Page 82 - ILL Annual Report 2019

MODERNISATION PROGRAMME AND INSTRUMENT UPGRADES
Christian Tötzke. German
Institute for Environmental Science and Geography, University of Potsdam
‘Fast neutron tomography is a unique tool for analysing the dynamic transfer of liquids in porous material systems, time-resolved and in three dimensions.’
Record-fast neutron tomography tracks water pathways into plants
Neutron tomography is ideally suited to visualising plant root systems and the 3D water distribution in the surrounding soil. However, until now the major limitation for 3D imaging of dynamic water transfer in root-soil systems has been insufficient acquisition speeds. We used the high neutron flux available at the tomography station NeXT to dramatically speed
up the acquisition time for fast neutron tomography. We succeeded in acquiring full tomographies (155 projections
over 180 °) with a physical spatial resolution of 200 μm within 1.5 s. This
is about 6.7 times faster than the current record for high-speed acquisition. We used the technique to investigate water infiltration in soil using a living lupine
root system. The fast-imaging set-up will be part of the future instrument NeXT at the ILL in Grenoble and will offer a vast array of possible future applications.
AUTHORS
Ch. Tötzke (University of Potsdam, Germany) A. Tengattini (ILL)
REFERENCES
[1] A.G. Bengough, Vadose Zone J. 11 (2012)
[2] N. Kardjilov, I. Manke, R. Woracek, A. Hilger and J. Banhart,
Mater. Today (2018)
[3] C. Tötzke, N. Kardjilov, I. Manke and S.E. Oswald, Sci. Rep. 7
(2017) 6192
[4] C. Tötzke et al., Opt. Express 27 (2019) 28640
How plants take up water and nutrients from soil depends largely on the transport properties of the soil next to the roots, an area known as the rhizosphere. Intense root-soil interactions modify the structural and biochemical properties of the soil in this area, which in turn affects the transfer of water and nutrients into the roots [1]. Neutron imaging is an ideal approach for studying hydraulic transfer in soil because it provides an excellent contrast between the water and soil matrices. Neutrons can also distinguish hydrogen isotopes and their compounds. For example, while normal water, H20, and heavy water, 2H20, are physically and chemically very similar, there is an order of magnitude difference in attenuation between then, making heavy water an ideal contrast agent to normal water [2]. However, the normally relatively slow acquisition
speed of neutron imaging made it challenging to use for time-resolved 3D studies of fast processes such as water infiltration of soil and root water uptake. Recent technological improvements to neutron imaging stations have opened up new avenues for the 3D imaging of fast processes at high spatiotemporal resolution [3]. Since NeXT has the most intense cold neutron flux for imaging purposes in the world, it offers extraordinary conditions for high-speed neutron tomography. We used this approach to analyse the imbibition of water in root-soil systems after the injection of deuterated water.
Figure 1 illustrates the principle of the set-up used
for the water infiltration experiment. The lupine plant placed in front of the scintillator rotated at a constant speed of 0.33 rps while the sCMOS camera recorded radiographic projection images at high speed. Figure 2 shows a time series of tomograms after the injection of 4 ml of deuterated water at the bottom
of the plant container. As the D2O invades the soil pores it displaces the light water (H2O) present, which consequently forms a water front that moves upwards in the soil column. At 90 s after injection the front comes to a halt, stopped by a hydraulic barrier, i.e. a layer of coarse sand installed halfway up the soil column.
ANNUAL REPORT 2019