Nuclear nature: Manhattan Project tour takes Los Alamos visitors off the beaten path

By Scott Wyland swyland@sfnewmexican.com
Oct 20, 2023

LOS ALAMOS — The old log cabin sitting in a meadow hardly looks like the site where a physicist once raced against the clock to develop an atomic bomb — and where he learned the device he was exploring would not work.

The physicist was Emilio Segre, and his failed device was a “gun-type” bomb that would shoot one piece of uranium into another to achieve fission and set off a blast. They are both lesser known in the annals of the Manhattan Project’s history.

The brightest star in that constellation of physicists remains J. Robert Oppenheimer, the father of the atomic bomb, whose fame was recently magnified with a blockbuster biopic.

Still, ruling out the gun assembly prototype dubbed “Thin Man” became an important step to developing the plutonium bombs “Fat Man” and “Little Boy” that did work as planned when dropped on the Japanese cities of Hiroshima and Nagasaki — some say far too well.

The 19th-century cabin is one of several sites featured in a guided public tour of places in Los Alamos where physicists, engineers and military leaders worked to develop not only the first atomic bomb but also the lab’s subsequent nuclear weapons program.

This site is part of the three-pronged Manhattan Project National Historical Park, established in 2015 at Los Alamos, Oakridge National Laboratory in Tennessee and the Hanford Site in Washington state.

Behind-the-fence tours of the Los Alamos portion of the park take place two weeks a year, loosely coinciding with the Trinity Site’s spring and fall tours.

They must be booked months in advance.

The crude dwelling, which became known later as the Dwight Young cabin, is a prime example of how Los Alamos’ then-rustic setting was in vivid contrast to a technological endeavor that, though having a lethal aim, was pushing science to uncharted territory.

“It’s incredible to think of that,” said Phil Tubesing, a retired Los Alamos National Laboratory engineer and one of the tour guides.

The tour doesn’t include sites in the original town of Los Alamos, which was hastily thrown together so scientists could dive into the project. Now located near Ashley Pond in the downtown area, the remaining structures from that chapter in World War II include Fuller Lodge and Bathtub Row.

Tour guides recommended people visit those places as well, and noted the sites they were seeing Wednesday were more off the beaten track but still historically significant.

“The Los Alamos we see now is much different than what people experienced living there in the hectic years of World War II,” said Chris Person, an interpretive ranger for the National Park Service.

Battleship Bunker, so named because its angular shape is akin to a ship’s prow, looks like a nondescript concrete slab.

But beneath it lies an underground chamber that once was filled with equipment to remotely measure whether a test bomb’s implosion would compress a material enough to cause fission if plutonium were used instead.

Within the bunker are some old dials and needle gauges from the old-time analog devices used. Their main purpose was to measure the magnetic fields the blast generated, a method for gauging how well the force compressed the material, Tubesing said.

Conducted a mere two days before the atomic bomb named “Gadget” was scheduled to be detonated at the Trinity Site, the test was a success, he said, though it remained uncertain how much force an actual bomb would produce.

That wouldn’t be known until the Trinity Site test.

Technical Area 18 houses a drab, empty building where teams did criticality tests in the early postwar years of the lab’s nuclear weapons program.

It also was the site of an accident known as the Slotin incident, which would forever change how scientists test criticality — a nuclear chain reaction that occurs during fission, producing high amounts of heat and radioactivity.

Canadian physicist Louis Slotin was known for using a risky method to “tickle the dragon’s tail,” a term physicist Richard Feynman coined for going to the edge of criticality.

Slotin used a flathead screwdriver instead of a mechanical spacer to raise and lower a beryllium half-sphere that reflected neutrons into a plutonium core, all while monitoring how fast the neutrons multiplied in the core as he moved it.

In 1946, during a demonstration, Slotin’s screwdriver slipped, causing the reflector to fall onto the core and generate what witnesses described as a blue flash and heat wave — which signaled the device had hit criticality.

Slotin was exposed to a lethal dose of radiation and later died in a hospital.

Others in the room survived. Still, the incident led to the lab director requiring all such tests be conducted remotely.

The remote testing was done at a larger building down the road. Thousands of tests were conducted there for 60 years before they were moved to the Nevada Test Site, Tubesing said.

Visitors also were shown a former storage chamber for uranium and plutonium, embedded inside a rock wall.

An upright, rectangular device scanned workers for radiation as they exited the chamber to ensure they didn’t try to steal any of the materials, said Dave Miko, an engineer for N3B, the lab’s contractor in charge of legacy waste cleanup.

Installed in the 1980s, the device was one of the first of its kind and is now standard equipment at any facility that keeps radioactive materials, he said.

Guides started the tour at the foot of a pocked mesa to point out where it literally all began, when a supervolcano erupted 1.2 million years ago, creating the landscape that made the area even more appealing for the Manhattan Project.

The mesas made the area defensible against any invading foes, Tubesing said.

Just as importantly, its sweeping mountain vistas offered stress relief for those working long days to fulfill a mission as quickly as possible to end a war that was taking thousands of American lives every week, he said.

“It had to be pretty” with other redeeming qualities, Tubesing said. “And it was all that.”