Determination of in-core power in low energy research reactors by measurement of16N and18F in the primary coolant

The measurement of¹⁶N and¹⁸F activity in the primary coolant of the JASON Argonaut reactor has been used to monitor in-core reactor power. The¹⁶N is produced by the¹⁶O(n, p)¹⁶N reaction and the 6.1 MeV photopeak was measured on-line using a BGO detector adjacent to the primary coolant circuit. These data provided a relative measure of power stability during steady state operation and a measure of linearity at different power levels. The¹⁸F is produced in the primary coolant by the¹⁸O(p, n)¹⁸F reaction and aliquots of primary coolant were sampled from the reactor dump tank for off-line radiochemical analysis. The¹⁸F was separated as trimethylfluorosilane and the activity was determined by measurement of the 0.511 MeV annihilation photopeak using a NaI(TI) detector. The measured¹⁸F activity was used to determine actual in-core reactor power using both ab-initio calculations and by comparison of results with a calibrated power reactor. The¹⁸F data also provided a method of nomalising the¹⁶N data for direct monitoring of in-core reactor power in JASON.     

Fluorine concentration profile determination in MAGNOX reactor fuel canning material

The role of fluorine, as a corrosion inhibitant was investigated by determining fluorine concentration profiles in corroded MAGNOX reactor fuel cladding material. A nuclear convolution method was employed, based on the¹⁹F(p, αγ)¹⁶O resonant reaction and prompt gamma detection. The investigation was carried out for scale thicknesses of 3.5 and 4.5 μm as determined using 4.5 MeV protons and a broad resonance in¹⁶O(p, p)¹⁶O back-scattering cross-section. The results indicate the presence of thin fluorine concentration layers near to the scale surface on both etched and pre-oxidized magnesium alloy samples. Furthermore, an additional lower concentration distribution was also observed throughout the scale of the pre-oxidized sample.     

Determination of oxygen in alkali halide salts by proton activation and radiochemical separation

A lanthanum fluoride precipitation method for the separation of¹⁸F produced from the¹⁸O(p,n)¹⁸F reaction in alkali halide salts is described. This radiochemical separation method minimizes interferences from other positron emitters produced by proton bombardment and makes the accurate determination of ppm-level¹⁸O in complex alkali halide systems feasible. The interference from the¹⁹F(p,d)¹⁸F reaction is eliminated by keeping the proton energy less than 8.2 MeV. Applications of this technique to studies of dissolved oxide species in molten alkali halide salts are discussed.     

Activation analysis with cyclotron-produced fast neutrons. Application to instrumental multi-element analysis and to the radiochemical determination of fluorine

Fast neutrons produced by irradiation of a thick beryllium target with 20–50 MeV deuterons are used for activation analysis. The spatial neutron flux distribution around the target is measured. A rotating sample holder is used for the simultaneous irradiation of samples and standards. Instrumental analysis can be applied for a number of elements. As an example, results for calcium and strontium in some reference materials are given. The¹⁹F(n, 2n)¹⁸F reaction is used for the radiochemical determination of fluorine in rocks with a fluorine concentration ranging from 9 to 5400 μg·g⁻¹ Aspirant of the N.F.W.O.     

Fast determination of the tin content in cassiterite ores by photon activation method

Photon activation analysis has been success-fully applied to the fast and non-destructive analysis of tin in cassiterite ores based on the 159.7 keV gamma line of^123mSn produced in the¹²⁴Sn/γ, n/^123mSn reaction. In order to improve the accuracy of analytical results, corrections for self-absorption and pile-up effects were performed. Under typical conditions /15 μA electron beam current, 15 MeV bremsstrahlung energy, 5 min irradiation time and 10 min measurement/ the sensitivity of the analysis is 10 ppm. The proposed method can be used for routine analysis of tin in geological samples.     

