In situ gamma spectrometry at low energies - Semi-empirical calibration of a semi-planar HPGe-detector for measurements in close geometrics


  • Angelica Hedman
  • Micael Granström
  • Lennart Johansson
  • Göran Ågren
  • Henrik Ramebäck

Publish date: 2019-03-25

Report number: FOI-R--4729--SE

Pages: 45

Written in: Swedish


  • gamma spectrometry
  • semi-planar HPGe
  • semi-empirical calibration
  • low energies
  • Monte Carlo simulations


A GEM-SP HPGe detector has been characterized and calibrated for in situ measurements of low energy gamma radiation in close geometries. The detector has a thin window and a thin wide crystal, which is optimal when measuring low energy photons. Within this project, the following steps have been carried out: 1. A detailed detector model has been created in MCNP based on data from the manufacturer in combination with data from computed tomography (CT). 2. An efficiency calibration was obtained through measurement in close geometry with a calibration solution on the detector window. 3. Measurements have also been conducted with point sources with different energies and angles of incidence between 0 and 90 degrees to measure the response at different angles. 4. An improved detector model has been created through comparisons of empirical efficiencies and Monte Carlo simulations. 5. Verification of the calibration has been performed through measurements on a calibrated surface traceable to a primary activity standard.