If by "dirty bomb" you mean a "radiological dispersal device" (RDD), which uses conventional explosives to disperse radioactive material over a large area, then yes. But, in general, an RDD would have to contain hundreds or thousands of curies of radioactive material to cause serious radiation doses to people from dispersing the material over many city blocks.
Using a bomb to disperse only 40-80 curies of gamma-emitting radioactivity over a few city blocks would result in lower dose rates per unit area, but would still cause a lot of psychological (or psychosomatic) effects, prevent the use of such contaminated areas/buildings until decontaminated, and/or cause internal dose concerns if the radioactive material (powder) were inhalable/ingestible and other types of decay (alpha or beta) are significant.
Thank you for your informative reply, much appreciated. I wonder why someone would steal this, doesn’t seem very useful for a bomb, unless maybe combined with more radioactive materials?