
My observations during the explosion at Trinity (1945) - luisb
http://fermatslibrary.com/s/my-observations-during-the-explosion-at-trinity
======
antognini
In one of my interstellar medium classes I remember learning about the
physicist Geoffrey Taylor's estimate of the yield of the first atomic bomb. At
the time, the energy of the atomic bomb was classified information, but
photographs of the explosion like this one [1] had been published in
newspapers and magazines. Crucially, this photograph was labelled with both
the time after the explosion, and a scale bar. With just this information
Taylor found it was fairly simple to calculate the energy of the explosion. He
ended up publishing two papers about it [2] [3]. In astrophysics, his
calculations are now used when modeling the effect of a supernova on the
surrounding interstellar medium.

[1]:
[https://upload.wikimedia.org/wikipedia/commons/thumb/7/77/Tr...](https://upload.wikimedia.org/wikipedia/commons/thumb/7/77/Trinity_Test_Fireball_25ms.jpg/250px-
Trinity_Test_Fireball_25ms.jpg)

[2]:
[http://rspa.royalsocietypublishing.org/content/201/1065/159](http://rspa.royalsocietypublishing.org/content/201/1065/159)

[3]:
[http://rspa.royalsocietypublishing.org/content/201/1065/175](http://rspa.royalsocietypublishing.org/content/201/1065/175)

~~~
semi-extrinsic
Those WW2 era photos are interesting, and I like the story about Taylor's
analysis, but what really spooks me from early atomic bomb tests are the
Rapatronic photos by Edgerton.

He took high-speed photography to the ultimate limits, at exposure times of
10^-8 seconds, and the pictures are absolutely eerie looking. Some are like
gaping skulls of pure energy, like this one:

[https://upload.wikimedia.org/wikipedia/commons/e/e9/Tumbler_...](https://upload.wikimedia.org/wikipedia/commons/e/e9/Tumbler_Snapper_rope_tricks.jpg)

[http://petapixel.com/2014/03/05/rapatronic-camera-atomic-
bla...](http://petapixel.com/2014/03/05/rapatronic-camera-atomic-blast-
captured-11000000000th-second/)

~~~
SamReidHughes
From the article: "This is 1/100,000,000th of a second after the first photo."

A 100 millionth of a light-second is about 10 feet, the tower was 100 feet. So
that couldn't have been the time between exposures, and they used multiple
cameras anyway.

The Wikipedia article
[https://en.wikipedia.org/wiki/Rapatronic_camera](https://en.wikipedia.org/wiki/Rapatronic_camera)
says the exposure times were several microseconds.

~~~
lobster_johnson
I don't think that's the first image in the sequence, just the most famous
one. They took a lot of images in sequence. Here they are edited together into
a sequence (several series, presumably from multiple tests, unfortunately
looks a bit incomplete): [https://m.youtube.com/watch?v=KQp1ox-
SdRI](https://m.youtube.com/watch?v=KQp1ox-SdRI)

------
pjmorris
Obligatory reference to 'The Making of the Atomic Bomb', Rhodes. Terrific book
on the people, physics, and politics behind 'The Bomb' and its use.

Any recommendations on biographies of Fermi?

~~~
rubidium
The one by his wife Laura is very interesting: "Atoms in the Family: My Life
with Enrico Fermi"

------
Kenji
I just love how practically minded these men were. Whatever they had available
to them, they made it work somehow. If you want to read another account of the
Manhattan Project / first nukes, I highly recommend the book "Surely you're
joking, Mr. Feynman!" which contains a wealth of interesting and funny (and
sometimes touching) trivia about the life of Feynman and how things went at
Los Alamos.

~~~
de_Selby
Fermi was famous for this kind of thing, he could calculate the answer to a
problem where it seemed like there wasn't enough information as if by magic.

~~~
dekhn
Not calculate, estimate. You come up with a simple mathematical model- often
just adding or multipling a few numbers together. It's not magic, he just had
a good sense for including all the 0th and 1st order terms.

------
meerita
Imagine to witness a Tsar Bomba
[https://en.wikipedia.org/wiki/Tsar_Bomba](https://en.wikipedia.org/wiki/Tsar_Bomba)
64km tall mushroom head. About 8 kilometres (5.0 mi) in diameter, was
prevented from touching the ground by the shock wave, but nearly reached the
10.5-kilometre (6.5 mi) altitude of the deploying Tu-95 bomber

~~~
phatfish
Wow, and the biggest threat we have today is immigration of (mostly) peaceful
people. How quickly we forget.

------
chiefofgxbxl
Due to the blast in the desert, quartz and other minerals in the sand were
melted to form Trinitite, a green glass. Would be interesting to hold this
piece of history in a museum (according to Wikipedia, it's safe to handle).

[https://en.wikipedia.org/wiki/Trinitite](https://en.wikipedia.org/wiki/Trinitite)

~~~
mgarfias
It was all bulldozed into a small "building" on the site as it was too hot to
leave around.

There were lots of signs warning about it on the bunker when I visited in
2003/4.

