We need your consent to use the individual data so that you can see information about your interests, among other things. Click "OK" to give your consent.
Standard Practice for Application and Analysis of Nuclear Research Emulsions for Fast Neutron Dosimetry
Translate name
STANDARD published on 1.7.2020
Designation standards: ASTM E2059-20
Publication date standards: 1.7.2020
SKU: NS-1001411
The number of pages: 18
Approximate weight : 54 g (0.12 lbs)
Country: American technical standard
Category: Technical standards ASTM
Keywords:
fast-neutron dosimetry, NRE, nuclear emulsions, optical microscopes, proton-recoil tracks,, ICS Number Code 17.240 (Radiation measurements)
Significance and Use | ||||||||||
4.1 Integral Mode Dosimetry—As shown in 3.2, two different integral relationships can be established using proton-recoil emulsion data. These two integral reactions can be obtained with roughly an order of magnitude reduction in scanning effort. Consequently, this integral mode is an important complementary alternative to the customary differential mode of NRE spectrometry. The integral mode can be applied over extended spatial regions, for example, perhaps up to as many as ten in-situ locations can be covered for the same scanning effort that is expended for a single differential measurement. Hence the integral mode is especially advantageous for dosimetry applications which require extensive spatial mapping, such as exist in Light Water Reactor-Pressure Vessel (LWR-PV) benchmark fields (see Test Method E1005). In low power benchmark fields, NRE can be used as integral dosimeters in a manner similar to RM, solid state track recorders (SSTR) and helium accumulation monitors (HAFM) neutron dosimeters (see Test Methods E854 and E910). In addition to spatial mapping advantages of these other dosimetry methods, NRE offer fine spatial resolution and can therefore be used in-situ for fine structure measurements. In integral mode scanning, both absolute reaction rates, that is I(E4.2 Applicability for Spectral Adjustment Codes—In the integral mode, NRE provide absolute integral reaction rates that can be used in neutron spectrum least squares adjustment codes (see Guide E944). In the past, such adjustment codes could not utilize NRE integral reaction rates because of the non-existence of NRE data. NRE integral reaction rates provide unique benchmark data for use in least squares spectral adjustment codes. The unique significance of NRE integral data arises from a number of attributes, which are described separately below. Thus, inclusion of NRE integral reaction rate data in the spectral adjustment calculations can result in a significant improvement in the determination of neutron spectra in low power benchmark fields. 4.3 The
Neutron Scattering Cross Section of Hydrogen—Integral NRE
reaction rates are based on the standard neutron scattering cross
section of hydrogen. For fast neutron spectrometry and dosimetry
applications, the accuracy of this (n,p) cross section over
extended energy regions is essentially unmatched. A semi-empirical
representation of the energy-dependence of the (n,p) cross section
is given in Eq 13. where: E is in MeV and σnp(4.4 Threshold Energy Definition—In contrast with all other fast neutron dosimetry cross sections, the threshold energy of the I and J integral reaction rates can be varied. NRE integral reaction threshold variability extends down to approximately 0.3 to 0.4 MeV, which is the lower limit of applicability of the NRE method. Threshold variation is readily accomplished by using different lower bounds of proton track length to analyze NRE proton-recoil track length distributions. Furthermore, these NRE thresholds are more accurately defined than the corresponding thresholds of all other fast neutron dosimetry cross sections. NRE therefore provide a response with an extremely sharp energy cutoff that is not only unmatched by other cross sections, but an energy threshold that is independent of the FIG. 2 Comparison of the I-Integral Response with the 237Np (FIG. 3 Comparison of the J-Integral Response for 4.5 Complimentary Energy Response—It is of interest to compare the differential energy responses available from these two integral relations. From Eq 4 and 11, one finds responses of the form σ(FIG. 4 Energy Dependent Response for the Integral Reactions 1.1 Nuclear Research Emulsions (NRE) have a long and illustrious history of applications in the physical sciences, earth sciences and biological sciences (1, 2)2. In the physical sciences, NRE experiments have led to many fundamental discoveries in such diverse disciplines as nuclear physics, cosmic ray physics and high energy physics. In the applied physical sciences, NRE have been used in neutron physics experiments in both fission and fusion reactor environments 1.2 NRE are passive detectors and provide time integrated reaction rates. As a consequence, NRE provide fluence measurements without the need for time-dependent corrections, such as arise with radiometric (RM) dosimeters (see Test Method E1005). NRE provide permanent records, so that optical microscopy observations can be carried out any time after exposure. If necessary, NRE measurements can be repeated at any time to examine questionable data or to obtain refined results. 