protons transfer energy by the inverse square of their velocity. The linear energy transfer (LET) peaks for low energies, just before the particle stops, forming the characteristic Bragg Peak in the Bragg Curve. By varying the particle energy, the Bragg Peak can be shifted along the material's depth. For polyenergetic particles the Bragg Peak is smeared out and no distinct peak is observed in the energy loss curve.

[0195] FIG. 3 shows RSS und aluminium microdosimetric spectra before the Bragg Peak. A significant amount of protons is stopped inside the material at sufficiently high shielding depths, leading to low overall doses behind the shielding. Although the primary 100 MeV protons are stopped, secondary particles, such as neutrons, protons, electrons, spallation ions, etc. can be produced successively inside the shielding.

[0196] FIG. 4 shows RSS und aluminium microdosimetric spectra after the Bragg Peak. Behind the Bragg Peak, the microdosimetric spectra of RSS and aluminium differ significantly. High-LET events are more prominent behind the aluminium shielding. Densely ionizing radiation with high LET is weighted stronger by q(γ), leading to a much higher quality factor Q behind the aluminium shielding: 3.03 vs. 2.44 for RSS. Although RSS has the lower shielding depth (14.8 g/cm.sup.2 vs. 16.2 g/cm.sup.2), it provides less absorbed dose per unit fluence D/UF, 2.12 pGy.Math.cm.sup.2 vs. 2.79 pGy.Math.cm.sup.2, and less dose equivalent per unit fluence H/UF, 5.17 pSv.Math.cm.sup.2 vs. 8.45 pSv.Math.cm.sup.2.

[0197] FIG. 5 and FIG. 6 show a comparison of measured and simulation microdosimetric spectra of the lineal energy distribution of the absorbed dose, D, and dose equivalent, H, for incident protons of 75 MeV and 100 MeV and different shielding depths (4.44 g/cm.sup.2-8.91 g/cm.sup.2).

[0198] FIG. 7 shows that the RSS shows a better shielding performance compared to the Aluminium reference shielding for incident protons of 100 MeV and all investigated shielding depths between 4.4 g/cm.sup.2 and 16.2 g/cm.sup.2 by a factor of about 1.7. The steep flank in the dose equivalent, as seen in FIG. 7, occurs shortly after the Bragg Peak, where the incident protons are stopped in the material. The RSS provides better shielding against protons than an aluminium reference of same shielding depth.

[0199] FIG. 8 shows the effective dose equivalent H.sub.E using the quality factor from ICRP 60 for a monoenergetic proton beam of 100 MeV. At the Bragg-Peak the incident protons are stopped, resulting in a significant exponential decrease in dose by more than one order of magnitude over only 3 g/cm.sup.2 shielding depth variation. At all shielding depths, the RSS provides lower doses than aluminium of equal shielding depth.

[0200] FIG. 9 and FIG. 10 show the depth dose profile of effective dose equivalent, H.sub.E, using the ICRP 60 and the NASA quality factor with the radiation environment spectrum from the mission scenario. Due to the mixed energy of the incident radiation, there is no single Bragg-Peak. Yet, it can be seen that also in the case of a mixed radiation field with a wide range of energies, the RSS outperform aluminium in terms of shielding performance by a factor of 1.4.

[0201] FIG. 11 and FIG. 12 show the effective dose equivalent, H.sub.E, contribution of protons and neutrons to the total dose, behind RSS and Aluminium shielding using ICRP 60 quality factor and radiation environment spectrum from the mission scenario vs. shielding depths.

[0202] The RSS shielding show a significantly better shielding performance regarding incident protons and less neutrons behind the shielding compared to aluminium.