Thermo Scientific NITON XL3t 500, Руководство пользователя

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Radiation and General Safety
3-14 NITON XL3 Analyzer User’s Guide Thermo Scientific
measurement window or of low density and/or thickness. Caution should be
taken when analyzing samples that are small, thin, and/or low in density as
they may allow much more of the primary beam to escape. In-beam primary
radiation dose rates are listed in
Table 3-4 and Table 3-5 and their location
identified relative to the analyzer in Figure 3-4 as Dose Point C.
Secondary Radiation
Under conditions of normal and proper use, individuals can be exposed to
secondary (or "scattered") radiation. Secondary radiation is low-level
radiation that emanates from the sample being analyzed as a result of
primary beam radiation scattering in the sample or primary beam radiation
inducing fluorescent x-rays in the sample. Dose points A, A’ and B in
Figure 3-4 are examples of where you can encounter secondary radiation.
The magnitude of this secondary radiation is sample dependent. Higher
density samples such as steel will emit the lowest levels as they absorb most
primary and secondary radiations. Lower density samples such as
aluminum, wood, and especially plastic, will produce higher levels of
secondary radiation. Secondary radiation dose rates are listed in
Table 3-6
and Table 3-7 for a few common sample types over a wide range of
densities.
The operator is reminded that one should never hold samples during
analysis, doing so will result in higher than necessary exposure to secondary
radiation and could expose the operator directly to the much higher
primary-beam dose rates.
Deep and Shallow Dose
You will find in Table 3-4 and Table 3-5 that shallow dose rates are listed for
some dose points. All dose rates listed in Table 3-4 and Table 3-5 are deep
dose unless they are specifically identified as shallow dose. Deep dose is dose
from penetrating radiation that is delivered to both skin and underlying
tissues and organs and is the type most commonly referred to when
describing external radiation hazards. Occupational deep dose is limited to a
maximum of 5 rem (50 mSv) per year in the United States and most
countries internationally. Deep dose is measured at 1.0 cm below the skin
surface.
Shallow dose is often referred to as "skin dose" because it is a result of
low penetrating radiation that only interacts with the skin. Shallow dose
is limited to a maximum of 50 rem (500 mSv) per year in the United
States and most countries internationally. Shallow dose is listed below for
primary in-beam dose points only because the low penetrating radiation
that causes shallow dose is nearly all absorbed by a sample and does not
produce any significant secondary radiation. Shallow dose is measured at
a point 0.007 cm below the surface.