The best source for information on the Goiania Accident is the International Atomic Energy Agency’s report following the tragedy. At 157 pages, it covers the Goiania accident from start to finish in extensive detail.
A shorter but still well-written summation of the disaster is this article from Veneer magazine.
There are several videos on YouTube available to watch regarding the disaster, but for the most part they are in Portuguese. A film about the disaster is available but there do not appear to be subtitles in other languages on the copies I found. There are also multiple news reports and short documentary films on the subject also on YouTube, but the majority of these are also in Portuguese and lack subtitles.
However, as I mentioned, the IAEA report is a very extensive read and an excellent summary of the events in Goiania.