Studies of electron exchange collisions and polarized electron production in a flowing helium afterglow

Thesis/Dissertation · Sun Jan 01 04:00:00 EST 1989

OSTI ID:5046574

Ratliff, J M

A flowing helium afterglow apparatus has been used to study thermal-energy electron exchange collisions between spin-polarized electrons and 0{sub 2} or NO molecules. Penning ionization of CO{sub 2} by spin-polarized He(2{sup 3}S) metastable atoms is used to produce electrons which retain the spin orientation of the metastables, and which rapidly thermalize in the CO{sub 2}. The reactant gas (0{sub 2} or NO), when introduced into the flowstream, causes a decrease in the electron spin-polarization. The electrons are then extracted from the flowtube for measurement of the polarization they retain. The rate constant for the reaction e{sup {minus}}({up arrow}) + X {yields} e{sup {minus}}({down arrow}) + X can then be determined, given the amount of polarization decrease, reactant-gas density, and reaction time. The rates are found to be k(O{sub 2}) = (8 {plus minus} 3.5) {times} 10{sup {minus}11} cm{sup 3}/sec and k(NO) = (9 {plus minus} 4) {times} 10{sup {minus}11} cm{sup 3}/sec. An upper limit to the electron attachment rate for formation of an excited negative ion is derived from these measurements, and the contribution of exchange to the total scattering is discussed. In addition, a new, non-invasive technique for measuring electron-drift velocity in the flowtube is describe. Modifications of the afterglow apparatus and use of laser radiation for He(2{sup 3}S) spin-orientation enable it to produce an electron beam having moderate to high current and high spin polarization. Polarizations of 80% are achieved for currents up to 1{mu}A, with 60% polarization retained at 25{mu}A. This compares favorably with other polarized electron sources, making the afterglow apparatus a candidate for use as a beam source in high-energy electron accelerators.

• Research Organization: Rice Univ., Houston, TX (United States)
• OSTI ID: 5046574
• Country of Publication: United States
• Language: English

Related Subjects

43 PARTICLE ACCELERATORS
430301* -- Particle Accelerators-- Ion Sources
ACCELERATORS
AFTERGLOW
CHALCOGENIDES
COLLISIONS
ELECTRON ATTACHMENT
ELECTRON BEAM ION SOURCES
ELECTRON COLLISIONS
ELECTRON-MOLECULE COLLISIONS
ELEMENTS
FLUIDS
GASES
HELIUM
ION SOURCES
MEASURING METHODS
MOLECULE COLLISIONS
NITRIC OXIDE
NITROGEN COMPOUNDS
NITROGEN OXIDES
NONMETALS
OXIDES
OXYGEN
OXYGEN COMPOUNDS
PENNING ION SOURCES
POLARIZATION
PRODUCTION
RARE GASES