Explain Like I'm Five | Don't Panic!
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Eli5: Radioactive decay, does it mean that the element is less radioactive? (self.explainlikeimfive)
submitted 1h ago by kirrathenerd
Ok. Trying to figure this out. If a half life is the time it takes for the elements isotope to decay to half of what it originally was, then does this mean that the element is half as radioactive as it was? I’m so confused.
javanator999 1 points 1h ago
So lets say that we have a gram of something pretty radioactive. And it emits a certain amount of radiation per second. After one half life, there will be half a gram of the original substance left. Which will emit half the radiation it did before. There will also be just slightly less than half a gram of whatever it decays into. Which may or may not be radioactive depending on how the decays works.
Gnonthgol 1 points 1h ago
Yes, sort of. The half time of an isotope is the time it takes for half the isotope to decay and therefore there is just half as much material which mean it is half as radioactive. But it is not uncommon for isotopes to decay to other radioactive isotopes. So while there is just half as much of the original radioactive isotope there may be newly created isotopes which are also radioactive bringing the total radioactivity up. This effect is more prominent in the beginning though as eventually the ratio of radioactive elements finds an equilibrium. So over longer timeframes the reduction in radioactivity due to less radioactive material will dominate.
kirrathenerd [OP] 1 points 1h ago
Okay I see what you’re saying I think. But doesn’t the element decay into a more stable isotope? So would that mean that if it decays into another radioactive element then the isotope of that element is still more stable, which means less radioactive? So in total the radioactivity would still be less ? I could be completely wrong about all this. No clue.
647843267b1 1 points 58m ago
Nope, lots of isotopes decay into MORE radioactive isotopes. And it's not a quick process either. Depleted uranium gets MORE radioactive for over a BILLION years
kirrathenerd [OP] 1 points 25m ago
Okay interesting thanks so much. I have so much to learn. I just find it so fascinating but so confusing
Gnonthgol 1 points 11m ago
No, isotopes decay into both more and less radioactive isotopes. But the more radioactive isotopes have shorter half lives. So for example if you start with an isotope with a half life of 1000 years it may decay into an isotope with a half life of 10 years which again decay into an isotope with a half life of a million years. The net result is that the initial material decay into the most stable isotope, but it is not a direct path. So you would expect that the radiation initially increases as more of the 10 year half life isotope is generated. But then as the generation and decay of this isotope becomes equal the radiation stops increasing and start decreasing.
kirrathenerd [OP] 1 points 8m ago
Ah thank you!!! Ok this is definitely helping me. The missing link for me was that I thought each half life decay would mean automatic lower radioactivity. This and the tent analogy another commenter mentioned is helping me understand .
Taxoro 1 points 31m ago
If there is only half the radioactive material left then yes the object is half as radioactive.
This is not always the case though. Radioactive elements essentially transforms into a new element each time it emits radiation(except for gamma radiation), sometimes that element is also radioactive. This happens a lot with larger elements, where they decay into a new radioactive element, and then again and again until they finally hit something that is stable(typically led). So for those elements the radioactivity is not halved one half life.
This is not always the case though. Radioactive elements essentially transforms into a new element each time it emits radiation(except for gamma radiation), sometimes that element is also radioactive. This happens a lot with larger elements, where they decay into a new radioactive element, and then again and again until they finally hit something that is stable(typically led). So for those elements the radioactivity is not halved one half life.
kirrathenerd [OP] 1 points 19m ago
Ok, Thank you! So the half life does not automatically mean half the radioactivity, it depends on what element it is decaying into.. I think it’s all coming together in my brain lol
Selfless- 1 points 23m ago
When an atom decays it no longer is its original element. It splits. That split is what produced the “radioactivity”. The remaining bits are usually a lighter atom and some energy and particles. Sometimes the particles are large and cohesive enough to also be atoms (usually Helium).
Half-life estimates the future time at which only half of the original atoms will still be in their original form and half will have decayed into something else. With only half of the remaining material, there’s only half as much probable source, so observed radiation should also be half. It’s like you have half as much of the original material, because you do.
