Preparative scale mass spectrometry: A brief history of the calutron

Calutrons were developed in the laboratory of E. O. Lawrence at the University of California at Berkeley. They were a modification of the cyclotrons he had invented and used in his Noble Prize winning investigations of the atomic nucleus. At the time their construction was undertaken, calutrons represented the only certain means of preparing enriched uranium isotopes for the construction of a fission bomb. The effort was successful enough that every atom of the 42 kg of ²³⁵U used in the first uranium bomb had passed through at least one stage of calutron separation. At peak production, the first stage separators, α tanks, yielded an aggregate 258-g/d ²³⁵U enriched to about 10 at. % from its natural abundance level of 0. 72 at. %. The second stage separators, β tanks, used the 10 at. % material as feedstock and produced a total 204-g/d ²³⁵U enriched to at least 80 at. %. The latter, weapons grade, material was used in fission bombs. Under typical operating conditions, each α tank operated at a uranium beam intensity at the collectors of approximately 20 mA and each β tank at a beam intensity of approximately 215 mA at the collectors. Bulk separation of isotopes for bomb production ceased in 1945. Since that time calutrons have been used to separate stable isotopes, but on a more limited scale than wartime weapons production. Stable isotope separations since 1960 have taken place using one modified beta tank.     

Performance of alpha spectrometry in the analysis of uranium isotopes in environmental and nuclear materials

The accuracy of alpha spectrometry in the determination of uranium isotopes at various concentrations levels and with various isotope ratios was tested in a round robin international intercomparison exercise. Results of isotope activity/mass and isotope mass ratios obtained by alpha spectrometry were accurate in a wide range of uranium masses and in isotopic ratios typical of depleted, natural, and low enriched uranium samples. Determinations by alpha spectrometry compared very satisfactorily in accuracy with those by mass spectrometry. For example, determination of U isotopes in natural uranium by alpha spectrometry agreed with mass spectrometry determinations at within ±1%. However, the ²³⁶U isotope, particularly if present in activities much lower than ²³⁵U, might not be determined accurately due to overlap in the alpha particle energies of these two uranium isotopes.     

Fission track–secondary ion mass spectrometry as a tool for detecting the isotopic signature of individual uranium containing particles

A fission track technique was used as a sample preparation method for subsequent isotope abundance ratio analysis of individual uranium containing particles with secondary ion mass spectrometry (SIMS) to measure the particles with higher enriched uranium efficiently. A polycarbonate film containing particles was irradiated with thermal neutrons and etched with 6 M NaOH solution. Each uranium containing particle was then identified by observing fission tracks created and a portion of the film having a uranium containing particle was cut out and put onto a glassy carbon planchet. The polycarbonate film, which gave the increases of background signals on the uranium mass region in SIMS analysis, was removed by plasma ashing with 200 W for 20 min. In the analysis of swipe samples having particles containing natural (NBL CRM 950a) or low enriched uranium (NBL CRM U100) with the fission track–SIMS method, uranium isotope abundance ratios were successfully determined. This method was then applied to the analysis of a real inspection swipe sample taken at a nuclear facility. As a consequence, the range of ²³⁵U/²³⁸U isotope abundance ratio between 0.0276 and 0.0438 was obtained, which was higher than that measured by SIMS without using a fission track technique (0.0225 and 0.0341). This indicates that the fission track–SIMS method is a powerful tool to identify the particle with higher enriched uranium in environmental samples efficiently.     

Separation of uranium and plutonium isotopes for measurement by multi collector inductively coupled plasma mass spectroscopy

Uranium (U) and plutonium (Pu) isotopes in coral soils, contaminated by nuclear weapons testing in the northern Marshall Islands, were isolated by ion-exchange chromatography and analyzed by mass spectrometry. The soil samples were spiked with ²³³U and ²⁴²Pu tracers, dissolved in minerals acids, and U and Pu isotopes isolated and purified on commercially available ion-exchange columns. The ion-exchange technique employed a TEVA^® column coupled to a UTEVA^® column. U and Pu isotope fractions were then further isolated using separate elution schemes, and the purified fractions containing U and Pu isotopes analyzed sequentially using multi-collector inductively coupled plasma mass spectrometer (MCICP-MS). High precision measurements of ²³⁴U/²³⁵U, ²³⁸U/²³⁵U, ²³⁶U/²³⁵U, and ²⁴⁰Pu/²³⁹Pu in soil samples were attained using the described methodology and instrumentation, and provide a basis for conducting more detailed assessments of the behavior and transfer of uranium and plutonium in the environment.     

