7Li Ions Research Articles

Identification of heavy ions by imaging individual particle tracks in CF4-filled gas scintillation detectors

We propose a novel method for identification of heavy charged particles, based on the principle that the distance between the Bragg peak position and the terminal position (Dpt) of an energetic ion track varies with the specie of the heavy charged particle. Online measurements can be achieved by imaging individual particle tracks in CF4-filled gas scintillation detectors using a real-time scientific camera. By calculating the integration of the image intensity along the recorded track, experimental Bragg curves can be obtained and then Dpt values can be extracted promptly. Proof-of-principle experiments have been performed with 6.30 MeV 1H, 5.49 MeV 4He, and 46.50 MeV 7Li ions. A number of clear individual ion tracks were imaged and analyzed, with the satisfactory results that both the type and energy of each ions were identified precisely, demonstrating good identification capability of the proposed method. Therefore, this study is of particularly importance not only in methodology but also in practical for online identification of heavy charged particles in many fields such as space radiation detection and nuclear reaction diagnostic experiments.

(Invited) Lithium Recovery and Lithium-6 Enrichment Using Innovative Electrodialysis with Lithium Ionic Conductor Membrane

As a means of addressing global warming, the world is increasingly turning to the use of Li-ion batteries in electric vehicles and as storage batteries in the home; therefore, there is a growing need for Li. Furthermore, as a fuel for fusion reactors, tritium is produced by the reaction of lithium with neutrons in a tritium-breeding material. Li is primarily recovered from salt lakes in South America but is also present in seawater. Thus, I propose a method for recovering Li from seawater by using innovative dialysis, wherein Li only permeates from the negative electrode side to the positive electrode side through a Li ionic superconductor functioning as a Li separation membrane (LISM) (Fig.1). Measurements of the Li ion concentration at the positive electrode side as a function of dialysis duration showed that the Li recovery ratio increased to approximately 7% after 72 h with no applied electric voltage, and an electrical power of 0.04 V and 0.1 mA was generated. Moreover, other ions in the seawater did not permeate the LISM. With both ends of the LISM bound with a negative and positive electrode, hydrated Li ion was transformed to Li ion only because Li ion can permeate through the LISM [1]. Furthermore, tritium needed as a fuel for fusion reactors is produced via neutron capture by lithium-6 (6Li). However, natural Li contains only about 7.8% 6Li, and enrichment of 6Li up to 90% is required for adequate tritium breeding in fusion reactors. Therefore, new Li isotope separation technique using a Li ionic rconductor functioning as a LISM have been developed. Because the mobility of 6Li ions is higher than that of 7Li ions, 6Li can be enriched on the cathode side of a cell. Using Li0.29La0.57TiO3 (LLTO) as the Li ionic superconductor was prepared, and the relationship between the 6Li separation coefficient and the electrodialysis time was investigated. After electrodialysis, we obtained a maximum of 1.05 for the 6Li isotope separation coefficient. This result showed that the 6Li isotope separation coefficient of this method is the same as that of the amalgamation process using mercury (1.06). Thus, this method has the potential to be a superior 6Li enrichment method to produce 90% enriched tritium breeder for fusion reactors. [1] T. Hoshino, Desalination, 359, 59-63 (2015). Figure 1

Innovative Separation Technology for Lithium-6 Enrichment Using Electrodialysis with Lithium Ionic Superconductor

Tritium needed as a fuel for fusion reactors is produced via neutron capture by lithium-6 (6Li). However, natural Li contains only about 7.8% 6Li, and enrichment of 6Li up to 90% is required for adequate tritium breeding in fusion reactors. The mercury amalgam method is superior to some of the lithium isotope enrichment methods. In Japan, lithium isotope enrichment methods have been developed to avoid the environmental hazards of using mercury. However, the isotope separation coefficient and efficiency is too low to meet the practical need of large mass production of 6Li. Therefore, new Li isotope separation technique using a Li ionic superconductor functioning as a Li isotope separation membrane (LISM) have been developed [1]. Li ions move by electrodialysis through LISM between the cathode and the anode in lithium solutions. Because the mobility of 6Li ions is higher than that of 7Li ions, 6Li can be enriched on the cathode side of a cell. It has been reported that the difference in the mobility between 6Li and 7Li become large in ionic superconductor. The isotope effect in ionic superconductor is expected to be applicable to isotope separation membrane. In this research, we numerically investigated the ionic mobility of Li isotopes in ionic superconductor. Combing the first principle and the kinetics Monte Calro simulation, we calculate the diffusion constant of 6Li and 7Li. I show the two important effects for the difference in the mobility between isotope of Li. The first is the quantum effect, which decrease the diffusion barrier for Li ion and increase the ratio of the diffusion constant of Li isotopes. The second is the correlation effect between 6Li, 7Li and vacancy. Using Li0.29La0.57TiO3 (LLTO) as the Li ionic superconductor was prepared, and the relationship between the 6Li separation coefficient and the electrodialysis time was investigated. After electrodialysis, we obtained a maximum of 1.04 for the 6Li isotope separation coefficient. This result showed that the 6Li isotope separation coefficient of this method is the same as that of the amalgamation process using mercury (1.06). Thus, this method has the potential to be a superior 6Li enrichment method to produce 90% enriched tritium breeder for fusion reactors. Figure 1

