33 research outputs found
Effective decrease of photoelectric emission threshold from gold plated surfaces
Many applications require charge neutralisation of isolated test bodies and
this has been successfully done using photoelectric emission from surfaces
which are electrically benign(gold) or superconducting (niobium). Gold surfaces
nominally have a high work function (\,eV)which should require deep
UV photons for photoemission. In practice it has been found that it can be
achieved with somewhat lower energy photons with indicative work functions of
(\,eV). A detailed working understanding of the process is lacking
and this work reports on a study of the photoelectric emission properties of
4.6x4.6 cm^2 gold plated surfaces, representative of those used in typical
satellite applications with a film thickness of 800 nm, and measured surface
roughnesses between 7 and 340 nm. Various UV sources with photon energies from
4.8 to 6.2 eV and power outputs from 1 nW to 1000 nW, illuminated a ~0.3 cm^2
of the central surface region at angles of incidence from 0 to 60 degrees.
Final extrinsic quantum yields in the range 10 ppm to 44 ppm were reliably
obtained during 8 campaigns, covering a ~3 year period, but with intermediate
long-term variations lasting several weeks and, in some cases, bake-out
procedures at up to 200 C. Experimental results were obtained in a vacuum
system with a baseline pressure of ~10^{-7} mbar at room temperature. A working
model, designed to allow accurate simulation of any experimental configuration,
is proposed.Comment: 35 pages, 12 figure
A parsec scale X-ray extended structure from the X-ray binary Circinus X-1
We present the results of the analysis of two Chandra observations of
Circinus X-1 performed in 2007, for a total exposure time of ~50 ks. The source
was observed with the High Resolution Camera during a long X-ray low-flux state
of the source. Cir X-1 is an accreting neutron-star binary system that exhibits
ultra-relativistic arcsec-scale radio jets and an extended arcmin-scale radio
nebula. Furthermore, a recent paper has shown an X-ray excess on arcmin-scale
prominent on the side of the receding radio jet. In our images we clearly
detect X-ray structures both on the side of the receding and the approaching
radio jet. The X-ray emission is consistent with being from synchrotron origin.
Our detection is consistent with neutron-star binaries being as efficient as
black-hole binaries in producing X-ray outflows, despite their shallower
gravitational potential.Comment: Accepted for publication in MNRAS-Letter