New:
PLRF 19 code for fitting of positron lifetime - binaries are available for download.
Digital CDB spectrometer
![](images/digital_cdb_spectr.jpg)
Detector part of digital CDB spectrometer
-
first digital CDB spectrometer in the world (built in 2010)
-
detectors: Canberra coaxial HPGe detectors, relative efficiency 30, 35 %.
-
digitizer: Detector signals are sampled in the real time using two channel
digitizer Acqiris DC440 (12-bit, maximum sampling frequency 420 MHz)
![](images/digital_cdb_digitizer.jpg)
Two-channel 12-bit digitizer used for sampling of detector signals
-
operation: Digital CDB spectrometer can work in two modes:
- semi-digital setup - detector pulses are firstly shaped by pseudo-Gaussian filter in spectroscopy amplifier in order to improve the signal-to noise ration.
Output signals from spectroscopy amplifier with pseudo-Gaussian shape are sampled by digitizer. Acquired waveforms are analyzed by our software cmfit
- the maximum of sampled waveforms is determined by parabolic fitting;
- digital filters are engaged to examine shape of each waveform and reject pulses distorted by pile-up or by ballistic deficit.
- pure-digital setup - detector pulses (i.e. output of the charge sensitive preamplifier) are digitized directly. Sampled
waveforms are fitted by a model function
consisting of exponential decay function convoluted with a Gaussian.
-
software: Analysis of sampled waveforms is performed by software developed in our group.
-
resolution:
semi-digital setup: 0.99 KeV (at 511 keV)
pure-digital setup: 0.88 KeV (at 511 keV)
Full description of the digital spectrometer can be found in the following paper:
Our digital CDB spectrometer was succesfully employed for a precise low background measurement of positron annihlation-in-flight.
![](images/aif.jpg)
Two-dimensional CDB spectrum measured on Mg target using 68Ge/68Ga positron generator and showing the contribution from positron annihilation-in-flight