Radioactive Decay: Are stable elements really stable?

In summary, radioactive decay occurs because of the instability of an atom's nucleus in terms of proton-neutron ratio and energy content. This leads to the emission of alpha, beta, and gamma particles. While highly radioactive elements like Uranium constantly decay into more stable elements, each half-life decay takes the same amount of time. Stable elements do not decay, but some isotopes, like Carbon-14, are created through cosmic ray collisions and can be used for dating. However, the rate of decay for these isotopes is relatively slow and does not affect the stability of the element.
  • #1
cshum00
215
0
Ok, so all elements undergo radioactive decay. But why?

I have been snooping around and what i find is that radioactive decay occurs because of instability of the atom nucleus in quantity, proton-neutron ratio and energy content; therefore we have alpha, beta and gamma decay consecutively.

Therefore highly radioactive elements like Uranium undergo constant decay into less radioactive and more stable elements. Each half-life decay takes longer and longer in a exponential manner; therefore theoretically speaking, it takes forever for any element to completely decay into zero.

Although it explains why radioactive decay occurs on unstable elements or isotopes, it doesn't explain why it occurs on stable elements. Unless, stable elements are not really "stable" but the rate of decay are rather slow and harmless to human beings so we label it "stable."

Then if that is the case, then why elements are always decaying or always "unstable"?
Of course, this just an assumption of mine. Anybody can provide me a more conclusive answer?
 
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  • #2
'Stable' is synonymous with 'doesn't decay'. Any stable nucleus will not decay. Some elements, like carbon, with 6 protons, have some stable isotopes, with 6 neutrons in this case, and some unstable, with 7 or 8. The reason there's still a proportion of these unstable isotopes in naturally occurring samples is because they're constantly being created by cosmic ray collisions.
 
  • #3
henry_m, if you were right; carbon dating would be useless. It is because "stable" carbon still undergo radioactive decay that people are able to measure precisely when certain historical artifacts are from.

Of course, carbon dating does not apply anymore to objects on the surface because nuclear testings messed up the isotopes on the surface. However, carbon dating still works for artifacts buried deep enough into the ground.
 
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  • #4
Ok, so all elements undergo radioactive decay.
No, actually they don't. Hydrogen, for example, does not.
Therefore highly radioactive elements like Uranium undergo constant decay into less radioactive and more stable elements.
Some of Uranium's decay products are more radioactive, not less.
Each half-life decay takes longer and longer in a exponential manner;
Each half-life decay takes exactly the same amount of time.
Although it explains why radioactive decay occurs on unstable elements or isotopes, it doesn't explain why it occurs on stable elements.
Stable isotopes do not decay.
henry_m, if you were right; carbon dating would be useless. It is because "stable" carbon still undergo radioactive decay that people are able to measure precisely when certain historical artifacts are from.
Carbon-12 is stable, but carbon-14 used for dating is not.
 
  • #5
Bill_K said:
Some of Uranium's decay products are more radioactive, not less.
Thanks for the remarks. I was trying to imply that the idea of radioactive decay is that atoms are trying to stabilize itself by decaying. Although like you said, sometimes the products are more radioactive.

Bill_K said:
Each half-life decay takes exactly the same amount of time.
I thought they were exponential not linear.

Bill_K said:
Stable isotopes do not decay.
Carbon-12 is stable, but carbon-14 used for dating is not.
Ok. It seems that i have it wrong then. It leads to my next question. How common is carbon-14?
 
  • #6
The decay of a sample of radioactive material is exponential, given by A(t) = A(0)exp(-lambda*t), where lambda is ln(2)/T (T = the half life), but the half life T (the time it takes for a sample to statistcially decay to 1/2 it's original activity) is constant. You can see this for yourself by taking A(t) = 0.5A(0), or 0.5=exp(-lambda*t) and you'll find t = T.

As for carbon-14, it is created by high energy cosmic rays interacting with the stratosphere and troposphere to produce neutrons, which causes the 14N(n,p)14C reaction. The carbon is taken up by living things, and when the creature dies, the rate of uptake ceases. The carbon decays witha half life of about 5715 years. Since the concentration of carbon-14 is relatively constant, we can date when the creature died. It has about a 1 part per trillion concentration in the atmosphere http://en.wikipedia.org/wiki/Carbon-14" [Broken]
 
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  • #7
To experimental accuracy, if an atom has a half life of over 10 billion years we can't tell that it isn't stable.
 
  • #8
robert2734 said:
To experimental accuracy, if an atom has a half life of over 10 billion years we can't tell that it isn't stable.
Not true:

"Bi-209 has been known as stable nuclide. But, alpha decay of Bi-209 with a half time of 2*10^19 years was found, recently.
Reference : PIERRE DE MARCILLAC, NOEL CORON, GERARD DAMBIER, JACQUES LEBLANC & JEAN-PIERRE MOALIC, " Experimental detection of a-particles from the radioactive decay of natural bismuth," Nature 422, 876-878 (2003); doi:10.1038/nature01541."
 
  • #9
mathman said:
Not true:

"Bi-209 has been known as stable nuclide. But, alpha decay of Bi-209 with a half time of 2*10^19 years was found, recently.
Reference : PIERRE DE MARCILLAC, NOEL CORON, GERARD DAMBIER, JACQUES LEBLANC & JEAN-PIERRE MOALIC, " Experimental detection of a-particles from the radioactive decay of natural bismuth," Nature 422, 876-878 (2003); doi:10.1038/nature01541."

When I found out about that one I nearly freaked at the calculation just to get enough of the material to produce decay events that could exceed an MDA. Foir just an activity of 1Bq, you need over 300kg!
 

1. What is radioactive decay?

Radioactive decay is the process by which an unstable atomic nucleus loses energy by emitting radiation in the form of particles or electromagnetic waves. This process can result in the transformation of one element into another.

2. How do we know that elements are unstable and can decay?

Scientists use a variety of methods to determine the stability of an element, including measuring its half-life (the time it takes for half of a sample to decay) and analyzing the properties of its atomic nucleus. Elements with an unstable nucleus are more likely to undergo radioactive decay.

3. Are all elements capable of radioactive decay?

Most elements are capable of radioactive decay, although some elements have very long half-lives and are considered virtually stable. In general, the larger and heavier an element is, the more likely it is to be radioactive.

4. Can stable elements become unstable and undergo radioactive decay?

Yes, stable elements can become unstable and undergo radioactive decay through a process called transmutation. This can occur naturally through high-energy processes, such as cosmic rays, or artificially through nuclear reactions.

5. Is there any danger associated with radioactive decay?

Radioactive decay can potentially be harmful if a person is exposed to high levels of radiation. However, many elements that undergo radioactive decay have short half-lives, meaning they decay quickly and do not pose a significant threat. In addition, there are safety measures in place to minimize the risk of exposure to radiation.

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