variations due to energy variation just after the collision and δ L3 is the path variation because of variation of energy loss along the outward path. Solving equations 5 and 6 by considering δ x = 0 for the derivative dL1/dE2 with L3=R(φα)L1,yields dL1/dE2 = 1/{Sr(E2)/Sr[K’E0(x)]}{[R(φ,α) Sr[K’E0(x)+K’S[E0(x)]} -----------Equation 7 In elastic spectrometry, the term[S] is called as energy loss factor [S] = K’S(E(x))/Cos θ1 + Sr(K’E(x))2Cos θ2 -----------------Equation 8 finally stopping cross section is defined by ε(E) ≡S(E)/N where N is atomic density of the target material. Stopping cross section factor [ε] = ((K^'ε(E(x) ))/cos θ1 )+(εr(K^' E(x) )/cosθ3)--------Equation 9 Depth Resolution An important parameter that characterizes recoil spectrometer is depth resolution. It is defined as the ability of an analytical technique to detect a variation in atomic distribution as a function of depth. The capability to separate in energy in the recoil system arising from small depth intervals. The expression for depth resolution is given as δRx = δET/[{Sr(E2)/SrK'E0(x)}][R(φ,α)SrK'E0(x)+K'SE0(x)]-----------Equation 10 Where δET is the total energy resolution of the system, and the huge expression in the denominator is the sum of the path integrals of initial, scattered and recoil ion beams. Practical importance Of Depth Resolution The concept of depth resolution represents the ability of Recoil spectrometry to separate the energies of scattered particles that occurred at slightly different depths δRx is interpreted as an absolute limit for determining concentration profile. From this point of view concentration profile separated by a depth interval of the order of magnitude of δRx would be undistinguishable in the spectrum, and obviously it is impossible to gain accuracy better than δRx to assign depth profile. In particular the fact that the signals corresponding to features of the concentration profile separated by less than δRx strongly overlap in the spectrum. A finite final depth resolution resulting from both theoretical and experimental limitations has deviation from exact result when consider an ideal situation. Final resolution is not coincide with theoretical evaluation such as the classical depth resolution δRx precisely because it results from three terms that escape from theoretical estimations: Incertitude due to approximations of energy spread among molecules. Inconsistency in data on stopping powers and cross section values Statistical fluctuations of recoil yield (counting noise) Influence of Energy Broadening on a Recoil spectrum Straggling: Energy loss of particle in a dense medium is statistical in nature due to a large number of individual collisions