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H-bomb’s power dwarfs A-bomb’s

By Roger Schlueter

An atomic cloud rises over Nagasaki, Japan, after the U.S. dropped the second atomic bomb on August 9, 1945.
An atomic cloud rises over Nagasaki, Japan, after the U.S. dropped the second atomic bomb on August 9, 1945. National Archives/Tribune News Service

Q: North Korea shook up the world last week by claiming it had successfully detonated its first hydrogen bomb. All of the news stories stressed that it marked an alarming advance over the three atomic bombs it had detonated since 2006. So, what is the difference between an H-bomb and an A-bomb? Are they all nuclear? Which is most destructive?

— D.S., of O’Fallon

A: Whether in school or through the media, you probably learned that splitting the atom opened the door to the production of energy on a scale previously unimaginable.

But what you may not realize is that scientists found they could get far more bang for their buck if they could squish two atoms together with such force that it created a single, larger nucleus.

That, in a nutshell, explains why an A-bomb usually is like a cap gun compared to the force that an H-bomb can unleash. It also explains why North Korea’s recent announcement caused shock waves around the globe because nobody wants to see such a rogue nation with such a frightening weapon. Now, a more detailed explanation in hopefully understandable terms:

First, yes, they are all “nuclear” weapons, because they derive their power from nuclear reactions. What sets them apart is which reaction drives them — fission or fusion.

In the case of the atomic bomb — the first type of nuclear weapon ever tested — it’s fission. This is what scientists call it when a single large nucleus splits into two smaller nuclei. When this happens, some of the energy that had been holding the original nucleus together is released.

Obviously, splitting just a few nuclei wouldn’t cause much of a blast. But if you could get a chain reaction going in which more and more nuclei keep breaking up and releasing more and more energy, you’d have a fearsome weapon on your hands.

That’s how an A-bomb works. By breaking apart plutonium-239 or uranium-235 nuclei, you release neutrons that, in turn, cause more nuclei to fission. Each fission reaction doubles the amount of neutrons and energy released. While it hardly seems possible, this chain reaction after only a few microseconds can produce an explosion equivalent to the detonation of thousands of tons of TNT.

This is exactly what ushered in the Atomic Age on July 16, 1945, when scientists set off the first atomic bomb 35 miles southeast of Socorro, N.M. Code named Trinity, the device exploded with the force of about 20,000 tons of TNT.

Three weeks later, Japan felt the new weapon’s horrific force when the only two A-bombs ever used in war were dropped on Hiroshima and Nagasaki, spurring Japan to surrender less than a week later.

Interestingly, although they worked on the same principle (fission), the two bombs were quite different. “Little Boy,” which was dropped on Hiroshima, was triggered by firing what amounted to a bullet of uranium-235 into a larger sphere of the same material. The resulting blast was the equivalent of some 15,000 tons of TNT.

“Fat Man,” dropped on Nagasaki three days later, was even more potent. It consisted of a core of plutonium-239 surrounded by a few thousand pounds of conventional high explosives. When these explosives were detonated, it created a sudden, violent compression that triggered the nuclear chain reaction and an explosion equivalent to 21,000 tons of TNT.

Both caused destruction on a scale never before thought possible. In Hiroshima, 80,000 people were killed and an estimated 70 percent of the buildings were nearly instantly destroyed. In Nagasaki, it is thought to have taken less than a second for the northern part of the city to disappear and perhaps as many as 40,000 people to die. Tens of thousands more in each city would succumb to radiation sickness in the coming months.

But as horrific as these bombs were, they were relative firecrackers compared to what came along just a few years later. On Nov. 1, 1952, the United States announced it had successfully tested its first hydrogen bomb. Dubbed “the Sausage,” it produced a blast equal to 10.4 megatons of TNT.

Allow me to repeat those numbers for emphasis. The two A-bombs dropped on Japan produced a combined force equivalent to about 36,000 tons of TNT. The first H-bomb went off with a blast of 10.4 million tons — or nearly 300 times more powerful.

Why such a huge difference? H-bombs employ the nuclear reaction known as fusion to produce a far more destructive device.

It works like this: At the heart of an H-bomb is a core consisting of isotopes of hydrogen, the lightest element in the universe. Squeezed with enough force from an initial fission blast, these hydrogen nuclei start to fuse, producing a heavier nucleus from two lighter ones. In turn, this also sets off a fusion chain reaction that produces light, heat and other forms of energy in massive quantities. In addition it continues to fuel the fission chain reaction as well.

As it turns out, fusion is the same reaction that is going on at the center of our sun, so maybe you can understand the power it can unleash, considering the sun keeps our planet warm from 93 million miles away.

There are other types of bombs. You may have heard of a neutron bomb, which produces a relatively small explosion but unleashes massive amounts of lethal radiation. There’s frequent talk of “dirty bombs,” which consist of conventional explosives that can spread radioactive material packed around them. There has been talk of a pure fusion bomb (no fission trigger), but efforts to develop one reportedly have been unsuccessful so far.

So H-bombs remain the weapon of choice because they are most efficient even though they are harder to build and detonate. Whether North Korea has developed one continues to be debated; some say last week’s blast had a yield of just six kilotons, which is minuscule by H-bomb standards.

But even if Kim Jong Un hasn’t joined the thermonuclear club yet, here’s one final figure to ponder: The Federation of American Scientists estimates that as of 2015, there are still 15,700 nuclear warheads worldwide, of which 4,100 are thought to be ready for immediate use.

Today’s trivia

Ironically, how do scientists think the nuclear reaction known as fusion led to life in the universe?

Answer to Saturday’s trivia: In January 1969, the soap opera “One Life to Live” came up with a novel way to explain a major casting change. When Jim Storm wanted to leave the show, they had his character, Dr. Larry Wolek, severely burned in a fire. By the time the bandages were removed from his face, Jim’s real-life brother Larry had taken over the role. The difference in facial features was explained away by the miracle of plastic surgery. Larry would continue the role for the next 35 years while the plastic surgery M.O. became a popular plot device on “Dynasty” and other soaps.

Roger Schlueter: 618-239-2465, @RogerAnswer