Thermal Neutron Dose Research Articles

Improved methods for measurement of thermal neutron dose by the fission track technique

We describe scanning electron microscope and reflected light observations of fission tracks that lead to highly reproducible track density measurements for different observers. These new observational techniques are used to calibrate two uranium-doped glasses for neutron dose measurements. The glasses are available to other investigators.

Use of divergent-beam x-ray diffraction to measure lattice expansion in LiF as a function of thermal-neutron dose up to 6 × 1016 nvt

The lattice expansion of LiF was measured by means of the divergent-beam (Kossel) x-ray diffraction method at three levels of thermal-neutron dose, 0.45, 2, and 6 × 1016 nvt, respectively. The lattice parameter of LiF increases due to the production of Frenkel defects resulting from the Li6(n, α)H3 reaction. At 6 × 1016 nvt, the lattice expansion was found to be 0.13±0.02% which is in good agreement with previously reported values.

Radiation induced variability in improvement of brown sarson

Kumar P.R. Radiation induced variability in improvement of brown sarson . Radiation Botany 12 , 309–313, 1972.-A study was undertaken to improve the flowering time and the number of seeds per siliqua in highly cross pollinated Brassica campestris L. var. dichotoma Watt. (cv. brown sarson). Dry seeds of three strains of cultivar brown sarson were exposed to varying doses of gamma rays and thermal neutrons and grown during 1965–1969. The pattern of release of polygenic variability and the degree of shifts in mean values were examined in terms of range, coefficient of variation and the mean from the M 2 to M 4 generation. Selection was practised in M 3 plants which were at least 10 days earlier in first flowering and with a minimum of 20 seeds per siliqua. The selected genotypes were permitted to intercross in isolations in the M 4 generation. The specific radiation treatments generated additional variability without altering the mean values of two traits in different generations. In the M 4 generation, a high degree of variability was released which afforded opportunity for stabilizing the mean values of these two polygenic traits of high economic value in the M 5 generation at a desired level.

Effect of tensile test conditions on the fracture behaviour of 20Cr-25Ni-Nb stabilised stainless steel after high-temperature irradiation

Tensile specimens were cut from 20 Cr-25 Ni-Nb stabilised austenitic steel tubes irradiated at 650–700 °C, in contact with UO 2 fuel at their inner surfaces and CO 2 at their outer surfaces, to a thermal neutron dose between 1 and 10 × 10 20 nvt. Tensile tests were made at temperatures between 450 °C and 800 °C using three strain-rates in thp range 1.4 × 10 −3 to 1.4 × 10 −6/ sec. The results were correlated using the expression σt n = K ε enp ( Q/ RT), where σt is the flow stress and n is an index which proves to be close to 7. Under test conditions giving full recovery-creep an activation energy Q of ∼ 68.5 kcal/ mole was obtained for the irradiated specimens and ∼ 80 kcal/mole for unirradiated thermal control specimens. The tensile elongation and rupture mode of the specimens were also related to the Zener-Holloman parameter Z = log 10 [ ε exp ( Q/ RT)]. The intergranular fracture mode of the irradiated specimens varied from development of micro-cracks at the higher values of Z to cavitation at lower values. The reduced ductility observed on the irradiated tubing is discussed in terms of the effect of helium from the 10B(n, < α) 7Li reaction on intergranular crack and cavity development. The fission-fragment-bombarded zone at the tube bore was ∼ 10 μm thick and contained numerous gas bubbles of 20–100 Å dia. This zone apparently had little overall effect on the ductility of the tubing.

Effect of Neutron Irradiation on Mechanical Properties of Al-Li Alloys

An increase in yield stress at room temperature was observed in Al-0.6W/0 Li alloy irradiated to thermal neutron doses of 2.9 × 1019 to 7.2 × 1019 cm−2. The hardening of as-irradiated specimens is accompanied with yield point followed by jerky yield-elongation in the stress-strain curve. The radiation hardening could not be annealed out by heating for 30 min at temperatures up to 350°C, whereas the yield-elongation disappeared gradually with increasing heating temperature in the l mm diam. specimens; with the 2 mm diam. specimens the yield-elongation still remained even after post-irradiation heating for 30 min at 350°C. Strengthening accompanied by jerky yield-elongation is considered to be due to He atom clusters precipitated along the dislocation. The hardening observed in the specimens heat-treated after irradiation at temperatures above 250°C is caused by randomly distributed gas bubbles. In heavily cold-worked Al-0.6%W/o Li specimens, recovery of work hardening occurred during neutron irradiation to...