------
maverick_iceman
Great resource on Fermi problems and related topics.[1]

[1][https://mitpress.mit.edu/sites/default/files/titles/free_dow...](https://mitpress.mit.edu/sites/default/files/titles/free_download/9780262526548_Art_of_Insight.pdf)

------
slackpad
Trinity site is an interesting place to visit - it's open to visitors twice a
year.
[http://www.wsmr.army.mil/PAO/Trinity/Pages/Home.aspx](http://www.wsmr.army.mil/PAO/Trinity/Pages/Home.aspx)

~~~
mgarfias
What I found most interesting about it, was the lack of interesting there. It
could very easily be missed.

------
tehchromic
Once had a job working in the basement of a building in Los Alamos NM
operating a digital scanner to digitize various documents from the lab
archives. I encountered a few boxes of photos of various atomic tests -
beautiful and spooky.

------
coldcode
Seeing a black and white description of an explosion estimated at 10,000 tons
of TNT is still mind-boggling. Even harder to believe that within a decade or
so there were explosions of 100,000,000 tons of TNT. E=MC2 gets big in a
hurry.

~~~
Retric
No single nuclear weapon detonation ever hit 100,000,000 tons of TNT. There
are designs for weapons in that range, and single example at 1/2 that power.
However, such designs are impractical as using the same material to carpet
bomb an area is more effective.

PS: Before the H-Bomb nuclear weapons where not actually cost effective per
ton. Their 'advantage' over high explosives was portability and fear.

~~~
astrodust
The Tsar Bomba was supposed to be in this range, but the allegedly the
designer of the weapon started to fear his own creation and decided to tamper
with it and tone down the yield.

[https://en.wikipedia.org/wiki/Tsar_Bomba](https://en.wikipedia.org/wiki/Tsar_Bomba)

~~~
krylon
I kind of remember reading that somebody involved in the creation / testing of
that bomb made a rough estimate of the area covered by the fallout and decided
to ditch the U-238 damper on the second (third?) stage.

Also, getting the plane dropping the bomb to a safe distance before the
explosion was kind of an act as it was, if the bomb had gone off at twice the
yield, it probably would have killed the crew.

(All this is from rather fuzzy memory, though! If somebody has less fuzzy
information, I'd be happy to stand corrected!)

~~~
arethuza
From my own fuzzy memories that's correct - a full 100MT device would have
been a pretty awful weapon, I've seen it described as something that could
have utterly destroyed Belgium but that would have killed people in Russia
with fallout.

I seem to recall that the Tsar Bomb had multiple tertiary stages?

Nitpick: it's tamper not damper.

Also without a fissioning tamper round it's secondary and tertiary stages the
Tsar Bomb actually was a "fusion bomb" in that a very high proportion of its
yield came from fusion. In most H-bomb designs most of the yield comes from
the fissioning of the tamper round the secondary.

~~~
astrodust
With bombs of this type you can chain things on several times and really amp
up the yield. The theoretical limit, if there is one, is absolutely nuts, like
500MT or more.

The problem is that beyond a certain yield most of the explosive force punches
up through the atmosphere and is wasted. Apart from shock and awe, not sure
what the utility of something that big would ever be.

Additionally since a spherical explosion of double the diameter takes eight
times as much energy to create, you quickly run into diminishing returns. Lots
of smaller bombs is more effective, hence MIRVs:
[https://en.wikipedia.org/wiki/Multiple_independently_targeta...](https://en.wikipedia.org/wiki/Multiple_independently_targetable_reentry_vehicle)

Nuclear weapons are so awesome and so utterly insane at the same time.

------
hwc
We did this calculation in a course I took in college. I've completely
forgotten how it worked.

~~~
Declanomous
Assuming the paper shifted perfectly laterally, I assume you'd just be
measuring the difference in the volume of half a sphere ten miles in radius,
and a sphere ten miles and 2.5 meters in radius. I think you could use the
ideal gas law at that point to figure out the energy.

I'm just guessing though.

~~~
iaw
I think you're right. Ideal gas law wouldn't apply to the plasma sphere but
knowing shockwave strength at some distance you can figure out how much energy
was transferred to the atmosphere.

~~~
adrianratnapala
I agree the calculation probably worked by measuring the kinectic energy of
that half-shell by measuring its velocity*thickness directly using pieces of
paper.

But I wouldn't count the ideal gas law out (see
[http://physics.stackexchange.com/questions/43696/will-
ideal-...](http://physics.stackexchange.com/questions/43696/will-ideal-gas-
law-apply-to-plasma)). My guess is that the huge temperatures involved will
work in favour of an ideal-gas approximation.

Perhaps the more important thing is that things are happening on very short
time-scales, far enough from equilibrium and temperature might not even be
well defined.

~~~
Declanomous
That probably would work better. I tried doing the math and ended up with some
really weird answers. Definitely not 10 kt.

------
spirographer
Is there any way to determine exactly when this document was written? I've
read accounts that indicate that it took some time (weeks, months, years?)
before the metaphor of mushroom shaped cloud entered into the vocabulary used
by witnesses of atomic weapons. Fermi's account would disprove that assertion
if it were written immediately after the test at Trinity.

------
craftandhustle
While reading this, I started wondering if there are any other 3rd party
(civilian?) accounts of the event or if the geography / remoteness made it
'invisible' to everyone else? I have a funny visual in my head of a random
farmer casually mentioning to his wife a 'weird glow in the horizon' on an
otherwise regular Monday morning.

------
tajen
Is there only one page? I'm on an iPad, there doesn't seem to be arrows for
next/previous page.

~~~
imglorp
Yes, just one.

------
AstralStorm
Excellent page that is completely unreadable on mobile.

Let us download a PDF at least.

~~~
ChristianGeek
Readable on my iPhone 6s in landscape mode.

