TY - JOUR
AU - Zarubin, Pavel, I
AB - Abstract Neutron detection using nuclear emulsions can offer an alternative in personal dosimetry. The production of emulsions and their quality have to be well controlled with respect to their application in dosimetry. Nuclear emulsions consist mainly of gelatin and silver halide. Gelatin contains a significant amount of hydrogen, which can be used for fast neutron detection. The addition of B-10 in the emulsion is convenient for thermal neutron detection. In this paper, standard nuclear emulsions BR-2 and nuclear emulsions BR-2 enriched with boron produced at the Slavich Company, Russia, were applied for evaluation of fast and thermal neutron fluences. The results were obtained by calculation from the presumed emulsion composition without prior calibration. Evidence that nuclear emulsions used in the experiment are suitable for neutron dosimetry is provided. INTRODUCTION Neutrons are neutral particles, which means that their detection is more complicated than the detection of charged particles. An economical and reliable neutron dosimeter is still in demand in personal dosimetry. One of the main questions of our research is if the present-day commercially available nuclear emulsions can be used for such purpose. The use of nuclear emulsions for passive track detection of charged ionizing particles represents a method that is more than 80 years old. They can record tracks of charged particles in a wide energy range(1,2) and determine track positions with an accuracy of tenths of a micrometer. Quantities directly measured by nuclear emulsions are lengths of tracks, their orientation, angles between tracks, number of tracks with specific properties(3), disintegration stars(4), etc. Tracks can be also evaluated according to the specific ionization (5). For our experiment, it is important to distinguish heavier particles with higher ionization (protons or helium and lithium ions) from lightly ionizing particles (mostly electrons originated in interactions of gamma radiation). Neutron dosimetry with nuclear emulsions has been widespread in the past, beginning in 1949 (6,7). Fast neutron fluence can be estimated from the number of recoil proton tracks inside the emulsion. There have been many different approaches to emulsion optimization for this purpose in the past: changes in emulsion composition were made(8), the methodology of using emulsions with additional layers of hydrogenous radiators and absorbers was described(9), less sensitive emulsions with bigger grains were prepared for easier and faster manual counting of the tracks(10) and not so long ago, emulsions with smaller grains for better electron–proton distinction were developed(11). It was shown by many that the energy of monoenergetic neutrons can be estimated from the lengths of recoil proton tracks(12,13). Calibration with known neutron sources has been used in the past for the estimation of neutron fluence F: F = A × N, where N is the number of recoiled proton tracks and A is an unknown constant(9). Our research is trying to explain the physical principle of constant A with measurements performed without any previous calibration. After the development of CR-39 Solid State Nuclear Track Detectors for neutron dosimetry in 1980(14), nuclear emulsions were gradually replaced. For example, in India the nuclear emulsions were replaced with CR-39 with a polyethylene radiator in 1990(15). The disadvantages of nuclear emulsions against the CR-39 SSNTD were: higher energy threshold (En > 500 keV against En > 100 keV), worse post irradiation fading, considerable sensitivity to beta and gamma radiation (background), more complicated despatch (packing needs special conditions) and tedious evaluation (in the past, it was done manually on a microscope).