Thermal neutron damage in CdS and CdTe

Abstract Photoluminescence and electrical resistivity changes in CdS and CdTe produced by thermal neutrons are discussed. The damage is produced principally by the neutron capture reaction 113Cd (n,y) 114Cd. Since the reaction product 114Cd is stable, complications arising from impurity introduction is minimal. The cumulative recoil nuclear recoil energy is about 143 eV, but is not the recoil energy at the time atomic displacement occurs. Thermal and fast neutrons enhance the CdS luminescence band at 7200A in the ratio of 28:1, but the resistivity changes are in the ratio of 40:1 Cd interstitial is suggested as the luminescence center. Hall measurements on n-type CdTe suggest that only Cd defects are produced for low thermal neutron doses. The acceptor introduction rate is about 1.0 to 0.6, compared to 0.098 for CdS. These are in good agreement with the values reported by R. O. Chester. The fast neutron effects in high resistivity CdS reported by Johnson indicate the need for further measurement.

Fission Track Dating of Archaeological Materials from Japan

THE method of dating by fission tracks1 has been used by several workers to date rock minerals and baked relics2. The method depends on the spontaneous fission of 238U atoms in mineral or glass taking place at a constant rate, and leaving fission tracks. Once formed, the fission tracks disappear if the material is heated above a critical temperature. The fission track age, T (yr), can be represented by the following equation3 where ρs is the fossil fission track density (cm−2), ρi is the induced track density by bombardment with thermal neutrons (cm−2), λ, is the total decay constant for uranium (yr−1), λf is the fission decay constant for 238U (we use 6.85 × 10−17 yr−1 (ref. 4), Φ is the thermal neutron dose (cm−2), σ is the thermal neutron cross section for fission 235U (cm−2), η) is the isotope ratio 235U/238U, and Rs and Rt are the mean values of the etchable length of the fragments produced by a spontaneous fission and that produced by the induced fission (cm).

The dependence of the tensile properties of irradiated aluminium-lithium alloys upon gas bubble size and distribution

The effect of inert gas bubbles on the tensile properties of neutron irradiated aluminium-lithium alloys was examined in the temperature range 103 to 523 °K. An analysis of the macroyield strength of alloys containing various size distributions of gas bubbles at 223 °K showed that bubbles are weak obstacles to dislocation movement with breaking angles which vary from 132° for 150 Å diameter bubbles to 144° for 50 Å bubbles. Below 50 Å diameter the breaking angle decreases rapidly and becomes 174° for bubbles approximately 15 Å in diameter. The temperature dependence of the macro-yield stress for alloys irradiated to thermal neutron doses of 1.2 × 10 19 nvt and less showed that the presence of small bubbles caused an additional friction stress. Higher irradiation doses produced dislocation locking, possible due to the formation of jogs on glide dislocations. Ductility was severely reduced at high temperatures by the presence of inert gas bubbles in the grain boundaries. The ductility of irradiated material at low temperatures increased significantly and material which contained bubbles became more ductile than the unirradiated alloy. During post-irradiation annealing, which results in the coarsening of an originally fine distribution of small bubbles, the macro-yield stress increases to a maximum value and then decreases.

The evaluation of the spatial parameters K and α in equations for fission track uranium analysis

Abstract The equations describing fission track densities registered in solid state detectors contain some spatial parameters whose values are not well known. The product of K, a geometric factor approximately equal to the range of fission fragments in a solid, and α, the etching efficiency, is determined by simultaneously producing fission tracks from a glass of known uranium content and monitoring the thermal neutron dose using gold foil. For tracks recorded in Lexan plastic and produced by uranium in alumino-silicate glass the value of this product is 8.1–10−4 cm (± 7 per cent), and for tracks etched in the glass matrix itself it is 3.7–10−4 cm (± 8 per cent). These values are consistent with analagous values calculated from other published data, and by assuming a value of α = 1 for Lexan plastic, K is found to be 8.1. 10−4 cm (±7 per cent).

