R. K. Duggal

Comparative study of plutonium-239, plutonium-240 and plutonium-242 spikes for determining plutonium concentration by isotope dilution-thermal ionization mass spectrometry

Abstract An experimental evaluation of 239Pu, 240Pu and 242Pu spikes in terms of precision and accuracy for determining the plutonium concentration by isotope dilution-thermal ionisation mass spectrometry (ID-TIMS) in irradiated fuels is presented. Results obtained on different plutonium samples covering a wide range of burn-up values are given. Mean precision values of 0.1–0.2% are achieved by using any of the three spikes and factors close to unity are obtained for the ratios ID-TIMS(240Pu)/ID-TIMS(242Pu) and ID-TIMS(239Pu)/ID-TIMS(242Pu). This study shows that there is no significant advantage in using 240Pu spike when compared to 239Pu spike. Further, it is shown that the overall error (internal+external) obtained in replicate determinations of 242Pu/239Pu atom ratio is larger due to enhanced isotope fractionation compared to that in the case of 240Pu/239Pu atom ratio.

Experimental evaluation of plutonium-239 spike for determining plutonium concentration by isotope dilution-thermal ionization mass spectrometry

Abstract The use of 239 Pu as a spike in isotope dilution-thermal ionisation mass spectrometry (ID-TIMS) for determining the plutonium concentration in irradiated fuels is demonstrated. The method is based on the high precision better than 0.1% determination of the 240 Pu/ 239 Pu atom ratio in the sample, the spike, and the spiked mixture. The precision and accuracy of the results obtained on different plutonium samples using a 239 Pu spike are compared with those obtained using a 242 Pu spike. A mean precision of 0.1–0.2% is achieved using a 239 Pu or 242 Pu spike and a factor close to unity is obtained for the ratio ID-TIMS ( 239 Pu)/ID-TIMS ( 242 Pu). This study provides a viable alternative spike material to those laboratories which do not have access to enriched 242 Pu, which is generally used in determining the plutonium concentration by ID-TIMS, and at the same time, offers certain advantages over the use of a 242 Pu or 244 Pu spike.

A comparative study of different methods of preparation of sources for alpha spectrometry of plutonium

Abstract A comparative study of different methods of preparation of sources for alpha spectrometry of plutonium is presented. Typical values of the percentage tail contribution per unit alpha activity ratio 238 Pu /( 239 Pu + 240 Pu ) , fwhm and peak to valley ratios are given for (1) drop deposited sources from aqueous medium without using a spreading agent, (2) drop deposited sources from aqueous medium by using tetraethylene glycol (TEG) as a spreading agent, (3) drop deposited sources from organic medium using TTA extraction and (4) electrodeposited sources. Results obtained on the determination of 238 Pu /( 239 Pu + 240 Pu ) alpha activity ratios in isotopic reference material SRM-947 and in a synthetic mixture of plutonium isotopes using an AuSi surface barrier detector for recording alpha spectra and geometric progression (GP) method for the evaluation of alpha spectra are presented. It is seen that preparation of drop deposited sources from TTA involves minimum effort and the quality of alpha spectra from these sources is comparable to those from the electrodeposited sources. Further, it is recommended that the uncertainty on 238Pu in SRM-947 can be considered as 0.8% (3σ) compared to 2% quoted by the National Bureau of Standards.

Experimental evaluation of the characteristic features of passivated ion implanted and surface barrier detectors for alpha spectrometry of plutonium

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.

Determination of K-factors for isotope abundance measurements of uranium and plutonium by thermal ionisation mass spectrometry

K-factors (= certified isotope ratio/observed isotope ratio) are determined for the isotope abundance measurements of uranium and plutonium by thermal ionisation mass spectrometry. An mdf of 0.07% and 0.18% per mass unit differing by a factor of about 3, is obtained for uranium and plutonium, respectively, employing double rhenium filament assembly in the ion source and Faraday cup as the detector using the presently available isotopic reference materials of uranium and plutonium.

Precision and accuracy in the determination of plutionium-239 /uranium-233, americium-241/ uranium-233 and curium-244 /uranium-233 alpha activity ratios by alpha spectrometry

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.

