Showing papers in "Journal of Nuclear Science and Technology in 1971"

Diffusion of Tc-99m in Neutron Irradiated Molybdenum Trioxide and Its Application to Separation

Abstract: The dry distillation method was studied for rapid separation of 99mTc from neutron irradiated MoO3. Upon heating, 99mTc produced in MoO3 crystal by the 98Mo(n,r)Mo99m β→ 99mTc process was found to be released by diffusion. From observations made of the deposition temperature, it was concluded that 99mTc was present in the form of 99mTc(IV) in the MoO3 crystal lattice and that it was released in the form of 99mTcO2, which, in air, further oxidized to 99mTc2O7. The release of 99mTc from neutron irradiated MoO3 powder was studied in the temperature range of 480°700°C, and its behavior was found to be in good agreement with the bulk diffusion mechanism based on Fick's law. The diffusion coefficient varied with temperature in compliance with Arrhenius' relation, except in the region of temperatures above 700°C. The separation of 99mTc from MoO3 was performed with a yield higher than 80% upon heating for 30 min at 800°C in air. The decontamination factor for 99Mo was consistently found higher than 105.

Measurements of Average Cross Sections for Some Threshold Reactions for Neutrons with Fission-type Reactor Spectrum

Abstract: The fast neutron spectrum in the core of the Kyoto University Reactor (KUR) was measured by using seven threshold reactions, a 6Li sandwich counter and also nuclear emulsion plates, and the results were compared with theoretical calculations by the Sn method. It was found that the shape of the fast neutron spectrum was approximately the same as that of fission neutrons. Making use of these neutrons with fission-type spectrum, measurements were made of the average cross sections for twelve threshold reactions (46Ti(n, p)46Sc, 47Ti(n, p)47Sc, 46Ti(n, p)48Sc, 28Si(n, p)28Al, 29Si(n, p)29Al, 30Si(n, α)27Mg, 51V(n, α)48Sc, 64Zn(n, p)64Cu, 92Mo(n, p) 92mNb(n, 2n)92mNb, 204Pb(n, n1 )204mPb and 204Pb(n, 2n)203Pb). For the purpose of comparison, the average cross sections for six among these reactions were measured also with neutrons from a fission plate. The results agreed within experimetal error with those obtained for neutrons in the KUR core. A Ge(Li) counter was mainly used for the measurement of γ-rays emit...

Detection of Fast Neutrons by Etch-Pit Method of Nuclear Track Registration in Plastics

Abstract: Plastics, such as polycarbonate, cellulose nitrate and cellulose acetate were irradiated with fast neutrons (2.5, 14 MeV) and a count was made of the number of etch-pits on the surfaces of the irradiated material after etching with suitable chemical reagents. The experiments proved that the number of etch-pits increases with the etching time, and that at least during the early period of etching, a close correlation seems to exist between ΔP the increment in the number of etch-pits per unit area and Δl the increment of thickness of layer removed for a common increment of etching time Δt. In other words, an approximate relation ΔP/Δl=ρ was observed to hold during this early etching period, ρ being a constant that seems to correspond to the number of etchable damages produced by fast neutron irradiation per unit volume. The value of ρ was found to correspond roughly to the estimated number of recoil carbon and oxygen atoms in a unit volume in the case of polycarbonate which consists of carbon, oxygen and hyd...

Fast Computer Analysis of the γ Spectrum from Ge(Li) Detectors

Abstract: A method for rapidly analyzing the γ spectrum obtained with Ge(Li) detectors was developed for a medium-size electronic computer. The analysis is based on the first derivative method, associated with a number of peak-shape tests. The effects of data smoothing and of changes in peak width were studied to determine the optimum conditions for spectrum analysis. The resulting computer program was subjected to various quality tests on the predicted values of the peak position and area. The results of the tests showed that the code thus developed works quite satisfactorily. The code requires 10 sec and a memory core of 29 k when using a FACOM 230–60 for the analysis of a 2,047 channel spectrum.

