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GRS-16/GRS-10/GRS-2 GAMMA
SPECTROMETER
Calibration Program
PEICalib
Operation Manual
Version 5.0
March 2006
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WARNING TO USERS!BE ADVISED THE CONTENTS OF THE CRYSTAL DETECTOR
ASSEMBLIES REPRESENT A THERMALLY STABLE MASS. DO NOT
OPEN THE CRYSTAL DETECTOR BOXES UNLESS THE INTERNAL
TEMPERATURE OF THE DETECTOR ASSEMBLY IS THE SAME AS
THE AIR TEMPERATURE OUTSIDE THE BOX.
A TEMPERATURE DIFFERENCE OF MORE THAN 5 DEGREES
CELCIUS BETWEEN INTERNAL AND EXTERNAL BOX
TEMPERATURES CAN CAUSE THE CRYSTAL MASS TO CRACK.
SIMILARILY A TEMPERATURE GRADIENT OF MORE THAN 10
DEGREES PER HOUR OF OUTSIDE AIR TEMPERATURE WILL
EXCEED THE DETECTOR PACKAGE ABILITY TO MAINTAIN A SAFETEMPERATURE GRADIENT INSIDE THE DETECTOR CONTAINER.
BEFORE OPENING THE DETECTOR ASSEMBLY ENSURE THE
OUTSIDE AIR TEMPERATURE HAS BEEN MAINTAINED AT A
CONSTANT LEVEL FOR AT LEAST 24 HOURS.
PICO ENVIROTEC ASSUMES NO RESPONSIBILITY FOR DECTECOR
ARRAYS DAMAGED BY THERMAL SHOCK
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Content:
1. GRS-16/GRS-10/GRS-2 INTELLIGENT GAMMA SPECTROMETER 4
1.1.PURPOSE OF THIS PROGRAM AND MANUAL 4
1.2.OVERVIEW 4
1.3.DIFFERENCES AMONG GRS-16/GRS-10/GRS-2 GAMMA SPECTROMETERS 51.4.NOTE ON THIS MANUAL 5
2. PEICALIB - CALIBRATION PROGRAM FOR GRS-16/GRS-10/GRS-2
GAMMA SPECTROMETER 6
2.1.GENERAL 6
2.2.PROGRAM REQUIREMENTS 6
2.3.PROGRAM LOADING 6
2.4.FINDING THE CONCENTRATOR 7
2.5.DOWN/UP DISPLAY 82.5.1. RESOLUTION CALCULATION 102.5.2. INDIVIDUAL DETECTOR DISPLAY 11
3. CALIBRATION PROCEDURE 123.1.INITIAL GAIN ADJUSTMENT 12
3.1.1. EASY GAIN ADJUSTMENT 123.1.2. USING TH SAMPLE FOR INITIAL GAIN ADJUSTMENT 123.1.3. CALIBRATION START 12
3.2.LINEARITY CALIBRATION 13
4. OTHER OPTIONS 14
4.1.DATA DISPLAY 14
4.2.DATA RECORDING 14
4.3.PROGRAM TERMINATION 14
4.4.FRONT-END ELECTRONIC TEST 14
4.5.SPECTROMETER VERIFICATION 145. PRINCIPLES OF AIRBORNE GAMMA RAY SPECTROMETRY 16
5.1.GAMMA RADIATION 165.1.1. RADIOACTIVE DECAY 165.1.2. GAMMA RAY SPECTRA 165.1.3. INTERACTION OF GAMMA RAYS WITH MATTER 17
6. QUALITY CONTROL 20
6.1.INSTRUMENTAL VARIABLES 206.1.1. SPECTROMETER RESOLUTION 206.1.2. SPECTRAL STABILITY 216.1.3. DIGITAL DATA FIDELITY 226.1.4. TEST LINE 22
6.2.OPERATIONAL VARIABLES 236.2.1. FLYING HEIGHT 236.2.2. FLIGHT PATH SPACING 236.2.3. FLYING SPEED 23
6.3.ENVIRONMENTAL VARIABLES 246.3.1. PRECIPITATION 246.3.2. ATMOSPHERIC RADON 24
APPENDIX A: GRS-16/GRS-10/GRS-2 TECHNICAL PARAMETERS 25
APPENDIX B: RECOMMENDED DATA ACQUISITION SYSTEMS (IRIS/AGIS) 27
APPENDIX D: REFERENCES 28
APPENDIX E: CONTACTS 29
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1.GRS-16/GRS-10/GRS-2 INTELLIGENT GAMMASPECTROMETER
This program operates the Pico Envirotec Inc. Intelligent GRS-16/GRS-10/GRS-2 Gamma
Spectrometer supporting up to sixteen/ten/two detectors. GRS-16 or GRS-10 is intended to be used
with or without the IRIS (Integrated Radiation Information System) or AGIS (AirborneGeophysical Information system) specific hardware. GRS-2 is used in PGIS Portable
Geophysical Information System.
