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.
Authors:V. Shivarudrappa, P. Mithapara, and H. Jain
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.
Authors:P. Nair, K. Lohithakshan, Mary Xavier, S. Marathe, and H. Jain
A method is described for the sequential determination of uranium and plutonium in plutonium bearing fuel materials. Uranium and plutonium are reduced to U(IV) and Pu(III) with titanous chloride and then titrated with dichromate to two end points which are detected amperometrically using two polarized platinum electrodes. Uranium-plutonium solutions of known concentrations containing plutonium in the proportions of 4, 30, 50, and 70% were analyzed with precisions better than 0.3%, maintaining the amounts of plutonium per aliquot in the range of 2–10 mg. No significant bias could be detected. Several samples of (U, Pu)O2 and (U, Pu)C were analyzed by this procedure. The effects of iron, fluoride, oxalic acid and mellitic acid on the method were also studied.
Authors:S. Aggarwal, R. Duggal, P. Shah, R. Rao, and H. Jain
Experimental evaluation of a commonly used silicon surface barrier detector and of the recently introduced passivated ion implanted detector for alpha spectrometry is reported in terms of FWHM, peak to valley ratio, tail parameter and % tail contribution per unit alpha activity ratio using electrodeposited sources of plutonium prepared on platinum backing material. For this purpose, detectors of nearly the same diameter were employed (100 mm2 silicon surface barrier detector with a diamater of 1.13 cm and 80 mm2 passivated ion implanted silicon detector with a diameter of 1.01 cm). It is shown that the recently introduced passivated ion implanted detectors give smaller tailing effects. But there is no significant difference between the two detectors used in the present work w.r.t. FWHM and peak to valley ratios. Further, it is observed that the peak to valley ratio can be used to get an idea about240Pu/239Pu and241Am/238Pu alpha-activity ratios in the sample.
Authors:S. Hasilkar, N. Gopinath, Keshav Chander, S. Marathe, and H. Jain
A method based on the complexometric titration of thorium using ethylene diaminetetra-acetic acid (EDTA) as complexant has been developed for the determination of thorium in thorium-plutonium solution without resorting to prior separation of plutonium. Plutonium in the form of Pu(VI) does not affect the thorium determination when present up to 10% in thorium—plutonium solution. For oxidation of plutonium to Pu(VI), HClO4 or AgO was used. HClO4 is preferred. The thorium values obtained without prior separation of plutonium are compared with those obtained after separating plutonium by anion exchange technique. A precision of ±0.5% has been obtained for 5–10 mg of thorium in the aliquot.
Authors:K. Ramakumar, V. Raman, V. Sant, V. Kavimandan, and H. Jain
Determination of trace impurities in zircaloy-2 and tellurium by Spark Source Mass Spectrometry (SSMS) is reported. The advantage of SSMS lies in the fact that along with metallic trace constituents even the nonmetallic impurities and gases including hydrogen can also be determined.
Authors:Mary Xavier, P. Nair, K. Lohithakshan, S. Marathe, and H. Jain
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.