 A South Korean spy expert suggested that it may have been an atomic bomb and not a hydrogen bomb.Experts in several countries, including South Korea have expressed doubts about the claimed technology because of the relatively small size of the explosion.Senior Defense Analyst Bruce W. Bennett of research organization RAND told the BBC that "Kim Jong-un is either lying, saying they did a hydrogen test when they didn't, they just used a little bit more efficient fission weapon – or the hydrogen part of the test really didn't work very well or the fission part didn't work very well."