def Nasv(macs,T):
Na = avogadro_constant<EOL>k  = boltzmann_constant<EOL>vtherm=(<NUM_LIT>*k*T/mass_H_atom)**<NUM_LIT:0.5><EOL>s  = macs*<NUM_LIT><EOL>Nasv = s*vtherm*Na<EOL>return Nasv<EOL>
Returns
-------
Na*<sigma v>
    for MACS [mb] at T [K].