The design of particular bombs also plays a part - in most H-bomb designs the bulk of the energy produced comes from the fission of the tamper round the secondary by neutrons produced by the fusion reaction in the secondary.
If a non-fissioning tamper is used then a relatively clean explosion happens (e.g. the Tsar-bomb) - if depleted or enriched uranium is used as a tamper then weapons will be much messier. Indeed some weapon designs explicitly came in "clean" and "messy" versions (the latter often with greater yield) e.g. the US B53:
Also there is an option of deliberately including a material in a bomb design that will be activated by the neutron flux from the secondary (e.g. cobalt or gold)- so called "salted bombs":
If a non-fissioning tamper is used then a relatively clean explosion happens (e.g. the Tsar-bomb) - if depleted or enriched uranium is used as a tamper then weapons will be much messier. Indeed some weapon designs explicitly came in "clean" and "messy" versions (the latter often with greater yield) e.g. the US B53:
http://en.wikipedia.org/wiki/B53_nuclear_bomb
Also there is an option of deliberately including a material in a bomb design that will be activated by the neutron flux from the secondary (e.g. cobalt or gold)- so called "salted bombs":
http://en.wikipedia.org/wiki/Salted_bomb