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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.

Relative Sensitivity Factors (RSFs) for the rare earth elements Ce, Nd, Sm, Eu, Gd, Dy, Er, and Lu have been determined in U3O6-graphite and pure graphite matrices under similar experimental conditions employing Spark Source Mass Spectrometry (SSMS) with electrical detection system in magnetic peak switching mode. The RSF values differ very much when the matrix element (uranium in U3 -graphite system or carbon in pure graphite) is the reference, But they show very good agreement when Er, one of the rare earth elements is chosen as internal standard. The literature data on RSF values for the rare earth elements in Y2O3 as well as Al matrices are compared with those obtained in the present work. An attempt has been made to explain the similar trend in the RSF values in all these Matrices in terms of the decomposition pattern of the rare earth oxides. An empirical equation relating the RSFs with the decomposition energies of the lanthanide sesquioxides and monoxides has been shown to be useful in co...

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.

The temperature dependence of the energy loss of 624-keV electrons in ferroelectric barium titanate (${\mathrm{BaTiO}}_{3}$) and triglycine sulfate [(${\mathrm{CH}}_{2}$${\mathrm{NH}}_{2}$COOH${)}_{3}$ ${\mathrm{H}}_{2}$${\mathrm{SO}}_{4}$] has been studied with the use of a single-gap magnetic spectrometer. The present measurements confirm the anomalous increase in energy loss of electrons near the Curie temperature ${T}_{C}$ and indicate its dependence on (a) the magnitude of the dielectric anomaly at ${T}_{C}$, (b) the effect of a dc electric field larger than the coercive field, and (c) the application of an alternating electric field. Probable mechanisms for the origin of the observed phenomenon are discussed.

A method is described for the determination of plutonium concentration in the presence of a bulk of other impurities by isotope dilution mass spectrometry /IDMS/ using239Pu as a spike. The method involves the addition of239Pu spike /≥ 90 atom%/ to samples with239Pu /≤ 70 atom%/ and vice versa. After ensuring chemical exchange between the sample and the spike isotopes, plutonium is purified by conventional anion exchange procedure in 7M HNO3 medium.239Pu/240Pu atom ratio in the purified spiked sample is determined with high precision /better than 0.1%/ using a thermal ionization mass spectrometer. Concentration of plutonium in the sample is calculated from the changes in239Pu/240Pu atom ratio in the spiked mixture. Results obtained on different plutonium samples using239Pu as a spike are compared with those obtained by the use of242Pu spike. Precision and accuracy comparable to those achieved by using242Pu are demonstrated. The method provides an alternative in the event of non-availability of enriched242Pu or244Pu required in IDMS of plutonium and at the same time, offers certain advantages over the use of242Pu or244Pu spike.

The half-lives and g-factors of high-spin states in 199,201,203pb were studied using 199,200,202Hg(α, 3n) reactions at Eα =41 and 53 MeV. In-beam γ-ray spectroscopy including γγt-coincidence measurements were performed in order to interpret the level schemes. The measured half-lives are T 1 2 = 7.5 (3) ns , 10.0 (2) μ s and 55 (5) ns for the previously known 25 2 − , 29 2 − and 33 2 + states, respectively, in 199 Pb and T 1 2 = 508 (5) ns and 63 (3) ns for the 29 2 − and the 25 2 − states, respectively, in 201Pb. A new isomer at 4559.2 + ° keV excitation energy with T 1 2 = 43 (3) ns and J π = 41 2 + is observed in 201Pb and a 33 2 − isomer at 2922.7 + Δ keV exitation energy with T 1 2 = 122 (4) ns in 203 Pb . The g-factors of the isomeric states were determined using the time differential perturbed angular distribution technique and the results are g( 29 2 − ) = −0.0742 (2) and g( 29 2 − ) = −0.0697 (4) for the 29 2 − states in 199Pb and 201Pb, respectively, indicating a predominantly three-neutron-hole configuration i −2 13 2 f −1 5 2 for these states. The g-factor of the 33 2 + state in 19 as g= −0.145(9) which agrees with a ν( i 13 2 −3 ) configuration. The g-factor of the 41 2 + sta g( 41 2 + ) = −0.18 (4) indicates a five-quasiparticle configuration. The probable configuration for the 25 2 − isomer has also been suggested on the basis of the measured value of the g-factor g( 25 2 − ) = −0.063 (3) in 201Pb and g( 25 2 − ) = −0.059 (3) in 203Pb and the B(E2) values for t 25 2 − → 21 2 − transitions in the odd Pb isotopes.

