Question

On the average, neutrons lose half their energy per collision with quasi-free protons. Nearly how many collisions, on the average, are required to reduce a 2 MeV neutron to a thermal energy of 0.04 eV –

• A. 12
• B. 26
• C. 15
• D. 32

Answer 1

Answer: (B)

26

Answer 2

$\frac { K _ { f } } { K _ { i } }$ = $\frac { 0.04 } { 2 \times 10 ^ { 6 } }$ = (0.5)^N

(0.5)^N = 2 × 10^–8

N ln $\frac { 1 } { 2 }$= ln 2 – 8 ln 10

N 26