AMA about Physics

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Wayne
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Re: AMA about Physics

Postby Wayne » Tue Sep 12, 2017 9:38 am

I will second Keith's comment about this being a fascinating thread. I am a Science nerd with Physics being my particular favorite branch. I love seeing the conversation.
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Knaight
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Re: AMA about Physics

Postby Knaight » Wed Sep 27, 2017 6:55 pm

This is both really specific and borderline chemistry, but what happens to chemical bonds (and other electrons around in general) when one of the constituent atoms undergoes a nuclear decay process? Does the energy break them? Is there some sort of ionization effect on top of bonds breaking? What goes on there?
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Gamma-Ray
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Re: AMA about Physics

Postby Gamma-Ray » Wed Sep 27, 2017 9:51 pm

Knaight wrote:This is both really specific and borderline chemistry, but what happens to chemical bonds (and other electrons around in general) when one of the constituent atoms undergoes a nuclear decay process? Does the energy break them? Is there some sort of ionization effect on top of bonds breaking? What goes on there?


That depends a bit on the nuclear decay process. Let's start with beta decay (electron emission from the nucleus, e.g., 131I goes to 131Xe). The atom undergoing decay now has a different nuclear charge, so bonds can break (or form, for example if you started from a noble gas). The iodine-to-xenon example I gave means that bonds are likely to simply break. The electrons simply go to a new configuration, possibly with some emission of energy. In addition, there is a high-energy electron (beta particle) zinging around, so it can cause ionization of other atoms and compounds in the vicinity. When you hear about "ionizing radiation", that's the serious stuff (more energetic than ordinary ultraviolet). I should mention that beta decay is often accompanied by emission of one or more gamma rays, which also run around ionizing things.

Other types of nuclear decay processes include:
- emission of a gamma ray (e.g., 99mTc goes to 99Tc), which does not change the nuclear charge, so the bonds don't change, but the high-energy photon (gamma-ray!) can also cause ionization and other trouble.
- emission of a positron. This is like a beta-decay, but the nuclear charge decreases instead of increasing, and instead of an electron zinging around you have a positron, which will shortly encounter an electron and annihilate, giving off two 511,000 electron volt gamma rays, which will also cause ionization.
- emission of an alpha particle (alias a helium nucleus). The nuclear charge decreases by two, so the bonding can undergo even more changes. Also, the alpha particle loses more energy in a shorter distance, so the local ionization is stronger than with beta decay or emission of a gamma ray. With the emission of the much heavier alpha particle, the recoil of the nucleus from the emitted alpha particle is energetic enough that bonds are likely to be broken by the recoil itself.
- nuclear fission. This is sort of the prince of energetic nuclear reactions (fusion is king), and the consequences are very complicated. Fissions emit neutrons and gamma rays as well as two (or sometimes three) unequal fission fragment nuclei. The fission fragments have a lot of energy and high nuclear charge, so they break their chemical bonds and deposit their energy in a very localized fashion. The energies involved are high enough that the fission fragments effectively melt little tunnels for themselves even in materials like uranium dioxide, which then resolidify very quickly. Many of the fission fragments themselves are more neutron-rich than the stable isotopes of those elements, so they tend to undergo beta decay (see above for consequences).

I haven't covered all the forms of nuclear reactions, but this is a good start.


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