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

Outline: Story of GEROS Motivation Characterization Techniques Simulations Conclusion

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

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

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

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):

IAEA Ref.154, C. Potiriadis Weight (g) Element Energy (keV) ε (%) δε (%) 3.245 137Cs 661.75 2.78 0.04 40Κ 1460.97 2.03 2.956 661.38 1.96 1461.29 1.43 19.781 661.68 1.427 0.012 1460.84 0.361 0.007 32.736 661.7 1.192 0.009 1460.83 0.228 0.004 92.48 661.71 1.155 0.011 0.125 IAEA Ref.154, C. Potiriadis

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

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

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

Reconstructed 3D model

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

The crystal appears to be tilted 25 mm 21 mm 18 mm 19 mm

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

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

MCNP simulation Eu-152 964 keV

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

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

Thank you for your attention!

Additional slide The inside-out of the detector