Rapid Separation of Fission-Product Rare Earths and Yttrium by Electromigration

Abstract: The separation of fission-product La, Ce, Pr, Nd and Y was performed in 4 min by electro-migration. As complexing agent, nitrilotriacetic acid was used at two concentrations of the NTA ion selected so as to optimize mutual separation of the elements. Rapid location of the zone on the paper strip reached after migration was obtained by color reaction of the carrier added to the irradiated sample. The purity of the elements thus separated was checked by γ-ray spectrometry. At the higher concentration of NTA ([[NTA]=1.0×10−2M, pH=4.1) under which all of rare earths and Y migrate toward the anode, the elements were well separated from each other, although appreciable amounts of other F.P. were also found in each fraction. On the other hand, at the lower NTA concentration ([NTA]=4.0 × 10−3M, pH=2.0) where the F.P. all migrate toward the cathode, each zone contained the isotopes of the respective element almost exclusively, except for a few small photo-peaks attributable to other elements. In each fraction, the...

Numerical Solution to Space-Angle Energy-Dependent Neutron Integral Transport Equation

Abstract: A numerical approach to the steady-state, space-, angle- and energy-dependent neutron transport equation is presented for neutron shielding calculations. The scattering integral, with anisotropic treatment of elastic scattering and isotropic treatment of inelastic scattering, is evaluated by the use of Gaussian and straightforward quadratures. A system of coupled one-group integral equations for all the energy meshes of interest, converted from the energy-dependent integral transport equation, is calculated by performing a line integration along the neutron path in the direction of motion. For this purpose the direction of neutron motion is represented by discrete-ordinate directions Ωpq on the unit sphere. The final presentation of the integral transport equation is derived in a difference form convenient for machine computation. A computation program PALLAS has been written in Fortran IV for IBM 360-75 computer to perform neutron transport calculations based on this approach. Comparisons are given of th...

Terrestrial gamma-radiation field in natural environment.

Abstract: The energy and directional distributions of the photon flux in air l m above mono-energetic semi-infinite isotropic volume sources were calculated with Monte Carlo technique for 5 different γ-ray energies from 0.35 to 2.65 MeV. The energy and directional distributions of the flux from U, Th and K were obtained with use made of the results of the mono-energetic calculations. The results agreed well with previously measured data on an actual natural radiation field.

Preparation of anhydrous uranium tetrachloride and measurements on its magnetic susceptibility.

Abstract: The reaction of UO2 with CCl4 vapor was carried out in a vacuum of 10−5 mmHg at 500°C in order to prepare UCl4 of high purity. The lattice parameters were calculated from X-ray analysis to be a0 =8.278±0.002, c0 =7.460±0.009. The product thus obtained was verified by chemical and X-ray analyses to be of anhydride form. The magnetic susceptibility was measured over the temperature range from liquid N2 to liquid He temperature, which revealed a deviation from the straight 1/χ–T relation toward lower temperature.

Measurements of Average Cross Section for 232Th(n, 2n)231Th Reaction to Neutrons with Fission-Type Reactor Spectrum and of Gamma-Ray Intensities of 231Th

Abstract: The average cross section for the 232Th(n, 2n)231Th reaction to neutrons with the energy spectrum close to that of fission neutrons was obtained in the core of the Kyoto University Reactor, KUR. The value obtained was 12.5±0.84 mb. This value agrees satisfactorily with Phillips' and with the calculated value obtained with the cross section in the U-K library and the Maxwellian fission neutron spectrum given by Leachman. A somewhat poorer agreement is seen with the calculated value obtained from Butler & Santry's cross section and Leachman's spectrum. The discrepancy amounts to 24 and to 39% respectively, for the average cross sections calculated with these two excitation functions and the fission neutron spectrum given by McElroy. By making use of a Ge(Li) counter whose photopeak efficiency had been carefully calibrated, the absolute intensities were determined for eleven photopeaks observed on the γ-ray spectrum emitted by 231Th.

