Optimization of moderator assembly for neutron flux measurement: Experimental and theoretical approaches

Optimization of moderator assembly for neutron flux measurement: Experimental and theoretical approaches 1 first-author 2 3 1 4 2 5 6 corresp Corresponding author. E-mail address: wazirm@hotmail.com Corresponding author. E-mail address: wazirm@hotmail.com wazirm@hotmail.com Radiation Physics Laboratory, Physics Department, COMSATS Institute of Information Technology (CIIT), Islamabad, Pakistan. Radiation Physics Laboratory, Physics Department, COMSATS Institute of Information Technology (CIIT), Islamabad, Pakistan. Physics Division, Pakistan Institute of Nuclear Science & Technology (PINSTECH), Islamabad 45650, Pakistan Physics Division, Pakistan Institute of Nuclear Science & Technology (PINSTECH), Islamabad 45650, Pakistan Department of Physics, College of Science, Majmaah University, Al-Zulfi, Saudi Arabia Department of Physics, College of Science, Majmaah University, Al-Zulfi, Saudi Arabia School of Physics, University Science Malaysia, Penang 11800, Malaysia School of Physics, University Science Malaysia, Penang 11800, Malaysia DCIS, Pakistan Institute Engineering & Applied Sciences (PIEAS), Islamabad 45650, Pakistan DCIS, Pakistan Institute Engineering & Applied Sciences (PIEAS), Islamabad 45650, Pakistan Health Physics Division (HPD), Pakistan Institute of Nuclear Science & Technology (PINSTECH), Islamabad 45650, Pakistan Health Physics Division (HPD), Pakistan Institute of Nuclear Science & Technology (PINSTECH), Islamabad 45650, Pakistan A moderator of paraffin wax assembly has been demonstrated where its thickness can be optimized to thermalize fast neutrons. The assembly is used for measuring fast neutron flux of a neutron probe at different neutron energies, using BF 3 ( Φ 1″and 2″) and 3 He( Φ 0.5″) neutron detectors. The paraffin wax thickness was optimized at 6 cm for the neutron probe which contains an Am-Be neutron source. The experimental data are compared with Monte Carlo simulation results using MCNP5 version 1.4. Neutron flux comparison and neutron activation techniques are used for measuring neutron flux of the neutron probe to validate the optimum paraffin moderator thickness in the assembly. The neutron fluxes are measured at (1.17 ± 0.09)×10 5 n/s and (1.19 ± 0.1)×10 5 n/s, being in agreement with the simulated values. The moderator assembly can easily be utilized for essential requirements of neutron flux measurements. Am-Be and 252 Cf neutron sources BF 3 & 3 He detectors Paraffin wax Neutron flux Monte Carlo simulation 1 Introduction 1 The Am-Be and 252 Cf neutron sources are widely used in neutron dosimetry laboratories. The important features of Am-Be source is its long half-life and emission of fast neutrons with rather wide energy spectra, while 252 Cf yields a highly concentrated and reliable neutron spectrum from a small assembly. The last feature of both sources is helpful in covering the energy domain of interest for many applications in ambient and personal dosimetry. Nevertheless, the neutron energy spectrum depends on materials and dimension of the capsule and on amount and physio–chemical properties of active material, thus affecting relevant quantities such as spectrum-averaged fluence-to-dose equivalent conversion coefficient [ 1 1 - 6 6 1-6 ] . It is important to be know the neutron flux accurately so as to measure different quantities related to a neutron source [ 7 7 ] . Neutron detection has a key role in development of nuclear technology and its applications [ 8 8 , 9 9 ] . High sensitive neutron detectors are required. However, most of the neutron detectors are also sensitive to gamma rays. Therefore, an effective technique is required to eliminate the gamma background for accurate neutron measurements. Generally, methods used to recognize neutron interactions within a detector rely on second-order effects. Two neutron interactions used for a variety of thermal neutron detectors are the 10 B(n,α) 7 Li [ 9 9 , 10 10 ] and 6 Li(n,α) 3 H reactions [ 11 11 , 12 12 ] . The α particles can be easily detected. Low atomic number materials, such as high-density polyethylene (HDPE), which has a