Which nuclide is produced when uranium-238 undergoes alpha decay?

• A. uranium-234
• B. thorium-234
• C. plutonium-238
• D. protactinium-234

Answer: (B)

Verified step by step guidance

1. Recall that alpha decay involves the emission of an alpha particle, which is a helium nucleus consisting of 2 protons and 2 neutrons. This means the original nucleus loses 2 protons and 2 neutrons.
2. Write down the original nuclide: uranium-238, which has an atomic number of 92 (number of protons) and a mass number of 238 (total number of protons and neutrons).
3. Subtract 2 from the atomic number to account for the loss of 2 protons: 92 - 2 = 90. This new atomic number corresponds to the element thorium.
4. Subtract 4 from the mass number to account for the loss of 2 protons and 2 neutrons: 238 - 4 = 234. This gives the mass number of the new nuclide.
5. Combine the new atomic number and mass number to identify the nuclide produced: thorium-234.