Intelligent GRS-16/GRS-10/GRS-2 Gamma Spectrometer is designed to communicate via
RS232 communication link. It is providing all necessary spectra correction (gain tracking and
linearization) separately for each Gamma detector in real time. The calibration program allows the
user to view individual detectors, adjust their parameters, calibrate them and verify the
spectrometer operation. Simple communication protocol allows the GRS-16/GRS-10/GRS-2 to be
connected to any data acquisition system via RS232 port. Simple calibration procedure and fully
automated individual detector tracking simplifies the operation and reduces a possibility of an error
introduced by the operator.
1.1. PURPOSE OF THIS PROGRAM AND MANUALAll tests, adjustments and calibrations described in this manual are related to the operational
performance of the GRS-16/GRS-10/GRS-2 Gamma spectrometers. PEICALIB program provides
means for verification of proper operation of the digital spectral detection. It does not provide
physical description of properties of the Gamma spectrometer such as sensitivities and stripping
constants. These parameters must be established by physical measurements on defined calibration
places (calibration pads etc.).
1.2. OVERVIEWThe GRS-16/GRS-10/GRS-2 Gamma spectrometer is an advanced Spectrometer utilizing
NaI(Tl) detectors with individual detector handling. It is hardware-software designed system,
exhibiting simplicity, easy interfacing and substantial versatility. Because of individual detector
processing and use of the Digital Peak Detector that reduces nonlinearity and almost eliminates
"zero base shift" and the "dead time"(see note 2.8.4.). This is achieved through digital processing of
each detected Gamma particle (photon). Elimination of internal DC coupling further reduces above
mentioned potential problems.
New - natural peak detection algorithm provides safe and fast system stabilization without
detector housing temperature stabilization and without implanted radioactive sources in the detector
housing. Elimination of implanted sources (usually Cs137) for stabilization means no spectra
pollution on low energies and therefore better sensitivity of the system for man-made isotopes.When calibrated (with Th source about once a year) linearity and zero offset of the each
detector are measured and mathematical correction coefficients are calculated. When operating in
real time (collecting data), the gain, linearity and offset of each detector is mathematically corrected
for each measurement.
Individual detector tracking (tuning) and linearity correction provide better fit of the individual
spectra that are being summed and therefore sharper (better resolution) spectrum is obtained.
Optionally the GRS-16/GRS-10/GRS-2 system can be controlled by the altitude of the aircraft
and calculate absolute values of contamination by individual radionuclei related to the ground and
provide the dose rate related to 1meter above the ground.
Interfacing via single RS232 communication channel makes the system very flexible.
This manual describes PEICALIB program.
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1.3. DIFFERENCES AMONG GRS-16/GRS-10/GRS-2 GAMMASPECTROMETERS
GRS-16 is able to handle maximum sixteen detectors with summed output for in real timerecording of 256 or 512 channels.
GRS-10 is able to handle maximum ten detectors with same output as GRS-16 but can as well
produce individual spectra for in real time recording on 256 or 512 channels or summed output
for 256 channels two times a second.
GRS-2 is able to handle maximum two detectors with summed or individual output for in real
time recording of 256 or 512 channels.
PEICALIB program always uses 256 channels mode.
1.4. NOTE ON THIS MANUALContinuous work on the GRS-16/GRS-10/GRS-2 performance improvement may cause that
the manual may slightly differ from the delivered software version. Any major changes in operation
will be indicated and supplied with the delivered product. Should there be some differences found
in the manual and real operation, manufacturer would appreciate reporting such discrepancies.
Generally the hardware of GRS-16/GRS-10/GRS-2 is referred as the CONCENTRATOR.
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2.PEICALIB - CALIBRATION PROGRAM FOR GRS-16/GRS-10/GRS-2 GAMMA SPECTROMETER
2.1. GENERALPEICALIB program is designed to verify performance of the "black box" type of an intelligent
spectrometer. It is supplied together with GRS-16/GRS-10/GRS-2 hardware containing a
Concentrator unit.
Program allows the operator to:
Set remotely High voltage for each sensor Turn remotely each sensor on or off Appoint it as an "downward" or "upward" looking detector Set the system threshold Calculate the resolution of the system Observe:
Each detector independently All detectors in two groups -down/up
Uncorrected/Corrected/Tracking spectra can be displayed Individually collected (one second) or time summed spectra may be selected Calibrate individual detectors for linearity with the help of a Tl208 radioactive source In case of verification of the system operation on calibration pads (portable or stationary)
collected data may be stored for verification by standard program
All calculated or pre-set parameters are automatically stored and used at any time afterwhen the GRS-16/GRS-10/GRS-2 is used either in operation with this program or any data
acquisition system.
2.2. PROGRAM REQUIREMENTSPEICALIB calibration program is designed to run on IBM-PC compatible computers equipped
with Windows 98 or XP operating system operating at minimum 66 MHz. The computer running
calibration program has to be connected via COM port with GRS-16/GRS-10/GRS-2 hardware
containing a Concentrator unit.
2.3. PROGRAM LOADINGFor operation safety a copy of the program is supplied on a CD. Keep it in a safe place.
The PEICALIB.EXE may be copied into any directory and run from that directory. Once initiatedthe Fig. 1 appears. The form shows which COM port and baud rate is used to detect the
Concentrator. Those parameters were restored from previous work session. PEICALIB.INI file is used
to store parameters for the next run of the program. If there is no PEICALIB.INI file detected the
program will use default parameters: port COM1, 115200 baud.
