GRS-500 OPERATIONS MANUAL

SCINTREX LIMITED Head Office: In the U.S.A.: In Australia: 222 Snidercroft Road 10816 East Newton Street 1031 Wellington Street Concord, Ontario Suite 110 West Perth L4K 1B5 Tulsa, Oklahoma West Australia, 6005 74116 Tel: (905) 669-2280 Tel: (918) 438-9255 Tel: 61 (9) 321-6934 Fax: (905) 669-6403 Fax: (918) 438-9226 Fax: 61 (9) 481-1201 . P.N.: 807 700 Version 2.0

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April 1997

TABLE OF CONTENTS

Paragraph Description Page 1 GENERAL INFORMATION .......................................................5 1.1 Scope of Manual...........................................................................5 1.2 Functional Description...................................................................5 1.3 Purpose of Unit ............................................................................5 2 DESCRIPTION ......................................................................... 10 2.1 Application................................................................................. 10 2.2 Physical Description.................................................................... 10 3 THEORY OF OPERATION ...................................................... 11 3.1 Introduction ................................................................................ 11 3.2 Gamma Ray Detection................................................................ 11 3.3 Liquid Crystal Display................................................................. 12 3.4 Audio Circuit and Threshold Controls ........................................... 13 3.5 Calibration Source....................................................................... 16 3.6 Description of Controls................................................................ 17 4. OPERATION ............................................................................ 20 4.1 Introduction ................................................................................ 20 4.2 Instrument Storage...................................................................... 20 4.3 Description of Controls, Switches and Indicators........................... 23 4.4 Instrument Assembly .................................................................. 23 4.5 Battery Replacement .................................................................. 24 4.6 Battery Test ............................................................................... 25 4.7 Operating Information ................................................................. 26 5 PREVENTIVE MAINTENANCE.............................................. 27 5.1 Introduction ................................................................................ 27 5.2 Fault Isolation ............................................................................. 27 6 INSTRUMENT CALIBRATION PROCEDURE........................ 28 6.1 Introduction ................................................................................ 28 6.2 Calibration Procedure.................................................................. 28 6.3 Long-Term Gain Adjustment Control............................................ 31 6.4 Dead Time ................................................................................. 32 6.5 Count Rate Capacity................................................................... 33 6.6 Measurements of Yellow Cake.................................................... 33 6.7 Analog Ratemeter Output Connector ........................................... 33 Appendix A Test Pad Calibration.................................................................... 34

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Appendix B Warranty and Repair................................................................... 37

LIST OF ILLUSTRATIONS

Figure Title Page 1-1 GRS-500 Differential Gamma-Ray Spectrometer / .........................1 Scintillometer 4-1 Location of Controls and Indicators.............................................. 21 4-2 Handle Assembly Procedures...................................................... 24 4-3 Battery Information..................................................................... 25 6-1 Typical Calibration Source Markings ............................................ 30 6-2 Calibration Sequence................................................................... 30

LIST OF TABLES

Table Title Page 3-1 Uranium (Radium) Series ............................................................ 14 3-2 Thorium Series ........................................................................... 15 4-1 Instrument Complement .............................................................. 20 4-2 Description of Controls and Switches ........................................... 22 6-1 Observed Count Rates vs. Actual Count Rate .............................. 33

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Figure 1-1 GRS-500 Differential Gamma Ray Spectrometer / Scintillometer

SECTION 1

GENERAL INFORMATION

1.1 SCOPE OF MANUAL This manual describes the GRS-500 Differential Gamma Ray Spectrometer / Scintillometer manufactured by Scintrex Limited Concord, Ontario, Canada. The information is provided for personnel responsible for operation of the unit. Technical Specification are given in Table 1-1. 1.2 FUNCTIONAL DESCRIPTION The instrument is a compact portable field spectrometer with simplified operation controls. It is carried in a leather holster either by a shoulder strap or by attachment to a waist belt for general reconnaissance work. In this mode, gamma radiation can be monitored and indicated by an audio tone, the pitch of which increases according to the concentration of gamma radiation. The instrument may also be hand held when precise measurements are made. In this mode, the detected gamma rays are counted for a specific period and the resultant counts per second are displayed on a numeric readout. 1.3 PURPOSE OF UNIT Effective uranium exploration programs involve several standard techniques and a variety of specialized tools. The selection of these depend on a number of factors including the nature of the target and its surrounding equipment, the time and personnel available and budget restraints.

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Spectrometers are essential in any exploration program because they identify the sources quickly in terms of the parent element. These are therefore used for detailed examination, either of individual occurrences or as part of a systematic survey over a grid. Spectrometers are also used to provide rapid quantitative radio-assays of the three elements of interest. They find extrusive use on outcrops and for examination of drill cores, chip samples or floats. Central to any program are two devices which measure the gamma radiation emitted by various daughter isotopes in the uranium decay series. The first of these, for general reconnaissance, is a sensitive wide energy band spectrometer. This is a simple instrument which measures total gamma ray activity from the uranium series, as well as emitters from the naturally occurring potassium and thorium series. It is an excellent tool for rapid location of airborne anomalies, detection of local concentrations of radionuclides in outcrop, and the location of finite sources occurring in boulder trains and detritus. The second instrument is more specific in its application and function, but is still fundamental to any project. It is an accurately-calibrated stable sensitive spectrometer which detects gamma radiation originating from certain discrete isotopes. These include 214Bi, 208Th and 40K isotopes with well defined energy peaks from the Uranium, Thorium and Potassium series respectively.

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Specifications Detector: NaI (Tl) crystal and high stability photomultiplier tube with a mu- metal (magnetic) shield. Detector volume 124 cc (7.5 cu. in.). Mechanically ruggedized. Resolution: Typically 8% FWHM in a 2π 137Cs Field at an observed count rate of 6000 cps over an energy interval from 80 kev to 700 kev. Resolution Less than 1% at an observed count rate of 6000 to Deterioration as 50,000 cps over an energy a function of interval from 80 kev to 700 kev. count rate: Energy Windows: Switch selectable to: tc1 Total count above 0.08 MeV tc2 Total count above 0.40 MeV k All gamma energies between 1.35 and 1.59 MeV u All gamma energies between 1.65 and 1.87 MeV t All gamma energies above 2.45 and 2.79 MeV cal Measures Barium-133 photo peak at 0.352 MeV Spectral shift: Less than 1% from 1,000 to 25,000 cps and less than 2% from 25,000 to 50,000 cps, integrated over an energy interval from 80 kev to 3 Mev. The specified count rates are the observed count rates and are subject to dead time corrections (ie., 50,000 cps observed = 62,5000 cps actual).

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Dead time: 4 microseconds. Observed count rates are subject to corrections due to dead time. Actual count rate equals CA = Co where Co is observed 1-Co Td count rate and Td is the dead time Display: .....Ruggedized five-digit liquid crystal display (LCD) including ‘cps’ ....descriptor, decimal point, battery charge status triangle with three bars. Overflow When count rate exceeds the 99,999 cps count capacity, the ‘cps’ Indicator: descriptor on the display will be removed to signify to the operator that the counts displayed are not normalized. Calibration Actual calibration number is stamped on the back of the calibration Number: source holder. Calibration Nil Source background interference: Calibration Barium-133 (133Ba). Typical activity 1 microcurie. Activity located in a Source: screw on plug. Incorporated into the unit is a 2π lead shield. Field Calibration An 11-position switch allows the operator to change the pulse height Control: gain in increments of ±2% from 0 to +12% and from 0 to -10%. This feature allows for rapid accurate field calibration. Long-Term A 10-turn continuous precision control protected by a screw-on cap Calibration allows for pulse height gain adjustments, when the field calibration Control: control is at the end of its range. A variation of about ±50% relative to the factory set pulse height gain is possible. Sample Rate: 1.0 or 10.0 seconds, automatic recycle for all energy levels except for the calibration position which utilizes a 1 second sample period only. Audio: High efficiency transducer coupled to an acoustic port for maximum sound pressure. Audio Sensitivity: Frequency of the sound is 5 times the actual displayed count rate. This feature permits detection of subtle anomalies.

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Audio Step Time 0.5 seconds from 0 to 2500 cps. Response: Automatic Audio The audio is cut-off automatically when the audio frequency exceeds Cut-Off: 3,500 cps. This feature will reduce unnecessary power drain from the batteries, specifically in high background areas or when the unit is calibrated. Spectral Shift as Less than 1% from fully charged batteries to fully depleted batteries. a function of battery charge: Spectral Shift as Typical, -0.3% per °C. a function of Temperature: Spectral Shift as Less than 1.5% from 0 to 20 seconds. a function of power turn-on settling time: Power: Four alkaline C-cells. Typical lifetime is about 45 hours at 6 hours/day at 23°C ambient temperature without audio and an average total count rate of 1,000 cps. Battery Life Time The battery monitor, located on the display consists of a triangle and three bars. When fully charged batteries are used, all three bars will be displayed. Each bar represents about 15 hours of operational time used. When all three bars disappear, the triangle commences to flash on and off, warning the operator that the batteries are nearly discharged (about 10 minutes later under load). A keyed siren-like sound is generated instructing the operator to change the batteries. Environmental The unit is completely sealed and may be operated in the rain. Scintrex Protection: does not guarantee complete immersion in water for long periods of time. Operating -10°C to +50°C. Temperature: Dimensions: 235 x 115 x 640 mm (9.25 x 4.5 x 2.5 ins). Net Weight: 5.5 lb (2.5 kg) including alkaline C batteries. Shipping Weight: About 10.0 lb (4.5 kg). Instrument The handle located on top of the instrument is removable.

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Handle: Standard System Spectrometer / Scintillometer, 8 C-size alkaline batteries, ruggedized Components: leather case with shoulder straps, screwdriver, operating manual, spare gaskets and shipping / storage case. Options: Rate meter output connector. Rubber trenching boot. Selectable audio sensitivity ratios (standard 1:5), available (1:1), (1:2), (1:3), (1:4). Spare parts provisioning maintenance program and audio loudness.

SECTION 2

DESCRIPTION

2.1 APPLICATION The instrument is a portable five-channel unit for measuring all terrestrial gamma radiation. It is a ruggedized, high-performance spectrometer which includes features not available in other similar instruments. The instrument is capable of operating in rain and very high humidity as well as low ambient temperatures. Primary design considerations included human engineering factors and long-term operational reliability. They also include production of a instrument with tremendous sensitivity while maintaining portability. 2.2 PHYSICAL DESCRIPTION The instrument is a hand-held device with the circuitry built into a rectangular cast-aluminum waterproof enclosure with sealed controls and battery compartment. When the unit is being hand carried by the cantilever type handle, the numeric readout is visible in front of the hand. All thumb-actuated controls and switches are located on the end of the enclosure below the wrist. All control knobs and caps are made from stainless steel for corrosion resistance.

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2.2.1. SCINTILLATION DETECTOR The instrument contains a thallium-activated, sodium iodide crystal with a volume of 124 cc (7.5 in3). The NaI (Tl) crystal is coupled to a high-stability photomultiplier tube (PMT) to form the detector. The geometry of the detector is optimized for maximum detection sensitivity . The PMT is shielded magnetically to protect it against influence from external magnetic fields. The entire detector is ruggedized mechanically and protected from normal ambient temperature changes as well as mechanical shock (30G). However, it is still a sensitive part of the instrument and accordingly should be treated with caution.

SECTION 3

THEORY OF OPERATION

3.1 INTRODUCTION This section is limited to general principles of scintillation together with functional descriptions of the operational and calibration switches and controls which are accessible to the operator. 3.2 GAMMA RAY DETECTION A scintillation phosphor is a special chemical which is capable of converting energy lost by ionizing radiation into small impulses of light. Ionizing radiation can be in the form of gamma photons, alpha or beta particles. The invisible light impulses generated by the phosphor are detected by a photomultiplier tube (PMT). The optical characteristics of the PMT match the optical characteristics of the light impulses. Therefore, they are compatible. The function of the PMT is to convert the light

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impulses into electrical impulses. The electrical impulses are then processed by electronic circuitry. There are many different scintillation phosphors, each with specific characteristics. One of the most widely used, and the best for this application is thallium-activated sodium iodide, NaI (Tl). This material has a high atomic number, (SG = 3.2), which exhibits efficient stopping power for gamma rays. It has the highest luminescent efficiency resulting in large light impulses or large pulse amplitudes for low energy gamma ray interactions. NaI (Tl) is an inorganic material. It is extremely hygroscopic and is relatively fragile when subjected to severe mechanical shocks or large temperature variations. NaI (Tl) is manufactured in a crystal form, packaged using specially developed optical techniques and sealed in moisture proof containers. The crystal and PMT are commonly referred to as the ‘detector’. One characteristic of the light impulses is that they contain information within their amplitudes. Therefore, the amplitudes of the light and resultant electrical impulses, vary in a random fashion. The amplitudes of each electrical impulse is directly proportional to the incident gamma ray energy that was deposited in the crystal. The detector detects virtually all gamma radiation to which it is exposed. In the terrestrial radiation environment, the gamma ray energy ranges from zero to 3000 keV. This range accommodates all naturally occurring radio isotopes, such as uranium-238 (238U), thorium-232 (232Th) and potassium-40 (40K). The probability of a gamma ray being absorbed by the crystal is a function of detector geometry. The probability of gamma ray detection is greater when the source emits low energy gamma rays than when it emits high energy gamma rays using the same detector. An analysis of the gamma photon spectrum indicates that the count rate increases from the high energy end to the low energy end. In general, the count rate versus energy curve (spectrum) is exponential. When gamma ray enters the detector and it happens to collide with an electron within the crystal material, it may impart a portion of its energy to the electron. Because of the collision, the gamma ray loses some of its initial energy. This results in a gamma ray with a lower energy level. This increases the probability of its being fully absorbed by the crystal. This phenomenon is called ‘Compton scatter”. 238U and 232Th have very complex decay chains. See Table 3-1. However, 40K has a single decay product argon-40. The industry standard energy lines for 238U, 232Th and 40K have been established as follows: (a) 1.76 MeV emitted from bismuth-214 (214Bi), a daughter decay product of 238U. (b) 2.62 MeV emitted from thallium-208 (208T1), a daughter decay product of 232Th. (c) 1.47 MeV emitted from argon-40 (40Ar), the sole daughter decay product of 4-K.

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Note that actinium-228 (228Ac), a decay product of 232Th, is a major contributor to the overall count rates obtained from the 232Th decay series. 3.3 LIQUID CRYSTAL DISPLAY A liquid crystal display is located in the upper face of the housing forward of the carrying handle. The custom display contains: (a) Five numeric digits. (b) A decimal point. (c) Cps descriptor. (d) Scintrex logo descriptor. (e) Battery charge status monitor. The display is capable of operating at ambient temperatures of -15°C but with considerable segment turn-over slow down. The five numerals display the count rates. The decimal point is used to normalize the count rates obtained during a 10 second sample to yield counts per second. The cps descriptor designates that the count rate is in counts per second. This descriptor is also used as a count rate overflow indicator, where cps disappears from the display when the count rate exceeds 99,999 count per second. Whenever the cps descriptor disappears, the displayed number must be defined as counts only and has no further meaning. The battery charge status monitor consists of a wedge shaped triangle with three bars along it base. This circuit monitors the battery charge and displays the approximate residual operational hours. The bars disappear in sequence as the power diminishes. When all three bars have disappeared, the wedge commences to flash on and off. This provides a visual warning that battery replacement is imminent (ie, within approximately 10 minutes). Subsequently this is followed by an overriding audio alarm. 3.4 AUDIO CIRCUIT AND THRESHOLD CONTROLS The instrument is equipped with an efficient audio transducer coupled to an acoustic port (cavity) to enhance the sound pressure.

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Isotope Symbol Half-Life Radiation Energy (MeV)

(% disintegration) Uranium-238 92U

238 4.5 X 109 yr α 4.18(77), 4.13(23)

Thorium-234 90Th234 24.1 day β

γ 0.19(65), 0.10(35) 0.09(15), 0.06(7) 0.03(7)

Uranium Group

Proactinium-234 90Pa234 1.18 min β γ

2.31(93), 1.45(6), 0.55(1) 1.01(2), 0.77(1) 0.04(3)

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Uranium-234 92U

234 2.50 x 105 yr α γ

4.77(72), 4.72(28) 0.05(28)

Thorium-230 90Th230 8.0 x 104 yr α 4.68(76), 4.62(24)

Radium-226 88Ra226 1622 yr α γ

4.78(94), 4.59(6) 0.19(4)

Radon-222 86Rn222 3.82 day α 5.48(100)

Polonium-218 74Po218 3.05 min α 6.00(100)

Lead-214 82Pb214 26.8 min β γ

1.03(6), 0.66(40), 0.46(50), 0.40(4) 0.35(44), 0.29(24) 0.24(11), 0.05(2)

Radium Group

Bismuth-214 83Bi214 19.7 min β γ

3.18(15), 2.56(4), 1.79(8), 1.33(33), 1.03(22), 0.74(20), 2.43(2), 2.20(6) 2.12(1), 1.85(3), 1.76(19), 1.73(2), 1.51(3), 1.42(4), 1.38(7), 1.28(2), 1.24(7), 1.16(2), 1.12(20), 0.94(5), 0.81(2) 0.77(7), 0.61(45)

Polonium-214 84Po214 160 x 106 sec α 7.68(100)

Lead-210 82Pb210 19.4 yr β γ

0.06(17), 0.02(83) 0.05(4)

Bismuth-210 83Bi210 5.0 day β 1.16(100)

Polonium-210 84Po210 138.4 day α 5.30(100)

Lead-206 82Pb206 Stable

Table 3-1 Uranium (Radium) Series

Isotope Symbol Half-Life Radiation Energy (MeV) (% disintegration)

Thorium-232 90Th232 14.1 x 1010yr α 4.01 (76), 3.95 (24) γ 0.06 (24)

Radium-228 88Ra228 6.7 yr β 0.05(100)

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Actinium-228 89Ac228 6.13 hr β γ

2.18(10, 1.85(9), 1.72(7) 1.13(53), 0.64(8), 0.45(13) 1.64(13), 1.59(12), 1.10 1.04, 0.97(18), 0.91(25) 0.46(3), 0.41(2), 0.34(11), 0.23, 0.18(3), 0.13(6),0.11, 0.10, 0.08

Thorium-228 90Th228 1.91 yr α γ

5.42(72), 5.34(28) 0.08(2)

Radium-224 88Ra224 3.64 day α γ

5.68(95), 5.45(5) 0.24(5)

Radon-220 86Rn220 54.5 sec α 6.28(99+)

Polonium-216 84Pb216 0.158 sec α 6.78(100)

Lead-212 82Pb212 10.64 hr β γ

0.58 (14), 0.34(80), 0.16(6) 0.30(5), 0.24(82), 0.18(1) 0.12(2)

Bismuth-212 83Bi212 60.5 min α β γ

6.09(10), 6.04(25) 2.25(56), 1.52(4), 0.74(1), 0.63(2) 0.04(1), with α 2.20(2), 1.81(1), 1.61(3), 1.34(2), 1.04(2), 0.83(8), 0.73(10) with β

Polonium-212 84Bi212 0.30 x 10-6sec α 8.78(100)

Thallium-208 81Tl208 3.1 min β γ

2.37(2), 1.79(47), 1.52, 1.25 2.62(100), 0.86(14), 0.76(2), 0.58(83), 0.51(25), 0.28(9), 0.25(2)

Lead-208 82Pb208 Stable

Table 3-2 Thorium Series

The transducer is completely sealed and water or rain entering the cavity under normal ambient conditions will not damage the transducer. If rain causes the cavity to fill, it will ultimately affect the sound pressure. Therefore, ensure that the cavity is drained. The audio signal response is directly proportional to the count rate being measured. The actual responses frequency is five times that of the observed count rate. This feature allows for a high

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degree of detectability of low intensity anomalies or just slight variances in background count rates which may have significant geological impact. This feature combined with the 10-turn audio threshold control allows for a hands-off operation for general reconnaissance work. The audio threshold control allows effectively for a threshold adjustment range anywhere from 0 to 700 cps observed count rate. This corresponds with an audio transducer frequency range of between 0 to 3500 Hz. Whenever the actual observed count rate exceeds 700 cps, the audio is disabled automatically to prevent excessive battery power consumption. If the threshold limit is set at an equivalent of 700 cps observed count rate (fully clockwise), any additional increase in observed count rate will not be heard. The threshold control maximum limit is the same as the automatic cut-off limit of the audio. Therefore, if the operator does not want to operate the audio at all, the threshold control must be set fully clockwise. Lower audio multiplication factors as well as higher or lower sound pressures are available as factory-installed options. NOTE:

When higher sound pressures are incorporated, there is a parallel reduction in battery life due to the increased power demand. A part of the audio circuit is also connected to the battery status monitor and is activated after the battery warning indicator has commenced flashing. If instrument operation is continued without renewing the batteries, a keyed audio alarm similar to a siren will start. At this point, battery replacement is mandatory to silence the alarm and also because instrument performance will be impaired. The siren alarm might also be activated, when the audio is in use and is subjected to large pitch variance when the batteries are nearly discharged. The reason for this is that the audio causes battery voltage changes which are sensed by the battery monitor. 3.5 CALIBRATION SOURCE The calibration source is a screw-in type attachment. The holder is formed in the shape of a threaded plug with a small cavity in its centre. The cavity houses a small bead containing a 1 microcurie Barium-133 radio isotope. A 2π lead shield is located behind the cavity to prevent gamma radiation from entering the detector. Therefore, the source will only emit gamma radiation through the source holder. For calibration, the source holder is unscrewed and hand held in a cavity at the opposite end of the unit.