(15) CR-39 can also cover the whole energy region 0.1–15 MeV.(16) However, nuclear emulsions also have some benefits. For example, smaller minimal measurable dose (0.05 mSv for emulsion against 0.20 mSv for CR-39) and smaller inherent background or longer shelf life (3–4 years against 1–2 years)(15). In addition, nuclear emulsions obtain information about lengths of proton tracks. That means it is theoretically possible to estimate the energy deposition of secondary protons even without knowledge of the neutron spectrum(17,12,13). The plastic detector CR-39 could be soon replaced in the neutron dosimetry by another type of track detector—fluorescent nuclear track detector (FNTD)(18,19,20,21). This passive track detector has similar problems with gamma background as nuclear emulsions(20). But in comparison with nuclear emulsions, FNTD needs to use additional convertors for the detection of neutrons. Convertors are placed on the surface of the detector and it means that the detection of neutrons is directionally dependent(18) and minimal measurable dose is higher for FNTD (0.1 mSv(21) against 0.05 mSv(15) for emulsions). Also, FNTD crystals need a very specific readout system for evaluation. On the other hand, FNTD crystals can be erased and reused and they do not need chemical processing or special handling (no light sensitivity) before readout(21). The main disadvantage of nuclear emulsions is the time-consuming manual viewing of emulsions with an optical microscope. If emulsions are to be used as neutron dosimeters again, it is necessary to make all processes around them automatic, simple and repeatable. Especially the standardization of packing and development and the automation of emulsion scanning are needed. Afterwards, faster and statistically more significant results should be obtained by image processing algorithms. The necessity of this automation is well known. An automatic evaluation system customized for neutron dosimetry was developed 20 years ago in CERN(22). Nowadays, the advanced automatic scanning systems for emulsions are being developed in Italy(23,24) or in Japan(13,25). Detection of thermal neutrons with nuclear emulsions has a long history as well. The addition of N-14, Li-6 or B-10 was used for the first time in 1949(6) and is still used now(26,27). The additional component, with large cross-section for interaction with thermal neutrons inside of the emulsion, makes it possible to convert detection of thermal neutrons to charged particles—fragments of previously mentioned atoms. In 10B(nth, α)7Li reaction, two fragments arise—lithium and helium. Their tracks are so specific that it is easy to recognize them in an optical microscope and analyze them with the image processing software(27). From the measured number of boron–thermal neutron interactions, the number of thermal neutrons in the mixed neutron field can be estimated. MATERIALS AND METHODS Nuclear emulsions consist mainly of gelatin and silver halide. Standard emulsions BR-2 from Slavich Company (Pereslavl-Zalessky, Yaroslavl region, Russia) and emulsions BR-2 with addition of natural boron (consisting of 80% of B-11 and 20% of B-10) made by the same company were used for the experiment. BR-2 emulsions should be prepared according to the same recipe as emulsion NIKFI-R (made in the past by company NIKFI). Measured composition of NIKFI-R emulsion is in Table 1(28). The