Determination of234U/238U and235U/238U ratios from commercially available uranium compounds by α-spectrometry

The²³⁴U/²³⁸U and²³⁵U/²³⁸U ratios from uranium compounds by -spectrometry technique have been obtained. Ten commercially available uranium reagents were analyzed. The well-separated peaks corresponding to uranium isotopes are evident, providing an energy spectrum of the -particles of uranium isotopes. It was found that some commerical uranium salts were depleted in²³⁴U and²³⁵U.     

Isotopic analysis of uranium in NIST SRM glass by femtosecond laser ablation MC-ICPMS

We employed femtosecond Laser Ablation Multicollector Inductively Coupled Mass Spectrometry for the determination of uranium isotope ratios in a series of standard reference material glasses (NIST 610, 612, 614, and 616). The uranium in this series of SRM glasses is a combination of isotopically natural uranium in the materials used to make the glass matrix and isotopically depleted uranium added to increase the uranium elemental concentration across the series. Results for NIST 610 are in excellent agreement with literature values. However, other than atom percent ²³⁵U, little information is available for the remaining glasses. We present atom percent and isotope ratios for ²³⁴U, ²³⁵U, ²³⁶U, and ²³⁸U for all four glasses. Our results show deviations from the certificate values for the atom percent ²³⁵U, indicating the need for further examination of the uranium isotopes in NIST 610-616.     

Radiochemical determination of fission products of uranium

An analysis has been elaborated to determine the long-living γ-emitting fission products of uranium. It consists of a sodium bisulphate melt of the fission product solution or the U-fuel, followed by liquid-liquid extractions. Afterwards the isotopes are absolutely counted with a standardized 3″×3″ NaI crystal. The total γ-spectrum of the original fission product solution, taken with a NaI crystal or a Ge−Li detector, is also analyzed mathematically by mixed γ-spectrometry. From a short post-irradiation of the fission product solution the concentrations of both²³⁵U and²³⁸U are determined. The absolute amount of fission products related to the U-concentration allows the calculation of the percent atomic burn-up, the irradiation time, the cooling period, the flux of the reactor and the original degree of enrichment of the uranium. Research associate of the I. I. K. W.     

The determination of uranium in biological materials by neutron activation analysis using the fission product134I

A method for the determination of uranium based on²³⁵U thermal neutron fission, has been developed and employed on samples of ashed fish tissue and seaweed. The method involves a post-irradiation ion exchange separation of iodine isotopes. The 884 keV photopeak of¹³⁴I is used for measurement. Uranium detection limits in the samples concerned have been estimated to be 1·10⁻⁸g in terms of natural uranium. The precision achieved in analysing several series of 3–5 samples was 4–10 per cent. The accuracy of the method was tested by employing an independent neutron activation procedure based on²³⁹U measurement. The accuracy of both methods was checked by analysing NBS SRM 1571 ‘Orchard Leaves’.     

Determination of235U abundance in uranium by neutron activation on the basis of the molybdenum fission interference

The purpose of the present paper is to suggest a method for determining the²³⁵U abundance in uranium samples (compounds, metallic alloys or other uranium materials, where this element may be natural or not) through a particular application of neutron activation analysis, based on the fission interference by molybdenum. The method lies on an a priori calibration with natural uranium, thus it does not require²³⁵U certified standards.     

Determination of uranium isotopes in environmental samples

The determination of isotopes of uranium by alpha spectrometry in different environmental components (sediments, soil, water, plants and phosphogypsum) is presented and discussed in this paper. The alpha spectrometry is a very convenient and good technique for activity concentration of natural uranium isotopes (²³⁴U, ²³⁵U, ²³⁸U) in environmental samples and provides the most accurate determination of isotopic activity ratios between ²³⁴U and ²³⁸U. The analysis were provided information about possible sources of high concentrations of uranium in the examined sites determined by anthropogenic sources. The calculation of values ²³⁴U/²³⁸U in all analyzed samples was applied to identifying natural or anthropogenic uranium origin. Activity concentration of uranium isotopes in analyzed environmental samples shows that measurement of uranium levels is of great importance for environmental and safety assessment especially in contaminated areas (phosphogypsum waste heap).     