high concentration of hydrogen, tend to have relatively high elastic scattering cross sections for fast neutrons, and often (n,p) reactions from fast neutrons interacting in hydrogen-filled materials are manipulated for fast neutron detection. For detection of thermal or low energy neutrons, polymers-based SSNTDs, i.e. Solid State Nuclear Track Detectors (such as CR-39), can be used only in combination with a neutron reactive film which converts neutrons into other detectable radiations, recoil nuclei [ 13 13 , 14 14 ] . Use of a BF 3 or 3 He neutron detector, one can measure the optimum thickness of the moderator accurately, which is essential to avoid excessive thermal neutron absorption in the moderator. The neutron activation analysis can determine accurately the major and trace elements in different samples [ 10 10 – 12 12 10–12 , 15 15 ] . In practice, aromatic hydrocarbons are considered as the most radiation-resistant hydrogenous substances and have properties to moderate slow neutrons more effectively [ 16 16 ] . A paraffin wax moderator assembly has been developed to find out optimum thickness of paraffin wax. It can be utilized for fast neutrons from various neutron-producing reactions on an accelerator or for measurement of neutron yield from a Mather type plasma focus device [ 17 17 – 20 20 17–20 ] . The assembly has been utilized to find out neutron flux of a neutron probe which contains Am-Be as a neutron source [ 21 21 ] . Neutron flux comparison and neutron activation are used to the measure neutron flux [ 24 24 ] . A 50 mCi Am-Be neutron probe is used as a neutron source for the measurement of moisture in soils [ 21 21 ] . The moderating materials should be of large scattering cross-section, small absorption cross-section and large energy loss per collision [ 23 23 ] , and paraffin wax is just a desired moderator. Its optimum thickness was calculated for 3 MeV neutrons [ 24 24 ] , and was experimentally determined at 7 cm and 2.5–4.5 cm for Am-Be and 252 Cf neutron sources, respectively [ 25 25 , 26 26 ] . The results were based on the maximum gamma ray yield due to neutron activation. The optimum thickness of HDPE moderator was measured at 4–6 cm for 2.8 MeV neutrons. For theoretical calculations, different codes such as MNCP, MNCPX, SRIM etc . are used [ 27 27 , 28 28 ] . The present paper is designed to determine the optimum moderator thickness that is required to be wrapped around a BF 3 detector used in monitoring fissile material. The experimental results are compared with MC simulations for Am-Be neutron source using MCNP5 code version 1.40 [ 29 29 ] . 2 Material and Methods 1 2.1. Theoretical calculations 2 The work of Goshal is referred for theoretical calculations [ 24 24 ] . The slowing down process involves elastic scattering by light nuclei like hydrogen and carbon in paraffin wax ( ρ = 0.93 g/cm 3 ) [ 5 5 ] . The average logarithmic decrease in neutron energy per collision is calculated. The average number of collisions needed to thermalize fast neutrons is also calculated. The transport, thermal neutron mean free paths are calculated for paraffin wax and finally the optimum moderator thickness is calculated at 6 cm for 3 MeV neutrons. 2.2. Experimental Approach 2 The paraffin wax moderator assembly consists of two parts as shown in Fig.1 Fig.1 . The first part consists of a removable paraffin wax discs, neutron detector and a neutron source (i.e. Am-Be/ 252 Cf neutron sources). The second part is a mounting frame with two parallel spring-loaded Φ 12 mm steel rods, each fixed at one end with the frame. The other two ends are fixed to a movable plastic ring around a 1.4 cm thick paraffin wax disc. The purpose of the plastic ring is to give strength to the paraffin wax discs. A number of paraffin wax discs are used. Sized at Φ 27 cm × 0.6–1.4 cm, each disk is mounted in a 6 mm thick plastic ring. The paraffin wax discs can be assembled easily on the mounting frame, between two semi cylindrical fixed pipes with the assembly at the same axes, one for the neutron detector and the other for the neutron source. The two parallel rods act as a guide for the paraffin wax discs, and keep the discs in close contact with