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3.6 DESCRIPTION OF CONTROLS The instrument contains the following controls, switches and indicators: (a) Field operation controls (i) Function switch (ii) Audio threshold control (b) Calibration controls (i) Fine gain adjustment switch (calibration switch) (ii) Long term gain adjustment control 3.6.1. Function Switch (Figure 4-1) The function switch has 12 positions. These comprise 10 operating positions (ie, energy channels), a cal (calibration) position and a power OFF position. The 10 operating positions consist of two identical groups of 5 each with the groups representing 1 second and 10 second counting periods respectively. The operating positions allow an operator to select the appropriate energy channel and the count period. The first two channels designated as tc1 and tc2 (ie, total count) are the lower energy thresholds preset at 80 kev and 400 kev respectively. When the instrument is operated in either of these modes, it processes all gamma rays with energies above that preset threshold. Then it displays the total accumulated pulse count which has been received during the specific sampling period (ie, 1 sec or 10 sec). Reconnaissance surveys usually require the instrument to be operated in either the tc1 or tc2 position. The highest sensitivity is usually obtained in the tc1 mode. However, caution must be exercised because the readings that are obtained in this mode are very sensitive to source geometry as well as to source / detector separation distance. To a large extent, this sensitivity is eliminated when the instrument is operated in the tc2 mode. When ore grade analyses are conducted, it is suggested that the instrument should be operated in the tc2 mode. The remaining three operating positions are designated as k, u and t. When the switch is set to k, the instrument processes all gamma rays from 40K (1.47 Mev). When the switch is set to u, the instrument processes all gamma rays from 214Bi (1.76 Mev). When the switch is set to t, the instrument processes all gamma rays from 208T1(2.62 Mev). NOTE:

The instrument also processes all cosmic-generated energy.

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Greater statistical accuracy may be achieved, when required, by recording a series of 10-second integrated readings preferably displaced laterally to provide both time and area averages. Regardless of the sample period selected, the numeric value displayed is normalized to counts per second. When the 1 sec sample period is selected, the actual sample period is set at 2 seconds and the data obtained is normalized to counts per second. The purpose of this feature is two-fold: (a) It allows the operator to read the display properly. (b) It compensates for the slow down in display response at lower temperatures specifically from 0°C to -10°C. 3.6.2. Audio Threshold Control The left hand control is a 10-turn audio threshold potentiometer. The control is marked with an arrow in a clockwise direction indicating an increase in the audio threshold or cut-off point. When the control is turned fully counterclockwise, the audio is on continuously. Gradual clockwise rotation adjusts the point or level at which the audio is disabled. This feature allows annoying background sound to be cut out while retaining high sensitivity to detect small anomalies above this background. One major feature is that the audio has an unusually large response to small count rate variations allowing the operator to be warned. Once the audio frequency reaches a frequency level of 3.5 kHz, equal to a count of 700 cps on the display, the audio is shut off automatically. This prevents excessive power drain from the batteries and silences the high pitch sound which contains virtually no additional information. CAUTION The audio threshold control is a ten turn precision potentiometer. Two mechanical stops are incorporated in the control: One located at the fully clockwise position and the other at the fully counterclockwise position. The knob which is mounted on the shaft of this control, contains a friction mechanism to prevent ‘free wheeling’. Extreme caution must be exercised with the mechanical stops on the control. If the knob is forced against the stops, damage may occur. 3.6.3. Calibration Switch The 11-position calibration switch in the centre contains a slot for screwdriver (or coin) selection. This switch is used to make pulse height gain changes in very small increments. This switch should only be used when the unit is to be calibrated. Otherwise do not touch it. Gain changes should only be made when the count rate readings obtained are not the same as the actual calibration number, stamped on the calibration source holder. The positive gain changes are from 0 to 12% in 2% increments. Negative gain changes are from zero to -10% in 2%

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increments. The positive and negative gain changes are relative to the 0 position on the switch. This method permits convenient fast in-field calibration to allow for compensation of pulse height gain changes due to day-to-day temperature variations as well as long-term pulse height gain changes due to detector aging. 3.6.4 Long-Term Gain Adjustment Control The instrument also includes a long-term gain adjustment for the gain switch. This is located behind a threaded cap adjacent to the source holder. When the gain switch reaches one of its extreme positions due to correction of long-term gain drift, the long-term gain adjustment control may be used to recalibrate the instrument to the original condition.

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SECTION 4

OPERATION

4.1 INTRODUCTION The instrument is complete and ready for field use after the operator has inserted the four C-size batteries into the instrument. It is recommended that the operator follow each step as outlined and become familiar with the various controls, indicators and survey procedures. The inventory of the shipping packing list is in Table 4-1. • The instrument complete with 133Ba calibration source holder and handle. • Leather carrying case. • Leather shoulder strap with two dog-leash clips. • One plastic bag containing two spare screws for handle. • Screwdriver. • Eight C-size alkaline batteries. • One plastic bag containing two battery cap sealing gaskets. • Operating manual • Short form, plasticized pocket instrument instruction card. • Optional. One rubber trenching boot.

Table 4-1 Instrument Complement 4.2 INSTRUMENT STORAGE When the instrument is not to be used for a long period of time, Scintrex suggests that the batteries should be removed from the battery compartment and stored separately. Store the instrument in a cool location.

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Figure 4-1 Location of Controls and Indicators

Description Function Function switch tc1 (Total count 1) tc2 (Total count 2) k u t cal

Selects the appropriate energy window to commence a count cycle and the count duration (ie, either 1 sec or 10 sec). It also selects the functions related to calibration. This is the lowest energy threshold. It processes all gamma rays with energies above 8keV and displays the total accumulated count received during the selected count duration. This is usually the most sensitive position but it is also the most critical with respect to geometry and source-detector distance. Processes all gamma rays with energies above 400 kev. This is less sensitive than the tc1 position but provides more reliable data. Processes all gamma rays within a energy window from 1.35 to 1.59 Mev. The observed counts in this channel are from 40K, 228Ac, 214Bi and Compton scattered events from higher 214Bi energies and 208Tl. Processes all gamma rays within an energy window from 1.65 to 1.87 Mev. The observed counts in this channel are from 214Bi and Compton scattered events from higher 214Bi energies and 208Tl. Processes all gamma rays within an energy window from 2.45 to 2.79 Mev. The observed counts in this channel are from 208Tl and about 4 to 6% of the observed counts are from the highest 214Bi gamma ray energy In this position, the gain switch and the long-term gain control may be used in conjunction with the calibration source. In this position, battery power is disconnected.

