ORTEC DSPEC Pro, Hardware User Manual

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794380D / 0914 1. INTRODUCTION
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Using our gamma-ray spectrum analysis software such as GammaVision
®
or ISOTOPIC.
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NOTE
When the spectrometer is placed in ZDT mode, the throughput of the instrument is
reduced somewhat as extra processing must be done on the spectrum; therefore, if the
gamma-ray flux is not changing as a function of time, but absolute highest throughput
is desirable, you might wish to store only the LTC spectrum in the MCB memory.
1.6.2. NORM_CORR — ZDT and Uncorrected Spectra Stored
When the ZDT mode is set to NORM_CORR, the two spectra stored are the LTC spectrum and
the ZDT spectrum (corrected for the dead-time losses; real time only). Unfortunately, in the
analysis of the ZDT spectrum, the uncertainty of the measurement cannot be determined using
either spectrum.
NOTE
This mode is not useful for quantitative analysis if the counting rate varies significantly
during the measurement time, particularly if the user desires an accurate counting rate
and standard deviation calculation. When you select the NORM_CORR mode, the
spectroscopy software ignores the ZDT spectrum and analyzes the LTC spectrum as it
would for the Off ZDT mode.
1.6.3. CORR_ERR — ZDT and Error Spectra Stored
In the CORR_ERR mode, the estimation of the statistical uncertainty is stored in place of the
LTC spectrum, and is referred to as the error spectrum (ERR). In this mode, the ZDT spectrum
is used to measure the counts in a peak, and the error spectrum is used to determine the uncer-
tainty of the measurement made in the corrected spectrum.
For example, if the area of a peak is measured in the corrected spectrum by summing channels
1000 to 1100, the variance of the measurement can be determined by summing the counts in
channels 1000 to 1100 in the error spectrum. Or, shown another way, the counts in channel i can
be expressed as ± with a 1-sigma confidence limit, where N is the corrected spectral
data and V is the variance (error) spectral data.
The live time is set to the real time within the analysis engine during the analysis of ZDT
spectra.
A CORR_ERR spectrum is analyzed
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as a regular spectrum most of the time, with a few
exceptions as listed below.
!
To calculate the peak area uncertainty, the error spectrum is used. If the peak limits are
from L and H channels, then the background variance is calculated as: