Advanced system for separation of rare-earth fission products

A microprocessor-controlled radiochemical separation system, which has been developed at the INEL, has been further advanced to separate individual rare-earth elements from mixed fission products in times of a few minutes. The system was composed of an automated chemistry system fed by two ∼300μg²⁵²Cf sources coupled directly by a He-jet to transport the fission products. Chemical separations were performed using two high performance liquid chromatography columns coupled in series. The first column separated the rare-earth group by extraction chromatography using dihexyldiethylcarbamoylmethylphosphonate (DHDECMP) adsorbed on Vydac C₈ resin. The second column isolated the individual rare-earth elements by cation exchange chromatography using Aminex A-9 resin with α-hydroxyisobutyric acid (α-HIBA) as the eluent. Significant results, which have been obtained to date with this advanced system, are the identification of several new neutron-rich rare-earth isotopes including¹⁵⁵Pm (T=48±4 s) and¹⁶³Gd (T=68±3 s). In addition a half-life of 41±4 s is reported for¹⁶⁰Eu. Work supported by the U.S. Department of Energy under DOE Contract No. De-ACO7-76IDO-1570.     

Yields of rare earth fission products in the spontaneous fission of californium-252

Cumulative fission yields of rare earth isotopes have been determined in the spontaneous fission of²⁵²Cf by fast radiochemical separation and gamma-ray spectrometry. The determined yield values are compared with the available literature data. The yield values for¹⁴⁷Nd,¹⁵¹Nd and¹⁵¹Pm differ from the reported values. The yield for¹⁴⁵Ce is determined for the first time.     

Separation of transplutonium and rare-earth elements by extraction with HDEHP from DTPA solutions

The extraction behaviour of Am, Cm, Bk, Cf, Es, La, Ce, Pr, Pm, Sm, Eu, Gd, Ho, Yb and Lu in the system HDEHP—DTPA in lactic acid has been studied from the point of view of group separation of the transplutonium and rare-earth elements. Optimum separation conditions have been found on the basis of the results obtained. Some test separations of transplutonium elements from rare-earth fission products have been carried out in real solutions by extraction chromatography. It has been shown that this method can be used successfully for the analytical determination of transplutonium elements as well as for recovery of the latter from irradiated samples.     

Nuclear decay studies of fission-product nuclides using an on-line mass separation technique

An isotope-separator-on-line (ISOL) system has been developed at the Idaho National Engineering Laboratory to enable a wide variety of nuclear decay studies to be made for fission-product radionuclides. The system is unique in that it utilizes the spontaneous fission source,²⁵²Cf, as the source of fission-product radioactivity. Fission products are transported to the ion source of the mass separator by the helium gas-jet technique. Mass-separated beams of previously unattainable rare-earth nuclides are produced with this system because of the higher yield of fission products with A>150, relative to that for thermal-neutron fission of²³⁵U, and the use of a relatively efficient ion source. Recent decay studies reported here include systematic measurements of rare-earth nuclide half-lives and comparison of them to theoretical prediction, a decay scheme investigation for¹⁵⁴Nd, and -strength function measurements for¹⁴⁰Cs.     

Cumulative yields of short-lived xenon isotopes in the spontaneous fission of252Cf

Cumulative yields of short-lived xenon isotopes^137,138,139Xe have been determined in the spontaneous fission of²⁵²Cf, using a fast radiochemical separation method followed by gamma spectrometry. Xenon-137 yield is reported for the first time. The measured cumulative yields are converted to chain yields assuming normal charge distribution systematics for comparision with the literature data.     

Xe-135 production from Cf-252

The presence of ¹³⁵Xe is often used as an indicator that fission has occurred, and is used to help enforce the Comprehensive Test Ban Treaty. There are no known commercial suppliers, though it can be acquired. Readily available standards of this isotope are very useful. ¹³⁵Xe can be produced through fission, or by neutron capture on ¹³⁴Xe. At the INL, scientists have previously transported fission products from an electroplated ²⁵²Cf thin source for the measurement of nuclear data of short-lived fission products using a technique called He-Jet collection. A similar system has been applied to the collection of gaseous ¹³⁵Xe, and ¹³³Xe, in order to produce standards of these isotopes.     

Preparatory investigations of fast separation for heavy ion reaction products

A method for separation and chemical identification of products formed in nuclear reactions or nuclear decay is to slow down the recoil products in a gas and to transport them to a trap, where a detecting system is arranged. The sources for the recoil products are²⁵²Cf and²²⁴Ra. As transport phase we used nitrogen or argon and added chemical reagents such as methyl and ethyl radicals, chlorine, oxygen, carbon monoxide or methane. The chemical additives lead to selective and fast separation of certain elements. As examples the results of two experiments are presented:²²⁴Ra with ethyl radicals, and²⁵²Cf with chlorine-oxygen-nitrogen mixtures. The registration of the recoil products at the trap was measured as a function of temperature, pressure and composition of the reactive gas.     

