Photodissociative generation of population inversion in alkali noble gas excimer systems

Alkali noble gas excimer molecules are produced by photodissociation of alkali halogen vapor in a high-pressure noble gas atmosphere. Experimental details for NaI-Xe and CsI-Xe systems excited by 193 nm ArF or 249 nm KrF laser radiation are given, and the possibility of realizing an optically pumped alkali noble gas excimer laser is discussed.     

Novel methodology for the quantitative assay of fissile materials using temporal and spectral β-delayed γ-ray signatures

An analytical model for the generation of β-delayed γ-ray spectra following thermal-neutron-induced fission of mixed samples of ²³⁵U and ²³⁹Pu is presented. Using an energy-dependent figure-of-merit to designate the spectral regions employed in the assay, the unique temporal β-delayed γ-ray signatures are utilized to determine the fraction of ²³⁹Pu in a mixed U-Pu sample. By evaluating the β-delayed γ-ray temporal signatures of both ²³⁵U and ²³⁹Pu within a 3 keV energy bin, traditional sources of systematic uncertainty in quantitative assay using β-delayed γ-ray signals, such as self-attenuation of the sample and energy-dependent γ-ray detection efficiency, are significantly reduced. The effects of the time-dependent Compton-continuum and growth of longer-lived nuclides on the quantitative assessment are explored. This methodology represents a promising extension of the conventional means of analysis for quantitative assay of fissile materials using β-delayed γ-ray signatures.     

Observation of beta and X rays with 3-D-architecture siliconmicrostrip sensors

The first silicon radiation sensors based on the three-dimensional (3-D) architecture have been successfully fabricated. X-ray spectra from iron-55 and americium-241 have been recorded by reading out a 3-D architecture detector via wire bonds to a low-noise, charge-sensitive preamplifier. Using a beta source, coincidences between a 3-D sensor and a plastic scintillator were observed. This is the first observation of ionizing radiation using a silicon sensor based on the 3-D architecture. Details of the apparatus and measurements are described     

Silicon Detectors for Low Energy Particle Detection

Silicon detectors with very thin entrance contacts have been fabricated for use in the IMPACT SupraThermal Electron (STE) instrument on the STEREO mission and for the Solid State Telescopes on the THEMIS mission. The silicon diode detectors were fabricated using a 200 Aring thick phosphorous doped polysilicon layer that formed the thin entrance window. A 200 Aring thick aluminum layer was deposited on top of the polysilicon in order to reduce their response to stray light. Energy loss in the entrance contact was about 350 eV for electrons and about 2.3 keV for protons. The highest detector yield was obtained using a process in which the thick polysilicon gettering layer was removed by chemical etching rather than chemical mechanical polishing.     

Frequency up-conversion by stimulated hyper-Raman scattering

Stimulated electronic hyper-Raman scattering has been obtained in lithium vapor via excitation of several two-photon resonances (2s-3d, 2s-4s, 2s-4d) with a pulsed dye laser. The wavelength of the generated radiation was shorter than the pump wavelength and tunable over a few nanometers. The tuning behavior of the hyper-Raman laser was influenced by two-photon induced self-focusing/self-defocusing effects.     

Vacuum ultraviolet anti-Stokes Raman lasers

Anti-Stokes Raman laser schemes in atomic sulphur and selenium are studied, allowing conversion of laser lines out of the 350- 178 nm range into the 200-130 nm range. The necessary population inversion with respect to the atomic metastable¹S0levels is produced by photodissociation of the molecules COS and COSe with F2and ArF laser radiation, respectively. Anti-Stokes laser radiation at 167.5 and 158.7 nm for Se and at 182.0, 148.7, and 148.3 nm for S has been generated. Threshold pump energies of 0.1-20 μJ and output energies up to 5 μJ have been observed. At present, the systems are operated at low pump energies, just above threshold. It is expected that by the use of much higher pump energies and by further improvement of system parameters, output energies in the mJ range at MW peak powers will be possible for the VUV transitions.     

Measurements of beam current density and proton fraction of a permanent-magnet microwave ion source

A permanent-magnet microwave ion source has been built for use in a high-yield, compact neutron generator. The source has been designed to produce up to 100 mA of deuterium and tritium ions. The electron-cyclotron resonance condition is met at a microwave frequency of 2.45 GHz and a magnetic field strength of 87.5 mT. The source operates at a low hydrogen gas pressure of about 0.15 Pa. Hydrogen beams with a current density of 40 mA/cm(2) have been extracted at a microwave power of 450 W. The dependence of the extracted proton beam fraction on wall materials and operating parameters was measured and found to vary from 45% for steel to 95% for boron nitride as a wall liner material.