事故使日本对宇宙中不可捉摸的粒子研究受阻

 

[东京 1112日电] 由于周末数以千计的光倍增管连续发生爆炸,曾对来自宇宙被称为不可捉摸的中微子进行过历史性观测的大型地下探测器遭到破坏。

神冈中微子观测站位于东京郊外,是一家大型粒子物理实验室。该事故使对自然界最难以理解的元素之一即中微子的研究遭受重大挫折,使被考虑为诺贝尔奖候选者的实验迫于中断。

“现场人们听到了爆炸声。”高能加速器组织总所长菅原孝宽说。“事故发生在水中,肯定与压力有关,但我不想做进一步评论。”他说,事故是在罐中的水被排干进行维修再充水时发生的。他把该事故称为“一场大悲剧”,并说要将损坏完全修复至少需要一年的时间。

在证实这次事故时,东京大学的官员就事故发生的原因提供了一些线索,称仅被称为超级神冈的充水罐中的光探测器遭到破坏。中微子探测装置依靠约20英吋被称为光倍增管的管子,这些光倍增管排列在装满非常纯净水的罐中,位于地下1000码处,收集没有电荷,质量轻到几十年来物理学家们都认为根本就没有质量的粒子存在的证据。

但在1998年,超级神冈的实验证实了三种中微子中,起码有一种中微子至少具有某些质量。这是宇宙的一大新闻,因为根据对描述宇宙产生于大爆炸的标准预测,在宇宙中中微子是为数众多的基本粒子,其累计的质量可对宇宙的布局及星系的形成产生影响。

 超级神冈探测器由罐中1250万加仑的水组成,其大小如同一座教堂,位于东京西北180英里处神冈锌矿1英里地下。该探测器于1996年建成,造价为1亿美元,由美国和日本的研究机构共同投资。

罐内排列着11242根光倍增管,彼此相距1码,用来探测高速粒子通过时在水中留下的不均匀的淡蓝色的光。熟悉该实验的一位研究人员说,此事故如同爆玉米花,或像放一串炮竹一样。探测器11000管子中有7000根发生爆炸,每根价值约3000美元。他估计总的损失为2000万到3000万美元。他说:“谢天谢地,我们已经获诺贝尔奖的提名。”

 

 

November 13, 2001

Accident Curbs Japan Research Into Cosmos’s Ghostly Particles

By HOWARD W. FRENCH with DENNIS OVERBYE

 

TOKYO, Nov. 12 - A huge underground chamber that made historic observations of ghostly particles called neutrinos that stream through the cosmos was crippled over the weekend when thousands of light detectors imploded in a chain reaction.

The accident at Kamioka Neutrino Observatory, a large particle physics laboratory outside of Tokyo, is a major setback to research on the neutrino, one of nature’s most elusive components. It brought to a halt an experiment that has been considered a candidate for a Nobel Prize.

“People at the site heard a sound,” said Hirotaka Sugawara, director of KEK accelerator laboratory. “it happened inside the water and surely must have had something to do with the pressure, but I will not comment further.” He said the accident happened as the water tanks were being refilled after having been drained for maintenance. He called the accident “a huge tragedy” and said it would take at least a year to repair the damage.

In confirming the accident, officials at Tokyo University gave few clues as to its origin, saying only that thousands of light detectors had been destroyed in the water-filled chamber, known as Super-Kamiokande. The neutrino detection apparatus relied upon roughly 20-inch tubes called photomultipliers that lined a tank filled with very pure water, over 1,000 yards underground, to gather evidence of the particles, which have no charge and are so light that physicists thought for decades that they had no mass at all.

But in 1998, experiments at Super- K established that at least one of the three types, or “flavors,” in which neutrinos come must have at least some mass. This was big news for the universe because according to the standard calculations that describe the big bang that started the universe, neutrinos are the most populous elementary particles in the universe and their cumulative mass could have an effect on cosmic geography and the formation of galaxies.

The Super-Kamiokande detector consists of 12.5 million gallons of water in a tank about the size of a cathedral a mile underground in the Kamioka zinc mine 180 miles northwest of Tokyo. It was completed in 1996 at a cost of $100 million by a consortium of American and Japanese researchers.

The tank is lined with 11,242 photomultiplier tubes spaced about a yard apart, which detect a bluish streak of light left in the water when a high-speed particle passes through. A researcher familiar with the experiment said compared the accident to corn popping or a string of firecrackers going off. About 7,000 of the detector’s 11,000 tubes imploded, he said, each of which costs about $3,000. He estimated the total loss at $20 to $30 million.  “Thank goodness we got our Nobel already cooking,” he said.