The device's primary source of neutron radiation was the radioactive element californium, but the stream of neutrons produced by the californium was multiplied by passing it through a lattice of highly enriched uranium U-235, whose nuclear fission released additional neutrons.

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In this case the source would have to be something far more exotic, such as a neutron star being swallowed by a black hole or colliding with another neutron star.

ECONOMIST: Astronomy

Dr Ardavan is confident that, if the machine can be coaxed into doing this, it will radiate in exactly the way he predicts, providing a tuneable and compact source of high-frequency microwaves in effect, a tabletop pulsar, without the neutron star.

ECONOMIST: Physics