Isotope Separation with Drift Tube, (I)

A new method of isotope detection and separation based on transport phenomena of ions in gases, which consist of a drift tube, is proposed and the analytical expression of resolution power of the method has been derived from a diffusion equation. The expression shows that the resolution power increases with the square root of the voltage supplied to the tube. A simple drift tube was constructed and natural Li was isotopically separated in Ne 100 Torr with the maximum resolution power, about 2. The variations of the resolution power with the applied voltage were measured by using the ion source of ⁶Li and ⁷Li separately and compared with calculations.     

Observation of Lithium Isotope Effect Accompanying Electrochemical Insertion of Lithium into Tin

Electrolysis of an organic electrolyte solution containing lithium ions was conducted to observe lithium isotope fractionation accompanying electrochemical insertion of lithium from the electrolyte to tin metal. The experimental setup consisted of a three-electrode electrolysis cell with a tin wire as cathode, lithium foils as anode and reference electrode and 1 M LiPF₆ dissolved in 1:2 volume ratio of ethylene carbonate and methylethyl carbonate as electrolyte and a power supply. The supplied electric energy was mostly consumed for the lithium insertion from the electrolyte to the tin cathode within the range of the cathode potential, relative to the reference electrode potential, from 0.05 V to 0.30 V. The single-stage separation factor increased with increasing cathode potential and seemed to asymptotically approach to the limiting value of 1.015 at 25®C, with ⁶Li being preferentially fractionated into tin metal.     

Cross Section Assessment by Measurement of Time Dependent Neutron Spectra from Lithium Assemblies

Time dependent neutron spectra from lithium assemblies were measured to assess the neutron cross sections of ⁷Li in ENDF/B-IV, which is important nuclide for the D-T fusion reactor blanket material. Pulsed neutrons produced by D-D or D-T reaction were used to measure leakage neutron spectra from cubical lithium assemblies as a function of time by the use of NE213 liquid scintillator. Calculations of time dependent neutron spectra were carried out by the Monte Carlo code SIMON, which was prepared for this study. The group constants used in these calculations were processed from ENDF/B-IV data. The calculated and the measured neutron spectra were compared for the following three; a stationary spectrum, spectra at each time interval and decay curves for specified energy groups. Discrepancies between the measured and the calculated neutron spectra were found in these comparisons. In order to assure the cause of these discrepancies, some calculations were carried out with recently measured cross sections of inelastic scattering which excite 0.478 and 4.63 MeV level of ⁷Li. It was concluded that some of the neutron cross section data of ⁷Li in ENDF/B-IV should be ameliorated.     

Lithium isotope effects upon electrochemical lithium insertion to host material from ionic liquid medium

Lithium was electrochemically inserted from a Li⁺ ion containing ionic liquid into graphite or tin to observe lithium isotope effects that accompanied the insertion. While no preferential uptake of the lithium isotopes was detected with graphite, the lighter isotope, ⁶Li, was preferentially fractionated into tin with the single-stage lithium isotope separation factors, S, ranging from 1.004 to 1.008 at 25 °C. It was speculated that a Li⁺ ion was inserted into graphite together with an anionic component of the ionic liquid and, upon the reduction of the Li⁺ ion to a lithium atom, the anion was released from graphite, while a Li⁺ ion alone was inserted into tin. Molecular orbital calculations supported this speculation in a qualitative fashion.     

Solvation of Lithium Ion in Organic Electrolyte Solutions and Its Isotopie Reduced Partition Function Ratios Studied by ab initio Molecular Orbital Method

To explore local structures around lithium ions and to estimate lithium isotopic reduced partition function ratios (RPFRs) ofsolvated lithium ions in ethylene carbonate (EC), methylethyl carbonate (MEC) and EC/MEC mixed solvent systems, ab initio molecular orbital calculations at the HF/6-31G(d) level of theory were carried out. Both EC and MEC were coordinated to lithium ions using their carboxyl oxygens and the Li-O bond distance increase with increasing solvation number up to 4 in the primary solvation sphere both in EC and MEC systems. Binding energy calculations suggested that EC was preferentially coordinated to the lithium ion in the EC/MEC mixed solvent system. RPFRs of solvated lithium ions were convex functions of the solvation number between 1 and 4 and took the maxima at 3 both in EC and MEC systems. The RPFR value in EC/MEC mixed solvent system was estimated to be 1.07818 at 25°C.     

