Using the average energy of the beta sources instead of their continuous beta spectrum can affect the accuracy of the
simulation results. But in the present work, more than 30 references are mentioned in which the average energy or the maximum
energy of the beta source is used instead of its continuous beta spectrum. Therefore, we calculated the amount of difference created
in Monte Carlo simulation results when the average energy of the beta source is used instead of its continuous beta spectrum. In this
regard, the continuous beta spectrum of some widely used sources such as 63 Ni, 90 Sr, 35 S, 14 C and 147 Pm were calculated using
the Golden Fermi law and computer code in Fortran language. Then, the amount of energy deposition in the soft tissue (nuclear
medicine) and semiconductor (nuclear battery) were calculated by MCNP code in two state. The first state is to use the average
energy of the beta source in the simulations and the second state is to use the continuous beta spectrum of the beta source in the
simulations. Then the difference between the two state was calculated. Studies show that using the average energy of the 63 Ni, 90 Sr,
35 S, 14 C and 147 Pm beta sources instead of their continuous beta spectrum causes 63.28%, 27.20%, 54.91%, 53.28% and 54.35%
difference in the amount of energy deposition in the soft tissue, respectively. Also, using the average energy of the 63 Ni, 90 Sr, 35 S, 14 C
and 147 Pm beta sources instead of their continuous beta spectrum causes 63.16%, 26.77%, 55.53%, 53.87% and 54.37% difference
in the amount of energy deposition in the semiconductor (Si), respectively.