Ilan Mor

Detectors for energy-resolved fast-neutron imaging

Two detectors for energy-resolved fast-neutron imaging in pulsed broad-energy neutron beams are presented. The first one is a neutron-counting detector based on a solid neutron converter coupled to a gaseous electron multiplier. The second uses an integrating imaging technique, based on a scintillator for neutron conversion and an optical imaging system with fast framing capability.

Low-Afterglow, High-Refractive-Index Liquid Scintillators for Fast-Neutron Spectrometry and Imaging Applications

For ion and neutron spectrometry and imaging applications at a high intensity pulsed laser facility, fast liquid scintillators with very low afterglow are required. Furthermore, neutron imaging with fiber (or liquid-core) capillary arrays calls for scintillation materials with high refractive index. To this end, we have examined various combinations of established mixtures of fluors and solvents, that were enriched alternatively with nitrogen or oxygen. Dissolved molecular oxygen is known to be a highly effective quenching agent, that efficiently suppresses the population of the triplet states in the fluor, which are primarily responsible for the afterglow. For measuring the glow curves of scintillators, we have employed the time-correlated single photon counting (TCSPC) technique, characterized by high dynamic range of several orders of magnitude in light intensity. In this paper we outline the application for the fast scintillators, briefly present the scintillation mechanism in liquids, describe our specific TCSPC method and discuss the results.

Multi-Frame Energy-Selective Imaging System for Fast-Neutron Radiography

A new instrument for high resolution imaging of fast-neutrons is presented here. It is designed for energy selective radiography in nanosecond-pulsed broad-energy (1-10 MeV) neutron beams. The device presented here is based on hydrogenous scintillator screens and single- or multiple-gated intensified camera systems (ICCD). A key element is a newly developed optical amplifier which generates sufficient light for the high-speed intensified camera system, even from such faint light sources as fast plastic and liquid scintillators. Utilizing the Time-of-Flight (TOF) method, the detector incorporating the above components is capable of simultaneously taking up to 8 images, each at a different neutron energy.

Time-resolved fast neutron imaging: simulation of detector performance

We have analyzed and compared the performance of two novel fast-neutron imaging methods with time-of-flight spectroscopy capability. Key parameters such as detection efficiency, the amount of energy deposited in the converter and the spatial resolution of both detector variants have been simulated by means of neutron and charged-particle transport codes.

Detectors for time-of-flight fast-neutron radiography 1. Neutron-counting gas detector

One of our two methods for fast-neutron imaging with spectrometric capability is presented here. It is a neutron-counting technique based on a hydrogenous neutron converter coupled to Gaseous Electron Multipliers (GEM). The principles of the detection techniques and the optimization of the converter, electron amplification and the readout are described. Evaluation of the properties is derived from a experiment in a pulsed neutron beam of spectral distribution between 2 and 10 MeV.

Nuclear‐Reaction‐Based Radiation Source For Explosives‐And SNM‐Detection In Massive Cargo

An automatic, nuclear‐reaction‐based, few‐view transmission radiography method and system concept is presented, that will simultaneously detect small, operationally‐relevant quantities of chemical explosives and special nuclear materials (SNM) in objects up to the size of LD‐3 aviation containers. Detection of all threat materials is performed via the 11B(d,n+γ) reaction on thick, isotopically‐enriched targets; SNM are primarily detected via Dual Discrete‐Energy Radiography (DDER), using 15.11 MeV and 4.43 MeV 12C γ‐rays, whereas explosives are primarily detected via Fast Neutron Resonance Radiography (FNRR), employing the broad‐energy neutron spectra produced in a thick 11B‐target. To achieve a reasonable throughput of ∼20 containers per hour, ns‐pulsed deuteron beam of the order of 0.5 mA intensity at energies of 5–7 MeV is required. As a first step towards optimizing parameters and sensitivities of an operational system, the 0° spectra and yields of both γ‐rays and neutrons in this reaction have been m...

High-frame rate imaging of two-phase flow in a thin rectangular channel using fast neutrons

We have demonstrated the feasibility of performing high-frame-rate, fast neutron radiography of air-water two-phase flows in a thin channel with rectangular cross section. The experiments have been carried out at the accelerator facility of the Physikalisch-Technische Bundesanstalt. A polychromatic, high-intensity fast neutron beam with average energy of 6 MeV was produced by 11.5 MeV deuterons hitting a thick Be target. Image sequences down to 10 ms exposure times were obtained using a fast-neutron imaging detector developed in the context of fast-neutron resonance imaging. Different two-phase flow regimes such as bubbly slug and churn flows have been examined. Two phase flow parameters like the volumetric gas fraction, bubble size and mean bubble velocities have been measured. The first results are promising, improvements for future experiments are also discussed.

Time-resolved fast-neutron radiography of air-water two-phase flows in a rectangular channel by an improved detection system.

In a previous work, we have demonstrated the feasibility of high-frame-rate, fast-neutron radiography of generic air-water two-phase flows in a 1.5 cm thick, rectangular flow channel. The experiments have been carried out at the high-intensity, white-beam facility of the Physikalisch-Technische Bundesanstalt, Germany, using an multi-frame, time-resolved detector developed for fast neutron resonance radiography. The results were however not fully optimal and therefore we have decided to modify the detector and optimize it for the given application, which is described in the present work. Furthermore, we managed to improve the image post-processing methodology and the noise suppression. Using the tailored detector and the improved post-processing, significant increase in the image quality and an order of magnitude lower exposure times, down to 3.33 ms, have been achieved with minimized motion artifacts. Similar to the previous study, different two-phase flow regimes such as bubbly slug and churn flows have been examined. The enhanced imaging quality enables an improved prediction of two-phase flow parameters like the instantaneous volumetric gas fraction, bubble size, and bubble velocities. Instantaneous velocity fields around the gas enclosures can also be more robustly predicted using optical flow methods as previously.

Quantitative discrimination between oil and water in drilled bore cores via Fast-Neutron Resonance Transmission Radiography.

A novel method utilizing the Fast Neutron Resonance Transmission Radiography is proposed for non-destructive, quantitative determination of the weight percentages of oil and water in cores taken from subterranean or underwater geological formations. The ability of the method to distinguish water from oil stems from the unambiguously-specific energy dependence of the neutron cross-sections for the principal elemental constituents. Monte-Carlo simulations and initial results of experimental investigations indicate that the technique may provide a rapid, accurate and non-destructive method for quantitative evaluation of core fluids in thick intact cores, including those of tight shales for which the use of conventional core analytical approaches appears to be questionable.

Radiography with a Terawatt Laser γ-Source

Electrons accelerated in laser plasma generated gamma-bremsstrahlung. The gamma-radiation was used for radiography with a time-resolved imaging system. We determined the modulation transfer function of the imaging system and have produced position and time-resolved gamma-images.