Double-Differential Neutron Emission Cross Sections of 6Li and 7Li at Incident Neutron Energies of 4.2, 5.4, 6.0 and 14.2 MeV

Energy-angle double-differential neutron emission cross sections of lithium isotopes were measured at incident neutron energies of 4.2, 5.4 and 14.2 MeV for ⁶Li and of 5.4, 6.0 and 14.2 MeV for ⁷Li using a time-of-flight spectrometer. Care was taken in background subtraction and in data correction for sample-size effects. Detailed comparison of the present results was made with the evaluated data in JENDL-3PR1. A spectrum fitting method was used to extract the ^6,7Li(n, n'x)α and (n, 2n) reaction cross sections. Neutrons emitted from the (n, 2n) reactions were well described by the conventional evaporation model. A simple calculation with a final-state Coulomb interaction was effectively applied for the ^6,7Li(n, n'x)α reactions. Angle-integrated cross sections of the ⁷Li(n, n't)α reaction were in good agreement with the JENDL-3PR1 data except the data measured at 6.0MeV. The angular distributions of elastically and inelastically scattered neutrons were successfully analyzed with the coupled-channel method at the incident neutron energy of 14.2 MeV.     

Alkali Metal Ion and Lithium Isotope Selectivity of HZr2(PO4)3

HZr₂(PO₄)₃ has been synthesized by the heat treatment of NH₄Zr₂(PO₄)₃ and its properties as an ion exchanger have been examined with the main focus on its alkali metal ion and lithium isotope selectivity. The distribution coefficients for alkali metal ions revealed that HZr₂(PO₄)₃ was lithium ion-specific and showed little affinity toward potassium, rubidium or cesium ion. The lithium and sodium ion uptakes from aqueous solutions were monotonously increasing functions of pH. Isotopically, HZr₂(PO₄)₃ was ⁶Li-specific. Contrary to ion uptake, the lithium isotope effect was a monotonously decreasing function of pH; a larger separation factor was observed at a lower pH. This result was consistent with the existence of two different ion exchange sites formed in lithium ion-inserted HZr₂(PO₄)₃.     

Neutron multiplier alternatives for fusion reactor blankets

A proposal is made to replace the neutron multiplier in fusion reactor blankets by an efficient moderator (⁷LiH or ⁷LiD). The advantageous effect of the intensified neutron-energy degradation is due to the $\text{1}\text{v}$ character of the main tritium-producing reaction. The slowing-down medium is designed to be the source of moderated neutrons for the surrounding Li region where the most of the tritium is to be produced. The surplus tritium produced remains stored in the moderator zone. Some preliminary calculations illustrating the above concept were carried out, and the neutron flux and tritium production distributions are presented. Indications regarding further studies are also suggested.     

Stopping powers of C,Al, Ni,Cu, In,Sn, Ag and Au for 7Li ions of 1.0–4.7 MeV

Stopping powers for ⁷Li ions in selected target elements were determined for the energy range 2.0–4.7 MeV. This range was extended below 1.0 MeV for elements for which measurements were not available. A surface barrier detector was used to compare the energy loss of ⁷Li and ⁴He ions in thin, self-supported films. The ⁴He energy loss was taken as the measure of the film thickness. An energy dependence was confirmed for the ratio of the effective charges of lithium to hydrogen ions at the same velocity.     

Stopping powers of C,Al, Si,Ni, Ag and Au for 7Li ions

Absolute stopping values for ⁷Li ions in selected target elements were measured over the energy range 0.2–1.8 MeV. Surface barrier particle detectors were used to measure the energy loss of ⁷Li ions in passing through thin, self-supported films. The results show that in the slowing down process, the effective charge ratio of lithium to hydrogen ions, at constant velocity, is not independent of the stopping medium.     

Outgassing from alpha particle irradiation of lithium hydride and lithium hydroxide

We have experimentally studied the effects of α-particle radiation on isotopically enriched lithium hydride (⁶LiH) and its corrosion product lithium hydroxide (⁶LiOH) to determine, in particular, the type and amount of gases evolved during irradiation. SRIM Monte Carlo simulations suggest that irradiating these materials with 2.2-MeV α-particles will ionize atoms and form hydrogen vacancies in the target material, and that these α-particles will penetrate 13.5 and 9 μm into LiH and LiOH, respectively. Using an accelerator to irradiate LiH and LiOH with 2.2-MeV α-particles released only H₂ and CO₂; no other product gases were observed. At 25 °C, doses that simulated 66.5 years of actinide exposure (with accelerated fluxes) produced 2.3 × 10⁵ mol/(cm³ J) H₂ in LiH and 2.3 × 10⁶ mol/(cm³ J) H₂ in LiOH, in the form of a ∼9-μm-thick surface layer on LiH. More H₂ evolved from LiOH than from LiH. We argue that the production of H₂ gas was the result of radiolysis, rather than radiation-induced chemical reaction.     

