Physics with Positrons 1

This module gives an introduction to positron physics with its applications in materials science, solid state physics and surface physics. After a historical outline, different techniques for producing positron sources and mono-energetic positron beams are introduced. The interaction of positrons with matter is described to show how positrons are used as probe particles to investigate crystal defects on an atomic scale. In addition, the generation and destruction of positronium is explained. Surface investigations are used as an example to show the specific differences to techniques using electrons. Then a systematic overview of crystal defects and the characterization of the free volume of amorphous solids is given. Afterwards, various radiation and particle detectors will be presented and their use for positron experiments will be discussed. Finally, different spectrometers will be presented to investigate defect types and concentrations. In particular, the measurement of positron lifetime in solids will be discussed in detail.

After successful participation in this module, the student will be able to

• explain the production of positron beams as well as the electrostatic and magnetic beam guidance
• understand and explain the interaction of positrons with matter.
• describe the interaction of gamma radiation with matter
• describe particle and radiation detectors
• describe crystal defects and identify positron techniques used to investigate them
• explain how a positron lifetime spectrometer works
• to explain the production and measurements with Positronium

No special prerequisites beyond the ususal Masters degree program.

In this lecture, the contents are presented by lecturing the theoretical basics and their experimental implementation, which are explained by illustrative examples. In particular, cross-references and the explanation of complementary measurement methods are used to bridge the gap to various topics. In the lecture, calculations and exemplary estimations are carried out on the basis of examples so that the students can independently explain and apply what they have learned. Great emphasis is put on stimulating interactive discussion with students about what they have just learned. This promotes students' own analytical ability to think through physical problems. The lecture contains hyperlinks and references to the relevant literature, which are intended to promote independent literature research.

Lecture, projector presentation, blackboard work, discussion, accompanying website, supplementary literature, PDF lecture documents

Textbooks in solid state and nuclear physics such as:

• C. Schaefer L. Bergmann. Lehrbuch der Experimentalphysik, Bd. 6: Festkörper. Gruyter, (2005);
• Neil W. Ashcroft and N. David Mermin. Solid State Physics. Saunders College, Fort Worth, (2001);
• G. Schatz and A. Weidinger. Nukleare Festkörperphysik. B. G. Teubner, (1997);
• Theo Mayer-Kuckuk. Kernphysik. Teubner, Stuttgart, (1984);

Positron physics:

• P. Coleman, Positron Beams and Their Applications, World Scientific, (2000).

References to Reviews will be given during the lecture.

There will be an oral exam of 30 minutes duration. Therein the achievement of the competencies given in section learning outcome is tested exemplarily at least to the given cognition level using comprehension questions, discussions based on sketches and basic formulas.

For example an assignment in the exam might be:

• What types of positron sources are there?
• Sketch the experimental setup to produce a monoenergetic positron beam.
• What is positron moderation?
• Why is moderation important (compared with electrons)?
• Describe the binding of positron and electron (positronium).
• Use the trapping model to investigate vacancies.