High-energy Tritons Research Articles

Modeling of the Creation of an Internal Cladding in Sapphire Optical Fiber Using the 6 Li(n,α)3H Reaction

The focus of this study is to model the creation of an internal waveguide in sapphire optical fiber. The model investigates ion implantation using the 6Li(n,α)3H reaction as a method for creating an internal waveguide in sapphire optical fiber. The method involves irradiating a sapphire fiber that is surrounded by an annulus of Li-6 enriched lithium carbonate (Li2CO3) powder, in a nuclear reactor. The 6 Li(n,α)3H reaction creates high-energy tritons and alpha particles that irradiate the fiber simultaneously to a depth of 24 μm, along the entire periphery of the sapphire fiber. The triton and alpha particle irradiation slightly reduces the index of refraction in the fiber's periphery, thus creating a refractive cladding within the fiber. Refractive index profiles are predicted by tracking tritons and alpha particles, using the Monte-Carlo radiation transport code MCNP. Measured transmitted light intensity profiles are compared with predicted light intensity profiles, by modeling the transport of 1550 nm light through modified sapphire fiber using FIMMWAVE software.

Neutron spectroscopy measurements of tritium beam transport at JET

A detailed description of the 14 MeV neutron emission in plasmas heated by neutral beam injection has been carried out by coupling Monte Carlo calculations of the neutron emission spectrum with TRANSP modelling of the beam ion energy distributions. The model is used to study tritium beam injection experiments of the JET trace tritium campaign for internal transport barrier (ITB) and H-mode discharges. For ITB discharges, the measured neutron emission spectrum is well described by modelling using as input the beam ion distribution calculated with TRANSP. For H mode discharges the neutron spectrum can be reproduced only if high energy tritons are lost from the plasma, suggesting the possible role of low frequency tearing modes on the beam ions. The presented results are of relevance for tritium beam transport studies in trace tritium experiments and, more generally, for deuterium and tritium transport studies in high power experiments using neutron emission spectroscopy.

Feasibility of Reduced Tritium Circulation in the Heliotron Reactor by Enhancing Fusion Reactivity Using ICRF

A scheme for reducing the tritium fraction in DT fusion reactors is investigated by means of enhancing the fusion reactivity using high-power ICRF heating in heliotron reactors. We assume a situation that the density fraction of tritons is less than 10%, and the minority tritons are accelerated by ICRF waves. We then analyze the increase of fusion reactivity by assuming an effective temperature of high-energy tritons and examine the possibility of realizing a fusion reactor with this concept. The required ICRF power and the generated fusion power are also estimated.

Surface loads and edge fast ion distribution for co- and counter-injection in ASDEX Upgrade

The fast particle flux onto the material surfaces and the fast ion edge distribution are compared between ASDEX Upgrade H-mode and quiescent H-mode (QH-mode) in the presence of toroidal ripple and radial electric field Er by using the orbit-following Monte Carlo code ASCOT. So far, the QH-mode has been obtained only with counter-injection of the neutral beams. The wall load caused by co-injected beams in H-mode is small and without ripple it is negligible. With counter-injection (QH-mode case), the wall load is substantial even without the ripple. The ripple always increases the wall load, but the divertor load is either decreased or is unchanged. The effect of Er alone is small, but it boosts the ripple-trapping of beam particles near the location of its maximum absolute value on the horizontal midplane. The fast ion density and its gradient in the pedestal region are higher for counter-injected than for co-injected particles. The ripple decreases the density gradient in both the cases. To make a connection with the experiment, the flux of high-energy tritons from beam–plasma interactions onto the surfaces is evaluated. The simulated flux of tritons impinging on the material surfaces is in qualitative agreement with the measured tritium distribution on the wall and divertor.

Puzzle for the existence of 3α + N structure in A=13 system

Spin-isospin excitations in 13 N have been studied by means of the (3 He ,t) and (3 He ,tp) reactions at the bombarding energy of E(3 He ) = 450 MeV . The zero-degree (3 He ,t) spectrum is found to be similar to those from the (p,n) reactions at intermediate energies, suggesting a simple direct reaction mechanism at E(3 He ) = 450 MeV . Three pairs of Gamow-Teller (GT) states with Jπ = 1/2- and 3/2- have been strongly excited at θlab. = 0°. Microscopic structures of the states in 13 N have been studied by observing decay protons in coincidence with high energy tritons measured at θlab. = 0°. The branching ratios for proton decay from the GT states in 13 N to the final low-lying T =0 states in 12 C were obtained. The wave functions of the excited states in 13 N are discussed in the view point of α cluster model.

PROMPT BETA SPECTROSCOPY AS A DIAGNOSTIC FOR MIX IN IGNITED NIF CAPSULES

The National Ignition Facility (NIF) technology is designed to drive deuterium–tritium (DT) internal confinement fusion (ICF) targets to ignition using indirect radiation from laser beam energy captured in a hohlraum. Hydrodynamical instabilities at interfaces in the ICF capsule leading to mix between the DT fuel and the ablator shell material are of fundamental physical interest and can affect the performance characteristics of the capsule. Here we describe new radiochemical diagnostics for mix processes in ICF capsules with plastic or Be (0.9% Cu ) ablator shells. Reactions of high-energy tritons with shell material produce high-energy β-emitters. We show that mix between the DT fuel and the shell material enhances high-energy prompt beta emission from these reactions by more than an order of magnitude over that expected in the absence of mix. We further show how a mix signal could be detectable in an ignition failure regime corresponding to yields greater than about 2 kJ.

Improved in situ calibration technique for ITER ex-vessel neutron yield monitor

The ITER neutron diagnostic system needs to cover both the DD- and DT-phases of ITER experiments. To ensure the required accuracy for diagnosing both phases, it is preferable to calibrate the diagnostic system to both DD and DT neutrons. In this paper, the feasibility of two kinds of calibration measurements has been verified through MCNP simulations for the ITER ex-vessel neutron yield monitor. It is indicated that both calibration procedures using DD and DT neutron generators can be implemented with the required accuracies within a realistic measurement time. In the advanced DD-phase of the ITER experiment with high density D plasma producing high energy tritons, where a number of DT neutrons are produced, the independent calibration to DD or DT neutrons could lead to unacceptable measurement uncertainty. An effective method to reduce the measurement uncertainty for the two-component neutron source is discussed.

Structure of the Gamow-Teller resonance in 58Cu studied via the proton-and γ-decay measurements

The Gamow-Teller (GT) states in 58Cu have been studied by 58Ni(3He, t + p) and 58Ni(3He, t + γ) coincidence experiments at E(3He)=450 MeV and θ=0°. Proton emissions from the GT states in 58Cu to the hole states in 57Ni have been observed with solid-state detectors in coincidence with high-energy tritons measured with a magnetic spectrometer. For the first time, γ-ray emissions from the excited states in 58Cu and in 57Ni, following the 58Ni(3He, t + p) reaction at intermediate energies, have also been observed in coincidence with tritons. The wave functions of the T=1 and T=2 GT states with the f72/−1 neutron-hole configuration are inferred to be strongly coupled to 2p-2h configurations, making fragmented GT strengths in 58Cu.

Nuclear structure of the spin-isospin excited states inN13studied via the(He3,t)and(He3,tp)reactions at450MeV

