The ANTECH Model 2108-G Combined Plutonium Scrap Multiplicity Counter & High Resolution

Gamma Spectrometer combines the Model 2108 plutonium scrap multiplicity counter and a high

resolution gamma spectrometer for fast and accurate determination of the plutonium content of scrap

and residues. Combining the two instruments saves considerably on measurement time and reduces

dose to operators through reduced handling of sample containers.

The neutron component performs passive neutron multiplicity counting whereby the moments of the

neutron probability distribution are used to determine the number of totals, doubles and triple coinci-

dences used to solve the point source model for three unknown parameters: spontaneous fission rate,

the detection probability, the source term (or multiplication, as appropriate) thus yielding the 240Puef-

fective mass (see Data Sheet for the PSMC Model 2108 for more details). The PSMC can be operated

using either the Time Correlation Analyzer or the Advanced Multiplicity Shift Register.

The neutron measurement requires knowledge of the Pu isotopic ratio (and 241Am content) at various

stages of the calculations in order to convert the measured 240Pueffective content from the passive neu-

tron system to a total Pu mass. Viewing the sample through a collimator in the bottom end plug of

the measurement chamber, a High Purity Germanium (HPGe) detector measures the relative intensi-

ties of gamma rays from the gamma ray spectrum of a plutonium-bearing sample. The isotopic ratios

are obtained using only spectral data and known fundamental nuclear constants. The atom ratio of

pairs of isotopes (at known energies) are related to the relative counting intensities for those gamma

rays, given the relevant known branching ratios, half-lives and detection efficiencies. The analysis

codes de-convolute the spectra to produce isotopic ratios independent of sample size, shape, packag-

ing, and physical and chemical composition; no calibration with standards is necessary.

Two types of analysis codes available are: a) PC/FRAM: developed by the Los Alamos National

Laboratory and licensed to ANTECH Corporation, and b) MGA: developed at the US DOE

Lawrence Livermore National Laboratory and licensed to ANTECH's strategic alliance partner

Ametek-ORTEC for use in non-destructive assay equipment. Safeguards coaxial detector is used if

PC-FRAM is selected and a planar detector if MGA is used.