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off Audio threshold control Calibration switch Long-term gain control

Sets up the threshold for silencing background noise. Audio cut-out level is increased by cw rotation. This 11 position switch is used during field calibration to make fine incremental pulse height gain changes. This control is used to recalibrate the zero selection of the gain switch.

Table 4-2 Description of Controls and Switches

4.3 DESCRIPTION OF CONTROLS, SWITCHES AND INDICATORS Operator controls and indicators are located for optimum access and visibility when the operator is using the instrument. The display is located in front of the carrying handle; controls are located below the wrist of the carrying hand for activation by the other hand (gloved if required). The calibration orifice is located on the edge of the unit in front of the display adjacent to the battery cap. The instrument includes all controls, switches and indicators necessary for operation and calibration. No other test equipment is required. The locations of controls, switches and indicators are shown in Figure 4-1. Their functions during normal operation are given in Table 4-2. 4.4 INSTRUMENT ASSEMBLY 4.4.1 Check-out When a new instrument is received, carry out the following inspection: (a) Check that the shipping container is undamaged. (b) Unpack the container and check that all items have been supplied. (c) Check that the controls and switches are in good mechanical condition. (d) If the handle is installed, check that the hardware is secure. (e) Check that the batteries are not damaged or leaking.

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(f) Check that the instrument housing is not damaged. NOTE: If any damage has occurred or parts are missing, report it immediately to Scintrex Limited or an authorized agent. 4.4.2 Handle Assembly and Removal The cantilever handle is attached to the top of the instrument by two screws. Refer to the procedures in Figure 4-2. (Two replacement screws are provided with the instrument as spares).

Figure 4-2 Handle Assembly Procedures

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4.4.3 Batteries Affixed to the underside of the unit is a chart which depicts battery loading and changing procedures; interpretation of battery life status indications; as well as calibration procedures. See Figure 4-3. NOTE: Prior to inserting new batteries into the unit, inspect batteries for leakage. Inspect compartment for cleanliness. 4.5 BATTERY REPLACEMENT The battery compartment is completely sealed and leakproof. This prevents any battery leakage, which is highly corrosive, from entering the electronics section. The battery cap is equipped with a special compression spring. When the cap is removed, a compression gasket can be seen. This gasket is compressed against a metal retaining ring and the battery cap to prevent water seepage into the compartment when the cap is screwed in hand tight.

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Figure 4-3 Battery Information

To install batteries: (a) Turn battery cap fully ccw and hold cap between two fingers. The battery cap will be pushed out, due to the internal spring action. (b) Empty battery compartment. (c) Observe carefully polarity on batteries and ensure power insertion into battery compartment. (d) If a gasket becomes worn or damaged, renew it. Two replacement gaskets are provided with the instrument, as spares. (e) Position battery cap in hole, press and rotate fully cw. 4.6 BATTERY TEST To test the batteries, proceed as follows: (a) Set the function selector to tc1. (b) Observe the wedge and bar status indicator. See Figure 4-3. NOTE: Each bar represents approximately 12 to 15 hours of operation based on alkaline C-size batteries only. (c) If wedge is flashing on and off, this is an advance warning that the batteries should be renewed. (ie, approximately 10 minutes operating life remains). After this period has elapsed, a keyed audio siren sound will be emitted. This indicates that the operating specifications may be impaired beyond this point with unreliable readings and that the batteries must be replaced. The keyed audio siren will override any background audio even when the threshold control is set fully cw. 4.7 OPERATING INFORMATION For general exploration programs, it is recommended that the instrument be carried in the leather case supplied and be attached to the waist belt. With the instrument in the leather case, it assumes the normal operating position when located downwards. To obtain accurate repeatable station readings on a grid, the operator lifts the leather case and swings it into a horizontal position for ease of reading the display and also for maintaining a constant detector source separation distance.

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CAUTION Avoid subjecting the instrument to large mechanical shocks. The detector is relatively fragile and can be damaged, although it has been ruggedized. Avoid sudden large temperature variations. In general, the unit should not be subjected to a temperature-time gradient of more than 15°C per hour. When an exploration program necessitates using the instrument in trenches or a muddy environment, it is suggested that an optional rubber trenching boot be used. This rubber boot slips over the rear of the unit thereby protecting the battery cap and the calibration source holder cavity. It prevents accumulation of radio-active mud in the actual cavities. CAUTION Avoid opening the instrument for visual inspection. This voids the warranty. Special tools are required including detailed knowledge regarding the instrument assembly. Refer to Section 5.

SECTION 5

PREVENTATIVE MAINTENANCE

5.1 INTRODUCTION The instrument is designed for field operation in a typically hostile environment. Generally, it needs virtually no maintenance under normal operating conditions. Periodically, the calibration will require checking to ensure that the unit is still operating effectively within published specifications. (a) Ensure that the unit is cleaned after use and is undamaged. Ensure that the controls are clean and function freely. (b) If the unit will not be used again for an extended period of time, remove and store the batteries. Close the battery compartment.

