Of the two isotopes of iodine, 136I and 122I, one decays by b emission and one decays by positron emission. Which does which? Explain.

Verified step by step guidance

1. Step 1: Understand the concept of beta decay and positron emission. Beta decay is a type of radioactive decay where a beta particle (an electron or a positron) is emitted. In beta minus decay, a neutron is converted into a proton and an electron, which is then emitted. In beta plus decay or positron emission, a proton is converted into a neutron and a positron, which is then emitted.
2. Step 2: Look at the atomic number of iodine. The atomic number of iodine is 53, which means it has 53 protons.
3. Step 3: Compare the atomic number with the mass number of the isotopes. The isotope 136I has more neutrons than protons (136-53=83 neutrons), while the isotope 122I has fewer neutrons than protons (122-53=69 neutrons).
4. Step 4: Apply the concept of beta decay. The isotope with more neutrons than protons (136I) will undergo beta minus decay (b emission) to convert a neutron into a proton and an electron. The isotope with fewer neutrons than protons (122I) will undergo beta plus decay (positron emission) to convert a proton into a neutron and a positron.
5. Step 5: Conclude that 136I decays by beta emission and 122I decays by positron emission.

Key Concepts

Isotopes

Isotopes are variants of a particular chemical element that have the same number of protons but different numbers of neutrons. This difference in neutron count results in varying atomic masses. For iodine, the isotopes 136I and 122I have different nuclear stability, which influences their decay processes.

Beta Decay

Beta decay is a type of radioactive decay in which a neutron in the nucleus of an atom is transformed into a proton, emitting a beta particle (an electron) and an antineutrino. This process increases the atomic number of the element by one, resulting in the formation of a new element. In the case of iodine isotopes, the one that undergoes beta decay will have a neutron-to-proton ratio that favors this transformation.

Positron Emission

Positron emission, or beta plus decay, occurs when a proton in the nucleus is converted into a neutron, releasing a positron (the antimatter counterpart of an electron) and a neutrino. This process decreases the atomic number by one, leading to the formation of a different element. The isotope that undergoes positron emission will typically have a neutron-to-proton ratio that is too low for stability, prompting this decay mode.