Activities of three radioactive substances and are represented by the curves and , in the figure. Then their half-lives are in the ratio :
A beam of electrons of energy scatters from a target having atomic spacing of . The first maximum intensity occurs at . Then (in eV) is _______.
(Plank constant
electron mass )
In the radioactive material fraction of active material remaining after time t is . The fraction that was remaining after t/2 is