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Fig. 1 Fig. 2
2.4. FINDING THE CONCENTRATORIf the Concentrator is connected to the different COM port or if it is using different baud rate
press button, otherwise press button. If button was pressed the programwould look for the Concentrator unit connected to the selected s baud rate erial communication port
and the Fig. 2 would appear. For GRS-2 type Concentrator baud rate 57600 baud required, for
GRS-16/GRS-10 baud rate 115200 baud required.
The Concentrator communicates with the host and at the same time communicates with
individual (up to sixteen) detectors as well as the optional four-channel analog to digital converter.
The search number is indicated at the top of the display box "Times nn". When the Concentrator is
detected the revision of the Concentrator will be displayed (see Fig. 3), otherwise the Fig. 2 will
stay on until button is pressed. If button is pressed then the revision Fig. 3 will
be displayed but checkbox will be checked. This means that the program will
simulate the Concentrator actions. If the Concentrator is connected to another port, it is possible to
select another COM port and baud rate on the form, uncheck checkbox and click button. The system will return to the Fig. 2 screen. This can be repeated till the
Concentrator is detected.
Fig. 3
When the program is switched to simulation mode the program does not perform any data
corrections or controls of the Concentrator (no serial communication are not physically executed).
The detector orientation, high voltage and the threshold can be changed using visual controls.
To transfer changes to the Concentrator button has to be applied.
The box is used to power off GRS-2 spectrometer via serial port. It is not used for
GRS-16/GRS-10 spectrometers.
To proceed to spectra data collection display press button. The button label will be
changed to . To terminate data collection apply button.
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2.5. DOWN/UP DISPLAYAll down and up looking detectors are summed into separate spectra and displayed as shown
on Fig.4. The blue color trace represents down looking spectra and the red color trace represents up
looking spectra. Total counts for both spectra are printed with appropriate colors. Traces are
updated every second with new data. To stop communicating between the host computer and theConcentrator press button. control allows changing visual scale of the traces.
The checkbox allows applying an auto scale mode.
control allows switching between accumulation (data is summed every
second) and single second measurements.
Fig. 4
Clicking on the mouse left button close to the graph draws ablack cursor. It can be moved left
or right by the [channel] control. If the cursor is visible the appropriate channel valueis displayed and updated each second when the traces are updated (Fig.5). If
checkbox is checked the peak resolution is displayed beside.
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Fig. 5
Cursor is inhibited from channel 1 to channel 4, since those channels are used for internal
functions.
PEAK ID checkbox indicates significant peaks positions visible (Fig.6 shows the single
detector spectra measuring Th (Tl208) sample in one-second readings).
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Fig. 6
2.5.1. Resolution calculationResolution is based on half peak width calculation, with background removed. If the statistics
of the peak is not acceptable the resolution will show 0.0 and if the peak is not defined properly it
will show 99.9. For proper calculation adequate number of pulses should form the peak.
Background is subtracted and the peak is analyzed. Peak position with background subtracted and
the resolution are displayed in the last two columns. Caution should be exercised because of the
automated simple background removal. The resolution automatically calculated does not represent
absolute resolution of the detector. Resolution of the same detector measured with different
instruments may vary. Consistency of the measurement assures that if the detector is measured with
the same instrument any changes in the quality of the detector can be detected. It should be used forcomparison only. See definition of resolution in 6.1.1. Differences of the resolution from individual
measurements within +- 0.3% are acceptable, as well as slightly lower resolution than the average
of individual detector resolutions when summed together.
STATUS tab on the form shows details of the crystal parameters and if equipped with analog
converter the analog channel readings (Fig. 7).
STATUS column indicates the state to the gain control algorithm for each detector
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Fig. 7
Status Meaning
T Gain latched on Thorium
U Gain latched on Uranium
K Gain latched on Potassium
A Gain controlled from almanac
N No gain adjustment - wait
n Error in spectra last spectrum repeated
0 Detector not connected
2.5.2. Individual detector displayIn order to be able to adjust and verify individual detectors the program must be switched toIndividual Detector Display by selecting menu item View/Individual/All. Each detector is
presented by its own trace. All controls are the same as for Down/Up display. The table displayed
beside traces describes some detector parameters or statuses:
the X column showsdetector number; the TC column shows total count for the detector; the State column shows the state of gain adjustment
If only one detector trace needs to be shown select View/Individual/DetectorX menu item, where X
is a number of the appropriate detector (Fig.5). Menu items Source/Input, Source/Output,
Source/Tune are used to switch between data displayed. To return to Down/Up display menu itemView/ View UpDown has to be applied.
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3.CALIBRATION PROCEDUREBegindata collection by pressing button. The screen will display spectra trace from
data collected (if Tab is selected) and will be updated once a second. To calibrate
individual detectors it is necessary to check checkbox for standard crystals or checkbox for small crystals. The screen will be switched the program to the IndividualDetector Display (Fig.8). It is necessary to use Th (Tl208) sample (approximate 5 micro Currie)
with low self-absorption of low energies.