Research progress and stress-induced variation of DNA methylation in plants

Chemical modification of DNA bases in recent years has been one of the hot areas of life science research. DNA methylation is a common epigenetic phenomenon and can change the genetic performance without changing the DNA sequence. Various stress factors can induce the variation of DNA methylation in plants, but the response mechanism is still unknown. In this paper, the progress of DNA methylation in plants was reviewed. In combination with the researchconclusions of our own research group, the DNA methylation variation induced by 7Li ion beam and gamma ray was reported to provide a basis for DNA methylation, which may be involved in the phenotypic plasticity of plants.

Distributions of deposited energy and ionization clusters around ion tracks studied with Geant4 toolkit

The Geant4-based Monte Carlo model for Heavy-Ion Therapy (MCHIT) was extended to study the patterns of energy deposition at sub-micrometer distance from individual ion tracks. Dose distributions for low-energy 1H, 4He, 12C and 16O ions measured in several experiments are well described by the model in a broad range of radial distances, from 0.5 to 3000 nm. Despite the fact that such distributions are characterized by long tails, a dominant fraction of deposited energy (∼80%) is confined within a radius of about 10 nm. The probability distributions of clustered ionization events in nanoscale volumes of water traversed by 1H, 2H, 4He, 6Li, 7Li, and 12C ions are also calculated. A good agreement of calculated ionization cluster-size distributions with the corresponding experimental data suggests that the extended MCHIT can be used to characterize stochastic processes of energy deposition to sensitive cellular structures.

Hybrid superconducting neutron detectors

A neutron detection concept is presented that is based on superconductive niobium (Nb) strips coated by a boron (B) layer. The working principle of the detector relies on the nuclear reaction, 10B + n → α + 7Li, with α and Li ions generating a hot spot on the current-biased Nb strip which in turn induces a superconducting-normal state transition. The latter is recognized as a voltage signal which is the evidence of the incident neutron. The above described detection principle has been experimentally assessed and verified by irradiating the samples with a pulsed neutron beam at the ISIS spallation neutron source (UK). It is found that the boron coated superconducting strips, kept at a temperature T = 8 K and current-biased below the critical current Ic, are driven into the normal state upon thermal neutron irradiation. As a result of the transition, voltage pulses in excess of 40 mV are measured while the bias current can be properly modulated to bring the strip back to the superconducting state, thus resetting the detector. Measurements on the counting rate of the device are presented and the basic physical features of the detector are discussed.

Composite boron nitride neutron detectors

Single phase polycrystalline hexagonal boron nitride (BN) or mixed with boron carbide (BxC) embedded in an insulating polymeric matrix acting as a binder and forming a composite material as well as pure submicron size polycrystalline BN has been tested as a thermal neutron converter in a multilayer thermal neutron detector design. Metal sheet electrodes were covered with 20–50μm thick layers of composite materials and assembled in a multi-layer sandwich configuration. High voltage was applied to the metal electrodes to create an interspacing electric field. The spacing volume could be filled with air, nitrogen or argon. Thermal neutrons were captured in converter layers due to the presence of the 10B isotope. The resulting nuclear reaction produced α-particles and 7Li ions which ionized the gas in the spacing volume. Electron-ion pairs were collected by the field to create an electrical signal proportional to the intensity of the neutron source. The detection efficiency of the multilayer neutron detectors is found to increase with the number of active converter layers. Pixel structures of such neutron detectors necessary for imaging applications and incorporation of internal moderator materials for field measurements of fast neutron flux intensities are discussed as well.

