Half-life of241Pu is of great importance in nuclear technology. In view of large variation in the values (13–15 y) reported till 1974 in literature, efforts have been made in different laboratories to determine this half-life with high precision and accuracy. In our laboratory, it has been determined by different methods which may be classified in two categories, viz. (1) parent decay method, and (2) daughter growth method. In the parent decay method, change in isotope ratios241Pu/239Pu,241Pu/240Pu and241Pu/242Pu was studied periodically by a thermal ionization mass spectrometer. Single as well as double ratio method was used to calculate the half-life. In the daughter growth method, the half-life was obtained in four independent ways. These were (1) alpha spectrometry taking239Pu and242Pu separately as reference isotopes and studying periodically the increase in alpha activity ratio, (2) alpha proportional counting for observing periodically the change in total alpha activity, (3) isotope dilution alpha spectrometry using243Am as a spike, (4) isotope dilution mass spectrometry using243Am as a spike. In all these methods, synthetic mixtures were prepared for achieving high precision and accuracy in different measurements. Based on the results obtained in this laboratory and the values reported by other laboratories, a half-life value of 14.4±0.1 y is recommended. The paper reviews the past history, puts forth the present status, highlights the current trends for studying the effect of chemical composition of plutonium on the half-life of241Pu and presents the future requirements for achieving higher accuracy in the half-life of241Pu.
Relative activity method offers the potentiality of providing half-life values over a wide range in a short time for different -emitting transactinium isotopes. The method involves the preparation of a synthetic mixture using another isotope of the same element followed by the determination of atom ratio and -activity ratio by thermal ionization mass spectrometry and -spectrometry, respectively. A double dilution technique is described which helps in maintaining the atom ratios as well as -activity ratios close to unity so that these could be determined with high precision and accuracy. Results obtained on the half-lives of232U,238Pu,242Pu and243Am using double dilution technique in relative activity method are summarized. Requirements, advantages and applications of this technique for determining the half-lives of other transactinium isotopes are presented.
Determination of actinides in the environmental and bioassay samples is important in view of the following factors: increasing energy production by nuclear reactors; environmental contamination due to fallout from nuclear weapons testing and burn up of nuclear-powered satellites; the growing emphasis on the desirability of a cleaner environment; and public concern over the potential hazards associated with nuclear reactors. Among the various actinides, plutonium is one of the most important due to the large amounts produced in the nuclear fuel cycle. Further, the extremely low levels of plutonium in the different biological and environmental samples demand the development of precise, accurate, and sensitive methods to arrive at meaningful conclusions from the results obtained in various studies. In addition to various other techniques available, alpha spectrometry is commonly used.
Extraction of plutonium from analytical waste solutions containing phosphoric acid using a solution of monooctylphenylphosphoric acid (MOPPA) is described. Effect of reagent concentration, presence of uranium, plutonium loading and back extraction of plutonium from the organic phase are described. Using a solution of 0.05 F MOPPA in xylene, more than 90% plutonium could be extracted in one cycle.
A method based on the geometric progression decrease of the counts in the far tail of the alpha spectrum is described for the simultaneous determination of plutonium, americium and curium by alpha spectrometry. For evaluating the precision and accuracy, synthetic mixtures were prepared from solutions of enriched isotopes and sources were prepared by direct evaporation method using tetraethylene glycol /TEG/ as a spreading agent and electropolished stainless steel discs as the backing material. Precision and accuracy of about 1% is demonstrated in the determination of244Cm/239Pu,241Am/239Pu,244Cm/233U,241Am/233U and239Pu/233U alpha activity ratios using a 450 mm2 silicon surface barrier detector.
A method is described for the determination of uranium in the presence of iron and plutonium. Ti(III) is used as the reductant in a mixture of H2SO4 and HNO3. Fe(II) and Pu(III) are selectively oxidized by the nitrous acid generated in the reaction between Ti(III) and HNO3. The U(IV) is determined by titration with K2Cr2O7 using biamperometry to detect the end point. The method is applicable to a variety of nuclear materials encountered at different stages of the nuclear fuel cycle and has no bias. The precision of the method is evaluated at different levels from 100 microgram to 100 milligram. The method is simple, rapid and convenient.
Studies have been carried out on the solubility of Pu(III) oxalate by precipitation of Pu(III) oxalate from varying concentrations of HNO3/HCl (0.5–2.0M) solutions and also by equilibrating freshly prepared Pu(III) oxalate with solutions containing varying concentrations of HNO3/HCl, oxalic acid and ascorbic acid. Pu(III) solutions in HNO3 and HCl media were prepared by reduction of Pu(IV) with ascorbic acid. 0.01–0.10M ascorbic acid concentration in the aqueous solution was maintained as holding reductant. The solubility of Pu(III) oxalate was found to be a minimum in 0.5M–1M HNO3/HCl solutions containing 0.05M ascorbic acid and 0.2M excess oxalic acid in the supernatant.
An experimental evaluation of the recently available passivated ion-implanted detectors, which appear promising for high resolution -spectrometry, is presented in terms of % tail contribution per unit -activity ratio, peak to valley ratio, and resolution /FWHM/. The two IPE detectors with areas of 20 mm2 and 450 mm2 were used for comparing these parameters. It is seen that the smaller area detector provides a better resolution for single nuclide sources, but there is no significant difference for sources containing nuclides with close lying -energies, e.g.,239Pu,240Pu. Further, the large area detector gives less tail contribution and should be preferred to minimize the error in -activity ratio determinations. However, the small area detector offers a possibility of qualitative or semiquantitative determination of nuclides with close lying -energies.
Determination of239Pu/233U,241Am/233U and244Cm/233U alpha activity ratios is required when using233U as a tracer for the determination of plutonium, americium and curium by alpha spectrometry. Precision and accuracy in the determination of these alpha activity ratios was evaluated by preparing synthetic mixtures from solutions of enriched isotopes of239Pu,241Am,244Cm and233U. Separate synthetic mixtures were prepared for each of the three alpha activity ratios. The sources from the synthetic mixtures were prepared by direct evaporation method using tetra ethylene glycol /TEG/ as a spreading agent, alpha spectra were recorded by employing solid state silicon surface barrier detectors coupled to a 4 K analyzer and the alpha spectra were evaluated by a method based on the geometric progression decrease for the far tail of the spectrum. Large area detector /i.e. 450 mm2/ was observed to reduce the effect of nonhomogeneous distribution, if any, of the two elements present in the source. Precision and accuracy of about 1% is demonstrated for the determination of239Pu/233U,241Am/233U and244Cm/233U alpha activity ratios using large area silicon surface barrier detector.
Application of dicesium metaborate ion /Cs2BO
/ in Thermal Ionisation Mass Spectrometry /TIMS/ for the determination of boron present at sub ppm level in heavy water moderator as well as for the isotopic composition of boron in boron carbide is reported. Contamination of samples with natural boron while determining trace levels of boron in heavy water was checked by analysing SRM-952 isotopic reference material. The atom ratios of boron in B4C were determined by directly fusing the material on the tantalum filament with Cs2CO3 as well as with Na2CO3 and also by following the conventional fusion procedures and the results were compared.