• physical: time interval in which half of the nuclei of a radioactive nuclide have decayed. Short half-lives lead to a high radiation activity, long half-lives yield a low radiation activity.
• biological: time interval in which a biological system, e.g. a human being or an animal, excretes (e.g. via the urine) half of the amount of a certain substance taken up in the body or a certain organ.
• effective: time interval in which the amount of a radionuclide in a biological system is reduced by half, as a result of a coaction of radioactive decay and excretion.

In epidemiological cohort studies a low frequency of falling ill often occurs in occupationally exposed groups of persons, compared to non-exposed persons of the general population, as for some professions a certain health constitution is a prerequisite. Not employed persons are usually "more ill" than employed persons. A reduced risk of falling ill based on the unilateral selection of healthier occupationally exposed persons is referred to as Healthy Worker Effect.

A hearing has a legally enshrined function as part of a public works planning procedure. Its object and purpose are to discuss the objections raised to a project.

Heat-generating waste encompasses highly radioactive and, sometimes, intermediate-level radioactive waste. In particular, this includes vitrified waste from the reprocessing of spent fuel elements as well as the fuel elements themselves. This category of waste is characterised by a high activity concentration on the one hand and high heat emission on the other.

hertz (abbreviated "Hz") is the unit of measurement for frequency, that is, for the number of oscillations per second.

High-altitude radiation is formed when cosmic radiation enters the atmosphere from outer space. The amount of cosmic radiation that can enter the atmosphere is closely linked to solar activity, which ebbs and flows in a cycle lasting around 11 years:

• If solar activity is high, the solar wind deflects a large part of the cosmic radiation.
• If solar activity is low, the solar wind and the deflection are also weaker, and the amount of high-altitude radiation increases.

On top of this, the Earth's magnetic field deflects part of the cosmic radiation long before it reaches the Earth's atmosphere. As the deflection is strongest over the equator and weakest near the poles, radiation exposure is significantly higher on a transatlantic flight following a near-polar route than on a flight of the same length from north to south. Therefore, the additional effective dose per person on a flight from Frankfurt to New York is between 0,032 - 0,075 millisieverts and from Frankfurt to Johannesburg between 0,018 - 0,030 millisieverts.

High-frequency electromagnetic fields. Here defined as frequencies between 100 kHz and 300 GHz.

Strongly shielded, tight housing where radioactive materials of high activity are handled by remote control with the help of manipulators and where work processes can be observed through leaded windows, thus not involving risks for the staff.

Spatially limited areas with particularly high absorption of electromagnetic fields.

Representative selection of households where interviews have been carried out in intervals.

Water-bearing