The group measured the activity of thorium, uranium-234, uranium-235 and uranium-238, but only had access to microgram quantities of plutonium-239. The first sample plutonium produced in the nuclear reactor at Oak Ridge was received in April 1944. Within days the group observed five times the rate of spontaneous fission as with the cyclotron-produced plutonium. This was not news that the leaders of the project wanted to hear. It meant that Thin Man, the proposed plutonium gun-type nuclear weapon, would not work and implied that the project's investment in plutonium production facilities at the Hanford Site was wasted. Segrè's group carefully checked their results and concluded that the increased activity was due to the plutonium-240 isotope.