Cumulative yields of short-lived isotopes of barium in the spontaneous fission of252Cf

Cumulative yields of short-lived/barium isotopes^{139, 141, 142}Ba have been determined in the spontaneous fission of²⁵²Cf, using fast radiochemical separation and gamma-ray spectrometry.¹⁴²Ba yield is reported for the first time. The measured cumulative yields are converted to chain yields, assuming normal charge distribution systematics for comparision with the literature data.     

Chemical analysis of heavy elements by identification of fission fragments through X-ray coincidence measurements

A two-parameter coincident (X-ray, X-ray) measurement was made using a Si(Li) X-ray detector and a Ge(Li) X-ray detector to study the X-ray production in the²⁵²Cf fission process.K X-ray peaks from adjacentZ fission products for elements Y through Rh and I through Pr are well resolved in both detectors. The measurement yields the result that there is a large number of coincident events with X-rays from the sameZ element as well as with X-rays from the complementary fission product (e.g. CsK X-rays are in coincidence with both the complementary TcK X-rays and the CsK X-rays). The various possibilities one may consider are: (1)K X-ray production by the primary fission process followed by internal conversion, (2) multipleK X-ray production in the stopping process of the fission products, (3)K shell ionization resulting from β-decay of the fission fragments followed by internal conversion in the same fragment, and (4) multiple internal conversion processes from cascading transitions. Each of these four possible causes for self-coincident X-ray production is explored. Further two-parameter measurements were made of low-energy γ-rays in coincidence with characteristicK X-rays from the individual elements formed in the fission. Combined with previous mass determinations, it was possible to identify many of the observed γ-rays with individual isotopes. However, a large number of low-energy transitions were observed and identified as to elemental charge, but which had not been seen previously so that no mass determination was possible.     

Specific activities of radioactive elements from fission product mixtures

Specific activities of radioactive elements at the time of chemical separation from fission product mixtures produced by thermal neutron fission of²³⁵U were computed byBateman's and other equations on an electronic computer. Computations were made for two fission times: fission was assumed to be complete in a few minutes in one case, and over a period of a year in the other case. It was also assumed that each element was separated instantly after allowing the fission products to decay for 1∼10 000 000 hrs (1 140 years). The computations were applied to 12 important elements: Ru, Zr, Nb, Cs, Sr, Pm, Tc, Ba, La, Ce, Kr and Y. Results are given as a diagram for each element. The diagrams are intended to be helpful in the chemical processing of a large quantity of fission products, and industrial or tracer application of these elements.     

Neutron activation analysis applications at the Savannah River Site using an isotopic neutron source

NAA using ²⁵²Cf is used to address important areas of applied interest of the Savanah River Site (SRS). Sensitivity needs for many of the applications are not severe; analyses are accomplished using a 21 mg ²⁵²Cf NAA facility. Because NAA allows analysis of bulk samples, it offers strong advantages for samples in difficult-to-digest matrices when its sensitivity is sufficient. Following radiochemical separation with stable carrier addition, chemical yields for a number of methods are determined by neutron activation of the stable carrier. In some of the cases where no suitable stable carriers exist, the source has been used to generate radioactive tracers to yield separations.     

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.     

Identification of iodoorganic compounds in kerosene from nuclear fuel reprocessing

In kerosene samples from nuclear fuel reprocessing, iodoalkanes with chain-lengths from C₄ to C₁₃ have been identified. The kerosene samples were purified by means of solid-phase extraction. By this method other fission products like¹²⁵Sb and¹⁰⁶Ru were quantitatively removed from the solution. The only remaining radioactive nuclide was thus¹²⁹I. The iodoorganic compounds in the kerosene from the solvent were enriched from 6000 Bq/L to 100 000 Bq/L¹²⁹I by vacuum distillation. Chromatographic separation by HPLC, fractionation, and -measurement of the fractions showed that at least one polar and one nonpolar iodoorganic compound were present. Derivatisation of the iodoorganic compounds with, 1,4-diazabicyclo-2,2,2-octane to quatermary ammonium salts and²⁵²Cf plasma desorption mass spectrometry of the products revealed that the main iodoorganic constituents in the kerosene were iodobutane as polar and iodododecane as nonpolar compound in approximately equal concentrations.     

