Investigation of Nanostructured Radiation-protective Composites

Available online at www.sciencedirect.com

ScienceDirect Physics Procedia 72 (2015) 540 – 543

Conference of Physics of Nonequilibrium Atomic Systems and Composites, PNASC 2015, 18-20 February 2015 and the Conference of Heterostructures for microwave, power and optoelectronics: physics, technology and devices (Heterostructures), 19 February 2015

Investigation of nanostructured radiation-protective composites GulbinV.N.a*, PetruninV.F.b a

OJSC “Engineering & Marketing Center of Corporation “Vega”, Moscow 125190, Russia b National Research Nuclear University MEPhI, Moscow 154109, Russia

Abstract There were studied mechanisms of radiation dispersion using nanoparticles, which increase effective path of radiation quantum in nanocomposites, and which increase neutron- and Roentgen rays-protective properties multiplying of mitigation by the composite and optimal sizes of nanocrystals and filler nanoparticles were calculated. The performed experimental studies to define absorbing capability of the composite materials with fillers of tungsten and lead oxides nanocrystalline powders shown, that application of these filler materials for radiation-protective materials allows increase efficiency of radiation protection for 1.341.43 times in comparison to analogue material with coarse crystalines. © Published by Elsevier B.V.B.V. This is an open access article under the CC BY-NC-ND license © 2015 2015The TheAuthors. Authors. Published by Elsevier (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the National Research Nuclear University MEPhI (Moscow Engineering Physics Institute) Peer-review under responsibility of the National Research Nuclear University MEPhI (Moscow Engineering Physics Institute) Keywords:nanocomposites, nanoparticles, nanocrystalline, tungsten, lead oxide, Roentgen- and neutron radiation.

1. Introduction The problem how to protect biological bodies and elements of equipment against radiation has the highest actuality. In available composites their high protective efficiency is combined with relatively high mass or thickness of such products, it leads to worse operational characteristics. In order to solve this problem, we suggest using nanopowders as filler materials to increase protective and operational characteristics of nanocomposites. Similar sizes of structural particles and radiation wave lengths (Roentgen quantum and slow neutrons) lead to additional dispersion of radiation and therefore, to increase of radiation effective path in such nanocomposites. Composite materials by their high mechanical properties under penetrating ionizing irradiation are subjected to significant radiation swelling and destruction, as well as due to structural changes. These structural changes can be prevented by using materials with low swelling and by modification with different nanosized filler materials. Rational structure of obtained composite mixture allows reliable adhesion of powders in the metal matrix and * Corresponding author. Tel.: +7-495-995-5558; fax: +7-499-151–5501.E-mail address: [email protected]

1875-3892 © 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the National Research Nuclear University MEPhI (Moscow Engineering Physics Institute) doi:10.1016/j.phpro.2015.09.048

V.N. Gulbin and V.F. Petrunin / Physics Procedia 72 (2015) 540 – 543

minimizes mass of products. Artemiev (1997) demonstrates that application of ultradispersed powder can ensure better radiation-protective characteristics against Roentgen radiation and heat neutrons. The fundamental investigations Akopdjanov et al. (2007) showed that application of nanoparticles in radiation-absorbing materials (BN, B4C, Pb and W) leads to better absorption of neutrons and dispersion of Roentgen- and gamma radiation. We used this effect to obtain nano-structured radiation-protective nanocomposites. This work is devoted to study and calculations of radiation-absorbing capability of the composites filled with nano-powders, as well as to develop a way to obtain nanopowders made of lead oxide (PbO). 2. Theoretical and experimental By description of interaction of Roentgen radiation with a substance, three main mechanisms shall be taken into account: photoelectrical absorption by Marenkov and Komyak (1988), coherent and non-coherent dispersion on atoms by Kitaygorodsky (1953), dispersion on phases borders by Landau and Lifshits (1982). This work gives qualitative and theoretical basement of the position, that mechanism of radiation non-coherent dispersion and on phases borders in a nanostructured material, differ from mechanisms in analogue materials with big crystals. Spreading of Roentgen radiation in nanocomposites is featured by the equation of radiation transfer, which for low-angular dispersion looks like: P

wI ( z, P ) wz

 K abs I ( z, P ) 

