RRFM 2009 Transactions - European Nuclear Society

Fig 3. Detailed view of MURR BNCT facility, shown in the “sample load” configuration
(1) The neutron and gamma ray filter system: This system consists of a 50 cm (19.7”) length
of single-crystal silicon and an 8 cm (3.2”) length of single-crystal bismuth. The silicon crystal
is housed within the beamport collimator liner which is installed in the 20.32 cm (8”) cutout
section of Beamport ‘E.’ The bismuth crystal is housed in a rotating drum within the bismuth
box outside of the biological shield, adjacent to the vestibule box.
(2) The beam shutters: The beamline shutters are positioned within the vestibule box and
the bismuth box. The vestibule and bismuth boxes each consist of an automated rotating
drum assembly that allows the researchers to turn the beam on and off. The vestibule box
drum consists of, starting on the reactor side, a 2.54 cm (1.0 in) steel plate, a 0.635 cm (0.25
in) boral plate, a 11.43 cm (4.5 in) Pb plate, a 1.27 cm (0.5 in) steel sprocket, 7.62 cm (3.0 in)
of polyethylene, a 2.54 cm (1.0 in) Pb plate and a 2.54 cm (1.0 in) steel plate. The drum
rotates into an open position for “beam on” and a closed position for “sample load” and
“beam safe.” Rotation of each drum is controlled by a fiber optic limit switch.
(3) The neutron and gamma ray detection system: The detection system consists of four
rhodium self-powered neutron detectors (Rh-SPND), two fission chambers and in some
experiments a set of FarWest TM paired ion chambers. The Rh-SPND detectors are mounted
on the reactor side of the vestibule box. The fission chambers are located inside the detector
housing between the vestibule box and the bismuth crystal. The paired ion chambers, when
used, are mounted in the irradiation chamber and are used to measure the neutron and
photon dose at the sample position.
(4) The sample loading system: The sample loading system is designed to reproducibly
place targets in the irradiation position and minimize the gamma and neutron radiation fields
that researchers are exposed to in the “sample load” position. The irradiation chamber is 0.9
m (3 ft) wide and extends 0.9 m (3 ft) from the bismuth crystal housing. The loading system
is designed around a TL LS4-24 hydraulic lift table manufactured by Southworth. The lift
table is used to raise and lower a beam stop that incorporates approximately 910 kg (2000
lbs) of heavy concrete into the beam path during the “beam safe” and “sample load”
positions. In the “beam on” position the lift table collapses to the floor, placing the sample
position reproducibly into the beam.
(5) The gross shielding: The gross shielding design was largely based on prior facility
experience and MCNP5 scoping calculations of neutron and gamma ray radiation fields. The
large, periphery shield blocks are constructed of a steel frame, re-enforced with rebar and
filled with a seven bag concrete mix provided by the MU campus. Whenever structurally
possible the shield blocks that face the irradiation chamber were constructed of bare
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