Vaporization and Surface lonization of LaC2, CeC2, PrC2, NdC2, ThC2 and UC2

Abstract: The Langmuir vaporization and the surface ionization of LaC2, CeC2, PrC2, NdC2, ThC2 and UC2 from a heated graphite filament have been studied mass spectrometrically. It was found that there were present small amounts of neutral and ionic metal dicarbide molecules in addition to neutral and ionic metal atoms in the LaC2, CeC2, PrC2, ThC2 and UC2-C systems with the exception of NdC2-C, where neither neutral nor ionic metal dicarbide molecules were observed. The reason for this exceptional behavior of the NdC2-C system is explained by the very small vaporization coefficients, as estimated from the measurements of neutral MC2/M ratios and ionic MC2/M ratios. From the measurements of the heats of vaporization, it was surmised that the ionization potential of Th measured by the surface ionization comparison technique might be too high.

Propagation of Pressure Wave in Air-Water Two-Phase System, (II)

Abstract: In an attempt to gain information on the propagation characteristics of pressure waves in a two-phase system consisting of gas and liquid, experiments were performed on a nonflowing air-water mixture in a range of pressures from 1.0 to 7.5 bar and void fractions from 0 to 60%. Stepwise pressure disturbancies were applied to a water column dispersed with rising air bubbles by bursting diaphragm. The pressure transients at several points down the fluid column were measured with strain gage type pressure transducers and recorded on magnetic tapes. The nonlinearity of the pressure wave records was scarcely marked. The propagation velocity of pressure wave front down the fluid column was found almost independent of the magnitude of the pressure change applied, nor whether it was depressive or compressive. At higher void fractions where the flow regime became sluggy, the measured propagation velocities showed increasing deviation from the calculated values based on the nonslip homogeneous adiabatic model, thoug...

Preparation of Tc-99m by Direct Adsorption from Organic Solution

Abstract: Purification of 99mTc extracted into methyl ethyl ketone from an alkaline solution of neutron irradiated MoO3 was studied in order to establish a rapid method for producing 99mTc.After removal of the organic solvent by evaporation, 99mTc could be purified from remaining traces of Mo and other contaminants by adsorption in an alumina column from an aqueous solution and by subsequent elution with 0.1N HCl or with physiological saline solution.Organic solvents containing 99mTc could also be treated directly in an alumina column to purify the 99mTc: this saved the time required for the evaporation of the solvent.Problems essential to the adsorption of 99mTc on alumina in organic media were studied to determine the optimum conditions for the adsorption.A standard procedure for 99mTc preparation would be: Extract 99mTc into methyl ethyl ketone from alkaline solution. Pass organic phase through cation exchange column to remove Na and then through alumina column. Finally, elute 99mTc from alumina column with 0.1N HCl or saline solution.The process can be finished within 1hr. About 500mCi of 99mTc is obtained with a chemical yield higher than 95%, and the product contains less than 10-4% of radiochemical impurities.

Oxidation of Thorium Nitrides

Abstract: An experimental study has been made on the oxidation of two thorium nitrides ThN and Th3N4, in oxygen under a pressure of 1/5 atm. The Th3N4 was prepared by reacting thorium hydride with N2 gas, and the ThN by decomposing Th3N4 in vacuo. The thorium nitrides were idenfied by X-ray powder diffractometry. The values of N/Th ratio were determined by chemical analysis to be 0.90–0.92 for ThN and 1.22 for Th3N4. Powder specimens of both thorium nitrides were isothermally oxidized in the temperature range of 340°–480°C. The oxidation behavior of ThN powder was found to be independent of oxygen pressure (1/5–1 atm). The reaction kinetics of both thorium nitrides were found amenable to representation by linear plots for the most part of the reaction. The apparent activation energies were 18±3 kcal/mole for ThN and 15±2 kcal/mole for Th3N4. X-ray examination revealed the oxidation product of both nitrides to be solely ThO2, and no other product was detected.

