Eberhard Lehmann

PROPERTIES OF THE RADIOGRAPHY FACILITY NEUTRA AT SINQ AND ITS POTENTIAL FOR USE AS EUROPEAN REFERENCE FACILITY

Abstract At December 3rd 1996, the spallation neutron source SINQ had its first proton beam onthe target. With a steady-state proton beam of 850 IlA this facility is now the strongest of its kind in the world. One of the first experimental facilities in operation was theradiography station NEUTRA (for NEUtron Transmission Radiography). The designwas described at earlier meetings [1,2] and the first validation measurements werereported [3]. There are some advantages in comparison to other radiography stations atresearch reactors. This will be demonstrated in detail by means of the measured valuesand examples of practical applications. The use as reference facility will be envisagedwithin an European project (COST-524).

Three‐dimensional visualization and quantification of water content in the rhizosphere

• Despite the importance of rhizosphere properties for water flow from soil to roots, there is limited quantitative information on the distribution of water in the rhizosphere of plants. • Here, we used neutron tomography to quantify and visualize the water content in the rhizosphere of the plant species chickpea (Cicer arietinum), white lupin (Lupinus albus), and maize (Zea mays) 12 d after planting. • We clearly observed increasing soil water contents (θ) towards the root surface for all three plant species, as opposed to the usual assumption of decreasing water content. This was true for tap roots and lateral roots of both upper and lower parts of the root system. Furthermore, water gradients around the lower part of the roots were smaller and extended further into bulk soil compared with the upper part, where the gradients in water content were steeper. • Incorporating the hydraulic conductivity and water retention parameters of the rhizosphere into our model, we could simulate the gradual changes of θ towards the root surface, in agreement with the observations. The modelling result suggests that roots in their rhizosphere may modify the hydraulic properties of soil in a way that improves uptake under dry conditions.

Novel Application of Neutron Radiography to Forced Convective Drying of Fruit Tissue

Neutron imaging is a promising technique to study drying processes in food engineering as it is a non-intrusive, non-destructive technique, which provides quasi-real-time quantitative information of the water loss during drying and of the internal water distribution, at a high spatial and dynamic resolution. Particularly, the high sensitivity to water is its main advantage for drying studies, despite the limited accessibility to reactor facilities, which produce neutrons. This technique was used to investigate forced convective drying of fruit tissue (pear and apple), placed in a small wind tunnel. Water loss, water distribution in the sample and sample shrinkage were evaluated as a function of time. The water loss, determined quantitatively from neutron radiographs, was underestimated slightly compared to gravimetrical measurements. The overall drying behaviour agreed well with control measurements performed in a climatic chamber and was very similar for both fruit tissues. The corresponding shrinkage behaviour of both tissues was also similar. The large shrinkage, which is characteristic for soft biological materials such as food products, however, hindered post-processing to some extent. From the internal water distribution, the water gradients within the sample, induced by drying, were visualised and were found to predominantly occur at the air–material interface, indicating that the water transport inside the tissue dominated the water loss, instead of the convective exchange with the air flow. Neutron imaging was shown to exhibit unique benefits for studying drying processes of food.

Neutron attenuation coefficients for non-invasive quantification of wood properties.

Abstract Attenuation coefficients and mass attenuation coefficients of wood were determined theoretically and experimentally for thermal and cold neutrons. Experiments were carried out at the neutron imaging facilities at the Paul Scherrer Institute, Villigen (CH). For the calculation of theoretical attenuation coefficients, only the three main elemental components (carbon, oxygen and hydrogen) were taken into consideration. While hydrogen accounts only for 6% (by wt) of wood, over 90% of the attenuation can be attributed to this element. Nitrogen and other trace elements were estimated to have a negligible impact on the theoretical attenuation coefficient. For the experimental determination of the attenuation coefficients, samples from different European and tropical wood species were tested in order to examine the influence of density and extractives content. Experimental results show a very strong linear correlation between attenuation coefficient and wood density irrespective of the tested species and extractives content that play only a minor role. As neutrons are very susceptible to scattering, it is necessary to apply a scattering correction if a quantitative evaluation is intended.

THE INVESTIGATION OF HIGHLY ACTIVATED SAMPLES BY NEUTRON RADIOGRAPHY AT THE SPALLATION SOURCE SINQ

Abstract In addition to conventional radiography investigations there is a demand to inspect highly activated samples of spent nuclear fuel or accelerator target materials to detectmaterial defects caused by the strong applied radiation and interaction with the coolant. For this purpose, special facilities and equipment have to be used which are wellshieldeFurthermore, neutron radiography detectors have to be found which are insensitive to the radiation emitted by the sample under investigation.The radiography station NEUTRA at PSI can be modified to such a facility to handle highly activated samples under dry conditions and can perform sensitive investigationswith high spatial resolution. The paper describes this experimental assembly and shows results from the first cycleof investigations. Several problems (technical and administrative ones) are discussed in some detail.