Q188 / 200 · MHT CET - Medical 2026 (22 April Shift 2) · Physics
For a radioactive nucleus that undergoes $\beta^+$ decay, which of the following CANNOT occur?
- ANuclei with lower atomic number than that of original nucleus is produced.
- BThe proton is converted to neutron
- CIsobar of original nucleus is produced.
- Correct answerDIsotope of original nucleus is produced.
Solution
In $\beta^+$ decay, a proton inside the nucleus is converted into a neutron, a positron, and an electron neutrino. The nuclear reaction is represented as:
$^{A}_{Z}X \rightarrow ^{A}_{Z-1}Y + e^+ + \nu_e$
The atomic number $Z$ decreases by $1$, so a nucleus with a lower atomic number is produced.
The mass number $A$ remains unchanged, meaning the daughter nucleus is an isobar of the original nucleus.
Since the atomic number changes, the daughter nucleus cannot be an isotope of the original nucleus, as isotopes must have the same atomic number.
Answer: Isotope of original nucleus is produced.
$^{A}_{Z}X \rightarrow ^{A}_{Z-1}Y + e^+ + \nu_e$
The atomic number $Z$ decreases by $1$, so a nucleus with a lower atomic number is produced.
The mass number $A$ remains unchanged, meaning the daughter nucleus is an isobar of the original nucleus.
Since the atomic number changes, the daughter nucleus cannot be an isotope of the original nucleus, as isotopes must have the same atomic number.
Answer: Isotope of original nucleus is produced.
Hence, the correct answer is option: 'D'.