Tritium Molecules Research Articles

Technique of Reactor Experiments of Tin-Lithium Alloy Interaction with Hydrogen Isotopes Under Neutron Irradiation Conditions

The implementation of the ITER and DEMO projects currently includes the investigation of the structural and functional material properties of fusion reactors (FRs). Research to support the use of liquid metals and alloys as plasma-facing materials (PFMs) is a crucial area of work during the development of new FRs. Recent studies indicate the prospects of the tin-lithium (Sn-Li) alloy as a new liquid metal for protecting the in-vessel elements of a FR from the energy flows and high-density particles. Sn-Li alloy has been widely explored for utilization as PFM; however, there is a shortage of investigations being performed at nuclear reactors. The utilization of Sn-Li alloy as PFM in a FR must be fully justified by validated experimental results on tests under extremely high heat, plasma, and radiation loads. The paper presents the methodology of in-pile experiments performed at the IVG.1M research reactor (Kurchatov, Kazakhstan) to study the interaction of hydrogen isotopes with Sn-Li alloy under neutron irradiation conditions. A Sn-Li sample with 73 at. % tin and 27 at. % lithium was manufactured. A unique experimental ampoule device (AD) with a Sn-Li sample had been developed and manufactured for in-pile tests. The results of neutron-physical and thermophysical calculations of designs of the experimental device with Sn-Li alloy under irradiation conditions of the IVG.1M reactor were performed to justify the AD design. Methodical experiments were performed to determine the temperature dependence of the change in the composition of the gas phase in the chamber with Sn-Li alloy. The time dependence of the partial pressure of hydrogen, tritium, and tritium-containing molecules in the AD volume with the Sn-Li alloy on its temperature under reactor irradiation conditions at a power of 3 MW has been studied. Key findings include the successful measurement of tritium release, the determination of temperature conditions for tritium generation and release, and the validation of our experimental AD for conducting such studies.

Characterization of the KATRIN cryogenic pumping section

The KArlsruhe TRItium Neutrino (KATRIN) experiment aims to determine the effective anti-electron neutrino mass with a sensitivity of 0.2eV/c2 by using the kinematics of tritium β-decay. It is crucial to have a high signal rate which is achieved by a windowless gaseous tritium source producing 1011β-electrons per second. These are guided adiabatically to the spectrometer section where their energy is analyzed. In order to maintain a low background rate below 0.01cps, one essential criteria is to permanently reduce the flow of neutral tritium molecules between the source and the spectrometer section by at least 14 orders of magnitude. A differential pumping section downstream from the source reduces the tritium flow by seven orders of magnitude, while at least another factor of 107 is achieved by the cryogenic pumping section where tritium molecules are adsorbed on an approximately 3K cold argon frost layer. In this paper, the results of the cryogenic pumping section commissioning measurements using deuterium are discussed. The cryogenic pumping section surpasses the requirement for the flow reduction of 107 by more than one order of magnitude. These results verify the predictions of previously published simulations.

Precision measurement of the electron energy-loss function in tritium and deuterium gas for the KATRIN experiment

The KATRIN experiment is designed for a direct and model-independent determination of the effective electron anti-neutrino mass via a high-precision measurement of the tritium upbeta -decay endpoint region with a sensitivity on m_nu of 0.2 hbox {eV}/hbox {c}^2 (90% CL). For this purpose, the upbeta -electrons from a high-luminosity windowless gaseous tritium source traversing an electrostatic retarding spectrometer are counted to obtain an integral spectrum around the endpoint energy of 18.6 keV. A dominant systematic effect of the response of the experimental setup is the energy loss of upbeta -electrons from elastic and inelastic scattering off tritium molecules within the source. We determined the energy-loss function in-situ with a pulsed angular-selective and monoenergetic photoelectron source at various tritium-source densities. The data was recorded in integral and differential modes; the latter was achieved by using a novel time-of-flight technique. We developed a semi-empirical parametrization for the energy-loss function for the scattering of 18.6-keV electrons from hydrogen isotopologs. This model was fit to measurement data with a 95% hbox {T}_2 gas mixture at 30 K, as used in the first KATRIN neutrino-mass analyses, as well as a hbox {D}_2 gas mixture of 96% purity used in KATRIN commissioning runs. The achieved precision on the energy-loss function has abated the corresponding uncertainty of sigma (m_nu ^2)< {{10}^{-2}}{hbox {eV}^{2}} [1] in the KATRIN neutrino-mass measurement to a subdominant level.

