An assembly for a charged particle detection device of high detection efficiency is described. The assembly comprising a metal grid for applying attractive potential to lure charged particles; a scintillator disc to absorb the energy from impinging charged particle and reemit the energy in form of light or photons; a light guide to transmit light or photons; and a photomultiplier tube (PMT) cohere with the end of light guide to receive light or photons from light guide and convert it into current signal. A light guide with a bullet-head-shaped front portion ensures total reflection of light propagating within the light guide. A frustum-cone-shaped scintillator disc releases the light that originally trapped in the scintillator disc due to the shape of scintillator.