Neutron Activation Procedure Research Articles

Design for an asymmetrical cyclic neutron activation process for determining fluorite grade in fluorspar concentrate

Conventional neutron activation procedures rely on cycles of equal length to test samples of fluorspar concentrate. This paper proposes a new procedure using “asymmetrical” cycles, in which the duration of the first cycle is different from that of the subsequent activation cycles, which are conducted once the radioactive concentration of the element of interest has been partly reduced through radioactive decay. A comparison is made between the two procedures, and the advantages of the new technique over the conventional one are examined.

Mathematical study to improve the sensitivity in the neutron activation analysis of fluorspar

A mathematical method to design a neutron activation procedure for analyzing a sample of fluorspar from a concentration plant has been created. The neutron activation is used to bombard a sample with neutrons and record the spectrum radioactive produced. The fluorspar grade is directly proportional to the fluorine content of the sample, and this in turn is directly proportional to the amount of 16N, the radioactive product produced in the bombardment. The ratio between both concentrations has been shown but the aim is to determine the activation parameters that increase the sensitivity of the method. This work discusses the mathematical models used and whose use is expected to increase the sensitivity of the reading.

Development of a radiochemical neutron activation analysis procedure for determination of rhenium in biological and environmental samples at ultratrace level

Radiochemical neutron activation procedures using liquid-liquid extraction with tetraphenylarsonium chloride in chloroform from 1M HCl and solid extraction with ALIQUAT 336 incorporated in a polyacrylonitrile binding matrix from 0.1M HCl were developed for accurate determination of rhenium in biological and environmental samples at the sub-ng . g-1 level. Concentrations of Re in the range of 0.1 to 2.4 ng . g-1 were determined in several botanical reference materials (RM), while in a RM of road dust a value of ~10 ng . g-1 was found. Significantly elevated values of Re, up to 90 ng . g-1 were found in seaweed (brown algae). Results for Re in the brown algae Fucus vesiculosus in which elevated 99Tc values had previously been determined suggested possible competition between Re and Tc in the accumulation process.

Highly siderophile element geochemistry of the Earth's mantle: new data for the Lanzo (Italy) and Ronda (Spain) orogenic peridotite bodies

Nine plagioclase/spinel lherzolites from the Lanzo (Italy) and Ronda (Spain) peridotite bodies were analysed for Re, Os, Ir, Ru, Rh, Pd, and Au using a high-precision instrumental neutron activation (INA) procedure after NiS fire assay. Our data conform with previous observations that orogenic lherzolite massifs sampled domains of the subcontinental lithospheric mantle (SCLM) displaying a characteristic enrichment of Ru, Rh and Pd (i.e. the light platinum group elements; PGEs) over Os and Ir. The Pd/Ir, Rh/Ir and Ru/Ir ratios are superchondritic and very similar in both suites (2.46±0.32 vs. 2.42±0.21; 0.46±0.07 vs. 0.45±0.10; 1.99±0.14 vs. 2.25±0.25, respectively). Rhenium and gold are generally depleted relative to PGEs, in agreement with their moderately incompatible behaviour in low-degree mantle melting events; however, in both suites, these elements do not correlate with melt depletion indices, indicating a small-scale remobilization by hydrothermal fluids. The Os/Ir ranges from chondritic values at Lanzo (1.09±0.13) to higher than chondritic at Ronda (1.37±0.17). The higher Os/Ir of the Ronda lherzolites is interpreted in terms of mobilization of Os by late magmatic fluids. By contrast, the light PGE excess cannot be ascribed to any geological processes that occurred in the lithosphere such as pervasive melt percolation at the asthenosphere–lithosphere boundary, nor to Fe–Ni sulfide precipitation processes during the low-degree melting event that affected both massifs prior to their incorporation into the SCLM. The fact that superchondritic Ru/Ir, Rh/Ir and Pd/Ir ratios have now been documented in a large number of pristine mantle samples from various tectonic settings as well as in ophiolitic and abyssal peridotites argues for primary variations of highly siderophile element (HSE) abundances in the terrestrial upper mantle.

Influence of neutron activation factors on matrix tablets for site specific delivery to the colon

The impact of the neutron activation procedure, i.e. incorporation of samarium oxide (Sm 2O 3) and neutron irradiation, on the compression properties (including the crushing strength) and in vitro dissolution of potential colonic delivery systems based on matrix tablets of amidated pectin (Am.P) or two types of hydroxypropyl methylcellulose (HPMC) was investigated. The neutron activation factors did not influence the compression properties of the tablets. Replacement of magnesium stearate with samarium stearate in directly compressed Am.P tablets to achieve both radiolabelling and lubrication resulted in a greater extent of concentration-dependent reduction of the crushing strength. Dissolution tests demonstrated that irradiation increased the release of the model drug ropivacaine from the tablets. The extent of this increase was unexpectedly low considering the previously observed degradation of the polymer expressed as an irradiation-induced viscosity reduction in solutions prepared from the polymers. Delayed-release coating with Eudragit ® L 100 protected the HPMC tablets against the release-increasing effect of irradiation until the late phases of release. Sm 2O 3 retarded the release to a varying extent depending on particle characteristics. Incorporation of Sm 2O 3 in the coating layer did not influence the release. However, one-third of the radioactivity leached from the coating within 60 min in 0.1 M HCl.

