% impact_parameter: Impact parameter
%
% Lambda=impact_parameter(Z1,Z2,T,n_e);
%
% ARGUMENTS
%  Z1	Charge on first ion.
%  Z2	Charge on second ion.
%  T	Temperature of the plasma [K]
%  n_e	Electron density [cm^-3]
%
% RETURNS
%  The impact parameter, Lambda, which is the Debye radius divided by the
%  true impact parameter, b (the ratio of the largest to smallest impact
%  parameters).
%  This is for an ionized gas.
%
% SEE ALSO
%  drag_coef, drag_force, dynamic_viscosity, Reynolds_number

% AUTHOR: Eric Tittley
%  From K. R. Lang, 'Astrophysical Formulae 2nd edition', Springer-Verlag 1980
%
% HISTORY
%  00 07 31 First version
%  06 03 01 Standardized header comments.

function Lambda=impact_parameter(Z1,Z2,T,n_e)

e=4.8032068e-10; % esu
k=1.380658e-16;	 % erg/K

Lambda =  3/(2*Z1*Z2*e^3) * (k*T)^(3/2) / (pi * n_e)^0.5 ;