YO, Thanks for the IM, but...........
What are the summations for your answer? This equation is going to give what dose, at what distance, based on what parameters, restrictions and assumptions? (Assumptions are Allowed, It's your Time to Shine)
Is this equation applicable to Alpha, Beta, Gamma and Neutron Emitters?
RG.. 
You asked for dose rate in a solution. This equation is for all of the above. The indication is that the dose rate is about one-half the calculated value at the surface of the solution.
I am not sure of what degree of accuracy you are looking for but the formula should help. The calculation can be found in
THE HEALTH PHYSICS AND RADIOLOGICAL HEALTH HAND BOOK By Bernard Shleian (sp), Lester A. Slaback and ............ Maybe this will help with your search.
As far a the information about MCNP...........MCNP and Scale are the languages used to develop input models in the xyz quadrants. Most Engineers use one or the other, rarely both. I had to learn both. The input is then ran against Keno, Monte Carlo, Bonami, Fortran and etc. for an out put. An input for Nuclear Criticality Safety will give you a k
eff. based on the chemical composition of the solution, the type of container, and other parameters. Radiation Transport will give you an energy output based on element and type of shielding. These are compared to the Benchmarks to verify adequacy. The may be beyond the scope of your search.
if this will help I have it as a pdf........ it is very detailed
Radioprotection 2002
Vol. 37, no 2, pages 149 à 160
DOI: IO.105l/radiopro:2002004
Article
Determination of the gamma-ray effective
dose from different cylindrical radioactive
solution sources in a biological tissue by
using Monte Carlo calculations
M.A. MISDAQ’, A. MERZOUKI’
(Munuscript recriivrl27 March 2001, Accrpted 9 Februugl2002)
A new method was developed based on calculating the ahsorption coefficients, selfabsorption
coefficients and transmission coefîlcients of the gamma-photons emitted
by different radioisotopes for evaluating gamma dose equivalent rates, at 1 meter
from varions cylindrical radioactive solution sources utilized in medicine, in a
biological tissue. Resnlts obtained were compared with data given in literatnre. The
influence of the radioisotope half-life and gamma-photon energy and number of
photons per disintegration on the gamma dose equivalent rate, effective dose and
threshold initial activity of the considered solution sources was studied.
I use to do put a lot of effort into knowing as much as possible about all of this stuff, but I don't any more. I find that the more I learn or know, the more difficult life is for me in the work place. You know......as a female, it's OK to be attractive or smart but not both.
I just wanted to let you know that the equations are out there. It depends on where you look and how precise you need the answer to be!
Good Luck!!!
YO!