Tritium is a radioactive isotope of hydrogen that decays via beta-minus (β−\beta^-β−) emission. It is widely used in self-luminous emergency exit signs installed in commercial buildings where electrical wiring is difficult to route.
The nuclear symbol for a tritium nucleus is 13H^{3}_{1}\text{H}13H. Identify the number of protons and the number of neutrons in this nucleus.
number of protons: ______
number of neutrons: ______
State three physical differences between an alpha (α\alphaα) particle and a beta-minus (β−\beta^-β−) particle.
Explain why it is impossible for a tritium nucleus to undergo alpha decay.
In a self-luminous exit sign, tritium gas is sealed inside borosilicate glass tubes coated internally with a phosphor material. The phosphor glows when struck by the emitted beta particles. Explain why these exit signs pose no radiation hazard to people inside the building, even though beta-minus radiation is ionising.
Define the term half-life of a radioactive isotope.
The graph below shows how the activity of the tritium inside a new exit sign changes over time.
Use the graph to estimate the half-life of tritium. Show your working clearly.
half-life = ______ years
To meet safety regulations for emergency escape routes, the exit sign must maintain an activity of at least 150 GBq150\text{ GBq}150 GBq to remain sufficiently bright. The manufacturer claims that these signs can be safely used for at least 17 years17\text{ years}17 years before they must be replaced. Evaluate whether the manufacturer's claim is valid, using evidence from the graph.
