3. Experiments on neutron transmission and Monte Carlo simulations on production of radioisotopes through 4, 5 MeV neutrons on several boron compounds

Transcription

1 Transworld Research Network 37/661 (2), Fort P.O. Trivandrum Kerala, India Nuclear Science and Technology, 2012: ISBN: Editor: Turgay Korkut 3. Experiments on neutron transmission and Monte Carlo simulations on production of radioisotopes through 4, 5 MeV neutrons on several boron compounds Turgay Korkut 1 and Abdulhalik Karabulut 2 1 Faculty of Science and Arts, Department of Physics, Ağrı İbrahim Çeçen University, 04100, Ağrı Turkey; 2 Faculty of Science, Department of Physics, Atatürk University, 25040, Erzurum, Turkey Erzurum Technical University, Erzurum, Turkey Abstract. In this work, four boron compounds (MgB 2, NaBH 4, H 3 BO 3 and KBH 4 ) were irradiated 4,5 MeV neutrons. Neutron transmissions were measured using by an equivalent dose rate detector. Experimental results were evaluated depending on number of boron atoms per unit volume of compounds. Also produced total radioisotopes per primary neutrons emanated interactions between neutrons with compound atoms were simulated using by FLUKA Monte Carlo code. We have found that neutron absorption capability is relate to density of boron atoms per unit volume. Total numbers of radioisotopes per primary neutrons are direct proportion of hydrogen content of compounds. Introduction Neutrons and protons make up the nucleus of an atom. Because neutrons don t have an electric charge, they don t influence by Coulomb force. So neutron radiation is hazardous a lot. To preserved neutron radiation several Correspondence/Reprint request: Dr. Turgay Korkut, Faculty of Science and Arts, Department of Physics, Ağrı İbrahim Çeçen University, 04100, Ağrı, Turkey. turgaykorkut@hotmail.com

2 26 Turgay Korkut & Abdulhalik Karabulut shield materials have been used up to now. Studies about neutrons are become widespread recently. For piperazinium hexachlorodicuprate under hydrostatic pressure, a neutron scattering study was made [1]. Mat'as et al. implemented a neutron diffraction study for KEr(MoO 4 ) 2 material [2].Fast neutron shielding characteristics of three boron compounds were investigated [3]. There are some studies on neutron transmission measurements in literature. Neutron transmission through pyrolytic graphite crystals was measured [4]. High-resolution neutron transmission and capture measurement results of Pb-206 nucleus were obtained [5]. Sato et al. designed a new material evaluation method by using a pulsed neutron transmission with pixel type detectors [6]. Korkut et al. determined neutron dose transmissions of several new concrete samples [7]. Epithermal neutron capture and transmission measurements of natural molybdenum were performed for resonance parameters and uncertainties analyses [8]. Monte Carlo simulation is a method for iteratively evaluating a deterministic model using sets of random numbers as inputs. These methods are used for designing detectors, comprehensing their conduct and comparing experimental results to theory, or on more large scale of the galaxy modeling in experimental particle physics [9]. FLUKA is a fully integrated Monte Carlo simulation code. FLUKA code has several applications in high energy physics and physical engineering, shielding processes, detectors and telescope design, cosmic ray physics, dosimetric studies, medical applications and biological physics [10]. There are several FLUKA simulation studies in literature. Gamma radiation absorption properties of amethyst mine were simulated by using FLUKA code [11]. A FLUKA simulation on parameterization of muon and electromagnetic signals was performed [12]. In this paper, interactions between 4.5 MeV neutrons with four boron bearing compounds are investigated. Neutron dose equivalent transmissions tested using by a neutron detector. Radioisotope nuclei production simulations were achieved by using FLUKA MC code. Experimental details In this study, we used a NP-100B neutron detector. It provides to detect slow and fast neutrons. Tissue equivalent dose rates of the neutron field can be measured by it. Our neutron detector contains a proportional counter which produces pulses resulting from neutron interactions within it. The probe includes components to alleviate and attenuate neutrons. Because of a neutron particle has no charge, it can only be detected indirectly through nuclear reactions that create charged particles. As the conversion target, the

3 Neutron experiments and simulations for three boron compounds 27 NP100B detector uses 10 B isotopes. Detector characteristics are shown in Table I. Fig.1 reveals energy response curve of detector. We used 241 Am-Be neutron source which emits 4.5 MeV effective energetic neutron particles. 241 Am-Be neutron source is compacted mixture of americium oxide with beryllium metal in a cylindrical shape. Alpha particles sending from 241 Am isotope have near to 5.5 kev maximum energy. Figure 1. Energy response curve of detector. Table 1. Characteristics of Canberra NP100B Neutron Detector.

4 28 Turgay Korkut & Abdulhalik Karabulut We have elaborated four disc samples; MgB 2, NaBH 4, H 3 BO 3 and KBH 4. It is necessary to pre-concentrate and homogenize samples and prepare a uniform specimen before detection process. Our boron bearing samples were then ground and sieved to a mesh size of 300 and then mixed the mixing time was 10 min. The samples have prepared as pellets with radius and thickness of about 1 and 1.5 cm, respectively. 241 Am-Be neutron source was coated using collimator box included paraffin and lead conformably to data sheet of source. A shield stick used to avoid interactions between neutrons with air molecules in collimator box. During measurements samples were fixed in collimator box as adjacent neutron source. The Canberra NP100B series neutron detector was fixed combined with the exit of collimator box. It is satisfied that neutrons passed from samples arrived to detector probe. Detector was positioned front of circular hole where is surface of collimator box. The background measurements were done 100 times. And then samples were put between collimator and detector, respectively. By this means 100 counts were done for boron compounds samples. Measurement results were read on 606M model transportable rate meter and system PC via RADACS software. Experimental design is illustrated in Fig.2. Monte Carlo simulations Figure 2. Experimental design. FLUKA is a general aim code for simulations of particle transport and interactions with matter. It is useful for simulate all particle physics, nuclear