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(c) Prior to use, ensure that the calibration source holder and battery cap are secure. (d) Prior to use, check the battery power status. Refer to Section 4. 5.2 FAULT ISOLATION The primary causes of faulty operation can be attributed to low battery power (or poor connections) and incorrect calibration by the operator. Correction of any other circuit fault is beyond the scope of field maintenance and would require factory assistance. WARNING All warranties will be null and void if, after examination by Scintrex Limited personnel, it is established that the instrument was opened. If it becomes necessary to open the unit, first contact the service department of Scintrex Limited, in Canada or the USA or an authorized agent. Scintrex Limited will be pleased to supply the special tools required and applicable documents upon request.

SECTION 6

INSTRUMENT CALIBRATION PROCEDURE

6.1 INTRODUCTION Calibration procedures for gamma ray spectrometers using numeric displays are generally difficult and extensive. The prime reason for this difficulty factor is that the observed count rate readings are subject to statistical variations (ie, the indicated count increases and decreases rapidly and randomly). Therefore, human limitations inhibit the processing of variable numeric data and the derivation of conclusions from it. However, with some patience, the instrument can be calibrated precisely.

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6.2 CALIBRATION PROCEDURE To calibrate the instrument proceed in the following sequence: (a) Rotate the barium source holder in a ccw direction to remove it from the housing. NOTE: 1. The calibration source holder may be handled freely with no cause for concern. The extremely low 133Ba activity presents no danger to health. 2. It is important that the source holder be held firmly and stationary in the cavity by side of the battery cap to prevent erroneous readings. 3. The isotope and the instrument have been calibrated as a single unit in the factory. The resultant calibration number is metal stamped on the source holder together with the instruments serial number. (b) Observe the two numbers stamped into the holder. One is the serial number; the other is the count rate calibration number. See Table 6-1. Record the count rate number. NOTE: There is a manufacturing tolerance associated with each isotope. Therefore, the isotope within the calibration source holder is assigned to a specific instrument and calibrated with that instrument during the factory testing calibration procedure. Therefore, do not interchange calibration source holders with the other instruments. If a source holder is lost, report it to Scintrex together with the serial No. (c) Set the mode switch to the ‘cal’ position. (d) Insert the source holder into the small cavity on the rear plate of the instrument and hold tightly in place. See Figure 6-2. (e) Observe and record the count rate displayed. Take several readings and average them. The count rate should be the same as the calibration count rate number, ±55 cps. If so, terminate procedure and reinstall the calibration source holder securely in its cavity. (f) If observed count rate is different from the source number, the instrument requires either an increase or decrease in gain (ie, cw rotation for positive increase gain, ccw for negative). (g) Insert a screwdriver or coin into the slot of the 11-position calibration control. (h) Apply a +2% gain increase and observe the displayed count rate several times. Usually

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five readings should give an indication. Take notice that this calibration control is a fine adjustment and some patience is required. (j) Continue to increase the gain increments of +2% to determine the direction of the observed count rate. Continue until the observed count rate is equal to the count rate number, ±55 counts per second.

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Figure 6-1 Typical Calibration Source Markings

Figure 6-2 Calibration Sequence

(k) When negative results are obtained by applying +2% gain increments, repeat steps (h) and (j) by applying -2% gain increments.

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NOTE: The instrument exhibits a negative gain temperature coefficient of typically -0.3%/°C. When the ambient temperature increases, the gain decreases and vice versa. (m) When negative results are obtained by applying -2% gain increments, a major gain correction must be applied, Refer to para 6.3. 6.3 Long-Term Gain Adjustment Control Ultimately, the 11-position calibration switch may reach the end of its range. To correct for this, a small, factory-type calibration procedure is required. Proceed as follows: (a) Reset the calibration switch to ‘0’. (b) Set the mode selector to ‘cal’. (c) Below the mode selector is a screw type blanking cap. Remove the cap with a screwdriver to expose a slotted potentiometer adjustment shaft. (d) Unscrew the calibration source, insert it in the calibration cavity and hold it tightly by hand against the housing. (e) With the calibration source in position, rotate the shaft slowly and gradually cw and ccw, using a screwdriver, until the reading on the display matches the number inscribed on the calibration source holder. NOTE: This procedure requires very small adjustments and patience because the rapid changes in the numeric readouts makes it necessary to average the random number. Usually it is sufficient to determine the direction of the observed count rate first, when applying gain correction. When the direction is determined, continue applying gain correction until the observed count rate number equals that of the number inscribed on the calibration source holder. The unit is now recalibrated. Future drifting of the gain can be corrected, once again, using the 11-position calibration switch.

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The Barium-133 reference source used with this instrument has a half-life of about 7 years. (7.2 years). As a result the 4 digit calibration number used, should be corrected for decay. Refer to the Table below:

Time (Years) Relative Activity % 0 100 ... ... 4.0 68.4 4.5 64.4 5.0 61.8 5.5 58.9 6.0 56.1 6.5 53.5 7.0 50 *

* (Time to replace the reference source)

Example: The original Calibration Number = 3278 The corrected NEW calibration number after seven years is 50% of 3278 = 1639 6.4 DEAD TIME The observed count rates are subject to corrections due to dead time. Dead time is defined as the time that it takes for the electronics to respond and process an incoming event as a result of gamma ray interaction in the detector. During this time, the electronic circuitry cannot process another incoming event. The dead time for this instrument has been determined to be 4 µsec by standard calculations as well as the well-known two-source method. The process is random in nature and to determine the actual count rate, the following algorithm is used: CA = Co 1 - Td.Co where: CA is the actual count rate, Co is the observed count rate, Td is the specified dead time Usually, when low count rates are observed, the errors are very small. However, when count rates are high, the errors become substantial. Table 6-1 gives a list for reference purposes.

