Newly developed irradiation facility at LAMPF Page: 4 of 14
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moving into the nozzle. This method has a sensitivity of about 25 x 10-6 in.
LVDTts have been used successfully at LASL and also by Dr. T. Blewitt (3) at
Argonne for measuring small strains during irradiation. Instead of using
the usual constant voltage system, a constant current method is employed. This
eliminates errors caused by electrical resistance changes.
At the present time, a 50-channel multiplexer, pneumatic controllers, a
200-channel Dymec Acquisition System, and several Brown recorders are available
for use by the experimenter on a priority basis.
Dosimetry considerations within the Radiation Damage Working Group have been
formalized into a Dosimetry Committee which met twice in November, 1972. Multi-
ple foil activation and spectrum unfolding is one method of neutron dosimetry
which is actively being pursued. Two members of the Committee, Dr. N. D. Dudey
of AIL and Dr. D. M. Parkin of BIL, are developing such dosimetry methods for
the Brookhaven Linear Isotope Producer (BLIP) and their work is expected to be
directly applicable to the LAMPF facility. Also, a program at Los Alamos
Scientific Laboratory is simultaneously establishing a multiple foil activation
and unfolding program for LAMPF based upon well established fission reactor
methods, using the SAND-II unfolding code.
In addition to foil activation methods, we plan to do time-of-flight measure-
ments. A time-of-flight (T-o-F) tube is installed at 1350 from the proton-beam
direction and can be used for neutron spectrum calibration from <100 keV to ~100
MeV. Comparisons of multiple-foil unfolded spectra will also be made with the
T-0-F tube for a 200-MeV proton beam incident on a beryllium target, in support
of the BLIP program. In addition, serious consideration is being given to using
a self-contained T-0-F spectrometer developed by Madey and Waterman. (5) Briefly,
this spectrometer measures the time-of-flight for neutrons scattered at a known
angle, using the time interval between pulses in two scintillators, the first
scintillator being also the scatterer. Madey and Waterman have used this "two-
fold coincidence spectrometer" to measure neutron spectra in the 1 to 500 1MeV
region,using 1- to 5-meter flight paths. Perhaps such a spectrometer could be
used for routine neutron flux monitoring at the LAM2F Radiation Effects Facility, .
as well as for calibration of spectra unfolded from foil activations.
Although gamma-ray flux levels are expected to be low based upon the results
of Fullwood, et al. (6) (e.g., one escaping photon per 12 escaping neutrons for
a 15-cm diameter 48 target), simple gamma-ray dose measurements will be made
at the radiation damage experimental locations. Such measurements, using silver
phosphate glass or other integral dosimeters, should provide reasonable estimates
of gamma-ray heating to be expected in the metallurgical experiments. Most of
the gamma rays considered by Fullwood, et al. arise from non-elastic neutron
interactions with the target and surrounding media; additional capture gamma rays
will originate in the predominantly steel and concrete shielding surrounding the
radiation damage facility.
Dosimetry requirements at the LAMIPF Radiation Damage. Facility can be classed
in two general categories; viz., irradiation cavity flux mapping and calibration-
performed by LASL in implementing the facility, and monitoring of individual
experiment exposures - performed by the experimenter with LASL support.
As soon as possible after sufficient beam current is available, mapping of
the irradiation cavity fluxes by multiple foil activation will commence. The
foils (actually foils and wires, referred to generically as foils) will be posi-
tioned on the three-dimensional aluminum grid to obtain reliable data on the
spatial distribution of the neutron flux absolute intensity and spectrum. One
perturbation which may be studied by 3-D foil activation maps is that due to the
presence of the 'radiation damage test furnaces. Present plans call for using
about 10 different types of foils in each packet, covering the energy range from
0 to 30 MeV, The 3-D grid will enable simultaneous neutron spectrum measure-
ments at all the spatial grid points. Gama-ray dosimeters will also be located
at selected grid points. In unfolding the neutron flux spectrum, advantage will
be taken of the AijL-BWL Nxzerience with BLIP dbsimetry below 13 MeV as well as
LASL experience with carbon and bismuth foils for neutron energies up to 30 MeV.
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Dudziak, D.J.; Green, W.V.; Regenie, T.R. & Zukas, E.G. Newly developed irradiation facility at LAMPF, article, October 31, 1973; New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc1028763/m1/4/: accessed April 22, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.