I really hope this is the right subreddit to ask about this. I certainly don't want to waste space.
I'm currently re-reading Kai Bird & Martin Sherwin's American Prometheus: The Life of J. Robert Oppenheimer, and same as the first time I read it, I'm intrigued by the idea of the Interim Committee. For some reason it just never occurred to me that people actually had to sit down and make the decision of when, where, and if to drop the bomb.
Through Google, I've been able to find some good sources, such as the Truman Library page about the decision, which includes notes/summaries of the meetings. I've also found excerpts from Stimson's own diaries, which give a fairly good summary of Stimson's activity at this time. Are there any other, more complete summations of what happened?
I'm interested in the entire history of the Committee, but especially the (seemingly) two days where the Scientific Panel was invited from Los Alamos to share their views. This is where I'm having some trouble. As far as I can tell, Oppenheimer himself didn't keep a diary, or at least it hasn't been published. Are there any sources that show the Scientific Panel's discussions before attending the Committee meetings, any disagreements they may have had among themselves, and how those disagreements were or were not sorted before presenting their views to Stimson & co? What I'd really like is to get my hands on some personal diaries of those involved, if such a thing exists, to try and see what was going on in their heads at the time, as well as anything that can highlight any philosophical differences between the Scientific Panel and the military brass.
Thanks for taking the time to consider my request and if this is the wrong place to just straight-up ask for resources I'd like to apologise and ask if you could point me in the right direction.
There are only a handful of sources that I know of which give us insight into the Scientific Panel meeting. You have already found the main ones, which is to say, the meeting notes themselves and the Stimson diary.
One is Arthur Compton's recollections in Atomic Quest. They were written a decade after the fact so they need to be viewed with some care, and they are, even at best, only Compton's views of things.
Another is Oppenheimer's discussions of these things in his security hearing in 1954. Again, about a decade after the fact, and notably a very different context for Oppenheimer to be talking about these things. But there are pertinent discussions in there about this topic. Notably Oppenheimer admits that he underestimated the amount of casualties dramatically (he thought it would be more like 20,000 rather than 60,000) and implies that this mattered for making his decision.
The other one — which to my mind has been not given enough attention — is a curious exchange between Ernest Lawrence and Karl Darrow in early August 1945. On August 9th, Darrow wrote Lawrence with a recollection of what Lawrence had apparently told him about the panel meeting. It is quite detailed. On August 17th, Lawrence wrote back and told Darrow he had misunderstood and that the meeting wasn't much of anything. The difference between these two more-or-less contemporaneous accounts is rather striking. I am inclined to suspect that what Darrow says Lawrence told him was true, but that after the bomb was now a "success" (in that Japan had indicated a willingness to surrender and this was being attributed to the bombing), Lawrence was revising his own memory or narrative of the event. (Many such "revisions" like this happened in the days between the use of the bomb and the confirmation of its "success," as Michael Gordin has written about in Five Days in August.) I have written about this here, and posted the documents in question (poor quality that they are). It is one of the only accounts that gives any credence to the idea that there was a serious discussion about this or any serious disagreement on the panel, and is the closest account given to the event itself. But of course it is tricky in that it is a written memory of someone who wasn't there (Darrow giving a second-hand account back to Lawrence) and the principle source of this account (Lawrence) appears to have repudiated it. So it's tricky.
I have never seen anything that gave Fermi's personal side of the story, which would be quite interesting, especially given his later, very strong moralist stand on the hydrogen bomb.
The Interim Committee, as an aside, was not really concerned about when and where to drop the bomb. They were more concerned about what to do after you drop the bomb. Hence their name: they were to take up the question of the Interim, the period between the bomb being used and the bomb being under some kind of formal domestic control (e.g. the Atomic Energy Commission). So most of their activities were things about planning for the future, or drafting press releases, or making plans for legislation. This particular question of the Scientific Panel is the only major one that was decided about the immediate use of the bomb, and was posed as a sort of policy question that would reflect on the Interim problem (e.g. if they use a bomb without warning, what happens then?). The committee that spent the most time talking about the logistics of dropping the bomb was the Target Committee. The National Security Archive has a very nicely curated set of documents relating to the use of the atomic bombs, including the notes of the three Target Committee meetings.