Spin-isospin excitations in $^{13}\mathrm{N}$ have been studied by means of the $(^{3}\mathrm{He},t)$ and $(^{3}\mathrm{He},tp)$ reactions at a bombarding energy of $E(^{3}\mathrm{He})=450\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$. The zero-degree $(^{3}\mathrm{He},t)$ spectrum is found to be similar to those from the $(p,n)$ reactions at intermediate energies, suggesting a simple direct reaction mechanism at $E(^{3}\mathrm{He})=450\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$. The Gamow-Teller $(\mathrm{GT})$ states with ${J}^{\ensuremath{\pi}}=1∕{2}^{\ensuremath{-}}$ and $3∕{2}^{\ensuremath{-}}$ have been strongly excited at ${\ensuremath{\theta}}_{\mathrm{lab}}=0\ifmmode^\circ\else\textdegree\fi{}$. The angular distribution of cross sections for the $^{13}\mathrm{C}(^{3}\mathrm{He},t)^{13}\mathrm{N}$ reaction and the elastic $^{3}\mathrm{He}$ scattering off $^{13}\mathrm{C}$ were obtained at ${\ensuremath{\theta}}_{\mathrm{lab}}=0\ifmmode^\circ\else\textdegree\fi{}--17\ifmmode^\circ\else\textdegree\fi{}$ and at ${\ensuremath{\theta}}_{\mathrm{lab}}=2\ifmmode^\circ\else\textdegree\fi{}--22\ifmmode^\circ\else\textdegree\fi{}$, respectively. The obtained experimental results were compared with calculations performed in distorted-wave Born approximation. Microscopic structures of the states in $^{13}\mathrm{N}$ have further been studied by observing decay protons in coincidence with high-energy tritons measured at ${\ensuremath{\theta}}_{\mathrm{lab}}=0\ifmmode^\circ\else\textdegree\fi{}$. The branching ratios for proton decay from the $\mathrm{GT}$ states in $^{13}\mathrm{N}$ to the final low-lying $T=0$ states in $^{12}\mathrm{C}$ were obtained. The wave functions of the excited states in $^{13}\mathrm{N}$ are discussed on the basis of obtained experimental data and relevant theoretical calculations.

Microscopic structure of the Gamow-Teller resonance inCu58

The Gamow-Teller (GT) states in $^{58}\mathrm{Cu}$ have been studied via the $^{58}\mathrm{Ni}(^{3}\mathrm{He},t+p)$ and $^{58}\mathrm{Ni}(^{3}\mathrm{He},t+\ensuremath{\gamma})$ coincidence experiments. The GT states in $^{58}\mathrm{Cu}$ at ${E}_{x}=6--12\phantom{\rule{0.3em}{0ex}}\text{MeV}$, where both $T=1$ and $T=2,{1}^{+}$ states exist, are excited strongly in the $^{58}\mathrm{Ni}(^{3}\mathrm{He},t)$ reaction at $E(^{3}\mathrm{He})=450\phantom{\rule{0.3em}{0ex}}\text{MeV}$ and $\ensuremath{\theta}=0\ifmmode^\circ\else\textdegree\fi{}$. Proton emissions from the GT states in $^{58}\mathrm{Cu}$ to the hole states in $^{57}\mathrm{Ni}$ have been observed with solid-state detectors in coincidence with high energy tritons measured with a magnetic spectrometer. For the first time, the $\ensuremath{\gamma}$-ray emissions from the excited states in $^{58}\mathrm{Cu}$ and in $^{57}\mathrm{Ni}$, following the $^{58}\mathrm{Ni}(^{3}\mathrm{He},t+p)$ reaction at intermediate energies, have also been observed in coincidence with tritons. Strengths of proton decay into several neutron-hole states in $^{57}\mathrm{Ni}$ and $\ensuremath{\gamma}$-decay strengths are used to discuss the wave functions of the GT states in $^{58}\mathrm{Cu}$. The $T=1$ and $T=2$ GT states do only weakly decay into a $T=3∕2,{f}_{7∕2}^{\ensuremath{-}1}$ neutron-hole state at $5.230\phantom{\rule{0.3em}{0ex}}\text{MeV}$ in $^{57}\mathrm{Ni}$, which is strongly excited via the $^{58}\mathrm{Ni}(p,d)^{57}\mathrm{Ni}$ reaction. The wave functions of the $T=1$ and $T=2$ GT states with the ${f}_{7∕2}^{\ensuremath{-}1}$ neutron-hole configuration are inferred to be strongly coupled to $2p\text{\ensuremath{-}}2h$ configurations, making fragmented GT strengths in $^{58}\mathrm{Cu}$.

