Princeton nuclear physicist Dan L. Fenstermacher stated that there is a fundamental problem associated with the Casaba Howitzer concept that becomes dire at higher yields: a good portion of the bomb's energy inevitably becomes black-body radiation, which would quickly overtake the propelled mass. This poses the risk that most of the particles will be vaporized or even ionized, rendering them useless for dealing damage to the target. He concluded: "The NKEW concept is thus one that may require subkiloton explosives to be feasible... Whatever the case may be, it is clear that demonstrating a rush of hypervelocity pellets from a nuclear blast, while perhaps impressive, in no way guarantees that a useful weapon will ever be derived from this concept."