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更新时间:2017-5-24 7:08:16 来源:纽约时报中文网 作者:佚名

U.S. Nuclear History Offers Clues to North Korea’s Progress

It started with Albert Einstein. His famous E = mc2 revealed a vast asymmetry in the cosmic relationship between matter and energy. In time, experts looked into the possibility of exploiting the disparity.

一切都始于阿尔伯特·爱因斯坦(Albert Einstein)。他那著名的E = mc2揭示了物质和能量之间复杂关系中的巨大不对称性。随着时间的推移,专家们研究了利用这种不对称性的可能性。

Today, North Korea is hard at work on that agenda. Its nuclear program has succeeded in producing blasts in the Hiroshima range. In each case, trillions of atoms in a tiny smidgen of matter — estimated at roughly 1 gram, the weight of a dollar bill — broke their nuclear bonds in violent bursts of primal energy.


The North now seeks to turn bits of nuclear fuel into even more powerful blasts. Experts say its ultimate goal is to transform an ordinary atomic bomb into a hydrogen bomb, which can raise its destructive force by 1,000 times.


“I can’t imagine they’re not working on true thermonuclear weapons,” said Siegfried S. Hecker, a Stanford University professor who from 1986 to 1997 directed the Los Alamos weapons laboratory in New Mexico, the birthplace of the atomic bomb, and whom the North Koreans in seeking recognition as a nuclear power have repeatedly let into their atomic facilities.

“我无法想象他们没在研制真正的热核武器,”斯坦福大学(Stanford University)教授西格夫里·S·赫克(Siegfried S. Hecker)说。赫克曾在1986至1997年间担任原子弹诞生地新墨西哥州洛斯阿拉莫斯武器实验室的主任;为本国寻求核大国地位的朝鲜人曾多次让他进入他们的核设施。

“But that’s a big step,” Hecker cautioned. “You have to pay attention to what they’re doing but take their claims with a grain of salt.”


On Sunday, the North fired a medium-range missile in an act of defiance, its second in a week. Both tests were successful and seen as demonstrating the slow improvement of its nuclear arsenal.


Experts say atomic history — especially that of the U.S. program, the world’s most successful, which other nations often seek to mimic — can help distinguish North Korea’s credible accomplishments from bluster and empty threats.


The nuclear age began in 1938 over a snowy Christmas holiday in Sweden when Lise Meitner and her nephew, Otto Frisch, tried to make sense of a colleague’s puzzling experiments on uranium. During a hike, the physicists sat on a tree trunk and discussed the unlikely possibility that its atoms had split in two.

核时代肇始于1938年瑞典的那个飘着雪花的圣诞假期。当时,莉泽·迈特纳(Lise Meitner)的一名同事已经做了关于铀的实验,迈特纳和她的外甥奥托·弗里施(Otto Frisch)试图对令人困惑的实验结果做出理论解释。一次远足期间,这两名物理学家坐在一根树干上,讨论一种看似不可能的可能性:铀原子一分为二。

Meitner knew Einstein’s equation. She did a calculation estimating how much energy a split atom might release. Suddenly, all the experimental facts fell into place.


“It was beautiful,” her biographer wrote. “Everything fit.”


The discovery, called nuclear fission, led to a global race to split heavy atoms in chain reactions. The fuels of the first atomic bombs were either uranium or plutonium, both heavier than lead.


Soon, scientists found another way to free the hidden energy — by fusing two light atoms into one. The fuels were deuterium and tritium, rare forms of hydrogen. They were known as thermonuclear because their ignition required the blistering heats of an exploding atomic bomb, which acted like a match.


Fusion — which powers the sun and the stars — turned out to release far more energy. It led to history’s most powerful blasts as well as decades of superpower brinkmanship with thousands of nuclear arms.


The United States in 1951 injected a tiny amount of thermonuclear fuel into the core of an atomic bomb, boosting its power. The explosion was roughly three times stronger than the Hiroshima blast.


What beckoned was the idea of installing near the atomic bomb a separate capsule that would hold much more thermonuclear fuel.


In 1954, on Bikini Atoll in the Pacific, the United States tried that approach. The fireball expanded for miles. The shock wave swept neighboring atolls clean of vegetation and animals. In minutes, the mushroom cloud rose some 25 miles. Slowly, its radioactivity spread around the globe.