A study of New Physics searches with tritium and similar molecules

Searches for New Physics focus either on the direct production of new particles at colliders or at deviations from known observables at low energies. In order to discover New Physics in precision measurements, both experimental and theoretical uncertainties must be under full control. Laser spectroscopy nowadays offers a tool to measure transition frequencies very precisely. For certain molecular and atomic transitions the experimental technique permits a clean study of possible deviations. Theoretical progress in recent years allows us to compare ab initio calculations with experimental data. We study the impact of a variety of New Physics scenarios on these observables and derive novel constraints on many popular generic Standard Model extensions. As a result, we find that molecular spectroscopy is not competitive with atomic spectroscopy and neutron scattering to probe new electron-nucleus and nucleus-nucleus interactions, respectively. Molecular and atomic spectroscopy give similar bounds on new electron-electron couplings, for which, however, stronger bounds can be derived from the magnetic moment of the electron. In most of the parameter space H_2 molecules give stronger constraints than T_2 or other isotopologues.

Project KATRIN: First results and future plans.

The KArlsruhe TRItium Neutrino (KATRIN) experiment aims to make a model-independent determination of the active electron antineutrino mass with an upper limit of 0.2 eV/c2 from the analysis of Tritium beta-spectrum shape near the endpoint. Experimental set-up is fully assembled and undergoes multiple tests. Small amount of Tritium molecules were injected at June 2018 and first spectra were measured. Experimental program for the nearest future includes determination of active electron antineutrino mass with an upper limit of 1.0 eV/c2 and preliminary search for sterile neutrinos with several keV mass.

The KATRIN superconducting magnets: overview and first performance results

The KATRIN experiment aims for the determination of the effective electron anti-neutrino mass from the tritium beta-decay with an unprecedented sub-eV sensitivity. The strong magnetic fields, designed for up to 6 T, adiabatically guide β-electrons from the source to the detector within a magnetic flux of 191 Tcm2. A chain of ten single solenoid magnets and two larger superconducting magnet systems have been designed, constructed, and installed in the 70-m-long KATRIN beam line. The beam diameter for the magnetic flux varies from 0.064 m to 9 m, depending on the magnetic flux density along the beam line. Two transport and tritium pumping sections are assembled with chicane beam tubes to avoid direct “line-of-sight” molecular beaming effect of gaseous tritium molecules into the next beam sections. The sophisticated beam alignment has been successfully cross-checked by electron sources. In addition, magnet safety systems were developed to protect the complex magnet systems against coil quenches or other system failures. The main functionality of the magnet safety systems has been successfully tested with the two large magnet systems. The complete chain of the magnets was operated for several weeks at 70% of the design fields for the first test measurements with radioactive krypton gas. The stability of the magnetic fields of the source magnets has been shown to be better than 0.01% per month at 70% of the design fields. This paper gives an overview of the KATRIN superconducting magnets and reports on the first performance results of the magnets.

First Operation of the Complete KATRIN Superconducting Magnet Chain

The neutrino mass experiment KATRIN recently operated its complete chain of the superconducting magnets for the first-light test. The superconducting solenoid magnets are designed to adiabatically guide electrons from the source to the detector within a magnetic flux of 191 T $\cdot$ cm $^2$ along the 70-m -long KATRIN beam line. The complete beam line is connected through the bore of ten stand-alone solenoids magnets and two large solenoids magnet systems. The six magnet modules of two transport sections are aligned with tilted angles to avoid direct molecular beaming of tritium molecules to the next sections. The first-light test performed at reduced magnetic fields with an electron source successfully confirmed the sophisticated beam alignment for the KATRIN experiment. The complete magnets were continuously operated about two weeks for the first-light tests in October, 2016. This paper reports on the first operation results of the complete KATRIN magnets.