Neutron Activation Procedures Used for the Calibration of a Nitrogen-16 Reactor Power Monitor

Personnel from the Pennsylvania State University's Breazeale Nuclear Reactor assisted NRC (Nuclear Research Corporation) personnel in calibrating a new MSL/16N Nitrogen-16 Monitor. This paper describes the neutron flux calibration procedures utilized and the results obtained for the production of a nitrogen-16 source of known activity for a BGO detector calibration.

GOLD, IRIDIUM, PALLADIUM AND PLATINUM IN REFERENCE STANDARD PCC‐1 AND A KOMATIITIC PERIDOTITE: IMPLICATIONS FOR SELECTION OF IGNEOUS ROCK REFERENCE MATERIALS FOR PPB‐LEVEL NOBLE METAL ANALYSIS

New analyses for AU, Ir, Pd and Pt in the USGS rock standard PCC‐1, carried out by two different radiochemical neutron activation procedures, are compared with similar analyses of a spinifex‐textured komatiitic peridotite. Better precision obtained for most of these elements on the komatiitic peridotite, in conjunction with consideration of literature values for PCC‐1, suggest that the volcanic peridotite is characterized by a more homogeneous distribution of noble metals than PCC‐1, a plutonic peridotite. These results suggest that reference materials for the analysis of sulfur‐poor mafic and ultramafie rocks with background levels of noble metals will be more satisfactory if volcanic rocks are selected.

Development and validation of neutron activation procedures for metal analysis in municipal solid waste

Development and validation of neutron activation procedures for metal analysis in municipal solid waste

An accurate procedure for the determination of low levels of platinum group elements in standard materials by neutron activation analysis

The paper describes a destructive neutron activation procedure for the determination of all platinum group elements (PGE). Only a few steps are required after irradiation, namely sample dissolution, osmium and ruthenium separation by solvent extraction, anion exchange separation of remaining noble metals and counting. The chemical yield is evaluated. The method has been used for the determination of noble metals in a large variety of standard reference materials, mainly of geological and technological origin. The results, given as the average of four independent analyses are reported and discussed. Average precision for the whole procedure is usually below 8% and sensitivities are adequate to meet the analysis requirements of terrestrial PGE- and Au-poor materials.

The effect of food on gastrointestinal (GI) transit of sustained-release ibuprofen tablets as evaluated by gamma scintigraphy.

The GI transit of radiolabeled sustained-release ibuprofen 800-mg tablets in eight healthy, fed volunteers was monitored using external gamma scintigraphy. Ibuprofen serum concentrations were determined from blood samples drawn over 36 hr following dosing. Sustained-release ibuprofen tablets containing 0.18% of 170Er2O3 (greater than 96% 170Er) in the bulk formulation were manufactured under pilot-scale conditions and were radiolabeled utilizing a neutron activation procedure which converted stable 170Er to radioactive 171Er (t1/2 = 7.5 hr). At the time of dosing, each tablet contained 50 mu Ci of 171Er. Dosage form position were reported at various time intervals. In five subjects the sustained-release tablet remained in the stomach and eroded slowly over 7-12 hr, resulting in gradual increases in small bowel radioactivity. In the remaining three subjects, the intact tablet was ejected from the stomach and a gastric residence time of approximately 4 hr was measured. This is in marked contrast to a previous study conducted in fasted volunteers in which gastric retention time ranged from 10 to 60 min. Differences in GI transit between fed and fasted volunteers had little effect on ibuprofen bioavailability. AUC and Tmax were unaltered and Cmax was increased by 24%, which is in agreement with results from a previous, crossover-design food effect study.

An automated neutron activation procedure for screening PCB content of oil

An analytical procedure for rapidly screening large numbers of oils for polychlorinated biphenyl (PCB) content has been developed and is now in routine use. Pontential levels of PCBs are inferred from chlorine concentrations as determined using the automated neutron activation analysis (NAA) facility at the Los Alamos National Laboratory Omega West Reactor. The technique is designed to screen up to 200 oil samples per eight hour working day, using a sample volume of approximately 1 milliliter. Because of the automated nature of the analysis, elements in addition to chlorine are determined, when present. These include fluorine, bromine, iodine and sulfur. U.S. National Bureau of Standards (NBS) and U. S. Environmental Protection Agency (EPA) Standard Reference Materials are routinely analyzed for quality assurance purposes. The results of our analyses of these materials for certified elements is discussed as well as results for other non-certified elements observed in the standard materials.

