首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
Characteristics of a source of thermal neutrons based on an evacuated NG-400 neutron generator with the maximum flux (Φf) 2 × 1011 neutron/s for 14 MeV neutrons and 2 × 109 neutrons/s for 3 meV neutrons have been investigated. The possibilities of its application for neutron activation analysis have been estimated. The distribution, composition, and density (φT) values of the thermal neutron flux have been measured in the inner cavity of the moderator using activation detectors. φT was 2 × 108 and 2 × 106 neutrons/cm2 s for thermalized neutrons with energies of 14 and 3 MeV, respectively. The possibilities of the apparatus have been estimated theoretically and experimentally for the cases of thermalized neutrons of 14 MeV and 3 MeV.  相似文献   

2.
The possible application of cyclotron-produced fast neutrons to activation analysis for oxygen based on the16O(n, p)16N reaction has been investigated. Neutrons were produced by bombarding a thick beryllium target with 22 to 45 MeV deuterons. It was found that the sensitivity increases rapidly with the energy of the deuterons. Using 45 MeV deuterons and a 10 μA beam current a sensitivity of about 20 counts per 1 μg oxigen could be achieved, enabling the determination of less than 1 μg oxigen. In a direct comparison it was experimentally established that the sensitivity for cyclotron-produced neutrons assuming a deuteron beam of about 10 μA, is up to two orders of magnitude higher than that achievable for 14 MeV neutrons with a flux of about 1010 n/s. The interference of fluorine is at about the same level for both the cyclotron-produced and 14 MeV neutrons. Using cyclotron-produced fast neutrons in the investigated energy range, sodium and magnesium can also interfere, but only to a very much lower extent.  相似文献   

3.
A procedure involving the irradiation of coal samples with 14 MeV neutrons and subsequent gamma-ray spectrometry of the irradiated sample for the estimation of solfur in coal, has been outlined. The samples were irradiated with 14MeV neutrons from a Cockroft-Walton type generator for one minute and then subjected to gamma-ray spectrometry for another minute using an automated transfer cyclic system. Ten such cycles were repeated for accumulating events under the 2130 keV gamma ray photopeak belonging to34P (T=12.4 s) produced by the34S(n, p)34P reaction for assessing the lower level of detection, LLD, of Sulfur. Interferences due to the presence of other elements in coal were also determined. Sulfur can be determined at LLD of 0.25% in coal provided a 5 g sample of the coal is irradiated with a neutron flux of 5·109 n·cm−2·sec−1 assayed with a gamma ray spectrometer having a large hollow core Ge(Li) detector and an anti-Compton shield.  相似文献   

4.
A rapid vertical transportation system for irradiation with thermal and fast neutrons is devised and partly constructed for inserting samples into the central thimble of our TRIGA MARK II reactor. Fast neutrons will be produced by a6LiD-converter, so that the energy distribution of neutrons is hardened by absorption of thermal and by the production of 14 MeV neutrons. In pulse irradiation, the 14 MeV-neutron flux is expected to be in the order of 1012/s. The transportation time is to be below 30ms to enable determination of short-lived nuclides down to 15ms. Helium will be used as propelling gas.  相似文献   

5.
Performance of a 241Am-Be neutron source-based and 2.8 MeV neutrons-based moisture measurement setups have been compared using Monte Carlo simulation. In the setup fast neutrons transmitted through the sample were detected by a fast neutron detector, which was placed behind a massive long double truncated collimator. The setup geometry was optimized to detect maximum effect of 1–7 wt.% moisture on the neutron intensity transmitted through the sample. The yield of neutrons transmitted through concrete, coal, wood and soil samples containing 1–7 wt.% moisture was calculated for 2.8 MeV neutrons and neutrons from an 241Am-Be source. The slopes of the fast neutron intensities transmitted through the samples vs. their moisture contents are very sensitive to the neutron energy and the sample composition. Higher slopes have been observed for the samples with larger bulk density. The slopes of fast neutron yield show dependence on the incident neutron energy. Larger slopes have been observed for neutrons with samller energy. Due to the overall large slopes of the transmitted intensity data of the samples for 2.8 MeV neutrons, it is expected to achieve better sensitivity in moisture measurements for a 2.8 MeV neutrons based moisture setup.  相似文献   

