Re/Os Cosmochronometer: Measurement of Neutron Cross Sections

The Re/Os cosmochronometer is a dating technique based on the decay of 187Re into 187Os. It determines the age of the universe by the time of onset of nucleosynthesis. The nucleosynthesis mechanisms, which are responsible for the 187Re/187Os pair, provide the possibility to identify the radiogenic fraction of 187Os by nuclear physics considerations. The neutron capture cross sections averaged over the stellar conditions of the s-process are the input for the calculations of the 187Os abundance

Counting neutrons with a commercial S-CMOS camera

It is possible to detect individual flashes from thermal neutron impacts in a ZnS scintillator using a CMOS camera looking at the scintillator screen, and off line image processing. Some preliminary results indicated that the efficiency of recognition could be improved by optimizing the light collection and the image processing. We will report on this ongoing work which is a result from the collaboration between ESS Bilbao and the ILL. The main progress to be reported is situated on the level of the on-line treatment of the imaging data. If this technology is to work on a genuine scientific instrument, it is necessary that all the processing happens on line, to avoid the accumulation of large amounts of image data to be analyzed off line. An FPGA-based real-time full-deca mode VME-compatible CameraLink board has been developed at the SCI of the ILL, which is able to manage the data flow from the camera and convert it in a reasonable “neutron impact” data flow like from a usual neutron counting detector. The main challenge of the endeavor is the optical light collection from the scintillator. While the light yield of a ZnS scintillator is a priori rather important, the amount of light collected with a photographic objective is small. Different scintillators and different light collection techniques have been experimented with and results will be shown for different setups improving upon the light recuperation on the camera sensor. Improvements on the algorithm side will also be presented. The algorithms have to be at the same time efficient in their recognition of neutron signals, in their rejection of noise signals (internal and external to the camera) but also have to be simple enough to be easily implemented in the FPGA. The path from the idea of detecting individual neutron impacts with a CMOS camera to a practical working instrument detector is challenging, and in this paper we will give an overview of the part of the road that has already been walked

Blind Benchmark Exercise for Spent Nuclear Fuel Decay Heat

The decay heat rate of five spent nuclear fuel assemblies of the pressurized water reactor type were measured by calorimetry at the interim storage for spent nuclear fuel in Sweden. Calculations of the decay heat rate of the five assemblies were performed by 20 organizations using different codes and nuclear data libraries resulting in 31 results for each assembly, spanning most of the current state-of-the-art practice. The calculations were based on a selected subset of information, such as reactor operating history and fuel assembly properties. The relative difference between the measured and average calculated decay heat rate ranged from 0.6% to 3.3% for the five assemblies. The standard deviation of these relative differences ranged from 1.9% to 2.4%

Fast neutron coincidences from induced fission as a method for detection of SNM

A method for the detection of special nuclear materials (SNM) in shielded containers which is both sensitive and easily applicable under field conditions is presented. The method applies neutron induced fission in SNM by means of an external pulsed neutron source with subsequent detection of the fast prompt fission neutrons. Liquid scintillation detectors surrounding the container under investigation are able to discriminate gamma rays from fast neutrons by the so-called pulse shape discrimination technique (PSD). One advantage of these detectors, besides the ability to do PSD analysis, is that the analogue signal from a detection event is of very short duration (typically few tens of nanoseconds). This allows the use of very short coincidence gates for multiple detectors for the detection of prompt neutrons from the same fission event while benefiting from a low accidental (background) coincidence rate. These features result in a relatively low detection limit of the fissile mass. Another principal advantage of this method derives from the fact that the external neutron source is pulsed. By proper time gating the interrogation can be done by either epi-thermal or thermal neutrons. These source neutrons do not appear in the neutron signal following the PSD analysis thus providing a fundamental method for separating the interrogating source neutrons from the response in form of fast fission neutrons. The paper describes laboratory tests with multiple detectors at the Pulsed Neutron Interrogation Test Assembly (PUNITA) for the purpose of investigating the measurement principle. Results of thermal and epi-thermal neutron interrogations are shown and discussed.JRC.E.8-Nuclear securit

Counting neutrons with a commercial S-CMOS camera

It is possible to detect individual flashes from thermal neutron impacts in a ZnS scintillator using a CMOS camera looking at the scintillator screen, and off line image processing. Some preliminary results indicated that the efficiency of recognition could be improved by optimizing the light collection and the image processing. We will report on this ongoing work which is a result from the collaboration between ESS Bilbao and the ILL. The main progress to be reported is situated on the level of the on-line treatment of the imaging data. If this technology is to work on a genuine scientific instrument, it is necessary that all the processing happens on line, to avoid the accumulation of large amounts of image data to be analyzed off line. An FPGA-based real-time full-deca mode VME-compatible CameraLink board has been developed at the SCI of the ILL, which is able to manage the data flow from the camera and convert it in a reasonable “neutron impact” data flow like from a usual neutron counting detector. The main challenge of the endeavor is the optical light collection from the scintillator. While the light yield of a ZnS scintillator is a priori rather important, the amount of light collected with a photographic objective is small. Different scintillators and different light collection techniques have been experimented with and results will be shown for different setups improving upon the light recuperation on the camera sensor. Improvements on the algorithm side will also be presented. The algorithms have to be at the same time efficient in their recognition of neutron signals, in their rejection of noise signals (internal and external to the camera) but also have to be simple enough to be easily implemented in the FPGA. The path from the idea of detecting individual neutron impacts with a CMOS camera to a practical working instrument detector is challenging, and in this paper we will give an overview of the part of the road that has already been walked