A method for charged-particle activation analysis and its application to fluorine determination by the19F(p, αγ)16O reaction

A simple method for calculating the sensitivity for detecting a nuclide distributed uniformly in any given matrix through charged particle activation is described. This method takes into account the actual values of the reaction cross section at different energies as the beam traverses through a thick target and the corresponding stopping power values. The detection sensitivity for fluorine in a number of matrices through the¹⁹F(p, αγ)¹⁶O reaction have been calculated as a function of the energy from threshold to 4.16 MeV using this method and the sensitivity curves plotted. The sensitivity values (dps/ppm/μA) for a thick or thin target and even for a layer of known thickness at a particular depth within a sample can be directly read from these curves for known bombarding conditions. The comparator methods for charged particle activation analysis of RICCI¹ and of CHAUDHRI,² especially when the matrices of the sample and standard are different, have been compared in the case of F determination through the¹⁹F(p, αγ)¹⁶O reaction. It has been found that the errors are reduced by almost a factor of two when the latter method is used compared to the former one. The fluorine concentration in animal bones and teeth, apatite crystal, and rocks have been determined through the¹⁹F(p, αγ)¹⁶O reaction using the Melbourne University Pelletron.     

Oxygen and nitrogen in coal by instrumental neutron activation analysis

The feasibility of using fast neutron (14 MeV) activation analysis techniques for the determination of oxygen and nitrogen in coal has been investigated. Conditions that favor instrumental neutron activation analysis (INAA) include the absence of problems associated with sample dissolution and the capability of extremely rapid analyses as compared to older techniques such as the Kjeldahl method for nitrogen. Most previous oxygen determinations have been by difference after major component analyses. In the present study, oxygen was determined in sized coal and its low temperature ash (LTA) with the difference representing the organic oxygen content. Both the oxygen and nitrogen analyses employ a multiscaling technique with the former based on the¹⁶O(n, p)¹⁶N reaction, while the latter utilizes the annihilation radiation produced by the product of the¹⁴N(n, 2n)¹³N reaction. The high-energy gamma-radiation associated with the decay of¹⁶N was essentially free of spectral interferences for coal analysis, although fluorine could cause a primary interference if the F/O ratio exceeds 0.02. In the nitrogen work, experiments were performed to determine correction factors to account for the effects of the¹²C(p, γ)¹³N and¹³C(p, n)¹³N “knock-on” reactions and the³⁹K(n, 2n)³⁸K reaction which produce interfering β⁺ emitting radionuclides. Data are presented for oxygen in Western Kentucky No. 9 and No. 11 coal and coal ash and for nitrogen in eleven different coals.     

Application of 14 MeV neutron activation analysis to the determination of Ce and Sm markers in biological materials

The rare-earth elements are very suitable multiple particulate markers for the investigation of matter flow in the gastro-intestinal tract of animals by means of the indicator activation method. A rapid determination of cerium and samarium in biological samples is possible with the aid of a 14 MeV neutron generator. The activity of^139mCe has to be corrected for the interferences of²⁸Al and^143mSm. For the determination of samarium the radionuclides¹⁵⁵Sm and¹⁵³Sm are used. In order to increase the specific activity of these nuclides, which are produced mainly by means of nuclear reactions with thermal neutrons, the samples are irradiated inside a polyethylene moderator block. The deviation from the linearity of the calibration curve for samarium is discussed.     

Sulfur determination in coal by 14 MeV neutron activation analysis

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.     

Utilization of cyclotron produced fast neutrons in the activation analysis for oxygen

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.     

Non-destructive profiling of fluorine in teeth to large depths

A new method for non-destructive depth profiling of fluorine has been developed which extends the profiling range to much larger depths than hitherto possible. In this method the thick-target yield of 6–7 MeV gammas from the reaction of ¹⁹F(p,αγ) ¹⁶O in the tooth sample, was measured as a function of the incident energy from threshold to up to 2.7 MeV and the yield curve plotted. This curve was compared to the calculated yield curve of 6–7 MeV gammas from the same reaction but on an enamel matrix containing uniformly distributed fluorine. The difference in the shape of the two curves was only due to the non-uniform distribution of fluorine in the tooth sample, which could then be calculated. By making use of this method F-depth profiles in teeth of monkeys were determined non-destructively to a depth of 14 μm. This method is also applicable for profiling other elements through appropriate resonant or non-resonant nuclear reactions.     

