CRI听力:Olympic Anti-doping

The scientists are all employed by Kings College London, which runs the UK's Drug Control Center. Professor David Cowan is the director here.

"If we're looking at a urine sample then it's what's left the body and it takes a little bit longer for substances to appear in the urine. Because our tests are so sensitive, even if it's just starting to appear in the urine sample, we are very likely to be able to detect that."

As soon as samples are taken from athletes at the Olympic Park, they're bar-coded, bagged and transported straight here. Each sample is scanned through each process so each can be tracked on its journey through the laboratories from the first minute it arrives.

In theory, it's impossible for a sample to go astray here. All the samples are in tamperproof bottles with seals, which have to be mechanically shattered in a vice.

Cowan says the biggest anxiety facing any laboratory is the introduction of a new substance which has been developed to resist detection, the production of so called designer drugs which target sports.

"Could there be something that we hadn't come across before that will actually miss our test? Well the answer to that is we have a very good probability of even catching those sort of substances."

Every human being is unique, and so is his physiology. That means our bodies don't all respond to substances or stress in the same way, and it raises questions about whether it's possible for some athletes to test positive even though they haven't consumed a prohibited substance.

But the team here says that's highly unlikely.

Athletes reaching the Olympics are usually at the pinnacle of their careers. Those taking part in the 2012 Games will have been tested through numerous trials and competitions and the detailed results of those tests will be on the data banks here.

So if an athlete's body starts behaving in a different way, Cowan says the scientists here should be able to spot it.

"Once we capture the data, we then review it and look at it. Now for certain substances, if you take a particular substance, what we'll see is a natural suppression of your hormones, and once we see that suppression we can start looking harder, and that will enable the previously unknown compound to be discovered."

Details from each sample will be compared with others, and vast banks of data will be stored for future reference. Half of all the samples are frozen and held in case there are disputes about test results.

For CRI, I am Li Dong.