Deconvolution of the energy loss function of the KATRIN experiment

The KATRIN experiment aims at a direct and model independent determination of the neutrino mass with 0.2 eV/c2 sensitivity (at 90% C.L.) via a measurement of the endpoint region of the tritium beta-decay spectrum. The main components of the experiment are a windowless gaseous tritium source (WGTS), differential and cryogenic pumping sections and a tandem of a pre- and a main-spectrometer, applying the concept of magnetic adiabatic collimation with an electrostatic retardation potential to analyze the energy of beta decay electrons and to guide electrons passing the filter onto a segmented silicon PIN detector.One of the important systematic uncertainties of such an experiment are due to energy losses of β-decay electrons by elastic and inelastic scattering off tritium molecules within the source volume which alter the shape of the measured spectrum. To correct for these effects an independent measurement of the corresponding energy loss function is required. In this work we describe a deconvolution method to extract the energy loss function from measurements of the response function of the experiment at different column densities of the WGTS using a monoenergetic electron source.

Anharmonicity of internal atomic oscillation and effective antineutrino mass evaluation from gaseous molecular tritium β-decay

Data analysis of the next-generation effective antineutrino mass measurement experiment KATRIN requires reliable knowledge of systematic corrections. In particular, the width of the daughter molecular ion excitation spectrum rovibrational band should be known with better than 1% precision. Very precise ab initio quantum calculations exist, and we compare them with the well-known tritium molecule parameters within the framework of a phenomenological model. The rovibrational band width with accuracy of a few percent is interpreted as a result of the zero-point atomic oscillation in the harmonic potential. The Morse interatomic potential is used to investigate the impact of anharmonic atomic oscillations. The calculated corrections cannot account for the difference between the ab initio quantum calculations and the phenomenological model.

Ortho–para nuclear-spin isomerization energies for all bound vibrational states of ditritium (T2) from non-Born–Oppenheimer variational calculations performed with explicitly correlated all-particle Gaussian functions

Direct variational calculations, where the Born–Oppenheimer (BO) approximation is not assumed, are performed for all 26 bound rovibrational states corresponding to the lowest rotational excitation (i.e. the N=1 states) of the tritium molecule (T2). The non-BO energies are used to determine the ortho–para isomerization energies. All-particle explicitly correlated Gaussian basis functions are employed in the calculations and over 11000 Gaussians independently generated for each state are used. The exponential parameters of the Gaussians are optimized with the aid of analytically calculated energy gradient determined with respect to these parameters. The non-BO wave functions are used to calculate expectation values of the inter-particle distances and the triton–triton correlation functions.

Theoretical study of Jesse effect in tritium measurements using ionization chambers

Jesse effect caused by impurities in helium might enhance the output signal significantly in tritium measurements with ionization chamber, which will lead to overestimation of tritium concentration in experiments. A theoretical method was proposed to evaluate Jesse effect quantitatively. Results indicate that besides Penning ionization, sub-excitation electrons also place very important influence on ionization enhancement by Jesse effect. An experiential expression about the relationship between enhancement factor and impurity concentration was established, in which second order of it fits experimental results very well. Theoretical calculation method in this paper is also applicable to evaluate Jesse effect in other kinds of mixtures besides hydrogen as impurities in helium. In addition, Jesse effects about tritium molecules as impurities have also been investigated.