Determination of fluorine in standard rocks by photon activation analysis

A highly sensitive determination of fluorine in standard rocks by photon activation using the¹⁹F(,n)¹⁸F reaction combined with pyrohydrolysis for the separation of¹⁸F has been reported. The irradiation energy was operated at 20 MeV to avoid the interference from Na, because Na is one of the major element in rocks and¹⁸F is also produced from Na via²³Na(,n)¹⁸F reaction above its threshold energy, 20.9 MeV. After irradiation, fluorine was extracted by pyrohydrolysis and separated as LaF₃ precipitate. It was ascertained that the average recovery of fluorine in standard rocks was about 90% and the precipitate was of high radiochemical purity. This method was applied to the analysis of ten GSJ rock reference samples and two USGS standard rocks issued by the Geological Survey of Japan and the United States Geological Survey, respectively. The detection limit of this method was 0.02 g/g, and the results obtained by this method were in good agreement with the recommended values. This method was easily applied to the determination of a few ppm level of fluorine in rock samples, such as ultrabasic rock and feldspar.     

Determination of fluorine in organic compounds by epithermal neutron activation analysis

Classical activation analysis of fluorine by thermal neutrons has a limited application because of frequent interference from chlorine, the short half life²⁰F (11.4 s) and too high dead time of detectors. A procedure is described for fluorine determination using¹⁹F (n,p)¹⁹O reaction. Use of a boron carbide shield has no effect on the activity of¹⁹O (boron ratio −1) but considerably reduces background and interference due to¹⁸O (n, γ)¹⁹O reaction. The technique has been successfully applied to the determination of fluorine in organic compounds even in the presence of large amounts of chlorine and oxygen.     

The preparation of carrier-free102Rh and102m Rh

Long-lived rhodium radionuclides were produced by the following reactions:¹⁰³Rh(n, 2n)^102(m)Rh;¹⁰³Rh(γ,xn)¹⁰⁰Rh,¹⁰¹Rh,^102(m)Rh;¹⁰⁴Pd(d, α)^102(m)Rh; Ru(d, n)⁹⁹Rh,^101(m)Rh,^102(m)Rh; and . The average cross-section of the¹⁰³Rh(n, 2n)¹⁰²Rh reaction in a fission neutron spectrum is about 0.75 mb. Irradiation of rhodium in the bremsstrahlung spectrum of 50 MeV electrons yielded a¹⁰²Rh activity of 0.11 μCi/g after 3 days at a power of 2 kW. The thick target yield of the reaction¹⁰⁴Pd(d, α)¹⁰²Rh was 0.002 μCi/μAh for 12 MeV deuterons. The thick target yield of the reaction Ru(d,xn)¹⁰²Rh was 0.05 μCi/μAh for 12 MeV deuterons and 4.8 μCi/μAh for 18 MeV deuterons. The best yield was obtained by deuteron bombardment of ruthenium. The chemical separation of carrier-free Rh radionuclides from deuteron-irradiated ruthenium is described, with a chemical yield better than 90%. The same procedure has also been applied for the isolation of¹⁰⁵Rh from neutron-irradiated ruthenium. γ-Ray spectra of⁹⁹Rh,^101(m)Rh and^102(m)Rh from deuteron-irradiated ruthenium and of¹⁰⁵Rh from neutron-irradiated ruthenium, taken with a Ge(Li) detector, are shown; a number of γ-rays, not reported in the literature, were observed. The γ-ray energies were determined with a precision of ca. 0.3–0.4 keV.     

Determination of silicon in cast iron by 14 MeV neutron activation

Silicon in cast iron was analyzed by 14 MeV neutron activation—high-resolution γ-ray spectrometry. Silicon was detected as²⁸Al, the product of the²⁸Si(n, p)²⁸Al reaction. Interference of⁵⁶Mn was separated using a Ge(Li) detector and a biased amplifying system. The 1. 81 MeV gamma-radiation of⁵⁶Mn, which is the product of the⁵⁶Fe(n, p)⁵⁶Mn reaction of the matrix of cast iron, was used as an internal standard and for correction of the self-absorption of the 1. 78 MeV gamma-radiation of²⁸Al by the sample. The interferences of aluminum, phosphorus and manganese could be neglected according to the results calculated from their nuclear properties and contents in the cast iron of this experiment. The results of this method agreed well with the results of the usual chemical method, with errors less than 5% of the results, and the precision of the method was satisfactory with a C. V. of less than almost 6% for rapid analysis of silicon in cast iron. The analytical line through the origin with a slope of the mean value of the repetition experiments could be used as the analytical line with almost the same precision and accuracy of the results as for the analytical line calculated by the least squares method.     

