Do you have any references for this? Because it doesn't make any sense to me.

Considering that chemotherapy is chemical, I'm not sure what it would have to do with radiation at all. Presuming you meant radiation treatments, those do not leave the patient radioactive at all.

In general, to the best of my knowledge, detecting items with radioactivity levels mildly above background inside a moving vehicle from the street is not practical, even theoretically, based on the probable lack of difference in radiation level outside the vehicle.

Here’s one example: http://copleydc.net/copleydc_staff/Cantlupe/cantlupe_1-27-04...

Aside, google has gotten worse than useless. In a first ever I had to scroll through a full page of cancer treatment ads. Zero organic results on the first page. Even then it needed careful tweaking to get Google off the “treatments for cancer” train of thought.

Was not able to find the dog story I remembered. Google wants to show me either national security or cancer treatment but not the intersection.

> Presuming you meant radiation treatments, those do not leave the patient radioactive at all.

Not categorically true, even with external beam radiation therapy.

https://www.ncbi.nlm.nih.gov/pubmed/25271934

Other kinds of treatment can leave the patient significantly radioactive, for example brachytherapy, which involves direct implantation of radiation sources in tissue.

Now that's interesting - I hadn't heard of cancer radiation treatments being performed with proton and fast-neutron beams, which can indeed cause activation of the subject material. I was mostly guessing at cancer treatments, given the weird reference in the GP post to Chemotherapy. Certainly there are other treatments that do result in increased radioactivity of the patient after treatment.

Nevertheless, I would still find it pretty surprising if any of these sources could be reliably detected from inside a moving vehicle by a stationary sensor. Or that cases of these medical treatments would not be overwhelmed by other incidental sources of radiation being slightly higher or lower than usual.

Regarding background sources, the fact that the target of interest is moving could actually be a great benefit for background rejection. Place two detectors on the path separated by some distance, knowing how long it takes for a typical vehicle to travel between them, and you can filter out simultaneous spikes as background fluctuation. Modern photon counting detectors are pretty amazing, and it would take only a small number of temporally correlated discrete events at each detector to reach the probability threshold of alarm.

I don't work on these systems, obviously - those who do aren't talking - and this is just idle speculation. But I do know that lots of DHS money is shoveled into R&D on this kind of thing every year and I would not be surprised if some of the tech does work.

Perhaps a very naive, question, but:

If someone were smuggling a radioactive weapon into DC, couldn't they just shield it with a lot of lead?

I'm guessing that your small-dog example would have been different if it were in a thick lead crate.

Lead is permeable to gamma rays.

Lead is quite a good gamma shield. It's modestly permeable to neutrons and high energy electrons.

It's really not hard to hide both neutron and gamma emissions, especially if you have a large enough container, like a ship's hold.

I would absolutely expect any nuclear exchange to start with ground-based stealth attacks.

Re. chemo: it was most likely radioactive iodine, taken in liquid form to destroy a thyroid tumor.

It is a form of radiotherapy.