X-ray and ion emission studies from subnanosecond laser-irradiated SiO2 aerogel foam targets

In this experiment, a comparative study of ion and X-ray emission from both a SiO2 aerogel foam and a quartz target is performed. The experiment is performed using Nd:glass laser system operated at laser energy up to 15 J with a pulse duration of 500 ps with focusable intensity of 1013–1014 W/cm2 on target. X-ray fluxes in different spectral ranges (soft and hard) are measured by using X-ray diodes covered with Al filters of thickness 5 µm (0.9–1.56 keV) and 20 µm (3.4–16 keV). A 2.5 times enhancement in soft X-ray flux (0.9–1.56 keV) and a decrease of 1.8 times in hard X rays (3.4–16 keV) for 50 mg/cc SiO2 aerogel foam is observed compared with the solid quartz. A decrease in the flux of the K-shell line emission spectrum of soft X rays is noticed in the case of the foam targets. The high-resolution K-shell spectra (He-like) of Si ions in both the cases are analyzed for the determination of plasma parameters by comparing with FLYCHK simulations. The estimated plasma temperature and density are T c = 180 eV, n e = 7 × 1020 cm−3 and T c = 190 eV, n e = 4 × 1020 cm−3 for quartz and SiO2 aerogel foam, respectively. To measure the evolution of the plasma moving away from the targets, four identical ion collectors are placed at different angles (22.5, 30, 45, and 67.5°) from target normal. The angular distribution of the thermal ions are scaled as cosnθ with respect to target normal, where n = 3.8 and 4.8 for the foam and quartz, respectively. The experimental plasma volume measured from the ion collectors and shadowgraphy images are verified by a two-dimensional Eulerian radiative–hydrodynamic simulation (POLLUX code

Chronometry and formation pathways of gypsum using Electron Spin Resonance and Fourier Transform Infrared Spectroscopy

Gypsum is an authigenic precipitate that forms under periods of accentuated aridity and occurs widely in arid zones. However its use in quantitative paleoclimatology has been limited due to the absence of a method to determine the timing of its formation. We present here the results of a feasibility study that demonstrates that the timing of the formation event of gypsum can be estimated using Electron Spin Resonance (ESR) analysis. We used well documented samples from White Sands in New Mexico, USA, the Thar Desert, India and lakes in the Simpson Desert and Mallee Region, Australia and found that ESR ages could be obtained using radiation sensitive SO4-, SO3- radicals and a photobleachable signal O3-. ESR signals were consistent with control ages based on contextual information. These suggest that the dating signals (SO4-, SO3-) are stable over time scales >100 ka. We propose that this stability of the SO4- signals over geological time scales arises due to hydrogen bonding between the water proton and the SO4- radical and that the suitability of these radiation-induced radicals comes from their being a part of the host matrix. Further, ESR along with Fourier Transform Infrared (FT-IR) Spectroscopy methods additionally inform on the geochemical pathways for gypsum formation and help elucidate complex formation processes even in samples that appeared unambiguous gypsum precipitates. Thus, the presence of Hannebachite (CaSO3.1/2H2O) and Mn2+ in Thar and Australian samples suggested a reducing environment such that low valence sulfur reacted with CaCO3 to form hannebachite and eventually gypsum. The presence of sulfur, partially as sulfite in Thar gypsum samples suggested that redox cycles were mediated by microbial activity. Absence of these features in White Sands samples suggested oxic conditions during gypsum precipitation

Muon Energy Estimate Through Multiple Scattering with the Macro Detector

Muon energy measurement represents an important issue for any experiment addressing neutrino induced upgoing muon studies. Since the neutrino oscillation probability depends on the neutrino energy, a measurement of the muon energy adds an important piece of information concerning the neutrino system. We show in this paper how the MACRO limited streamer tube system can be operated in drift mode by using the TDC's included in the QTPs, an electronics designed for magnetic monopole search. An improvement of the space resolution is obtained, through an analysis of the multiple scattering of muon tracks as they pass through our detector. This information can be used further to obtain an estimate of the energy of muons crossing the detector. Here we present the results of two dedicated tests, performed at CERN PS-T9 and SPS-X7 beam lines, to provide a full check of the electronics and to exploit the feasibility of such a multiple scattering analysis. We show that by using a neural network approach, we are able to reconstruct the muon energy for $E_\mu<$40 GeV. The test beam data provide an absolute energy calibration, which allows us to apply this method to MACRO data.Comment: 25 pages, 11 figures, Submitted to Nucl. Instr. & Meth.

K-shell X-ray spectroscopy of laser produced aluminum plasma

Optimization of a laser produced plasma (LPP) X-ray source has been performed by analyzing K-shell emission spectra of Al plasma at a laser intensity of 1013-1014 W/cm2. The effect of varying the laser intensity on the emissivity of the K-shell resonance lines is studied and found to follow a power law, E α I α with α=2.2, 2.3, 2.4 for Heβ, Heγ, Heδ respectively. The emission of these resonance lines has been found to be heavily anisotropic. A Python language based code has been developed to generate an intensity profile of K-shell spectral lines from the raw data. In theoretical calculations, the temperature is estimated by taking the ratio of the Li-like satellite (1s2 2p-1s2p3p) and the Heβ (1s2 -1s3p) resonance line and the ratio of the He-like satellite (1s2p-2p2 ) and the Lyα (1s-2p) resonance line. To determine the plasma density, stark broadening of the Lyβ spectral line is used. Simulation was carried out using the FLYCHK code to generate a synthetic emission spectrum. The results obtained by FLYCHK are Te=160 eV, Th=1 keV, f=0.008, ne=5 x 1020 cm-3 and the analytical model resulted Te=260-419 eV and ne=3x1020 cm-3

Localized 1ℏomega\hbar omega particle-hole strength in nuclei

A cross section enhancement, persisting to high momentum transfer, has been observed around 1HBAR omega in excitation energy in spectra from inelastic proton-, alpha- and electron scattering on Zr-90, Sn-116, Pt-196 and Pb-208. Data are presented for (p,p') at 201 MeV, (alpha,alpha') at 120 MeV and analyzed together with existing data obtained with 133.8 MeV polarized ((p) over right arrow,p') on Sn-116 and electron-scattering data on Sn-116 and Pt-196. Two different interpretations of the observed enhancement are discussed: that of the incoherent sum of all 1HBAR omega cross section and alternatively the sum over the isoscalar normal modes of all multipolarities