The stopping powers and energy straggling of heavy ions in polymer foils

The stopping power and energy straggling of 7Li, 12C and 16O ions in thin poly(etheretherketone) (PEEK), polyethylene terephthalate (PET) and polycarbonate (PC) foils were measured in the incident beam energy range of 9.4–11.8MeV using an indirect transmission method. Ions scattered from a thin gold target at an angle of 150° were registered by a partially depleted PIPS detector, partly shielded with a polymer foil placed in front of the detector. Therefore, the signals from both direct and slowed down ions were visible in the same energy spectrum, which was evaluated by the ITAP code, developed at our laboratory. The ITAP code was employed to perform a Gaussian-fitting procedure to provide a complete analysis of each measured spectrum. The measured stopping powers were compared with the predictions obtained from the SRIM-2008 and MSTAR codes and with previous experimental data. The energy straggling data were compared with those calculated by using Bohr’s, Lindhard–Scharff and Bethe–Livingston theories.

MCNP simulation of the dose distribution in liver cancer treatment for BNC therapy

AbstractThe Boron Neutron Capture Therapy (BNCT) is based on selective uptake of boron in tumour tissue compared to the surrounding normal tissue. Infusion of compounds with boron is followed by irradiation with neutrons. Neutron capture on 10B, which gives rise to an alpha particle and recoiled 7Li ion, enables the therapeutic dose to be delivered to tumour tissue while healthy tissue can be spared. Here, therapeutic abilities of BNCT were studied for possible treatment of liver cancer using thermal and epithermal neutron beam. For neutron transport MCNP software was used and doses in organs of interest in ORNL phantom were evaluated. Phantom organs were filled with voxels in order to obtain depth-dose distributions in them. The result suggests that BNCT using an epithermal neutron beam could be applied for liver cancer treatment.

Mutagenic characteristics of maize variety (Zheng 58) radiated by7Li ion beams

To shorten the time required for breeding new cultivars of Zea mays L., a better understanding of radiation mutagenesis by heavy ions is required to link initial DNA damage and assess how this varies with radiation quality. The dry seeds of Zheng 58 variety of maize were radiated by 7Li ion beams with 43MeV/u at doses of 0Gy, 10Gy, 20Gy, 30Gy, 40Gy and 50Gy. The mutagenic biological effects were analyzed from morphology to genomics by statistics and molecular biological technology including random amplified polymorphic DNA, SDS-PAGE electrophoresis assay and simple sequence repeats assay. The statistic results of morphology showed that germination and survival rates were inhibited. In the M1 generation, germination rate, plant height and ear height changed in the way of saddle curve as the dose increased. The results of molecular biology suggested that the biological effects were significant at 10Gy and 40Gy, and the relationship between genomic variation results and dose was also saddle curve. 7Li ion beams is expected to become an effective source for directed mutagenesis.

Investigation of local symmetry in LiH3(SeO3)2 single crystals by 1H and 7Li nuclear magnetic resonance

The local environments of 1H and 7Li nuclei in LiH3(SeO3)2 crystals were investigated using FT NMR. The 7Li spectrum does changes from three resonance lines to one resonance line near Tm (=383K). The variation in the splitting of the 7Li resonance lines with temperature indicates that the EFG at the Li sites produced by the (SeO3)2− groups varies with temperature. The changes in the temperature dependence of the intensity, line width, and spin–lattice relaxation time T1 near Tm for the 1H and 7Li nuclei coincide with the distortion of the structural framework surrounding each 1H and 7Li ion. Finally, the NMR results obtained here are compared to MH3(SeO3)2 (M=Na, K, and Cs) crystals previously reported.

Lithium ion diffusion in solid electrolyte (Li2S)7(P2S5)3 measured by pulsed-gradient spin-echo 7Li NMR spectroscopy

The sulfide based solid electrolyte (Li2S)7(P2S5)3 has large ionic conductivity, and thus its application in solid-state lithium rechargeable batteries as an electrolyte has been developed. We observed the 7Li and 31P nuclear magnetic resonance (NMR) spectra of crystallized (Li2S)7(P2S5)3 in the steady state and found that narrow and broad components coexist in wide temperature range of the 7Li resonance. The measurement of 7Li ion diffusion was performed for the narrow component between 303 and 353K by the pulsed-gradient spin-echo (PGSE) NMR method. Lithium ion diffusion scattered in a polydispersive manner and the apparent diffusion constants of the Li+ (DLi) varied depending on measurement conditions at a certain temperature. The temperature-dependent ionic conductivity was observed from 263 to 353K and the activation energy was 31.4kJmol−1 for the crystallized (Li2S)7(P2S5)3. The DLi evaluated from ionic conductivity using the Nernst-Einstein relation was consistent with the scattering apparent DLi observed by the PGSE NMR method. The translational movement of Li+ observed by the PGSE NMR is extremely complex. Within a short distance and a short period, Li+ ions move quickly and slow down with time and distance. This is the first trial to measure the lithium diffusion directly for continuous space in the solid electrolyte.

