The half-life of a radioactive nucleus is $5$ years. The fraction of the original sample that would decay in $15$ years is

What is the mass of $1 \, \text{curie}$ of $U^{234}$?

In a radioactive disintegration,the ratio of the initial number of atoms to the number of atoms present at time $t = \frac{1}{2 \lambda}$ is $[\lambda = \text{decay constant}]$

Two species of radioactive atoms are mixed in equal number. The disintegration constant of the first species is $\lambda$ and of the second is $\lambda / 3$. After a long time,the mixture will behave as a species with a mean life of approximately:

Two radioactive materials $R_1$ and $R_2$ have decay constants $6 \lambda$ and $\lambda$, respectively. The half-life of $R_2$ is $1.4 \times 10^{17} \,s$. Initially, they contain the same number of nuclei. The time at which the ratio of the remaining nuclei of $R_2$ to that of $R_1$ will be $e$ is (Let $\ln 2 = 0.7$):

In a sample of radioactive material,what percentage of the initial number of active nuclei will decay during one mean life?