why are there so many ways to measure radioactivity, like Röntgen, Becquerel and sievert

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why are there so many ways to measure radioactivity, like Röntgen, Becquerel and sievert

In: Physics

They measure [different things and in different measurement systems](https://www.remm.nlm.gov/radmeasurement.htm).

_Becquerels_ (and _Curies_) are radioactivity, _Gray_ and _rad_ are absorbed dose of radiation into a given mass of tissue,
_sievert_ and _rem_ are ‘equivalent dose’;
_coulomb/kg_ and _Röntgen_ are exposure.

Some are antiquated units, but there are also very different sorts of measurements made. You can measure total energy, the biological effect depending on tissue, or total decays. There are a bunch of antiquated units still used, but many units are measuring different effects. Becquerel is measuring decays per second, and is the most fundamental, sievert is based upon biological impact, and gray is based on total exposure. Most have alternative units as well.