However, with large nuclear weapons the majority of the harm is caused by the explosion itself and the harm caused by the radioactivity is peripheral, although obviously still potentially horrific.)
The damage caused by a dirty bomb would be twofold: There would be damage caused by the conventional parts of the bomb (in this case, the det cord) and damage caused by the radioactive elements. A dirty bomb's effects would be greater in terms of the conventional aspects of the weapon, and we are not given enough information in this scenario to determine the amount of energy that will result in an explosion of the detonation cord. There is no single standard for detonating cord, although given that we know that it has come from a mining company we can assume that it is some of the stronger -- or more explosive -- type. We also do not know how much of it is used in the bomb. We can guess -- fudging all of these unknowns -- that the conventional explosive effect would be about the same as one or two sticks of dynamite.
The major damage caused from the cesium-1377 would be the radiological effects. Cesium has a half-life in the environment of thirty years, which would seem to make the site of the detonation uninhabitable for generations. However, there is a great deal of disagreement about exactly how long the contamination from such a bomb would last...
Given that this scenario predicates an essentially windless day, the potentially contaminated area would be relatively small.
The more salient half-life in the case of this isotope is that of seventy days -- which is the half-life of the Cesium-137 in the body. While it remains radioactive in the body, the cesium could do a significant amount of damage. The dangerous effects of a radioactive bomb come primarily in the form of ionizing radiation (including X-rays along with alpha and beta particles and gamma rays). Ionizing radiation knocks ions off of atoms, thus potentially setting off complex chemical reactions in the body, many of which can have a variety of negative health consequences, including cancer.
Ionizing radiation also has the potential to change a person's DNA. Not only would this have consequences in terms of the person's ability to have children, but DNA malfunctions can affect the regulation of a range of cells and biochemical subsystems that can cause whole organ systems to go haywire.
All in all, however, dirty bombs (like the biological weapons discussed above) are more effective on a psychological level than on an actual destructive level. This being said, it would never do to underestimate the power of psychological consequences in a population, including the effects of stress and panic.
