System and method to count neutrons
A radiation detection system and a method for a parallel detection of gamma-rays and neutrons are provided, comprising a gamma-ray detector comprising a scintillator crystal comprising 127 I, a digitizer to generate digitized time series and an analyzer, characterized in that the analyzer is adapted to identify a primary signal component, a first delayed signal component and a second delayed signal component in the digitized time series. The first and second delayed signal components, respectively, correspond to an energy deposition of about 30 keV and about 138 keV, and follow the primary and first delayed signal components in time. The analyzer is further adapted to count the number of digitized time series comprising at least the first and the second delayed signal components as neutron events, thereby providing a measure for a neutron flux the scintillator crystal is exposed to.
1 . A radiation detection system for a parallel detection of gamma rays and neutrons, comprising:
a gamma-ray detector comprising a scintillator crystal comprising 127 I and a photodetector with an amplifier, wherein the scintillator crystal is adapted to convert energy deposited by gamma rays or conversion electrons to optical photons, wherein the photodetector is adapted to convert the optical photons to an electrical signal and the amplifier is adapted to amplify the electrical signal, and wherein the electrical signal is in a known relationship with the energy deposited by the detected gamma rays or conversion electrons in the scintillator crystal;
a digitizer comprising sampling an analog to digital converter (ADC) wherein said digitizer is adapted to sample the electrical signal of said gamma-ray detector with a predetermined frequency of at least 20 mega samples per second to generate digitized time series of the electrical signal; and,
an analyzer operatively coupled to said digitizer, wherein said digitizer is adapted to transmit the digitized time series to the analyzer, and wherein the analyzer is adapted to analyze the digitized time series in order to identify signal components in the digitized time series with time delays of at least 20 ns and at most 10 μs between consecutive signal components, wherein each signal component is due to an energy deposition in the scintillator, wherein the analyzer is further adapted to:
identify a primary signal component in the digitized time series corresponding to an energy deposition E 0 in a predefined range;
identify a first delayed signal component in the digitized time series, wherein the first delayed signal component corresponds to an energy deposition E 1 ranging between 15 keV and 50 keV; and,
identify a second delayed signal component in the digitized time series, after the first primary signal component, wherein the second delayed signal component corresponds to an energy deposition E 2 ranging between 100 keV and 200 keV; and occurring after the first delayed signal component, and;
count the number of digitized time series comprising at least the first delayed signal component and the second delayed signal component as neutron events, thereby providing a measure for a neutron flux exposure to the scintillator crystal.
2 . The radiation detection system of claim 1 , wherein the analyzer is further adapted to:
quantify at least one event parameter of a group of event parameters for each of said digitized time series, wherein the group of event parameters comprises at least one of: a time difference between said primary signal component and said first delayed signal component, a time difference between said primary component and said second delayed signal component, a time difference between said first delayed signal component and said second delayed signal component, the energy deposition in the scintillator crystal corresponding to the primary signal component, the energy deposition in the scintillator crystal corresponding to the first delayed signal component, and the energy deposition in the scintillator crystal corresponding to the second delayed signal components;
evaluate for each of said digitized time series whether at least one event parameter of the group of event parameters fulfills a predefined criteria to classify said digitized time series as a neutron event; and
count the number of digitized time series classified as a neutron event, thereby providing a measure for the neutron flux exposure to the scintillator crystal.
3 . The radiation detection system of claim 2 , wherein the photomultiplier tube comprises a super-bialkali photokathode or an ultra-bialkali photokathode.
4 . The radiation detection system of claim 1 , wherein the photodetector of the gamma-ray detector is a photomultiplier tube, a silicon photomultiplier (SiPM), or an avalanche photodiode.
5 . The radiation detection system of claim 1 , wherein said scintillator crystal is at least one of a NaI crystal or a CsI crystal.
6 . The radiation detection system of claim 5 , wherein said scintillator crystal is a NaI crystal with Tl doping.
7 . The radiation detection system of claim 5 , wherein said scintillator crystal is a CsI crystal with at least one of Na or Tl doping.
8 . The radiation detection system of claim 5 , wherein said scintillator crystal is a NaI crystal with Tl doping and a co-dopant of at least one of Li or B.
9 . The radiation detection system of claim 1 , wherein the gamma-ray detector, the digitizer and the analyzer are configured in a handheld device.
10 . The radiation detection system of claim 1 , wherein the gamma-ray detector, the digitizer and the analyzer are configured in a backpack.
11 . The radiation detection system of claim 1 , wherein the first delayed signal component corresponds to an energy deposition E 1 of about 30 keV.
12 . The radiation detection system of claim 1 , wherein the second delayed signal component corresponds to an energy of about 138 keV.
