The Iraqi ambassador to the U.N. has written a letter confirming this ISIS social media claim.  The U.K. Daily Mail:

In a letter to the United Nations, Iraq's U.N. Ambassador Mohamed Ali Alhakim told Ban Ki-moon 'Terrorist groups have seized control of nuclear material at the sites that came out of the control of the state,' adding such materials 'can be used in manufacturing weapons of mass destruction.'

'These nuclear materials, despite the limited amounts mentioned, can enable terrorist groups, with the availability of the required expertise, to use it separate or in combination with other materials in its terrorist acts.'

An effective dirty bomb would probably use small fragments of a radioactive metal, to disperse the effect.  Smaller fragments would spread measurable radioactivity more widely.  Forty kilograms of uranium could be machined into thousands of radioactive pieces. 

The greatest danger is mass panic.  Since ISIS understands this, and does a lot of psywar through social media, it is not impossible that they will target a town like Kobane with a dirty bomb.  Uneducated people – like many  journalists – do not understand the difference between a dirty bomb and a nuclear weapon.  A panic triggered by a dirty bomb could escalate into a full-scale regional war along the Shi'ite-Sunni divide. 

In a related report, the Turks have allowed ISIS to attack the Kurdish defenders of Kobane from the Turkish border. This is consistent with reports that the Turks have supplied ISIS from the beginning, and that they have colluded with ISIS to establish "consulates" that serve as recruiting centers. The use of the word "consulate" signals recognition of ISIS's claim to be an Islamic State. 

Turkey's Erdoğan is claimed to be Obama's "closest friend" in the Middle East, along with Qatar and the Muslim Brotherhood (a multinational terror support network, with agents in this administration). 

In my judgment, it is impossible for Obama to have close relations with three major ISIS-supporters – Turkey, Qatar, and the MBs – without knowing a great deal about ISIS origins, organization, funding, recruitment, and operational tactics. 

This administration has consistently resisted intervening against Islamist radical entities before they rose to great power.  Valerie Jarrett started back-channel talks with the mullahs even before the administration took office.  By failing to act against the Iranian nuclear program early on, Obama effectively gave the green light to an Iranian bomb.  At this point, any nuclear "agreement" with Iran will be purely ritualistic. 

The evidence strongly suggests that Obama has actively colluded in empowering extreme radicals on both the Shi'ite and Sunni divisions of Islam.  This pattern is much too consistent to be a coincidence. 

Reckless gambling with human lives seems to be a signature for this administration.