Cross-sections of 14 MeV neutron reactions producing short-lived nuclides

The cross-sections for the production of the short-lived nuclides:^26mAl,^197mAu,^136mBa,^79mBr,^139mCe,³⁴Cl,^167mEr,^114m3In,^114m2In,^38mK,^38mCl,²⁶Na,²⁰F,¹⁹²Re,^207mPb,^203mPb,^46mSc,^183mW,^90mZr obtained from (n, 2n), (n, n′), (n, alpha), (n,p) reactions using 14 MeV neutrons, were evaluated by the activation method. The experimental results of this work were compared with those obtained by other authors.     

Kinetics of chlorine isotope exchange reaction between sodium chloride-36 and triphenyltin chloride in mixed solvents

Fluorine is an important trace element for life and human well-being. Food, in general, provides about 40 percent of the fluorine intake in the human body. In order to measure fluorine levels in human diet samples, Instrumental Neutron Activation Analysis (INAA) and Proton Induced Gamma-ray Emission (PIGE) analysis were used. Reactions¹⁹F(n,)²⁰F and¹⁹F(n, p)¹⁹O were employed for determination of the fluorine concentration using a reactor neutron spectrum and epithermal neutrons. Corrections were made for the sodium matrix interference caused by the²³Na(n, )²⁰F threshold reaction in the case of reactor neutron cyclic activation analysis and for the oxygen interference via¹⁸O(n, )¹⁹O reaction when using the epithermal cyclic NAA method. The fluorine content of the diet samples was also determined by PIGE analysis making use of the resonance reaction¹⁹F(p, )¹⁶O at 872 keV. Cyclic Neutron Activation Analysis (CNAA) when combined with mass fractionation was found to be the most suitable for determination of low concentration of fluorine, through the¹⁹F(n, )²⁰F reaction with a detection limit of 2.2 ppm in Bowen's Kale elemental standard.     

Determination of silicon in aluminium by 14 MeV neutron activation analysis

A method has been developed for determining silicon in aluminium by fast neutron activation. It is based on the separation of two gamma lines by a Ge(Li) detector: the 1.73 MeV line from the product of²⁷Al(n, α)²⁴Na and the 1.78 MeV line from the²⁸Si(n, p)²⁸Al reaction. In the case of aluminium-silicon alloys 100 μg silicon can be determined, with an error of 10% in an aluminium sample of 1 g. This work was supported in part by the International Atomic Energy Agency.     

Oxygen isotope measurement by instrumental neutron activation analysis using reactor neutron—Revisited

The oxygen isotopes¹⁶O and¹⁸O were determined using reactor instrumental neutron activation analysis by utilizing the¹⁶O(n, p)¹⁶N and the¹⁸O(n, )¹⁹O reaction in the UCI 250 kw TRIGA research reactor.¹ Such measurements were used to follow an exchange reaction between H₂ ¹⁸O and finely ground coal. The best conditions for the determination were explored and interference reactions quantified. Single irradiation/count sequences were used to determine 30 parts per thounsand of¹⁶O and 1 part per thousand of¹⁸O in a 400 mg sample of an HVA rank coal to a 25% (1) precision. Reactor pulses were shown to improve these detection limits significantly. Special attention was given to correcting for the high count rates from other induced activites.     

Determination du fluor dans les milieux aqueux par activation au moyen de photons gamma

An apparatus ensuring identitical irradiation conditions for three samples and a standard of large volumes is reported. The interference caused by the protons originating from the¹⁶O(γ, p)¹⁵N reaction is determined. Results show that the secondary rection¹⁸O(p, n)¹⁸F induced by the protons of the former reaction gives an apparent fluorine content in natural waters of 0.015 μg/g for a maximum gamma photon beam energy of 21 MeV.