Spur contribution to positronium formation in molecular media

Thesis/Dissertation · Tue Jan 01 04:00:00 EST 1980

OSTI ID:5331231

Schachter, R

Postitrons, when slowing down in molecular substances, can capture an electron to form positronium (Ps) with experimentally discernible annihilation characteristics. Positronium formation is usually attributed to electron capture by positrons in a kinetic energy range, called the Ore Gap, near the ionization potential of the molecules, of width comparable to 6.8 eV, the Ps ionization potential. This thesis investigates experimentally to what extent Ps can also be formed by the combination of a thermalized positron with one of the thermalized electrons which constitute with the geminate ions the spur produced by the positron during the last ionizing collisions with the molecules. A method was developed for the purpose of increasing systematically the subexcitation stopping power in the medium and, hence, to decrease the ranges and the mobilities of epithermal positrons and electrons, and to increase the rate of dissipation of the 6.8 eV necessary for Ps formation to occur. This was achieved through the introduction of increasing concentrations of dipoles in the form of (-CO-) groups into a nonpolar (-CH/sub 2/-) liquid. The objective was to initially enhance the probability of Ps formation in spurs at small dipole concentrations and, then, diminish the spur contribution when the positron mobility becomes so small that all thermalized positrons annihilate before encountering a spur electron for Ps formation. Positron lifetime measurements on dilute solutions of various ketones in n-hexane show that the Ps yield reaches a maximum at a CO concentration of 2 x 10/sup -3/ (CO/CH/sub 2/). It is concluded that spurs can contribute up to 20% to the total Ps yield in such systems. The dependence of the spur contribution on experimental parameters elucidates the subexcitation process underlying transient electronic effects induced by ionizing radiation in molecular insulators.

• Research Organization: New York Univ., NY (USA)
• OSTI ID: 5331231
• Country of Publication: United States
• Language: English

Related Subjects

640303* -- Atomic
Molecular & Chemical Physics-- Positronium
Muonium
& Muonic & Mesic Atoms & Molecules
74 ATOMIC AND MOLECULAR PHYSICS
ALKANES
ANNIHILATION
ANTILEPTONS
ANTIMATTER
ANTIPARTICLES
BASIC INTERACTIONS
CAPTURE
COLLISIONS
DIPOLES
ELECTRIC FIELDS
ELECTROMAGNETIC INTERACTIONS
ELECTRON CAPTURE
ELEMENTARY PARTICLES
ENERGY RANGE
EV RANGE
EV RANGE 01-10
FERMIONS
HEXANE
HYDROCARBONS
INTERACTIONS
IONIZATION POTENTIAL
KETONES
LEPTONS
LIFETIME
MOBILITY
MOLECULE COLLISIONS
MOLECULES
MULTIPOLES
ORGANIC COMPOUNDS
POSITRON COLLISIONS
POSITRON-MOLECULE COLLISIONS
POSITRONIUM
POSITRONS
STOPPING POWER