High-intensity lasers as radiation sources

In the last decade or so, an evolution in experimental relativistic laser-plasma physics has led to highly sophisticated lasers which are now capable of generating ultra-short pulses and can be focused to intensities in excess of 10²¹ W cm^-2. The laser interaction with solid or gas targets can generate collimated beams of highly energetic electrons, protons and ions. These high-intensity laser systems, therefore, turn out to be versatile and powerful sources of radiation and high-energy particles, without recourse to large-scale facilities such as nuclear reactors or particle accelerators. The potential to induce various kinds of nuclear reactions with laser-induced radiation fields has been demonstrated at several laboratories in recent years. The present paper lays out a comprehensive overview of nuclear reactions induced by high-intensity laser matter interactions. Mechanisms for electron, proton and ion acceleration, in addition to secondary bremsstrahlung, positron and neutron production, are addressed, with a focus on the types of nuclear reactions that are possible and potential applications. Discussion of the extrapolation of these processes and applications to the next generation of table-top lasers under construction is also presented.     

Multi-species detection using multi-mode absorption spectroscopy (MUMAS)

The detection of multiple species using a single laser and single detector employing multi-mode absorption spectroscopy (MUMAS) is reported. An in-house constructed, diode-pumped, Er:Yb:glass micro-laser operating at 1,565 nm with 10 modes separated by 18 GHz was used to record MUMAS signals in a gas mixture containing C₂H₂, N₂O and CO. The components of the mixture were detected simultaneously by identifying multiple transitions in each of the species. By using temperature- and pressure-dependent modelled spectral fits to the data, partial pressures of each species in the mixture were determined with an uncertainty of ±2 %.     

Glutathionyl transferase catalyzed addition of glutathione to COMC: a new hypothesis for antitumor activity

[reaction: see text] Data are presented indicating that the potent antitumor activity of 2-crotonyloxymethyl-(4R,5R,6R)-4,5,6-trihydroxy-2-cyclohexenone (COTC) and 2-crotonyloxymethyl-2-cyclohexenone (COMC) is not likely the result of glyoxalase I inhibition, as has long been assumed. An alternative hypothesis is presented, based on the finding that COMC is a substrate for human glutathionyl transferase, which produces a transient, highly electrophilic glutathionylated 2-exomethylenecyclohexanone that can covalently modify proteins and nucleic acids.     

Total Synthesis of (-)-lasubine II by the conjugate addition and intramolecular acylation of an amino ester with an acetylenic sulfone

[reaction: see text] The conjugate addition of methyl (S)-(2-piperidyl)acetate (3) to 2-(3,4-dimethoxyphenyl)-1-(p-toluenesulfonyl)ethyne (4), followed by LDA-promoted intramolecular acylation, stereoselective reduction, and desulfonylation, afforded (-)-lasubine II.     

Density-dependent spin polarization in ultra-low-disorder quantum wires

There is controversy as to whether a one-dimensional (1D) electron gas can spin polarize in the absence of a magnetic field. Together with a simple model, we present conductance measurements on ultra-low-disorder quantum wires supportive of a spin polarization at B=0. A spin energy gap is indicated by the presence of a feature in the range (0.5-0.7)x2e(2)/h in conductance data. Importantly, it appears that the spin gap is not constant but a function of the electron density. Data obtained using a bias spectroscopy technique are consistent with the spin gap widening further as the Fermi level is increased.     

Ground state shaoe and crossing of near spherical and deformed bands in 182Hg

The energy levels of ¹⁸²Hg have been identified for the first time through comparison of in-beam studies of the reactions ^156,154Gd(³²S, 4n)^184,182Hg and γ-X-ray coincidences. Levels up to 12⁺ in ¹⁸²Hg were established from γ-γ coincidences and singles measurements. The data establish that the ground state shape is near spherical, and that the ground band is crossed by a well-deformed band at 4⁺. In contrast to IBA model predictions that the deformed band will rise in energy in ¹⁸²Hg compared to ¹⁸⁴Hg, the energies of the deformed levels in ¹⁸²Hg continue to drop.     

Detailed Ge(Li)-Ge(Li) coincidence studies of levels in152Sm and152Gd

The decay of 12.4 y¹⁵²Eu to¹⁵²Sm and¹⁵²Gd was studied in a high resolution singles measurement and two 4096×2048 Ge(Li)-Ge(Li) coincidence studies. Forty-five gates were analyzed in order to confirm or establish the placement of the γ rays as well as to accurately determine the intensities of the 12 doublets, which included several not previously reported. A new γ-β interband transition, 4 _γ ⁺ →2 _β ⁺ (561.4 keV), a possible 3 _γ ⁺ →2 _β ⁺ (423.7 keV) transition, and a new 330.9 keV transition between the 4 _γ ⁺ level and theI ^π K=3^?0 octupole level were established from coincidence data. Levels at 1757.0 keV in¹⁵²Sm and 1282.5, 1318.7, and 1692.2 keV in¹⁵²Gd are now established on the basis of coincidence data. These data also establish for the first time the population in the¹⁵²Eu decay levels at 1680.0 and 1047.9 keV in¹⁵²Sm and¹⁵²Gd, respectively, as well as a new level at 1700.8 keV in¹⁵²Sm.     

Luminescence excitation spectra of toluene and mesitylene in rare-gas matrices

Total luminescence yield of toluene and mesitylene, isolated in rare-gas matrices, has been measured as a function of excitation energy in the energy range covering the absorption region of both host and guest. Energy transfer from the host to the dopant is apparent. An increase in the luminescence yield is observed at the host exciton state. Luminescence excitation spectrum of pure mesitylene is presented.     

Atomistic and lattice model of a grain boundary defaceting phase transition

Recent calculations have shown that grain boundary (GB) stress is too small to stabilize finite GB facets, suggesting that the existing theory of GB defaceting phase transitions is incomplete. We perform molecular dynamics calculations, which show a reversible phase transition at approximately 400 K with a concerted shuffle of two atoms at the facet junction as the elementary excitation. Based on this excitation we formulate an appropriate lattice model, perform Monte Carlo simulations, and establish an analytical relationship between the elementary excitation energy and the transition temperature.