Method for the detection of neutrons with scintillation detectors used for gamma ray spectroscopy

A method of measurement of both gamma radiation and neutrons with energies above 500 keV—fast neutrons—for the use in homeland security applications, preferably in portable handheld devices, utilizing a scintillation crystal, said scintillation crystal having a first light decay time (T1) following the interaction of a gamma quant with the scintillation crystal and a second and shorter light decay time (T2) following the interaction of a fast neutron with the scintillation crystal, a photo detector together with an amplifier, as well as sampling Analog to Digital Converters—ADC—and a digital signal processing device including a Multi-Channel-Analyzer, said devices selected in a way they are able to perform a pulse shape discrimination, being able to distinguish light decay times of a few nanoseconds up to several microseconds, and to process count rates of more than 10 counts per second for interactions of gamma quanta and of more than 1 count per second for interactions of neutrons with the scintillation crystal, comprising the steps of

• allowing gamma quanta and neutrons to interact with the scintillation crystal,
• collecting the light, emitted by the scintillation crystal, guiding it to a glass window optically coupled to the scintillation crystal and letting that light interact with a photo detector,
• amplifying the signal output from the photo detector with a suitable amplifier, preferably a photomultiplier tube—PMT—thus generating an amplifier output signal,
• digitizing the amplifier output signal,
• determining the charge collection time for each interaction measured,
• determining the light decay time of the scintillator from said charge collection time for each interaction measured,
• separating the signals with a first decay time (T1) from those with a second decay time (T2),
• determining the total charge (Q1) collected for each signal with a first decay time (T1), that total charge being a measure for the energy deposed in the scintillation crystal,
• sorting said total charge signals (Q1) in a spectrum, i.e. with by using a Multi-Channel-Analyzer (MCA), said spectrum representing the energy distribution of the gamma quants having deposed at least 10 keV and therefore at least a part of their energy in the scintillation crystal,
• counting the signals with a second decay time (T2) and determining the count-rate, that is the number of signals per given time interval, that count rate being a measure for the number of neutrons having deposed at least part of their energy in the scintillation crystal.