Shutters and slats for the integral sunshade of an optical reception antenna

Optical reception antennas used at a small Sun-Earth-probe angle (small solar elongation E) require sunshading to prevent intolerable scattering of light from the surface of the primary mirror. An integral sunshade consisting of hexagonal tubes aligned with the segmentation of a large mirror was proposed for use down to E = 12 degrees. For smaller angles, asterisk-shaped vanes inserted into the length of the hexagonal tubes would allow operation down to about 6 degrees with a fixed obscuration of 3.6 percent. Two alternative methods are investigated to extend the usefulness of the integral sunshade to smaller angles by adding either variable-area shutters to block the tube corners that admit off-axis sunlight or by inserting slats (partial vanes) down the full length of some tubes. Slats are effective for most operations down to 6 degrees, and obscure only 1.2 percent. For E between 10.75 and 12 degrees, shutters cause even less obscuration

Climax spent fuel dosimetry. Progress report, September 1980-September 1981

This progress report covers dosimetry work at the Climax Spent Fuel Test Facility up to September 1981. During this time the gamma calibrations were completed, the temperature-induced fading study was completed, the first set of exposed dosimeters was retrieved, and the second set of dosimeters was placed in the field. These were installed in stainless steel tubes located on the inside wall of five canister emplacement holes (0.61 m in diameter), numbers 1, 3, 4, 7, and 11. Hole 3 also had dosimeters in similar stainless steel tubes placed at radii of 0.51 and 0.66 m from the canister centerline. Data obtained from the first exposure (about 270 days in duration) are reported. Significant neutron exposures were measured; in some cases they were sufficiently high that neutron spectra could be calculated

Multiwavelength transit observations of the candidate disintegrating planetesimals orbiting WD 1145+017

We present multiwavelength, ground-based follow-up photometry of the white dwarf WD 1145+017, which has recently been suggested to be orbited by up to six or more short-period, low-mass, disintegrating planetesimals. We detect nine significant dips in flux of between 10% and 30% of the stellar flux in our ~32 hr of photometry, suggesting that WD 1145+017 is indeed being orbited by multiple, short-period objects. Through fits to the asymmetric transits that we observe, we confirm that the transit egress is usually longer than the ingress, and that the transit duration is longer than expected for a solid body at these short periods, all suggesting that these objects have cometary tails streaming behind them. The precise orbital periods of the planetesimals are unclear, but at least one object, and likely more, have orbital periods of ~4.5 hr. We are otherwise unable to confirm the specific periods that have been reported, bringing into question the long-term stability of these periods. Our high-precision photometry also displays low-amplitude variations, suggesting that dusty material is consistently passing in front of the white dwarf, either from discarded material from these disintegrating planetesimals or from the detected dusty debris disk. We compare the transit depths in the V- and R-bands of our multiwavelength photometry, and find no significant difference; therefore, for likely compositions, the radius of single-size particles in the cometary tails streaming behind the planetesimals must be ~0.15 μm or larger, or ~0.06 μm or smaller, with 2σ confidence

Climax spent fuel dosimetry. Progress report, September 1982-January 1984

This report covers work done during FY83. These tasks included: (1) recovery and readout of the final set of dosimeters from the Climax facility, (2) a calibration exposure at the Sandia Gamma Irradiation Facility (GIF) to verify temperature effects during irradiation, and (3) a recalculation of new and existing calibration data over the range of 2 x 10{sup 3} to 10{sup 8} rads-LiF. This new set of calibration data is slightly different from that previously reported, and incorporates the best temperature corrections determined thus far. Data previously reported have been corrected and tables of a consistent set of these data are provided. The high-range dosimetry required for this project was achieved by exploiting the radiation-induced increases in optical absorption in LiF. This phenomenon is manifested as a series of peaks in the absorption spectrum; two of these peaks have proved useful for the dosimetric purposes at hand. The first, centered at 247 nm, covers the range of 2 x 10{sup 3} to 9 x 10{sup 6} rads-LiF; while the second, at 374 nm, covers the overlapping range of 2 x 10{sup 6} to 10{sup 8} rads-LiF. Optical absorption was measured with a double-beam spectrometer in absorbance units (AU), equivalent to the common log of the reciprocal of the optical transmission

