Tritium Atoms Research Articles

Using cold atoms to measure neutrino mass

We propose a β-decay experiment based on a sample of ultracold atomic tritium. These initial conditions enable detection of the helium ion in coincidence with the β. We construct a two-dimensional fit incorporating both the shape of the β-spectrum and the direct reconstruction of the neutrino mass peak. We present simulation results of the feasible limits on the neutrino mass achievable in this new type of tritium β-decay experiment.

Interaction of tritium atoms with solid composite targets: Adsorption layers of nonionic surfactants on hydrophobic supports

The capability of tritium atoms to penetrate deep into solids was used for revealing nonuniformity of coating of polymeric [polyethylene, poly(ethylene terephthalate)] supports by adsorption layers of a nonionic surfactant Brij-35, formed by adsorption from aqueous solutions. The permeability to atomic tritium of Brij-35 adsorption layers on polyethylene appeared to be close to that obtained for hydrocarbon fragments of cationic surfactants in adsorption layers on the water/air boundary. A decrease in the coefficients of attenuation of the tritium atom flow at formation of adsorption polylayers was revealed. This decrease suggests less ordered structure of the polylayers relative to the monolayer. The developed approach involving preparation of adsorption coatings of tritium-labeled surfactants, their treatment with tritium atoms, and subsequent removal of the surfactant from the support, with the autoradiographic detection of tritium distribution on the plate in all the steps of the work, can be used for studying the structure of surfactant adsorption layers on flat solid surfaces.

Laser and isotope effects in charge transfer processes in atomic collisions

Charge transfer processes are fundamental to the understanding of matter neutralization in atomic and molecular processes. Due to the polarizability of the material, charge transfer can be enhanced or suppressed during the interaction with electromagnetic radiation. Furthermore, charge transfer has different contributions arising from the radial and rotational regions of the potential interaction in the collision, which depend on the mass of the target and projectile. Since these effects appear in a very short time (femtoseconds), the dynamics must be carried out outside the Born–Oppenheimer approximation. In this work, we present charge transfer results for He2+ ions colliding with atomic hydrogen and tritium atoms for collision energies from 100 eV/amu up to 1.5 keV/amu, assisted by a fast, short laser pulses of intensity 3.5×1012 W/cm2 and wave length of 790 nm by means of an electron-nuclear dynamic treatment. We find large isotope effects in the low-energy region up to one order of magnitude in the charge transfer cross-section in the absence of the laser pulse. In the presence of the laser pulse, the isotope effect is negligible and the charge transfer cross-section is enhanced up to two orders of magnitude in the low-energy region.

Theoretical treatment of hydrogen abstraction by hot tritium atoms

Extended Huckel calculations using Cusachs's modification were performed for the methane–tritium system with the objective of determining how the overlap populations (and energies) varied as a function of GHT distances. The model chosen was axial attack of the hot tritium atom along the CH(1) bond direction which leads to abstraction of the H(1) atom. A position of maximum H(1)T overlap population was found at about the same place as the position of minimum CH(1) overlap population, thus setting certain limits on geometric configurations which would be expected to undergo the H(1) abstraction reaction. Attention is drawn to the pertinence of overlap population results to the bond energy–bond order method of Johnston for obtaining potential energy surfaces. The overlap populations also indicate why in compounds containing very electronegative substituents, the abstraction reaction occurs at a lower energy than would be predicted by the simple bond dissociation energy dependence found experimentally by Rowland for all other systems. A potential energy surface was also traced out for the CH4–T reaction and a basin was found indicating a stable CH4T (or CH5) molecule. Examination of activation energies calculated previously by Eyring and Polyani for axial attack compared to direct attack shows clearly why at low kinetic energies of T the abstraction reaction is favored over the substitution reaction; and why only the abstraction reaction occurs at T kinetic energies lower than ∼1.8 eV.

