The time constraints on foreign body detection in food using Compton scatte
red X-rays were examined. An equation was developed to calculate the number
of scatter counts detected per second, given the geometry of the sample an
d the X-ray system. This was used to calculate the minimum time required to
detect a contaminant in a sample, given that a signal-to-noise ratio of at
least 7.4 was required for production line applications. The predicted tim
es required to detect a glass fragment in a cube of water ranged from 0.018
s for a 5 mm fragment to 280 s for a 1 mm fragment in a 10 cm cube, or res
pectively, 0.00036 and 5.5 s in a 5 cm cube.
The detection of a 4 mm glass fragment in water, instant coffee and muesli
using Compton scatter was demonstrated by experiment. The contrasts obtaine
d between the glass and the samples were, respectively, 0.5, 2.7 and 2.6, a
nd the signal-to-noise ratios were, respectively, 10.1, 23.4 and 24.3. The
minimum measurement times implied by the experiments were similar to those
predicted by theory. The glass fragment was detected with strong contrast i
n the experiments, but the measurement times for whole-sample scanning were
slow compared to production line speeds in the food industry.
The detection of glass from the mean energy of the scattered X-ray spectrum
was also demonstrated. A high contrast of 9 was obtained for glass in wate
r, but the measurements were more noisy than the corresponding photon count
ing measurements, giving a signal-to-noise ratio of only 3.3. (C) Silsoe Re
search Institute.