Note: Small detector is considered detector volume of less than approximately 1litre (60 cci).
If the box contains DOWN looking detectors only than one sample placed above or beneath
the box and the distance adjusted to Total count measuring about max 4000(+/-200) for large
detectors and about 2000(+/-140) cps for small detectors. is adequate. If the box contains Up
looking detectors two samples may be necessary to assure that all the detectors are well exposed to
the radiation of the calibrating samples. Th sample is used because of its multi energy radiation
peaks.
The calibration procedure consists of two parts:
Initial Gain adjustment Linearity calibration.
3.1. INITIAL GAIN ADJUSTMENTBefore the program is switched into calibration mode, individual input spectra mode should be
selected. Experienced operator may skip the next paragraph.
3.1.1.
Easy gain adjustmentBecause of single energy peak, Cs137 sample (less than 5 microCu) may be used to establish
the setting of the detector. The Cs peak of the input (uncorrected) spectra should be located
approximately around the channel 50. The initial gain adjustment is achieved by the High Voltage
(HV) change. When the HV is adjusted up or down in the Status Window, it has to be transmitted
to the Concentrator. After the high voltage application you will see the shift of the peak and re-
adjustment may be necessary. Once the Cs peak is located in the approximate position Cs
sample should be removed.
3.1.2. Using Th sample for initial gain adjustmentThe Th sample should be placed close to the detector container that the Th (Tl208) 2.82MeV
sample is visible. The position of this peak should be located between by theadjustment of the HV. The operating range of the gain correcting algorithm is from channel 160 to
230 referring to the Th sample.
3.1.3. Calibration startThe Th sample should be placed (observe max total cont.) close to the detector container in
such a position that the total counts on individual detectors are similar and limited to the counts
mentioned in 3. After a short period of time the Th peak will be detected. Once stabilized the
process can system will detect parameters of the detector and proceed with automated calibration.
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3.2. LINEARITY CALIBRATIONMessage Calibration: CALIBRATING is displayed on the top of the form. For each
crystal being calibrated a progress bar is displayed with label X1...X16 (Fig.8). When all detectors
are calibrated screen will display message Calibration: FINISHED (Fig.9). When the Coef3
coefficient reaches 1.00 the detector is calibrated. Unchecking (or )checkbox terminates the coefficient calculation process. Calculated coefficients are stored in an
almanac file in the Concentrator unit and used in real time spectrum tracking and correction.
Correction of each detector provides better fit of each detector improving resolution mainly on the
low energy side. After the calibration, spectral adjustment should be checked with a Cs sample.
With spectra switched to accumulation and output mode.
Fig. 8
Calibration Progress bar
Fig. 9
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4.OTHER OPTIONS4.1. DATA DISPLAY
Program may request and display three different spectra:
Raw input spectra, Corrected output spectra and Tracking spectra.Raw and corrected spectra may be displayed as accumulated or one-second spectra. The
Tracking spectra are already accumulated in the Concentrator. This spectrum serves for detection of
natural reference peaks.
4.2. DATA RECORDINGAcquired data can be recorded in the standard PEI data file format and reviewed by the
PEIVIEWprogram using File/Record data menu item. Recording will be stopped if an operator is
changing data requesting format (All UP-Down Individual). To stop recording manually
simply click File/Record data menu item again. In all cases the data file will be closed. File name is
generated with same rules as it is done by AGIS application.
4.3. PROGRAM TERMINATIONTo terminate the calibration program simply close main form.
4.4. FRONT-END ELECTRONIC TESTThis program may be used by the expert users to test the front-end detector electronics. For
this program application please contact the manufacturer.
4.5. SPECTROMETER VERIFICATIONCharacteristic of the Spectrometer calibration can be verified with Verify menu item. Theverification can be based on Cs137 reference (Cs137 sample is required) or K40 reference (no
samples required). To perform the verification it is necessary to create a reference file after the
standard calibration is done by clicking menu item. The form
Fig.10 will appear. Select a reference element and fill up the Client Name and location fields and
click OK.
Fig. 10
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The form Fig.11 will appear (the K reference was selected to produce the screenshot).
If you have a Cs sample and want to create a new statistics file with it you have to place your
sample close to the detector container now. First the program will wait for all crystals to be
Thorium tuned, and then it will collect the appropriate statistics during several minutes. Wait until
the verification form is closed. The appropriate reference file CS_STAT_{YYMMDD}.txt or
K_STAT_{YYMMDD}.txt will be created on the hard drive, where {YYMMDD} is a string
containing two last digits of the year, two digits of the month and two digits of the day of the file
creation. The message Statistics was stored will come. After the file was created with
spectrometer properly calibrated it is possible to check periodically the spectrometer status using
Verify menu item. To do it is necessary to select menu item and place a Cs
sample close to the detector container if the file was created with Cs sample, or choose menu item if K40 reference was used to create a reference file. A form with progressbar will reflect the verification progress. The message Verification is successful or Verification
failed! will notify about verification result. In case of verification failure it is necessary to
recalibrate the spectrometer.
Fig. 11
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5.PRINCIPLES OF AIRBORNE GAMMA RAY SPECTROMETRY(Extract from the document: Airborne Gamma Ray Spectrometer Surveying 1991.)
