In radioactive decay, what happens to the mass number (A) and atomic number (Z) of a nucleus during beta⁺-decay (positron emission)?
Show answer & explanation
Correct answer: A
Explanation
Solution: The correct answer is A remains unchanged, Z decreases by 1.
Explanation:
☛ In beta-plus (β⁺) decay, also known as positron emission, an unstable nucleus converts a proton into a neutron.
☛ During this process, a positron (e⁺) and an electron neutrino (νₑ) are emitted from the nucleus.
☛ Nuclear equation: p → n + e⁺ + νₑ.
☛ Since a proton converts into a neutron, the atomic number (Z), which is the number of protons, decreases by 1.
☛ The total number of nucleons (protons + neutrons) remains the same, so the mass number (A) remains unchanged.
Extra Exam-Relevant Facts:
☛ Beta-minus (β⁻) decay: A neutron converts into a proton, emitting an electron and an antineutrino; here, A remains unchanged and Z increases by 1.
☛ Alpha (α) decay: A helium nucleus (₂⁴He) is emitted; the mass number (A) decreases by 4 and the atomic number (Z) decreases by 2.
☛ Gamma (γ) decay: The excited nucleus releases excess energy as high-energy photons; both A and Z remain completely unchanged.
☛ Positron: It is the antiparticle of the electron, having the same mass but a positive charge, discovered by Carl D. Anderson in 1932.
Important One-Liners for Upcoming Exams:
☛ Which subatomic particle is known as the antiparticle of the electron? → Positron
☛ Which radioactive emission has the highest penetrating power? → Gamma rays
☛ Who discovered natural radioactivity in 1896? → Henri Becquerel
☛ What happens to the atomic number during electron capture? → Decreases by 1
☛ What is the SI unit of radioactivity? → Becquerel (Bq)