Ion acceleration and D-D nuclear fusion in laser-generated plasma from advanced deuterated polyethylene

Deuterated polyethylene targets have been irradiated by means of a 10¹⁶ W/cm² laser using 600 J pulse energy, 1315 nm wavelength, 300 ps pulse duration and 70 micron spot diameter. The plasma parameters were measured using on-line diagnostics based on ion collectors, SiC detectors and plastic scintillators, all employed in time-of-flight configuration. In addition, a Thomson parabola spectrometer, an X-ray streak camera, and calibrated neutron dosimeter bubble detectors were employed. Characteristic protons and neutrons at maximum energies of 3.0 MeV and 2.45 MeV, respectively, were detected, confirming that energy spectra of reaction products coming from deuterium-deuterium nuclear fusion occur. In thick advanced targets a fusion rate of the order of 2 × 10⁸ fusions per laser shot was calculated.

Three-dimensional simulation strategy to determine the effects of turbulent mixing on inertial-confinement-fusion capsule performance

In this paper, we present and justify an effective strategy for performing three-dimensional (3D) inertial-confinement-fusion (ICF) capsule simulations. We have evaluated a frequently used strategy in which two-dimensional (2D) simulations are rotated to 3D once sufficient relevant 2D flow physics has been captured and fine resolution requirements can be restricted to relatively small regions. This addresses situations typical of ICF capsules which are otherwise prohibitively intensive computationally. We tested this approach for our previously reported fully 3D simulations of laser-driven reshock experiments where we can use the available 3D data as reference. Our studies indicate that simulations that begin as purely 2D lead to significant underprediction of mixing and turbulent kinetic energy production at later time when compared to the fully 3D simulations. If, however, additional suitable nonuniform perturbations are applied at the time of rotation to 3D, we show that one can obtain good agreement with the purely 3D simulation data, as measured by vorticity distributions as well as integrated mixing and turbulent kinetic energy measurements. Next, we present results of simulations of a simple OMEGA-type ICF capsule using the developed strategy. These simulations are in good agreement with available experimental data and suggest that the dominant mechanism for yield degradation in ICF implosions is hydrodynamic instability growth seeded by long-wavelength surface defects. This effect is compounded by drive asymmetries and amplified by repeated shock interactions with an increasingly distorted shell, which results in further yield reduction. Our simulations are performed with and without drive asymmetries in order to compare the importance of these effects to those of surface defects; our simulations indicate that long-wavelength surface defects degrade yield by approximately 60% and short-wavelength drive asymmetry degrades yield by a further 30%.

Optimization of the neutron yield in fusion plasmas produced by Coulomb explosions of deuterium clusters irradiated by a petawatt laser

The kinetic energy of hot (multi-keV) ions from the laser-driven Coulomb explosion of deuterium clusters and the resulting fusion yield in plasmas formed from these exploding clusters has been investigated under a variety of conditions using the Texas Petawatt laser. An optimum laser intensity was found for producing neutrons in these cluster fusion plasmas with corresponding average ion energies of 14 keV. The substantial volume (1-10 mm(3)) of the laser-cluster interaction produced by the petawatt peak power laser pulse led to a fusion yield of 1.6×10(7) neutrons in a single shot with a 120 J, 170 fs laser pulse. Possible effects of prepulses are discussed.

The long-term evolution of D2+ nuclear wave-packet with interaction of intense femtosecond laser pulse

We investigate the long-term evolution of D2+ nuclear wave-packet after interacting with a 5 fs, 800 nm laser pulse at an intensity of 0.5 x 10(14) W/cm2. The nuclear wave-packet evolves in field-free condition for very long time after the laser pulse. The collapse and revival of nuclear wave-packet is studied. The scale of the classical time (approximately 25 fs), the revival time (approximately 580 fs) and the super-revival time (approximately 12 ps) are determined from the simulation as well as the calculation. The constituents of long-standing nuclear wave-packet are also analyzed.

Effect of low and zero magnetic field on the hyperpolarization lifetime in parahydrogenated perdeuterated molecules

Hyperpolarization can be kept for times longer than T(1) if it is maintained in a singlet state, from which transitions are not allowed. Another, more direct, way to slower the relaxation process consists in the use of perdeuterated molecules. Here both methods have been applied and the hyperpolarization (induced by para-H(2)) decay rate has been measured at two different magnetic fields: earth field and zero field. While relaxation is very slow at earth field, it becomes faster at zero field: this rather unexpected finding has been explained on the basis of isotropic mixing between (1)H and (2)H.

Near ultraviolet photolysis of deuterated pyrrole

High resolution time-of-flight (TOF) measurements of the D atom fragments arising in the near ultraviolet (UV) photodissociation of deuterated pyrrole are reported. Structures evident in the measured TOF spectra are all interpretable in terms of N-D bond fission, and population of selected vibrational states of the pyrrolyl-d(4) co-fragment -- thereby clarifying previous uncertainties regarding the branching into different vibronic states of the pyrrolyl radical following UV excitation of pyrrole.