Normal Mode Expansion in Neutron Thermalization Theory with a Simple Scattering Kernel

Abstract: Elementary solutions to the energy-dependent Boltzmann equation with a one-term degenerate scattering kernel are derived in plane geometry, and the weight function W (z) is obtained which makes these solutions mutually orthogonal over the half-range interval of the continuum. The weight function greatly facilitates determination of the expansion coefficients in general solutions and is applied to the problems in infinite half space. The diffusion length (discrete space eigenvalue) υ0 is exactly expressed by using the halfrange characteristic function X(z). In a 1/υ-absorbing medium, as the absorption concentration q increases from zero to a critical value g*, the diffusion length decreases from infinity to the end of the continuum 1/σmin. For q≥q*, v0 vanishes and the neutron density can be represented by the transient term alone, whose exact expression is obtained.

An Improvement to the G.G. Approximation in Neutron Slowing Down through the Method of Generalized Function

Abstract: The neutron slowing down problem in an infinite homogeneous medium is treated within the G.G. approximation through the theory of generalized function (g.f.). As test function for defining the g.f.'s, the source importance for the slowing down is chosen. In place of the Taylor expansion of the collision term of slowing down equation in the G.G. method we expand the adjoint collision term of the importance equation. Solutions obtained with this method clearly reproduce the Placzek wiggles, which do not appear in corresponding solutions by the orthodox G.G. method using the same order of approximation, and our solutions are in very good agreement with the exact Placzek function.

A New Approximation in the Calculation of Collision Probabilities in Cluster-Type Fuel Lattices

Abstract: A new approximation is proposed for calculating the first flight collision probabilities in cluster-type fuel lattices, based on the subcell model. In this method the unit cluster is divided into subregions of fuel pins (with or without cladding) arranged in rings, associated coolant, and homogeneous annular regions surrounding the fuel region. The fuel pins and associated coolant are treated separately, and each is distinguished ringwise as a different subregion. The collision probability is then calculated for a neutron proceeding from one subregion to another. The method treats rigorously the fuel annulus where a neutron starts with consideration given to the non-uniform structure of the annulus. The other fuel annuli, however, are treated approximately as if each annulus were homogeneous. The values of the homogenized cross sections of the annuli are determined in such manner that the number of outgoing neutrons from the homogenized annuli equals that from the actual non-uniform fuel annuli. The colli...

Anisotropic Collision Probabilities in Cell Problems

Abstract: A new first-flight collision probability that takes into account the effect of the anisotropic scattering in the moderator is derived in a cylindrical cell. This probability is obtained by expanding the scattering kernel, angular flux and angular source into spherical harmonics series and retaining the first two terms in the integral Boltzmann equation. Making use of a new reciprocity relation and the conservation law, we introduce the probability relevant to a lattice cell under the condition that all neutrons impinging on the cell boundary should reflect with isotropic distribution back into the original cell. This probability also satisfies both the usual reciprocity theorem and the conservation law. Though we have here treated only a 2-medium problem, the method can be easily extended to the problem of a cell containing many regions. As an example of application, we calculate the flux ratios in a two region cell by one-group theory and the neutron spectra in fuel and moderator using the Fermi-age kern...

Studies on the Uranium Dicarbide Phase

Abstract: The lattice parameters of UC2 are examined as a function of carbon content and annealing: conditions on sintered carbides between UC1·5 and UC2·2 (7.0 to 10.0W/0 of carbon). The values of UC2 obtained under equilibrium state are around a 0=3.5253 A and c 0=5.9994A. The lattice parameter measurements were made also on UC2 obtained under non-equilibrium conditions by are-melting and carbothermic reaction of UO2. The lattice parameters were appreciably smaller than on the specimens obtained under equilibrium. With annealing, both the lattice parameter and the combined carbon content showed a tendency to increase.

