One possible method of revealing the presence of concealed nuclear weapons is to detect the neutrons emitted in the spontaneous fission of in the warhead. In an actual trial, a neutron detector of area , carried on a helicopter, measured a neutron flux of at a distance of 35 m from a missile warhead. We have to estimate the mass of in the warhead. The half-life for spontaneous fission in is and 2.5 neutrons, on the average, are emitted per fission.

Solution:             Click For PDF Version

The half-life for spontaneous fission in is and 2.5 neutrons, on the average, are emitted per fission. The disintegration constant of will therefore be

Let the warhead contain of . The number of nuclides in m g will be

It is given that on an average 2.5 neutrons are emitted per fission of nuclide. Therefore, rate of neutron emission of neutrons from m g of will be

At a distance of 35 m from the missile warhead, a neutron detector of area measures a neutron flux of . We can, therefore, obtain the amount of in g from the equation

The amount of in the warhead is 23.9 g.