6 July 2012

Next: atom-smashers with gold-plated diamonds

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Physicists are developing high-tech gold-plated diamonds for the next generation of particle detectors, as regions of new physics open up beyond the search for the Higgs boson.
inside the ATLAS detector

Workers inside the ATLAS detector during a shutdown over the Christmas period 2011/2012. As the detectors are irradiated they become radioactive, meaning these workers must carefully measure their radiation dose. Credit: ATLAS/CERN

MELBOURNE: Physicists are developing high-tech gold-plated diamonds for the next generation of particle detectors, as the regions of new physics beyond the search for the Higgs boson opens up.

Currently, the building-sized detectors on the Large Hadron Collider (LHC) at CERN use an array of thousands of silicon detectors to precisely measure the position of any charged particles flying out of the proton-protons collisions.

But the silicon detectors have some flaws, and diamond detectors would last longer, and allow the proton-proton collisions at a faster rate than the current silicon technology, researchers argue.

“Our goal is to replace the silicon tracking layers of the LHC detectors with diamond,” said William Trischuk, from the University of Toronto and director of the Institute for Particle Physics in Canada.

How to make a diamond

The diamond being considered is a manmade material. “We don’t just take gemstones out of the ground,” said Trischuk. “It’s called chemical vapour deposited (CVD) diamond. It’s artificially grown.”

The South African mining group De Beers make the diamond itself by taking a gas that contains carbon, such as methane, and striping out all the hydrogen or other atoms. Under enough pressure and with a high enough temperature the carbon atoms will precipitate and stick to a surface, said Trischuk.

Physicists then pattern the diamond with very fine amounts of pure gold, which carries an electrical signal to a computer when a particle passes through the diamond.

Radiation damage to current detectors

“We have about a 10 million budget for diamonds … I consider that dirt cheap, because it will last for a whole decade,” said Trischuk. “If they can last through the 2020s, it would be a real cost saver.”

The problem with detectors is that, because they are sitting within a metre of proton-proton collisions spewing out high-energy particles, they are slowly degrading.

Eventually, the detectors start to throw off random signals of particles that aren’t really there. And, in total, the silicon detectors are expected to survive about five years of continuous use, and will be replaced in 2020.

Diamond detectors faster, last longer

Diamonds, however, are not as affected by the radiation. “The advantage of diamond is that the carbon atoms in the diamond are much more strongly bound and are not as susceptible to be jostled around,” said Trischuk.

The ATLAS detector already uses about 20 diamond detectors – a small proportion of the total number of detectors. These particular detectors are used to measure whether the proton beams operated by CERN are misaligned or losing protons.

The results from these detectors were presented at the 36th International conference on High Energy Physics being held in Melbourne, Australia.

Detectors become radioactive

During the next shutdown of the Large Hadron Collider, planned for 2013 -2014, engineers are planning to put 24 diamond detectors into ATLAS, according to Marko Mikuz, from the University of Lujbaljana, in Slovenia, who presented at the conference.

But the researchers also face another problem: as the silicon detectors are irradiated, they also become radioactive. That could make installing the diamond detectors in the ATLAS detector a difficult task, and one they still have to figure out.

“No one can stand next to it for more than a couple of hours before they get their annual dose of radiation, which is equivalent to about 10 or 20 chest x-rays,” said Trischuk.

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