Sterilization of Boll Weevils with Combinations of Chemosterilants and X-Rays, Gamma Rays, Thermal Neutrons, or Fast Neutrons12

This study was undertaken to determine whether satisfactory sterility without mortality could be induced in Anthonomus grandis Boheman. Adult boll weevils irradiated with 2.5 had of X-rays and immersed in a 1.0% solution of apholate within 8 hours had a greater cumulative percentage mortality at 3 weeks than when the 2 treatments were separated by several days. However, the treatments failed to destroy completely the germarium in all males. Destruction of the germarium occurred more frequently if the males were still soft bodied when they were immersed. Thus, when 2-day-old males were immersed in apholate and X-irradiated 80 hours later, the majority sustained permanent destruction of the germarium, Weevils treated with 2.5 had of y-rays and a 1.0% solution of apholate reestablished the spermatogenic cycle as early as 13 days later and usually within 3 weeks; in 1 test, recovery of fertility occurred 11–13 days after treatment, and in 2 other tests, recovery occurred at 14–16 days after treatment. Sublethal doses of thermal neutrons did not sterilize boll weevils, but 1 had of fast neutrons significantly reduced the fertility of treated males and the fecundity of treated females. Doses of fast neutrons greater than 1.2 had caused high mortality, but a dose of 2 kard was necessary to sterilize all sperm and destroy all spermatogonia. Fecundity of treated females was greatly reduced with 1.5 and 2 kard. However, their fertility was depressed only moderately. Irradiation. of either sex with 1 krad of fast neutrons and immersion 3 days later in a 1.0% solution of apholate resulted in almost complete sterility, though the spermatogenic cycle was re-established in some individuals at 4 weeks after treatment. Moreover, this treatment reduced mating competitiveness of males treated as adults less than treatment with 2,5 had γ-rays and a 1.0% solution of apholate.

On the protection of UO 2, U and UC by metal films against fission induced losses of uranium

Pellets of UO 2, U and UC, either bare or covered with thin films of nickel or gold were irradiated at thermal neutron doses of 0.2 × 10 19 to 0.9 × 10 19 n/cm 2, to determine by the collector method the ejection rates of uranium from their surfaces. The ejection rates found for bare emitters were comparable to those observed by other authors. The losses of uranium from the Ni-covered emitters were lower by a factor of 2 to 4, those of the Au-covered emitters were widely scattered. The ejected matter was deposited on carbon films in the form of spots (islands). The spot density and the size of the spots varied, depending on the nature of the emitting material and the distance of the carbon films from the emitter.

Fission Track Dating of Archaeological Glass Materials from Japan

THE method of dating by fission tracks1 which has been applied to glass2 depends on the spontaneous fission of 238U atoms contained in glass taking place at a constant rate, and leaving fission tracks (that is, detectable damage trails of nuclear fragments). Once formed, the fission tracks in a glass disappear if the glass is heated above a critical temperature. It may be assumed that the density, ρs, of spontaneous fission tracks of 238U atoms in a glass is proportional to the lapse of time T after the glass was either produced or last heated above the critical temperature, and to the density of 238U atoms contained in the glass. The latter can be determined from the density of 235U atoms, ρi, which are induced by bombarding the glass with a known dose of thermal neutrons φ. Then the lapse of time T is given approximately by the simplified formula3

Dwarf-twisted: An induced mutation in Triticum durum Desf

A mutant phenotype, mainly characterized by undulated leaf surface, dwarfism and sterility, has been repeatedly induced by physical (X-rays; thermal and fast neutrons) and chemical (diethylsulphate and ethylmethanesulphonate) mutagenic agents in different varieties of durum wheat. This phenotype is easily detectable at the seedling stage. Neutron treatments are the most effective method to induce this phenotype and a maximum of 0.6% mutations per M1 spike-progeny was induced after the highest dose of thermal neutrons. On the average 0.23 mutations per 100 M1 spike progenies and 0.55 mutant seedlings per 1000 M2 plants were found after all treatments.

On the Detection of Neutrons with the Etch-Pit Counting Method

Fission fragments mark scars on such an insulator as glass or mica, when fissions take place on the surface of or inside the insulator material. Very small scars on the surface of the insulator material caused by the fission fragments can be etched by the suitable chemical treatment to form etch-pits visible under the ordinary microscope. Therefore the combination of the fissionable material and the insulator material can be used for neutron detection or neutron dosimetry.We used thin film of uranium or thorium electrodeposited on gold foil as the fissionable material and the glass or mica as the detector material of the fission fragments. The thin film of the fissionable material was kept in contact with the surface of the glass or mica. The effect of the different etching condition and the stability of the scars have been studied. It has been shown by the fission film-glass or mica combination that a good agreement exists between the expected number of fissions and the number of etch-pits. Distribution of thermal neutron flux in the reactor (UTR-B) was estimated with this system. The results of the etch-pit counting were in good agreement with those estimated with the activation method. A wide range of thermal neutron dose 10 mrem to 1000 rem may be measured with a single detector of this type with reasonable accuracy.