A novel approach to the determination of iridium via Ge-coincidence/NaI(Tl)-anticoincidence gamma-ray spectrometry

Iridium has proven to be a useful fingerprint of extraterrestrial material, and neutron activation analysis is the method of choice for its determination because of the high thermal cross section (910 b) of 191Ir (37.3% natural abundance) and the favorable decay characteristics of the product nuclide. However, radiochemical separations are frequently required for the determination of iridium at low concentrations (in the ppb range). The present work describes a precise, nondestructive neutron-activation procedure that is capable of analyzing samples of both high (ppm) and low (ppb) Ir content. Advantage is taken of the fact that the principal gamma lines of 73.8-d 192Ir are in various coincidences with one another. Instead of conventional gamma-gamma coincidence spectrometry with two Ge detectors, we utilize the 784.6- and 920.9-keV sum peaks which are generated when an iridium containing sample is placed in the well of a highly-efficient HPGe detector. The well-type detector is positioned centrally in a large annular NaI(Tl) detector which is operated in an anticoincidence mode. This improves the quality of the gamma spectra by suppressing the Compton backgrounds due to nuclides such as 60Co by a factor of 4–6 in the regions of interest without affecting the intensities of the two sum peaks. The sensitivity of this method under our experimental conditions (20-mg sample irradiated at 1.5 × 10 14 n cm −2 s −1 for 5 min and counted 3–4 weeks after irradiation) is ∼5 ppb Ir in a relatively unfavorable matrix such as peridotite.

Application of tomographic techniques to an investigation of elemental distributions following neutron irradiations

The use of tomographic image reconstruction techniques for the creation of three-dimensional images of the distribution of activity in solid samples has been examined. The aim has been to determine whether the method offers a finish to neutron activation procedures wich is capable of providing detailed position-sensitive information. Investigations with a phantom have shown that good images can be produced, even with relatively low-cost equipment.

Simultaneous determination of P and N in human tissue by 14 MeV neutron activation analysis

A simple 14 MeV neutron activation procedure for the simultaneous determination of P and N in human tissue has been developed. Paired 12.7 × 12.7 cm NaI(Tl) detectors were used for γ-ray detection. A coincidence counting system was used to monitor annihilation radiation from 13 N, and a dual sum-invert amplifier and MCA were used to count the 28 Al γ-ray from P. NBS SRM 1577 (Bovine Liver) was chosen as the primary standard for both determinations. For replicate runs, the observed standard deviation of the specific activities for standard samples is typically ±3%, relative.

An accurate procedure for the determination of low levels of iridium in standard reference materials by neutron activation analysis

The paper describes a destructive neutron activation procedure especially set up for the determination of low levels of iridium. Only a few steps are required after irradiation, namely sample dissolution, noble metals adsorption on an ion-exchange column, removal of interfering radionuclides and counting. Successively iridium is removed from the column and the chemical yield evaluated. The method has been used for the determination of iridium in a large variety of standard reference materials, including materials of geological, biological and technological origin, with iridium levels ranging from about 0.005 to 18 ng/g. Results, given as the average of three or more independent analyses, and relative standard deviations, are reported and discussed. Average precision is about 8%, and the sensitivity is 0.004 ng.

Methods and application of bone densitometry in clinical diagnosis.

With the awareness of osteoporosis as a major health problem for an aging population, there is great interest in early recognition and treatment of abnormal bone loss. Effective prevention of bone loss has to occur prior to the occurrence of irreparable damage. Standard radiographic procedures are not sensitive enough for the task. Therefore, a number of alternative procedures to estimate bone loss have been developed over the years, ranging from efforts to quantitate information obtained from radiographic images to sophisticated procedures such as neutron activation analysis or procedures based on the Compton scatter phenomenon. Only two procedures, photon absorptiometry and computed tomography (CT), have emerged as applicable for routine clinical use. In photon absorptiometry the entire bone mineral (cortical and trabecular bone) of a specific skeletal site is measured. CT allows measuring of bone mineral of trabecular or cortical bone alone. Normally, bone mass reaches a maximum in the third decade and then continuously declines. This age-related bone loss is greater in women in whom an accelerated rate of loss occurs at the menopause. When bone density reaches a critical fracture threshold, skeletal fractures occur (spine, hip, and distal long bones). The age at which this critical fracture threshold is reached depends on the maximal bone mass achieved in early adulthood and the rate of loss with increasing age. With the exception of NaF, present-day therapeutic efforts only retard or prevent bone loss but do not significantly add bone mineral to the skeleton. Recognition of high-risk groups and early treatment are therefore required. Absorptiometry, and probably in the future CT, also permit the measuring of bone mineral at sites of fracture with sufficient accuracy and precision to allow an early detection of lower than normal (for age and sex) bone mass, estimating fracture risk, and monitoring of the rate of bone loss by repeated measurements. An operational diagnosis of osteoporosis based on fracture risk has also been attempted from bone mineral measurements. And last, the effect of a drug regimen used to prevent or decrease bone loss can be monitored with these procedures.