each other. The Φ 27 cm discs keep the axis same with respect to the axes of the neutron detector and the neutron source. Paraffin wax discs can be added or removed for measurement of optimum thickness of paraffin wax, where the neutron detector counts is the maximum. Two BF 3 ( Φ 1″and 2″) and one 3 He ( Φ 0.5″) neutron detectors are used for measuring the optimum thickness with Am-Be or 252 Cf neutron sources. The associated electronics with detector assembly consisted of pre-amplifier, amplifier, single channel analyzer and counter/timer manufactured by the ORTEC. The background counts per second were measured without the neutron sources, and they were subtracted from the actual neutron count rates emitted from neutron sources. For different paraffin wax thicknesses, counts emitted from either Am-Be or 252 Cf neutron sources, were taken for 100 seconds by using the BF 3 and one 3 He neutron detectors. For both the Am-Be and 252 Cf neutron sources, the paraffin wax thicknesses were increased to find the maximum counts, and on further increase in thickness, the counts started decreasing. Here, the maximum counts represent optimum paraffin wax thickness that is required to thermalize fast neutron (of course, the process is the tradeoff between absorption and moderation). To minimize scattering from the walls, the heavy shielding was placed about 4 m away from the source. The scattering contribution at the detector position was checked with and without the shielding, with the source at its position. The difference was negligible and hence an evidence of no scattering contribution from shielding walls was seen. Furthermore, BF 3 or 3 He detectors can detect only slow or thermal neutrons and the gases have very low interaction cross-section for fast or scattering neutrons. The moderator assembly ( Fig. 1 Fig. 1 ) was also used for the measurement of neutron flux emitted from the Am-Be and 252 Cf neutron sources to check the validity of the optimum thickness of the paraffin wax moderator, using the neutron flux comparison method and the neutron activation analysis method [ 22 22 ] . 2.2.1. Neutron flux comparison method 3 The comparison of counting rates was carried out, between the standard Am-Be neutron source of known flux ( F 1 ) and that from the neutron probe of unknown flux ( F 2 ) under conditions insensitive to the energy of neutrons. Let C 1 be the average counts per sec for F 1 recorded by a BF 3 ( Φ 1″) neutron detector in contact with the 6 cm thick paraffin wax moderator and C 2 be the average neutron counts per sec, with their background subtracted, from the neutron probe under the same condition. The neutron flux F 2 from the neutron probe is given by F 2 = F 1 C 2 / C 1 . 2.2.2. Neutron activation analysis method 3 The paraffin wax moderator assembly was used to measure the neutron flux of the neutron probe through activation analysis technique by using silver foil, and the 6 cm optimum thickness of the paraffin wax moderator was validated. Thermal neutron activation analysis is the absolute method to determine the neutron flux of a neutron probe. The silver isotopes of 108 Ag ( T 1/2 =0.39 min) and 110 Ag ( T 1/2 = 24.6 sec) are produced through nuclear reactions of 107 Ag(n, γ) 108 Ag and 109 Ag(n, γ) 110 Ag with thermal neutron. After a few half-lives of 110 Ag most of the radioactivity in silver foil is due to 108 Ag [ 30 30 ] . A G.M counter with Mylar end-window is used for the neutron activation analysis. The silver foil is placed at the Mylar window. Both the neutron probe and the end-window of G.M detector are placed at the same axis in opposite and in contact with the paraffin wax moderator ( Fig.2 Fig.2 ). The optimum paraffin wax thickness of 6 cm was used in the moderator assembly. At the termination of activation, the flux φ of the neutron probe (in n/cm 2 /sec) is given by φ =[ A 0 w (1− e − λt )/( σA av αm )] ε (4π/ Ω ) [ 24 24 ] , where A 0 is the activity of 108 Ag at t =0, w is the atomic weight of silver, λ is the decay constant, t is the irradiation time, σ = 37.6 barns (taken from the ENDF library [ 31 31 ] ) is the thermal neutron capture cross section of 107 Ag, A av is the Avogadro’s number, α is the