A museum assesses two sealed radioactive mineral specimens, A and B, before placing them in storage. Each specimen contains the same number of undecayed nuclei and emits gamma radiation with the same energy. Exposure rates are measured at the same distance through identical shielding. The initial exposure rate from A is lower than the initial exposure rate from B.
Which statement about the half-lives of A and B is correct?
The half-lives cannot be compared, because half-life does not depend on the number of nuclei.
A has the longer half-life, because a smaller fraction of its nuclei decays each second.
A has the shorter half-life, because a source with a lower activity decays away sooner.
A and B have the same half-life, because they contain the same number of undecayed nuclei.