First-Hand:Adventures at Wartime Los Alamos

Adventures at Wartime Los Alamos

Contributors: Lawrence Johnston, IEEE Life Fellow.  Submitted on his behalf by the IEEE History Center Staff.

This article will discuss three major topics. First about how we experienced life in wartime Los Alamos. Second, the work we did on the Fat Man Implosion type of bomb, and third, the three wartime bomb events: the Trinity Test of the Fat Man bomb, and the job that took us to the Tinian Pacific base, and the delivery missions of the bombs to Japan - Hiroshima and Nagasaki.

Life at Wartime Los Alamos

Luiz Alverez (From Discovering Alverez)

When I say "we" I mean Luis Alvarez and me. Of course there were others involved. I was just out of Berkeley as a physics major when the War in Europe started (I was born in 1918), and I hitched the start of my career to this fascinating man, Alvarez.

Ernest Lawrence

It is interesting that Alvarez in turn considered himself to be a disciple of Ernest Lawrence, now regarded as the founder of the "Big Science" trend during and after the War. Lawrence had a big hand in establishing and staffing the MIT radar lab, the Metalurgical Lab in Chicago, and Los Alamos.

As the war and technology went forward, Lawrence followed the progress of each Lab, and which lab most critically needed the help of particular scientists. Thus in early 1944 Lawrence decided that the now critical work at Los Alamos on the Fat man bomb needed the insights and ideas of Luis Alvarez; and Alvarez brought me.

Now about wartime Los Alamos living: Was it burdensome living in such an isolated environment? It may have been for some people with a liking for urban civilization, but for us, a young couple with a one-year old, it was an adventure. To us, it was more like living in a wilderness resort. On a weekend, you could take scenic hikes where the beauty started right at your back door. And we could see the pine forest starting right outside our kitchen window. Here is the kind of 4-plex apartment building we lived in (below).

Los Alamos Apartment Building

 

Hiking. That kid in the packsack is Ginger, our eldest, now a Presbyterian pastor.

Here are a few of my outstanding memories:

▪ Steak night each week, at the cafeteria. A great chef. Meat was under wartime rationing, but no ration coupons were needed at the cafeteria.

▪ On a hike, seeing a tree blown to kindling wood by lightning. Lightning at Los Alamos? Tell me about it! This was poignant, because just the day before the talk we experienced the fiercest lightning storm any of us had ever seen. Drenching rain and frequent lightning and hail. They said later there was 1.9 inches of rain, in less than an hour.

▪ The Easter 1945 sunrise service outdoors. Jim Roberts, a Physics professor from Northwestern University brought the inspiring message of Jesus' resurrection.

Here is an interesting anecdote. When you were expecting a new member of the family, you went to the housing office and put up a card on the bulletin board. Accordingly when Geraldine Alvarez was expecting, they placed a card on the board applying for a larger apartment for the Alvarez family. At the next meeting of the town council, the wife of a well-known Austrian physicist came and complained that they were allowing those Spanish American workers named "Alvarez" to live in the prime housing of the site. Alvarez was a very good friend of this woman's husband, and they both got a big kick out of the incident. However, a subsequent conversation with Geraldine Alvarez herself in September 2006 indicates this story is not true. But she says there were complaints from the other occupants of the apartment building. Since we lived in the apartment just below the Alvarez’s, that leaves two families that may have complained.

Another incident-- I got a speeding ticket from one of the military police, and appeared before a court of 3 townspeople. I was fined $5 by the presiding judge, a very likeable Victor Weisskopf. He was one of the prime theorists there. More on that occasion.

Victor Weisskopf

Going back to my arrival at Los Alamos, I got off the train at Lamy, May 8, 1944. My wife and baby would arrive 2 weeks later. I was met by Alvarez and Kistiakowsky. We drove to The Hill in an army sedan, chaufeured by an army woman, a WAC. On the way they briefed me on the situation they faced. The Implosion bomb, the "Fat Man" had recently been given very high priority at the Lab, and Kistiakowsky had been brought in to head up a new Explosives Division. Alvarez had been there a few weeks, as his chief troubleshooter.

We stopped at the Santa Fe office to get me properly registered. Dorothy McKibbin gave me a white numbered badge to wear, and a pass card which indicated that I had a Q clearance, which meant I could be told anything in the Manhattan Project. It occurs to me that one reason for having both Alvarez and Kistiakowsky with me was to certify my identity with Dorothy, before she gave me the credentials for Los Alamos.

Main Gate

 

Fuller Lodge

I found Kistiakowsky's office and he and Alvarez were soon telling me about the status of the Fat Man implosion bomb, and their problems with it.

George Kistiakowsky

 

Work on the Fatman Implosion Type Bomb

The idea of the Implosion bomb is to have an almost critical plutonium sphere and make it go supercritical by compressing the metal so all the Pu atoms get closer together. The compression is done by surrounding the metal with a large sphere of high explosive. To uniformly compress the metal, the explosive sphere is imploded, that is, a spherical wave of detonation starts at the outside of the sphere, and converges inward to compress the central plutonium ball.

This imploding wave is a very unnatural thing to accomplish, since most wavefronts go outward from the starting point, like the ripples when you throw a pebble in a pond. It takes a special optical system to make a converging wave out of a diverging one. A great deal of Los Alamos talent went into solving this problem.