natural isotopic abundance of 107 Ag, m is the mass in grams of 107 Ag, ε is the intrinsic efficiency of the detector, and Ω is the solid angle subtended by the G.M detector at the neutron source (Am-Be) of the probe. The intrinsic efficiency of the G.M detector was determined from a 137 Cs γ-ray source of known activity. The silver foil was activated for 5 min. Although both 108 Ag and 110 Ag are produced, most of the activity is due to 108 Ag at the time of counting. The neutron probe was taken far away from the moderator assembly as quickly as possible, so the G.M detector background count was made almost negligible at the time of counting. The activated silver foil was counted immediately, and was repeated several times for better results. The background of the G.M detector was measured in advance. 2.3. Monte Carlo simulation 2 MCNP is an advanced Monte Carlo code for simulation of the neutron transport [ 29 29 , 32 32 ] . It has the ability to model complex geometry of designed experiment and contains all necessary cross-section data for neutron, photon and electron transport calculations [ 32 32 ] . For a neutron detection process, the history of each starting neutron is followed between collisions, its energy deposition is recorded, throughout its life to its death, until its energy is low enough to be neglected. In present study, the experimental set up was simulated in the School of Physics, University Science Malaysia, Penang, Malaysia, using the MCNP5 code version 1.40 [ 29 29 , 32 32 ] . The experimental setup as described in Fig. 1 Fig. 1 was modeled. According to this model, the neutron source was located at one side of the paraffin wax moderator while the neutron detector was simulated facing the source at the other side of the moderator. The experimental setup was simulated on wooden table top. To calculate the detector neutron flux, F2 tally (calculates the flux averaged over a surface [ 29 29 ] was used. Surface segmentation was utilized to calculate the flux at a surface segment facing the neutron source. 3 Results and Discussion 1 The measured counts per 100 seconds for different wax thicknesses by using the three neutron detectors for the Am-Be and 252 Cf neutron sources plotted against wax thickness are shown in Fig.3 Fig.3 . The maximum counts for each neutron detector and source represent the optimum paraffin wax thickness that is required to thermalize fast neutrons. From Fig.3 Fig.3 , the optimum paraffin wax thicknesses were 6 cm and 5.5 cm for Am-Be and 252 Cf neutron sources, respectively. The yield of thermal neutrons increases with the thickness of paraffin wax from 1.6 to 6 cm, due to fact that the fast neutrons lose their energy through elastic collision with hydrogen atoms of paraffin wax. The yield of thermal neutrons at these thicknesses is found to be maximum, as a large number of fast neutrons lose their maximum energy through elastic collisions. However, on further increase in thickness of the paraffin wax from 6.5 cm to 12 cm, the yields of thermal neutron decreases due to elastic and inelastic scattering reactions. The neutrons lose their energy through the interactions until they are captured by paraffin wax (shielding material) [ 23 23 ] . Normally, the neutron capture cross section is larger only for thermal neutron energies, that is why the neutrons slowing down by scattering are important before capture [ 23 23 ] . To validate the optimum thickness of paraffin wax, the neutron flux was calculated. By the neutron flux comparison method, the average neutron counts per second, C 1 , were 141.3 ± 0.66 with the known neutron flux of F 1 = (8.3±0.66)×10 4 n/s. With C 2 =199.1 ± 0.79 of the neutron probe, the F 2 was (1.17 ± 0.09)×10 5 n/s. On the other hand, the neutron flux deduced by the activation method was (1.19 ± 0.1)×10 5 n/sec. The two results are virtually the same, considering the measurement errors. The neutrons emerging out of paraffin wax are of both thermal and epithermal in energy. The fluence of epithermal neutrons was estimated from Ref. [ 30 30 ]. The ratio of epithermal to the total neutrons at a distance of 18.9 cm in air from the neutron source is 5.56% where the total fluence is maximum as calculated from Ref. [ 33 33 ]. Therefore, this ratio is the same for the paraffin moderator at 6 cm in thickness. By using MCNP5, the energy spectra of Am-Be neutron source at 3, 5, and 8 MeV were produced with the relative probabilities of 1.000, 0.986 and 0.551, respectively. The simulation results for the Am-Be source are shown in Fig.4 Fig.4 , and the counts are maximized at 6 cm thickness of the paraffin wax moderator, agreeing well with the experimental results. 