1.3 Since NRE measurements are conducted with optical microscopes, high spatial resolution is afforded for fine structure experiments. The attribute of high spatial resolution can also be used to determine information on the angular anisotropy of the in-situ neutron field (4, 5, 7). It is not possible for active detectors to provide such data because of in-situ perturbations and finite-size effects (see Section 11). 1.4 The existence of hydrogen as a major constituent of NRE affords neutron detection through neutron scattering on hydrogen, that is, the well known (n,p) reaction. NRE measurements in low power reactor environments have been predominantly based on this (n,p) reaction. NRE have also been used to measure the 6Li (n,t) 4He and the 10B (1.5 Limitations—The NRE method possesses four major limitations for applicability in low power reactor environments. 1.5.1 Gamma-Ray Sensitivity—Gamma-rays create a significant limitation for NRE measurements. Above a gamma-ray exposure of approximately 0.025 Gy, NRE can become fogged by gamma-ray induced electron events. At this level of gamma-ray exposure, neutron induced proton-recoil tracks can no longer be accurately measured. As a consequence, NRE experiments are limited to low power environments such as found in critical assemblies and benchmark fields. Moreover, applications are only possible in environments where the buildup of radioactivity, for example, fission products, is limited. 1.5.2 Low Energy Limit—In the measurement of track length for proton recoil events, track length decreases as proton-recoil energy decreases. Proton-recoil track length below approximately 3μm in NRE cannot be adequately measured with optical microscopy techniques. As proton-recoil track length decreases below approximately 3 μm, it becomes very difficult to measure track length accurately. This 3-μm track length limit corresponds to a low energy limit of applicability in the range of approximately 0.3 to 0.4 MeV for neutron induced proton-recoil measurements in NRE. 1.5.3 High-Energy Limits—As a consequence of finite-size limitations, fast-neutron spectrometry measurements are limited to ≤15 MeV. The limit for 1.5.4 Track Density Limit—The ability to measure proton recoil track length with optical microscopy techniques depends on track density. Above a certain track density, a maze or labyrinth of overlapping tracks is created, which precludes the use of optical microscopy techniques. For manual scanning, this limitation arises above approximately 104 tracks/cm2, whereas interactive computer-based scanning systems can extend this limit up to approximately 105 tracks/cm2. These limits correspond to neutron fluences of 106 − 10 7 cm−2, respectively. 1.6 Neutron Spectrometry (Differential Measurements)—For differential neutron spectrometry measurements in low-power reactor environments, NRE experiments can be conducted in two different modes. In the more general mode, NRE are irradiated 1.7 Neutron Dosimetry (Integral Measurements)—NRE also afford integral neutron dosimetry through use of the (n,p) reaction in low power reactor environments. Two different types of (n,p) integral mode dosimetry reactions are possible, namely the I-integral (see 3.2.1) and the J-integral (see 3.2.2) (10, 11). Proton-recoil track scanning for these integral reactions is conducted in a different mode than scanning for differential neutron spectrometry (see 3.2). Integral mode data analysis is also different than the analysis required for differential neutron spectrometry (see 3.2). This practice will emphasize NRE (n,p) integral neutron dosimetry, because of the utility and advantages of integral mode measurements in low power benchmark fields. 1.8 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee. |
||||||||||
2. Referenced Documents | ||||||||||
|
Do you want to make sure you use only the valid technical standards?
We can offer you a solution which will provide you a monthly overview concerning the updating of standards which you use.
Would you like to know more? Look at this page.
Latest update: 2024-12-22 (Number of items: 2 217 000)
© Copyright 2024 NORMSERVIS s.r.o.