Radiation Safety Practice Exam

Which hydrogen isotope is known to be unstable?

1. Protium

2. Deuterium

3. Tritium

4. Hydrogen-1

The correct answer is: Tritium

Tritium is the hydrogen isotope known to be unstable. It is a radioactive isotope consisting of one proton and two neutrons, which contributes to its instability. Tritium undergoes beta decay, where it transforms into helium-3, releasing a beta particle in the process. This decay occurs over a half-life of approximately 12.3 years, making tritium not only unstable but also a source of low-level radiation during its decay. In contrast, protium (the most common isotope of hydrogen), which contains only one proton and no neutrons, and deuterium, which consists of one proton and one neutron, are stable and do not undergo radioactive decay. Hydrogen-1 is another name for protium and shares the same stability characteristics. Thus, tritium stands out as the only unstable hydrogen isotope among the choices presented.