Interaction of tritium atoms with solid composite targets: Amino acids under adsorbed cetylamine layers

The capability of atomic tritium to penetrate deep into anhydrous targets of complex composition was examined. Amino acids coated with cetylamine were used as targets. With an increase in the cetylamine layer thickness, the yield of labeled amino acids drastically decreased, whereas the yield of labeled by-products increased. Measurements of the radioactivity of the amino acids allowed evaluation of the capability of cetylamine layers to transmit tritium atoms, which was characterized by gravimetric attenuation coefficients. The attenuation coefficient depends on particular amino acid used as indicator and on the cetylamine layer thickness. The most accurate values of the attenuation factors were obtained from the radioactivity of all the reaction products, taking into account the nonuniformity of cetylamine application onto the target. A decrease in the attenuation coefficient in thick cetylamine coatings was attributed to the open-work (porous) structure of these layers.

Stability limits of mixed spin-polarised tritium clusters

We present variational and diffusion Monte Carlo studies of pure and mixed spin-polarised tritium clusters. Our results for pure clusters, consisting of only tritium atoms T↓, are in good agreement with previous calculations. We show that mixed clusters, consisting of up to 60 T↓ atoms and one spin-polarized deuterium D↓ atom are stable. On the other hand, we verified that tritium clusters of up to N = 60 atoms do not bind even one H↓ atom; the ground-state energy of the considered mixed T↓-H↓ clusters is within the errorbars equal to or higher than the energy of the pure tritium cluster. In addition to the energy, we present results of the structure of the clusters, which has been determined using unbiased estimators. For larger N, a D↓ atom forms an Andreev state on the surface of a tritium cluster core. The H↓ atoms stay further away from the center of the cluster than the D↓ atoms and slowly increase their separation as the simulation proceeds, indicating instability.

Quantitation of the glycoprotein spike area on the surface of enveloped viruses

The density of glycoprotein (GP) distribution on the virion surface substantially influences the virus infectivity and pathogenicity. A method to quantitatively determine the area occupied by surface GP spikes was proposed for influenza virus (Flu) strain A/PR/8/34 on the basis of data of tritium bombardment and dynamic light scattering. The latter was used to measure the diameter of intact virions and subviral particles (Flu virions lacking GP spikes after bromelain digestion). Intact virions and subviral particles were bombarded with a hot tritium atom flux, and the specific radioactivity of the matrix M1 protein was analyzed. The tritium label was incorporated into the amino acid residues of a thin exposed protein layer and partly penetrated through the lipid bilayer of the viral envelope, labeling M1, located under the lipid bilayer. The tritium label distribution among different amino acid residues was the same in M1 isolated from subviral particles and M1 isolated from intact virions, demonstrating that the M1 spatial structure remained unchanged during proteolysis of GP spikes. The difference in specific radioactivity between the M1 proteins isolated from intact virions and subviral particles was used to calculate the GP-free portion of the viral surface. Approximating the Flu virion as a sphere, the GP-covered area was estimated at 1.4 × 104 nm2, about 40% of the total virion surface. This was consistent with the cryoelectron tomography data published for Flu strain A/X-31. The approach can be applied for other enveloped high pathogenic viruses, such as HIV and the Ebola virus.

The effect of deuterium and tritium on formation and annealing of vacancy‐type defects in deformed nickel

AbstractPure nickel and nickel loaded with deuterium or tritium were examined during deformation at 270–300 K to 3–45% and subsequent annealing up to 850 K using the measurements of the electrical resistivity and positron annihilation spectroscopy. Three‐dimensional vacancy clusters were formed during deformation in nickel loaded with the hydrogen isotopes unlike in pure nickel. Vacancy clusters decorated with deuterium or tritium atoms created at room temperature, i.e. below a temperature at which monovacancies, are mobile in nickel. Vacancy clusters decorated with deuterium atoms have two types of atomic configurations or degrees of decoration with the binding energy of 0.73 eV and 1.05 eV, respectively. Only one configuration having the binding energy of 1.05 eV was detected for vacancy clusters decorated with tritium atoms. Possible reasons for different behaviors of vacancy clusters in T‐ and D‐loaded nickel are also discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Gas Diffusion Barriers on Polymers Using Multilayers Fabricated by Al2O3 and Rapid SiO2 Atomic Layer Deposition