Tritium retention of plasma facing components in tokamaks

The areal distribution of tritium retention in tiles from TEXTOR, TFTR, JT-60U and JET has been measured via the imaging plate technique and the results are discussed from the perspective of carbon–hydrogen chemistry. It is found that the observed tritium distribution clearly shows asymmetries in poloidal and toroidal directions and also reflects the local temperature history of the analyzed tiles. We show the first clear evidence of the loss of high energy tritons by toroidal magnetic field ripple. We distinguish three different contributions to tritium retention in tokamaks with carbon plasma facing components: high energy tritons escaping from the core plasma, low energy ions and neutrals from the edge plasma, and molecular tritium from gas fueling. These components are retained at different depths and with different concentrations. Tritium from the edge plasma dominates the retained inventory but could be reduced if the surface temperature was higher. We propose tokamak operation with plasma facing components above 1000 K as a possible way to reduce the tritium inventory.

Tritium Profiles on the Surface of Graphite Tiles used in JT-60U

Tritium Imaging Plate Technique (TIPT) is used to measure the tritium areal distribution on plasma facing graphite tiles of JT-60U. Measurement of the W-shaped divertor region showed that the surface tritium distribution of tiles used under the “both-side pumping” system was similar to that of tiles used under the “inner-side pumping” system. This result suggests that tritium retained in those tiles is not affected by the type of exhaust system because this tritium was implanted with high energy. Thus, tritons produced by D-D reaction were implanted in the plasma facing wall without completely losing their initial energy. The tritium level beneath the redeposited layer on the inner divertor target tile was about three times as high as that of the surface of the redeposited layer. The toroidal surface tritium distribution suggested ripple loss of high energy tritons. These results also indicate that long-term tritium retention in JT-60U was caused by implantation of high-energy tritons.

Tritium detection in plasma facing component by imaging plate technique

Tritium imaging plate technique (TIPT) has been successfully applied to measure the tritium areal distribution on various graphite tiles used as limiters in TEXTOR. It is observed that tritium distribution on the ALT-II tile is quite homogeneous and different from deuterium distribution and the tritium in redeposited layer is rather small. Such tritium distribution on the graphite tiles in TEXTOR behaves different compared to those in JET and TFTR where tritium was used as fueling gas or NBI injection. In JET and TFTR the tritium is part of the fuel and is co-deposited and retained in a similar manner as the deuterium. In a device like TEXTOR, the high-energy tritons are decoupled from the thermalized deuterons and show different behavior of retention; the main retention mechanism is deep implantation rather than co-deposition with eroded carbon on redeposition-dominated areas. It is also found that the tritium distribution measurements give useful new information on plasma-wall interactions.

Release of tritium from boron carbide

The release of tritium from B4C powder and a single crystal has been investigated in the temperature range 400–800 °C. High-energy tritons, produced by bombarding a Cu target with 104 MeV α-particles, were used to prepare samples with a uniform tritium distribution. The release curves were analysed under the assumptions that (a) the diffusion within the B4C is the rate-controlling step and (b) the effective average grain size can be deduced from the specific surface area of the powder. The obtained diffusion coefficients (in cm2 s–1) can be described with the following equation: D(B4C)= 2.3 × 10–4 exp(–96 ± 10 kJ mol–1//RT). The release of tritium from sintered material, with densities of 70–95% of the theoretical density, as well as from preoxidized samples has also been investigated. The diffusion coefficient D(B2O3) for tritium in B2O3 is more than two orders of magnitude smaller than D(B4C).

36 MeV triton inelastic scattering and one-nucleon transfer reactions

Differential cross sections have been obtained for inelastic scattering and one nucleon transfers on targets of 28,30Si and 26Mg using a 36 MeV beam of tritons. CCBA and DWBA fits have been applied to these data and the deformation parameters and spectroscopic factors obtained compared to previous measurements and shell model predictions. Comparisons are made of the fits obtained with zero-range, local energy approximation and exact finite range calculations. High energy tritons are shown to be a precise and valuable spectroscopic tool.

Some thoughts on the production of muons for fusion catalysis

For muon-catalyzed fusion to be of practical interest, a very efficient means of producing muons must be found. We describe here some schemes for producing muons that may be more energy efficient than any heretofore proposed. There are, in particular, some potential advantages of creating muons from collisions of high-energy tritons confined in a magnetic mirror configuration. If one could catalyze 200 fusions per muon and employ a uranium blanket that would multiply the neutron energy by a factor of ten, one might produce electricity with an overall plant efficiency (ratio of electric energy produced to nuclear energy released) approaching 30%.

