1. Full characterization of an old HPGe detector (GEROS)
V. Angelopoulou
E. Kouvaris
V. Lagaki
T.J. Mertzimekis
P. Papagiannis

2. Outline: Story of GEROS Motivation Characterization Techniques
Simulations
Conclusion

3. What is GEROS GEROS stands for Germanium for Environmental
RadiOactivity Studies
An old, p-type, 20% HPGe detector, coaxial crystal geometry
Has already been used for some environmental γ-ray spectroscopy

4. Why ? Only information available:
A full characterization was needed before putting it back to operation
14 mm
53.6 mm
48.6 mm
53.4 mm

5. At 15 cm :
Sources
60Co
137Cs
152Eu
226Ra

6. Fit with 2nd order polynomial E = A+B(chn)+C(chn)2
Linearity:
152Eu, 15 cm
Parameters
Curve fit A
9.2 B
0.6435 C
9.2∙10-8
Resolution
(FWHM):

8. IAEA Ref.154, C. Potiriadis Weight (g) Element Energy (keV) ε (%)
δε (%)
3.245
137Cs
661.75
2.78
0.04
40Κ
2.03
2.956
661.38
1.96
1.43
19.781
661.68
1.427
0.012
0.361
0.007
32.736
661.7
1.192
0.009
0.228
0.004
92.48
661.71
1.155
0.011
0.125
IAEA Ref.154, C. Potiriadis

9. The experimental setup
Liquid N2
Dewar container
Alignment
laser
Pb collimator
134Cs source
Shield consists of four 5-cm thick Pb bricks:
2 used for vertical dimension and 2 for parallel
3 x 3 mm2 collimation hole
X-Y motion
platform

10. The 134Cs spectrum (t1/2 = 2.0652 y) Δt = 10 min
The energy spectrum of 134Cs, from GEROS, taken at (x,y)=(0,0) position More than 700 spectra were collected and analyzed
Δt = 10 min
SpectrW, C.Kalfas

11. Results of gamma ray tomography
Diagrams of counts in a vertical scanning, for fixed x position
x = -9 mm
x = -3 mm
x = 0 mm
x = 3 mm
x = 6 mm
x = 9 mm
Diagrams of counts in a horizontal scanning, for fixed y position
y = -12mm
y = -6 mm
y = -3 mm
y = 0 mm
y = 3 mm
y = 9 mm

12. Reconstructed 3D model

13. Study of the results
Estimation of the center of the crystal : (0, -2)

14. The crystal appears to be tilted
25 mm mm
18 mm mm

15. Estimation of the crystal’s diameter
Int. Diam.: 8 ± 1.5 mm Int. Diam.: 12 ± 3 mm
Ext. Diam.: 46 ± 1.5 mm Ext. Diam.: 48 ± 3 mm

16. Can we confirm this? GEROS was CT scanned (X-ray Computed Tomography)
Front view
GEROS was CT scanned (X-ray Computed Tomography)
Side view
Full view

17. MCNP simulation
Eu keV

18. Conclusions An old HPGe detector was put back
to operation and fully characterized
From γ-ray and CT tomographies the exact geometry was deduced and fully reconstructed in 3D
The detector has suffered some loss of efficiency due to prolonged inactivity (dead layer built up)
MCNP simulations have been performed and found to agree well with the experimental data
Efficiencies for several bulk sample geometries were estimated by means of an IAEA reference material
Overall the detector can be used for γ-ray spectroscopy and educational activities at UoA

19. Thanks to The TANDEM accelerator staff, and especially Dr. M.Axiotis
The Lefkos Stavros hospital and staff
Dr. C.Potiriadis for the IAEA reference material
Dr. C.Kalfas for SpectrW licences

20. Thank you for your attention!

21. Additional slide The inside-out of the detector