Combined application of alpha-track and fission-track techniques for detection of plutonium particles in environmental samples prior to isotopic measurement using thermo-ionization mass spectrometry

The fission track technique is a sensitive detection method for particles which contain radio-nuclides like ²³⁵U or ²³⁹Pu. However, when the sample is a mixture of plutonium and uranium, discrimination between uranium particles and plutonium particles is difficult using this technique. In this study, we developed a method for detecting plutonium particles in a sample mixture of plutonium and uranium particles using alpha track and fission track techniques. The specific radioactivity (Bq/g) for alpha decay of plutonium is several orders of magnitude higher than that of uranium, indicating that the formation of the alpha track due to alpha decay of uranium can be disregarded under suitable conditions. While alpha tracks in addition to fission tracks were detected in a plutonium particle, only fission tracks were detected in a uranium particle, thereby making the alpha tracks an indicator for detecting particles containing plutonium. In addition, it was confirmed that there is a linear relationship between the numbers of alpha tracks produced by plutonium particles made of plutonium certified standard material and the ion intensities of the various plutonium isotopes measured by thermo-ionization mass spectrometry. Using this correlation, the accuracy in isotope ratios, signal intensity and measurement errors is presumable from the number of alpha tracks prior to the isotope ratio measurements by thermal ionization mass spectrometry. It is expected that this method will become an effective tool for plutonium particle analysis. The particles used in this study had sizes between 0.3 and 2.0 μm.     

Direkte Bestimmung von Uran in organischen Extrakten

Uranium was extracted with a 0.15M di-(2-ethylhexyl) phosphate solution in toluene, and directly determined in the organic phase by the liquid scintillation technique. The selection of the optimum conditions of measurement is explained using an established isoamplitude curve, and²³⁵U is determined in the presence of small amounts of fission products. The proposed method also allowed the determination of²³⁴U in 1 mg of enriched uranium, with a relative error of ±0.52%.      

Fallout of uranium isotopes from the 1980 eruption of Mount St. Helens

A marked increase in the concentration of²³⁸U in rain was observed at Fayetteville (36 °N, 94 °W), Arkansas, after the 18 May 1980 eruption of Mount St. Helens. The fallout of natural uranium observed during the summer months of 1980 can be attributed to the 18 May 1980 events, which ejected an amount of ash material on the order of 4 km³ or about 8·10¹⁵ grams into the atmosphere.²³⁴U and²³⁵U were found to be highly enriched relative to²³⁸U in several rain samples collected at Fayetteville, Arkansas, prior to the volcanic eruption. The anomalous uranium seems to have originated from the Soviet satellite Cosmos-954, which fell over Canada, on 24 January 1978. The effect of the 25th Chinese nuclear test, which occurred on 16 October 1980, on the concentrations of uranium isotopes in rain appears to have been insignificant.     

On line ion exchange separation of short-lived Zr, Hf, Mo, Ta and W isotopes as homologs of transactinide elements

The short-lived isotopes of W and their descendants have been separated from nuclear reaction products arising in the bombardment of samarium target with²⁴Mg ions at the U-400 cyclotron of JINR-Dubna. Chemical separations were performed using previously elaborated fast and continuous ion exchange. In similar way products of²³⁵U fission, obtained at the microtron MT-25 during irradiation of²³⁵U target with photoneutrons were separated.     

Uranium series disequilibrium in the coastal surface sediments and sea water of the Arabian Sea

Nearshore surface sediments from various locations of the West Coast of India were leached by saturated ammonium carbonate solution for the extraction of uranium isotopes. The reagent chosen was found to have high efficiency for leaching uranium isotopes without attacking the mineral core of the sediment particle. The activity ratios of²³⁴U/²³⁸U are in the range of 1.11 to 1.14 and the activity ratios of²³⁵U/²³⁵U are in the range of 0.045 to 0.047. The respective activity ratios in leachates, and residues after removal of surface organic matter from the sediment particles by treatment with hydrogen peroxide and 0.05M HCl, revealed disequilibrium between²³⁸U and²³⁴U only in the surface organic matter. The activity ratios of²³⁴U/²³⁸U and²³⁵U/²³⁸U have also been determined in some seawater samples from the Arabian Sea.     

