The substance used in cancer therapy is

Which of the following is used in dating archaeological findings,or in a method of absolute dating of fossils,a radioactive element is used. It is:

$\gamma$ rays are

Which of the following statements is not true for radioactive decay?

The disintegration of an isotope of sodium,$_{11}Na^{24} \to _{12}Mg^{24} + _{-1}e^0$,shown is due to

The radionuclide $_{90}^{234}Th$ undergoes two successive $\beta$-decays followed by one $\alpha$-decay. The atomic number and the mass number respectively of the resulting radionuclide are