size of the silver bromide crystals in the emulsions is between 200 and 300 nm. The thickness of the emulsions before development was 55 μm for boron-loaded emulsions and 100 μm for standard emulsions, both were poured on a glass plate. The size of nuclear emulsion plates used in the experiment was 9 × 12 cm2. Composition of emulsion NIKFI-R (humidity 58%)(28). Table 1 Composition of emulsion NIKFI-R (humidity 58%)(28). Element . Mass of the element in 1 cm3 (g) . Mass percent composition (%) . Number of atoms in cm3 . Silver 1.8423 47.01 1.028 × 1022 Bromine 1.3658 34.85 1.028 × 1022 Iodine 0.0051 0.13 0.002 × 1022 Carbon 0.2794 7.13 1.400 × 1022 Hydrogen 0.0497 1.27 2.968 × 1022 Oxygen 0.2880 7.35 1.083 × 1022 Sulfur 0.0019 0.05 0.004 × 1022 Nitrogen 0.0870 2.22 0.374 × 1022 Element . Mass of the element in 1 cm3 (g) . Mass percent composition (%) . Number of atoms in cm3 . Silver 1.8423 47.01 1.028 × 1022 Bromine 1.3658 34.85 1.028 × 1022 Iodine 0.0051 0.13 0.002 × 1022 Carbon 0.2794 7.13 1.400 × 1022 Hydrogen 0.0497 1.27 2.968 × 1022 Oxygen 0.2880 7.35 1.083 × 1022 Sulfur 0.0019 0.05 0.004 × 1022 Nitrogen 0.0870 2.22 0.374 × 1022 Open in new tab Table 1 Composition of emulsion NIKFI-R (humidity 58%)(28). Element . Mass of the element in 1 cm3 (g) . Mass percent composition (%) . Number of atoms in cm3 . Silver 1.8423 47.01 1.028 × 1022 Bromine 1.3658 34.85 1.028 × 1022 Iodine 0.0051 0.13 0.002 × 1022 Carbon 0.2794 7.13 1.400 × 1022 Hydrogen 0.0497 1.27 2.968 × 1022 Oxygen 0.2880 7.35 1.083 × 1022 Sulfur 0.0019 0.05 0.004 × 1022 Nitrogen 0.0870 2.22 0.374 × 1022 Element . Mass of the element in 1 cm3 (g) . Mass percent composition (%) . Number of atoms in cm3 . Silver 1.8423 47.01 1.028 × 1022 Bromine 1.3658 34.85 1.028 × 1022 Iodine 0.0051 0.13 0.002 × 1022 Carbon 0.2794 7.13 1.400 × 1022 Hydrogen 0.0497 1.27 2.968 × 1022 Oxygen 0.2880 7.35 1.083 × 1022 Sulfur 0.0019 0.05 0.004 × 1022 Nitrogen 0.0870 2.22 0.374 × 1022 Open in new tab Both types of emulsions were exposed to the mixed neutron field in the reference point of the experimental channel of nuclear reactor LR-0 at the Research Centre Řež (Husinec-Řež, Czech Republic). The field should be homogeneous and isotropic in the reference point(29). Energy spectrum of the neutron field in the experimental channel is shown in Figure 1(29). Irradiation was performed in two consecutive days and on both days it took 30 minutes. The reference neutron fluences (given by Research Centre Řež) with examined energies are listed in Table 2 for both irradiation days. neutron spectrum of nuclear reactor LR-0(29). Figure 1 Open in new tabDownload slide Figure 1 Open in new tabDownload slide Reference neutron fluences (cm−2). Table 2 Reference neutron fluences (cm−2). Energy region . Exposition 1 . Exposition 2 . 0–1 eV 5.93 × 107 6.28 × 106 1 eV to 0.1 MeV 9.87 × 107 1.04 × 107 > 0.1 MeV 1.23 × 108 1.30 × 107 > 0.8 MeV 7.28 × 107 7.69 × 106 Energy region . Exposition 1 . Exposition 2 . 0–1 eV 5.93 × 107 6.28 × 106 1 eV to 0.1 MeV 9.87 × 107 1.04 × 107 > 0.1 MeV 1.23 × 108 1.30 × 107 > 0.8 MeV 7.28 × 107 7.69 × 106 Open in new tab Table 2 Reference neutron fluences (cm−2). Energy region . Exposition 1 . Exposition 2 . 0–1 eV 5.93 × 107 6.28 × 106 1 eV to 0.1 MeV 9.87 × 107 1.04 × 107 > 0.1 MeV 1.23 × 108 1.30 × 107 > 0.8 MeV 7.28 × 107 7.69 × 106 Energy region . Exposition 1 . Exposition 2 . 