1. Matter is made up of tiny indestructible units called  83artificial radioactivityatomscathodeJames Chadwicknatural radioactivityNucleusparentradioactiveRadioactivity.
2. J J Thomson discovered  83artificial radioactivityatomscathodeJames Chadwicknatural radioactivityNucleusparentradioactiveRadioactivity rays, known as electrons.
3.  83artificial radioactivityatomscathodeJames Chadwicknatural radioactivityNucleusparentradioactiveRadioactivity discovered the chargeless particles called neutrons.
4. Ernest Rutherford explained that the mass of an atom is concentrated in its central part called  83artificial radioactivityatomscathodeJames Chadwicknatural radioactivityNucleusparentradioactiveRadioactivity.
5.  83artificial radioactivityatomscathodeJames Chadwicknatural radioactivityNucleusparentradioactiveRadioactivity is a phenomenon of spontaneous disintegration of the nucleus of an atom with the emission of one or more penetrating radiations.
6. The elements, which undergo radioactivity are called ' 83artificial radioactivityatomscathodeJames Chadwicknatural radioactivityNucleusparentradioactiveRadioactivity elements'.
7. The phenomenon of spontaneous emission of radiation from certain elements on their own is called  83artificial radioactivityatomscathodeJames Chadwicknatural radioactivityNucleusparentradioactiveRadioactivity.
8. The elements whose atomic number is more than  83artificial radioactivityatomscathodeJames Chadwicknatural radioactivityNucleusparentradioactiveRadioactivity undergo spontaneous radioactivity.
9. The phenomenon by which even light elements are made radioactive, by artificial or induced methods, is called  83artificial radioactivityatomscathodeJames Chadwicknatural radioactivityNucleusparentradioactiveRadioactivity.
10. During a disintegration, the nucleus which undergoes disintegration is called  83artificial radioactivityatomscathodeJames Chadwicknatural radioactivityNucleusparentradioactiveRadioactivity nucleus.