This section outlines briefly the physics of gamma rays and the principles of instrumentation
used to detect them. The emphasis is on aspects relevant to the practical details of AGRS. Fordetailed accounts of these topics the reader should consult the texts noted in the Bibliography.
Pico Envirotec advanced spetral stabilization technique and advanced QC software makes
some of the below described techniques redundant, but for the completness of the understanding
of AGRS they are included and it is upon the user or contract to ensure properly collected data.
5.1. GAMMA RADIATION5.1.1. Radioactive decay
There are many naturally occurring radioactive elements. However, only three have isotopes
that emit gamma radiation of sufficient intensity to be measured by AGRS. These three major
sources of gamma radiation are:
(a) Potassium-40 which is 0.011 8% of total potassium,
(b) Daughter products in the 238U decay series,
(c) Daughter products in the 232Th series.
Many man-made radioactive isotopes also emit gamma radiation which can be measured by
AGRS. These man-made isotopes are produced by nuclear reactors or are the result of atomic
weapons testing programs.
High energy cosmic rays produced outside the Earths atmosphere can also be detected by
AGRS. This cosmic radiation interacts with the molecules of the atmosphere, the aircraft structure
and the detector itself to produce a variety of high energy radiation. This cosmic ray component
increases exponentially with the height above sea level.
5.1.2. Gamma ray spectraThe energies of gamma rays produced by radioactive decay are characteristic of the decaying
nuclide. For example 40K decays to 40Ar with the emission of gamma rays at 1460 keV. Gamma ray
spectrometers are designed to measure the intensity and energies of gamma rays and hence the
abundance of particular radioactive nuclides.
Figures 1, 2 and 3 show the gamma ray spectra for potassium, the uranium series and the
thorium series. The spectra were obtained with a typical airborne spectrometer system on large
concrete calibration pads at Walker Field, Grand Junction, Colorado in the USA. The concrete
potassium, uranium and thorium. Figure 4 is a typical airborne spectrum showing gamma ray peaks
from all three radioelements.
The energy windows used to detect the gamma rays from potassium and the uranium and
thorium decay series are shown in Figs 14 and it can be seen that each window contains some
contribution from all three radioelements. Owing to gamma ray scattering in the ground, the aircraft
structure and the detector, some counts from 2614 keV 208T1 photons from a pure thorium source
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are recorded in the lower energy potassium and uranium windows. Counts in these lower energy
windows can also arise from low energy gamma ray photons in the thorium decay series. Similarly,
counts will be recorded in the lower energy potassium window from a pure uranium source and can
also appear in the high energy thorium window owing to high energy gamma ray photons of 214Bi
in the uranium decay series. As a result of the poor resolution of sodium iodide detectors, counts
can also be recorded in the uranium window from a pure potassium source. A correction procedure,known as stripping, must be made to gamma ray spectrometer data to compensate for this spectral
overlapping.
5.1.3. Interaction of gamma rays with matterIt is clear from Fig. 1 that the monoenergetic spectral lines emitted during decay have been
smeared and broadened by the time they are recorded by an airborne spectrometer. These
broadened lines are generally called photopeaks and are the result of the limited resolution of the
spectrometer. The gamma rays also interact with material in the ground and in the intervening air
before reaching the detector. These interactions, as well as those within the detector itself, have asignificant effect on the measured gamma ray spectrum.
Gamma rays interact with matter by several mechanisms including the photoelectric effect and
Compton scattering. In the photoelectric effect the whole energy of a low energy gamma photon is
given up to an atomic electron. In Compton scattering, gamma rays lose part of their energy to
electrons and are scattered at an angle to their original direction. Because both these effects involve
electrons, the attenuation of gamma rays in a particular material is proportional to its electron
density. A third effect is pair production, in which the whole energy of a gamma ray is lost in the
production of an electronpositron pair. This process predominates at high energies, particularly
in materials with high atomic numbers, and is a significant process in the absorption of high energy
gamma rays in sodium iodide detectors.
Because most materials (rocks, soils, air and water) encountered in airborne radioactivitymeasurements have a low atomic number and because most natural gamma rays have moderate to
low energies (less than 2614 keV), Compton scattering and the photoelectric effect are the
predominant absorption processes occurring in the ground and in the air. Since both these processes
involve interactions with electrons, the attenuation of gamma rays in most materials is proportional
to the electron density of the materialIn airborne spectrometry,the absorbtion of the gamma rays
from the ground by the air beneath the aircraft must be taken into account.
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6.QUALITY CONTROL(Extract from the document: Airborne Gamma Ray Spectrometer Surveying 1991.)
Three types of variables must be monitored or checked periodically to ensure high quality
radiometric data. Instrumental variables include detector gain settings, spectral stability and thefidelity of digital records, Operational variables, which include flight path position and flying
height, are similar to the operational variables of any airborne geophysical survey. The main
environmental variables which affect spectrometer surveys are weather conditions.
The quality control goals and procedures described in this section apply mainly to
spectrornetric mapping of the distribution of natural radioelements or of fallout. Search procedures
are not likely to require the same rigorous quality checking.
