$^{238}_{92}$U  + $^1_0$n → $^{239}_{92}$U  The process above produces

1. Analyze the Question

The reaction provided is: $^{238}_{92}\text{U} + ^{1}_{0}\text{n} \rightarrow ^{239}_{92}\text{U}$

We are looking at a nuclear reaction where a Uranium-238 nucleus captures a neutron to become Uranium-239. We need to identify the nature of the product formed.

2. Explain the Concept

• Isotopes: These are atoms of the same element (same atomic number) that have different mass numbers due to a different number of neutrons.
• Radioactivity: Many heavy isotopes, especially those created by neutron bombardment (like $^{239}\text{U}$), are unstable. Because they have an excess of neutrons, they are inherently radioactive; they will eventually undergo radioactive decay (usually beta decay) to become more stable.
• Nuclear Transmutation: This is the conversion of one chemical element or isotope into another. While this is a transmutation, the specific characteristic of the product $^{239}\text{U}$ is that it is an unstable, radioactive isotope.

3. Show the Solution

• Step 1: Observe the atomic number (bottom number). It remains 92, meaning the element is still Uranium.
• Step 2: Observe the mass number (top number). It increases from 238 to 239.
• Step 3: Recognize that $^{239}\text{U}$ is an isotope of $^{238}\text{U}$.
• Step 4: In nuclear chemistry, when a heavy nucleus captures a neutron, the resulting isotope is almost always unstable and undergoes radioactive decay. Therefore, the product is classified as a radioactive isotope.

4. Identify the Answer

• A (Atomic mutation): This is a vague term not typically used to describe this specific outcome.
• B (A radioactive isotope): This is correct. $^{239}\text{U}$ is an isotope of Uranium, and it is radioactive.
• C (Other neutrons): No additional neutrons are released in this specific equation.
• D (Radiations): While the isotope will eventually emit radiation, the product itself is the isotope, not the radiation.

5. Exam Tip

Whenever you see a nuclear equation where a neutron ($^{1}_{0}\text{n}$) is added to a nucleus, the product is almost always a heavier isotope of the original element. Because these "neutron-rich" isotopes are unstable, they are almost always radioactive. Remember: Neutron capture = Radioactive isotope formation.