Building the Bomb

Back in 1939, Albert Einstein and his former student Leo Szilard - who shared a 1926 patent for a refrigerator of all things - wrote a letter to the White House, pointing out that Germany might develop the atom bomb and so the USA should hurry to build one first. Thus the Manhatten Project was started whereby the USA would develop their own bomb(s) as quickly as possible.

Einstein was denied a security clearance, the lead roles were given to General Leslie Groves (left, in the photo) and physicist Robert Oppenheimer (right in the photo). On the right below is the Fat Boy implosion-style bomb used for the Trinity test and dropped onto Nagasaki on August 9th 1945.

The Manhatten Project employed many engineers, mostly forgotten :-(, and several leading nuclear physicists. The photo below - taken during a visit by Niels Bohr, shows Bohr, Oppenheimer, Feynmann (to get a Nobel prize in 1965) and Fermi (who built the first US reactor, at Chicago).

While the bomb-builders were moved to Los Alamos, the work of separating the sought-after U-₂₃₅ uranium isotope from the depleted U-₂₃₈ uranium isotope was given to Oak Ridge. The isotopes differ only in mass, not in their chemistry, and so were hard to separate. At Oak Ridge the separation was done by diffusing UF₆ through layers of Teflon. This increased the concentration of the lighter isotope ever so slightly as it diffused ever so slightly faster than the heavier isotope, and so multiple steps were needed. The photo shows the original Teflon separator built by Oak Ridge.

Nowadays separation is done by a chain of multiple centrifuges, the 238 being pressed preferentially to the outside and the lighter 235 remaining in the centre. Again, multiple steps are needed.

The result of all this work was two bomb designs. The gun-type bomb shoots a sub-critical mass along a barrel into another sub-critical mass. It was deemed so reliable that it wasn't even tested before Little Boy was dropped onto Hiroshima on August 6th 1945. However, the second type, Fat Man, was an implosion-type design. Conventional explosives in a spherical shell were carefully timed to all go off at once. Each drove a small sub-critical mass towards the centre where the masses added to become critical, giving the fission explosion. So this "careful timing" needed to be tested.

This test was called Trinity (after the Christian god?). The US army had soldiers in ditches just 6 miles from Ground Zero, the scientists were positioned 20 miles away and issued with black sunglasses to protect their eyes and/or told to look away. But physicist Feynmann figured out that it could only be the UV-radiation burst that might blind him. So he positioned himself behing the glass windscreen of an army truck (glass stops UV) and watched without dark glasses. Thus Feymann may be the only person to have seen the Trinity test with his bare eyes! Photo taken at about 35 milliseconds after the red button was pressed (shock front about 600 yards across).

After the successful test, preparations were made to nuke Japan using B-29 bombers like the one shown below (this is FiFi, not Enola Gay or Bockscar).

The photo below shows the mushroom cloud over Hiroshima on August 6th.

Comments (2)
Cop Car wrote " In a roundabout way, you are correct about the naming of the Trinity test/site. Per https://www.osti.gov/opennet/manhattan-project-history/Events/1945/trinity.htm, "Robert Oppenheimer chose to name this the "Trinity" test, a name inspired by the poems of John Donne. The site chosen was a remote corner on the Alamagordo Bombing Range known as the "Jornada del Muerto," or "Journey of Death," 210 miles south of Los Alamos." See John Donne's Divine Poems: A Litany at https://www.bartleby.com/357/111.html. The White Sands Missile Range Museum made such an interesting visit for me (in Summer of 1970) that, came the weekend, I took Hunky Husband (who was on temporary duty at Holloman AFB near Alamagordo). My photos include representations of "Little Boy" and "Fat Man"; but, unlike other displays, there were no identifying placards for them. Nuclear weaponry/testing was a really hot topic in those days ; )" I hadn't known about the name "Jornada del Muerto", so thanks for the info.
Just Your Average Maple Syrup Bot (Canada) wrote " A lot of the heavy water used in the [Manhatten Project] reactors was developed in the P-9 program which centered around the Cominco refinery here in Trail BC (see here)." I hadn't known that either, so thanks for that info too.

Copyright ^© Ole Phat Stu on August 6, 2019 permalink Comments Email

Cold War border museum @Schifflersgrund

This year will see the 30th anniversary of the fall of the Iron Curtain. The Iron Curtain was a mined, fenced, cold war border between East(GDR) and West(FRG) Germany before the reunification of Germany. At the time, I used to take all of my US and UK visitors to see (the west side of) it, as it ran just 90 km east of my house as the crow flies. Communist GDR claimed they built the Iron Curtain to stop us western capitalists from invading their country. In truth it was built to keep their own people IN, because so many were fleeing to the West.

Now it is mostly gone. But there is still a mile of the former border at the border-museum at Schifflersgrund. Turns out a friend of mine, who is too young to have seen it in use, had never seen the Iron Curtain, so last month I took her to see the museum at Schifflersgrund.

The Border Museum Schifflersgrund preserves a piece of the fortifications along the former border. On a hill above Bad Soden-Allendorf an original GDR watchtower is at the centre of the museum's exhibits, which include historical displays and an extensive collection of East and West German military equipment which was used to guard the border.

Approaching the Iron Curtain from the west back then you would have seen (many of the) warning signs so you wouldn't cross the border by accident. Some were in English for the benefit of US troops.

The museum's website contains a misleading photo, which you would purportedly see looking east through the steel fence at a GDR border warning post and the GDR observation tower. In fact, if you were standing where this photo was taken, you would already be on East German territory and likely to be shot by them on sight :-( This is because they built the Iron Curtain (two fences separated by a minefield) well within the actual border, which would typically be tens of yards to the west.

The photo below shows the border through the rift at Schifflersgrund. I've labelled it at places with red letters. The actual border is along the centre of the road on the west(left) of the photo, labelled A. I took this photo from an East German pillbox, looking north. The west side GDR steel fence with automatic guns shooting at anyone touching it is labelled B. East of this is the minefield, labelled C. At point D is a GDR pillbox on the service road to the east of the minefield. Label E shows where an escapee who had made it across the minefield and fence trying to escape from East Germany was shot half way up the slope to the actual border road.

The photo below shows the cross (put there after German reunification) on the hillside at E near the border where the escapee was shot and killed.

Going into the museum, which is on East German territory, some border poles are shown. The cylindrical white unmarked pole would have marked the actual border. The striped square pole bearing an official GDR badge would have been between 2 and 5 yards east of the border, misleading any potential escapee into thinking they'd already reached West German territory. And every 100 yards or so there would be a concrete East German machine-gun pillbox with an over 270° field of fire, as shown below.

At places which could be well seen from roads in the West, the communists often erected pacifistic propaganda signs along the border facing west.

The museum has a collection of military vehicles used by the border guards such as this jet-powered winged heavy-duty Russian MiG helicopter.

There were also several Soviet tanks on display. Here am I doing an imitation of how I remembered the Soviet march into Prague in 1968. I remembered that the Czeck protestor looked directly down the Russian gun-barrel, but had forgotten that he bared his chest rather than going for a crucifixion pose.

Finally, after looking at all the assorted weaponry, we went to see the reunification sculpture. This about 12 feet high and made of wood. It shows hands from both sides of the border breaking down a GDR border post. Very symbolic and, indeed, inspiring. Shivers ran down my spine.

This museum reminds us what a terrible thing walls are. Go see it, Donald!

Copyright ^© Ole Phat Stu on August 1, 2019 permalink Comments Email

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