The element used for dating the ancient remains is

Which has the least penetrating power?

The carbon dating is based on

Radioactive carbon dating was discovered by

The number of $\alpha$ and $\beta$-particles emitted in the nuclear reaction $_{92}U^{238} \to _{90}Th^{234} \to _{91}Pa^{234}$ are respectively:

The number of $\beta$-particles emitted in the radioactive decay process $_{92}U^{238} \to _{82}Pb^{206} + x(_{2}He^{4}) + y(_{-1}e^{0})$ is: