I’ve been searching and can’t quite find the explanation I’m looking for. I’ve read that radioactivity comes from an atom containing too many neutrons, and so the neutrons will end up breaking off of the atom and go flying in some direction until it collides with something. Which leads me to my first part:
* What happens when this neutron collides with something?
* If we’re talking a person, I’m assuming it damages/destroys the cell it hits, does it bounce and keep destroying more? What if a person was exposed to insanely high radiation of this sort. Do they melt into a pile of goop as their cells are broken down?
I’ve read that the number after an element is supposed to represent the amount of neutrons. So Uranium-238 would have more neutrons than Uranium-235. But isn’t the protons/neutron/electron the entire makeup of the atom?
* How can the amount of neutrons differ and they still be considered the same element?
From what I understand, radioactive decay is what happens to a radioactive element naturally as it’s neutrons fire off.
* What happens to the element? Does it just eventually disappear or “evaporate”? What exactly happens to these atoms once the neutrons have all fired off?
* If the radioactive substance is a metal such as iridium, does it become super brittle once fully decayed? Crumble into dust?
I have absolutely no education or experience in this field, but it fascinates the hell out of me.
In: Chemistry
Initial clarification: it’s not necessarily too many neutrons, it’s the wrong number of neutrons. Once you go past hydrogen (1 proton), you need at least one neutron to get the nucleus to be stable(ish). “Stable” means “does not radioactively decay into something else.” Decay can happen by turning a proton into a neutron by ejecting a positron (beta+ decay), by turning a neutron into a proton by ejecting an electron (beta- decay), by rejecting a pair of protons and neutrons entirely (a helium nucleus, alpha decay), or by splitting entirely and possibly spewing out some free neutrons and/or gamma rays and/or heat (fission).
If any of this happens with enough energy, the particles coming out can hit other atoms hard enough to rip electrons off them. This is called “ionizing radiation”. And ions like to undergo chemical reactions, including bonding to other things or breaking existing bonds. This can screw up chemistry in cells and, in particular, damage DNA. If you do enough of that you get cancer. Even more of that and you physically damage the cells enough to kill them (radiation poisoning). Even more of that and you can just burn a person up because they’re absorbing too much energy.
The number after some elements isn’t the number of neutrons, it’s the total number of protons+neutrons in the nucleus. U-238 has 92 protons and 238-92=146 neutrons. When it changes to U-235 it’s still got 92 protons but it lost 3 neutrons. The number of protons is what makes it uranium…uranium always has 92 protons. If the number of protons changes it’s a different element. But if *just* the number of neutrons changes it’s a different “isotope”…chemically the same, since the electrons are what makes chemistry happen and they balance the protons, but different numbers of neutrons so it weights slightly more or less. And, since the neutrons influence stability, different isotopes have different stability.
If an element just loses a neutron, it changes isotopes. It will keep doing that until it hits a stable isotope or some other kind of decay happens to change the number of protons (alpha, beta, or fission will all change the proton count). If that happens it becomes a new element or elements (fission), called “transmutation”. Which may or may not be stable. This keeps going on until everything that’s left is stable or the age of the universe runs out, whichever happens first.
>What happens when this neutron collides with something?
Radioactive elements don’t usually release just neutrons. They usually release alpha particles (two neutrons+two protons all stuck together), release a beta particle (electron) and transform one of their electrons into a proton, or release gamma rays (pure energy in the form of extremely high energy electromagnetic waves). The details of exactly why they release certain ones at certain times is more ELIaphysicsgradstudent but the basic idea is “the atom has too much energy packed into a nucleus and needs to release that energy in particular-sized bursts.
>If we’re talking a person, I’m assuming it damages/destroys the cell it hits, does it bounce and keep destroying more? What if a person was exposed to insanely high radiation of this sort. Do they melt into a pile of goop as their cells are broken down?
The radiation particles or energy smacks into atoms in the cells (especially in DNA) and excites them, causing them to break out of whatever bonds they’re in. This makes the cells either die outright, destroy themselves because their DNA is so messed up, or not repair the damage properly and become cancerous. If you are exposed to a massive massive dose yes you would melt–think of somebody with an incredibly severe sunburn (which is a radiation burn). But even the most severe radioactive accidents usually result in a slow awful death over several days as all the body’s tissues break down.
>How can the amount of neutrons differ and they still be considered the same element?
An element is defined by the number of protons it has, since that affects the number of electrons it normally has, which affects the way it interacts with other atoms.
>What happens to the element? Does it just eventually disappear or “evaporate”? What exactly happens to these atoms once the neutrons have all fired off? If the radioactive substance is a metal such as iridium, does it become super brittle once fully decayed? Crumble into dust?
