Neutron Elastic Scatter (NES) may be used for non-destructively assaying materials for the presence of narcotics, explosives, or other contraband. The technology relies on the high penetrating power of neutrons to reach through varying thickness of shielding materials, and also on the large probabilities for elastic scattering of neutrons. Elastic scattering probabilities are the largest of all neutron induced events, exceeding any single non-elastic process typically by a factor of ten or more. Indeed, usually the elastic scattering probability is larger than the sum of all inelastic processes.

Reliable detection of explosives and narcotics depends on generating signatures of compounds which characterize them. Major explosives and also alkaloid narcotics contain unique concentrations of Carbon (C), Nitrogen (N), and Oxygen (O). The kinematic energy shifts of neutrons scattered through angles larger than 140{degrees} allows separate determinations of C, N, and O; ratios of N/C and O/C together give clear signatures of the presence of plastic explosives or narcotics. The ability to detect these signatures under conditions similar to those that would obtain for airport screening has been demonstrated for neutrons for energies less {le} 3 MeV. Strong N resonances and a deep window for scattering from O enhance the confidence of element quantification. Detection of contraband in large cargo containers presents a much more difficult problem. Use of higher energy neutrons is now being tested for shielding penetration, so narcotic signatures could be identified behind the shielding of cargo containers. Scattered neutron spectra, or {open_quotes}signatures{close_quotes} of different organic compounds will be presented.

In the course of conducting laser-target interaction experiments at 20-ps pulse length using Al and Mg targets, to determine the ionization balance of these elements, time-resolved K-shell spectral line strengths were obtained, suggesting population inversions between excited levels in both He-like and H-like ions. Effects of resonance-line opacities need to be analyzed in more detail, but opacity effects alone do not account for the anomalous line-intensity ratios that are observed to persist 200-300 ps after the laser pulse. Comparisons with 50-ps and 100-ps pulse shots do not show evidence of inversion, although nonequilibrium spectral line-intensity distributions are observed.

Supersonic, counterstreaming plasmas were produced by ablating plasma from the inside surfaces of two parallel disks made of aluminum and magnesium, respectively, with a 0.53 μm laser at an intensity of 1014 W/cm2 for 1.3 nsec. Diagnostics included holographic interferometry, a time-integrated x-ray pinhole camera and a gated x-ray crystal spectrograph with imaging slits. The plasmas interpenetrate for the first half of the laser pulse but stagnate once the electron density exceeds 5×1020 cm−3. Spectroscopic measurements suggest a coronal electron temperature of ∼800 eV and an ion temperature of ∼15 keV in the stagnated plasma. The observations are in good agreement with a two ion fluid model of interpenetrating plasmas in which the dominant slowing down process is ion–ion collisions.

An X-ray lasing oscillator is being developed which uses visible laser irradiation of solid targets in multipulse, multipass, operation to produce dramatic, rather than incremental, improvement in almost any X-ray lasing scheme. Hydrodynamic code simulations indicate reproducible plasma conditions are possible with multiple pulses, while ray trace simulations define mirror cavity configurations in a refracting carbon plasma under multipass operation.

Hydrogen-like recombination X-ray lasers are currently under investigation as an alterative candidate to collisional pumped soft X-ray amplifiers. Efforts are being concentrated on the n = 3 to n = 2 transitions in H-like Mg and NaF.

Predictions for the gains of the 4p-4d laser lines (0-1, 2-1, 1-1) in Nickel-like Ta and W are compared to the results of experiment. Effects which can resolve the discrepancies are pointed out. 11 refs., 3 figs., 1 tab.

A quasi-steady state, collisional-radiative model is used to analyze spectra from aluminum and magnesium plasmas produced by irradiation with 20 picosecond pulses of 0.53-mu laser light. The model infers the ionization balance and electron density of a plasma from the relative intensities of H-like and He-like x-ray transitions.

By means of two exploding foils, we have achieved inner-shell photoionization of Zn-like Pd resulting in the soft X-ray transition 3d94s2 → 3d104p at 46 Å.

Predictions for the gains of the 4p-4d laser lines (0-1, 2-1, 1-1) in Nickel-like Ta and W are compared to the results of experiment. Effects which can resolve the discrepancies are pointed out.