The theoreticians and explosives people decided they would need to produce the converging wave in a piecemeal fashion, and then join up the partial waves further in to make a complete converging spherical wave. A very ambitious undertaking.

So they conceived of the surface of the explosive sphere as divided up into 32 areas, like the patches on a soccer ball, and they would make 32 separate optical systems to feed a converging explosive wavelet into each such area.

Fat Man Implosion Schematic (L.J. Paint)

Soccer Ball

 

File:Optics-S10-.jpg

Optical Lens (L.J. Paint)

 

The usual way to do this with an ordinary light optical system would be to use a glass lens (right). 

Light travels more slowly in glass than in air, so the central parts of the wavefront get delayed more than the edges. This transforms an outward-going diverging wave into a converging one.

So the explosives experts invented an explosive lens that would perform the same job, assuming that explosive waves obeyed the same optical laws of propagation. They made their explosive lenses out of a slow-propagating explosive.

Here is the same optical system, in the explosives regime (below).

Explosive Lens (L.J. paint)

So when 32 of these explosive lens sectors were assembled around the inner sphere, they could produce wavelets that would join up to make the required large converging wave.

Parenthetically, I would like to pay tribute to the skill and courage of those men who made those lenses and other explosive components of the bomb, out at S site. They first poured molton explosives into roughly shaped molds, and then machined the molded blocks into the precise shapes needed to fit together in the bomb assembly. I picture all this casting and machining to be precarious work, on explosive blocks of 50 to 100 pounds. Any slipup could have been lethal. I have not heard of any such accidents in the explosives fabrication program. You always wondered when you heard a big boom coming from several miles South of town.

All that is then needed is a way of starting the tips of all those 32 lenses at exactly the same time, so each lens system contributes its timely matching sector of the spherical imploding wave. When I arrived on the scene, the way of doing this was the way an explosives man would think of: Do it with explosives. They would use a harness of 32 10' long pieces of Primacord, a kind of explosive cord that is filled with a very fast high explosive. You could simply transfer an explosion from here to there, by joining the two places with a length of primacord.

Fat Man Configuration, with 32 Explosive Lenses (L.J. Paint)

Fat Man with Primacord Initiating Harness (L.J. Paint)

 

This system of timing the lenses resulted in a scatter of lens timing events in the tens of microseconds, which was not nearly good enough for the requirement, that all the lenses should initiate within a tenth of a microsecond. This scatter was due to slight variations in the propagation speed of the wave in the primacord, and perhaps even the bending pattern of each cord. What was their solution? To try to get DuPont to make better primacord!

When Alvarez heard of this problem with the primacord timing, he suggested to Kistiakowsky that instead of 32 lengths of primacord, they should use 32 lengths of electric cable, each ending in an electric detonator. The speed of electric signals is 30,000 times faster than the speed in primacord. (There's a 6-volt battery to set them all off) But Kistiakowsky smiled and told him that the problem is that electric detonators have a long time delay of milliseconds before the full explosion starts.

Electric Detonators (L.J. Paint

Conventional Electric Detonator (L.J Pictures)

 

Here's a usual dynamite blasting detonator, about a quarter inch in diameter (right). A 6-volt signal makes a tiny bridge wire glow red hot, and that starts a primary explosive burning, and that burning rapidly accelerates into a detonation, which starts the high explosive at the end.

Alvarez then came up with his celebrated idea that instead of burning that bridgewire with 6 volts, the wire could be made to explode by applying a much higher voltage - maybe 6000 volts. This small explosion might be able to start a high explosive directly, with no primary explosive and very little time delay.

So soon after I appeared in Kistiakowsky's office that first morning, they asked me to try out this idea for an ultra-fast electric detonator. It didn't take long to get something started, in those days, with all the services and supply storerooms available on the Hill, and the lack of red tape. I assumed that there was now plenty of red tape at Los Alamos, but nobody clapped. My conjecture was amply fulfilled when I later went thru the process of collecting my travel expenses. Within two days I was the sole proprietor of South Mesa, which was then a sagebrush covered few acres of territory. South Mesa is now densely built up. Most of the Tech area is now on South Mesa.

South Mesa

I had a government automobile, a 15x15 foot hutment delivered and erected, an electric generator, a work bench, a set of hand tools, a surplus high voltage power supply, an assortment of high-voltage capacitors, a box of 25 Dupont electric blasting caps, some lengths of glass tubing from the Chemistry Storeroom, and a 100' roll of primacord. If only I had thought to get some ear plugs, to protect my ears!  But we were in a hurry.

My first experiment out on South Mesa violated most of the safety rules in the book. I did not have any such book, and I probably wouldn't have stopped to read it anyway. But I imagine one rule would have said "Never play with blasting caps, and never, never try to take them apart to see what's inside." As an aside, one of our young daughter's favorite toys was a box of those discarded yellow cardboard tubes in which the detonators came.

I took one of those blasting caps out of the box, pulled it out of its yellow cardboard tube, and straightened out the folded-up wires. I examined the copper shell critically, and noticed that where the wires went into the shell, some of the thin copper shell projected. It couldn't hurt to work on that, could it? So I used a pair of long-nosed pliers to grab that thin shell, and gently twisted it. The shell split open a bit, and when I twisted some more I noticed that the plug with the wires was loosening. It couldn't hurt to wiggle the plug out of the shell, could it?