A neutron collides with a stationary He + atom in its ground state, What should be minimum value of energy of neutron (in eV), so that all type of collisions (Elastic, inelastic and perfectly inelastic) can take place ? (Consider mass of He + atom is 4 times mass of neutron).

Answer

`60.45`

Explanation

For all collision ot take place electron has to excite to `n=3.`
`underset("EnergE")underset(to) (m) underset(**)(4m) underset(toV )underset(m+4m)("Perfectly inelstic collision")`
`m u + 0= 5mV`
`Loss =1/2 m u ^(2) -1/2 5m xx((4)/(5)) ^(2) =(4E)/(5)`
`(4E)/(5) =12.09 xx(2) ^(2) eV`
`implies E =60 . 45 eV`