Victory And Beyond ‘Just So Blown Away’ Physicist’s Work Turned Theory Into A Weapon
Larry Johnston helped spark the atomic age to life. Then he watched from the sky as bombs mushroomed over New Mexico, Hiroshima and Nagasaki.
Fifty years ago today, he was about eight miles - mostly straight up - from Hiroshima.
The radio tone from the Enola Gay had gone quiet, signaling the bomb had been dropped.
In a nearby B-29 called The Great Artiste, scientists around Johnston were marking time with stopwatches while the 27-year-old physicist checked and rechecked the signal from a floating microphone that would help measure the blast.
A flash of the whitest white shot into the scientists’ compartment. Forty-five seconds later, the shock wave hit the microphone drifting below the plane on a parachute.
Then it hit the plane with a small jolt, cracking against the B-29’s metal skin like a smack from a 2-by4.
As The Great Artiste circled the damaged city, the scientists took turns looking out the compartment’s single porthole at the mushroom cloud sprouting above the city - and at the devastation below.
“I was thinking about those people and looking at those fires starting,” said Johnston, now a retired professor of physics at the University of Idaho. “It was just so completely blown away.”
Johnston knew what kind of destruction an atom bomb could cause. He had helped develop it and had witnessed a test explosion three weeks earlier in the New Mexico desert. He knew many people below had been killed or injured.
“But I was braced for it. I was not feeling remorse or regret,” he said. “Anyone who had lived through the war was used to newsreels and pictures of devastation from conventional (non-nuclear) bombing, and that, too, was horrendous.
“You can’t be killed twice.”
Three days later, Johnston would be on The Great Artiste again when it measured the blast of the Nagasaki bombing. He was the only person to witness all three of the first atomic blasts.
Johnston had embarked on what he still regards as a great scientific adventure in 1941 when he left the University of California at Berkeley to join his mentor, Professor Luis Alvarez, who was working on secret projects.
By 1944, they were in Los Alamos, N.M., where scientists and military experts desperately were trying to turn atomic theory into a weapon.
One design would use a new substance called plutonium to release atomic energy.
The project was “in deep trouble,” Johnston recalled, in part because no one could find a way to set off 32 simultaneous, equally spaced explosions around a sphere of plutonium. In theory, those highly focused blasts would drive the plutonium inward at great speed until the rapidly compressing atoms would collide, breaking apart in a chain reaction that would release the energy for the bomb.
After weeks of studying detonators and electronics, Johnston developed a device that set off all 32 explosions in less than a millionth of a second.
The next task for Alvarez and Johnston was to find a way to measure the bomb’s explosive power. Everyone believed the blast would release unprecedented destructive power.
But how much?
They decided to measure sound waves from the blast. To do that, they dropped microphones on parachutes from a B-29 flying above the blast. When the sound wave hit the microphones, radio transmitters sent signals to measuring devices in the plane. The size and shape of the waves indicated the bomb’s energy.
The system worked for the Trinity test explosion in July, and the scientists were sent to the South Pacific island of Tinian.
On Aug. 6, three B-29s left the island for Hiroshima before dawn. They returned that afternoon after having dropped a bomb which instruments in The Great Artiste showed was more powerful than any other weapon used in war - about 17,000 tons of TNT. It killed an estimated 140,000 people.
Johnston said he and other scientists involved in developing the bomb were convinced the Japanese would have fought to the death if their islands had been invaded.
“We assumed that after the first city was hit, they would surrender.”
On Tinian, they listened to Radio Tokyo for word of surrender. But the Japanese military’s announcement that day didn’t mention Hiroshima.
On Aug. 9, The Great Artiste followed Bock’s Car for the dropping of “Fat Man,” a plutonium bomb which used Johnston’s detonator. It hit Nagasaki with the force of 20,000 tons of TNT, killing some 70,000 people.
This time, parachutes also carried copies of a letter to a Japanese physicist who had studied at Berkeley. It asked Professor R. Sagane to use his influence to convince Japanese military commanders to end the war.
“As scientists, we deplore the use to which a beautiful discovery has been put,” the unsigned letter from the Atomic Bomb Command headquarters said, “but we can assure that unless Japan surrenders at once, this rain of atomic bombs will increase many fold in fury.”
The Japanese military found the letter, but no one knows what effect it had. On Aug. 15, Japan surrendered.
After the war, Johnston finished his doctorate in physics at Berkeley. He did research in nuclear physics and taught at several universities before coming to the University of Idaho in 1967. He retired in 1988.
With each anniversary of the first atomic blasts, Johnston is asked about his part in the building of the bomb. He answers directly - and without regret.
“I’m thankful God put me in a place where I could save a lot of lives.”
, DataTimes ILLUSTRATION: 3 Photos (1 Color) Graphic: The Enola Gay