Sample specifications for a typical radioelement mapping survey are given in the Appendix.
6.1.
INSTRUMENTAL VARIABLES
6.1.1. Spectrometer resolutionResolution is a measure of the precision with which the energies of gamma rays can be
measured by the spectrometer. The resolution will be poor if the gain setting of any of the detectors
is faulty or if one of the detectors is damaged.
Resolution is measured using the 662 keV gamma rays from a 137Cs source. A spectrum is
plotted as shown in Fig. 10. The amplitude of the peak due to YCs is found and the width of the
peak (as a number of channels) at half maximum amplitude is measured. This is defined as the full
width at half maximum, orFWHM.
The resolution is then calculated as:
R% = 100 (keV per channel) FWHM/662 keV
For quality control purposes during survey operations, the resoluon should be found each
morning immediately after any detector gain adjustments have been made. The resolution should
also be determined after work each day, without making any further gain adjustment. The second
value will show if there is excessive drift in any detector, owing to instrument problems such as
poor temperature stability, or an electronic fault. Resolution should be 8.5 to 9.5% and must never
exceed 12%. The results of tests should be recorded in a table or on a graph as the survey
progresses and should be included in the operations report.
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Spectrum showing the 137CS peak used for determining the resolution ofa system
(FWHMfull width at half maximum).
6.1.2. Spectral stabilityAirborne spectrometers are very stable and it is unusual for sufficient drift to occur which
would affect the results significantly. However, drift can occur if the temperature of the crystals
changes or if electronic faults occur in the instrument. For this reason it is important to monitor
spectral stability to ensure data quality.
If full spectral, 256 channel data, are recorded, the best way to check spectral stability is to plotspectra summed over segments of the survey data. Typically, spectra summed over bOOs are used.
During this period the flight line will cover a range of geology, so peaks of all three main
radioelements should occur. The spectral plots should be made on a field computer if possible, to
provide the check as soon as possible. Each plot should be checked to see that the K and Th peaks
lie in the correct channels (2 channels) and that the peaks are not unusually wide. If any one of the
criteria is not met, the instrument should be thoroughly checked as a fault has probably occurred.
Any flight lines affected should be reflown.
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A second check of stability is provided by daily source checks made on the ground before
survey work each day. These also provide a check of the spectrometer sensitivity. Source checks
are mandatory if only four window data are being recorded and are normal procedures for all
natural radioelement mapping surveys. The sources must always be placed at exactly the same
point relative to the detectors in the aircraft, using a rigid locating frame if possible. The radioactive
homogeneity of the airfield apron where the source checks are to be carried out should be inves-tigated and, if necessary, a particular location occupied for every source check. A set of dead time
determinations should be made at this location, for the background and for each source. Dead time
is found in the manner described in Section 4 for calibration pads.
A standard daily source check procedure is composed of: a 60 s background recording, with
sources placed at least 30 m from the aircraft, Th source recording, U source recording and 60 s
background recording (repeated).
The U and Tb recordings should be carried out over sufficient time to accumulate at least 10
000 counts in the U window for the U source and in the Tb window for the Th source. The digital
average of each recording should be determined, on a field computer if possible, and dead time
corrected. The average of the two background recordings must be subtracted from each sourcereading, and the results plotted against time over the survey period for inclusion in the operations
report. If a source check gives results which differ by more than 5% from the mean of checks to
date, the cause of the change should be investigated.
6.1.3. Digital data fidelityThe digital data should be checked as soon as possible to ensure that all instruments are
functioning and the data system and recording system are working correctly.
If possible, profiles should be plotted from the digital data and examined to identify any
spikes, gaps or other problems in the data. If a field computer is available, it should be used for this
checking so that any faults can be identified as early as possible.
6.1.4. Test lineIf upward detectors are not used, regular flights should be made at survey altitude over water
or over a repeatable test line over land, in order to monitor atmospheric radon variations. An
overland test line also provides a daily dynamic check of instrument performance and some
indication of the effects of environmental variables such as rainfall.
If a body of water at least 2 km long and 0.5 km wide is available, then flights over water can
be used to provide a direct estimate of radon background. If upward detectors are used, then flights
over are required to determine the coefficients for the calculation of radon background. Separateoverwater flights are not necessary if many lakes are crossed during the survey as, for example, in
northern Canada.
If no suitable body of water is available, a test line should be chosen to be logistically
convenient, easily repeatable and as far as possible typical of the survey area. These requirements
are usually fulfilled by using a straight road or railway close to the aircraft base. The line should be
about 5 to 8 km long, equivalent to a flying time of about 100 s. The start and end of the line should
be marked by features which can be clearly identified on the tracking film or video. If possible the
radio-element concentrations should be more or less uniform along the length of the line. It is worth
taking a little trouble to get the best line possible.
When flying the test line at survey altitude, one should take care to maintain constant flying
height and the correct flight path. When the data are returned to the field base, the fiducials of the
start and end points of the line should be determined. and the averages of the various radiometric
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and altimeter data determined over the. interval using the field computer. The data should be
corrected for dead time, as well as cosmic and aircraft background. The results should be plotted
against time over the survey period and the plots included in the operations report. Use of test line
results to estimate radon background is described in the section on data processing.
