Start by setting "scattering_region_initial_scaled_spin" to zero for all atoms, then your code will go in and change some atoms to another value. So, something like
scattering_region_initial_scaled_spin = [0,]*len(scattering_elements)
for index in range(len(scattering_elements)):
if (scattering_elements[index]==Carbon) :
if (scattering_coordinates[index][2]> 17):
scattering_region_initial_scaled_spin[index]=1
elif (scattering_coordinates[index][2]< 13):
scattering_region_initial_scaled_spin[index]=1
(You don't need the "else" part any more now :) )