6.
The γ-spectra of fission products of235U are analysed by a Ge(Li) detector after colling times of 3, 7 and 110 hrs. The possibility of the use of these results is demonstrated for measuring the mass distribution. Some preliminary values for the fission of232Th by 14 MeV neutrons are given.   相似文献   

7.
The Si-contents of flue-dust and sedimented dust from Czechoslovak mines were determined by instrumental activation analysis with 14 MeV neutrons using a flux of 107 cm−2·s−1. The amounts determined range from 3 to 30 mg.  相似文献   

8.
Three experimentally different methods for analysing silicon in steel by activation with fast neutrons are described. By bombardment of28Si with fast neutrons28Al is obtained after a (n, p) reaction.28Al emits a γ-radiation of 1.78 MeV. The difficulty lies in discriminating the 1.78 MeV peak out of the emitted radiation. The first method consists in determining the ratio of the 1.8 MeV peak to the 2.1 MeV peak of an activated iron sample. From this ratio one can deduct the contribution of28Al to the 1.8 MeV peak of a silicon containing sample. The other method of separation makes use of the different half-lives of the 1.78 MeV γ-rays from28Al and the 1.81 MeV γ-rays from56Mn. The direct separation of the peaks with a Ge(Li) detector is the third method. This paper illustrates the possibilities of activation analysis with fast neutrons. For this reason the values measured are compared with the results of chemical analyses.  相似文献   

9.
Monochromatic MeV-energy neutron source for secondary reaction was developed utilizing tritium embedded titanium (Ti-3H) thin film via 3H(p,n)3He reaction. We have measured the neutron energies and the energy spread by resonance reactions of 12C(n,tot) and 28Si(n,tot). The available energy was within the range from 0.6 to 2.6 MeV. Energy spread was 1.6% at energy of 2.077 MeV. The flux in the beam direction was determined to be 3.76·107 n/s/sr by irradiating 197Au by about 2 MeV neutrons. This source was shown to be useful for measurements of nuclear data by measuring the total cross sections of neutrons on Fe and comparing these data to the data of ENDF-6.  相似文献   

10.
The size distributions of 38Cl, 39Cl, 82Br and 84Br aerosols generated by irradiations of argon and krypton gases containing di-octyl phthalate (DOP) aerosols with 45 MeV and 65 MeV quasi-monoenergetic neutrons were measured in order to study the formation mechanism of radioactive particles in high energy radiation fields. The effects of the size distribution of the radioactive aerosols on the size of the added DOP aerosols, the energy of the neutrons and the kinds of nuclides were studied. The observed size distributions of the radioactive particles were explained by attachment of the radioactive atoms generated by the neutron-induced reactions to the DOP aerosols.  相似文献   

11.
Due to a need for security screening instruments capable of detecting explosives and nuclear materials there is growing interest in neutron generator systems suitable for field use for applications broadly referred to as active neutron interrogation (ANI). Over the past two years Thermo Electron Corporation has developed a suite of different compact accelerator neutron generator products specifically designed for ANI field work to meet this demand. These systems incorporate hermetically-sealed particle accelerator tubes designed to produce fast neutrons using either the deuterium-deuterium (E n = 2.5 MeV) or deuterium-tritium (E n = 14.1 MeV) fusion reactions. Employing next-generation features including advanced sealed-tube accelerator designs, all-digital control electronics and innovative housing configurations these systems are suitable for many different uses. A compact system weighing less than 14 kg (MP 320) with a lifetime exceeding 1000 hours has been developed for portable applications. A system for fixed installations (P 325) has been developed with an operating life exceeding 4500 hours that incorporates specific serviceability features for permanent facilities with difficult-to-access shield blocks. For associated particle imaging (API) investigations a second-generation system (API 120) with an operating life of greater than 1000 hours has been developed for field use in which a high resolution fiber-optic imaging plate is specially configured to take advantage of a neutron point-source spot size of ∼2 mm.  相似文献   

12.
As an altemative to129I measurement by X-ray spectrometry or ICPMS, we explored the possibilities of activation analysis using thermal or 14 MeV neutrons. Preliminary qualitative measurements were done with samples of about 5 mg. These samples were exposed to two neutron sources:252Cf and DT neutron generator. The most interesting reaction is the neutron capture which leads to useful signatures at 536.1, 668.5, and 739.5 keV, associated with a half-life of 12.36 h.  相似文献   

