If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

### Course: Modern Physics (Essentials) - Class 12th>Unit 4

Lesson 2: Nuclei can change in multiple ways, but how do they choose their path?

# Writing nuclear equations for alpha, beta, and gamma decay

Alpha, beta, and gamma decay are all ways that an unstable atom can decay into a more stable form. Let’s model each type of decay through equations. Created by Jay.

## Want to join the conversation?

• A beta particle is an electron. But I was told that it doesn't behave like one. It can't take the place of an electron in a regular chemical reaction. Why is that?
• A beta particle can be either an electron OR a positron. If it is a positron, it will not act like an electron because it has a positive charge, which will repel it from anything that an electron would interact with. Most often they will be annihilated by colliding with an electron eventually.

If it is an electron though, and has a negative charge as usual, it will fly away from the atom at a high energy until it crashes into something, and then will react with whatever it crashes into. Hope this helped!
• When Thorium performs beta decay and becomes protactinium, would the product be an ion since a proton was added, and a beta particle was released out of the atom, not keeping the charges equaled?
• Probably, but also probably not for very long, since any free electrons in the area will be attracted to it's positive charge.
In studying nuclear physics we really are focused on what's going on in the nucleus. What happens with the electrons doesn't matter much.
• Is neutron made up of proton and electron and antineutrino? If yes, do the sum of these masses equal the mass of neutron? If no, what else is neutron made up of?
• No, a neutron is not made of a proton, electron and antineutrino. It is made of two down quarks (charge -1/3) and one up quark (charge 2/3).

When it decays, the weak force causes a down quark to change into an up quark, effectively making it a proton. This process also releases an electron and an antineutrino.
• I have a bunch of confusion how the Gama ray decays. Sal had't clarify about the Gama decays. Can any one help??
• Gamma rays are produced by an acceleration of charged particles. Usually, in terms of high energy decay, this is due to a rearrangement of nucleons in a nucleus into a lower energy state (this is what is referred to as gamma decay), nuclear fission, or various other means. Many of the other types of decay can also produce gamma radiation of various energy levels.
• How do you know charge and nucleons are conserved? Reason?
• We do not "know" that a given conservation law is true, instead we have observed, over and over again, that in every reaction things like the total electric charge stays the same. From this, scientist have created a model that up to now has always shown to be correct.
• So he talks about the three types of radioactive decay, but how do you know what kind of decay say, Uranium, for instance, would give off? Or any other element for that matter?
Thanks!
• We measure it using detectors. Each particle can be detected using different methods due to its ability to penetrate materials. So, for U-235 for example, when it decays via α-decay, a Geiger counter will only detect it if there is no 'window' on the detector as alpha particles cannot penetrate through solid matter very far. Scintillation counters can use different materials specialized for specific types of radiation as well.
• At , how can nucleus become excited? Wasn't that electrons?
• The nucleus has nuclear energy levels, just like the atom has atomic energy levels. The reason for this is that you get energy levels whenever you have things bound together. The electron is bound to the nucleus by the electric force, so you get quantized energy levels related to that "system" of nucleus + electrons. But inside the nucleus, the nucleons are bound to one another by the strong nuclear force, so you also get quantized energy levels for that smaller system. Since the strong force is much stronger than the electric force at subatomic range, the energy levels in the nucleus are much larger than those for the atom, and this is why the energy released in nuclear reactions is so much greater than the energy released in chemical reactions (eg a nuclear electric power facility produces energy from a lot less fuel than a similarly powerful coal-fired electric power facility)
• How do we know which elements will undergo which kind of decay without actually observing them? E.g, why can't U-238 do beta decay?
• You can't. You would need to look it up in a reference source. Some atoms can decay in more than one way, and you can't predict which one will happen first.