I don't know anything about this specific test, but the military goes to extraordinary lengths to train realistically for unusual and new war scenarios. (E.g., most US soldiers have been preparing for fighting in the presence of chemical weapons with gas masks, etc., for decades even though, to my knowledge, there's never been a large-scale usage since WW2.) But in this case, I'd wager they're taking scientific data for understanding the performance of the bomb; terrestrial bomb tests were huge exercises in data taking, and I don't know why airbursts would be different.

The link between radiation and cancer was established in the '20s, and certainly well-known (if poorly understood) by the time atomic weapons were developed. For instance, Muller got the Nobel prize for this work in 1947.

https://en.wikipedia.org/wiki/Radiation-induced_cancer#Histo...

Certainly, safety rules weren't as conservative and stringent as they are today, but it's silly to think US soldiers were routinely and openly used as guinea pigs.

Probably gamma ray spectroscopy which measures the energy of gamma rays in the cloud. When radioactive particles decay, they emit gamma rays at very specific energies so it would give us an understanding of the yield of the bomb and other important things for designing better weapons.

They were taking samples of the air to obtain fission products and other clues to the performance of the weapon.

This is pretty important since you can both evaluate your weapon, and also to calibrate your instruments to use when collecting downwind of Soviet tests. Thus you can evaluate their weapons too.