Stopping powers of C, Al, Si, Ni, Ag and Au for Li ions

Absolute stopping values for ⁷Li ions in selected target elements were measured over the energy range 0.2–1.8 MeV. Surface barrier particle detectors were used to measure the energy loss of ⁷Li ions in passing through thin, self-supported films. The results show that in the slowing down process, the effective charge ratio of lithium to hydrogen ions, at constant velocity, is not independent of the stopping medium.     

Scattering of 14.1 MeV Neutrons by 6Li, 7Li, 9Be, 10B and 11B

Using a time-of-flight spectrometer, the differential cross sections were measured for the elastic and inelastic scattering of 14.1 MeV neutrons by ⁶Li, ⁷Li, ⁹Be, ¹⁰B and ¹¹B. In the case of elastic scattering by ⁷Li and ¹⁰B, correction was applied to subtract the contribution of inelastic scattering from the unresolved first excited state, after which, the elastic scattering data were compared with predictions based on the optical model. The potential parameters derived with a seven-parameter search yielded angular distributions agreeing with the present experimental data. The expressions for these parameters are presented as a function of mass number.

The experimental data on inelastic scattering were analyzed with the distorted wave Born approximation. The deformation parameters were estimated to be nearly equal to or larger than unity for these nuclei.     

Thermoluminescence measurements of neutron streaming through JET Torus Hall ducts

Thermoluminescence detectors (TLD) were used for dose measurements at JET. Several hundreds of LiF detectors of various types, standard LiF:Mg,Ti and highly sensitive LiF:Mg,Cu,P were produced. LiF detectors consisting of natural lithium are sensitive to slow neutrons, their response to neutrons being enhanced by ⁶Li-enriched lithium or suppressed by using lithium consisting entirely of ⁷Li. Pairs of ⁶LiF/⁷LiF detectors allow distinguishing between neutron/non-neutron components of a radiation field. For detection of neutrons of higher energy, polyethylene (PE-300) moderators were used. TLDs, located in the centre of cylindrical moderators, were installed at eleven positions in the JET hall and the hall labyrinth in July 2012, and exposure took place during the last two weeks of the experimental campaign. Measurements of the gamma dose were obtained for all positions over a range of about five orders of magnitude variation. As the TLDs were also calibrated in a thermal neutron field, the neutron fluence at the experimental position could be derived. The experimental results are compared with calculations using the MCNP code. The results confirm that the TLD technology can be usefully applied to measurements of neutron streaming through JET Torus Hall ducts.     

Ion beam analysis of partial lithium extraction of LiMn2O4 by chemical delithiation

Lithium manganese oxide, LiMn₂O₄, has been studied by many research groups. This material is a great candidate to be used as positive electrode in rechargeable lithium-ion batteries because of its low cost, abundant precursors and non-toxicity. LiMn₂O₄ has a spinel Fd-3m structure and shows a reversible extraction and insertion of lithium ions that is one of the most important characteristic of positive electrodes in rechargeable batteries.In this work, LiMn₂O₄ samples were synthesized by solid state reaction. A partial lithium removal was performed on this system by chemical delithiation using HCl aqueous solutions at different concentrations. Six partial-extracted compounds were obtained and characterized by Ion beam analysis (IBA) in order to obtain the Li concentrations. X-ray diffraction (XRD) and Rietveld analyses were also performed. A rigorous study of lithium contents is critical to analyze the structure properties of these compounds and samples production parameters. The IBA method used in this work was the analysis of energy spectra of elastic backscattered (EBS) proton from Mn, O and Li nuclei and the α-particles energy from the ⁷Li(p,α)⁴He nuclear reaction (NR).     

Chemical properties of element 104

Using a method of rapid continuous separation of elements of the side groups III and tV of the D. L Mendeleev Periodic System, developed by the authors of this work, the properties of the chlorides of curium, californium, hafnium, and the isotope 104²⁶⁰ were compared. The isotope 104²⁶⁰ had until now been identified only by physical methods. It was established that its chemical properties differ from those of the actinide elements and are close to those of hafnium. An independent confirmation of the atomic number of the new nucleus was obtained, and it was simultaneously demonstrated that the element 104 is a member of group IV. In the experiments, 12 atoms of the isotope 104²⁶⁰ were recorded.Translated from Atomnaya Énergiya, Vol. 21, No. 2, pp. 83–84, August, 1966.     