Chemical Dosimeters for Mixed Radiations in a Nuclear Reactor

Abstract: The dose rates due to mixed reactor radiations were measured by five gaseous chemical dosimeters – nitrous oxide (natural), 15N-enriched nitrous oxide, ethylene, ethane and carbon dioxide. The observed dose rates for these gases at the same irradiation position in a nuclear reactor were, 1.8×108, 1.5×l08, 1.9×108, 2.5×l08 and 1.0×108 rad/hr, respectively. These values were compared with those calculated from the mass stopping power of the gases for secondary electrons produced by γ-rays and those from thermal and fast neutron fluxes. No contradiction was found among them. A method of analysis of the reactor radiation dose rates into γ, thermal and fast neutron components is proposed, which is based solely on chemical dosimetry.

Separation of Uranium from Fission Products

Abstract: A simple procedure has been developed for separating U from FP and neutron-irradiated Th The separation is performed with tri-n-butyl phosphate in a system of dodecane-mixture of sulfuric acid and aluminium nitrate Uranium dioxide was irradiated with 20 MeV bremsstrahlung, which produced both 237U and FP The target was dissolved in dilute nitric acid and U was extracted into the organic phase of the above mentioned system Finally, U in the organic phase was back-extracted into an aqueous phase The γ-ray spectrum and decay curve of the separated U fraction show no radioactive nuclides other than U isotopes and its decay products This method can also be applied to the preliminary separation of 238U from neutron- irradiated Th The distribution ratios (Kd) for U, Th and some other elements in the extraction system are also given

Measurement of Temperature Fluctuations in a Natural Convection Water Loop

Abstract: Investigations of reactor noise in water-cooled research reactors show that the power spectral density rises in the low frequency domain. The cause of this phenomenon is often attributed to fluctuations in the coolant temperature, but this has never been proved experimentally. The present experiment is an attempt in this direction. The temperature fluctuation in a natural convection heat transfer loop decoupled from neutronics was measured and analyzed in the frequency domain. The test section of the loop had a rectangular channel measuring 5 mm × 50 mm in cross section and 500 mm in length. This configuration simulated a coolant channel of the MTR-type fuel element used in swimming-pool reactors. The power spectral density of the temperature fluctuation at the channel exit showed a shape similar to the power spectral density of the noise-equivalent source obtained in the Kyoto University Reactor at comparable power levels.

Hydrolysis of Thorium Nitrides and Carbonitrides

Abstract: Studies were made on the hydrolysis by water and water vapor of thorium nitrides—ThN, Th3N4, Th2N2O—and carbonitrides. All the thorium nitrides and carbonitrides were found to decompose in water below 100°C, changing thereby into ThO2. The order among the thorium nitrides in their propensity toward hydrolysis is: ThC1-xNx>ThN>Th3N4>Th2N2O. Upon hydrolysis, ThN produced NH3 and H2, but in the case of the higher nitrides no H2 was found to evolve. In the reaction between ThN and water vapor, no higher nitride was produced, in contrast to the case of UN. The difference in behavior between ThN and UN was studied from the standpoint of differences in crystallographic conditions for the transformation from mononitride into higher nitrides. Through the hydrolysis of ThC1-xNx in water vapor, products containing C-C, C-C-C and C-N bonds, such as ethane and amines, were found in smaller quantities than for the case of UC1-xNx. This fact as well as the difficulty of formation of higher nitrides has resulted in a fai...

Pressure Drop Performance of Fuel Pin Bundle with Spiral Wire Spacer

Abstract: The pressure drop characteristics of a JEFR type fuel pin bundle were obtained from hydraulic tests. The coefficient of drag attributable to the spiral wire spacer wound round each fuel pin, as defined by de Stordeur, was found to be approximately 0.30 for the hexagonal lattice arrangement adopted. The coefficient is independent of spiral wire pitch, which ranged from 90 to 260 mm. The pressure drop to be expected in a fuel pin bundle with spiral wire spacer, such as used in current fast breeder applications, can be satisfactorily estimated by using the coefficients reported.

