Studies of short-lived fission products by means of the multistage solvent extraction system SISAK

The multistage solvent extraction system SISAK is described. The system is used for online studies of nuclides with half-lives down to 1 s. Some of the chemical separation procedures are presented, and a survey is given on the results obtained so far. The possiblity to gain access to nuclides with even shorter half-lives is also discussed.     

Experimental measurements of short-lived fission products from uranium,neptunium, plutonium and americium

Fission yields are especially well characterized for long-lived fission products. Modeling techniques incorporate numerous assumptions and can be used to deduce information about the distribution of short-lived fission products. This work is an attempt to gather experimental (model-independent) data on short-lived fission products. Fissile isotopes of uranium, neptunium, plutonium and americium were irradiated under pulse conditions at the Washington State University 1 MW TRIGA reactor to achieve ~10⁸ fissions. The samples were placed on an HPGe (high purity germanium) detector to initiate counting in less than 3 min post irradiation. The data was analyzed to determine which radionuclides could be quantified and compared to the published fission yield data.     

Identifying and quantifying short-lived fission products from thermal fission of HEU using portable HPGe detectors

Due to the emerging potential for trafficking of special nuclear material, research programs are investigating current capabilities of commercially available portable gamma ray detection systems. Presented in this paper are the results of three different portable high-purity germanium (HPGe) detectors used to identify short-lived fission products generated from thermal neutron interrogation of small samples of highly enriched uranium. Samples were irradiated at the Washington State University Nuclear Radiation Center’s 1 MW TRIGA reactor. The three portable, HPGe detectors used were the ORTEC MicroDetective [1], the ORTEC Detective [2], and the Canberra Falcon [3]. Canberra’s GENIE-2000 software was used to analyze the spectral data collected from each detector. Ultimately, these three portable detectors were able to identify a large range of fission products showing potential for material discrimination.     

Beta-gamma counting system for Xe fission products

A beta-gamma coincidence counting system has been developed for automated analysis of Xe gas samples separated from air. The Xe gas samples are contained in a cylindrical plastic scintillator cell located between two NaI(T1) scintillation detectors. The X-ray and gamma spectra gated by coincident events in the plastic scintillator cell are recorded for each NaI(T1) crystal. The characteristic signatures of the^131mXe,^133gXe,^133mXe, and^135gXe isotopes of interest for nuclear test-ban verification as well as the procedures and results of absolute efficiency measurements are described. A NaI(T1) crystal with provision for 4 sample cells has been implemented for the system to be deployed in the field. Examples of data on ambient air samples in New York City obtained with the field prototype are presented.     

Chemical characterization of short-lived selenium and their daughter isotopes from thermal neutron induced fission of 235U at a gas-jet facility

Selenium nuclides are available from thermal neutron induced nuclear fission of ²³⁵U at the gas-jet facility at the Swiss spallation neutron source (SINQ) at Paul Scherrer Institute, Switzerland. The formation of stable selenium compounds, their transport yields using the gas-jet system and their relative thermal decomposition temperature were investigated under oxidizing and reducing conditions in the target chamber. Using O₂, H₂, CO, and propene as additional gases, the selenium isotopes are suggested to form H₂SeO₃, H₂Se, COSe, and C₃H₆Se, respectively, with overall ⁸⁴Se yields of 1.5%, 4.7%, 6.3%, and 21.9%, respectively. Adsorption enthalpy, vapour pressure, solubility and acidity data for these species were collected from the literature or estimated from other known thermochemical properties. Carrier free bromine isotopes (⁸⁴Br, ⁸⁶Br) in the form of HOBr were obtained by thermally decomposing H₂SeO₃ and retaining elemental Se under oxygen rich conditions on quartz at 400 K.     

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.     

A transportable gamma spectroscopy system applied to the measurement of fission products

Normally, gamma-ray spectroscopy is performed by equipment positioned in the SLOWPOKE-2 Facility at the Royal Military College; however, there have occasionally been requirements for analyses externally. A transportable gamma spectroscopy system was thus assembled by acquiring a commercially available multichannel analyzer, analysis program and detector, and by designing and constructing a transportable shielding castle. It was then used to take measurements of fission product concentrations at several research reactors.     