Investigation of induced fission of natPb by accelerated 7Li ions

Cross-sections for fragments produced by the fission reaction induced by accelerated 7Li ions impinged into an natPb target at 245 MeV were obtained. We have applied the induced-activation method in off-line analysis. The analysis of charge and mass distributions of fission products allowed the determination of the total fission cross-section for the 7Li+Pb system. The recoil technique (thick target- thick catcher), based on the two step model mathematical formalism, is used to determine the kinematics characteristics of reaction products. Analysis concerning transferred linear momentum provided information on the initial projectile-target interaction, and is compared with proton-induced fission measurements.

Experimental observation of ion heating by mode-converted ion Bernstein waves in tokamak plasmas

We report the experimental observation of ion heating by the mode-converted ion Bernstein waves (MC IBWs) in tokamak plasmas. The MC IBW is created from the fast waves launched from the high-field-side antenna in the HT-7 tokamak in plasmas consisting of deuterium majority, hydrogen minority and 7Li ions. Experimental evidence and numerical simulation show that the interaction between the MC IBW and 7Li ions at the first ion-cyclotron harmonic resonance of 7Li (i.e. ω = 2ΩLi-7) is the main mechanism for radio-frequency power deposition. By comparing with previous experiments of direct-launch IBW flow drive on tokamaks and existing theories, we hypothesize that this MC IBW and 7Li interaction also leads to the observed flow drive effect.

Crystalline phase content and ionic conductivity correlation in LATP glass–ceramic

Li2O–Al2O3–TiO2–P2O5 (LATP) glass was fabricated by conventional melt quenching route. Glass transition temperature (T g = 296 °C) and crystallization temperatures (T C1,2) were obtained from thermal analysis. LATP glass was converted to glass–ceramic by heat treatment in the range 550–950 °C for 6 h. X-ray diffraction analysis revealed LiTi2(PO4)3 as a major phase. Ionic conductivity increased monotonically with concentration, reaching a maximum of ~10−4 S/cm. AlPO4 phase was detected in samples heat-treated above 850 °C. Its presence decreased the conductivity, suggesting LiTi2(PO4)3 phase as main contributor to high ionic conductivity. NMR spectra confirmed the presence of mobile 7Li ions in the entire sample series and also gave some information on the structure and dynamics of conductivity.

A Monte Carlo evaluation of carbon and lithium ions dose distributions in water

Purpose: To compare dose distributions on the central- and off-axis for 12C and 7Li ion beams simulated by the codes SHIELD-HIT (Heavy Ion Transport) and FLUKA (FLUKtuierende KAskade), and compare with experimental data for 300 MeV/u 12C and 185 MeV/u 7Li ion beams.Materials and methods: The general purpose Monte Carlo codes, SHIELD-HIT10 and FLUKA 2008.3d.1 were used for the ion dose distribution calculations. SHIELD-HIT transports hadrons and atomic nuclei of arbitrary charge and mass number in an energy range from 1 keV/u up to 1 GeV/u. Similarly, FLUKA transports charged hadrons in an energy range from 100 keV up to 20 TeV. Neutrons are transported down to thermal energies in both codes. Inelastic nuclear interactions are modelled in SHIELD-HIT by the Many Stage Dynamical Model (MSDM), whereas in FLUKA the Pre-Equilibrium Approach to Nuclear Thermalisation (PEANUT) package which includes a Generalized Intra-Nuclear Cascade model was used.Results: The dose distributions in water irradiated with 300 MeV/u 12C and 185 MeV/u 7Li ion beams were simulated with the two codes. Studies were performed of the energy deposition both on the central axis and at lateral distances up to 10 cm off-axis. The dose distributions calculated by SHIELD-HIT and FLUKA were compared with published experimental data. The dose mean lineal energy , frequency mean lineal energy , dose mean specific energy , and frequency mean specific energy were calculated with the ion track-structure code PITS99 (Positive Ion Track Structure 99), coupled with the electron code KURBUC for the primary and secondary ions average energies at 1 mm before the Bragg peak.Conclusion: The Monte Carlo codes show good agreement with experimental results for off-axis dose distributions. The disagreements in the Bragg peak region for the central-axis dose distributions imply that further improvements especially in the nuclear interaction models are required to increase the accuracy of the codes.

