1. Analysis of a gamma spectrum: -Identification and evaluation Henrik Ramebäck (FOI) Trygve Bjerk (IFE)

2. The spectrum
Some significant peaks:
129 keV
414 keV
375 keV
60 keV

3. The low E region
51.62 keV
45.24 keV
38.66 keV

4. Identification Eg (keV) Possible ID 413.71 Pu-239 375.05 129.30 38.66
51.62
45.24
Pu-240
59.54
Am-241
Also 662 keV: Am-241 or Cs-137?
The major part of the peak seems to be from Cs-137

5. Activities
From the calibration data the efficiencies can be calculated, and thereafter the activities… -APu239=(10.55±0.60) kBq (using the keV line) -AAm241=(134.2±7.0) Bq (using the 59.5 keV line)
Am-241: What about U-237 in Pu materials? Pu-241 decay to either Am-241 (beta minus, %) or to U-237 (alpha, %). Both daughters go to Np-237 Many gamma energies in common! Some unique though… So, how much comes from Am-241 in a specific peak?

6. U-237 in Pu materials
59.54 keV: >99% after about 1.3 y

7. Isotopic composition (Low E region)
Eg (keV)
Possible ID
38.66
Pu-239
45.24
Pu-240
51.62
Possible to evaluate the 239/240 isotope ratio…

8. Isotopic composition 
239Pu: keV ( %) and keV ( %)
240Pu: keV (0.0462%)
Internal response via keV and keV: InterpolationThe keV!!! Activity ratio: 240/239=(NA45keV/(Eff45keV·I45keV))/(NA52keV/(Eff52keV·I52keV)) Isotope ratio, R240/239=Activity ratio·l240/l239 Abundance, f240=R240/239/(1+R240/239); f239=1/(1+R240/239) (If we only consider 240Pu och 239Pu) [In general: fi=Ri/(SRi), OBS: Ri for the ’reference isotope’=1, i.e. R239/239=1, since R239/239=n239/n239] 
(98.71±0.10)% 239Pu, (1.29±0.10)% 240Pu Super grade Pu (SGPu), i.e. very low burn-up…
[Assuming the same response at keV as at keVabout 11% error!]

9. Isotopic composition (alternative approach)
Isotopic composition using the calibration data: Efficiencies at and keV, peak areas and photon emission probabilities: f240=(1.11±0.10)%
[A small residual difference between the two methods…]