4 Conclusion 1 The paraffin wax moderator assembly can be used easily to thermalize fast neutrons of various energies produced from neutron-producing reactions on an accelerator. Neutron flux comparison and neutron activation techniques are used for accurate determination of neutron flux of the neutron probe to validate the optimum thickness of the paraffin wax moderator in the assembly. The neutron flux of (1.17 ± 0.09) ×10 5 n/s by the neutron flux comparison method agree well with the flux of (1.19 ± 0.1) ×10 5 n/s by neutron activation analysis method. The techniques can be utilized for the measurement of neutron yield from Mather type plasma focus device. The optimum thickness of the paraffin wax moderator is 6 cm for Am-Be and 5.5 cm for 252 Cf neutron sources. References R. Bedogni , C. Domingo , N. Roberts , et al ., Investigation of the neutron spectrum of americium-beryllium sources by Bonner sphere spectrometry . Nucl Instru and Meths in Phys Res Section A , 763 : 547 - 552 . ( 2014 ) doi: 10.1016/j.nima.2014.06.040 http://doi.org/10.1016/j.nima.2014.06.040 Investigation of the neutron spectrum of americium-beryllium sources by Bonner sphere spectrometry F.D. Becchetti , M. Febbraro , R. Torres-Isea , et al ., 252Cf fission-neutron spectrum using a simplified time-of-flight setup: An advanced teaching laboratory experiment . American Journal of Physics , 81 : 112 - 119 . ( 2013 ) doi: 10.1119/1.4769032 http://doi.org/10.1119/1.4769032 252Cf fission-neutron spectrum using a simplified time-of-flight setup: An advanced teaching laboratory experiment S. Croft K.A.M. , Group representation of the prompt fission neutron spectrum of 252Cf . Esarda Bulletin : 112 - 114 . ( 2011 ) https://esarda.jrc.ec.europa.eu/images//Bulletin/Files/B_2011_046.pdf https://esarda.jrc.ec.europa.eu/images//Bulletin/Files/B_2011_046.pdf Group representation of the prompt fission neutron spectrum of 252Cf J.W. Marsh , D.J. Thomas , M. Burke , High resolution measurements of neutron energy spectra from Am-Be and Am-B neutron sources . Nucl Instru Meths in Phys Res Section A , 366 : 340 - 348 . ( 1995 ) doi: 10.1016/0168-9002(95)00613-3 http://doi.org/10.1016/0168-9002(95)00613-3 High resolution measurements of neutron energy spectra from Am-Be and Am-B neutron sources J.H. Wu , Y.J. Xu , S.L. Liu , et al ., Energy spectrum measurement and dose rate estimation of natural neutrons in Tibet region . Nucl. Sci. Tech ., 26 : 060202 . ( 2015 ) doi: 10.13538/j.1001-8042/nst.26.060202 http://doi.org/10.13538/j.1001-8042/nst.26.060202 Energy spectrum measurement and dose rate estimation of natural neutrons in Tibet region Z.G. Jiang , Y.G. Yuan , H.Y. Wang , et al ., Development of a spherical tissue equivalent proportional counter for neutron monitoring . Nucl. Sci. Tech ., 26 : 060403 . ( 2015 ) doi: 10.13538/j.1001-8042/nst.26.060403 http://doi.org/10.13538/j.1001-8042/nst.26.060403 Development of a spherical tissue equivalent proportional counter for neutron monitoring B. Wolle , R. BÃtzner , T. Baloui , et al ., Special absorber neutron detector moderator assembly: A new detector system for flux measurements of collimated 2.5 MeV neutrons . Review of Scientific Instruments , 70 : 1194 - 1196 . ( 1999 ) doi: 10.1063/1.1149322 http://doi.org/10.1063/1.1149322 Special absorber neutron detector moderator assembly: A new detector system for flux measurements of collimated 2.5 MeV neutrons M. A. Rana , Research and applications of nuclear tracks: Developments in Pakistan and global comparison . Natural Science , 2012 . ( 2012 ) doi: 10.4236/ns.2012.431124 http://doi.org/10.4236/ns.2012.431124 Research and applications of nuclear tracks: Developments in Pakistan and global comparison G.F. Knoll , Radiation detection and measurement . 