Many unstable nuclie can decay spontaneously to a nucleus of lower mass but differnet combination of nucleons. The process of spontaneous emission of radiation is called radioactivity substance.
Radioactive decay is a statistical process. Radiaactivity is independent of all external conditions. The number of decays per unit time or decay rate is called activity. Activity exponentially decrease with time. Mean lifetime is always greater than half-life time.
Choose the correct statemnet about radioactivity:
A. Radioactivity is a statistical process
B. Radioactivity is independent of high tempreture and high pressure
C. When a nucleus undergoes `alpha`- or `beta` -decay, its atomic number changes
D. All of these