Chromium, selenium, and other trace element intakes of a selected sample of Canadian premenopausal women

Daily Cr, Se, Ag, Cs, Rb, Sb, and Sc intakes of 84 Canadian women aged 30.3±6.1 yr (mean±SD) living in a University community and consuming self-selected diets were determined by analyses of 1-d food composites collected by the subjects. Aliquots of the homogenized food composites were freeze-dried and then analyzed by instrumental neutron activation procedures following irradiation for 72h. In all cases, trace element concentrations in the food composites were non-Gaussian. Median daily intakes were: Cr, 47 μg; Se, 74 μg; Ag, 7.1 μg; Cs, 4.4 μg; Rb, 1.5 mg; Sb 2.0 μg; and Sc, 0.38 μg. Sixty percent and 24% of the subjects received daily Cr and Se intakes, respectively, below the US Food and Nutrition Board safe and adequate range. High Cr density diets were associated with a significantly higher consumption of cheese and dry legumes and nuts (p<0.05). In the high Se density diets, intakes of grain products and breakfast cereals were significantly higher (p<0.05), and intakes of potatoes, table fats, total fat, saturated fat, and oleic acid were significantly lower (p<0.05) compared to the low Se density diets. The low daily Cr intakes evident in this study may be cause for concern in view of the increasing evidence that women may be at greater risk for deficiency of Cr than men because of Cr depletion during pregnancy.

Regional differences in hair zinc concentrations: a possible effect of water hardness

AbstractHair Zn, Cu, and Mn concentrations were determined by neutron activation procedures in two groups of healthy, Caucasian children aged 4.5 to 5.5 yr from Halifax, Nova Scotia and Guelph, Ontario and consuming soft water (hardness = 33 ppm) and very hard tap water (hardness = 330 ppm), respectively. Median hair Zn level for the Halifax children (26 males and 26 females) was 140 μg/g, significantly higher (p > 0.0001) than the Guelph children (median = 82 μg/g; 25 males and 26 females). No significant differences existed between the two groups for median hair Cu and Mn levels (Halifax hair Cu 12.1 μg/g, Guelph hair Cu 11.0 μg/g; Halifax hair Mn 0.17 μg/g, Guelph hair Mn 0.18 μg/g). The Halifax children were significantly heavier (p > 0.001) and slightly taller (p = 0.09) than their Guelph counterparts, although mean daily intakes of energy, protein, Zn, Cu, Mn, and dietary fiber, calculated from 3-day food records were not significantly different in the two groups. The large differences in the hair zinc levels may be due to the high concentration of calcium in the Guelph hard water, which may decrease the absorption of zinc.

Changes in hair arsenic levels in breast and bottle fed infants during the first year of infancy

Hair samples were collected from 13 breast fed and 19 bottle fed infants at one, three, six and twelve months of age. Food frequency data were also collected. Arsenic and antimony concentrations determined in washed hair samples by neutron activation procedures, rose significantly with age, the highest levels being evident at twelve months. Hair arsenic and antimony levels were independent of sex, and method of milk feeding. However, at twelve months, the median hair arsenic level for those infants receiving cereal at six months of age (0.655 μg/g) was significantly higher ( p = 0.05) than for those infants fed exclusively a milk based diet at this time (median = 0.225 μg/g). Recent data show that cereals are major dietary sources of arsenic during infancy. Hence findings of this study suggest that changes in hair arsenic levels during infancy are related to the introduction of cereals in the diet.

Changes in serum zinc concentrations of some Canadian full term and low birthweight infants from birth to six months.

Serum samples were collected from 99 infants at birth, and when they were 1, 3 and 6 months old. Thirty-seven were preterm infants with a mean birthweight of 1880 g and 26--36 wk gestation; 24 were full term low birthweight with a mean birthweight of 2371 g and 38--42 wk gestation; and 38 were full term normal birthweight infants with a mean birthweight of 3590 g and 38--42 wk gestation. Serum zinc concentrations were determined by instrumental neutron activation procedures. No significant differences in serum zinc levels were apparent between sexes or among the 3 groups. Levels were highest at birth and declined during the first 3 months. Between 3 and 6 months, serum zinc levels remained fairly constant, and were lower than reported levels for North American adults. It is concluded that the decline in serum zinc concentration in all three groups was not significantly correlated with birthweight or gestational age and the low birthweight infants in this study did not show any evidence of zinc deficiency. The general decline in serum zinc levels appeared to be associated with low dietary zinc intakes.