Single Al2O3 atomic layer deposition (ALD) films on polymers have demonstrated excellent gas diffusion barrier properties. Further improvements can be achieved using multilayers of Al2O3 ALD layers with other inorganic layers. In this study, multilayers of Al2O3 ALD and rapid SiO2 ALD were grown on Kapton and heat-stabilized polyethylene naphthalate substrates. Transmission rates for tritium through the films were measured using the radioactive HTO tracer method. Comparison with previous Ca tests and tritium exchange experiments with alcohols indicated that the tritium in HTO may diffuse as either molecular HTO or atomic tritium. Assuming that the tritium diffuses only as HTO, single Al2O3 ALD films reduced the effective water vapor transmission rate (WVTR) to ∼1 × 10-3 g/m2/day. When the Al2O3 ALD film was directly exposed to the saturated H2O/HTO vapor pressure, the barrier properties deteriorated markedly after 4−5 days. Al2O3 ALD barriers that were not subjected to direct H2O/HTO exposure indefinitely...

Quantum Monte Carlo study of small pure and mixed spin-polarized tritium clusters

We have investigated the stability limits of small spin-polarized clusters consisting of up to ten spin-polarized tritium T downward arrow atoms and the mixtures of T downward arrow with spin-polarized deuterium D downward arrow and hydrogen H downward arrow atoms. All of our calculations have been performed using the variational and diffusion Monte Carlo methods. For clusters with D downward arrow atoms, the released node procedure is used in cases where the wave function has nodes. In addition to the energy, we have also calculated the structure of small clusters using unbiased estimators. Results obtained for pure T downward arrow clusters are in good accordance with previous calculations, confirming that the trimer is the smallest spin-polarized tritium cluster. Our results show that mixed T downward arrow-H downward arrow clusters having up to ten atoms are unstable and that it takes at least three tritium atoms to bind one, two, or three D downward arrow atoms. Among all the considered clusters, we have found no other Borromean states except the ground state of the T downward arrow trimer.

124: Metabolism of 17-hydroxyprogesterone caproate by human hepatic and placental microsomes

PLACENTAL MICROSOMES RU YAN, TATIANA NANOVSKAYA, DONALD MATTISON, GARY D.V. HANKINS, MAHMOUD AHMED, University of Texas Medical Branch, Obstetrics and Gynecology, Galveston, Texas, Obstetric-Fetal Pharmacology Research Units (OPRU) Network, Center for Research For Mother and Children NICHD, Bethesda, MD, Bethesda, Maryland OBJECTIVE: Administration of 17 -hydroxyprogesteronecaproate (17-P) is associated with prevention of preterm deliveries in 30% of the patients. However, the mechanism of action of 17-P and whether it is a drug or prodrug remains unclear. Recently, we demonstrated that 17-P is not hydrolyzed by human hepatic and placental homogenates. The aim of this investigation is to determine whether 17-P is metabolized by human hepatic and placental microsomes by a pathway that does not involve its hydrolysis by esterases. STUDY DESIGN: Crude microsomal fractions from human livers and term placentas were ued. A dual radioactive labeled 17 -[3H]-hydroxy progestrone [14 C]-caproate was utilized. The metabolites formed were separated and identified by HPLC/MS and their amounts determined by scintillation spectrometry. RESULTS: Hepatic and placental microsomes catalyzed the formation of several hydroxylated derivatives of 17-P that retained the tritium and 14C atoms. In human liver, the metabolites formed were divided into the following three groups according to the extent of their hydroxylation as revealed by their mass: mono-, diand tri-hydroxylated 17-P which accounted for 63, 37 and 1% of the total formed, respectively. The major mono-hydroxylated compound formed by the liver accounted for 38% of the total metabolites formed. In human placenta, only monohydroxylated metabolites were formed. Two of these metabolites accounted for 16% of the total and were not formed by hepatic microsomes. The rates of metabolites formation by the placenta were approximately 7% of that by the liver. CONCLUSION: Human liver CYP isozymes metabolize 17-P to mono-, diand tri-hydroxylated compounds while in the placenta only mono-hydroxylated compounds are formed. Two of the metabolites formed by the placenta are not formed by the liver. At this time, it is unclear whether one or more of 17-P metabolites could contribute to its reported physiological effect. Supported by the Obstetric Pharmacology Research Network (OPRU/NICHD).

