Measurement of positron reemission from thin single-crystal W(100) films

Journal Article · Mon Apr 01 04:00:00 EST 1985 · Phys. Rev. B: Condens. Matter; (United States)

DOI:https://doi.org/10.1103/PhysRevB.31.4123· OSTI ID:5884590

Chen, D M; Lynn, K G; Pareja, R; Nielsen, B

Epitaxial thin single-crystal (100) tungsten films 1000, 2500, and 5000 A thick have been fabricated by high-vacuum electron-beam evaporation. These films were subsequently used as thin-film moderators for the study of the positron-transmission-reemission process with a variable-energy (0--80 keV) monoenergetic positron beam in an ultrahigh-vacuum system. The films were shown to be routinely cleanable by heating first in oxygen (10/sup -6/ Torr) and then in vacuum (10/sup -9/ Torr). Transmission and back reemission of slow positrons from these surfaces was observed. The positron work function, phi/sub +/ has been determined to be approx. =3.0 eV ( +- 0.3 eV). The transmission slow positrons were emitted in a narrow cone with a full width at half maximum of approx. =30/sup 0/ consistent with the angular distribution of back-reemission positrons. The reemitted yields as a function of incident positron energy were found to be very different between forward reemission and back reemission. The maximum forward-reemission yields were 18% for 1000-A-thick W film and 12% for 2500-A-thick W film at 5 and 10 keV optimum incident positron energies, respectively. These results show that one can use thin single-crystal tungsten films as positron moderators or remoderators.

• Research Organization: Physics Department, Brookhaven National Laboratory, Upton, New York 11973
• OSTI ID: 5884590
• Journal Information: Phys. Rev. B: Condens. Matter; (United States), Journal Name: Phys. Rev. B: Condens. Matter; (United States) Vol. 31:7; ISSN PRBMD
• Country of Publication: United States
• Language: English

Related Subjects

654001* -- Radiation & Shielding Physics-- Radiation Physics
Shielding Calculations & Experiments
73 NUCLEAR PHYSICS AND RADIATION PHYSICS
ANGULAR DISTRIBUTION
ANTILEPTONS
ANTIMATTER
ANTIPARTICLES
BACKSCATTERING
CHARGED-PARTICLE TRANSPORT
CONVERSION RATIO
CRYSTALS
DISTRIBUTION
ELEMENTARY PARTICLES
ELEMENTS
ENERGY LOSSES
ENERGY RANGE
FERMIONS
FILMS
FUNCTIONS
KEV RANGE
KEV RANGE 10-100
LEPTONS
LOSSES
METALS
MODERATORS
MONOCRYSTALS
POSITRONS
RADIATION TRANSPORT
SCATTERING
SMALL ANGLE SCATTERING
THIN FILMS
TRANSITION ELEMENTS
TRANSMISSION
TUNGSTEN
WORK FUNCTIONS