Measurement of the γ + 4He total photoabsorption cross-section using a gas-scintillator active target

A large number of experiments have been performed in the past 60 years in an attempt to understand the near threshold photodisintegration of 4He. Available experimental data are inconsistent and do not provide reliable guidance for theoretical calculations for the total and partial cross-sections in the energy regime near breakup threshold. Even with the most recent experimental work done on the subject, the situation still has not been fully clarified. This thesis reports a measurement of the total cross-section for photodisintegration of 4He below pi-production threshold, carried out in 2009 at the up-graded tagged photon facility at MAX-lab in Lund, Sweden, in collaboration with the Photonuclear group of Lund University. The aim of this measurement is to provide a reliable and precise set of data so that the accuracy of theoretical models can be judged reliably. The experiment was performed using a Helium Gas-Scintillator Active Target (HGSAT), built and developed at the University of Glasgow. The helium target acts also as a detector of the 4He photodisintegration charged products. A photon beam, energy tagged in the range 11-68 MeV, was directed towards the HGSAT, which operated at a pressure of 2MPa, at room temperature. The resultant scintillation is collected and detected by a number of photomultiplier tubes (PMT) mounted on the HGSAT. 12 external neutron detectors and two 10" sodium iodide (NaI) detectors were used during the experiment to distinguish 4He(γ,n)3He and 4He(γ,γ')4He events, although these events have not been analysed here. The tagged photon coincidence signal was separated from random background using two methods: background filtering and fitting procedure. The two methods produced similar results. A Geant4-based Monte-Carlo simulation was developed to derive the HGSAT detection efficiency. Trigger thresholds needed in the simulation were estimated by evaluation and matching the normalised yield to previously measured γ+4He cross-sections above 40 MeV where more consistency in the dataset is observed, hence the results presented in this thesis are preliminary and will remain so until the absolute detection efficiency is determined. The preliminary total γ+4He cross-section obtained in this work peaks at ~2.85mb at a photon energy (Eγ) of ~27MeV, falling to ~1mb at Eγ = 60MeV. The measured cross-section is compared with previous data and recent theoretical calculations made using the Lorentz Integral Transform (LIT) technique. The present cross-section is already in reasonable agreement with the theoretical calculations and a number of previous experimental data. Future work to reduce systematic uncertainties will include analysis of the pulse height response of the HGSAT and further lower intensity experimental runs

Novel muon imaging techniques

Owing to the high penetrating power of high-energy cosmic ray muons, muon imaging techniques can be used to image large bulky objects, especially objects with heavy shielding. Muon imaging systems work just like CT scanners in the medical imaging field—that is, they can reveal information inside of a target. There are two forms of muon imaging techniques: muon absorption imaging and muon multiple scattering imaging. The former is based on the flux attenuation of muons, and the latter is based on the multiple scattering of muons in matter. The muon absorption imaging technique is capable of imaging very large objects such as volcanoes and large buildings, and also smaller objects like spent fuel casks; the muon multiple scattering imaging technique is best suited to inspect smaller objects such as nuclear waste containers. Muon imaging techniques can be applied in a broad variety of fields, i.e. from measuring the magma thickness of volcanoes to searching for secret cavities in pyramids, and from monitoring the borders of countries checking for special nuclear materials to monitoring the spent fuel casks for nuclear safeguards applications. In this paper, the principles of muon imaging are reviewed. Image reconstruction algorithms such as Filtered Back Projection and Maximum Likelihood Expectation Maximization are discussed. The capability of muon imaging techniques is demonstrated through a Geant4 simulation study for imaging a nuclear spent fuel cask

Recent Developments SoNDe High-Flux Detector Project

New high-flux and high-brilliance neutron sources demand a higher count-rate capability in neutron detectors. In order to achieve that goal, the Solid-State Neutron Detector (SoNDe) project is developing a scintillation-based neutron detector. It will be capable of fully exploiting the available flux at small-angle neutron scattering (SANS) instruments at high brilliance sources, such as SKADI at the European Spallation Source (ESS). The read-out of the scintillator is based on a pixelized multi-anode PMT (MaPMT), where each pixel is treated separately. In addition to enabling higher achievable count-rates, one of the design goals was to develop a modular and scalable solution that can also be used in other instruments or even contexts, such as for laboratory setups. This has been achieved by combining the complete read-out electronics along with the MaPMT into modules that can be controlled and read-out individually via a network without additional any infrastructure. An overview of the present state of development and current test results is presented, highlighting the results of previously published project reports

General considerations for effective thermal neutron shielding in detector applications

