Zielgas

Zielgas, literally "target gas" in German, is a term used in nuclear and particle physics to denote a gas that serves as the interaction target in beam-target experiments. The properties of a Zielgas, including its composition, pressure, and temperature, determine the effective target thickness and reaction rates.

The term is common in German-language literature and is descriptive rather than referring to a specific chemical species. In practice, Zielgas can be any gaseous material chosen to study particular reactions, with hydrogen and its isotopes, helium, nitrogen, and noble gases among common choices depending on experimental goals and the desired interaction channel.

Technical implementation often involves gas cells or jet targets within vacuum systems. The gas density is controlled via pressure and temperature, and environments may be windowless or use very thin windows to minimize energy loss. Accurate dosing and monitoring are essential for reliable cross-section measurements and for understanding energy deposition and background contributions in detectors.

Advantages of gas targets include adjustable density, reduced radiation damage to surrounding materials, and lower background for certain observables. Limitations include lower maximum areal density compared with solid targets and safety considerations for flammable gases such as hydrogen, as well as handling challenges for cryogenic or toxic gases.

Zielgas is primarily discussed in German-language literature as part of the broader concept of gas targets used in fixed-target experiments, where gaseous targets provide a flexible option for studying nuclear and particle interactions.