>T

2 s

@

 M s2 ª w 2 wI ( z , P ) º « wP (1  P ) wP » 4 ¬ ¼, G

GG

here: I(z,μ) - density of Roentgen radiation flow with transfer direction : , ( P :: 0 cos(T )) , Kabs - coefficient of photoelectrical absorption of Roentgen radiation in ultradispersed particle's Roentgen radiation material. In the case of nanostructured material, the equation looks like: I ( z)

>

@

1

§ · T s2  M s2 I 0 exp(  K abs z ) ˜ ¨1  K abs z 2 ¸ ¨ ¸ 2 © ¹ .

By development of the calculation methodic for the Roentgen radiation absorption coefficient, we supposed, that reflection of Roentgen radiation from the phase border is resulted by different dielectric penetrability of linking nanocomposites and nanoparticles distributed in it. By real ratio of dielectric penetrability of the media and the nanoparticles by inclined angles, there was the effect of full reflection of Roentgen radiation from particle's surface. For easier calculations instead inclination angles θ were applied radial angles φ (Fig. 1): θ=π/2 - φ. Δa θ θ φ

Fig.1. The dispersion diagram for Roentgen radiation on spherical nanoparticle.

As result, the following formula was obtained to calculate coefficient β of mitigation of Roentgen radiation flow after going through the nanomaterial, in comparison to large crystal analogue material with the same thickness:

541

542

V.N. Gulbin and V.F. Petrunin / Physics Procedia 72 (2015) 540 – 543

E

>T 1

2 s

 M s2 2

@K

abs

z2

Real form of nanoparticles surface makes ignificant contribution (due to reflection from phases borders) in increase of coefficient β. So, the obtained values of β are the values listed below. Mitigation of neutron radiation by going through the composite is featured by the radiation transfer equation, which looks like: qL § x· n( x ) exp¨  ¸ . 2D

© L¹

Analysis of the curve obtained for n(x) shows (Fig. 2), that if middle cosine of coherent dispersion angle coh decreases by increase of particles size (Fig. 2а), and intensity of passed neutron radiation decreases by cosine increase (Fig. 2b), and then it will increase by decrease of nanoparticles sizes.

a

b

Fig.2. The calculated curves: а - < cos θ >coh depending on nanoparticles sizes, b - intensity W of neutron radiation passed through nanoparticles depending on < cos θ >coh.

Using the calculations results, it is possible to make a conclusion: to obtain a high-effective radiation-protective composite, it is necessary to use nanosized and nanocrystalline powders of heavy metals and their compositions and have sizes of non-homogeneities (particles or crystals) to be with in 10÷40 nm. For experimental purposes, nanocrystalline powders PbO were obtained by the chemical synthesis method based on thermal decomposition of pre-cursors of formerly synthetic hydroxides, and nanotungsten by mean of electric explosion of a conductor by high-density current pulse (j≥106 A/cm2) by Il'in et al. (2005). The first method developed for this experimental work used a two-staged chemical synthesis of PbO powder, which provided neutralization of Pb salts, obtaining hydroxide and following thermal treatment. Selection of this method allows solve a number of practical tasks: a) to obtain nanocrystalline powders of heavy metals oxides, because of reaction of building of the oxide compositions goes at the moment of decomposition of their pre-cursors (hydroxides), and the process is featured by high speed at relatively low temperatures; b) optimal mixing of initial elements in liquid phase, it allows obtain pre-cursors with maximally homogeneous distribution of elements; c) accurate control of composition of obtained oxide compositions due easy dozing of elements in solution; d) high purity of obtained products. Study of radiation-absorbing capability of the nanocomposites was performed using plate specimens made from the composite on base of epoxide resin with the fillers from W and PbO nanopowders, both fine fractions (nanocrystallite ~ 18 nm) and large crystalline fractions (>100 nm), with use the Roentgen radiation generator and the detecting system. The specimens had geometry in order to have Roentgen radiation intensity on maximal depth ten times exceeding relative error. In order to obtain reduced Roentgen radiation in process of the experiment, combinations of plates were used to increase total thickness. In result of the experiment the curves were obtained, which demonstrated dependence of radiation intensity on material thickness and sizes of the nanoparticles (Fig. 3). The experimental results shown for plate thickness ~360 mcm multiplying of mitigation of the specimen with the nanocrystalline filler material increased for 1.34÷1.43 times and reached maximal value for the specimens, whereas