A multicomponent plasma consisting of two-ion species having different mass and temperature is considered. Linear and non-linear dispersion relations have been derived. These are used to study the effect of turbulent fluctuations on the plasma resistivity. Results have been applied to the cases of a hydrogen-helium and a hydrogen-argon mixture. It is seen that the resistivity increases or decreases significantly with the addition of a light ion impurity depending upon temperature and mass ratio.

Investigations were carried out on the determination of isotopic composition of boron using Cs2BO 2 + ion and thermal ionisation mass spectrometry. The results show distinct advantage over the normally used Na2BO 2 + ion.

Relative activity method offers the potentiality of providing half-life values over a wide range in a short time for different α-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 α-activity ratio by thermal ionization mass spectrometry and α-spectrometry, respectively. A double dilution technique is described which helps in maintaining the atom ratios as well as α-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.

Application of Spark Source Mass Spectrometry(SSMS) for the determination of hydrogen in zircaloy clad material used in nuclear reactors is reported. The advantage of SSMS lies in the fact that along with the metallic trace constituents even the nonmetallics including the gaseous impurities can also be determined in a single analysis using the photoplate detection system. The value obtained for H2 using photoplate detection system is compared with that obtained in electrical detection system in SSMS and also with the value obtained employing the conventional inert gas fusion technique.

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.

The sensitivity calibration factor commonly expressed as relative sensitivity coefficient (RSC) is used in quantitative spark source mass spectrometry. The RSC was studied from the viewpoint of element-sensitive physicochemical properties and a linear correlation was attempted. Statistical analysis of the experimental data was carried out to justify the linear correlation. This permits quantitative spark source mass spectrometric analysis of trace constituents whose relative sensitivity coefficients have not been experimentally determined. The variation of RSC with respect to specific element-sensitive properties was shown to be the same for certain oxide/graphite-type matrices.

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.

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.

Effect of ion-tail formation on the resistivity of a plasma in the presence of ion-acoustic instability has been studied. It is found that the resistivity is significantly modified due to ion-tail formation. The effect is particularly significant for higher fluctuation levels. The variation of the drift velocity, ion tail population, and resistivity as function of Ti/Te is investigated for different fluctuation levels and the results have been presented graphically. Conservation of momentum and energy is also checked.

The half-life of /sup 243/Am was determined by the relative activity method. Synthetic mixtures were prepared by using solutions of /sup 241/Am and /sup 243/Am isotopes. The ..cap alpha.. activity ratios and the atom ratios in these mixtures were kept close to unity by employing the double dilution technique so that these could be measured with high precision and accuracy. The ..cap alpha.. activity ratios were determined by ..cap alpha.. spectrometry on electrodeposited sources using a silicon surface barrier detector and the atom ratios were obtained by mass spectrometry. A value of 17.010 +- 0.095 was obtained for the /sup 243/Am//sup 241/Am half-life ratio which leads to a value of 7358 +- 42 yr for the half-life of /sup 243/Am using the half-life of /sup 241/Am as 432.6 yr. The uncertainty specified on the values is a combination of the one standard deviation on the average value and the error evaluated from the estimate on the various error components.

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.

The yrast structure of 200,202Pb was studied using the 200,202Hg(α, 4n) reactions at Eα = 53 MeV. The de-excitation of the excited states was studied using conventional in-beam γ-ray spectrosopic methods including γγ(t) coincidence, pulsed-beam γ(t) and angular distribution measurements. Levels with a possible spin up to 21 ħ were observed in both nuclei. In addition to the previously known isomers, a 16+ isomeric state at 4069.8 + δ keV with T 1 2 = 5(1) ns and a 19 − isomeric state at 4932.0+ e keV with T 1 2 = 67 (5) ns were observed in 200Pb. A new 19−isomeric state at 5241.9 + S keV with T 1 2 = 107 (5) ns was also observed in 202Pb. The g-factors of the isomeric states were determined using the time differential perturbed angular distribution technique and the results are g = −0.094 (7) and g = −0.099 (3) for the 19− states in 200Pb and 202Pb, respectively. The measured g-factors indicate a predominantly four-quasineutron configuration ν f 5 2 −1 i 13 2 −3 for the 19− isomeric states.

Expressions for anomalous resistivity and energy transfer collision frequency in the presence of ion-acoustic instability have been derived. It is found that the rapid electron heating may be attributed to the flattening of the top of the electron distribution function to a high degree. Results are valid under the situation when krrc « 1 where τc is the correlation time for turbulence.

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.

