The number of beta particles emitted by a radioactive substance is twice the number of alpha particles emitted by it. The resulting daughter is an

A radioactive sample is $\alpha$-emitter with half life $138.6$ days is observed by a student to have $2000$ disintegration/sec. The number of radioactive nuclei for given activity are

The phenomenon of radioactivity is

The graph in figure shows how the count-rate $A$ of a radioactive source as measured by a Geiger counter varies with time $t.$ The relationship between $A$ and $t$ is : $($ Assume $ln\,\, 12 = 2.6)$

If half life of an element is $69.3$ hours then how much of its percent will decay in $10^{\text {th }}$ to $11^{\text {th }}$ hours. Initial activity $=50\, \mu Ci$

Consider two nuclei of the same radioactive nuclide. One of the nuclei was created in a supernova explosion $5$ billion years ago. The other was created in a nuclear reactor $5$ minutes ago. The probability of decay during the next time is