2000 : John Wiley & Sons . Radiation detection and measurement M.U. Rajput , N.L. Maidana , V.R. Vanin , et al ., Measurement of thermal neutron cross section and resonance integral for the 165Ho(n,γ) 166Ho reaction . Radiochimica Acta International Journal for Chemical Aspects of Nuclear Science and Technology , 97 : 63 - 69 . ( 2009 ) doi: 10.1524/ract.2009.1575 http://doi.org/10.1524/ract.2009.1575 Measurement of thermal neutron cross section and resonance integral for the 165Ho(n,γ) 166Ho reaction M. Akram , A. Iqbal , S.N. Husaini , et al ., Determination of boron contents in water samples collected from the Neelum valley, Azad Kashmir, Pakistan . Biological Trace Element Research , 139 : 287 - 295 . ( 2011 ) doi: 10.1007/s12011-010-8665-6 http://doi.org/10.1007/s12011-010-8665-6 Determination of boron contents in water samples collected from the Neelum valley, Azad Kashmir, Pakistan K. Haygarth , D. Janik , I. Janik , et al ., Neutron and β/γ radiolysis of water up to supercritical conditions. 1. β/γ yields for H2, H· atom, and hydrated electron . The Journal of Physical Chemistry A , 114 : 5034 - 5034 . ( 2010 ) doi: 10.1021/jp101790p http://doi.org/10.1021/jp101790p Neutron and β/γ radiolysis of water up to supercritical conditions. 1. β/γ yields for H2, H· atom, and hydrated electron M. Barbagallo , L. Cosentino , V. Forcina , et al ., Thermal neutron detection using a silicon pad detector and 6LiF removable converters . Review of Scientific Instruments , 84 : 033503 . ( 2013 ) doi: 10.1063/1.4794768 http://doi.org/10.1063/1.4794768 Thermal neutron detection using a silicon pad detector and 6LiF removable converters A.A. Naqvi , M.S. Abdelmonem , G. Al-Misned , et al ., New source-moderator geometry to improve performance of 252 Cf and 241 Am-Be source-based PGNAA setups . Nucl Instru Meths in Phys Res Section A : 562 : 358 - 364 . ( 2006 ) doi: 10.1016/j.nima.2006.02.004 http://doi.org/10.1016/j.nima.2006.02.004 New source-moderator geometry to improve performance of 252 Cf and 241 Am-Be source-based PGNAA setups S. Ahmad , S.S. Hussain , M. Sadiq , et al ., Enhanced and reproducible neutron emission from a plasma focus with pre-ionization induced by depleted uranium (U238) . Plasma Physics and Controlled Fusion , 48 : 745 . ( 2006 ) doi: 10.1088/0741-3335/48/6/003 http://doi.org/10.1088/0741-3335/48/6/003 Enhanced and reproducible neutron emission from a plasma focus with pre-ionization induced by depleted uranium (U238) V. Ananiev , A. Belyakov , M. Bulavin , et al ., The world's first pelletized cold neutron moderator at a neutron scattering facility . Nucl Instru Meths in Phys Res Section B , 320 : 70 - 74 . ( 2014 ) http://www1.jinr.ru/Preprints/2012/113(P13-2012-113).pdf http://www1.jinr.ru/Preprints/2012/113(P13-2012-113).pdf The world's first pelletized cold neutron moderator at a neutron scattering facility S.N. Ahmed , Physics and engineering of radiation detection . 2007 : Academic Press . Physics and engineering of radiation detection M. Zakaullah , A. Waheed , S. Ahmad , et al ., Study of neutron emission in a low-energy plasma focus with β-source-assisted breakdown . Plasma Sources Science and Technology , 12 : 443 . ( 2003 ) doi: 10.1088/0963-0252/12/3/320 http://doi.org/10.1088/0963-0252/12/3/320 Study of neutron emission in a low-energy plasma focus with β-source-assisted breakdown M. Zakaullah , K. Alamgir , A. Rasool , et al ., Correlation of plasma electron temperature with neutron emission in a low-energy plasma focus . Plasma Science, IEEE Transactions on , 29 : 62 - 68 . ( 2001 ) doi: 10.1109/27.912943 http://doi.org/10.1109/27.912943 Correlation of plasma electron temperature with neutron emission in a low-energy plasma focus M. Zakaullah , I. Akhtar , A. Waheed , et al ., Comparative study of ion, X-ray and neutron emission in a low energy plasma focus . Plasma Sources Science and Technology , 7 : 206 . ( 1998 ) doi: 10.1088/0963-0252/7/2/015 http://doi.org/10.1088/0963-0252/7/2/015 Comparative study of ion, X-ray and neutron emission in a low energy plasma focus C. International , Neutron probe method using a 503DR Hydroprobe, ICT, Editor , International Pty Ltd : Australia . Neutron probe method using a 503DR Hydroprobe, ICT, Editor M. Borsaru and P.L. Eisler , Neutron Activation Analysis (Slow Neutrons) , in United States Patent. 