Proton Recoil and Other Spectrometers - doe-std-1128-98

DOE-STD-1128-98

Figure 6.5.

Neutron Energy Spectra as Measured by the Multisphere Spectrometer a

50 cm from Plutonium Metal, PuO2, and PuF4 Sources

The liquid scintillator spectrometer has the advantage that it is very

sensitive and can operate at low dose rates. It is useful over an energy

range extending from about 1 MeV to 20 MeV. Neutron dose equivalent

can be calculated from the measured spectra using the conversion factors

given in the Implementation Guide, External Dosimetry Program (DOE,

1999e). The dose equivalents calculated from liquid scintillator

measurements are reasonably accurate (10% to 20%) for lightly

moderated plutonium spectra. Because of the lower energy cut-off of

liquid scintillator spectrometers, they may not provide accurate dose

equivalent values outside heavily shielded facilities, such as plutonium

storage vaults with thick concrete walls.

6.3.6.4 Proton Recoil and Other Spectrometers

There are a number of other spectrometer systems that are available that

have been used successfully for neutron spectral measurements in the

field. Of particular interest is a spectrometer employing five different

proton recoil proportional counters filled with gasses at different

pressures. Each counter measures a different portion of the neutron

spectrum, and quite accurate spectra can be obtained by "linking" all the

measurements together. Unfortunately, this type of spectrometer is quite

expensive, bulky, and difficult to use for workplace measurements.

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