13 . A method to detect neutrons and gamma rays, comprising a gamma-ray detector including a 127 I scintillator crystal and a photodetector with an amplifier, a digitizer comprising an analog to digital converter (ADC) and, an analyzer operatively coupled to said digitizer, wherein the method comprises the following steps:
generating 128 I upon neutron capture of neutrons interacting with 127 I of the scintillator crystal, wherein 128 I de-excites both under a prompt emission of gamma radiation and at least partially via at least one long-lived excited state feeding another long-lived excited state, which at least sometimes leads to two delayed energy depositions in the scintillator crystal corresponding to two delayed de-excitation steps producing either conversion electrons or gamma radiation interacting with the scintillator crystal, following a primary signal component which is due to the prompt emission;
generating, by said gamma ray detector, an electrical signal in succession of an interaction between gamma rays or conversion electrons and said scintillator crystal, wherein said electrical signal is in a known relationship with the energy deposited by the detected gamma rays or conversion electrons in said scintillator crystal;
sampling, by said digitizer, the electrical signal of said gamma-ray detector with a predetermined frequency of at least 20 mega samples per second to generate a digitized time series of the detected gamma rays, and transmitting the digitized time series to the analyzer;
identifying, by said analyzer, a primary signal component in the digitized time series corresponding to an energy deposition E 0 in a predefined range;
searching, by said analyzer, for a first delayed signal component in the digitized time series, wherein the first delayed signal component corresponds to an energy deposition ranging between 15 kV and 50 keV, and following the primary signal in time;
searching, by said analyzer, for a second delayed signal component, wherein the second delayed signal component corresponds to an energy deposition ranging between 100 keV and 200 keV; and
counting, by said analyzer, the number of digitized time series comprising at least the first delayed signal component and the second delayed signal component as neutron events, thereby providing a measure for the neutron flux exposure to the scintillator crystal.
14 . The method of claim 13 , wherein the analyzer is further configured to:
quantify at least one event parameter of a group of event parameters for each of said digitized time series, the group of event parameters comprising at least one of: a time difference between said primary signal component and said first delayed signal component, a time difference between said primary component and said second delayed signal component, a time difference between said first delayed signal component and said second delayed signal component, the energy deposition in the scintillator crystal corresponding to the primary signal component, the energy deposition in the scintillator crystal corresponding to the first delayed signal component, the energy deposition in the scintillator crystal corresponding to the second delayed signal components;
evaluate, for each of said digitized time series, whether at least one event parameter of the group of event parameters fulfills a predefined criteria to classify said digitized time series as a neutron event; and
count the number of digitized time series classified as neutron a event, thereby providing a measure for the neutron flux exposure to the scintillator crystal.
15 . The method of claim 14 , wherein said analyzer is further configured to finds and identify at least one delayed signal component in said digitized time series by means of pulse pile-up reconstruction techniques and decompose the digitized time series comprising piled-up signal components, thereby quantifying at least one of the group of event parameters.
16 . The method of claim 13 , wherein said analyzer is further configured to:
identify a second primary signal component in the digitized time series corresponding to an energy deposition in a predefined range;
search for a delayed signal component in the digitized time series, wherein the delayed signal component corresponds to an energy deposition ranging between 100 keV and 200 keV; and,
quantify at least one event parameter of the group of event parameters for each of said digitized time series, wherein the group further comprises at least one of: a time difference between said primary component and said delayed signal component, the energy deposition in the scintillator crystal corresponding to said primary signal component, and the energy deposition in the scintillator crystal corresponding to said delayed signal components,
evaluate, for each of said digitized time series, whether at least one event parameter of the group of event parameters fulfills a predefined criteria to classify said digitized time series as a thermal neutron event; and,
count the number of digitized time series classified as a neutron event, thereby providing a measure for the neutron flux exposure to the scintillator crystal.
17 . The method of claim 13 , wherein the first delayed signal component corresponds to an energy deposition E 1 of about 30 keV and wherein the second delayed signal component corresponds to an energy of about 138 keV.
18 . The method of claim 13 , wherein the scintillator crystal is adapted to convert energy deposited by gamma rays or conversion electrons to optical photons, wherein the photodetector is adapted to convert the optical photons to an electrical signal, wherein the amplifier is adapted to amplify the electrical signal, and wherein the electrical signal is in a known relationship with the energy deposited by the detected gamma rays or conversion electrons in the scintillator crystal.
19 . The method of claim 13 , wherein the digitizer comprises an analog to digital converter (ADC), and wherein said digitizer is adapted to sample the electrical signal of said gamma-ray detector with a predetermined frequency of at least 20 mega samples per second to generate digitized time series of the electrical signal.
20 . The method of claim 13 , wherein the analyzer is operatively coupled to said digitizer, wherein said digitizer is adapted to transmit the digitized time series to the analyzer, wherein the analyzer is adapted to analyze the digitized time series in order to identify signal components in the digitized time series with time delays of at least 20 ns and at most 10 μs between consecutive signal components, and wherein each signal component is due to an energy deposition in the scintillator.