Silicon has been found to be an essential element for the growth and development of many ecomomically important plants such
as sugarcane, rice, oats, and wheat. A method is described for the quantitative determination of silicon in plant samples.
Measurements were made with two Ge(Li) detectors matched with a multiplexing unit to provide a single amplified signal to
a computerized analyzer system. For those materials containing greater than 0.5 weight percent silicon, the reaction29Si(n, p)29Al (1273 keV) provides a direct measurement of the quantity of silicon provided the irradiation is done in a special boron
nitride capsule to reduce interferences from thermal neutron reactions and a correction is made for the single escape line
from28Al (1268 keV). For lesser quantities of silicon, a technique which utilizes the fast neutron reaction28Si(n, p)28Al is preferred. Corrections for the interference produced by the presence of phosphorus31P(n, α)28Al are made by determining the phosphorus content following the instrumental analysis using a unique application of neutron
activation analysis, i. e., measurement of tungsten in tungstomolybdophosphoric acid produced when molybdate and tungstate
ions are added to dissolved samples of the plant material containing phosphorus. Aluminum, which may also produce an interference
by thermal neutron reaction27Al(n, γ)28Al, is determined directly from the original activation data after subtracting out the effect of the phosphorus. Thus, three
irradiations in the pneumatic sample irradiator are necessary; one short irradiation (1 min) without thermal neutron shielding,
a longer irradiation (6 min) in the boron capsule, and a final irradiation of the tungstomolybdophosphoric acid provide all
data required to accurately determine silicon in plant materials. A computer program has been developed that provides rapid
reduction of the data in final report format. Elements such as sodium, chlorine, calcium, manganese, potassium, and magnesium
extrinsic to the analysis for silicon are also determined by this method. The method has been tested on a large number of
samples and reliable results are obtained with less than 0.2 g of sample.