In this case there is no possibility of using that material to construct a Hiroshima type bomb - it's simply the wrong element, it isn't capable of either a fission or a fusion reaction.
The Hiroshima type bomb requires a critical mass of an element that is capable of a fission reaction. It also has to be of a sufficient purity that the mass can be contained within the critical radius - these two numbers are specific to every fissionable material. That's going to be the biggest sticking point, since that requires a pretty good quantity of a sufficiently pure and specific isotope of the element - usually uranium or plutonium. There are a few somewhat tricky issues about the construction of the "shotgun" and the trigger mechanism but they aren't at all insurmountable once you have the reaction mass.
A dirty bomb is a whole other animal - almost any radioactive matieral will do, and the more radioactive the better. In fact uranium isn't a particularly good source since even the fissionable isotopes aren't radioactive enough (!). There are any number of such elements - radium, radon, cesium-137, etc. Once you have that (and it's just about everywhere - paricularly in hospitals), it's quite easy to construct a dirty bomb from it.
The barrier for constructing a "dirty" bomb is much, much lower than for a true nuclear bomb.
Thank you for using all the right words on the nuclear bombs, I don't even try to recall them.
I decided many years ago, that if one fell, I would not be
able to outrun it, so refuse to get up tight about them.
If you do not know Dr. Bill Wattenberg, he is a Nuclear Weapons designer for the U.S. Government and a University
teacher, for about 50 years. Google will find him.
He has talked about bringing in the needed materials, he thinks it will be through the ports as his first choice, over the border is second choice.
Google will find him, or he has a page at KGO.com.
He is now on vacation for the next 2 weeks, so will not be on the radio.
He does not do conspiracy, I have listened to him for about 30 years.