A direct evaporation method is described for the preparation of sources using stainless steel as the backing material and tetraethylene glycol (TEG) as a spreading agent in the presence of large amounts of uranium. It is shown that FWHM and tail contribution at the low energy peak due to energy degradation of the high energy peak can be optimized by heating the source under controlled conditions in a furnace at 500–600°C for about 15 min. An accuracy of 0.5–1% is demonstrated for the determination of238Pu/(239Pu+240Pu) alpha activity ratio in the U/Pu range of 10 to 1500 generally encountered in dissolver solution of irradiated fuel.

In-beam nuclear spectroscopic studies of182Re, following the reaction181Ta(α, 3n)182Re have been made using gamma-ray and internal conversion electron techniques.K-conversion coefficients for several transitions have been measured and the multi-polarities of the various transitions assigned. In particular, the spin and parity of the four-quasi-particle isomeric level at 2256 keV were determined to be 16−. Theg-factor of this level has been measured to beg = 0·32 ± 0·05. On the basis of theg-factor and the decay pattern of this level, a configuration {v9/2+ [624↑]v7/2− [514↓]v7/2− [503↑]π9/2− [514↑]} k x = 16− has been assigned to this level. The nature of the retardation of the gamma transitions deexciting this level is discussed. It is argued that the measured retardation factors can be explained if the nucleus has a triaxial shape.

The anisotropy of the 133–182 keV γ-γ cascade in181Ta measured as a function of temperature between 70K and 298K shows lattice instability, the phenomenon of hysteresis in the vicinity of the lattice transformation temperature (TL) and a temperature dependent electric field gradient (EFG) at the cubic Hf sites in the superconducting cubic Laves phase (C15) compounds Hf1−xZrxV2 (x=0.0, 0.25 and 0.75). These observations are qualitatively understood by assuming the presence of γ-recoil effects and microdomains fluctuating between the high temperature (T>TL) and the low temperature (T < TL) phases of these compounds.

The intensity of carbon clusters in an rf-spark source was investigated in four different matrices. The periodicity of cluster formation in pure graphite could not be significantly observed in other matrices. Also, the abundance of lower clusters C 2 + and C 3 + was found to depend on the mass number of the major element present in the matrix. Interpretation of these results led to the consideration of sputtering of the electrode material by ion bombardment as a possible mechanism for cluster formation followed by their redistribution in the vapour phase through an irreversible momentum transfer resulting in larger abundance of lower clusters.

The g-factor of the high-spin K-isomer at 2256.3 keV in 182Re has been measured through the in-beam time differential perturbed angular distribution technique. The measured value of the g-factor g = +0.239(8) indicates a four-quasiparticle configuration involving one proton and three neutron Nilsson states as opposed to previous assignments. The isomeric half-life, remeasured as T 1 2 =82(1) ns , corresponds to an unusually low K-hindrance factor. The decay mode of the isomer is discussed in connection with possible triaxiality.

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.

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.

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.

The 245 keV (5/2+) state in 111Cd has been used as a probe to study the lattice instability at the V site in the superconducting compound HfV2. The temperature dependence of the electric quadrupole interaction frequency omega 0 has been understood by assuming the presence of soft-phonon modes, the gamma -recoil effects and a small (about 1%) increase (decrease) in the charge at the V (Hf) site above the lattice transformation temperature TL approximately=120 K. A high-temperature phase transition has also been observed in HfV2 at T approximately=520 K.

The temperature dependence of the electric quadrupole interaction frequency ω l o , experienced by the181Ta probe occupying Hf site in the compounds Hf1-xTaxV2 has been measured for x=0.06, 0.10 and 0.20 in the temperature region between 8.5 K to 296 K. The measurements show lattice transformation in all the three compounds below 120 K.

The ion yield distribution of elements with respect to charge in the beam produced from an rf-spark ion source has been studied for eight matrices. The thermochemical behaviour of the elements as well as the features of the matrix plasma are found to be the key factors. It is shown that the consideration of charge distribution helps to improve the precision of the spark source mass spectrometric analysis. It is argued that, in the course of the development of the matrix plasma, the vaporised particles in the sparking zone undergo element-sensitive multiple ionization. It is further concluded that, during the process of expansion of the plasma into the vacuum, the ions of different elements suffer different rates of recombination. Thus, the ionization energy available per particle controls the charge distribution of the elements in the plasma while the abundances of ions according to charge in the beam are regulated by the average energy available per particle and different recombination rates.

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.

Isotope Dilution Alpha Spectrometry (IDAS) and Reverse Isotope Dilution Alpha Spectrometry (RIDAS) have been developed for determining the concentration of plutonium in the irradiated fuel dissolve...

