Measurement result and performance parameters are presented for fast neutron detectors exploiting the scintillation of natural helium at high pressure. This detection medium has a very low electron density, minimizing the sensitivity to gamma radiation and thus enabling neutron detection also in high gamma radiation environment. Contrary to proportional counters, scintillation detection enables fast (nanosecond) timing and pulse shape discrimination, a technique that enables a lower neutron detection threshold. In this work, the basic principles of the detector are described, followed by a study of gamma rejection capabilities. Methods to calibrate the detector are discussed. Finally, a brief description of a 4 He scintillation based detector system including data acquisition electronics is given.

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He NE-213 Scintillation Gamma-rays Fast neutrons Pulse-shape discrimination a b s t r a c t A first comparison has been made between the pulse-shape discrimination characteristics of a novel 4 He-based pressurized scintillation detector and a NE-213 liquid-scintillator reference detector using an Am/Be mixed-field neutron and gamma-ray source and a high-resolution scintillation-pulse digitizer. In particular, the capabilities of the two fast neutron detectors to discriminate between neutrons and gamma-rays were investigated. The NE-213 liquid-scintillator reference cell produced a wide range of scintillation-light yields in response to the gamma-ray field of the source. In stark contrast, due to the size and pressure of the 4 He gas volume, the 4 He-based detector registered a maximum scintillationlight yield of 750 keV ee to the same gamma-ray field. Pulse-shape discrimination for particles with scintillation-light yields of more than 750 keV ee was excellent in the case of the 4 He-based detector. Above 750 keV ee its signal was unambiguously neutron, enabling particle identification based entirely upon the amount of scintillation light produced.

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2016-11-02T18:49:00

We demonstrate the unambiguous detection of the fission neutron signal produced in natural uranium during active neutron interrogation using a deuterium-deuterium fusion neutron generator and a high pressure 4He gas fast neutron scintillation detector. The energy deposition by individual neutrons is quantified, and energy discrimination is used to differentiate the induced fission neutrons from the mono-energetic interrogation neutrons. The detector can discriminate between different incident neutron energies using pulse height discrimination of the slow scintillation component of the elastic scattering interaction between a neutron and the 4He atom. Energy histograms resulting from this data show the buildup of a detected fission neutron signal at higher energies. The detector is shown here to detect a unique fission neutron signal from a natural uranium sample during active interrogation with a (d, d) neutron generator. This signal path has a direct application to the detection of shielded nuclear material in cargo and air containers. It allows for continuous interrogation and detection while greatly minimizing the potential for false alarms.

Laboratory-based X-ray computed tomography (CT) with resolutions around 100nm per line pair is technically feasible since a few years [1]. However, this measurement principle is still not widely usedespecially not for industrial and medical applications. Reasons for this are high costs, the complex operation of systems based on optical elements, as well as the restricted flexibility of their field-of-view. As applied development center for X-ray technology, the Fraunhofer EZRT is currently developing an easy-to-handle, flexible setup for industrial use. The setup uses standard projection geometry, a small Xray source and large detector pixel; thus it operates using high geometric magnification. Due to significant advances made on the component side combined with a high stability of the setup, we are able to resolve in standard operation 150nm lines and spaces. Compared to modified SEM X-ray sources, the sample does not need to be placed in vacuum [3]. Moreover, due to the source's peak energy of 60kV, sample diameter and material can be chosen relatively flexible.For our setup we utilize an X-ray tube developed by Excillum in the framework of the NanoXCT Project, which is now commercially available as "NanoTube". In our acquisition geometry, the penumbral blurring of the source's focal spot defines the achievable resolution. Besides a thin transmission target combined with a suited design of the electron optics to guarantee a small source size, also high spatial spot stability is required for computed tomography. The latter is established by advanced temperature and noise control. In order to provide good heat dissipation, the transmission target is made of tungsten deposited on a 100µm diamond window. With this, we reach a source size diameter of a few hundred nanometers.Although the brightness of the spot is high, the total emitted flux is still relatively low, which is a major drawback compared to an optics-based setup [4]. Thus, we need an efficient detector and a large solid angle to achieve reasonably short exposure times. Therefore, we use 750µm CdTe as sensor material with a quantum efficiency greater than 80% over the full spectrum. The Hybrid Photon Counting "SANTIS" detector possesses 2048 x 514 pixel with 75µm edge length, and was provided by DECTRIS. Each pixel of a dedicated readout chip is directly bonded to a semiconducting X-ray sensor [2]. Besides the high efficiency due to the photon counting technique, it possesses virtually zero noise. Furthermore, two energy thresholds enable us to perform dual-energy computed tomography without additional filters. Moreover, the quasi-rectangular point spread function of the detector supersedes oversampling.Large solid angles are obtained by a short source-detector-distance of minimum 380mm. This also requires small distances between the source and sample. Therefore, an optical collision avoidance system is implemented to be able to adjust source-object-distances below 500µm without risking a damage of the source's window. In combination with this, the syst...

In this paper we report the experimental study of high-pressure xenon used as a scintillator, in the context of developing a gamma ray detector. We measure a light yield near 2 photoelectrons per keV for xenon at 40 bar. Together with the light yield, we also measured an energy resolution of ∼9% (FWHM) at 662 keV, dominated by the statistical fluctuations in the number of photoelectrons.