In the hands of the terrorists, I believe, beryllium could be more dangerous than radioactive materials which are extremely easy to detect. Be-metal could be converted into the fine powder by firing it in the cheapest pottery kiln.
But most important Be-oxide is undetectable and highly inert. It could be easily mixed with a foodstuff (or almost anything). If terrorists would dump Be-oxide powder in the air conditioning/heating system of a building — few weeks later — suddenly every occupant of that building will get ill having (seems to be) a fast progressing lung cancer. If I would have a horrible dilemma to choose to be exposed to a dirty-bomb or Be-oxide powder I would choose dirty-bomb in a heart beat. The chance of surviving a dirty-bomb is very good and it is highly unlikely someone would bring undetected radioactive stuff home and kill the whole family.
Exposure to the Be-oxide dust is very difficult to detect and it is always fatal.
Beryllium toxicity information is usually based on Be-metal info, the fact that the killer is Be-oxide, a fine dust, is always somewhat camouflaged. For example, a machinist working with beryllium bronze (alloy of copper with ~1% Be — very popular family of industrial alloys) could develop beryllium disease in thirty years, but his exposure to Be-oxide is so negligible that it is practically impossible to measure.
Now, I’m an utter layman in these matters. However, I ask the commenters who pooh-poohed the idea of using of beryllium as a terrorist weapon to answer G.O.’s points substantively; i.e., why do you think beryllium oxide is not a concern?
Remember, a ton of beryllium went missing in Sweden a while back. That could make a lot of Be-oxide powder…
I know it’s difficult to work with and transport, but would the payoff be high enough to make it attractive?