Counting neutrons with a commercial S-CMOS camera

It is possible to detect individual flashes from thermal neutron impacts in a ZnS scintillator using a CMOS camera looking at the scintillator screen, and off line image processing. Some preliminary results indicated that the efficiency of recognition could be improved by optimizing the light collection and the image processing. We will report on this ongoing work which is a result from the collaboration between ESS Bilbao and the ILL. The main progress to be reported is situated on the level of the on-line treatment of the imaging data. If this technology is to work on a genuine scientific instrument, it is necessary that all the processing happens on line, to avoid the accumulation of large amounts of image data to be analyzed off line. An FPGA-based real-time full-deca mode VME-compatible CameraLink board has been developed at the SCI of the ILL, which is able to manage the data flow from the camera and convert it in a reasonable “neutron impact” data flow like from a usual neutron counting detector. The main challenge of the endeavor is the optical light collection from the scintillator. While the light yield of a ZnS scintillator is a priori rather important, the amount of light collected with a photographic objective is small. Different scintillators and different light collection techniques have been experimented with and results will be shown for different setups improving upon the light recuperation on the camera sensor. Improvements on the algorithm side will also be presented. The algorithms have to be at the same time efficient in their recognition of neutron signals, in their rejection of noise signals (internal and external to the camera) but also have to be simple enough to be easily implemented in the FPGA. The path from the idea of detecting individual neutron impacts with a CMOS camera to a practical working instrument detector is challenging, and in this paper we will give an overview of the part of the road that has already been walked

SNM detection by means of thermal neutron interrogation and a liquid scintillation detector

The feasibility of using a pulsed neutron generator in a graphite assembly together with a single liquid scintillation detector for the detection of special nuclear materials is investigated. Thermal source neutrons induce fission in fissile material present in the sample. By means of pulse shape discrimination the detector signals from fast fission neutrons are easily identified among the signals from gamma rays and the interrogating thermal neutrons. The method has potential in applications for detection of special nuclear materials in shielded containers.JRC.E.8-Nuclear securit

A Method for Detection of SNM by Pulsed Neutron Interrogation

We present a method for the detection of special nuclear materials (SNM) in shielded containers which is both sensitive and applicable under field conditions. The method uses an external pulsed neutron source to induce fission in SNM and subsequent detection of the fast prompt fission neutrons. The detectors surrounding the container under investigation are liquid scintillation detectors able to distinguish gamma rays from fast neutrons by means of the pulse shape discrimination method (PSD). One advantage of these detectors, besides the ability for PSD analysis, is that the analogue signal from a detection event is of very short duration (typically few tens of nanoseconds). This allows the use of very short coincidence gates for the detection of the prompt fission neutrons in multiple detectors while benefiting from a low accidental (background) coincidence rate yielding a low detection limit. Another principle advantage of this method derives from the fact that the external neutron source is pulsed. By proper time gating the interrogation can be conducted by epithermal and thermal source neutrons only. These source neutrons do not appear in the fast neutron signal following the PSD analysis thus providing a fundamental method for separating the interrogating source neutrons from the sample response in form of fast fission neutrons. The paper describes laboratory tests with a configuration of eight detectors in the Pulsed Neutron Interrogation Test Assembly (PUNITA). The sensitivity of the coincidence signal to fissile mass is investigated for different sample and configurations and interrogation regimes. For the purpose of estimating performance values for a scaled-up facility for investigation of air cargo, Monte Carlo simulations of both the experimental configuration and the scaled-up facility were carried out. Preliminary results of this study are also reported.JRC.E.8-Nuclear securit

Detection of Combined n/γ Fission Signatures Induced by an Epithermal Neutron Source

In this paper, a method is presented for the detection of special nuclear materials (SNMs) in shielded containers, which is both sensitive and applicable under field conditions. The method uses an external pulsed neutron source to induce fission in SNM and subsequent detection of the fast prompt fission neutrons. The detectors surrounding the container under investigation are liquid scintillation detectors able to distinguish gamma rays from fast neutrons by means of pulse shape discrimination method (PSD). One advantage of these detectors, besides the ability for PSD analysis, is that the analog signal from a detection event is of very short duration (typically few tens of nanoseconds). This allows the use of very short coincidence gates for the detection of the prompt fission neutrons in multiple detectors, while benefiting from a low background coincidence rate, yielding a low detection limit. Another principle advantage of this method derives from the fact that the external neutron source is pulsed. By proper time gating, the interrogation can be conducted by epithermal source neutrons only. These neutrons do not appear in the fast neutron signal following the PSD analysis, thus providing a fundamental method for separating the interrogating source neutrons from the sample response in the form of fast fission neutrons. This paper describes laboratory tests with a configuration of eight detectors in the Pulsed Neutron Interrogation Test Assembly (PUNITA). Both the photon and neutron signature for induced fission is observed, and the methods used to isolate these signatures are described and demonstrated.JRC.G.II.7-Nuclear securit

Blind Benchmark Exercise for Spent Nuclear Fuel Decay Heat

International audienceThe decay heat rate of five spent nuclear fuel assemblies of the pressurized water reactor type were measured by calorimetry at the interim storage for spent nuclear fuel in Sweden. Calculations of the decay heat rate of the five assemblies were performed by 20 organizations using different codes and nuclear data libraries resulting in 31 results for each assembly, spanning most of the current state-of-the-art practice. The calculations were based on a selected subset of information, such as reactor operating history and fuel assembly properties. The relative difference between the measured and average calculated decay heat rate ranged from 0.6% to 3.3% for the five assemblies. The standard deviation of these relative differences ranged from 1.9% to 2.4%