The determination of uranium using short-lived fission products by cyclic and other modes of activation analysis

The determination of elemental concentration in biological and environmental samples through the detection of short-lived nuclides has been of considerable interest in the last few years. In this context the relative advantages and disadvantages of cyclic activation analysis (CAA) with respect to single conventional one-shot irradiation and counting sequence (for one sample or replicate samples) and what has been termed pseudo-cyclic activation have been discussed with conflicting interpretations. It is the objective of this study to demonstrate through the irradiation of uranium standards by measurement of short-lived fission products how each mode of activation is best utilised. Application of CAA to the problem, in order to enhance signal-to-noise ratio, must also take into account an increasing dead-time with each cycle and therefore mass fractionation of a given sample and standard are investigated for replicate and pseudo-cyclic activation conditions. The variation of timing parameters in the cyclic mode, as well as irradation in a mixed reactor flux and epi-cadmium neutron flux, produces a set of equations from which half-life can be determined to confirm fission product identification in these complex gamma-ray spectra.     

Liquid-liquid microbatch extraction system for rapid mutual separation of fission products

The liquid-liquid microbatch extraction system (LMES) was developed for rapid separation of short-lived metal ions. The equipment is composed of three simple extraction cells for phase mixing, phase separation, and collection of a solvent. Metal separation can be completed in a single operation, lasting only a minute, from solvent extraction to preparation for gamma-ray spectrometry. As a demonstration of the rapid operation of the LMES, fission products were each separated into several categories after three stages of operation. The extractability in the LMES was comparable to that of traditional methods, and the developed method was feasible for rapid separation.     

A new method for the radiochemical separation of copper from fission products

A new method for obtaining radiochemically pure⁶⁷Cu from highly active fission product solutions is described. The method is based on the solvent extraction of the Cu(II)-diethyldithiocarbamate complex in n-butyl acetate in the presence of hold-back carriers for Ni, Co, Mn, Mo, rare earths, Cd, Te and Sb, and subsequent purification steps involving scavengings for Ag, Ba, Sr and Fe followed by an anion-exchange purification step for decontamination from Te. Copper is finally extracted as the α-benzoin oxime complex in which form it is mounted and counted. The method has several advantages over other methods in that decontamination is very high and it is sufficiently fast considering the stringent radiochemical purity achieved. The⁶⁷Cu separated by this procedure from a one-day-old mixture of fission products arising from 10¹⁰ fissions was found to be completely free of any contamination.     

A fast radiochemical procedure for separating iodine from fission products

The iodine isotopes produced by thermal neutron fission of²³⁵U were separated by a fast chemical procedure, with a separation yield of 95%. The gamma-ray energies and relative intensities in the decay of¹³¹I,¹³²I,¹³³I,¹³⁴I and¹³⁵I were determined using a Ge(Li) detector.     

A critical evaluation of short-lived and long-lived neutron activation products for trace element determinations

The application of short-lived nuclides in routine instrumental neutron activation analysis can reduce total experimental time per sample. The experimental sensitivities of short- and long-lived thermal neutron activation products of 32 elements are compared. The advantages of using short-lived nuclides are evaluated by comparing the precision, accuracy, and detection limits, using both short- and long-lived nuclides, for elemental determinations in biological, environmental and geological standard reference materials.     

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.     

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

⁶⁷Ga is produced by the⁶⁶Zn(d,n) reaction at 9 MeV bombarding energy. Deuterons of about 30 A obtained from the T-11 Tandem accelerator are used to bombard targets of natural Zinc prepared by electroplating onto thick copper disks. Radiochemical separation of gallium is performed by using a cation exchange column. The optimum conditions for an efficient separation are given in detail.     

Yields of fission products with masses A=131 to 135 for the fast neutron induced fission of U-238

Yields of eleven fission products with masses A=131 to 135 have been determined for the reactor neutron induced fission of²³⁸U by means of radiochemical separation combined with high-precision Ge(Li) -ray spectrometry. The charge distribution in the isobaric chains 131 to 134 and the isotopic distribution of₅₂Te have been studied.