Separation of heavier rare earths from neutron irradiated uranium targets

A radiochemical method is described for the separation of heavier rare earths from the fission of uranium. The method is particularly suitable for the separation of low yield (10⁻⁵%–10⁻⁷%), highly asymmetric rare earth fission products viz.^179,177Lu,¹⁷⁵Yb,¹⁷³Tm,^172,171Er,¹⁶⁷Ho and^161,160Tb in the neutron induced fission of natural and depleted uranium targets. Additional separation steps have been incorporated for decontamination from²³⁹Np (an activation product) and^93-90Y (a high fission-yield product) which show similar chemical behaviour to rare earths. Separation of individual rare earths is achieved by a cation exchange method performed at 80°C by elution with α-hydroxyisobutyric acid (α-HIBA).     

Effect of chelated mineral supplementation on the absorption of Cu, Fe, K, Mn and Zn in horse hair

The effects of gamma-irradiation at a dose range of 5-56 Mrad on the fission track registration efficiency of the Tuffak polycarbonate track detector from dry (K _dry) as well as the solution media (K _wet) are investigated. Fission tracks were recorded in the gamma-irradiated detectors along with the unirradiated ones by an electrodeposited source of ²⁵²Cf and also separately from a ²⁵²Cf solution. The fission track registration efficiencies for the irradiated detectors were determined in comparison with those of the unirradiated detectors. The results show that while the K _dry values for the irradiated detectors decrease by about 2-10%, the corresponding K _wet values decrease by about 3-20% as compared to unirradiated detectors . Further, the bulk etch rates were found to increase with the increase in gamma dose. The changes induced in the gamma-irradiated detectors as a function of dose have been studied also by thermogravimetry (TG).     

Automatic registration of fission fragment tracks with a spark gap counting system

The theoretical aspects of fission track production in polycarbonate foils are briefly discussed. An automatic couning system for fissio tracks based on a spark gap chamber is described. A linear response for a low fission track density, typical of environmental and biological samples, was obtained with a²⁵²Cf source using an electrode of 33.2 mm² The system also functions with electrodes of larger and smaller areas without any major changese in the instrument.     

Chemical study on the separation and purification of promethium-147

A chemical process for the separation of¹⁴⁷Nd/¹⁴⁷Pm from fission products of synthetic radioactive waste solution has been developed. The process includes: (1) denitration, (2) removal of high concentration of uranium by 30% TBP/kerosene extraction, (3) removal of⁹⁵Nb,¹⁰³Ru,¹³⁷Cs and part of⁹⁰Sr by 50% TBP/dodecane extraction, (4) separation of¹⁴⁷Nd/¹⁴⁷Pm from part of⁹⁰Sr and⁹⁵Zr by oxalic acid precipitation, and (5) removal of¹⁴⁴Ce by mixture of 0.4M D2EHPA and 0.2M TBP extraction. Experimental results indicate that the recovery of¹⁴⁷Nd/¹⁴⁷Pm in the final separated solution is about 90%. The purification of¹⁴⁷Nd and¹⁴⁷Pm from some other rare earth elements, viz.¹⁵³Sm,¹⁵⁴Eu and¹⁴⁴Ce was further investigated by using a Dowex 50W×8 ion-exchanger. Parameters of flow rate, eluent concentration and pH were examined. The results show that the recovery and radionuclide purity of¹⁴⁷Nd plus¹⁴⁷Pm under the present separation conditions are 77.8% and 98.6% for diethylenetriaminepentaacetic acid (DTPA) and 87.3% and 99.5% for nitrilotriacetic acid (NTA), respectively.     

Anion exchange separation of the light lanthanoids with nitric acid-methyl alcohol mixed media at elevated temperature

Anion exchange chromatography with nitric acid-methyl alcohol mixed media at elevated temperature has been applied to mutual separation of the light lanthanoids, La, Ce, Pr, Nd and Pm. The individual elements could be effectively separated from each other, main fission products and actinoids with 0.01M HNO₃-90% CH₃OH or 0.5M HNO₃-80% CH₃OH eluent at 90 °C.     

Fabrication of 50-mg252Cf neutron sources for the FDA activation analysis facility

The Transuranium Processing Plant (TPP) at the Oak Ridge National Laboratory (ORNL) has been requested by the Food and Drug Administration (FDA) to furnish 200 mg of²⁵²Cf for use in their new activation analysis facility. This paper discusses the procedure to be employed in fabricating the californium into four neutron sources, each containing a nominal 50-mg of²⁵²Cf. The completed neutron sources will be assayed using a precision fast-neutron counter, decontaminated and loaded into a concreete-shielded shipping container weighing 10.7 Mg for shipment to the FDA facility located at Howard University in Washington, D. C.Research sponsored by the Office of Basic Energy Sciences, U. S. Department of Energy, under contract DE-AC05-840R21400 with Martin Marietta Energy Systems, Inc.