0–1 eV 5.93 × 107 6.28 × 106 1 eV to 0.1 MeV 9.87 × 107 1.04 × 107 > 0.1 MeV 1.23 × 108 1.30 × 107 > 0.8 MeV 7.28 × 107 7.69 × 106 Open in new tab After irradiation, the emulsions were developed (in amidol developer) and the latent image of tracks became visible under the microscope. Evaluation of emulsions was performed with a KSM-1 microscope. A circular area with a 45 μm radius is outlined in the ocular of KSM-1 microscope. By examining the whole depth (30 or 67 μm after development, which corresponds to 55 or 100 μm before development) of the emulsion in the set circular field, it is possible to inspect part of the emulsion with a fixed volume: VS = 3.50 × 105 μm3 for boron-loaded emulsion and VS = 6.36 × 105 μm3 for standard emulsions (both calculated from thickness of emulsions before development). Only the tracks inside of this volume are counted. Tracks going through the side (curved surface) of the cylinder are counted only when crossing the right part of the cylinder. Tracks entering the emulsion at the emulsion–air interface are omitted and tracks crossing the emulsion–glass interface are counted. The previously mentioned volume with established rules stands for one measured sample. The sample volume is different according to the thickness of the viewed type of emulsion. The number of such viewed samples varies from 100 to 200 for individual emulsions. Depending on the neutron energy (thermal or fast neutrons), distinct tracks corresponding to different reactions are counted. Tracks of particles with higher ionization (in this case protons, alpha and lithium) are straight and in the structure of track there are not large gaps between developed AgBr crystals. Examples of the counted tracks can be seen in the Figure 2. examples of detected tracks in emulsion. Figure 2 Open in new tabDownload slide Figure 2 Open in new tabDownload slide Fast neutrons (En > 0.1 MeV) can scatter on hydrogen atoms and recoil a proton with energy corresponding to the angle θ it is recoiled to: Ep = En cos2θ.(10) It needs to be highlighted that the proton tracks with length around 8.6 μm should not be misinterpreted as reactions of thermal neutron with B-10 10B(nth, α)7Li (mentioned below). Therefore, only tracks longer than 10 μm are counted as recoil proton tracks. From the proton ranges inside of the emulsion matter, taken from Rotblat(30) and Barkas,(1) it was found that this range (10 μm) corresponds to protons with energy (0.79 ± 0.02) MeV. Minimum energy of detected neutrons is then En > 0.8 MeV. Fast neutron fluence can be estimated from the average number of proton tracks |$\overline{N_{\mathrm{p}}}$| in the sample with volume VS according to the relation: $$ {F}_{\mathrm{fast}}=\frac{\overline{N_{\mathrm{p}}}}{N_{\mathrm{H}}\times{V}_{\mathrm{S}}\times{\sigma}_{\mathrm{H}}}, $$ where NH is the number of hydrogen atoms in 1 cm3 of the emulsion and σH = 3.203 b (1 b = 10−28 m2) is the cross-section for elastic scattering of fast neutron on a hydrogen atom. NH = (2.97 ± 0.24) × 1022 for the standard emulsion and NH = (2.52 ± 0.50) × 1022 for the boron-loaded emulsion. Value of NH for boron-loaded emulsions was calculated according to the boron addition recipe from personal notes of Bradna, Beneš and Kubal (Institute of Nuclear Research in Řež, 1960). The cross-section was calculated from data given in TENDL-2017(31) with help of interpolation in JANIS(32) as an average weighted by fast neutron spectrum of reactor LR-0. The correction factor for undetected proton tracks with small energy (recoiled in the angle bigger than critical) was also calculated with help of the neutron spectrum. For this purpose, it can be assumed that energy distribution of protons originating in elastic scattering of neutrons with energy En is uniform from 0 to En(33). The portion