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Results of FlexiSpec for WBC @ JRC Ispra

In this news we present the official results of the background reduction obtained thanks to the CAEN FlexiSpec acquisition system installed at the Whole Body Counter (WBC) laboratory at the Joint Research Center (JRC) in Ispra.

The results of the upgraded WBC at JRC Ispra

The Whole Body Counter (WBC) at the Joint Research Centre (JRC) Ispra is an upgraded monitoring device available for European research in internal dosimetry.

A VETO anti-muonic system has been installed on the ceiling of the WBC and connected in anti-coincidence to four new detectors by interfacing with an Integrated Digital Acquisition System (IDAS) (CAEN FlexiSpec solution), permitting a reduction in the background level of more than 30%.

Moreover, using the new HpGe detector it’s possible to obtain MDA=24 Bq of 137Cs in a 20 min measurement, similar to Minimum Detectable Activity (MDA) using 203 mm (diam) x 102 mm NaI(Tl) (25 Bq), with better resolution.

The previous WBC and the upgrading

At first, only one NaI(Tl) detector composes the first version of the WBC.

Afterward, 3 HPGe detectors has been added to the system during some smaller upgrade.

However, two fully filled crates with analogical NIM electronics manages the four detectors.

The last update added a new NaI(Tl) detector read by 3 PMTs with a majority/add back logic and 11 plastic scintillators on the ceiling of the chamber to make anti-cosmic veto.

At the present time only one crate filled with VME multi-channel digital electronics composes the CAEN acquisition system and it manages:

  • 3 HPGe detectors
  • 3 PMTs to read-out 1 huge NaI(Tl) detector with majority and add-back logic
  • 11 plastic veto detectors in an anti-coincidence logic with the above listed detectors

All managed with a simple GUI on a PC.

But in addition to the ease of use, big goals regarding the spectroscopy results were targeted.

The addition of the 11 cosmic veto detectors was done to reduce the count rate of the spectroscopy detectors inside the lead chamber. The main goal was to enhance the Minimum Detectable Activity (MDA) with the same measurement time on a patient.

This challenge was really difficult because inside the lead chamber the count rate was only 3.5 Hz on a 124% efficiency HPGe detector.

CAEN FlexiSpec

CAEN acted as system integrator providing multichannel High Voltage, Low Voltage, preamp and MCA to perfectly manage heterogeneous detectors type (i.e. HPGe, NaI(Tl), plastic scintillators) coming from different providers.

FlexiSpec IDAS JRC Ispra

connection scheme FlexiSpec IDAS JRC Ispra

All the system is now managed by a unique electronic with a single software that allows to:

  • set independent voltage for each detector,
  • power on or shut down each detector
  • make independent energy calibration for each detector
  • set parameters (i.e. gain, shaping time, …) for each channel
  • set single channel or board logic (i.e. coincidence, anti-coincidence…)
  • make digital add back between selected channels

JRC Technical Report