13.
The use of 2.8 MeV neutrons produced by the D(d, n)3He reaction should be taken into consideration in some applications of radioactivation analysis. The low number of elements activable by these neutrons makes possible to minimize the matrix interference and the background below the characteristic photopeaks. The very low dead-time of the spectrometric measurements permits the use of the maximum neutron flux available now and in the future. The purpose of this paper is to define experimentally the sensitivity of determination for the 16 main elements activable with a 400 keV Van de Graaff accelerator at a 2.8 MeV neutron flux of 2·106 n·cm−2·sec−1 on the sample.  相似文献   

14.
A neutron activation analysis procedure utilizing 14 MeV neutrons produced by an accelerator is described. The six elements Si, Cl, K, P, Ca and Al are determined in biological material without any chemical separation. For avoiding the interpretation of very complex spectra, the half-life of the nuclides was applied for the measurement as an important characteristic.   相似文献   

15.
A compilation of the cross sections (n, p), (n, n′ p), (n, α) (n, n′ α) and (n,3He) for93Nb,92,95,96,97,98,100Mo by 14 MeV neutrons is presented in the form of a table containing the results of nearly 70 different measurements, mainly obtained by activation analysis. Brief assessments of the experimental methods and the data status are given.  相似文献   

16.
A compilation of the cross section (n, 2n) for46Ti,50, 52, 54Cr,55Mn,54,56Fe,59Co,58,59Ni,93Nb,92,100Mo with 14 MeV neutrons is presented in the form of a table containing the results of nearly 190 different measurements, mainly obtained by activation analysis. Brief assessment of the experimental methods and the data status are given.  相似文献   

17.
Carbon, nitrogen and oxygen were determined in gases by time-of-flight spectrometry of prompt neutrons from the respective reactions12C(d, n)13N,14N(d, n)15O and16O(d, n)17F, produced by a pulsed beam of deuterons of 2 MeV (for nitrogen) or 3 MeV. The analysis is non-destructive and requires about 15 min. per sample. The relative standard deviation for all three elements was about ±3%. Detection limits, using a total irradiation current of 20 millicoulombs, for carbon, nitrogen and oxygen, respectively, were 6·10−8 g, 2·10−7 g and 1.7·10−7 g per cm2 cross-sectional area of irradiating beam.  相似文献   

18.
The potential for using a small, sealed tube, DT neutron generator for neutron activation analysis has been well documented but not well demonstrated, except for 14 MeV activation analysis. This paper describes the design, construction and characterization of a neutron irradiation facility incorporating a small sealed tube DT neutron generator producing 14 MeV neutrons with fluence rates of 2·108 s−1 in 4π (steady state) and 1011 s−1 in 4π (pulsed). Monte Carlo modeling using MCNP4c and McBend9 has been used to optimize the design of this facility, including the location of a thermal irradiation facility for conventional neutron activation analysis. A significant factor in designing the facility has been the requirement to conform with Ionising Radiation Regulations and the design has been optimized to keep potential radiation doses to less that 1 μSv/h at the external walls of the facility. Activation of gold foils has been used for flux characterization and the experimental results agree well with the modeling.  相似文献   

19.
The yield and average cross section for the reactions11B(p, n)11C,12C(p, )13N,13C(p, n)13N, 12 12 C(d, n)13N,14N(p, )11C,16O(p, )13N,16O(d, n)17F,16O(t, n)18F, and18O(p, n)18F have been measured in different compounds. The charged particles were created in the samples themselves either through recoil by scattering of 14 MeV neutrons off hydrogen and deuterium, or by the (n, t) reaction on6Li using thermal neutrons. The yields of reactions12C(d, n);16O(p, );16O(t, n) and18O(p, n) have been measured using proton, deuteron and triton spectra generated by 14 MeV neutrons in the reactions D(n, p)2n;6Li(n, d);7Li(n, d) and10B(n, d);7Li(n, t) and10B(n, t), respectively.  相似文献   

20.
Osmium isotope, 197Os, produced with 14 MeV neutrons through the reaction of 198Pt(n,2p)197Os, has been identified and its decay properties have been studied with a g(X) spectroscopic method. The ten new g-rays of 41.2, 50.7, 196.8, 199.6, 223.9, 233.1, 250.2, 342.1, 403.6, and 406.4 keV assigned to the decay of 197Os were observed. The half-life of 197Os has been determined as 2.8±0.6 minutes. A partial decay scheme of 197Os was proposed.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号