SNS Partnerships:
Oak Ridge National Laboratory
The Target
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SNS target inside the hot cell. Mercury was loaded into the target in December 2005.
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Oak
Ridge National Laboratory was responsible for
the design and construction of the liquid mercury
target. Because of the enormous amount of energy
that the short, powerful pulses of the incoming 1-GeV
proton beam will deposit in the spallation target,
it was decided to use a liquid mercury target rather
than a solid target such as tantalum or tungsten.
SNS is the first scientific facility to use pure
mercury as a target for a proton beam.
Mercury was chosen for the target for several
reasons: (1) it is not damaged by radiation, as
are solids; (2) it has a high atomic number, making
it a source of numerous neutrons (the average mercury
nucleus has 120 neutrons and 80 protons); and (3)
because it is liquid at room temperature, it is
better able than a solid target to dissipate the
large, rapid rise in temperature and withstand
the shock effects arising from the rapid high-energy
pulses.
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Installation of the target inner reflector plug.
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The
neutrons coming out of the target must be turned
into low-energy neutrons suitable for research—that
is, they must be moderated to room temperature
or colder. The neutrons emerging from the target
are slowed down by passing them through cells
filled with water (to produce room-temperature
neutrons) or through containers of liquid hydrogen
at a temperature of 20 K (to produce cold neutrons).
These moderators are located above and below
the target. Cold neutrons are especially useful
for research on polymers and proteins.
SNS is an inherently
safe way to produce neutrons because the neutron
production stops when the proton beam is
turned off. It also produces few hazardous
materials. To maximize the safety of the facility,
SNS was designed to have many levels of
containment to keep potentially hazardous
material from getting into the environment.
To learn more . . .
Partner Labs Home
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