I gave you a golden ring to show you my love
You went to stick it in a printed circuit
To fix a voltage leak in your collector
You plug my feelings into your detector.– Les Horribles Cernettes, “Collider”
But never mind gold. The material that’s really good for building particle detectors, for some applications, is diamond. This very strongly-bonded lattice of carbon is almost uniquely sturdy, with a high melting point and — more importantly — a very good ability to take radiation damage and keep working the same way. It can also act as a semiconductor, carrying charge deposited by high-energy particles in the same way that the LHC’s more “ordinary” silicon-based tracking detectors do.
Diamond is already used in both ATLAS and CMS, as part of the Beam Condition Monitors. These are very small detectors designed to detect when the LHC beams stray too far from their expected path; if this happens, they can automatically request that the LHC beam be dumped. This is necessary because the silicon pixel detectors at the center of ATLAS and CMS would be damaged if they were hit with a large number of protons. Of course, operating so close to the beam, the Beam Condition Monitors have to be able to take a lot of damage themselves, and that is why they are made of diamond. Particle physicists have also studied making entire tracking detector layers out of diamond, not so that they could take a direct hit from the LHC beam, but simply so they could last longer in the punishing environment of particles emerging from LHC collisions.
Such applications are possible because the industrial processes that make synthetic diamonds get cheaper and more efficient all the time, as well as better at making large, flat, uniform diamonds. But It turns out that you can also cut diamond gemstones from these processes. They are entirely the same as the “real” ones made underground over millions of years, unless you study them with special equipment designed to tell the difference. Of course, the diamond mining and distribution industry would like you to appreciate that it is the rarity and naturalness of diamonds that makes them special: a synthetic one simply won’t do.
I mention this because, when my fiancée and I went ring shopping this past weekend, we decided to take this argument one step further. A few centuries ago, diamonds were a lot more difficult to come by and to process, and they rarely had the “perfect” cuts and transparency that many people expect today. Diamonds on antique rings are small and cloudy, and the rings themselves are a bit weathered, so they’re surprisingly affordable. But the point we took is this: it’s not the price or appearance of the diamond that matters, it’s how unique and special it is. Like, say, the ones on this ring:
Of course, for building particle detectors, I’ll probably stick to the synthetics.
Can someone on this blog give us readers a sense of what it would be like to look at the collisions as they’re taking place? What would it be like?
Also, just how punishing is the environment inside the detector. When parts are removed, for example, are they radioactive? Or pitted? Or more fragile?
More concrete details of the LHC would be very welcome!
Many thanks,
Brad.
Hi Brad!
I’m glad you weren’t fooled by the boring bit at the end about my fiancée’s engagement ring, and got straight to the important things in life.
Some of your questions are worth entire entries, but let me try to answer them briefly.
You can’t look directly at collisions as they take place, because “looking” at something means detecting photons of an energy of a few electron volts, and most of the action in an LHC collision is of other particles with much higher energy. Particle accelerators produce sort of a blue glow when fired into open air (it’s only been tried with much lower energy than the LHC). Of course, we have pictures representing more abstractly the energy deposited in our detector; for example: http://www.interactions.org/cms/?pid=2100&image_no=CE0268
Particles from collisions don’t pit or damage the structure of detector elements. They do make them a bit radioactive, though — so we wait until the radiation dies down before working on the detector. But most of all, they change the microscopic properties like atomic structure and the mix of charge carriers, so that parts of the detector stop working the way they should. Of course, we’ve designed the silicon detectors near the beam to take quite a bit of such damage and still work, but they’re not diamond.
There’s lots of general information about the LHC linked from here: http://uslhc.us/What_is_the_LHC
Seth
I think what he meant to say was: Congratulations, Seth!!!