of neutrons that can be detected (track of the recoiled proton will be long enough) is given by the relation: $$ {k}_{\mathrm{u}}=\frac{\int_{0.8}^{E_{\mathrm{max}}}\frac{E_{\mathrm{n}}\left(\mathrm{MeV}\right)-0.8}{E_{\mathrm{n}}\left(\mathrm{MeV}\right)}\times{N}_{\mathrm{S}}\left({E}_{\mathrm{n}}\right)\ d{E}_{\mathrm{n}}}{\int_{0.8}^{E_{\mathrm{max}}}{N}_{\mathrm{S}}\left({E}_{\mathrm{n}}\right)\ d{E}_{\mathrm{n}}}. $$ NS (En) is the number of neutrons with energy En in the spectrum and Emax is the maximal energy of the spectrum in MeV (in this case Emax = 10.2 MeV). For the spectrum of reactor LR-0, the numerical value of ku is ku = 0.53. Final fluence estimation is adjusted according to the relation: $$ {F}_{\mathrm{fast}}^{\ast }={k}_{\mathrm{perp}}\cdotp \frac{F_{\mathrm{fast}}}{k_{\mathrm{u}}}, $$ where kperp is a small correction implemented because proton tracks perpendicular to scanning plane were sometimes hard to spot or distinguish from electron tracks. Tracks in the spatial angle 0.1 sr (10° from axis of the viewed plane) were not counted. Value of this correction factor is kperp = 1.015. Thermal neutrons (En < 1 eV) have a considerable cross-section for interaction with atoms of isotope B-10: σB-10 = 2011.6 b (1 b = 10−28 m2). Value of cross-section was taken from data given by TENDL(31) accessed through JANIS web database(32) as an average of the cross-section for energy 0.005–1.0 eV weighted with energy spectrum of the reactor LR-0.(29) After the B-10 neutron capture, the excited nucleus B-11 is divided into two fragments—lithium Li-7 and alpha particle He-4. The reaction can be schematically written as 10B(nth, α)7Li. The energy of this reaction, transformed into kinetic energy of fragments, is in 93% of cases Q = 2.31 MeV and in 7% of cases Q = 2.79 MeV.(34) From the conservation laws of energy and momentum, it follows that the mentioned fragments are flying in most cases (if nothing else is produced) in opposite direction. Lengths of their tracks should be in the same ratio as their mass (4:7). Measured lengths of tracks are lLi = (3.1 ± 0.3) μm and lHe = (5.5 ± 0.5) μm.(35) This characteristic pair of tracks is easy to recognize and the number of such events NLi + He in the measured sample can be counted. It is hard to estimate the amount of boron in the emulsion. The Slavich Company uses a recipe from personal notes of Bradna, Beneš and Kubal (Institute of Nuclear Research in Řež, 1960) for making emulsions enriched with boron. From this recipe, it was estimated that the number of B-10 atoms in 1 cm3 of boron emulsion NB10 = (3.635 ± 0.75) × 10(20). It is possible to use a simple relation for the estimation of the number of thermal neutrons crossing 1 cm3 of emulsion: $$ {F}_{\mathrm{th}}={k}_{\mathrm{perp}}\times \frac{{\overline{N}}_{\mathrm{Li}+\mathrm{He}}}{N_{10\mathrm{B}}\times{V}_{\mathrm{S}}\times{\sigma}_{\mathrm{B}}}, $$ where |${\overline{N}}_{\mathrm{Li}+\mathrm{He}}$| is the average number of counted tracks in the analyzed volume VS of one sample, σB is the cross-section for the reaction and kperp = 1.015 is the same correction factor for hard to count perpendicular tracks as for fast neutrons. Measured parameters for fast neutrons. Table 3 Measured parameters for fast neutrons. FAST NEUTRONS . Number of viewed sample volumes . Average number of tracks in one sample volume . Boron emulsion 55C(B)-9 (exp. 1) 100 1.06 ± 0.10 Standard emulsion 55II-7 (exp. 2) 200 0.239 ± 0.036 Boron emulsion 55C(B)-6 (exp. 2) 200 0.120 ± 0.024 FAST NEUTRONS . Number of viewed sample volumes . Average number of tracks in