PeiCalib.pdf

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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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Rev: 5.0 GRS-16/GRS-10/GRS-2 Operation Manual

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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GRS-16/GRS-10/GRS-2 Operation Manual Rev: 5.0

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

Pico Envirotec Inc. 3/29


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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]

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