Georges Charpak: Dachau survivor who won the 1992 Nobel Prize for Physics for his subatomic particle detector
Thursday 28 October 2010
A man invents a device for detecting subatomic particles. Sounds dull and boring, doesn't it? Nothing could be further from the truth. The device not only revolutionises our understanding of the ultimate building blocks from which the universe is made, but makes it far safer for you and me whenever we have a medical X-ray.
And the man? Well, it is impossible to think of Georges Charpak without two contrasting images jumping to mind. The first is of a smiling, white-haired 68-year-old, climbing the stairs to the stage in Stockholm where he will receive the 1992 Nobel Prize for Physics. The other is of a hollow-eyed and emaciated young man, huddled among the dead and dying, behind the wicked barbed wire of the Dachau concentration camp.
Charpak's life, above all, is the story of the triumph of the human spirit. It began long before Dachau, in a town in eastern Poland (now in the Ukraine). In 1931, his Jewish parents moved to Paris to escape persecution. But fate played a cruel trick on them. They discovered they had not fled far enough when the Nazis invaded France in 1940.
Charpak's parents refused to wear the infamous yellow star, marking them out as Jews, and obtained false identification papers in the name Charpentier. Meanwhile, Charpak, still only a teenager, joined the French resistance. In the Nazi puppet state of Vichy France, he was captured, imprisoned and, in 1943, deported to Dachau in Germany. Against the odds he survived, and was freed when the camp was liberated by the US Seventh Army on 29 April 1945.
In the ruins of post-war France, Charpak attended the École des Mines in Paris, graduating in 1948 with a degree in civil engineering. He then found himself working in the laboratory of Frédéric Joliot-Curie, son-in-law of Marie Curie. With essentially no scientific equipment surviving, Charpak used his ingenuity to build instruments out of whatever material he could scavenge. It was a skill that he put to good use when, in 1959, he gained a post at Cern, the European laboratory for particle physics, near Geneva.
Particle accelerators – popularly known as "atom smashers" – slam together subatomic particles such as protons at ultra-high speed. In the collisions, the energy of motion of the particles is converted into the mass-energy of new and more basic particles, conjured out of the "vacuum" like rabbits out of a hat. These building blocks of matter may not have existed since the super-energetic inferno of the big bang, 13.7 billion years ago.
The problem is to detect and identify the subatomic shrapnel emerging from collisions. Since the particles are far too small to be seen directly, physicists infer their existence from the trails they leave behind just as we infer the passage of a jet aircraft from its vapour trail. The "trails" are the tiny bubbles left in the wake of a particle as it punches through a "bubble chamber" of superheated liquid hydrogen.
The "vapour trails" must be photographed. Thereafter, armies of people scour them, sifting through thousands upon thousands of tracks for the needle-in-a-haystack that signals a novel particle or process. It is a mind-bogglingly tedious and inefficient task. And it is this that Charpak set out to change.
In 1968, he took a hollow metal box, painstakingly threaded through it layer upon layer of parallel metal wires, and filled the box with an inert gas. When a subatomic particle flew through the chamber, it smashed electrons from gas atoms in its path. The wires were held at a voltage that attracted these electrons. And, as they sped towards the nearest wires, they "ionised" more atoms, generating an avalanche of electrons. This avalanche, on reaching the wire, created a tiny electrical current, which was then boosted by electronics.
The size of the current indicates the energy of the particle, and the precise timing of the current in each wire yields the path of the particle. Overnight, Charpak increased the rate at which physicists can detect subatomic particles by more than a factor of 1,000. He dragged particle physics from the manual era into the age of the computer.
For the invention of the "multi-wire proportional counter" (MWPC), Charpak was awarded the Nobel Prize in 1992. But his device detected not only subatomic particles but any electron-liberating "ionising radiation" such as X-rays. After the prize, Charpak adapted his invention to a myriad other tasks – such as the detection of X-rays used in breast scans and, in the last years of his life, the detection of "radon" gas liberated in advance of earthquakes.
But Charpak's life ranged far wider than science. In the detention camp in France, before his deportation to Dachau, he and his fellow prisoners donated two spoonfuls of their thin daily gruel to the weakest and sickest. In this way, they retained their humanity and dignity. And, throughout his life, Charpak fought tirelessly for the humanity and dignity of others incarcerated across the world, most famously Andrei Sakharov in the Soviet Union.
He became a member of the French Academy of Sciences in 1985.
Georges Charpak, physicist: born Dabrowica, Poland (now Dubrovytsia, Ukraine) 1 August 1924; Nobel Prize in Physics 1992; married 1953 Dominique Vidal (two sons, one daughter); died Paris 29 September 2010.
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