High level test lines, flown at 800 m above ground level, have been used to estimate radon
background, but this procedure cannot be recommended. The radon measured at this level may notbe representative of the value at survey height and there may also be a significant contribution from
the ground if the area contains granites or other radioactive rocks,
6.2. OPERATIONAL VARIABLES6.2.1. Flying height
Flying height at AOL is an important operational variable, because gamma rays are attenuated
by air, and corrections must be made for variations in flying height.The normal acceptable variation in flying height is 20% of the nominal height, that is from
110 to 135 m for a nominal survey height of 120 in. In hilly or~ mountainous terrain, it may not be
safe to remain within these limits, and pilots must~ use skill and judgement to provide the best
results without endangering the aircraft. As a general rule, spectrometric data obtained at a height
greater than 250 m over a distance greater than 12 km will be of little value.
To monitor flying height, one should examine the profiles of radar altitude and any areas
where the flying height is out of specification should be discussed with the pilot. Provided aircraft
safety permits, these tines should be retlown or infill lines introduced. In some cases, deviation of
the flight line may be preferable to a large deviation from nominal flying height.
6.2.2. Flight path spacingEach survey flight should be plotted onto the navigation maps as soon as possible. Any out of
tolerance flying should be identified quickly so that infill or repeat flights can be specified.
The tolerance normally permitted for flight path spacing for natural radio-element mapping is
150% of the nominal spacing over a maximum distance of 5 kin, or 200% of nominal spacing at
any point. For 1 km spacing, this means that any gap greater than 1.5 km x 5 km between two
adjacent lines must be infilled, and that any flight lines more than 2 km apart are out of tolerance.
Safety considerations override the specifications for flight line spacing.
Flight path spacing is of importance in a search for radioelements as poor navigation can result
in a target being missed. The same tolerances as those used for mapping surveys can be set andmust be taken into account when deciding the optimum search pattern.
6.2.3. Flying speedThe aircraft speed is rarely the cause of problems in spectrometric surveying. The area of
ground sampled by the detector during each second will be greater as the speed increases and a
point source anomaly will be reduced in amplitude. For highly detailed mapping surveys, a
maximum acceptable speed may be set.
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6.3. ENVIRONMENTAL VARIABLES6.3.1. Precipitation
Rain affects the results of a natural radioelernent mapping survey because waterlogged soil
attenuates radiation from the ground. Areas of recent heavy rain ~ should therefore be avoided
during surveying.
Rain during a fallout mapping survey will bring down more radioactive dust f4~ onto the
ground. Contamination of the survey aircraft by fallout in rain, either while ~ the plane is in flight
or on the ground, should be avoided.
Snow forms a radiation attenuating blanket over the ground: l0 cm of fresh snow is equivalent
to about 10 m of air. Mapping surveys should be discontinued if there are more than I or 2 cm of
snow on the ground.
6.3.2. Atmospheric radonAs discussed in the section on calibration, there are ways to estimate and remove the effects of
atmospheric radon. However, the problems caused by radon are greatest when temperature
inversion conditions occur, as the radon becomes trapped beneath the inversion. If possible. these
conditions should be avoided, particularly if no upward detectors are used.
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APPENDIX A: GRS-16/GRS-10/GRS-2 TECHNICAL
PARAMETERS
Spectra resolution: 256 channels optional 512.
Data sampling: 1sec and longer. 0.5sec optional
Energy spectra: 47keV to 3MeV with threshold adjustable fromThreshold: 47keV to 300keV.
Energy channel width: @255 channels 11.7keV.
Cosmic Rays: All energies above 3MeV are detected as Cosmic Rays in
channel 255.
Anticoincidence: For improvement peak-valley ratio on lower energies,
coincidental pulses detected among neighboring detectors are
removed and placed in channel 0.
Spectra tracking: Fully automatic on natural radionuclei. Independent tracking
for individual detectors - Extended range via fine control of
high voltage (resolution 0.3V).
Time to stabilization: Usually less than 30 seconds on the ground and less than 3
minutes in the air at 100m altitude (based on 4 liters of
individual detector volume). In case of a power failure old
tracking parameters (almanac) are used till new tracking is re-
established.
Spectra correction: Automatic after system calibration. Calibration is required
once a year or when a detector is replaced.
Max number of detectors: 10 detectors controlled by one GRS-10 concentrator, 16
detectors controlled by one GRS-16 concentrator, 2 detectors
controlled by one GRS-2 concentrator. Each detector can be
specified as down or up looking or it can be remotely turnedoff.
Signal sampling: 25 MHz by an internal 12bit A to D for each detector.
Quantizing error: The least significant bit at 25MHz sampling flash 12 bit
analog to digital converter
Peak detector: Digital - time resolution 40nsec.
Dead time: Insignificant for less than 2000cps per detector (2.8.4)
Maximum pulse rate: > 30000cps per each detector. If more than one detector is
used substantial number of coincidental events is recorded in
channel 0. These events are part of the maximum pulse rate
per detector.
