Beta Decay - Online Tutor, Practice Problems & Exam Prep

Beta decay is a nuclear process where an unstable nucleus emits a beta particle, which is a high-speed, high-energy electron. This decay occurs in nuclei with an excess number of neutrons and serves to reduce the neutron count while increasing the proton count, thereby achieving a more stable nucleus. During beta decay, a neutron is converted into a proton and an electron; the proton remains in the nucleus while the electron is ejected. For example, selenium-81 can transform into bromine-81 through beta decay, maintaining the mass number of 81 but increasing the atomic number by one. Beta particles, being smaller than alpha particles (helium-4 isotopes), have lower ionizing power but higher penetrating power, meaning they can pass through materials more easily. To shield against beta particles, denser materials like metal sheets or thick wood are required due to their higher penetrating ability. The characteristics of beta particles, including their size and ionizing and penetrating powers, are crucial to understanding their behavior and potential impact on biological tissue.

Beta Decay

Now beta decay occurs when an unstable nucleus emits a beta particle. Now what is a beta particle? Well, a beta particle is a high energy and high speed electron. Now if we're talking about an electron, we can symbolize it two different ways. So here electrons, remember are very small compared to neutrons and protons. Their weight is so small that it's almost insignificant. So we have a mass number of 0 for them. Electrons are negatively charged, so we have -1 here in the atomic number slot.

Here we could symbolize it by E for electron or we can say it's a beta particle. We use the beta symbol now here. This usually occurs in nuclei with an excess number of neutrons. When we do beta decay, what are we trying to do? Well, when we do beta decay, we're trying to actually bring down our number of neutrons, and we're trying to increase our number of protons. We're trying to balance them out with each other. Since we have an excess of neutrons, we need to get rid of some of those neutrons, and we do this by converting them into protons.

Now neutrons split into a proton and an electron. The electron is ejected from the nucleus. So here we're basically bringing down a number of neutrons to help us increase our number of protons. In the process, we also eject an electron from the nucleus. But the proton that's created stays within the nucleus. Here we have what we have, selenium 81. It's going to undergo beta decay. So we're ejecting our electron. And remember, when it comes to our mass number, it has to be the same on both sides and our total number of protons has to be the same on both sides.

Here we have 81 as our mass number. So on the product side, we need to have a total mass number of 81 as well. Well, the electron doesn't contribute anything to that. So our new isotope would still have a mass number of 81. On the reactant side, we have 34 protons. So on the product side we need to have 34 protons. But here we have a minus symbol subtracting -1. So to get 34 on the product side, I actually have to add 35 here because 35 - 1 gives me 34 protons just like the reactant side.

And if we look at the periodic table, what's the only element that has an atomic number of 35? So we converted Selenium 81 into Bromine 81 by way of beta decay. So this will represent our beta decay reaction.

Beta Decay Example

Here it says to write a balanced nuclear reaction for beta decay of iodine 129. All right, so iodine 129. If we look on the periodic table, iodine has an atomic number of 53 beta. Decay means that our energetic particle, in this case the electron, will be a product.

Remember the mass numbers on both sides have to be the same. The total number of protons on both sides have to be the same. Here this would still be 129 because 129 + 0 gives me 129. On the reactant side we have 53 protons, so on the product side we also need 53 protons. The number here would have to be 54 because 54 - 1 gives me 53.

Now if we look on the periodic table, what element has an atomic number of 54? That's right, it will be xenon. So here we'd say that iodine 129 turns into xenon 129 by way of beta decay. So this will represent our beta decay reaction of iodine 129.

I 129 → Xe 129 + e -

Characteristics of Beta Particles

Now when it comes to the characteristics of beta particles, we can compare them to alpha particles. Here we can say the beta particles are much smaller than alpha particles. That's because an alpha particle is basically a helium-4 isotope, pretty large. We have two protons and two neutrons, whereas a beta particle is only an electron, incredibly small.

Now here we'd say that they're going to have lower ionizing power if an alpha particle were to get inside of biological tissue, since it's so large, it'll move much more slowly, giving it time to ionize all surrounding tissue. Beta particles, being electrons, move very rapidly, so they go through the material much quicker, not giving themselves ample time to ionize all biological tissue. And as a result of this, because they're so much smaller, because they can move faster, we can say that beta particles have a higher penetrating power.

If we continue looking at this chart down below, we're going to say we have our alpha decay of platinum-171 that gave us osmium-167. For beta decay, we have selenium-81 becoming bromine-81. In terms of size, alpha particles are the largest because they're represented by the helium-4 isotope. For beta particles, they're going to be smaller.

In comparison, ionizing power of alpha particles is the highest. We're going to say here that in comparison, beta particles have lower ionizing power. Since alpha particles are the largest, they have very slow penetrating power. We're going to say here that beta particles in comparison are higher.

Now what can shield us if the penetrating power is higher for beta particles? Well, here we need much more dense material, so like a sheet of metal or a thick chunk of wood. OK, so we need more dense material to stop the progression of a beta particle. So just remember we can compare these two to one another. Remember, size of them can contribute a lot to our ideas of ionizing power and penetrating power.

