2011 S3: Jacob Voetberg

Investigating Antimatter-Matter Interactions in Gases

A positron is the antimatter counterpart to the electron, and when they meet they annihilate converting all of their mass into energy. It has exactly the same properties as the electron, but with an opposite electric charge. When a positron interacts with matter, several things may occur: the positron may annihilate with an electron, the positron may simply scatter off of an atom or particle, or the positron may become bound to an electron. A positron binds to an electron because they are a positive-negative pair, much like in the hydrogen atom; this exotic, short-lived, atom is called positronium. There are two different states of positronium, and the longer-lived state called orthopositronium (o-Ps) offers many interesting atomic interactions to explore.

Theoretical work on the heavier noble gases, xenon in particular, has suggested that the temperature dependence of the rate at which orthopositronium decays is non-linear with increasing temperature. However, there is little experimental data on the heavier noble gases to support the theory. This is in opposition to both the theoretical and experimental work on the lighter noble gases like helium, neon and argon, which have shown a linear dependence with respect to temperature. The goal of this experiment is to investigate the temperature dependence of the decay rate of o-Ps in xenon gas. We will use a high-pressure gas cell with a positron source inside as the basic setup of the experiment. So far, design and construction has been completed on the temperature control system including the temperature controller electronics, the heaters, and the insulated housing for the gas cell. In addition, construction is nearly completed for the gas handling system. Pressure and temperature tests are underway on the seal of the gas cell. The first sets of data for our temperature range of 20 to 300 deg. C. will be collected in the near future.

Faculty Mentor: Richard Vallery, Physics


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