Question

The uranium- 238 decay series begins with the emission of an alpha particle. The daughter product emits a beta particle to give which nuclide?

Short answer

Thorium-234 ( \( ^{234}_{90} \text{Th} \) ) is formed.

Step-by-step solution

Understand Alpha Decay

In alpha decay, an alpha particle, which consists of 2 protons and 2 neutrons (a helium nucleus), is emitted from the original element. When this occurs, the atomic number decreases by 2 and the mass number decreases by 4.

Apply Alpha Decay to Uranium-238

Uranium-238 ( \( ^{238}_{92} \text{U} \)) emits an alpha particle ( \( ^{4}_{2} \text{He} \)), resulting in a new element with a mass number of 234 and atomic number of 90, which is Thorium-234 ( \( ^{234}_{90} \text{Th} \)).

Key concepts

Alpha Decay

Alpha decay involves the release of an alpha particle from a nucleus. An alpha particle is composed of 2 protons and 2 neutrons, resembling a helium nucleus. When a heavy nucleus like Uranium-238 undergoes alpha decay, it loses these 2 protons and 2 neutrons:

• The atomic number decreases by 2 because of the loss of 2 protons.
• The mass number decreases by 4 due to the loss of total 4 nucleons.

This transformation results in the element changing to a different isotope or even a completely different element. In this case, Uranium-238 becomes Thorium-234 after alpha decay. This process is common in heavy elements and is a crucial step in the decay series of radioactive materials.

Beta Decay

Beta decay is another type of radioactive decay helping in the transformation of elements. Unlike alpha decay, which ejects a helium nucleus, beta decay involves the emission of a beta particle. A beta particle can be either an electron or a positron. For beta decay involving electrons (common in Uranium decay sequences), a neutron in the nucleus transforms into a proton, releasing an electron:

• The atomic number increases by 1 due to the conversion of a neutron to a proton.
• The mass number remains unchanged because the overall count of nucleons is the same.

For our example involving Uranium-238, Thorium-234 further undergoes beta decay, transforming into Protoactinium-234. These decay steps are vital as they explain the changes different elements undergo over time.

Uranium-238

Uranium-238 is an isotope of uranium and is one of the most significant isotopes concerning nuclear decay. It contains 92 protons and 146 neutrons in its nucleus. This isotope serves as an excellent example of how heavy elements naturally break down over time, releasing particles in the form of radiation.

• Uranium-238 is involved in a long decay series, starting with alpha decay to form Thorium-234.
• Over several steps through alpha and beta decay processes, Uranium-238 ultimately transforms into stable Lead-206.

It's crucial for students to grasp how Uranium-238 changes as it decays since it's widely used in geological dating, providing insights into the age of earth materials and meteorites.