The half-life of /sup 241/Pu was determined by studying the ingrowth of /sup 241/Am in two independent sets of experiments: (i) by ..cap alpha.. spectrometry taking /sup 242/Pu as well as /sup 239/Pu and /sup 240/Pu as reference isotopes, and (ii) by ..cap alpha.. proportional counting. In these experiments, separate synthetic mixtures, prepared by mixing different isotopes of plutonium, were used with an objective of obtaining periodically a desired change in the ..cap alpha.. activity ratio (as in ..cap alpha.. spectrometry) or in the total ..cap alpha.. activity (as in ..cap alpha.. proportional counting) and to measure this change with high precision and accuracy. In ..cap alpha.. spectrometry, from the 65 measurements carried out on five electrodeposited sources over a period of 574 days, a value of 14.37 +- 0.09 yr was obtained for the half-life of /sup 241/Pu. In the ..cap alpha.. proportional counting, from the 20 measurements carried out on five sources over a period of 704 days, a value of 14.50 +- 0.08 yr was obtained. The average of these two independent determinations leads to a value of 14.44 +- 0.06 yr for the half-life of /sup 241/Pu. The uncertainty quoted on the values is a combinationmore » of one standard deviation on the average value and the error evaluated from estimates on various error components. The half-life obtained in this work is in good agreement with the results reported earlier from this laboratory by ..cap alpha.. spectrometry, taking /sup 239/Pu and /sup 240/Pu as reference isotopes as well as with the preliminary results reported by other laboratories using different methods.« less

Magnetic hyperfine interactions in highly stripped oxygen ions recoiling in vacuum have been measured with perturbed angular correlations. The second excited state of16O(I π=3−,E X=6.13 MeV, τ=26.6 psec, |g|=0.55) was produced with the nuclear reactions19F(p,α)16O and16O(α,α′)16O and the angular correlation of the γ-rays observed in coincidence with α particles emitted at 180°. Five recoil velocities between 1.0 and 3.3% c produced average ion charge states from 2.1 to 5.5. The perturbation of the angular correlation and hence the decoupling of the hyperfine interactions was observed as a function of an external axial magnetic field varied between 0 and 33 kG. The perturbation is expected to arise primarily from hyperfine interactions of unpaired 1s electrons with smaller contributions from 2s electrons and other configurations. The maximum external field was strong enough to decouple all hyperfine interactions except that of the 1s electrons. The decoupling curves obtained were successfully fitted by calculations using the hyperfine interactions of the pertinent atomic Hartree-Fock-Slater orbitals.

The input end of a reprocessing plant is the first point in the fuel cycle where the plutonium produced in reactors can be accurately measured. The current practice for measuring the plutonium entering a reprocessing plant is to determine the total amount of this element in each batch in an accountability tank by the volume concentration method. This involves the measurement of the concentration of plutonium in the sample and the volume, density, and temperature of the solution in the tank; each of these measurements contributes to the total error in the input accountability measurement. Other approaches being studied are the Pu/U ratio method and the isotope correlation technique. These depend heavily on data from the fabrication plant and the reactor and require a good estimate of the losses through hulls. Through developing tracer techniques for the input accountability of plutonium in reprocessing plants, two tracers have been identified and tested: magnesium and lead. The corresponding techniques have been named MAGTRAP (Magnesium Tracer technique for the Accountability of Plutonium) and LEADTRAP (Lead Tracer Technique for the Accountability of Plutonium). The method involves the addition of a known amount of tracer to the input accountability tank and the subsequent measurement of more » the plutonium-to-tracer ratio in a sample of the tank solution. By knowing the amount of tracer element added, the total amount of plutonium in the tank can be obtained. The validity of this technique has been established by a series of experiments in the input accountability tank of a reprocessing plant. Accuracies of better than 1% are attainable by this method. « less

The electric quadrupole interaction at the Hf site in the cubic HfV2 compound, which shows lattice instability when cooled below 120 K, has been studied using the 482 keV (5/2+) state in181Ta. The time differential perturbed angular correlation (TDPAC) studies involving (133+136)-482 keV γ-γ cascade at room temperature show that only a fraction of181Ta nuclei see a cubic symmetry while the remaining experience a weak, randomly oriented, electric quadrupole interaction described by a Gaussian frequency distribution with ωQ=6.1±1.0 Mrad/sec and the relative width δ=0.5. There is a dramatic change in TDPAC pattern indicating a phase transition when the compound is cooled down to 77 K. At this temperature the quadrupole interaction frequency is found to be ωQ=40.6±3.0 Mrad/sec with δ=0.35. The experimentally observed EFG both at the Hf and the V sites are compared to the theoretical estimates based on ‘point charge model’.

