Sensitive detection

Quite the detector - from Chicago's CBS affiliate:

Feds Swarm Metra Train After Detecting Nuclear Risk
It was stunning for those who watched Thursday night as federal agents investigated a possible nuclear threat at Chicago�s Ogilvie Transportation Center.

CBS 2′s photojournalist Lana Hinshaw-Klann happened to be at the scene and used a cell-phone camera to record agents in action. Reporter Dave Savini looks into what agents were looking for and what they found.

Sources say the agents were members of the elite TSA VIPR team on the 5:04pm Union Pacific West line. They were carrying hand-held nuclear-detection devices that picked up a reading.

And the source?

Jerry Jones, a Chicago lawyer, was heading home on that train. He says the federal officers narrowed the trouble to the area where he was sitting.

�I had no idea I was the center of the activity,� he says.

The special security team must have picked up on him as he entered the station and walked up the stairs, Jones says. Little did he know a nuclear stress test he had at a hospital earlier in the day had set off silent alarms and sent security scurrying.

The TSA team passed by him several times before ending up on his train car. Finally, he got a clue when an agent questioned the man right next to him and asked, �Sir, do you have an explanation as to why I am getting a high isotope reading on your bag?��

�The fellow�s jaw dropped,� Jones said.

Once the agent said the word �isotope,� Jones says he realized he was the one they were looking for. He raised his hand to say he had a nuclear stress test.

The tests can leave patients emitting radiation for some time. After showing identification and proof of the nuclear test, Jones and the other passengers were allowed to go on their way.

I cannot imagine the kind of detector that could pick up the radiation from so far away. The most common isotope used in Cardiac Stress Tests is Thallium 201 which is a gamma emitter so the distance is not a factor but the amount of radiation is so small that detecting it from 20 feet away through bodies and the train walls is quite the feat. Curious that they are monitoring subway trains...