Beta Decay Example

Which are not the characteristics of beta decay. Beta particles are smaller in size but have higher ionizing power due to their speed. This is not true. Yes, they're smaller in size, but because they're smaller in size, they move much more quickly, giving them less time to ionize tissue that they enter. So they would have lower ionizing power. So this is our answer.

Let's look at the other options. A high energy, high speed electron is injected from a nucleus of an unstable atom. That's true. Due to higher penetrating power, beta particles can be blocked by your cannot be blocked by your skin. That is also true. You need thicker material. Beta particles carry a mass number of 0. Yes, a beta particle is an electron, so it's 0/-1 and then your electron.

So here the only statement that's not true not a characteristic of beta decay, is option A.

Here’s what students ask on this topic:

What is beta decay?

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Beta decay is a type of radioactive decay in which an unstable atomic nucleus transforms into a more stable one by emitting a beta particle. There are two types of beta decay: beta-minus (<sub>β<sup>-</sup></sub>) and beta-plus (<sub>β<sup>+</sup></sub>).

In beta-minus decay, a neutron in the nucleus is transformed into a proton, an electron (the beta particle), and an antineutrino. The electron and antineutrino are ejected from the nucleus, while the proton remains, resulting in an element that moves one place up the periodic table.

Beta-plus decay, also known as positron emission, occurs when a proton in the nucleus is converted into a neutron, a positron (the beta particle, which is the antimatter counterpart of the electron), and a neutrino. The positron and neutrino are emitted from the nucleus, and the element moves one place down the periodic table.

Both processes are mediated by the weak nuclear force, one of the four fundamental forces in physics. Beta decay changes the atomic number of the nucleus, thus transforming the original element into a different element, while the mass number remains unchanged.

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Which of the following describes radioactive decay by beta particle emission?

Radioactive decay by beta particle emission occurs when an unstable atomic nucleus transforms into a more stable nucleus by emitting a beta particle. There are two types of beta decay: beta-minus (₋) and beta-plus (₊).

In beta-minus decay, a neutron in the nucleus is transformed into a proton, and in the process, it emits an electron, known as a beta-minus particle, along with an antineutrino. The atomic number of the element increases by one due to the additional proton, but the mass number remains the same, resulting in the formation of a different element.

In beta-plus decay, also known as positron emission, a proton is converted into a neutron, releasing a positron, which is a beta-plus particle, and a neutrino. Here, the atomic number decreases by one, but again, the mass number does not change, leading to a different element.

Both processes are a way for the nucleus to achieve a more stable configuration of protons and neutrons.

Which of the following describes radioactive decay by beta particle emission?

Radioactive decay by beta particle emission occurs when an unstable atomic nucleus transforms into a more stable nucleus by emitting a beta particle. There are two types of beta decay: beta-minus (₋) and beta-plus (₊).

In beta-minus decay, a neutron in the nucleus is transformed into a proton, and in the process, it emits an electron, known as a beta-minus particle, along with an antineutrino. The atomic number of the element increases by one due to the additional proton, but the mass number remains the same, resulting in the formation of a different element.

In beta-plus decay, also known as positron emission, a proton is converted into a neutron, releasing a positron, which is a beta-plus particle, and a neutrino. Here, the atomic number decreases by one, but again, the mass number does not change, leading to a different element.

Both processes are a way for the nucleus to achieve a more stable configuration of protons and neutrons.

What happens in beta decay?

In beta decay, an unstable atomic nucleus transforms into a more stable nucleus by emitting a beta particle. There are two types of beta decay: beta-minus (β^-) and beta-plus (β⁺).

In beta-minus decay, a neutron in the nucleus is transformed into a proton, an electron (the beta particle), and an antineutrino. The emitted electron is ejected from the nucleus, while the antineutrino escapes with a portion of the energy. This process increases the atomic number of the element by one while keeping the mass number the same, effectively changing the element into its next neighbor on the periodic table.

In beta-plus decay, a proton is converted into a neutron, a positron (the beta particle), and a neutrino. The positron is the antimatter counterpart of the electron and is emitted from the nucleus along with the neutrino. This type of decay decreases the atomic number by one, turning the element into its previous neighbor on the periodic table.

Both types of beta decay are governed by the weak nuclear force, one of the four fundamental forces of nature, and they play a crucial role in the process of radioactive decay and the transmutation of elements.

What is ejected in a beta decay event?

In a beta decay event, there are two types of beta decay: beta-minus (₋) and beta-plus (₊).

In beta-minus decay, a neutron in an unstable atomic nucleus is transformed into a proton, and in the process, it emits an electron (also called a beta particle) and an antineutrino. The emitted electron is what is commonly referred to when talking about beta particles being ejected in beta decay.

In beta-plus decay, the reverse happens: a proton is converted into a neutron, and the nucleus emits a positron (the electron's antimatter counterpart) and a neutrino. The positron is the beta particle ejected in this type of decay.

Both of these processes result in the transformation of one element into another in the periodic table and are accompanied by the release of energy. These processes are examples of weak nuclear interactions and are important for understanding radioactive decay and the stability of atomic nuclei.