For thermal neutron detectors, effective shielding is a crucial aspect of signal-to-background optimization. This is especially important for cold to thermal neutrons, as the detectors are most sensitive in this energy range. In this work, a few common shielding materials, such as cadmium, B4C and epoxy-Gd2O3 mixtures, are analytically evaluated based on interaction cross sections extracted from Geant4. For these materials, the neutron absorption and scattering dependence on material thickness and incident neutron energy are examined. It is also considered how the absorption and scattering change with different material compositions, such as 10B-content in B4C, and component ratio in epoxy-Gd2O3 mixtures. In addition, a framework is introduced to quantify the effectiveness of the neutron shielding, comparing the relationship between absorption and scattering of different shielding materials. The aim is to provide a general tool kit, which can be used to quickly identify an appropriate shielding material, with the required thickness, to reach a desired thermal neutron shielding performance. Finally, as an example, the developed tool kit is applied to the specific shielding application for the Multi-Grid CSPEC detector, currently in development for the European Spallation Source

FLASH Portals: Radiation Portal Monitor SNM Detection using Time Correlation Techniques

The "FLASH Portals Project" is a collaboration between Arktis Radiation Detectors Ltd (CH), the Atomic Weapons Establishment (UK), and the Joint Research Centre (European Commission), supported by the Technical Support Working Group (TSWG). The program's goal was to develop and demonstrate a technology to detect shielded Special Nuclear Materials (SNM) more efficiently and less ambiguously by exploiting time correlation. This study presents experimental results of a two-sided portal monitor equipped with 16 He-4 fast neutron detectors as well as 4 polyvinyltuolene (PVT) plastic scintillators. All detectors have been synchronized to ns precision, thereby allowing to resolve time correlations from timescales of tens of microseconds (such as (n,γ) reactions) down to prompt fission correlations directly. Our results demonstrate that such correlations can be detected in a typical RPM geometry and within operationally acceptable time scales, and that exploiting these signatures significantly improves the performance of the RPM compared to neutron counting. Furthermore, the results show that some time structure remains even in the presence of heavy shielding, thus significantly improving the sensitivity of the detection system to shielded SNM.JRC.E.8-Nuclear securit

FLASH portals: radiation portal monitor SNM detection using time correlation techniques

No abstract available

Muon tomography for the analysis of in-container vitrified products

Alternate treatment routes for radioactive waste are a key research area for much of the nuclear industry, with potentially significant savings available through volume reduction of waste. Achieving this requires a full and demonstrable understanding of waste product behaviour. For this purpose, the UK's National Nuclear Laboratory (NNL) has been collaborating with the University of Glasgow and Lynkeos Technology to develop passive techniques for analysis of waste containers over a number of years. In this instance, novel muon tomographic techniques have been applied to the analysis of thermally treated nuclear waste surrogates as part of a project to build and deploy a first of a kind muon imaging system for nuclear waste. The system has been deployed at NNL's Central Laboratory, Cumbria, UK, to analyse products from a series of thermal treatment technology trials, funded by the Nuclear Decommissioning Authority (NDA) through the Direct Research Portfolio (DRP). Analysis of the waste products using this technique has proven the value of muon analysis in the development of waste management technologies, proving an ability to understand the homogeneity of products and direct further destructive testing. Results from three different thermal treatment trials are presented, with three different surrogate intermediate level waste (ILW) forms in each

Characterising Encapsulated Nuclear Waste Using Cosmic-ray Muon Tomography (MT)

A prototype scintillating-fibre detector system has been developed at the University of Glasgow in collaboration with the UK National Nuclear Laboratory (NNL) for the non-destructive assay of UK legacy nuclear waste containers. This system consists of four tracking modules, two above and two below the container under interrogation. Each module consists of two orthogonal planes of 2 mm-pitch fibres yielding one space point. Per plane, 128 fibres are read out by a single Hamamatsu H8500 64-channel MAPMT with two fibres multiplexed onto each pixel. The configuration allows the reconstruction of the incoming and scattered muon trajectories, thus enabling the container content, with respect to atomic number Z, to be determined. Results are shown from experimental data collected for high-Z objects within an air matrix and within a shielded, concrete-filled container. These reconstructed images show clear discrimination between the low, medium and high-Z materials present, with dimensions and positions determined with sub-centimetre precision

A helium gas scintillator active target for photoreaction measurements

A multi-cell He gas scintillator active target, designed for the measurement of photoreaction cross sections, is described. The target has four main chambers, giving an overall thickness of 0.103 g/cm3 at an operating pressure of 2 MPa. Scintillations are read out by photomultiplier tubes and the addition of small amounts of N2 to the He, to shift the scintillation emission from UV to visible, is discussed. First results of measurements at the MAX IV Laboratory tagged-photon facility show that the target has a timing resolution of around 1 ns and can cope well with a high-flux photon beam. The determination of reaction cross sections from target yields relies on a Monte Carlo simulation, which considers scintillation light transport, photodisintegration processes in 4He, background photon interactions in target windows and interactions of the reaction-product particles in the gas and target container. The predictions of this simulation are compared to the measured target response