Tritium permeation considerations in the MARS direct convertor

The direct convertors located in the end cells of the MARS Tandem Mirror Fusion reactor recover the electrostatic energy of plasma particles that leak out of the center cell region. Since the direct convertors will be implanted in part by escaping high energy (> 40 keV) tritons at fluxes of over 10 16 T cm −2 s −1 and low energy (∼30 eV) tritons at fluxes of over 10 18 T cm −2 s −1, the possibility of tritium permeation into the water coolant, must be assessed. The current design calls for a TZM (Mo-0.5Ti-0.1Zr) structure; vanadium has also been under consideration. Combined nuclear reaction profiling and thermal desorption spectroscopy measurements on TZM show that deuterium retention is dominated by radiation damage traps with 1–1.5 eV detrapping energy, and bulk chemical traps of ≈ 0.7 eV presumably from the Ti and Zr alloying additions. Analysis of deuterium reemission data from vanadium demonstrates that molecular recombination controls the bulk retention. Values of the recombination constant for vanadium vary from 1.1 × 10 −22 cm 4 sec −1 at 500 °C to 3.6 × 10 −24 cm 4 sec −1 at 300 °C. Using these results and available literature data, calculations for Be on TZM, V, and V on Cu using DIFFUSE predict steady state permeation rates in excess of 10 8 Ci day −1 for bare V, 2000 Ci day −1 for Be on TZM, and ≈ 300 Ci day −1 for V on Cu.

Charge-exchange reaction on 12C with 217 MeV 3He particles

Differential cross sections for the ( 3 He, t) charge-exchange reaction have been measured on a 12 C target with 217 MeV 3 He particles. High energy tritons were detected using a thick Ge(Li) crystal (43 mm) and a 4 mm Si(Li) detector in an E - ΔE telescope. Microscopic DWBA calculations have been carried out, using the rather well known wave functions of the 12 C levels from Gillet and Vinh-Mau. The sensitivity of this reaction to the different terms of the two-body effective interaction is discussed. A comparison of the ( 3 He, t) and ( 3 He, 3 He') reactions populating analog final states is also presented. The two-step mechanisms ( 3 He,α)(α, t) and ( 3 He, d)(d, t) are introduced for the first two levels 1 + (g.s.) and 2 + (0.969 MeV) and the results emphasize the importance of such processes at high energy.

Extensions to the pre-equilibrium statistical model and a study of complex particle emission

Griffin's pre-equilibrium statistical model for nuclear reactions has been further extended to take account of the distinguishability between protons and neutrons as well as of the competition of particle emission with particle-hole pair creation and destruction. In addition, an empirical factor equal to the factorial of the mass number of the emitted particle has been introduced into the rate expressions for particle emission. In this extended form, the model has been used to analyze the spectra of protons, deuterons, tritons, 3He and 4He ions emitted in protoninduced reactions. For each reaction system, the model parameters were varied to reproduce the proton spectrum, and the spectra for the remaining four particle types were calculated with no added adjustable parameters. For systems lighter than gold, the relative charged particle yields are well reproduced by the model, while for 197Au and 209Bi too few tritons are predicted. The spectral shapes for the complex particles are approximately reproduced at bombarding energies around 30 MeV, but for higher energies the data show more high-energy tritons, 3He and 4He ions than can be accounted for with the model. It is thought that these high-energy particles may be produced in direct two and three nucleon pick-up processes which are not included in the model. The initial exciton numbers obtained from the analysis appear to be consistent with earlier values if strong collective excitations are removed from the proton spectra. The fraction of pre-equilibrium emission is found to increase with increasing bombarding energy.

Emission of fast helium nuclei and tritons from high-energy nuclear disintegrations

On the basis of the result that from high-energy nuclear disintegration fast helium nuclei and tritons with energies greater than 50 MeV are emitted with equal frequencies, various known mechanisms for the emission of these particles are examined. It is suggested that such emission can also take place through the absorption of mesons in4Heclusters present in the outer region of the nucleus.