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the filler material we used obtained by dispersion the very fine fraction of the synthetic nano-powder. It was also defined, that increase of thickness of the radiation-protective specimen to critical value (about 2.5÷2.8 mm for PbO), the coefficient for mitigation of Roentgen radiation increases. It can be explained by growth of number of the dispersion centers. The results obtained for absorbing capability of the nanocomposites exceed the calculated values for such concentration and sizes of the crystals. The comparative analysis of results obtained for nanocrystalline (crystal size 20 nm, average size of nanoparticles 83 nm) and large crystalline (>100 nm) state of the filler material, demonstrated lower positions of the experimental curves of Roentgen radiation mitigation. They are below the theoretical curve (the table values) and the curve of previously calculated values. Maximal multiplying of Roentgen radiation mitigation in process of this experiment was reached 1.64 times for 2.8 mm thickness of the protective layer from lead oxide, in comparison to the large crystalline analogue material. The obtained experimental data has a good correlation with the results of previous calculations, however multiplying of Roentgen radiation mitigation exceeds the calculated values (it was awaited), because the calculations did not take into account real form of the nanoparticles and the calculations was the evaluation of radiation-absorbing capability of the nanopowders from below.

Fig.3. The curves of Roentgen radiation mitigation.

3. Conclusion The mechanism of Roentgen radiation dispersion were investigated, which can be realized by using of nanoparticles-with additional radiation dispersion on phase’s borders and coherent dispersion by a nanoparticle, as well as features of Roentgen radiation mitigation Roentgen radiation dispersion by a composite material with nanosized filler material. The calculated curves were obtained for middle angle of Roentgen radiation dispersion. Their analysis shown, that using nanopowders as filler materials for nanostructured composites increase their radiation-protective properties. The features were studied for neutron radiation mitigation by nanostructured composite. The equation was solved for nanostructured media transfer and the calculated curves were obtained for the main parameters: a) size of nanoparticles, b) intensity (speed) of neutron radiation passed through nanoparticles. The experimental data was obtained for Roentgen radiation mitigation by the specimens with nanopowders of PbO and W. The comparative analysis shown, that the experimental mitigation curve is below the theoretical curve and the previously calculated curve. It was defined, that multiplying of Roentgen radiation mitigation in the specimen with nanocrystalline filler material increases for 1.34÷1.43 times and reaches maximal value in the specimens with the very fine fraction of nanopowders. 4. References Artemiev, V.A. 1997. Mitigation of Roentgen radiation by ultra-dispersed medias. State R&D Institute of materials technology. Letters to GTF, vol. 23, No. 6. Akopdjanov, A.G., Petrunin, V.F., Verzun, A.S. 2007.The mechanisms of interaction of radiation with nanostructured materials. Belgorod. Marenkov, O.S., Komyak, N.I. 1988.The photon coefficients of interfaces in Roentgen-radiometric analysis. L.: Energoatomizdat. Kitaygorodsky, A.I. 1953. Roentgen-structural analysis for small-crystalline and amorphous bodies. М.: GITTL. Landau, L.D., Lifshits, E.M. 1982. Electrodynamics of solid medias. М.:Nauka. Il'in, A.P., Nazarenko, O.B., Tikhonov, D.V., Yablunovsky G.V. 2005. Obtaining of tungsten nano-powders by mean of electric explosion of conductors // Izvestiya TPU. No.4.

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