The radionucleide Th 234 90 undergoes two s cces ive ß-decays followed by one a-decay. The atomic num- ber and the mass number respectively of the resulting radionucleide are

To determine the atomic number and mass number of the resulting radionuclide after the specified decay processes of Th-234 (Thorium-234), we need to carefully analyze each decay step. Let's break it down step by step.

Understanding the Decay Process

Thorium-234 has an atomic number of 90 and a mass number of 234. The decay processes involved are beta (β) decay and alpha (α) decay. Here’s how each of these processes affects the atomic and mass numbers:

Beta Decay

In beta decay, a neutron in the nucleus is transformed into a proton, emitting a beta particle (an electron) and an antineutrino. This process increases the atomic number by 1 but does not change the mass number. Therefore:

• Initial state: Th-234 (atomic number 90, mass number 234)
• After first β-decay: The atomic number becomes 91 (now it’s Protactinium, Pa), and the mass number remains 234.
• After second β-decay: The atomic number increases to 92 (now it’s Uranium, U), and the mass number remains 234.

Alpha Decay

In alpha decay, the nucleus emits an alpha particle, which consists of 2 protons and 2 neutrons. This process decreases the atomic number by 2 and the mass number by 4. Now, applying this to our current state:

• Before α-decay: U-234 (atomic number 92, mass number 234)
• After α-decay: The atomic number decreases to 90 (back to Thorium, Th), and the mass number decreases to 230 (234 - 4).

Final Result

After completing the two beta decays followed by one alpha decay, we find that the resulting radionuclide is Th-230. Therefore, the atomic number and mass number of the resulting radionuclide are:

• Atomic Number: 90
• Mass Number: 230

This process illustrates the transformation of elements through radioactive decay, showcasing how the atomic structure changes with each decay event. Understanding these transformations is crucial in fields like nuclear physics and radiochemistry.