Towards the enhancement of the photon/neutron discrimination of C6D6 detectors in the range from 1 to 10 MeV using liquid scintillator materials doped with high-Z elements

The study on the behaviour of deuterated benzene detectors in the energy range from 1 to 10 MeV has been carried out. It is shown that the photon-to-neutron discrimination, attained with standard detectors, can be improved by doping the C6D6 liquid scintillator with high-Z elements. The motivation for doping the organic scintillator stems from the fact that they should increase the gamma detection efficiencies with no significant changes in the abilities to detect neutrons. The results obtained using the MCNP and EGS4 codes show that increasing the fraction of high-Z elements: (a) the energy deposited in the medium by photons increases, (b) the energy deposited by neutrons decreases and (c) the rate of detection of photon/neutron is enhanced. Owing to their low sensitivity to neutrons and the enhanced gamma detection efficiency, these detectors could be ideally used to carry out studies in mixed neutron-photon fields in the energy range considered and to assess the gamma backgrounds in noisy neutron environments.

Studies on depth-dose-distribution controls by deuteration and void formation in boron neutron capture therapy

Physical studies on (i) replacement of heavy water for body water (deuteration), and (ii) formation of a void in human body (void formation) were performed as control techniques for dose distribution in a human head under neutron capture therapy. Simulation calculations were performed for a human-head-size cylindrical phantom using a two-dimensional transport calculation code for mono-energetic incidences of higher-energy epi-thermal neutrons (1.2-10 keV), lower-energy epi-thermal neutrons (3.1-23 eV) and thermal neutrons (1 meV to 0.5 eV). The deuteration was confirmed to be effective both in thermal neutron incidence and in epi-thermal neutron incidence from the viewpoints of improvement of the thermal neutron flux distribution and elimination of the secondary gamma rays. For the void formation, a void was assumed to be 4 cm in diameter and 3 cm in depth at the surface part in this study. It was confirmed that the treatable depth was improved almost 2 cm for any incident neutron energy in the case of the 10 cm irradiation field diameter. It was made clear that the improvement effect was larger in isotropic incidence than in parallel incidence, in the case that an irradiation field size was delimited fitting into a void diameter.

Photo-induced fractionation of water isotopomers in the Martian atmosphere

The history and size of the water reservoirs on early Mars can be constrained using isotopic ratios of deuterium to hydrogen. We present new laboratory measurements of the ultraviolet cross-sections of H2O and its isotopomers, and modeling calculations in support of a photo-induced fractionation effect (PHIFE), that reconciles a discrepancy between past theoretical modeling and recent observations. This supports the hypothesis that Mars had an early warm atmosphere and has lost at least a 50-m global layer of water. Likely applications of PHIFE to other planetary atmospheres are sketched.

Hydrogen atom formation by ultrasound in D2O solutions of nitrone spin traps

To elucidate the mechanism of ultrasonically induced H atom formation in D2O solutions of nitrone spin traps, alpha-phenyl-N-tert-butylnitrone (PBN) and alpha-(4-pyridyl-1-oxide)- N-tert-butylnitrone (POBN) were exposed to 50 kHz ultrasound in the presence of Ar, and the ratio of the ESR signal of the H-spin adduct to that of the D-spin adduct (H/D ratio) was examined. The H/D ratio increased with the concentration of the spin traps. The magnitude of the H/D ratios correlates with the hydrophobicity of the spin traps. The H/D ratios for the more hydrophobic spin trap, PBN, are larger than those for POBN at all concentrations. Xenon, which has a lower thermal conductivity than argon, was employed for creating higher final temperatures of the cavitation bubbles. For the less hydrophobic spin trap POBN the H/D ratio is lower for xenon than for argon. A similar result was found for PBN at lower concentrations. These results show that the H adducts of PBN and POBN are formed from the spin traps or their decomposition products by homolytic scission of C-H bonds due to pyrolysis.

Neutron microscopy. The low-damage imaging of specialized organic materials

It is shown that, insofar as radiation damage is concerned, transmission neutron microscopy using neutrons in the energy range approximately 0.0001-1.0 eV is extremely attractive for the imaging of specialized organic materials. By "specialized organic materials" is meant organic specimens composed entirely of specific isotopes that have been selected on the basis of their favorable properties with regard to radiation damage. In connection with such specimens, it is demonstrated that at a resolution of, for example, 100 A, neutrons will have an advantage over soft X-rays in terms of radiation damage, provided that the inherent (neutron) bright field image contrast turns out to be greater than 10(-5). Suggestions relating to (a) the comprehensive calculation of the radiation damage sustained by specialized organic specimens under slow neutron irradiation, (b) the construction of a theory of image formation in the neutron microscope, (c) the development of neutron lenses/focusing devices, and (d) the development of a brighter neutron source (essential for neutron microscopy) are outlined in some detail. The paper concludes with two appendices, which provide important background material.