New Mexico

106

Trinity Test Site, White Sands Missile Range, NM

33° 40′ 38.28″ N, 106° 28′ 31.44″ W

July 16, 1945

Twice a year, on the first Saturday of April and October, the Trinity Test Site, where the first nuclear bomb was exploded, is open to the public. Entry is free, there’s no need to reserve, and cameras are allowed.

The Trinity Site is located inside White Sands Missile Range, New Mexico. The missile range covers over 8,000 square kilometers of New Mexico and is actively used for missile and ordnance testing. It is also where German scientists captured by the U.S., such as Wernher von Braun, worked on rocketry and launched modified V-2 missiles (renamed to the Bumper).

The range is also used today by NASA as a training area for space shuttle pilots. In 1982, the space shuttle Columbia landed there at NASA’s White Sands Space Harbor.

Outside the missile range and near the main gate is the White Sands Missile Range Museum, which has an open-air missile park containing more than 50 missiles, rockets, and drones (see Chapter 108).

But the Trinity Site is the highlight of a visit, even though little remains. On July 16, 1945, the world’s first nuclear explosion (Figure 106-1) occurred there; today the exact spot is marked by a small obelisk made of lava rock. The surrounding land is mildly radioactive, but safe for a short visit. The McDonald Ranch House, a small house where the bomb’s final construction was done, has been restored to its 1945 state and is part of the visit.

All that’s left of the tower in which the bomb was mounted are the stumps of its legs.

On the sandy floor of the test site there are pieces of trinitite, blue-green pebbles of glass that were created when the bomb exploded. Some of the trinitite is also red or black, and contains copper or iron from the vaporized bomb and tower. Most of it has been bulldozed away, but small samples have been preserved in a glass box to show the state of the sand after the explosion. A specially constructed cover opens to show the only part of the bomb crater that was not filled in.

Figure 106-1. 0.016 seconds after detonation

Also visible is a 214-ton steel container called Jumbo. The bomb that was exploded at the Trinity site contained two kinds of explosive: TNT and the plutonium nuclear bomb. The TNT was designed to explode first, inward, and compress the plutonium, which would then create the nuclear explosion. Since plutonium is highly toxic, the scientists working on the bomb worried that the TNT might explode and scatter plutonium everywhere, without the nuclear bomb going off.

So Jumbo was created to contain the entire bomb. It was strong enough to withstand the TNT explosion, and would have been vaporized had the nuclear bomb gone off. In the end, however, Jumbo was not used because the team was confident the bomb would explode, and it was left about 700 meters from the nuclear bomb. It survived the nuclear explosion and hasn’t been moved since.

Also on display is the bomb casing for a Fat Man nuclear bomb, the type of bomb dropped on Nagasaki a month after the Trinity Test.

Practical Information

Information about the next open day at the Trinity Test Site is available from the website of the White Sands Missile Range at http://www.wsmr.army.mil/wsmr.asp?pg=y&page=576. Details of the White Sands Missile Range Museum are at http://www.wsmr-history.org/.

About two hours’ drive from the Trinity Test Site is the Very Large Array astronomical radio observatory. Although the observatory is open daily for visitors, it offers a special guided tour twice per year on the same open days as the Trinity Test Site. See Chapter 107.

Fat Man

On August 9, 1945, the Japanese city of Nagasaki was destroyed by a bomb, nicknamed Fat Man, of the same design that had been successfully exploded in New Mexico.

The nuclear bombs exploded by the United States during the Second World War relied on bringing enough nuclear material together to create an uncontrolled chain reaction, resulting in a massive explosion.

Two materials, uranium (in the form U-235) and plutonium (in the form Pu-239), were used because they both undergo a chain reaction if enough of the material, called the critical mass, is present. To get the explosion going, a source of neutrons is needed. The neutrons hit the nuclear material, causing atoms to split apart and release more neutrons (which go on to hit other atoms and create the chain reaction) and an enormous amount of radiation and energy. It is the energy released that creates the explosion.

The Fat Man bomb used plutonium to create the explosion. The bomb’s interior consisted of four concentric spheres: a small neutron source, a ball of plutonium, a layer of uranium, and a TNT exterior (see Figure 106-2).

Figure 106-2. The Fat Man bomb

To set off the bomb, the TNT was exploded, which forced the rest of the bomb inward, compressing it. Once compressed, the bomb’s plutonium became a critical mass, underwent a chain reaction, and exploded. To get the nuclear explosion going, the center of the bomb consisted of a neutron initiator made of polonium and beryllium.

Polonium is an alpha-emitter—it decays and gives off alpha particles (which consist of two protons and two neutrons stuck together). The alpha particles hit the beryllium, which then gives off neutrons. Those neutrons hit the plutonium to start the chain reaction.

As the chain reaction started, the plutonium heated up, causing it to expand. This expansion actually slowed down the explosion. To maximize the explosive power of the bomb, the plutonium core had to be contained while the chain reaction built up. This was achieved by wrapping the core in a layer of depleted uranium (Uranium-238), called the tamper. The tamper contained the chain reaction and reflected neutrons coming out of the core back into the plutonium, helping to increase the chain reaction.

At Nagasaki, just 6 kilograms of plutonium was enough to produce an explosion equivalent to 21,000 tons of TNT.