Al Disk Research Articles

Laser and plasma conditions at the onset of Raman scattering in an underdense plasma

The laser and plasma conditions at the onset of Raman scattering have been measured in plasmas formed from thin-foil targets. The targets were Al disks 50 to 250 nm thick and 200 to 500 μm in diameter mounted on 100 nm polymer films. The incident wavelength was 526 nm. Raman scattering was observed for nominal intensities from 1014 W/cm2 to 5 × 1014 W/cm2. The most important observation of the experiment is that the density-gradient scale-length at onset is independent of intensity. One would expect the scalelength at onset to be inversely related to the intensity, since the convective gain for stimulated Raman scattering (SRS) is proportional to the product of intensity and scalelength.

Uranium density and enrichment in fuel tubes determined from 232U and 235U γ-activities

Gamma spectroscopy is used to determine 235U density and enrichment in UAl fuel tubes containing recycled fuel. A collimated HPGe γ-detector views the tube surface, such that UAl disk volumes of 6.35 mm diameter and ∼1.0 mm thickness are examined. The γ-activities from 232U and 235U, along with the tube design parameters, are used to deduce the attenuation-corrected results. Respective density and enrichment variations of <1% and <0.6 e% were measurable with 2000 s counting time per tube location. Such measurements are useful for certifying tube quality and characterizing problems associated with blending the UAl alloy.

Study of preheat effects in ND-laser irradiated finite Al disk targets

Energy streaming around and through an Al disk target irradiated with a Nd-glass laser delivering a 0.8-ns pulse is discussed as a function of target thickness, disk diameter, and laser irradiance from 5×1012 to 5×1014 W cm−2. Front and rear surface behaviors of the disk are studied by means of frame and streak shadowgraphy, short-time exposure interferometry, ion calorimetry, and charge collectors. Experimental data clearly show that preheat of the rear side of a 500-μm-diam disk is due to plasma encompassing the target and occurs even at laser irradiance as low as 3×1013 W cm−2. Moreover, it is seen on time-resolved photography of double-disk targets, that the second foil expands before being struck by the first disk (irradiated disk) at laser irradiance as low as 1013 W cm−2. This effect is ascribed to preheating by particle bombardment. Numerical simulations do not match the experimentally observed temporal behaviors for the 500-μm-diam disks even with some preheat included in the hydrodynamic code, but they agree quite closely with the experimental results when the irradiated disk diameter is much larger than the characteristic density gradient length.

Three Surface TEM Observations of Cold Rolled 1100 Aluminum

As part of an on-going study of 1100 Al at large plastic strains, we have examined cold-rolled samples from three orientations; through the sheet surface, and in the thickness direction along the rolling direction (RD) and transverse to the RD. Cell and subgrain sizes were determined in the same manner as for the earlier work.The starting plates of 1100 Al were annealed at 500 C and then rolled at room temperature to various thicknesses. These rolled plates were used to produce final samples rolled to 0.5 mm thickness with 62, 80, and 90% reductions. Thin foils were produced by lapping and jet electropolishing. A method was developed to make thin foils perpendicular to the sheet by lapping small pieces of sheet (1 mm wide) edgewise from both edges. This produces sheet 0.25 mm thick by 0.5 mm wide which were mounted between two 0.25-mm-thick 1100 Al disks 3 mm in dia. These disks had been slitted in the center to have slits ≪ 0.5 mm wide.

A new type of extremity dosimeter

A three element sandwich type dosimeter has been developed. The beta element is LiF cold pressed to an Al disc the response of which follows the energy dependence of the true skin beta dose for E max⩾ 0.2 MeV. Filtered LiF hot pressed chips measure gamma dose and indicate the radiation quality.

Alignment of small He-Bubbles during in situ deformation of Al-foils

The low Z metal aluminium is a potential matrix material for the first wall in fusion reactors. A drawback in the application of A1 is the rel= atively high amount of He produced in it under fusion reactor conditions. Knowledge about the behaviour of He during irradiation and deformation in Al, especially near the surface, is therefore important.Using the TEM we have studied Al disks of 3 mm diameter and 0.2 mm thickness, which were perforated at the centre by double jet polishing. These disks were bombarded at∽200°C to various doses with α-particles, impinging at any angle and energy up to 1.5 MeV at both surfaces. The details of the irradiations are described in Ref.1. Subsequent observation indicated that in such specimens uniformly distributed He-bubbles are formed near the surface in a layer several μm thick (Fig.1).After bombardment the disks were deformed at 20°C during observation by means of a tensile device in a Philips EM 300 microscope.

Use of semiconductor spectrometric counters for measuring the energy of fragments

Surface-barrier type counters, prepared by vacuumsputtering of Au on n- type Si, were used for determining the energy of fission fragments. The target, placed in a vacuum chamber with thin Al walls. consisted of a UF/sub 4/coated Al disc and contained 92.8% enriched U/sup 235/. The Si counter was placed about 1.5 cm from the target in a collimated beam. The amplified pulses were recorded on a 100-channel analyzer. The spectra thus obtained differed from those derived from time-of-flight data. Further study indicated that design of the counter caused fission fragment energy losses in the surface layer which were larger than when the counter was used for studying alpha particles. On the basis of these results it was decided to reduce the surface area of the counter to 10 mm/sup 2/. The differences in the results may be due to losses within the fissioning material, to energy removal by neutron, and to ionization defects in the Si counter. As a general rule, Si counters yield more precise results in the field of the fission fragment energy measurements than ionization chambers. (TTT)