Development of a Tritium Monitor Combined with an Electrochemical Tritium Pump Using a Proton Conducting Oxide

To fabricate a tritium monitoring system with electrochemical hydrogen pumping attached, a tritium monitor system was constructed and assembled with a commercial tritium monitor and an electrochemical hydrogen pump using a proton conducting oxide. The hydrogen pump with CaZr0.9In0.1O3−α as the proton conducting oxide was operated at 973 K under electrolysis conditions using tritiated water vapor (HTO). The tritium molecules (HT) were extracted and controlled by the applied current over a range of two orders of magnitude. The tritium molecules have an advantage with respect to the tritium memory effect in the monitor because the tritium contamination is reduced. Next, a system feasibility test was conducted under various water vapor partial pressure conditions. Thus, the measurement of the tritium concentration via this proposed system was successfully demonstrated.

Assessment of molecular effects on neutrino mass measurements from tritiumβdecay

The best direct limits on absolute neutrino mass come from tritium $\ensuremath{\beta}$ decay. This work discusses in detail how molecular effects distort the $\ensuremath{\beta}$-decay spectrum following decay of the tritium molecule. It closes an open detail in setting a stringent limit on the neutrino mass from the shape of the tritium spectrum.

Theoretical investigation of isotope exchange reaction in tritium-contaminated mineral oil in vacuum pump

The mechanism of the isotope exchange reaction between molecular tritium and several typical organic molecules in vacuum pump mineral oil has been investigated by density functional theory (DFT), and the reaction rates are determined by conventional transition state theory (TST). The tritium–hydrogen isotope exchange reaction can proceed with two different mechanisms, the direct T–H exchange mechanism and the hyrogenation–dehydrogenation exchange mechanism. In the direct exchange mechanism, the titrated product is obtained through one-step via a four-membered ring hydrogen migration transition state. In the hyrogenation–dehydrogenation exchange mechanism, the T–H exchange could be accomplished by the hydrogenation of the unsaturated bond with tritium followed by the dehydrogenation of HT. Isotope exchange between hydrogen and tritium is selective, and oil containing molecules with OH and COOH groups can more easily exchange hydrogen for tritium. For aldehydes and ketones, the ability of T–H isotope exchange can be determined by the hydrogenation of T2 or the dehydrogenation of HT. The molecules containing one type of hydrogen provide a single product, while the molecules containing different types of hydrogens provide competitive products. The rate constants are presented to quantitatively estimate the selectivity of the products.

Improvement of hydrogen isotope exchange reactions on Li4SiO4 ceramic pebble by catalytic metals

Abstract Li4SiO4 ceramic pebble is considered as a candidate tritium breeding material of Chinese Helium Cooled Solid Breeder Test Blanket Module (CH HCSB TBM) for the International Thermonuclear Experimental Reactor (ITER). In this paper, Li4SiO4 ceramic pebbles deposited with catalytic metals, including Pt, Pd, Ru and Ir, were prepared by wet impregnation method. The metal particles on Li4SiO4 pebble exhibit a good promotion of hydrogen isotope exchange reactions in H2–D2O gas system, with conversion equilibrium temperature reduction of 200–300 °C. The out-of-pile tritium release experiments were performed using 1.0 wt% Pt/Li4SiO4 and Li4SiO4 pebbles irradiated in a thermal neutron reactor. The thermal desorption spectroscopy shows that Pt was effective to increase the tritium release rate at lower temperatures, and the ratio of tritium molecule (HT) to tritiated water (HTO) of 1.0 wt% Pt/Li4SiO4 was much more than that of Li4SiO4, which released mainly as HTO. Thus, catalytic metals deposited on Li4SiO4 pebble may help to accelerate the recovery of bred tritium particularly in low temperature region, and increase the tritium molecule form released from the tritium breeding materials.

Neutrino Mass Experiment at The University of Texas at Austin (NEXTEX)

NEXTEX is the next generation experiment designed to determine the electron antineutrino mass to at least 0.5 eV. The experiment is based on the shape of the beta endpoint energy spectrum from gaseous tritium molecules. Two high throughput electrostatic differential electron analyzers coupled with spherical deflection accelerator are key components of the apparatus. The voltages at the electrodes of the spectrometers ultimately determine the energy of the electrons reaching the detector. The correlations between voltages and the energy of the transmitted electrons will be calibrated with diffraction on the T 2 gas of electrons emitted from the auxiliary gun. The coherent electron diffraction pattern from T 2 will provide a series of calibration markers for the spectrum with uncertainties better than 100 mV. Extremely low background count-rates from cosmic rates of less than one count a day at the detector has been already demonstrated. A numerical model predicts residual background from tritium sources of few counts per day. The tritium source and its recycling system is designed to prevent the formation of HT to better than 1% during the fiduciary runs.

