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Register a new userImproved modelling of helium and tritium production for spallation targets
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Reliable predictions of light charged particle production in spallation reactions are important to correctly assess gas production in spallation targets. In particular, the helium production yield is important for assessing damage in the window separating the accelerator vacuum from a spallation target, and tritium is a major contributor to the target radioactivity. Up to now, the models available in the MCNPX transport code, including the widely used default option Bertini-Dresner and the INCL4.2-ABLA combination of models, were not able to correctly predict light charged particle yields. The work done recently on both the intranuclear cascade model INCL4, in which cluster emission through a coalescence process has been introduced, and on the de-excitation model ABLA allows correcting these deficiencies. This paper shows that the coalescence emission plays an important role in the tritium and $^3He$ production and that the combination of the newly develop
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Spallation neutron production in proton induced reactions on Al, Fe, Zr, W, Pb and Th targets at 1.2 GeV and on Fe and Pb at 0.8, and 1.6 GeV measured at the SATURNE accelerator in Saclay is reported. The experimental double-differential cross-sections are compared with calculations performed with different intra-nuclear cascade models implemented in high energy transport codes. The broad angular coverage also allowed the determination of average neutron multiplicities above 2 MeV. Deficiencies in some of the models commonly used for applications are pointed out.
The neutron yields observed in inertial confinement fusion experiments for higher convergence ratios are about two orders of magnitude smaller than the neutron yields predicted by one-dimensional models, the discrepancy being attributed to the development of instabilities. We consider the possibility that ignition and a moderate gain could be achieved with existing laser facilities if the laser driver energy is used to produce only the radial compression of the fuel capsule to high densities but relatively low temperatures, while the ignition of the fusion reactions in the compressed fuel capsule will be effected by a synchronized hypervelocity impact. A positively-charged incident projectile can be accelerated to velocities of 3.5 x 10^6 m/s, resulting in ignition temperatures of about 4 keV, by a conventional low-beta linac having a length of 13 km if deuterium-tritium densities of 570 g/cm^3 could be obtained by laser-driven compression.
Targets consisting of 3,4He implanted into thin aluminum foils (approximately 100, 200 or 600 ug/cm^2) were prepared using intense (a few uA) helium beams at low energy (approximately 20, 40 or 100 keV). Uniformity of the implantation was achieved by a beam raster across a 12 mm diameter tantalum collimator at the rates of 0.1 Hz in the vertical direction and 1 Hz in the horizontal direction. Helium implantation into the very thin (approximately 80-100 ug/cm^2) aluminum foils failed to produce useful targets (with only approximately 10% of the helium retained) due to an under estimation of the range by the code SRIM. The range of low energy helium in aluminum predicted by Northcliffe and Shilling and the NIST online tabulation are observed on the other hand to over estimate the range of low energy helium ions in aluminum. An attempt to increase the amount of helium by implanting a second deeper layer was also carried out, but it did not significantly increase the helium content beyond the blistering limit (approximately 6 x 10^17 helium/cm^2). The implanted targets were bombarded with moderately intense 4He and 16O beams of 50-100 particle nA . Rutherford Back Scattering of 1.0 and 2.5 MeV proton beams and recoil helium from 15.0 MeV oxygen beams were used to study the helium content and profile before, during and after bombardments. We observed the helium content and profile to be very stable even after a prolonged bombardment (up to two days) with moderately intense beams of 16O or 4He. Helium implanted into thin (aluminum) foils is a good choice for thin helium targets needed, for example, for a measurement of the 3he(a,g)7Be reaction and the associated S34 astrophysical cross section factor (S-factor).
In order to perform quantitative tritium and helium analysis in thin film sample by using enhanced proton backscattering (EPBS), EPBS spectra for several samples consisting of non-RBS light elements (i.e., T, 4He, 12C, 16O, natSi), medium and heavy elements have been measured and analyzed by using analytical SIMNRA and Monte Carlo-based CORTEO codes. The CORTEO code used in this paper is modified and some non-RBS cross sections of proton scattering from T, 4He, 12C, 14N, 16O and natSi elements taken from ENDF/B-VII.1 database and the calculations of SigmaCalc code are incorporated. All cross section data needed in CORTEO code over the entire proton incident energy-scattering angle plane are obtained by interpolation. It is quantitatively observed that the multiple and plural scattering effects have little impact on energy spectra for light elements like T, He, C, O and Si, and the RBS cross sections of light elements, instead of the non-RBS cross sections, can be used in SIMNRA code for dual scattering calculations for EPBS analysis. It is also observed that at the low energy part of energy spectrum the results given by CORTEO code are higher than the results of SIMNRA code and are in better agreement with the experimental data, especially when heavier elements exist in samples. For tritium analysis, the tritium depth distributions should not be simply adjusted to fit the experimental spectra when the multiple and plural scattering contributions are not completely accounted, or else inaccurate results may be obtained. For medium and heavy matrix elements, when full Monte Carlo RBS calculations are used in CORTEO code, the results from CORTEO code are in good agreement with the experimental results at the low energy part of energy spectra, at this moment quantitative tritium and helium analysis in thin film sample by using enhanced proton backscattering can be performed reliably.
The beta decay of tritium in the form of molecular TT is the basis of sensitive experiments to measure neutrino mass. The final-state electronic, vibrational, and rotational excitations modify the beta spectrum significantly, and are obtained from theory. We report measurements of the branching ratios to specific ionization states for the isotopolog HT. Two earlier, concordant measurements gave branching ratios of HT to the bound HHe$^+$ ion of 89.5% and 93.2%, in sharp disagreement with the theoretical prediction of 55-57%, raising concerns about the theorys reliability in neutrino mass experiments. Our result, 56.5(6)%, is compatible with the theoretical expectation and disagrees strongly with the previous measurements.
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