1982 . Neutron Activation Analysis (Slow Neutrons) M.H. Jasim and N.T. Abdulameer , Neutron capture cross section measurements of paraffin wax . International Journal of Application or Innovation in Engineering of Management , 3 : 112 - 114 . ( 2014 ) http://ijaiem.org/volume3issue4/IJAIEM-2014-04-20-034.pdf http://ijaiem.org/volume3issue4/IJAIEM-2014-04-20-034.pdf Neutron capture cross section measurements of paraffin wax S.N. Goshal , Nuclear Physics . 1994 , S Chand Publisher Nuclear Physics V.M. Thakur , A. Jain , K. Biju , et al ., Studies on optimization of moderator thickness for BF3 detectors used for monitoring of fissile material . Indian Journal of Pure and Applied Physics , 50 : 811 - 813 . ( 2012 ) http://nopr.niscair.res.in/handle/123456789/14910 http://nopr.niscair.res.in/handle/123456789/14910 Studies on optimization of moderator thickness for BF3 detectors used for monitoring of fissile material A.A. Naqvi , M.M. Nagadi , M. Maslehuddin , et al ., Verification of design calculations of a PGNAA setup using nuclear track detectors . Radiation Measurements , 38 : 37 - 41 . ( 2004 ) doi: 10.1016/S1350-4487(03)00252-X http://doi.org/10.1016/S1350-4487(03)00252-X Verification of design calculations of a PGNAA setup using nuclear track detectors J.K. Zhao , J.L. Robertson , K.W. Herwig , et al ., Optimizing moderator dimensions for neutron scattering at the spallation neutron source . Review of Scientific Instruments , 84 : 125104 . ( 2013 ) doi: 10.1063/1.4841875 http://doi.org/10.1063/1.4841875 Optimizing moderator dimensions for neutron scattering at the spallation neutron source J.F. Ziegler , M.D. Ziegler , and J.P. Biersack , SRIM-The stopping and range of ions in matter (2010) . Nucl Instru Meths in Phys Res Section B , 268 : 1818 - 1823 . ( 2010 ) DOI: 10.1016/j.nimb.2010.02.091 http://doi.org/10.1016/j.nimb.2010.02.091 SRIM-The stopping and range of ions in matter (2010) R. A. Forster T.N.K.G. , MCNP - A General Monte Carlo N-Particle Transport Code , Version 5 . 2003 MCNP - A General Monte Carlo N-Particle Transport Code J.R. Parrington , D.K. Harold , L.B. Susan , et al ., Chart of radionuclides-Knoll Atomic Power Laboratory . Washington, DC : Naval Reactors, US Department of Energy . ( 1996 ). Chart of radionuclides-Knoll Atomic Power Laboratory M.B. Chadwick , M. Herman , P. Obložinský , et al ., ENDF/B-VII. 1 nuclear data for science and technology: cross sections, covariances, fission product yields and decay data . Nuclear Data Sheets , 112 : 2887 - 2996 . ( 2011 ) doi: 10.1016/j.nds.2011.11.002 http://doi.org/10.1016/j.nds.2011.11.002 ENDF/B-VII. 1 nuclear data for science and technology: cross sections, covariances, fission product yields and decay data X-5 Monte Carlo Team , MCNP - A General Monte Carlo N-Particle Transport Code , Version 5 . 2003 . MCNP - A General Monte Carlo N-Particle Transport Code M. Tohamy , M. Fayez-Hassan , M.M. Abdel-Khalek , et al ., A dual-hemisphere (spherical) irradiation facility for Am-Be neutron field optimization . ( 2009 ) http://www.iaea.org/inis/collection/NCLCollectionStore/Public/42/009/42009903.pdf http://www.iaea.org/inis/collection/NCLCollectionStore/Public/42/009/42009903.pdf . A dual-hemisphere (spherical) irradiation facility for Am-Be neutron field optimization The authors gratefully acknowledge services provided by Mr. Usman Ali, RPL, CIIT, in the fabrication of mechanical assembly and safe handling of neutron sources. 10.1007/s41365-017-0213-z 2016-06-24 2016-09-02 2016-09-24 2017-03-28 2017-05-01 2021-04-11 © China Science Publishing & Media Ltd. (Science Press), Shanghai Institute of Applied Physics, the Chinese Academy of Sciences, ChineseNuclear Society and Springer Nature Singapore Pte Ltd. 2017 This is a post-peer-review, pre-copyedit version of an article published in Nuclear Science and Techniques. The final authenticated version is available online at: http://dx.doi.org/10.1007/s41365-017-0213-z http://dx.doi.org/10.1007/s41365-017-0213-z . 2017 Nuclear Science and Techniques 05 28