$\beta$-rays emitted by a radioactive material are

In the uranium radioactive series,the initial nucleus is ${ }_{92}^{238} U$ and the final nucleus is ${ }_{82}^{206} Pb$. When the uranium nucleus decays into lead,the number of $\alpha$-particles and $\beta$-particles emitted are

The particles emitted in the decay of $ { }_{92}^{238} U $ to $ { }_{92}^{234} U $ are:

$\gamma$-decay occurs when

During a $\beta^{-}$-decay,

Some radioactive nucleus may emit