Uranium isotopes in carbonate aquifers of arid region setting

Groundwater in arid and semiarid regions is vital resource for many uses and therefore information about concentrations of uranium isotopes among other chemical parameters are necessary. In the study presented here, distribution of ²³⁸U and ²³⁵U in groundwater of four selected locations in the southern Arabian peninsula, namely at two locations within the United Arab Emirates (UAE) and two locations in Oman are discussed. The analyses of the uranium isotopes were performed using ICP-MS and the results indicated a range of concentrations for ²³⁵U and ²³⁸ U at 3–39 ng L^?1 (average: 18 ng L^?1) and 429–5,293 ng L^?1 (average: 2,508 ng L^?1) respectively. These uranium concentrations are below the higher permissible WHO limit for drinking water and also comparable to averages found in groundwater from similar aquifers in Florida and Tunisia. Negative correlation between rainfall and uranium concentrations suggests that in lithologically comparable aquifers, climate may influence the concentration of uranium in subtropical to arid regions.     

INAA of Zr,La, Ce and Nd in geological samples in the presence of different uranium concentratios

Rock samples which contain relatively high concentrations of uranium may create problems of interference produced by fission products, when instrumental neutron activation analysis is used. The isotopes⁹⁵Zr,¹⁴⁰La,¹⁴¹Ce, 143Ce and 147Nd, which are commonly used in the neutron activation analysis of the corresponding elements, are also produced as fission products of²³⁵U. For each of these radioisotopes, a contribution factor is calculated theoretically and meaured experimentally using geological samples with different uranium contents.     

Application of neutron activation analysis in a fission molybdenum separation study

The separation of⁹⁹Mo from low-enriched uranium (LEU, 19.5%²³⁵U) targets was evaluated using natural uranium (NU) and non-radioactive tracers. Neutron activation analysis was used to determine (1) the efficiency of molybdenum recovery and (2) the decontamination factor of numerous fission product elements from the molybdenum product. Using NU and non-radioactive elements simplified procedures and allowed tests to be completed in a fume hood instead of a shielded cell. During activation of the non-radioactive tracers, uranium fission occurs, which can interfere with subsequent gamma-ray analysis. A comparison was made of the interferences caused by these fission products from both NU and LEU.     

Fine structure of mass and charge distribution in low energy fission

Studies of finer details in mass and charge distribution fission leads to a better understanding of the fission process. Experimental determination of independent and cumulative yields using radiochemical techniques as well as mass spectrometers and fission product recoil separators form the basis of such studies. It has been established that closed shells as well as an even number of nucleons influence both mass and charge distributions. The magnitudes of these effects may be estimated from existing experimental yield data and various fission models. Using our measurements of several fission yields and those existing in the literature we have calculated even-odd proton and neutron effects for various low energy fissioning systems. Where enough data existed, direct calculations were made, whereas for other cases the Z_p-model of WAHL has been used. It is found that the even-odd proton effect is well established and pronounced in thermal neutron fission of²³⁵U and²³³U. Lesser effects were found for reactor neutron induced fission of²³²Th, thermal neutron fission of²³⁹Pu and spontaneous fission of²⁴⁵Cm and²⁴⁹Cf. No effect seems to exist in the thermal neutron fission of²⁴¹Pu and the spontaneous fission of²⁵²Cf. The even-odd neutron effect is found to be much lower than the corresponding proton effect in²³⁵U and²³³U fissions and is nonexistent in the rest of the fissioning systems.     

Uranium enrichment measurements using the intensity ratios of self-fluorescence X-rays to 92 keV gamma ray in UXKα spectral region

In this paper, the known multigroup γ-ray analysis method for uranium (MGAU) as one of the non-destructive γ-ray spectrometry methods has been applied to certified reference nuclear materials (depleted, natural and enriched uranium) containing ²³⁵U isotope in the range of 0.32-4.51% atom ²³⁵U. Its analysis gives incorrect results for the low component ²³⁵U in depleted and natural uranium samples where the build-up of the decay products begins to interfere with the analysis. The results reveal that the build-up of decay products seems to be significant and thus the algorithms for the presence of decay products should be improved to resulting in the correct enrichment value. For instance, for the case of ²³⁵U analysis in depleted uranium or natural ore samples, self-induced X-rays such as 94.6 keV and 98.4 keV lying in UXK_α spectral region used by MGAU can be excluded from the calculation. Because the significant increases have been observed in the intensities of uranium self-induced X-rays due to γ-ray emissions with above 100 keV energy arising from decay products of ²³⁸U and ²³⁵U and these parents. Instead, the use of calibration curve to be made between the intensity ratios of self-fluorescence X-rays to 92^* keV γ-ray and the certified ²³⁵U abundances is suggested for the determination of ²³⁵U when higher amounts of decay products are detected in the γ-ray spectrum acquired for the MGAU analysis.