-4of a moving fragment, but no simple approach seems available to reduce the
charge spread of the original fragments. One would therefore like to design
a system suchthat exactly the right amount of matter could be interposed be-
tween the fission source and the mass-separation device to reduce the most
likely charge on each fragment to unity.
The appropriate amount of matter is
presumably a function of fission fragment mass number, nuclear charge, and
original kineiic energy; since these factors all vary widely, the selection of
an "appropriate amount" is extremely difficult.
The problem can be very
simply avoided by using the fissionable material itself as the absorber; if one
uses a source of fissionable material that is thicker than one range of fission
fragments, there will always be some appropriate depth within the source that
will be covered with the proper amount of matter such that any given species
will have maximum probability of emerging from the surface with a single
charge.
Fragments originating at a greater depth will emerge uncharged, or
fail to emerge; those originating at a lesser depth will emerge with charges
greater than one,
The questf6n of the intensity of the singly- charged frag-
ment beam from such a thick source remains to be determined; for proper
design of an apparatus for mass separation we also require information about
the energy spectrum of such a beam.
The feasibility of this experimental approach, then, depends 1) on the
intensity of the singly-charged fission fragment beam emergent from a thick
piece of fissionable material immersed in an available neutron flux, and 2) on
the ability to design and build a device for separating such fragments.
Deter-
mination of the abundance and approximate energy spectrum of the singlycharged fission fragment beam emergent from a thick source constitutes the
experimental part of this report.
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