Neutron radiography, a technique for studying young roots growing in soil

The indirect technique for taking neutron radiographs using indium collector foils has been used to study root growth into soils. The work was done at Ames Laboratory Research Reactor, Iowa, USA, where a neutron beam of 107 n.cm-2.s-1 was available and 5x109 n.cm-1 were needed to obtain satisfactory radiographs. The experiments carried out included studying germination and root and shoot growth of seeds planted at different depths, with different orientations and with simulated surface crusts. Seed swelling, root length and rate of shoot growth were measured and with the surface crust qualitative information was observed. Seed orientation and surface crusts (wax layers) delayed penetration of the surface but no effect was noticed on germination. Shoot growth rates were constant no matter what depth the seed was planted, to depths of approximately 80 mm, a maximum depth below which many agricultural crops are not planted. Other experiments are considered and also other potential sources of slow neutrons mentioned. (author)