Estimation of Reactor Parameters by Optimal Filtering Method

Abstract: Measurements of reactor parameters, such as prompt neutron generation time and subcriticality, have been made in the past using band pass filters or else applying the correlation technique. Other new methods of reactor parameter estimation would now appear to be available thanks to the recent developments in optimal filtering technique, such as optimal linear (Kalman) filter and some of the nonlinear optimal filters. Such new methods should prove very promising for on-line estimation of the reactor parameters. In this paper a description is given of the application of some of these new methods to subcriticality measurements. The results of computer simulation of estimates using the Kalman filter are presented, as also on account of experiments with the actual reactor noise obtained on the Toshiba Training Reactor (TTR-1), using a nonlinear analog filter. The results agreed with those reported by Nomura using conventional methods.

Ion Exchange Behaviors of Inorganic Ions in Ion Exchange Resins of Diaion SKN-1 and SAN-1:Distribution Ratios of Ions in the System of Diaion-Hydrochloric Acid

Abstract: The distribution ratios of 42 inorganic ions were radiochemically determined in a system of Diaion SKN-1 in H-form and 0–4M hydrochloric acid, and in another system of Diaion SAN-1 in Cl-form and 1–9M hydrochloric acid. The results are presented in an arrangement that follows the sequence of the periodic table. Several data were also obtained on Amberlite IRN-77 and −78 for comparison.

Reactivity Balance for Reactor Diagnosis, (I):Accuracy of Reactivity Balance Technique in Hitachi Training Reactor

Abstract: The reactivity balance method commonly used for measuring inserted anomalous reactivities was applied to the HTR (Hitachi Training Reactor). The reactivities taken into consideration included the kinetic reactivity, as well as those associated with the control rod, power feedback, coolant inlet temperature and Xe buildup. The reactivity balance data were obtained to cover start-up operation, as well as at various power levels including full rated power. These results obtained show that the errors associated with power feedback and with Xe buildup reactivity are both below approximately 1¢ these errors being due to the one point approximation and to inaccuracies in the constants used in the equations. The fluctuations of residual reactivity are attributed to power fluctuations, to uncertainties in the measurement of the coolant inlet temperature and in the determination of control rod position. The scattering about the zero reactivity line caused by these fluctuations was evaluated to be within 0.8 ¢. Anom...

Chemical Forms of Airborne Radioiodine in the Exhaust Air from Iodine-131 Production Plant

Abstract: Airborne radioiodine released from the reaction cell into the exhaust air during the processing operations at an 131I production plant has been analyzed by radio-gaschromatography. The iodine compounds observed were CH3 131I, C2H5 131I, H131IO4 and H131IO3. The distribution of the total 131I among these compounds differs greatly according to the time of sampling after the start of processing. In the beginning, H131IO3 is highly predominant, but the content of organic iodides increases with progress of the processing operation. The removal efficiency of the charcoal filter installed in the stream of the exhaust air was better than 85% for the total 1311 but less than 50% when organic iodides alone were taken into account, indicating poorer efficiency of the filters for the latter compounds. The total amount of CH3 131I released was of Mc1 order. This suggests a very promising new method for obtaining CH3 131I as a by-product without any special chemical treatment.

A Study of Dissociation Constant of p-Toluenesulfonic Acid by Nuclear Magnetic Resonance

Abstract: The chemical shifts of the photon magnetic resonance of ptoluenesulfonic acid in aqueous solution were measured as a function of acid concentration. The acid dissociation constant for p-toluenesulfonic acid calculated from the chemical shifts is 3.4. These results show that the p-toluenesulfonic acid is a strong acid.