shock wave of the high explosive component. The passage of the shock wave through the assembly was measured and recorded using detectors and high-speed photography. Tim tests used real nuclear weapon assemblies, but cores of natural or depleted uranium, which is chemically identical to highly enriched uranium but not fissile, and only feebly radioactive. They took place from 1955 to 1963, and involved 321 trials with uranium and beryllium tampers at the Naya and Kuli areas at Maralinga. Twelve of the Tim tests at the TM100 and TM101 areas involved studies of plutonium compression. These experiments used and dispersed of beryllium, of natural uranium, of uranium-238 and about 1.2 kg of plutonium about the test sites. Rat series Rat trials also investigated the properties of shock waves. They had the same objectives as the Tims, and differed only in the way that measurements were carried out. Instead of using external sensors, the Rats employed an intense but short-lived gamma ray source the size of a pea that was placed inside the assembly. X-ray detectors gave a picture of the progress of the explosion from the inside. Between 1956 and 1960, 125 Rat trials took place at the Naya and Dobo areas at Maralinga. The Rat tests used of uranium-238; of scandium-46, a beta and gamma emitter with a radioactive half-life of 83.8 days; of polonium-210, with a half-life of 138 days; and of lead-212, a beta emitter with a half-life of 10.6 hours. With such short lifetimes, these soon decayed away to negligible amounts. Vixen series Vixen trials involved safety testing. They were about assuring that the core of a nuclear weapon would not accidentally undergo criticality in the event of a fire or unintended crash. These were messy, for a successful test subjected the core to high explosives in the hope that it simply scatters rather than undergoes criticality. These tests sometimes involved some yield from fission, but in every case this was less than the yield from the weapon's conventional explosive component. The British Government's position was that so long as the nuclear explosion component was less than there was no violation of the Partial Nuclear Test Ban Treaty, which was then under discussion, but no such limit was agreed upon. While the AWTSC could determine whether there were public health and safety issues with a test, it could not assess whether there were political issues. However, after