Malvern Zetasizer Nano Series, Руководство пользователя

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.
For samples that do not scatter much light, such as very small particles or
samples of low concentration, the amount of scattered light must be in-
creased. In this situation, the attenuator will allow more laser light through
to the sample.
.
For samples that scatter more light, such as large particles or samples of
higher concentration, the amount of scattered light must be decreased. This
is achieved by using the attenuator to reduce the amount of laser light that
passes through to the sample.
The appropriate attenuator position is automatically determined by the Zetasizer
during the measurement sequence.
The scattering intensity signal for the detector is passed to a digital signal
processing board called a
correlator
/
. The correlator compares the scattering
intensity at successive time intervals to derive the rate at which the intensity is
varying.
This correlator information is then passed to a computer
0
, where the specialist
Zetasizer software will analyse the data and derive size information.
As mentioned earlier, depending upon the Zetasizer Nano model the detection
optics will either be arranged at positions of either 173° or 90°.
173° detection optics - Backscatter detection
The Zetasizer Nano Z, S and ZS measure the scattering information close to
180°. This is known as backscatter detection.
The application of the Backscatter detection is by a patented technology called
NIBS ( N on- I nvasive B ack- S catter).
Why measure backscatter? There are several advantages to doing this:
.
Because the backscatter is being measured, the incident beam does not have
to travel through the entire sample. This reduces an effect known as multi-
ple scattering, where the scattered light from one particle is itself scattered
by other particles. As the light passes through a shorter path length of the
sample, then higher concentrations of sample can be measured.
.
Contaminants such as dust particles within the dispersant are typically large
compared to the sample size. Large particles mainly scatter in the forward
C H A P T E R 1 3
Z e t a s i z e r N a n o S e r i e s
P a g e 1 3 . 7
Laser
Sample
Detector
173°
ILL
6097