De Broglie used Einstein’s special theory of relatively together with Plank’s quantum theory to establish the wave property of particles. He gave fundamental relationship λhp; where lambda and p are wavelength and momentum respectively and h is Plank’s constant. A de-Broglie wave associated with an electron can form a standing wave between the atoms arranged in a one dimensional array with node at each of the atomic sites. A standing wave is formed when the distance between the atoms of any array is d=3A∘. A similar standing wave is again formed if d=3.5A:∘ but not for any intermediate value of d. For thermal neutron at ordinary temperature, energy is given by relation E=kT, where K is Boltzmann constant mass of Neutron is 1.67×10–23g. The least value of d for which standing wave can be formed is