Climax spent fuel dosimetry. Short term exposure, 8 March 1983

The second short-term exposure (performed 8 March 1983) in Hole CFH3 at the Climax Spent Fuel Test site is described. These short-term (1 hour long) exposures are intended to provide an independent measurement of the exposure rate at the wall and the 0.51-m and 0.66-m locations. Only CaF{sub 2} TLD`s were used in the second short-term exposure. Harshaw chips were cut to 0.32 x 0.18 x 0.09 cm size and aged by several exposure/readout/bakeout cycles until all odd chips were weeded out and the remaining chips exhibited stable sensitivities. Exposure at Climax was done by removing the existing long-term dosimetry strings and inserting identical strings using the CaF{sub 2} TLD`s in the stainless steel holders. The first short-term exposure produced absorbed doses as high as {similar_to}000 rads-LiF. The linearity corrections determined for the CaF{sub 2} TLD`s at these exposure levels were {similar_to}2%. The present post-exposure calibration method used calibration doses very close to those encountered in the field

Climax spent-fuel dosimetry. Progress report, September 1981-September 1982

Data from the second exchange of dosimeters from the Climax Spent Fuel Test Facility were evaluated for gamma-ray and neutron exposures. The data followed the previous trend of significant disagreement between the various exposures derived from measurements of different absorption peaks. The effects of temperature during irradiation were investigated and shown to be the major, if not the only, cause of the differences observed and commented on in the previous data collected last year. New data concerning irradiation temperature can be used to eliminate from consideration any neutron-caused effects, of at least a gross magnitude, at the Climax facility. Corrected data taking into account the effects of temperature during irradiation are provided for last year`s data as well as for the current year. The gamma-ray data show an overall decline in integrated dose, as expected from decay considerations. The neutron data are less consistent, with some apparent spectral shifts with time. The 247-nm and 374-nm absorption peaks in LiF chips can provide dosimetry coverage from 10{sup 4} to 10{sup 8} rads-LiF. Calibration data at 25 to 30{sup 0}C have verified that the dosimetry system is essentially temperature-independent over this range. The neutron fluence at the facility is small but measurable, and produces little effect on the gamma-ray dosimeters

Multiwavelength Transit Observations of the Candidate Disintegrating Planetesimals Orbiting WD 1145+017

We present multiwavelength, multi-telescope, ground-based follow-up photometry of the white dwarf WD 1145+017, that has recently been suggested to be orbited by up to six or more, short-period, low-mass, disintegrating planetesimals. We detect 9 significant dips in flux of between 10% and 30% of the stellar flux from our ground-based photometry. We observe transits deeper than 10% on average every ~3.6 hr in our photometry. This suggests that WD 1145+017 is indeed being orbited by multiple, short-period objects. Through fits to the multiple asymmetric transits that we observe, we confirm that the transit egress timescale is usually longer than the ingress timescale, and that the transit duration is longer than expected for a solid body at these short periods, all suggesting that these objects have cometary tails streaming behind them. The precise orbital periods of the planetesimals in this system are unclear from the transit-times, but at least one object, and likely more, have orbital periods of ~4.5 hours. We are otherwise unable to confirm the specific periods that have been reported, bringing into question the long-term stability of these periods. Our high precision photometry also displays low amplitude variations suggesting that dusty material is consistently passing in front of the white dwarf, either from discarded material from these disintegrating planetesimals or from the detected dusty debris disk. For the significant transits we observe, we compare the transit depths in the V- and R-bands of our multiwavelength photometry, and find no significant difference; therefore, for likely compositions the radius of single-size particles in the cometary tails streaming behind the planetesimals in this system must be ~0.15 microns or larger, or ~0.06 microns or smaller, with 2-sigma confidence.Comment: 16 pages, 12 figures, submitted to ApJ on October 8th, 201