Maximum channel capacity: 65500 countsOptional Outputs: Absolute activities and radiation exposure can be calculated in
real time. (Aircraft altitude must be transmitted to the
GSR410.)
Communication: Serial from the detector unit to Concentrator.
Serial from Concentrator to Data acquisition system.
Serial from Concentrator to Superconcentrator and Data
acquisition system.
Power requirements: Version 12V voltage: 9 to 18V,
Version 24V voltage: 18 to 36V,3.5W per detector 12W per concentrator.
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APPENDIX B: RECOMMENDED DATA ACQUISITION
SYSTEMS (IRIS/AGIS)
Airborne or truck-borne system IRIS (Integrated Radiation Information System) and AGIS
(Airborne Geophysical Information System) support fully the Gamma Spectrometer GRS-16/GRS-
10/GRS-2. Both systems include precise DGPS navigation with flight path guidance and completereal time data acquisition.
This picture presents gamma spectrometers connected to the IRIS/AGIS main console.
Appendix D: 44
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APPENDIX D: REFERENCES
Aviv, R., and Vulcan, U., 1983. Airborne gammaray survey over Israel: the methodology of the
calibration of the airborne system. Israel Atomic Energy Commission, Report No. Z.D. 58/82
Dickson, B.L., and Lovborg, L-, 1984. An Australian fiicility for the calibration of portable gammarayspectrometers. Exploration Geophysics, 15(4), pp. 260263.
Grasty, Ri., 1979. Gamma ray spectromete methods in uranium exploration theory and operational
procedures; in Geophysics and Geochemistry in the Search for Metallic Ores; Peter 5. Hood, editor;
Geological Survey of Canada, Economic Geology Report 31, pp. 14716 1.
Grasty, R.L., 1982. Utilizing experimentally derivrd multichannel gaxnn]aray spectra for the analysis of
airborne data. Uranium Exploration Methods, OECD, Paris, pp. 653-669.
Grasty, RE, 1987. The design, construction and application of airborne gammaray spectrometer
calibration pads Thailand; Geological Survey of Canada, Paper 8710,34p.
Grasty, R.L., Wilkes, P.O., and Kooyman, R., 1988. Background measurements in gammaray surveys.
Geological Survey of Canada, Paper 8811.Grasty, R.L., Holman, P.B., and Blanchard, 1, 1991. Transportable calibration pads for ground and airborne
gammaray spectrometers, Geol Sun. Can., Paper 9023, 26 p.
Green, Ak, 1987. Levelling airborne gammaradiation data using betweenchannel correlation
information. Geophysics, 52(11), 15571562.
IAEA, 1976. Reporting Methods and Calibration in Uranium Exploration. Technical Report Series no. 174,
International Atomic Energy Agency, Vienna.
IAEA, 1991. Airborne gamma ray spectrometer surveying. Technical report series, no. 323, International
Atomic Energy Agency, Vienna
Kirkegaard, P. and Lovborg, L. , 1974. Computer modelling of terrestrial gammaradiation fields. Riso
Report No. 303.Lovborg, L., 1984. The calibration of portable and airborne gamma-ray spectrometers - Theory, problems,
and facilities. Riso National Laboratory, DK-4000 Roskilde, Denmark, Report RisoM-2456.
Lrbcrg, L., Kirkegaard, P., and RoseHansen, 3., 1972. Quantitative interpretation of the gammaray
spectra from geologic formations; Proceedings of the Second International Symposium on the Natural
Radiation Environment, Houston, Texas, edited by J.A.S. Adams, W.M. Lowder, and TI. Gesell, p.
155180.
Markkanen, M., At-vela, H., 1992. Radon emanation from soils; Radiation Protection Dosimetry, Vol. 45
No. 1/4 pp. 269272.
Minty, B.R.S., 1992. Airborne gammaray spectxometric background estimation using full spectrum
analysis. Geophysics, 57(2), 279-287.Minty B.R.S. and Kennett B.L.N., 1995. Optimum channel combinations for multichannel airborne
gammaray spectrometxy. Exploration Geophysics, 25, 173178.
Rogers, Vt., Nielson, ICK and Kalkwarf DR., 1984. Radon attenuation handbook for uranium mill tailings
cover design. National Technical Information Service, U.S. Dept. of Commerce,
NUREG/CR-3533.
Wilde, S.A. and Low, G.E., 1978. Perth, Western Australia, 1:250,000 Geological Series Explanatory
Notes, Sheet SHSO14, Geological Survey of Western Australia.
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APPENDIX E: CONTACTS
Pico Envirotec Inc.
752 Madeline Heights,
Newmarket, Ontario,
L3X 2J7 Canada
Tel: +1 905 853 8536,
Fax: +1 905 853 9668,
e-mail:[email protected].
www.picoenvirotec.com
AURA, s.r.o.
Uvoz 56
602 00 BrnoCzech Republic
Tel: +420 5 43 245 111
Fax: +420 5 43 245 111
e-mail: [email protected]
http://www.aura.cz/
mailto:[email protected]://www.picoenvirotec.com/mailto:http://www.aura.cz/http://www.aura.cz/mailto:http://www.picoenvirotec.com/mailto:[email protected]Recommended