Alpha spectrum evaluation method for the simultaneous determination of plutonium, americium and curium

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.

Simultaneous determination of the 235U/238U isotope ratio and concentration at nanogram levels of uranium employing a mixed spike in thermal ionization mass spectrometry

Abstract A method for the simultaneous determination of the 235U/238U isotope ratio (at 235U abundances close to that of natural uranium) and the concentration of uranium in the sample at nanogram levels of uranium using a commercially available thermal ionization mass spectrometer with secondary electron multiplier (SEM) detector is presented. The method depends on the use of a spike of 233U + 235U with about 4 at.% of 235U which is added to the unknown sample solution. This increases the ion current of 235U+ in the mass spectrometer, thereby facilitating the use of the peak integration option with peak centring each time during data acquisition for the 235U peak. The 235U/238U isotope ratio and the concentration or total amount of uranium in the sample are calculated from the data obtained on the 238U/233U and 235U/233U isotope ratios in the spiked mixture. An accuracy of better than 1% is demonstrated for the determination of the 235U/238U isotope ratio. This methodology will be useful for determining the abundances of the minor isotopes of different elements using the recently available multi-Faraday cup detector system. From the analyses of isotopic reference materials of uranium, the overall mass discrimination factor determined using a Faraday cup detector is 0.09% per mass unit which is due to the mass-dependent isotope fractionation in the ion source using the double rhenium filament assembly. The overall mass discrimination determined using SEM in the current mode at an operating voltage of 1.87 kV is 0.33% per mass unit, which leads to a contribution of 0.24% (= 0.33−0.09)% per mass unit due to the electron multiplier.

Determination of the plutonium concentration by Isotope Dilution Alpha-Spectrometry without purification from americium-241 and a bulk of other impurities

ZusammenfassungBei dem beschriebenen Verfahren der Isotopenverdünnungs-Alpha-Spektrometrie (IDAS) wird238Pu als Spike benutzt. Eine vorgeeichte Spike-Lösung wird zu einem bekannten Aliquot der Probe gegeben und anschließend die Strahlungsquelle unter Verwendung von Tetraethylenglykol als Spreading-Reagens vorbereitet. Die nach diesem Verfahren erhaltenen Ergebnisse werden in bezug auf Präzision und Genauigkeit mit solchen verglichen, die mit Isotopenverdünnungs-Massenspektrometrie unter Verwendung von242Pu als Spike oder mit IDAS unter Verwendung von Thenoyltrifluoraceton zur Reinigung erhalten wurden. Eine Präzision von 0,3–0,5% und eine Genauigkeit von 0,5% wurden erzielt. Durch das beschriebene Verfahren erübrigt sich eine Reinigung des Pu von241Am und anderen Verunreinigungen.SummaryA method is described for determining the plutonium concentration by Isotope Dilution Alpha Spectrometry (IDAS) using238Pu as a spike. It involves the addition of a pre-calibrated spike solution to a known aliquot of the plutonium sample solution followed by source preparation using TEG as a spreading agent. The results obtained on a number of samples using this method are compared with those of IDMS using242Pu as a spike as well as with those obtained by IDAS using TTA for purification, with respect to precision and accuracy. Precision of 0.3–0.5% and an accuracy of 0.5% is demonstrated. This method eliminates the need of any separation and purification of plutonium from241 Am and a bulk of other impurities.

Electrodeposition of milligram amounts of uranium on electropolished stainless steel disks

Investigations have been carried out for the electrodeposition of milligram amounts of uranium on electropolished stainless steel disks with an objective of preparing good quality sources for α-spectrometric studies on uranium. The parameters studied include the variation of electrodeposition yield as a function of voltage, time, distance between the cathode and anode, and the volume of 0.2M ammonium oxalate solution. The conditions selected for preparing good quality sources with nearly 100% yield were: electrodeposition voltage 25 V, time of deposition 15 min, volume of 0.2M ammonium oxalate solution in the cell 4 ml and a distance of 2 cm between the cathode and anode. The sources prepared using this method have been used successfully for the α-spectrometric determination of234U/238U ratios in uranium samples.