Radiochemical Reactions between Tritium and Carbon Dioxide at Elevated Temperatures

Radiochemical reactions between tritium and carbon dioxide molecules at elevated temperatures have been investigated. There is no significant temperature dependence of the radiochemical reactions in the temperature range from 373 to 573 K. It has been found that concentration of such reaction products as tritiated methane and carbon monoxide molecules increases with time, whereas the concentration of tritiated water molecules remains practically constant. Additionally, influence of γ-ray radiation on radiochemical reactions in H2 and CO2 gas mixture was examined. Water and methane molecules are formed as radiation products, however, carbon monoxide is not detectable.

Molecular hydrogen in graphite: A path-integral simulation

Molecular hydrogen in the bulk of graphite has been studied by path-integral molecular dynamics simulations. Finite-temperature properties of H_2 molecules adsorbed between graphite layers were analyzed in the temperature range from 300 to 900 K. The interatomic interactions were modeled by a tight-binding potential fitted to density-functional calculations. In the lowest-energy position, an H_2 molecule is found to be disposed parallel to the sheets plane. At finite temperatures, the molecule explores other orientations, but its rotation is partially hindered by the adjacent graphite layers. Vibrational frequencies were obtained from a linear-response approach, based on correlations of atom displacements. For the stretching vibration of the molecule, we find at 300 K a frequency omega_s = 3916 cm-1, more than 100 cm-1 lower than the frequency corresponding to an isolated H_2 molecule. Isotope effects have been studied by considering also deuterium and tritium molecules. For D_2 in graphite we obtained omega_s = 2816 cm-1}, i.e., an isotopic ratio omega_s(H) / omega_s(D) = 1.39.

The Windowless Gaseous Tritium Source of KATRIN

The objective of KATRIN is the determination of the mass of the electron anti-neutrino with a sensitivity of 200 meV by investigating the kinematics of the electrons from tritium β decay. It is currently under construction at KIT (Karlsruhe Institute of Technology). A key component of the KATRIN experiment is the Windowless Gaseous Tritium Source (WGTS), in which molecular tritium decays with an activity of 10 11 Bq. A precise understanding of the properties of the WGTS is mandatory for the neutrino mass determination. In particular the gas dynamics is crucial since the measured energy spectrum is influenced by inelastic scattering of the decay electrons with the tritium molecules as well as Doppler broadening of the electron energy. Therefore parameters of the WGTS such as purity, temperature, density and velocity distributions of the tritium gas and the magnetic field strength inside the WGTS have to be modeled in detail. This talk gives an overview of the simulation and modeling program package currently in development which allows us to study the influence of the WGTS parameters on the measured electron energy spectrum.

A broad-band FT-ICR Penning trap system for KATRIN

The KArlsruhe TRItium Neutrino experiment KATRIN aims at improving the upper limit of the mass of the electron antineutrino to about 0.2 eV (90% c.l.) by investigating the β -decay of tritium gas molecules T 2 → ( HeT 3 ) + + e − + ν ¯ e . The experiment is currently under construction to start first data taking in 2012. One source of systematic uncertainties in the KATRIN experiment is the formation of ion clusters when tritium decays and decay products interact with residual tritium molecules. It is essential to monitor the abundances of these clusters since they have different final state energies than tritium ions. For this purpose, a prototype of a cylindrical Penning trap has been constructed and tested at the Max-Planck-Institute for Nuclear Physics in Heidelberg, which will be installed in the KATRIN beam line. This system employs the technique of Fourier-Transform Ion-Cyclotron-Resonance in order to measure the abundances of the different stored ion species.