Plunger group

We are a subgroup of the Jolie group specialized on the recoil distance Doppler-shift (RDDS) method. This method for the measurement of lifetimes of excited states employs so-called plunger devices, which we also develop ourselves. A detailed description of the RDDS method (or plunger method) can be found in this paper. Our plunger devices are employed during experiments at the particle accelerator in Cologne as well as at many other institutes world wide. Since we are a relatively small group we take the time for a guiding supervision of students during their thesis projects.

The plunger method

The recoil distance Doppler-shift method (also RDDS or plunger method) makes use of the Doppler shift of gamma radiation to measure lifetimes of excited states of atomic nuclei. The Doppler effect occurs when the source of a wave is moving relative to the observer. An example from everyday life is an ambulance passing by. While the ambulance is coming closer the sirene has a higher pitch, whereas when the ambulance is moving away from you, the pitch is lowered. This change in pitch corresponds to a change in frequency of the sound wave. Since gamma radiation also is a wave, this effect also occurs when a moving nucleus emits gamma radiation. A detector for gamma radiation will detect this change in frequency as a change in energy of the radiation.
A plunger device in principle consists of two foils. The first foil is called the target foil and is bombarded by a beam of nuclei from a particle accelerator. This leads to the production of excited nuclei in different reactions, which recoil out of the foil due to the momentum of the incoming beam. Downstream of the target foil is a stopper foil in which the recoiling nuclei are stopped. Now a decay of an excited state - and thus the emission of the gamma radiation - can happen either in flight or after the nucleus has been stopped in the stopper foil. In the former case the gamma radiation is Doppler shifted due to the recoil velocity of the emitting nucleus; in the latter case the radiation is not shifted. Thus it can be determined if the nucleus decayed in flight or after being stopped. Combined with knowledge about the flight time between the two foils, the lifetime of the decay can be determined from this information.
The distance between the foils is typically in the range of 10-1000 micrometers, allowing the measurement of lifetimes of the order of a few picoseconds (a millionth of a millionth of a second).

A detailed description of the RDDS method and of plunger devices can be found in this paper.

Topics for Bachelor and Master theses

• Analysis of lifetime measurements and theoretical discussion of the results
• Development of plunger devices
• Development of control software and analysis software

Contact us if you are interested!