There are several types of machines used to measure radiation. The 'classic' is the Geiger Counter which dates back to the late 40's or 50's. It's quite efficient, especially in measuring α and ß Emissions and passably so on Γ Rays. It works by counting the electric arc discharges inside the counter sensing probe caused by impinging radioactive particles.
Slightly newer, is the Scintillation Counter which is far more accurate in Γ Ray work. The Scintillation Counter, in spite of it's impressive name is really a rather simple instrument. They are comprised of a Photoelectric coupled with a Crystal that emits a tiny flash of light when it is exposed to Γ Rays ... the stronger the Γ field, the more the flashes.
Those are 2 basic types of Radiation Monitors. The designs cited above are the 2 prototypical flavors.
Geiger counter
The most dangerous type of radiation is Nuclear radiation which is the one that should be most worried about.
energy/electricity/weapons
A nuclear accident is the unintended release of nuclear radiation into the environment, such as damage to a nuclear reactor or to a nuclear weapon (plane crash carrying nuclear bombs, etc). The two basic forms of nuclear weapons are fission and fusion weapons.
Background radiation come from black body radiation which is mostly infrared and microwave. Background radiation is not harmful at all. Fear from background radiation come from confusion of the word radiation where we mostly concern nuclear radiation, but light is also a form of radiation and we live within the bright day light on a normal basis.
coal gives off nuclear radiation
It is used to measure radiation and is commonly used to detect objects that produce nuclear radiation.
Geiger meter
That depends on the initial amount and type. It also depends on altitude (or depth) of burst. If you know the isotopes involved you can look up their half lives, measure current radiation intensity, and calculate time until radiation will drop to desired level. You can also periodically measure radiation intensity over a period of time, then extrapolate to get a reasonable estimate of time to drop to desired level without knowing isotopes.
It is used to measure radiation and is commonly used to detect objects that produce nuclear radiation.
to control the radiation
There are no immediate signed of nuclear radiation.
Nuclear weapons emit nuclear radiation, with gamma radiation being the most common and dangerous.
The device is called a Geiger counter and it has a measurement scale in Microsieverts.
people are planning to store nuclear radiation there.
Nuclear radiation is not affected at all, but radiation by Electromagnetic Radiation is. This is a straight Physics topic, not Nuclear Energy.
Radiation is a consequence of nuclear energy. In fact, without the radiation of a large neutron flux, nuclear energy would not exist.
Yes, the decay of unstable atomic nuclei is the source of nuclear radiation.