Medicinal Plants Classification Biosynthesis and ... - Index of

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Chien-Yi Chen
(IAEA 336), also weighing around 150 and 350 mg, was irradiated together with AK to
quantify the elemental concentrations in the samples. An empty PE bag of identical size was
taken as blank correction also double-sealed. Each sample and standard was prepared in
triplet to minimize the statistical uncertainty as published everywhere (Chen and ChangLai,
2001; Chen and Pan, 2001; Wei et al., 1997). Blank correction for ENAA and INAA methods
were also performed to determine possible interference. Each irradiated sample was paired
with a 10 mg Ni-foil monitor used for neutron flux fluctuation (Chen, 2004; Chen, 2002;
Chen and Pan, 2001).
3.2. Irradiation Filters and Irradiation Schemes
The larger boron-polyethylene (BPE) flexible shield cylinder container with a 164 mm H×44
mm D with 3.2 mm wall thickness (Flex/Boron, Reactor Experiments, UK) and smaller cadmium
cylinder container with a 40 mm H×25 mm D with 1 mm wall thickness filter were used to screen
thermal neutrons herein. Three irradiation schemes were developed: (a) short irradiations (ti = 10
min) wrapped with Cd filter in the PT; (b) long irradiations (ti = 24 h) wrapped with BPE filter in
the VT; (c) long irradiation (ti = 24 h) but without any wrapped in the PT. All of the irradiation
schemes and decay properties for the interested nuclides are illustrated in Table 1. Details of the
experimental conditions for ENAA and INAA are given elsewhere (Chen, 2009; Chen, 2004;
Chen, 2003; Chen, 2002; Chen and Pan, 2001; Shirley and Lederer, 1978).
3.3. Counting and Analysis
The γ-ray spectra were measured using a calibrated HPGe detector with 15% relative
efficiency. The counting system uses herein provided an energy resolution of 2.5 keV at 1333.2
keV of 60 Co. γ-ray spectra were analyzed by Micro SAMPO90 software coupled with personal
computer connecting to a System-100 multichannel analyzer board for spectral acquisition (Chen,
2009; Chen, 2004; Chen, 2003; Chen, 2002; Chen and Pan 2001). Statistical errors in each of
these values did not exceed 15% and dead times were kept below 10% (Chen and Pan, 2001; Wei
et al., 1997). The difference in Mg measurement may be attributed to inaccurate determination
caused by the interference of 56 Mn during the γ-ray measurement by ENAA. Even if the
deduction of multiple γ-rays 843.8 and 846.6 keV for 28 Mg and 56 Mn, respectively, is resolvable
using Micro SAMPO90 software, the relative high concentration of 56 Mn to 28 Mg in the herb
samples can still decrease the statistical control of Mg in INAA measurement.
Activities of 80 Br and 128 I had less relevance to the attenuated thermal neutron in ENAA,
whereas alternately, activities of 24 Na, 38 Cl and 28 Al were suppressed easily with the
attenuated thermal neutrons. In addition, there was another kind of interfering γ-peak at 439.9
keV to the interested gamma-peak 442.9 keV from 128 I in this work. This unwanted gammapeak
was generated by the 23 Na nuclide absorbing fast neutrons with a half-life of 37.2
second to give a proton and 23 Ne. Since, it exists with such a comparatively short half life; it
can be easily suppressed by a longer cooling time. Further, the irradiated samples also had to
be cooled for at least 10 minutes for avoiding a too high Compton scattering plateau on