Half-life estimates the future time at which only half of the original atoms will still be in their original form and half will have decayed into something else. With only half of the remaining material, there’s only half as much probable source, so observed radiation should also be half. It’s like you have half as much of the original material, because you do.
kirrathenerd [OP] 1 points 15m ago
Ok this is how I was somewhat understanding it originally, but I guess now i’m understanding that some elements decay into other radioactive elements so the radioactivity would still be there? I am still slightly confused on wether it can decay into a MORE radioactive element though. But slowly i’m getting there lol
Neither_Hope_1039 1 points 1h ago
Yes, it does.
The radioactive activity of an element (measured in Becquerel, or decays per second) of a sample will decrease as the sample decays.
The radioactive activity of an element (measured in Becquerel, or decays per second) of a sample will decrease as the sample decays.
kirrathenerd [OP] 1 points 1h ago
Okay thank you! So if you don’t mind me asking- how does radon 222 decay into polonium 218? Is polonium more radioactive than radon? So i don’t understand how it can decay into a element more radioactive
Xerxeskingofkings 1 points 50m ago
When you see "radioactivity," read it as "stability". While the general trend is towards a more stable nucleus, it can transition through states that are more unstable than the start or end states as it sheds particles.
For example, a fully erected tent is stable, and so is a fully packed away tent, but it's very UNstable while it's transitioning between the two states
For example, a fully erected tent is stable, and so is a fully packed away tent, but it's very UNstable while it's transitioning between the two states
kirrathenerd [OP] 1 points 24m ago
Okay, thanks so much! This actually really helps clarify it. The tent analogy definitely helps me to understand
boundbylife 1 points 34m ago
All atoms want to reach stability, and do do that, they decay.
There are three types of decay - alpha, beta, and gamma.
Alpha decay happens when 2 protons and 2 neutrons (so, Helium) are ejected from the nucleus, and can be stopped by a sheet of paper . Beta decay happens when an electron is ejected; this can be stopped by alumninum. And gamma decay occurs when a high-frequency EM wave is emitted to shed energy; this is also referred to as a gamma ray, and is incredibly damaging to any living organism. It takes a large chunk of lead to stop gamma radiation.
Rn-222 decays into Po-218 via alpha decay over about 4 days. But Po-218 is ALSO not stable, so it quickly undergoes another alpha decay, converting to Pb-214. Still not stable, so we release a beta particle, and we get Bi-214. 19 minutes later, another Beta decay gets us to Po-214, which lasts all of .0002 seconds before decaying into Pb-210. This isotope of lead is stable-ish, taking 22 years to decay, but after two more decays(1 beta, 1 alpha), we land and perfectly stable Pb206.
There are three types of decay - alpha, beta, and gamma.
Alpha decay happens when 2 protons and 2 neutrons (so, Helium) are ejected from the nucleus, and can be stopped by a sheet of paper . Beta decay happens when an electron is ejected; this can be stopped by alumninum. And gamma decay occurs when a high-frequency EM wave is emitted to shed energy; this is also referred to as a gamma ray, and is incredibly damaging to any living organism. It takes a large chunk of lead to stop gamma radiation.
Rn-222 decays into Po-218 via alpha decay over about 4 days. But Po-218 is ALSO not stable, so it quickly undergoes another alpha decay, converting to Pb-214. Still not stable, so we release a beta particle, and we get Bi-214. 19 minutes later, another Beta decay gets us to Po-214, which lasts all of .0002 seconds before decaying into Pb-210. This isotope of lead is stable-ish, taking 22 years to decay, but after two more decays(1 beta, 1 alpha), we land and perfectly stable Pb206.
kirrathenerd [OP] 1 points 21m ago
Thank you!!! I’m learning that just because the end result is stable, that doesn’t mean the stages to get there are stable as well..
Just want to clarify to make sure i’m understanding- is Po 218 more or less stable than Rn 222? I understand both are unstable but is one more or less stable than the other?
Just want to clarify to make sure i’m understanding- is Po 218 more or less stable than Rn 222? I understand both are unstable but is one more or less stable than the other?
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