perrymichaela said: “It was launched from only 7 miles? That may seem like a lot of distance, but I wonder how high the radiation dose was that the artillery crew received. I know I would not want to be within 7 miles of a nuclear explosion.”

There was ONE single person other than the aircrew of the Enola Gay that definitely saw and survived both explosions- he was farming 5 miles from the epicentre at Hiroshima when that was dropped, so decided to flee to his mothers – at Nagasaki. Three days later the train he was on was seven miles from Nagasaki when the send bonb went off.

One could feel justfied in feeling a little paranoid after that…..

I got curious and googled: http://www.imdb.com/title/tt0083590/

Disturbing!

Second is thermal/visible radiation, this is the most immediate danger of a nuclear weapon (other than the blast). A vast amount of energy is converted into visible and thermal energy and will cause the vast majority of initial deaths and injuries due to burning etc, and the flash itself can cause blindness miles and miles away depending on yield.

Finally there is what you are referring to, prompt nuclear radiation, the “flash” of radiation that pulses along with thermal/visible energy at the moment of detonation. This is typically non consequential depending on the weapons yield. Why? Because for anything but the smallest of nuclear weapons (like the davy crockett etc) anyone within range of dangerous prompt nuclear radiation is likely already dead due to the thermal pulse or the nuclear blast. Radiation sickness is the least of your concerns when you are charred to a toasty crisp or blown several miles downrange of the detonation. The radiation flux is absorbed very readily by air, the thermal pulse and shockwave have greater range.

However the ratio between the range/danger of thermal pulse/shock wave and prompt nuclear radiation is related to the yield. For very small weapons like the davy crockett or the nuclear demolition munition the blast is small enough that the prompt radiation is actually the greatest danger. However these were TINY nukes compared to even a typical small tactical weapon.

In the case of this bomb, the prompt nuclear radiation at seven miles would have been a non issue, especially considering personal would be behind shelter and thus shielded from the pulse.

The real reason the precursor was caused was because of the low burst height. The explosion instantly heated up the air and ground in the vicinity, causing the ground to popcorn and creating a superheated ground-air layer. This heated ground air layer was more conductive to shockwave propagation and allowed the reflected wave to surpass the incident wave instead of creating a mach stem like normal. The results were a less defined overpressure, but a much stronger dynamic pressure.

They don’t explain the whole thing in Trinity and Beyond. You have to look at the DOE film Operation Upshot-Knothole, as it provides a much more in depth explanation.