A quantum-chemical study of the interaction of the HeT+ ion with cycloalkanes and their oxidation products

The RHF/6-311G*(3d), RHF/6-311++G**(3df, 3p) and MP2/6-311G*(3d) ab initio methods were used to calculate the equilibrium structure of the products of the ion-molecular reaction of tritium ion transfer from HeT+ to cyclopentane and cyclohexane. Similar reactions with cyclopentanol and cyclopentanone were calculated at the RHF/6-311G*(3d) level. The interaction of HeT+ with cycloalkanes was found to produce onium ions with cyclic structures, in which the tritium atom held neighboring methylene groups together. With the alcohol and ketone, not only cyclic but also stabler linear cations could be formed, and the addition of the tritium ion directly to the oxygen atom was possible. The suggestion was made that the chain of tritium ion transfer reactions was the mechanism of the accumulation of tritium by hydrocarbon oxidation products when T2 was dissolved in mineral oils.

Hydrogen isotope sputtering of graphite by molecular dynamics simulation

We used a molecular dynamics simulation with the modified Brenner reactive empirical bond order potential to investigate the erosion of a graphite surface due to the incidence of hydrogen, deuterium, and tritium atoms. Incident particles cause pressure on the graphite surface, and the chemical bond between graphene layers then generates heat to erode the graphite surface. We evaluated the speed of surface destruction by calculating the pseudo-radial distribution function. The speed of surface destruction due to incident hydrogen isotopes was higher than that due to hydrogen atoms. The surface destruction increased exponentially and its decay time constant was a power function of the incident energy. We measured the erosion yield, which indicated a steady state for the graphite erosion. The erosion yield flux in the steady state increased linearly with the incident energy. The erosion yield flux was almost independent of the type of incident particle, and the erosion yield start time was smaller for hydrogen isotopes than for hydrogen atoms.

Rational Design of Transition-State Analogues as Potent Enzyme Inhibitors with Therapeutic Applications

The structures of the transition states for a variety of enzyme-catalyzed ribosyl group transfer reactions, determined by computational evaluation of multiple tritium and heavy atom kinetic isotope effects on these enzymatic reactions, have been found to show a considerable variation in the extent of bond cleavage at the ribosyl anomeric carbon. The calculated transition-state structures have been used to guide the design of high-affinity transition-state analogue inhibitors for 5'-methylthioadenosine nucleosidases with potential as therapeutic agents.

Decrease in the probability of tritium decay in an external electric field

The probability of tritium beta decay is shown to decrease under the effect of a constant uniform external electric field on the atom. For the tritium atom, the effect is due first to the reduction of the beta-decay endpoint energy and second to the reduction of the density of vacant bound electron states at the nucleus. Both of these factors reduce the beta-decay probability: the first reduces the probability of decay to continuum electron states, while the second reduces the probability of decay to a bound state.

Strong Isotope Effects on the Charge Transfer in Slow Collisions ofHe2+with Atomic Hydrogen, Deuterium, and Tritium

Probabilities and cross sections for charge transfer by He2+ impact on atomic hydrogen (H), deuterium (D), and tritium (T) at low collision energies are calculated. The results are obtained using an ab initio theory, which solves the time-dependent Schrödinger equation. For the H target, excellent agreement is achieved between the present and previous results. Differences by orders of magnitude are observed between the cross sections for H, D, and T. A method is introduced to separate the contributions of charge-transfer mechanisms due to radial and rotational coupling. The large differences observed for H, D, and T are attributed to isotope effects in the rotational coupling mechanism.

