Thanks Ken, that is nearer to the middle of the range, but it concerns me that the results I have seen are spread over 3 orders of magnitude. I can see that random walks is tricky with short path lengths. That is why I also phrased the question in terms of the radiation content of the Sun and the rate at which it comes out. It is in fact the radiation content that I am actually most interested in. I would have thought that it should be known quite accurately from the temperature and density profile of the Sun at various depths.