Nuclear Security Challenges

I recently attended two talks by Ambassador Linton Brooks (START Treaties (Strategic Arms Reduction Treaties)) in which he talked about nuclear security challenges.  I few of the more intresting items I learned.

• One of the largest problems facing America is orphan sources.  I thought these were mostly small things, (a few curies), but evidently they are large - and most come from Radiosotope Thermal Generators that were used to power lighthouses along the Soviet coastline.  I think the idea behind RTG's are nifty - they are used to power deep space craft - but the dose rate / chance for proliferation makes them sort of impratical.  For example, Sr90 (used by the Russian RTG's) has a beta decay of 0.546 MeV to Y90, which then has a beta decay of 2.28 MeV to Zr90, which is stable. The half life of Sr90 is about 20 years, and the half life of Y90 is days, so we can assume that all we are essentially getting 2.82 MeV per decay.  In order to get 1 Watt we would then need 2.74E12 decays/s or 74 Ci, and this doesn't account for any efficiencies.
• A majority of Russians still consider the US a threat, while the US no longer considers Russia to be a nuclear threat.  I thought both nations no longer considered each other to be threats.
• The reduction treaties only count strategic weapons, not tactical ones.  Counting tactical weapons is a lot more sensitive.
• There was a dirty bomb incident in Russia.  The device never went off.  
• Perhaps the largest threat for the US is preventing a conflict escalation between Pakistan and India.
• Nobody knows how to deal with North Korea, a "Jerkwater State"