My family owns property in Canada and I have traveled back and forth many times across the Canadian/US border in the Thousand Island region of upper New York State. Coming back into the US on a Sunday during the 2008 Labor Day Weekend, I was sitting in the passenger seat of our VW Toureg - my wife was driving and my teenage daughter in the back seat. Entering Customs (now Border Control of the Division of Homeland Security) is similar to entering a toll booth on a highway, except that you have to drive a gauntlet of various detectors and video equipment 20 feet before you reach the booth housing the DHS agents.
When we reached the booth on this particular day, the DHS agent had a very peculiar look on her face. Without saying a word, she left her booth and slowly walked around our SUV holding a small handheld device pointed at the car. After her completed tour around the vehicle, she returned to her booth to confer with another officer who had just arrived.
As we waited, quite perplexed, she approached us again and, without emotion, asked if any of us had recently undergone any medical treatment. Even more perplexed, we asked why. The agent explained that we had set off the radiation detectors as we approached the booth. I remembered the nuclear cardiac stress test I had taken just 12 days before and filled her in, at which point she looked quite relieved and said that probably explains the positive result from the vehicle radiation detectors. Relieved or not, however, this now began the process to determine if this positive trigger of the Homeland Security radiation detectors was a possible security threat!
As a Certified Industrial Hygienist (CIH), I work in the Environmental Science, Safety and Industrial Hygiene consulting field and have been abundantly trained in hazard detection and detector technology, so, all inconveniences aside, I knew I was in the middle of an interesting process. What the DHS folks had to do now was prove that when our vehicle set off the radiation detectors it was indeed nothing more than a harmless security issue, also known as a false positive. In our case this was caused because one the vehicles occupants was still glowing (emitting sufficient radiation energy) from a medical treatment.
Step one - the DHS agents asked me to get out of the vehicle and directed my wife to drive the vehicle through a secondary battery of radiation detectors. The vehicle was clean, so deductively, the radioactive culprit was me!
Step two - I was invited into the DHS office where they asked me to sit in a chair next to another agent with yet another handheld radiation meter the size of a loaf of bread.
Step three - he turned on the detector and pointed it at me for approximately 2 minutes. The detectors LCD display identified the radioisotope as Thallium, which is the isotope used in the cardiac stress tests. The DHS agents were all happy with the results and I was free to continue our trip.
I was impressed with the detection technology being used at our borders to monitor for ionizing radiation. I was also impressed with the ease of use of the detectors being used by the DHS agents who are not trained radiation technicians. It was all fast and accurate. From a security perspective, this is good news and here is why
Thallium has a half life of 72 hours. This means, 12 days after my stress test, my Thallium dose was barely 7% of the original injected dose. Therefore, internally (in my body) the radioactive energy level remaining from my Thallium injection was at 7% of the original dose.
Additionally, when I set off the detectors, I was sitting in the front seat of a slowly moving SUV, constructed with a significant amount of metal to shield me from the radiation detectors. These detectors were located approximately 4 feet from the vehicle, and still picked up this low level amount of radioactive energy. Either these detectors have impressive sensitively, or I had one significant dose of Thallium during my stress test. Ill need to research that next.