The decoupling experiments involving the time-differential perturbed angular correlation (TDPAC) of the 133–482 keV γ-γ cascade in the presence of an external magnetic field applied along the quantization axis have been performed to measure the electric quadrupole and the magnetic hyperfine interactions experienced by the181Ta nuclei at Hf sites in the pseudobinary compounds HfFe2-xSix, withx=0.1 andx=0.3. The hyperfine magnetic fields measured at 298 K areHhf=133.1±12.0 kG in the cubic (C15) Laves phase compound HfFe1.9Si0.1 andHhf=76.8±7.0 kG in the hexagonal (C14) Laves phase compound HfFe1.7Si0.3. The decoupling technique has also been used to obtain a —ve sign for the hyperfine field experienced by181Ta nuclei at the Ti or Hf sites in the Heusler compound Co2Ti0.8Hf0.2Sn and a+ve sign for the hyperfine field at Zr sites in the cubic (C15) Laves phase compound ZrFe2.

Magnesium and lead have been identified as tracers for the input accountability of plutonium in reprocessing plants where'as fission product 148Nd is used as a burn-up monitor. Ion exchange procedures developed for the separation and purification of Mg, Pb, and Nd from the dissolver solution of irradiated fuel for their mass spectrometric analyses are presented. Distribution ratio curves of Pb, Ce, Nd, and Sm in CH3OH-HNO3-H2O medium used in the development of the separation and purification procedure are also shown.

Application of dicesium metaborate ion /Cs2BO 2 + / 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.

A gamma-spectrometric method using an intrinsic high resolution germanium detector has been developed for the determination of isotope ratios of plutonium from samples in solution form. The method is based on the assay of low energy gamma-rays of238Pu,239Pu,240Pu and241Pu and does not require the use of branching intensities or the knowledge of detection efficiencies for different gamma rays. Since low energy gamma-rays are used, the effect of241Am has also been studied. It is found that results are not affected up to 0.5 wt% of241Am in plutonium samples. An accuracy of 3% is achievable in the determination of240Pu/239Pu and241Pu/239Pu atom ratios as demonstrated by carrying out measurements on isotopic standards of plutonium.

The half-life of /sup 242/Pu was measured relative to the half-lives of /sup 239/Pu and /sup 238/Pu in two independent sets of experiments. Synthetic mixtures were prepared using enriched isotopes of /sup 238/Pu, /sup 239/Pu, and /sup 242/Pu. The ..cap alpha.. activity ratios in these mixtures were determined by ..cap alpha.. spectrometry on electrodeposited sources using a silicon surface barrier detector while the atom ratios were obtained by mass spectrometry. The ..cap alpha.. activity ratios and the atom ratios were so chosen that these could be measured with a high precision and accuracy. A half-life value of (3.742 +- 0.024) x 10/sup 5/ yr is obtained using the half-life of /sup 239/Pu as 24110 yr. The value obtained using the half-life of /sup 238/Pu as 87.74 yr is (3.766 +- 0.025) x 10/sup 5/ yr. The average of these two independent sets of experiments leads to a half-life value of /sup 242/Pu as (3.754 +- 0.025) x 10/sup 5/ yr. The uncertainty given on the values is a combination of the one standard deviation on the average value and the error evaluated from estimates on various error components. The discrepancy existing in the earlier published values for the half-life ofmore » /sup 242/Pu determined relative to the half-lives of /sup 239/Pu and /sup 238/Pu is resolved.« less

The yields of different probable homo- and heteronuclear M+n ions due to a given multi-isotopic element M and a given value of n in the ion beam produced from an r.f.-spark ion source have been measured for eleven elements using different matrices. For each of the elements carbon, chlorine, potassium, strontium, antimony, tellurium and barium, the abundance distribution of M+n ions for given M and n in the recorded ion beam follow the statistical abundance distribution governed by , where xi is the fractional isotopic abundance of the ith isotope of the element (M). However, among the elements studied a divergence from the statistical prediction is observed for a few other elements such as nickel, zinc and especially molybdenum. That the matrix plays an important role is implied in the studies of Ag+2 ions using the matrices of silver alone and a mixture matrix of silver and graphite. The yield distribution of Ag+2 ions among its two homonuclear (107Ag+2 and 109Ag+2) and heteronuclear (107Ag109Ag)+ component ions in the beam from silver metal matrix obeys the statistical model, , while this is not true for silver graphite matrix.