A neutron of kinetic energy 65 eV collides inelastically with a singly ionised helium atom at rest. It is scattered at an angle `90^@` with respect to original direction. If the energy of scattered neutron is 6.36 eV, find the frequency of emitted radiation from the helium atom after suffering collision.

Explanation

To solve the problem step by step, we will analyze the collision between a neutron and a singly ionized helium atom, applying the principles of conservation of momentum and energy.

### Step 1: Understand the Initial Conditions
- A neutron with kinetic energy \( K_n = 65 \, \text{eV} \) collides with a singly ionized helium atom (He\(^+\)) at rest.
- The neutron is scattered at an angle of \( 90^\circ \) after the collision, and its final kinetic energy is \( K_n' = 6.36 \, \text{eV} \).

### Step 2: Calculate the Initial and Final Energies
- The initial kinetic energy of the neutron is given as \( K_n = 65 \, \text{eV} \).
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