one sample volume . Boron emulsion 55C(B)-9 (exp. 1) 100 1.06 ± 0.10 Standard emulsion 55II-7 (exp. 2) 200 0.239 ± 0.036 Boron emulsion 55C(B)-6 (exp. 2) 200 0.120 ± 0.024 Open in new tab Table 3 Measured parameters for fast neutrons. FAST NEUTRONS . Number of viewed sample volumes . Average number of tracks in one sample volume . Boron emulsion 55C(B)-9 (exp. 1) 100 1.06 ± 0.10 Standard emulsion 55II-7 (exp. 2) 200 0.239 ± 0.036 Boron emulsion 55C(B)-6 (exp. 2) 200 0.120 ± 0.024 FAST NEUTRONS . Number of viewed sample volumes . Average number of tracks in one sample volume . Boron emulsion 55C(B)-9 (exp. 1) 100 1.06 ± 0.10 Standard emulsion 55II-7 (exp. 2) 200 0.239 ± 0.036 Boron emulsion 55C(B)-6 (exp. 2) 200 0.120 ± 0.024 Open in new tab Results for fast neutrons. Table 4 Results for fast neutrons. Fast neutrons . Reference fluence (cm−2) . Measured fluence (cm−2) . Boron emulsion 55C(B)-9 (exp. 1) 7.04 × 107 (7.2 ± 2.0) × 107 Standard emulsion 55II-7 (exp. 2) 7.44 × 106 (7.6 ± 1.5) × 106 Boron emulsion 55C(B)-6 (exp. 2) 7.44 × 106 (8.2 ± 2.5) × 106 Fast neutrons . Reference fluence (cm−2) . Measured fluence (cm−2) . Boron emulsion 55C(B)-9 (exp. 1) 7.04 × 107 (7.2 ± 2.0) × 107 Standard emulsion 55II-7 (exp. 2) 7.44 × 106 (7.6 ± 1.5) × 106 Boron emulsion 55C(B)-6 (exp. 2) 7.44 × 106 (8.2 ± 2.5) × 106 Open in new tab Table 4 Results for fast neutrons. Fast neutrons . Reference fluence (cm−2) . Measured fluence (cm−2) . Boron emulsion 55C(B)-9 (exp. 1) 7.04 × 107 (7.2 ± 2.0) × 107 Standard emulsion 55II-7 (exp. 2) 7.44 × 106 (7.6 ± 1.5) × 106 Boron emulsion 55C(B)-6 (exp. 2) 7.44 × 106 (8.2 ± 2.5) × 106 Fast neutrons . Reference fluence (cm−2) . Measured fluence (cm−2) . Boron emulsion 55C(B)-9 (exp. 1) 7.04 × 107 (7.2 ± 2.0) × 107 Standard emulsion 55II-7 (exp. 2) 7.44 × 106 (7.6 ± 1.5) × 106 Boron emulsion 55C(B)-6 (exp. 2) 7.44 × 106 (8.2 ± 2.5) × 106 Open in new tab Measured parameters for thermal neutrons. Table 5 Measured parameters for thermal neutrons. Thermal neutrons . Number of viewed sample volumes . Average number of tracks in one sample volume . Boron emulsion 55C(B)-9 (exp. 1) 100 13.51 ± 0.33 Boron emulsion 55C(B)-6 (exp. 2) 200 1.48 ± 0.08 Thermal neutrons . Number of viewed sample volumes . Average number of tracks in one sample volume . Boron emulsion 55C(B)-9 (exp. 1) 100 13.51 ± 0.33 Boron emulsion 55C(B)-6 (exp. 2) 200 1.48 ± 0.08 Open in new tab Table 5 Measured parameters for thermal neutrons. Thermal neutrons . Number of viewed sample volumes . Average number of tracks in one sample volume . Boron emulsion 55C(B)-9 (exp. 1) 100 13.51 ± 0.33 Boron emulsion 55C(B)-6 (exp. 2) 200 1.48 ± 0.08 Thermal neutrons . Number of viewed sample volumes . Average number of tracks in one sample volume . Boron emulsion 55C(B)-9 (exp. 1) 100 13.51 ± 0.33 Boron emulsion 55C(B)-6 (exp. 2) 200 1.48 ± 0.08 Open in new tab Results for thermal neutrons. Table 6 Results for thermal neutrons. Thermal neutrons . Reference fluence (cm−2) . Measured fluence (cm−2) . Boron emulsion 55C(B)-9 (exp. 1) 5.93 × 107 (5.4 ± 1.8) × 107 Boron emulsion 55C(B)-6 (exp. 2) 6.28 × 106 (5.9 ± 1.9) × 106 Thermal neutrons . Reference fluence (cm−2) . Measured fluence (cm−2) . Boron emulsion 55C(B)-9 (exp. 1) 5.93 × 107 (5.4 ± 1.8) × 107 Boron emulsion 55C(B)-6 (exp. 2) 6.28 × 106 (5.9 ± 1.9) × 106 Open in new tab Table 6 Results for thermal neutrons. Thermal neutrons . Reference fluence (cm−2) . Measured fluence (cm−2) . Boron emulsion 55C(B)-9 (exp. 1) 5.93 × 107 (5.4 ± 1.8) × 107 Boron emulsion 55C(B)-6 (exp. 2) 6.28 × 106 (5.9 ± 1.9) × 106 Thermal neutrons . Reference fluence (cm−2) . Measured fluence (cm−2) . Boron emulsion 55C(B)-9 (exp. 1) 5.93 × 107 (5.4 ± 1.8) × 107 Boron emulsion 55C(B)-6 (exp. 2) 6.28 × 106 (5.9 ± 1.9) × 106 Open in new tab RESULTS For the fast neutrons, the average number of counted tracks in one measured sample volume of emulsion is written in Table 3 together with the number of viewed samples. Results calculated from measurements were compared with the reference fluence of neutrons with energy higher than 0.8 MeV (see Table 4). Values of average number of lithium and helium pairs from reaction 10B(nth, α)7Li are written in Table 5. Resulting thermal neutron fluences corresponding to the counted tracks are shown in Table 6 in comparison with reference thermal neutron fluences. CONCLUSIONS The relative difference between measured and reference neutron fluence is in two statistically more significant measurements <3% for the fast neutrons (see Table 4). Difference between the third measurement and corresponding reference fluence is approximately 10%; however, this measurement has the worst statistical significance denoting possible major inaccuracy. From this point of view, the emulsion composition seems verified and the method for the neutron fluence estimation with uncalibrated nuclear track emulsions was confirmed. Dose equivalent can be estimated, when the neutron fluence-to-dose equivalent conversion factors are used(36). For thermal neutrons, the relative difference between measured and reference fluence is <10%. Even though the statistical significance of measurement is better than for fast neutrons (see Tables 3 and 5), the estimation of fluence is not more accurate. In this case, the uncertainty in the fluence estimation could be given by the imprecise boron amount estimation. Concentration of B-10 can be inaccurate insomuch as it is suspected that a part of the boron salt is crystalizing on the surface of the emulsion due to the imperfect process during production. In the future, it is planned to try to mix standard emulsion BR-2 with boron salts in a more controlled manner. In order to improve statistical significance of the measurements, which would be needed for practical use of nuclear emulsions for neutron dosimetry, application of automatic scanning of emulsions and image processing is required. It must also be pointed out that there is a big gap in detectable energy. It is not possible to detect neutrons with energy 1 eV < En < 0.8 MeV. This gap could be slightly reduced by using reaction on Li-6 or gadolinium filter for thermal neutrons or by counting shorter tracks of recoil proton tracks from fast neutrons. Another restriction of the presented fluence estimation method is that spectrum of the neutron field must be known. Although it is possible to measure neutron spectrum with thick nuclear emulsions(12,37,38), it must be done in specific geometry and it is not applicable for routine dosimetry now. Nevertheless, the developed method of neutron fluence estimation can serve as a confirmation that emulsions BR-2 are suitable for personal neutron dosimetry and their response has a physical meaning. Even without previous calibration, the measured neutron fluences are in good agreement with the reference fluences. 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TI - INVESTIGATION OF NUCLEAR EMULSIONS IN TERMS OF NEUTRON DOSIMETRY
JF - Radiation Protection Dosimetry
DO - 10.1093/rpd/ncz208
DA - 2019-12-31
UR - https://www.deepdyve.com/lp/oxford-university-press/investigation-of-nuclear-emulsions-in-terms-of-neutron-dosimetry-D9CmeuCCve
DP - DeepDyve
ER -