5 Neutron experiments and simulations for three boron compounds 29 physics, medical physics, accelerator physics applications. FLUKA Monte Carlo tool simulates with high precision the interaction and spread in matter of about 60 different particles as photons, electrons, neutrinos, muons etc [10]. In our simulations, four boron compounds were irradiated 4,5MeV neutron particles and radioisotope production outputs were considered. Firstly, atomic structures and densities of samples were written in MATERIAL and COMPOUND cards. Then primary neutron energy (BEAM card), transmission geometry parameters (sample dimensions, distances source-sample and sample-detector), detector properties were typed in FLUKA input file. Secondly, simulation has been started for primary neutron particles. After running, number of total radioisotopes, mass numbers of produced radioisotopes and their efficiencies read from RESNUCLEI output. Results and discussion In this section experimental results and outputs of FLUKA simulations are presented. In Fig.3, neutron equivalent dose rate transmissions are evaluated to number of boron atoms per unit volume for each compound. As can be seen in Fig.3, transmission is a negative function of number of boron 0,50 0,45 0,40 MgB 2 Linear Fit (R 2 = ) B atoms/cm 3 0,35 0,30 0,25 NaBH 4 0,20 0,15 H 3 BO 3 KBH 4 0,10 0,800 0,805 0,810 0,815 0,820 0,825 0,830 0,835 Transmission Figure 3. Neutron equivalent dose rate transmissions.

6 30 Turgay Korkut & Abdulhalik Karabulut atoms. That is to say, neutron absorption capacity increases with number of boron atoms in a compound. If we want to enhance neutron absorption capability of compounds, we should applied boronization process. Table 2. Mass numbers of produced isotopes and isotope efficiencies of MgB 2. Table 3. Mass numbers of produced isotopes and isotope efficiencies of NaBH 4. Table 4. Mass numbers of produced isotopes and isotope efficiencies of H 3 BO 3.

7 Neutron experiments and simulations for three boron compounds 31 Table 5. Mass numbers of produced isotopes and isotope efficiencies of KBH 4. Table.2, Table.3, Table.4 and Table.5 demonstrate mass numbers and isotope efficiencies of MgB 2, NaBH 4, H 3 BO 3 and KBH 4 respectively. Judging by these tables, KBH 4 has maximum number of radioisotope. Total number of radioisotopes per primary neutrons as a function of hydrogen percentages is shown in Fig.4. As can be seen in Fig.4, total number of radioisotopes increases with increasing hydrogen content. If compounds which have high hydrogen amount are used to shield 4.5MeV neutrons, number of radioisotopes increases the same amount. 0,10 0,09 Number of Radioisotopes per primary n 0,08 0,07 0,06 0,05 0,04 0,03 0,02 0,01 Linear Fit(R 2 =0.9946) MgB 2 H 3 BO 3 KBH 4 NaBH 4 0, Hydrogen(%) Figure 4. Total number of produced radioisotopes per primary neutrons.

8 32 Turgay Korkut & Abdulhalik Karabulut Radiation protection is an important issue about protecting people and the environment from the harmful effects of ionizing radiation, which includes both particle radiation and high energy electromagnetic radiation. Radiation technologies widely used in industry and medicine. The most important disadvantage of radiation is causing microscopic damage to living tissue, resulting in skin burns and radiation sickness at high exposures and statistically elevated risks of cancer, tumors and genetic damage at low exposures. In this paper, we aimed to obtain neutron transmissions and simulate radioisotope products for some boron compounds. Our findings may be useful for nuclear processes, nuclear science laboratories, neutron experiments, radiation therapy hospitals especially BNCT rooms, etc References 1. Hong, T., Stock, C., Cabrera, I., Broholm, C., Qiu, Y., Leao, J.B., Poulton, S.J., Copley, J.R.D. 2010, Phys. Rev. B 82 (18), Mat as, S., Dudzik, E. Feyerherm, R., Gerischer, S., Klemke, S., Prokes, K., Orendacova,A. 2010, Phys. Rev. B 82 (18), Korkut, T., Karabulut, A., Budak, G., Korkut, H. 2010, J Radioanal Nucl Chem 286, Adib, M., Habib, N., Fathaalla, M. 2007, Annals of Nuclear Energy 33 (7), Borella, A., Gunsing, F., Moxon, M., Schillebeeckx, P., Siegler, P. 2007, Phys. Rev. C 76 (1), Sato, H., Takada, O., Satoh, S., Kamiyama, T., Kiyangi, Y. 2009, Nucl Instrum Methods Phys Res A 623(1), Korkut, T., Ün, A., Demir, F., Karabulut, A., Budak, G., Şahin, R., Oltulu, M. 2010, Ann of Nucl Energy 37, Leinweber, M., Barry, D.P., Burke, J.A., Drindak, N.J., Danon, Y., Block, R.C., Francis,N.C., Moretti, B.E. 2010, Nuclear Science and Engineering 165 (2), Mac Gillivray, H. T., Dodd, R. J. 1982, Astrophysics and Space Science 86(2), Ferrari, A., Sala, P.R., Fasso, A., Ranft, J. 2005, FLUKA: a multiparticle transport code.cern INFN/TC 05/11, SLACR Korkut, T., Korkut, H., Karabulut, A., Budak, G. 2011, Ann Nucl Energy 38 (1) Yushkov, A., Ambrosio, M., Aramo, C., D'Urso, D., Valore, L., Guarino, F. Phys. Rev. D 81 (12) Canberra Data Sheet Am-Be Radioactive Material Safety Data Sheet