A monoenergetic beam a alpha particle , each of them having kinetic E is incident on a sample of singly ionised Helium gas in ground state . The Helium gas in ground state. The Helium sample may start emitting radiation Since the Kinetic energy of incident alpha particle in sufficiently high . A part of this radiation (if any) is allowed to pass through atomic Hydrogen sample in ground state. A detector placed near the hydrogen records both radiation and electrons. Assume all `He^(+)` ions to be initially at rest.
If no electrons are interpected by the detector the energy of photons detected by it can be -

Options

A. `10.2eV`
B. `40.8eV`
C. `12.1eV`
D. none of these

Answer

D

Explanation

Electrons will not be detected if and only if there is no excitation of the `He^(+)` Sample . Thus no photons are emitted by `He^(+)` and hence by `h` sample , and hence none are detected by the detected by the detector.