Hydrothermal synthesis of Ni 2FeBO 5 in near-supercritical PWR coolant and possible effects of neutron-induced 10B fission in fuel crud

The hydrothermal synthesis of a nickel–iron oxyborate, Ni 2FeBO 5, known as bonaccordite, was investigated at pressures and temperatures that might occur at the surface of high-power fuel rods in PWR cores and in supercritical water reactors, especially during localized departures from nucleate boiling and dry-outs. The tests were performed using aqueous mixtures of nickel and iron oxides with boric acid or boron oxide, and as a function of lithium hydroxide addition, temperature and time of heating. At subcritical temperatures nickel ferrite NiFe 2O 4 was always the primary reaction product. High yield of Ni 2FeBO 5 synthesis started near critical water temperature and was strongly promoted by additions of LiOH up to Li/Fe and Li/B molar ratios in a range 0.1–1. The synthesis of bonaccordite was also promoted by other alkalis such as NaOH and KOH. The bonaccordite particles were likely formed by dissolution and re-crystallization by means of an intermediate nickel ferrite phase. It is postulated that the formation of Ni 2FeBO 5 in deposits of borated nickel and iron oxides on PWR fuel cladding can be accelerated by lithium produced in thermal neutron capture 10B(n,α) 7Li reactions. The process may also be aided in the reactor core by kinetic energy of α-particles and 7Li ions dissipated in the crud layer.

Equilibrium and pre-equilibrium processes in theMn55(Li6,xp) andFe57(α,xp) reactions

Spectra of outgoing neutrons and protons from the 6Li+55Mn reaction and protons from the a+57Fe reaction have been measured with beams of 15 MeV 6Li ions and 30 MeV alpha-particles. These reactions proceed through the same 61Ni nucleus at the same excitation energy, thus allowing the difference in reaction mechanism to be studied. It is shown that spectra from the first reaction measured at backward angles are due to emission from a traditional compound nucleus reaction, in which the intermediate nucleus has reached statistical equilibrium; the spectra from the second reaction contain a significant fraction of pre-equilibrium emission at all angles. Level density pa- rameters of the residual nucleus 60Co have been obtained from the first reaction. Both emission spectra and angular distributions have been measured for the second reaction. It was found that the pre-equilibrium component exhibits a forward-peaked angular distribution, as expected, but with a steeper slope than predicted and with an unusual slight rise at angles above 120\deg. The backward- angle rise is explained qualitatively by the dominance of the multi-step compound mechanism at backward angles.

Stopping power measurements of heavy ions (3 ⩽ Z1 ⩽ 14) in Mylar foil by time-of-flight spectrometry

Heavy ions elastic recoil detection analysis coupled with time of flight spectrometer (HIERDA_ToF-E) have been used to measure energy loss of charged particles in thin absorber. The stopping power of heavy ions has been determined in Mylar for 28Si, 27Al, 24Mg, 19F, 16O, 12C and 7Li ions over a continuous range of energies 0.14–0.80 MeV/nucleon. The ions were recoils from the bombardment of different samples (Si, MgO, Al 2O 3, LiF and C) with a 27.5 MeV Kr + beam. The energy loss of the recoil atoms is measured with and without additional foils placed in front of a Surface Barrier Detector (SBD). The energy of individual ions is determined from its ToF data; the exit energy after the stopping foil is measured using the SBD detector. We have compared our stopping values to those predicted by SRIM-2008 computer code, ICRU-73 stopping data tables, MSTAR calculations and to the published data from literature. The results show good agreement with limited existing data but indicate a large deviation among the predicted theoretical values at the low energy side of the stopping maximum peak.

Secondary absorbed doses from light ion irradiation in anthropomorphic phantoms representing an adult male and a 10 year old child

Secondary organ absorbed doses were calculated by Monte Carlo simulations with the SHIELD-HIT07 code coupled with the mathematical anthropomorphic phantoms CHILD-HIT and ADAM-HIT. The simulated irradiations were performed with primary 1H, 4He, 7Li, 12C and 16O ion beams in the energy range 100–400 MeV/u which were directly impinging on the phantoms, i.e. approximating scanned beams, and with a simplified beamline for 12C irradiation. The evaluated absorbed doses to the out-of-field organs were in the range 10−6 to 10−1 mGy per target Gy and with standard deviations 0.5–20%. While the contribution to the organ absorbed doses from secondary neutrons dominated in the ion beams of low atomic number Z, the produced charged fragments and their subsequent charged secondaries of higher generations became increasingly important for the secondary dose delivery as Z of the primary ions increased. As compared to the simulated scanned 12C ion beam, the implementation of a simplified beamline for prostate irradiation with 12C ions resulted in an increase of 2–50 times in the organ absorbed doses depending on the distance from the target volume. Comparison of secondary organ absorbed doses delivered by 1H and 12C beams showed smaller differences when the RBE for local tumor control of the ions was considered and normalization to the RBE-weighted dose to the target was performed.