Sy
clone Portable Gamma-Ray Spectrometer, Revision 10 5.0 MANUAL MODE
Ra
dComm – Proprietary Page 42 Revision Date: March 3, 2016
10% Dead-Time
= a DOSE Rate for Cs-137 of approx. 0.5mR/h
= a count rate of approx. 5000cps in the Search mode
The LIVE-TIME data is what is important and it is used to correct the data for the “lost”
sampling time as shown in the following example:
ST = 100.000 secs
LT = 91.373 secs
Channel 128 = 1850 counts after the 100 secs sample = 18.5 counts/sec
The REAL value for Channel 128 = 1850/91.373 = 20.25 counts/sec
As can be clearly seen – LIVE-TIME correction is essential for proper data analysis.
To make data analysis simpler, the user has 2 options to correct this effect:
LIVE – This setting enables an automatic correction method and this correction
ess
entially increases the sample-time by the Dead-Time to account for all the
pulses that would have been lost because the electronics were “too busy” to
process the incoming pulse.
If LIVE mode is selected, the preset sample period is AUTOMATICALLY
extended by the Dead-Time so the final data is automatically Dead-Time
correc
ted. Thus if you set a 100 second sample period and there is a 10% Dead-
Time, then the actual sample period will be approximately 110 seconds thus all
the “lost” time has been compensated for and the data represents a true 100
second sample. The selection of LIVE mode is an advantage to users who want
“automatic” operation to minimize data processing. In low count areas extending
the sample period also give slightly more accurate data. The main drawback to
this mode of operation is that the actual duration of the sample is variable.
CLOCK – In this mode, the preset sample time is the actual sample time and any Dead-
Time occurring must be corrected manually. The data output includes the system
Live-Time so that correction is quite simple especially if using a spreadsheet
program. The CLOCK mode is used primarily when several analyses are being
compared without time normalization and it is necessary to have the same
sample time.
REP. – This setting enables the unit to do multiple spectrum sampling and analysis.
Each spectrum measurement is sampled over the user defined sample time
(MEASURE TIME) and stored as a unique spectrum #. The routine is stopped by
pulling the joystick down (ENTER), which will then display the IDENTIFY sub-
menu.
c) AUDIO ALERT – selections are ON, OFF
This sets a mode so that at the end of the data sample the audio will beep to remind
users that the sample is complete. The OFF selection sets no beep.
USERS ARE REMINDED THAT IN THE LIVE MODE – ACTUAL SAMPLE TIMES
WI
LL BE MUCH SMALLER IN HIGH COUNT RATE AREAS. IF ONLY NUCLIDE-
ID IS REQUIRED THEN USE OF CLOCK
WILL ENSURE THAT THE PRESET
SA
MPLE TIME IS THE ACTUAL SAMPLE TIME.
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