Production of Fluorine-18 by Small Research Reactor

High purity ¹⁸F was prepared by irradiating 1 g of lithium hydroxide or otherwise 0.14 g of enriched lithium carbonate containing 50% ⁶Li in the pneumatic tube of a TRIGA-II research reactor at a thermal neutron flux of 1.2×10¹² n/cm²-sec.

After cooling for 20 min, the irradiated lithium hydroxide was dissolved in distilled water. The resulting ¹³F was separated from the irradiated target by passing the lithium hydroxide solution successively through ion exchange columns of H-, OH- and H-forms. Use was also made of the Co- form ion exchange column in place of the H-form for the elimination of impurities. In the case of ⁶Li enriched lithium carbonate, the irradiated lithium carbonate was dissolved in hydrochloric acid, and ion exchange columns of Ag-, OH- and H-forms were used for purifying the ¹⁸F. The product ¹⁸F was obtained in the form of water containing ¹⁸F. The chemical yield for the purification of ¹⁸F was about 80 % and the final radioactive impurities were less than 1 ppm.

A neutron activation method for determining the isotopic abundance of ⁶Li was developed using the nuclear reactions ⁶Li(n, γ)³H and ¹⁶0(t, n)¹⁸F. Aqueous solutions containing lithium were irradiated in pneumatic tube for 1 hr. ¹⁸F was separated by steam distillation from the irradiated solutions and precipitated as magnesium fluoride. The chemical yield for the separation of ¹⁸F was about 80%. The sensitivity limit was estimated to be 4μ of natural lithium.     

Studies on Isotope Separation of Lithium by Electromigration in Fused Lithium Bromide and Potassium Bromide Mixture, (I) Enrichment of Lithium-7

Lithium-7 was enriched by electromigration at 500° C in fused LiBr-KBr mixture.

The migration cell was made of Pyrex glass; zircon sand (100–200 mesh) was used for packing material, and graphite rods as electrodes.

The electromigration was carried out for 13.4 days at a constant electric current of 165 mA.

The distribution of the abundance ratio of the Li isotopes and of the composition of the salt in the migration cell were investigated. The abundance ratio of the Li isotopes (⁷Li/⁶Li) in the anode compartment was found to change from the original value of 12.20 to 46.9. The composition (Li/K in chemical equivalent ratio) of the salt reached roughly constant at 1.41 throughout the migration cell except in the vicinity of the cathode, and the value was not affected by the composition of the feed salt. It is the selective transport of salt of this composition toward the anode compartment by capillary action in the migration cell that is considered the mechanism that makes sustained electromigration possible. The mechanism of the accumulation of the isotope effect is also discussed.     

Selectivity of Alkali Metal Ion and Lithium Isotopes on Ion Exchangers in H Form Prepared from LiTi x Zr2-x (PO4)3 (x=0, 1)

Inorganic metal (IV) phosphate-based ion exchanges in the hydrogen form, HTi _x Zr_2-x (PO₄)₃ (x =0, 1), have been prepared by leaching lithium ions from the precursors, LTi _x Zr_2-x (PO₄)₃ (x=0, 1), through ion exchange with protons. The degrees of leaching of lithium ion were more than 99%. Both ion exchangers showed high selectivity toward lithium and sodium ions and little affinity to rubidium and cesium ions among alkali metal ions. The lithium ion uptakes from aqueous solutions were monotonously increasing functions of pH. Isotopically, both ion exchangers were ⁶Li-specific like other inorganic ion exchangers so far examined. The ⁷Li-to-⁶Li isotopic single-stage separation factor, S, of HTiZr(PO₄)₃ was larger than that of HZr₂(PO₄)₃ at a given pH-value. The relatively large S-values of 1.022 and 1.042 were found for HZr₂ (PO₄)₃ for HTiZr(PO₄)₃, respectively, at 25°C when the pH of the solution phase was around 5.     

Hartree-Fock-Roothaan wavefunctions for diatomic molecules: I. First- and second-row hydrides AH,AH±, and AH1

Tables of electronic wavefunctions are presented for the diatomic hydrides AH where A denotes the elements Li through F and Na through Cl. The results are given for the exprimental (or theoretical) internuclear separation. These wavefunctions are approximate solutions to the restricted Hartree-Fock equations obtained by means of the expansion method with extensive basis sets of Slater-type-functions. The repertory of states includes the ground states of the systems indicated, a few low-lying excited states, and positive and negative ions. The calculations are restricted to states involving either closed-shell electronic configurations or open-shell configurations with one incompletely filled open shell. A brief introduction to the formalism and the key expressions for this and the two following paper⁴ are included.