Near-optimum conditions for lasing in Ni-like W are calculated for a 90-\ensuremath{\mu}g/${\mathrm{cm}}^{2}$ foil irradiated by a 2\ensuremath{\omega} (\ensuremath{\lambda}=0.53 \ensuremath{\mu}m), 2.3\ifmmode\times\else\texttimes\fi{}${10}^{14}$-W/${\mathrm{cm}}^{2}$, 550-ps trapezoidal pulse. The gain coefficient for the J=0--1, 4d-4p Ni-like transition at 43.1 A\r{} is predicted to be 5.5 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. The electron density and temperature are 2.5\ifmmode\times\else\texttimes\fi{}${10}^{21}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ and 860 eV at x-ray laser time.

We report on the measurement of density-sensitive electric quadrupole transitions in neonlike molybdenum and silver laser-produced plasmas. These observations are unique in that they represent data which are simultaneously space and time resolved. The electron densities were determined using holographic interferometry. We test the predicted density sensitivity of the electric quadrupole transitions and find excellent agreement with calculations using a detailed, steady-state, collisional-radiative model of the neonlike charge state.

From an x-ray image recorded on film, it is our task to calculate the radiation profile of a plasma. The radiation from a three dimensional plasma is projected onto the two dimensional surface of the film. A one dimensional slice of the data is the projection of a two dimensional cross section of the plasma. If the plasma is cylindrically symmetric, a slice of the data corresponding to a cross section that is orthogonal to the axis of symmetry is a collection of discrete values of the Abel transform of the radiation profile. The radiation energy of a plasma contains information about its electron density and temperature. The radiation energy from the plasma is focused through an x-ray slit onto a crystal that reflects the energy into a streak camera. A microdensitometer is used to measure film densities of the x-ray images of the plasma.

The variation of Al XII resonance line intensities with the electron density has been measured in a recombining, laser-produced plasma. A detailed, quasi-steady-state model of the population kinetics for these ions is used to successfully describe the measured X-ray spectra. The collisional transfer of population between excited states must be included in detail to account for the observed line intensity dependence for late-time, recombining coronal plasmas.

AbstractWe have conducted a series of experiments at the KMS CHROMA facility using dot spectroscopy techniques to characterize uncertainties associated with spectral line ratio models commonly applied in determining electron temperatures and densities. Temperatures determined from the slope of the H-like free-bound continuum and densities via holographic interferometry, are compared to line ratio methods. Dot targets of (typically 100µmD Mg or Al) are irradiated with 2 to 40 × 1013W/cm2of 0.53µmlight. Time and spatial gradients are resolved using 4 diagnostics: a 4-frame holographic interferometer, an x-ray streak crystal spectrograph with a spatial imaging slit, a framing crystal x-ray spectrometer, and a conventional space-resolved time-integrating crystal spectrograph used for survey and calibration purposes. Preliminary results indicate the ionization distribution of these laser produced plasmas is not steady-state which plays an important role in measuring the temperature and and density. Electron temperatures derived from line-ratio techniques, assuming steady state conditions, disagree dramatically from simultaneous measurements using the slope of the H-like continuum. Electron densities using He-like triplet to singlet line ratios also differ from densities measured interferometrically.

The CHROMA laser facility at KMS Fusion has been used to irradiate a variety of microdot targets. These include aluminum dots and mixed bromine dots doped with K-shell (magnesium) emitters. Simultaneously time-and space-resolved K-shell and L-shell spectra have been measured and compared to dynamic model predictions. The electron density profiles are measured using holographic interferometry. Temperatures, densities, and ionization distributions are determined using K-shell and L-shell spectral techniques. Time and spatial gradients are resolved simultaneously using three diagnostics: a framing crystal x-ray spectrometer, an x-ray streaked crystal spectrometer with a spatial imaging slit, and a 4-frame holographic interferometer. Significant differences have been found between the interferometric and the model-dependent spectral measurements of plasma density. Predictions by new non-stationary L-shell models currently being developed are also presented.

We report a new diagnostic technique that allows us to measure simultaneously time- and space-resolved x-ray spectra of high-powered laser-produced plasmas. The simultaneously time- and space-resolved x-ray spectra were measured using a multiframe, electrically-gated, imaging x-ray spectrometer with 100 ps time resolution, and an x-ray streaked crystal spectrograph with a spatial imaging slit. A 4-frame holographic interferometer was used to measure the electron density profiles of the plasma. All three instruments were run simultaneously and allow for the first direct comparison of electron density spatial profiles determined via interferometry and spatially-resolved emission spectra from the plasma at the same instant in time. The CHROMA laser facility at KMS Fusion has been used to irradiate a variety of microdot targets. These targets include aluminum and magnesium microdots as well as targets consisting of a mixture of bromine and magnesium. Preliminary comparison between density and temperature profiles derived from line-intensity-ratio techniques and determined from holographic interferometry and free-bound continuum measurements are presented.