The destructive force of that single hydrogen device turned out to be far greater than all explosives used in World War II, including the atomic bombs dropped on Hiroshima and Nagasaki. The blast, code-named Bravo, was 1,000 times more powerful than the Hiroshima bomb. It was the nation’s most violent thermonuclear test ever.


But as Einstein foretold, the amount of matter that Bravo converted into energy was mind-bogglingly small — on the order of 1,500 grams, or about 3 pounds.


Few experts think North Korea will get close to mastering the secrets of true hydrogen bombs any time soon, if ever. But they cite a range of evidence suggesting that the isolated nation is now working hard to raise the destructive force of its nuclear arsenal with thermonuclear fire.


“It’s possible that North Korea has already boosted,” Gregory S. Jones, a scientist at the RAND Corp., said of the first step down the thermonuclear road.

“朝鲜可能已经进行了强化,”兰德公司(RAND Corporation)的科学家格雷戈里·S·琼斯(Gregory S. Jones)谈及朝鲜在热核道路上迈出的第一步时说。

The prospect of the North making strides in missiles topped with nuclear arms that could threaten the United States has prompted the Trump administration to increase pressure on Kim Jong Un, the North’s leader.

朝鲜正研制搭载那些会威胁到美国的核武器的导弹,它在这方面大踏步前进的可能性,促使特朗普政府加大了对朝鲜领导人金正恩(Kim Jong Un)施压的力度。

The world’s first atomic bomb, the Gadget, tested in 1945 in the New Mexican desert, had a fuel efficiency of less than 20 percent. Thereafter, over years and decades of experimentation, designers learned how to raise the burn rate. Exactly how far is a federal secret.


The North, like most countries with nuclear ambitions, has followed the U.S. playbook. The question is how much progress it has made since its first atomic test more than a decade ago.


Two detonations last year helped clarify the picture. The first, in January, was about as powerful as the Hiroshima blast. With typical swagger, the North declared it had detonated a hydrogen bomb — a claim experts universally rejected. The explosion was far too small.


Still, emerging clues suggested the North was indeed going down the thermonuclear road — particularly in enhancing its atomic bombs.


Experts found evidence that it had modified a reactor to make tritium, built a plant that could gather up the radioactive gas, and produced a thermonuclear fuel ingredient in such abundance that it was selling it online.


“I think it’s pretty clear they’ve weaponized and miniaturized,” Bruce Klingner, a former head of the CIA’s Korea branch, recently told a group in Washington.

“我认为他们很显然已经实现了武器化和小型化,”曾任中央情报局(CIA)韩国分部负责人的布鲁斯·克林纳(Bruce Klingner)最近告诉华盛顿的一个团体。

The finding went to warheads for short- and medium-range missiles able to hit much of Japan and South Korea. Experts say the North still has a long way to go in perfecting warheads for its intercontinental ballistic missiles, none of which have undergone flight testing.


Last September, the North set off another blast — its fifth. By some estimates, the explosion was twice as strong as the Hiroshima bomb. That suggested its designers had used more atomic fuel, had achieved a higher rate of burning, or had engaged in thermonuclear boosting.


Albright of the Institute for Science and International Security has argued for another possibility. The North, he says, may be pursuing an intermediate stage of thermonuclear arms design known as layering.

科学与国际安全研究所(Institute for Science and International Security)的戴维·奥尔布赖特(David Albright)提出了另一种可能性。他说,朝鲜或许正在推进名为层叠法的过渡性热核武器设计工作。

In that step, weapon designers wrap alternating layers of thermonuclear fuel and uranium around atomic bombs. That burns more hydrogen than simple boosting. When the Russians first tried that approach, Albright noted in a recent report, the test device produced a blast over 25 times stronger than the Hiroshima bomb.


All of which leads to the question of what to expect if the North decides to detonate another nuclear device — which would be its sixth.


Whether the nuclear test is big or small, delayed or scrapped, botched or successful, experts say the North’s program is now moving steadily beyond the rudiments of nuclear arms design, raising not only global alarms but the geopolitical stakes.


For his part, Einstein was horrified by the spread of nuclear arms and often spoke out against them. He worried that the human race had insufficient wisdom to free the primal energies.


“The unleashed power of the atom has changed everything save our modes of thinking,” he remarked, “and we thus drift toward unparalleled catastrophe.”