Nope. Every time an atom fires off an alpha particle or a beta particle, it actually *changes the type of atom it is.* You can see an image of what’s called a “decay chain” for an element [here](https://upload.wikimedia.org/wikipedia/commons/thumb/2/25/Decay_Chain_Thorium.svg/300px-Decay_Chain_Thorium.svg.png). A thorium-232 atom releases 2 protons and 2 neutrons in an alpha decay and becomes a radium-228 atom. That atom then releases an electron, turns one of its neutrons into a proton, and becomes an actinium-228 atom. This continues until it finally hits a stable type of atom–usually lead.
Inbetween those steps, it might fire off gamma rays if it needs to release a bit of extra energy before it can get to the next step.
There’s a few different ways radiation can affect your cells.
DNA is important. It’s a big molecule made of atoms bonded together. When a fast neutron or other particle comes by and happens to collide with it, it’s like taking that nice orderly structure and hitting it with a cannonball. So now you have broken DNA, and that doesn’t work right. Usually that means the cell can’t do something it needs to do and the cell will die. Get enough of your cells affected, and the mass cell death across your entire body is very bad for you. This is radiation poisoning. Your body has cells die all the time, and it has cleanup and regeneration protocols to handle it. But this kind of mass death is too much for your body to deal with, so everything just stops working right. Bleeding out of your capillaries, organs no longer doing their job, that sort of thing.
Sometimes the cell doesn’t die, but it’s still not working right and so becomes cancerous.
If the radiation is really intense, simply absorbing a ton of energy from it hitting you is enough to heat up your tissue enough to cause burns.
As far as the decay process itself, it has to do with how the nucleus of an atom is held together. The identity of an atom is determined by its protons, change the number of protons and you have a new element. Change the amount of neutrons and you have the same element, chemically, but the weight is different so we call it an “isotope.” The protons want to fly apart due to their charge, but the whole thing is held together with the nuclear strong force. This force is, well, strong, but it’s not infinite. Neutrons help balance the two forces, but the ratios are important to stability. Too few neutrons or too many can both lead to instability, or even just not quite the right number. Add or subtract even one neutron and you can dramatically change the nucleus’s stability.
There’s different ways atoms can spontaneously decay. Sometimes a nucleus will eject a neutron, changing its isotope but not its atomic number so it’s the same element. “Alpha decay” is emitting two protons and two neutrons, aka a helium nucleus. So the original element changes, and is now a new element. Beta decay is when a neutron splits itself into a proton and an electron – the proton stays put in the nucleus, raising atomic number by one, and the electron flies off as radiation. Sometimes the whole nucleus will crack into two big pieces, making two new atoms that add up to the atomic number of the first.
Just to clarify one part of this:
> How can the amount of neutrons differ and they still be considered the same element?
Chemical elements — what we mean when we say “elements” — are defined by the number of _protons_ they have. So uranium always has 92 protons, and hydrogen always has 1, and helium always has 2, and so on. The reason we use the number of protons for this is because the number of protons determines how the atom will deal with _electrons_, and that determines how the atom’s chemistry will work. So any atom with the same number of protons will behave chemically the same way as any other atom with the same number of protons, _no matter how many neutrons they have_. So helium is always helium, uranium is always uranium, and so on, as long as their proton counts stay the same. The periodic table of elements is a list of elements that orders them by their chemical affinities — a chemist can glance at it and say, “oh, this element would behave cheicallylike this other element other th
But as you note atoms can have different numbers of neutrons. Each type of element with different neutron counts is called an _isotope_. So Uranium-235 has 143 neutrons (92 protons + 143 neutrons = 235 nucleons). Uranium-238 has 146 neutrons (92+146 = 238). They behave _chemically_ identically, because they are both uranium (92 protons). But they behave different _physically_ because they have different neutron counts. So they have different radioactive half-lives, have different nuclear properties (U-235 is fissile, U-238 is not), and weigh different amounts (which is how they separate the two when they want to make U-235; because you can’t do it chemically, you have to rely on that tiny difference in mass).
When atoms undergo radioactive decay, their proton and neutron counts change, and so they become different elements. So Uranium-238 can lose an alpha particle (a helium nucleus, 2+2), and so it goes from 92+146 to 90+144, and thus becomes Thorium-144, a totally different element and isotope with different chemical and nuclear properties. Thorium-144 can also decay, and its decay product can decay, and so on, until you finally end up, after quite a long time, with Lead-206 (82+124), which is stable and won’t decay anymore.
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