Dissemination means to get something delivered in mass to people or places. Like Mikkel said, it can mean to spread information. Dispersion or to disperse means to get something away or diluted etc. "The police came and the crowd dispersed." So this means that the crowd went in all directions and ceased being a crowd. The difference here is that with dissemination the target is many different people or locations while with dispersion we don't necessarily care where everything/everyone goes we just want them to be gone/spread out. You could also say that when spreading a substance we want it to disperse "Spread the fertilizer on your entire lawn at the required rate of dispersion." Meaning we want to evenly cover the lawn in fertilizer. -Eric

“dissemination” mostly has to do with spreading information. “dispersion” has several meanings. You can look them up here: https://en.oxforddictionaries.com/definition/dispersion