Modern physics virtual laboratory: gamma spectrometer system

Abstract

This paper describes how was implemented a computer simulation of an ionizing radiation detection system similar to those found in traditional modern physics laboratories. The simulation models a system with radioactive “sources” of photons with well-defined energies and a “detector” that behaves like a photon spectrometer (scintillator + photomultiplier tube + multichannel analyzer). As with the real system, besides choosing the source, it is possible to adjust the high voltage applied at the photomultiplier tube, the gain of the analog amplifier and the conversion gain of the multichannel analyzer, observing the corresponding changes in the acquired “data”. There are presented and discussed results obtained with the simulator for some experimental set-ups (energy calibration, identification of unknown energies, system energy resolution, etc.). The simulation was used with two groups of undergraduate students from a distance learning physics course at UFSC in 2011 and 2014, along with the execution of the real experiment. Throughout the text there are comments on the motivations and problems of using simulations in this context. Finally, it is discussed how this work relates to the main goals of introductory physics laboratories, according to an American Physical Society committee especially created to evaluate that.