(D, D) and (D, T) Neutron Depth Dose Measurements in a Tissue-Equivalent Phantom

The components of dose due to 1H(n, γ)2D, 14N(n, p)14C and proton recoils have been resolved experimentally for D, D and D, T neutron beams in tissue. Some modifications to the theory of Snyder and Neufeld are necessary to account for discrepancies in the proton recoil depth dose and the position of the peak thermal neutron dose. Isodose curves are presented for various beam sizes.A simple technique for measuring proton recoil quality factors with a plastic phosphor Bragg-Gray detector is described, and the quality factor for the total dose from 14 MeV neutrons is deduced to be 8·5.

Outgassing of Glass Caused by Thermal Neutrons and Gamma Radiation

Prebaked evacuated glass bulbs were exposed to gamma radiation and thermal neutrons. The gases initially present in the bulb plus those evolved in a subsequent baking were measured and analyzed with a mass spectrometer. Several glasses were exposed to a gamma dosage of more than 107 rads. Small quantities of hydrogen as well as some CO, CO2, and water were detected. Several boron-containing glasses were exposed to more than 10 17 thermal neutrons/cm2. The gas evolved was almost entirely helium, formed as a result of alpha-particle emission in the reaction The total quantity of helium formed can be predicted from the thermal neutron dose and the boron content of the glass. The role of helium permeability is also discussed.

Untersuchungen über die Hochtemperatur-versprödung von austenitischen chrom-Nickel-Stählen und Nickellegierungen durch Neutronenbestrahlung

In order to study the high temperature embrittlement due to neutron irradiation, tensile specimens of different austenitic steels and Ni-alloys ( 16 13 CrNi , 20 25 CrNi , Inconel 600, Inconel 625, Inconel X750) were subjected to a thermal neutron dose of 3 × 10 15 to 2.5 × 10 20 n/cm 2. The experimental programme was based on the assumption that high temperature embrittlement is caused by the formation of helium in the reaction 10B (n, α) 7Li. The yield strength and the ultimate tensile strength showed no systematic changes due to neutron irradiation. On the other hand, the elongation to fracture was lowered by considerable amount up a certain threshold-neutron dose. The threshold neutron doses depend on the materials; they lie between 10 16 and 10 18 n/cm 2 and tend to indicate a relationship with the tensile strength of the materials. The observed saturation of the embrittlement effect above about 3 × 10 20 n/cm 2 could be explained by the far advanced 10B burn-up in the specimen. By means of a 2 mm Cd shield, the decrease in ductility was reduced to values which correspond to the amount of epithermal neutrons. Metallographs of the fracture-area of tensile specimens which were subjected to tensile tests at temperatures of 500–750° C after irradiation with 1.3 × 10 21 thermal neutrons/cm 2, showed a stronger grain boundary crack formation starting at lower temperatures after neutron irradiation.

Neutron dose measurement in graphite irradiations in BR-2

Fast and thermal neutron doses have been measured in graphite irradiation experiments in the Belgian Reactor BR-2 using iron (enriched in 54Fe) and cobalt activation monitors respectively. These data are analysed to derive peak neutron fluxes at full power for inner and outer ring positions in the BR-2 core in 5-plate fuel elements with central support tubes.

Gamma and neutron dosimetry in nuclear reactors by means of colored polyvinyl alcohol films

It is shown that polyvinyl alcohol films containing methylene blue which become discolored under the effects of radiation are suitable for gamma and neutron radiation dosimetry in nuclear reactors. The degree of discoloration varies linearly with the dose in the 104–106 rad range and, over a broad range of values, is practically independent of variations in linear energy transfer, dose rate, and temperature. Films containing boric acid in addition to the dye can be used for recording thermal-neutron doses in the 1012–1014 neutrons/cm2 range. The measurement error is within ±10% in every case.

Neutron Flux Measurement by Fission Tracks in Solids

Thermal-neutron doses can be simply and inexpensively measured over many orders of magnitude of integrated flux by a count of induced-fission-damage tracks in a solid with uranium impurities. Examples are given of the use of a single ordinary glass to measure neutron flux from 3 × 1014 to 4 × 1018nvt and of the use of glass to measure the spatial variation of neutron flux. Other materials, either glassy or crystalline, allow a wide range of fluxes to be measured.