High Temperature Behaviour of Positrons in Argon
نویسنده
چکیده
When a swarm of positrons is introduced into a gaseous assembly, there are many processes by which the positrons can arrive at their eventual annihilation fate. Depending on the energy, some positrons form positronium prior to annihilation. However, when the energy is less than the positronium formation threshold, Eth (9 eV for argon, 17.8 eV for helium, etc.), then only elastic collisions are important. The study of the behaviour of such positrons in noble gases under the influence of uniform electric, magnetic and temperature fields has been the subject of many recent investigations [1 — 5] . Most of the studies have been concerned with moderate electric fields because at high fields complications due to positronium formation arise. No such difficulties come into play in high magnetic fields because this field quenches positronium [6] . An electric field enhances the positron life time while a magnetic field has the opposite effect. This is due to the fact that the positron energy is increased in electric and decreased in magnetic fields. The positron energy can also be influenced by the temperature of the gas. Increasing temperature leads to increase in energy, and thus the positron life time is also enhanced. Electric/magnetic fields have no effect on the energy of the gas atoms (being neutral) directly. However, temperature increases the energy of the gas atoms directly much more than the energy of the positrons. Positrons gain energy via collisions with the gas atoms. The question arises how these fields compete to influence the life time of positrons in gases.
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تاریخ انتشار 2013