Gamma rays to detect the level in bottles.

Dangerous or not dangerous!?
X-rays and gamma rays are both types of high energy (high frequency) electromagnetic radiation. They are packets of energy that have no charge or mass (weight). These packets of energy are known as photons. Because X-rays and gamma rays have the same properties and health effects, they are grouped together in this document.
Both x-rays and gamma rays are forms of high-frequency ionizing radiation, which means they have enough energy to remove an electron from (ionize) an atom or molecule. Ionized molecules are unstable and quickly undergo chemical changes.
If ionizing radiation passes through a cell in the body, it can lead to mutations (changes) in the cell’s DNA, the part of the cell that contains its genes (blueprints). Sometimes this causes the cell to die, but sometimes it can lead to cancer later on. The amount of damage caused in the cell is related to the dose of radiation it receives. The damage takes place in only a fraction of a second, but other changes such as the beginning of cancer may take years to develop.
Gamma rays and x-rays aren’t the only kinds of ionizing radiation. Some types of ultraviolet (UV) radiation are also ionizing. Ionizing radiation can also exist in particle form, such as protons, neutrons, and alpha and beta particles.