Radioactive decay is a spontaneous process. State what the term spontaneous means in this context.
Two radioactive isotopes X and Y each decay to produce a stable isotope. One sample initially contains only atoms of isotope X. At this time, its activity is $4A$. A second sample initially contains only atoms of Y. At this time, its activity is $A$. Fig. 10.1 shows how the activity of each sample varies with time $t$ for $t = 0$ to $t = 6T$.
Complete Table 10.1 by giving expressions, in terms of either or both of $A$ and $T$, for the quantities listed for each sample.
Determine, in terms of $T$, the time when the activities of the two samples are equal.
A radiation detector is placed close to one of the samples in (b). Explain why the count rate registered by the detector is lower than the activity of the sample.