For the given reaction, the particle $X$ is $_6C^{11} \to _5B^{11} + \beta^+ + X$.

Give a brief explanation about radioactivity.

In the following nuclear reaction,$x$ stands for: $n \rightarrow p + e^{-} + x$

$U^{238}$ decays into $Th^{234}$ by the emission of an $\alpha$-particle. There follows a chain of further radioactive decays,either by $\alpha$-decay or by $\beta$-decay. Eventually,a stable nuclide is reached,and after that,no further radioactive decay is possible. Which of the following stable nuclides is the end product of the $U^{238}$ radioactive decay chain?

$A$ nucleus with mass number $220$ initially at rest emits an $\alpha$-particle. If the $Q$ value of the reaction is $5.5\, MeV$,calculate the kinetic energy of the $\alpha$-particle in $MeV$.

What happens to the mass number and atomic number of an element when it emits $\gamma$-radiation?