Concerning the detection of photons, the conventional gamma-ray detectors with high energy resolution such as Ge detectors, are not suitable for the measurements in the neutron environment.
The selected counters for detecting the photons emitted by the de-excitation of Pa* were liquid scintillators of CD type used as total energy detectors with the application of a weighting method. It is important that the detection efficiency of photons be independent of the detected photon energy.
For each detected event, one must multiply the height of the registered pulse by the quantity that was defined beforehand in such a manner that the detection efficiency for the (n,γ) capture reaction was proportional to the total energy of the de-excitation cascade which is constant.
In the first stage, (see the publication Nucl. Inst. and Meth. A511 (2003) 388) we studied at CENBG the response of CD detector to monoenergetic photons in the region of γ-ray energies 100 keV - 6 MeV using radioactive sources and reactions (p,γ) on light nuclei. The obtained results were compared to the calculation of the simulation with MCNP code. The excellent agreement between experiment and simulation is the proof that the functioning of these detectors was perfectly understood.
We have constructed by interpolation the response matrix ranging from 100 keV to 6 MeV from which the weighting functions were determined through least squares procedure.
This preliminary work was followed by the experiment Th(He,p)Pa* that was realized with a He beam of 24 MeV obtained from the Tandem accelerator of Orsay. The Pa nucleus was identified from the detection of the associated proton in one of four E-E telescopes. Gamma-rays were detected in coincidence with charged particles by one of four CD detectors placed around the reaction chamber. The measurements were carried out in neutron energy range 0-1 MeV.
The closed reaction chamber surrounded by 4 CD detectors
The open reaction chamber: to the left - the back view of the chamber, to the right - the front view with installed telescopes and target.
For more information, see the publication (Nucl. Phys. A 775 (2006) 175)