Kinetic properties during absorption in aged palladium–tritium system

The time-dependence of tritium absorption on aged (3 years) palladium powder in α and α&β areas has been experimentally measured for initial tritium pressures in the range 40–200 kPa and tritide temperatures in the range 22–65 °C. The results show that the absorption rate increases with initial tritium pressure (at constant temperature) in both α and α&β areas, and decreases with increasing temperature at constant pressure in the α&β area. The overall tritium absorption process of aged palladium is determined by two steps: (1) the chemisorption reaction on the surface of palladium tritide at the start of the absorption, when only the temperature of the palladium tritide influences the chemisorption reaction rate; (2) diffusion of tritium atoms through tritide during tritium absorption, when both the tritide temperature and the initial pressure of tritium molecules affect the reaction rate. The diffusion activation energy and chemisorption activation energy are 13.66 and 19.38 kJ/mol, respectively at 22–65 °C, the sum of which agrees with absorption and desorption transition enthalpies of the same unaged and aged palladium tritide at 35–75 °C.

Tritium redistribution between water and clay minerals

Hydrogen-isotope exchange between clay minerals and tritiated water was studied with kaolinite, montmorillonite and palygorskite. At all possible positions, tritium accumulated most intensively during the initial stage (10 to 20 days) but further increase of tritium concentration in experimental systems was much less intensive. Interaction of tritiated water with clay minerals decreased in a similar manner. In all samples, the highest amounts of tritium atoms and the maximum accumulation rates (V) were observed in the surface-adsorbed water (Vsurf) over the complete study period. The modes of tritium accumulation in the interlayer space (montmorillonite) and in the channels (palygorskite) (Vinter) are quite similar and both types of structures are very suitable for hydrogen-isotope exchange. Availability of well-developed paths for the access of T+ ions to structural OH-groups (Vstruct) enables intense tritium accumulation at these positions in montmorillonite and palygorskite (Vinter≅Vstruct). In kaolinite the access of T+ ions to structural OH-groups is more difficult, in spite of the considerable number of potential exchange positions in its structure, therefore resulting in lower tritium adsorption in comparison with the other two clay minerals.

Nonequilibrium processes in reactions of hot tritium atoms with cooled solid targets. Attenuation of the flow of tritium atoms in adsorption layers of alkyltrimethylammonium bromides

The permeability for atomic tritium of adsorption layers of aqueous solutio ns of alkyltrimethylammonium bromides RN(CH3)3Br differing in the length of the hydrocarbon radical R (C12H25, C14H29, C16H33) was studied. The change in the radioactivity of alanine present in the examined solutions was used as the measure of the attenuation of the flow of reactive tritium atoms. The formation of an adsorption monolayer of surfactant molecules on the liquid-gas phase boundary caused the radioactivity of alanine to decrease by a factor of 6.5 (R = C12H25) to 8 (R = C16H33) relative to the experiment with a straight alanine solution. A correlation between the structure of the adsorbed layers of alkyltrimethylammonium bromides and their permeability to atomic tritium is discussed.

Nonequilibrium processes in reactions of hot tritium atoms with cooled solid targets. Influence of the atomizer temperature on formation of labeled substances

A system consisting of a cold target and “hot” atoms generated by dissociation of tritium on a tungsten wire was studied with the aim to determine conditions for preparing tritium-labeled organic compounds with the maximal radiochemical yield. The influence of the atomizer temperature on the result of the reaction of tritium atoms with amino acids and tetraalkylammonium bromides was studied; homological series of the substrates were examined with the aim to evaluate the contributions of functional groups and hydrocarbon tail to the processes occurring in the target. The dependence of the yield of the labeled parent compound on the atomizer temperature varied in the range 1600–2000 K was determined. The rates of decarboxylation and deamination sharply grew with increasing temperature of the tungsten wire. The highest yield of labeled amino acids was attained at an atomizer temperature of 1800–1900 K, and at higher temperature their yield decreased. The difference between the activation energies of the elimination of the carboxy and amino groups and of the isotope exchange of hydrogen for tritium in the C-H bond appeared to be 93 and 59 kJ mol−1, respectively. For alkyltrimethylammonium bromides with the alkyl radicals C12H25, C14H29, and C16H33, the yield of the labeled parent compound reached 80–90% and was virtually independent of the atomizer temperature. The capability of tritium atoms to penetrate into the targets was evaluated. For the exponential model of the attenuation of the flow of tritium atoms inside the target, the attenuation factor for freeze-dried amino acids and alkyltrimethylammonium bromides as targets was 1.8 nm−1.