What exactly does it mean for something to be radioactive?

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I know now that when isotopes are unstable, something may become radioactive. But what exactly does that mean?

In: Physics

Something is radioactive if it releases nuclear radiation. Nuclear radiation is the result of radioactive decay of an unstable nucleus. When a nucleus undergoes radioactive decay, it spits out a particle of some kind, and the nucleus may change as a result of whatever it spit out. This will could result in the nucleus becoming a different isotope or element. That particle that the nucleus spit out is the nuclear radiation.

There are three types of decay possible, alpha, beta and gamma. Each of these emits a different type of particle, and has a different effect on the nucleus. In alpha decay, the nucleus emits an alpha particle, which is a “helium nucleus” or two protons and two neutrons. In beta decay, the nucleus emits an electron and a neutron in the nucleus flips to become a proton. Gamma decay happens when the nucleus just has some extra energy and gets rid of that energy in the form of a high energy photon.

It means those isotopes are decaying into other, more stable isotopes. When they do, they emit either alpha particles (essentially helium nuclei), or energetic fast elections (alpha decay and beta decay respectively). Some isotopes also land in a highly unstable nucleus arrangement that needs to be rebalanced, which causes the emission of a very high energy photon (gamma decay).

Radioactive means that the isotope undergoes decay in a relatively short time-span and emits one of a handful of choices of radiation, Alpha, Beta, or Gamma. There are a few more versions of Beta decay(double beta being one), but generally atoms will fall apart in those same three ‘styles’, and generally as atoms decay, they become more and more stable or will become a daughter product that decays extremely rapidly to reach stability faster than a relatively similar isotope of a different level of instability.
For something to not be radioactive, it needs to be stable for exceptionally large time-spans, like billions or trillions of years or even as far as we can calculate. Generally you can make things that are stable, become unstable by bombarding them with neutrons or protons of specific energies/speeds that they can be caught/ballistically impacted by that atom.

There are some theories that the streams of neutrinos that pour out of the sun influence decay rates, but its not conclusive and there is no consensus as to the why and how of that, but I like to imagine its true and it would be even harder to do things outside of our solar system than we expect to, but neutrinos are a part of the newer standard model with sub-atomic particles and those really don’t come easy to me since I wasn’t exposed to those terms until I was old enough to buy alcohol yet had looked into the makings of the atom reading 60 year old books by the age of 8…

I believe a lot of the newer standard model involving sub-atomic particles is based on the probabilities of nuclear decays, with the triplets of quarks making protons and neutrons and their arrangements (up-up-down to up-down-down etc) to achieve changing a proton to a neutron and their disintegration into smaller particles sort of sheds light into nuclear physics, so it helps wrap up some of the uncertainty of it by containing it within another subset of data, but I can’t seem to really wrap my head around it but looking it up just now for this part of this comment did look a lot easier than it did ten years ago the last time I tried so maybe I’ll come back with a concise reply wrapping it up and probably concluding the sun and its lepton emissions don’t affect nuclear decays.

Edit: yeah I’m struggling getting it as usual, but I do at least remember learning that protons/neutrons were made of quarks within 4 years of learning of how protons and neutrons make up atoms and how each element is made of a different number of them, but it was through a science fiction book and was mostly a thought experiment so I simply knew protons had subatomic constituent parts, I guess I need to make an ELI5 post myself about the generations of fermions and energies of bosons to understand nuclear physics better but I have a feeling it wouldn’t help as much as simply hunkering down and studying. It just seems too much like stopping time to play cards using the colors and shapes of cars and their suspension response in traffic that you’re traveling with.

A radioactive isotope is the same thing as an unstable isotope. It means it can spontaneously decay into a smaller isotope, emitting particles and electromagnetic radiations.
We often associate “being radioactive” with “emitting dangerous radiations”, these radiations are produced by the decay of the unstable atoms. They are electromagnetic radiations, same as visible light microwaves or radiofrequencies, however they are often of particularily high frequency (which means high energy), high enough to be harmful to the cells of our bodies.