I have always had a hard time grasping this. Radioactivity has many units of measure: Grays, Rads, Rems, Curies, Roentgen, Sieverts, Becquerels.
Why are there so many different unit types, and how do they inter-relate? I have a decent understanding of physics, but not in this specific area. To date I haven’t read or heard an explanation that gives an “ah-ha!” moment or makes me quite understand what all these measures actually mean.
Yes, I have seen the XKCD radioactivity chart.
In: Physics
rfkile is correct. Part of the challenge lies with the fact that “radiation” and radioactivity and the understanding of radionuclides and their interactions with each other, inert and living matter have occurred over a period of time and to some extent in earlier times with an ongoing misunderstanding or incomplete understanding of many of their facets. Not mentioned so far is that there are different classes of classic radiation – Alpha particles (α-particles), Beta particles (β-particles) and Gamma rays (γ-rays) adding to the matter of radiation measurement complexity. Today each of the standardized measurements represents a particular effect – whether dose (or dose rate), emission rate or impact. Units used are now usually tailored to the circumstances and effects involved or of interest. Note: I also agree with WRSaunders as well.
The term “radioactivity” is used for things that aren’t the same. X-rays are photons whereas alpha and beta radiation is streams of particles.
Initially, the idea was to measure their impact on life. There are existing units for the energy in something, but sometimes more energy isn’t directly related to more dangerous.
Then the idea was to keep consistency with the rest of the SI units. All this gives is lots of units with hard to remember conversion factors.
Most of these aren’t units of radioactivity. Only Becquerels and Curies are. Radioactivity is a measure of how many atoms are undergoing radioactive decay each second.
Rads and Gray are units of dose, which is a measure of how much energy (per unit mass) is being absorbed from radiation. This is important, because it impacts how both materials and cells react to radiation.
Sieverts and REM are measures of biological impact from radiation. They tell us about how much cell damage and long term health impact is expected.
Roentgen is a really weird unit that measures how much ionization radiation causes in otherwise stable materials, and ionization leads to funky cell chemistry.
> Radioactivity has many units of measure: Grays, Rads, Rems, Curies, Roentgen, Sieverts, Becquerels.
You forgot [Banana Equivalent Dose.](https://en.wikipedia.org/wiki/Banana_equivalent_dose)
Latest Answers