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6.5 COUNT RATE CAPACITY The instrument is capable of producing accurate count rates up to 50,000 cps. Up to this count rate level, only dead time corrections have to be applied. Beyond the 50,000 cps count rate level, additional errors other than dead time, will be introduced such as spectral shifts in excess of 2%. Observed Count Rate Actual Count Rate (cps) (cps) 1,000 1,000 5,000 5,100 10,000 10,400 20,000 21,730 30,000 34,000 40,000 48,000 50,000 62,500 60,000 80,000 70,000 97,000

Table 6-1 Observed Count Rates vs Actual Count Rate

6.6 MEASUREMENTS OF YELLOW CAKE The instrument is capable of detecting concentrations of yellow cake. However, it is necessary to operate the instrument in the tc1 mode only, because, basically one low energy gamma ray is available. 6.7 ANALOG RATEMETER OUTPUT CONNECTOR Scintrex Limited will supply, as an option, an analog ratemeter output connector. The output is calibrated to 100 mV/100 cps with a single maximum dynamic range of 5000 mV or cps. Termination impedance shall not be less than 10 kohms. This option may be used in conjunction with a chart recorder for land vehicle or helicopter surveys.

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APPENDIX A

TEST PAD CALIBRATION

A.1 INTRODUCTION The unit is a precision instrument with sophisticated circuits which are necessary for stability accurate field assays using simplified procedures. To ensure correct interpretation of results from complex deposit geometrics it is imperative that data be collected in a careful manner. A.2 CALIBRATION PRINCIPLES The instrument may be calibrated using specially designed test pads which contain known amounts of equivalent uranium, potassium and thorium. Once calibrated, the instrument may be used to determine quantitively eU, eTh and eK. However, one constraint remains. The actual data obtained from the test pads is ideal and actual field conditions do not always reveal the source geometry, or how homogenious a certain area might be. It is of great importance that a specific area is first fully tested to determine the size of the area which is yielding approximately the same readings. If the area is about the same size as the test pad, then the equivalent parts per million uranium and thorium can be determined to within a certain accuracy. It is mandatory that the instrument be located in physical contact with the source area. It is mandatory that the instrument be located in physical contact with the source area (the same as in test pad conditions) and that it be positioned in the middle of the area which yielded a near constant count rate. A.2.1 STRIPPING RATIOS Several consecutive measurements shall be made with the instrument operating in the k, u and t positions. If necessary, operate in the 10 sec sample mode for improved statistical data. Once this data is collected, the results must be stripped by applying stripping ratios. These stripping ratios eliminate Compton scatter from higher energy photo peaks as well as spectral interference. Assume that the readings taken were as follows: In the t position: Ct (cps) from the thorium bearing test pad, where Ct’ = Ct - CtB (B = background) In the u position: Cu (cps) from the uranium bearing test pad, where Cu’ = Cu - CuB

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In the k position: Ck (cps) from the potassium bearing test pad, where Ck’ = Ck - CkB Also assume that the following background readings were derived from a barren test pad. In the t position: CtB cps In the u position: CuB cps In the k position: CkB cps A.2.2 EQUIVALENT ELEMENT VALUES The equivalent thorium can be calculated directly from the formula: eTh = 1/ST [C’T] [ppm] = [ppm/cps][cps] where, ST is the sensitivity factor for Thorium (in cps/ppm), and C’T is the background corrected count rate in the Thorium channel (in cps). C’T can be derived by simply subtracting the background count rate from the actual count rate. Please note the correction in dimensionality to “ppm”. Thorium causes a Compton scattered count rate in the u position as well as some spectral interference for actinium-228 (228Ac). This ratio is referred to as α where: α = Cu’ Ct’ where Ct’ is the actual count rate in the t position due to thorium and Cu’ is the count rate in the u position due to thorium. The formula for eU can be corrected like wise. However, this time a “stripping factor” needs to be included for Thorium correction. Therefore, eU = 1/Su [C’u - αC’t] where Ct’ is the actual count rate in the t position due to thorium and Cu‘ is the count rate in the u position due to uranium and / or thorium. α is the stripping ratio from thorium to uranium, as defined by C’u / C’t. Su is the uranium sensitivity factor expressed in counts per second per ppm eU. α and Su are obtained from the test pads. Similarly, potassium concentration can be obtained as:

K(%) = 1/Sk [C’k - γ (C’u - α C’T) - β C’T]

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where, β and γ are stripping factors defined as C’k / C’T and C’k / C’U respectively. Due to the decay nature of 40K (ie, an extremely long half life), the instrument appears to be very insensitive to 40K even at 5 to 6% e40K levels. Detailed tests at the DOE calibration pads at Walker Field Airport, Grand Junction, Colorado revealed that a 1200 square foot test pad containing 5.14% e40K produced only an average count rate in the k position of about 8 counts per second. The same test pad contained only a 5.1 ppm eU and 8.5 ppm eTh with an average pad density of 2.00. Because of this problem, it is suggested that, in general, no effort be made to measure 40K specifically when it is anticipated that the 40K is combined with uranium or thorium. Calculations are complex and errors are usually substantially large thereby prohibiting proper quantitative analysis of e40K. Also, it should be noted that the thorium sensitivity is low due to the fact that the detector has a relatively small cross section and the measurement is made at the 2.62 MeV energy line of thallium - 208 with a total branch decay activity of 1/3 from the main decay chain. A.3 TEST PAD CALIBRATION DATA Calibration constants have been derived from standard test pads located in Ottawa, Canada and Grand Junction, Colorado, USA The values for the computational constants are given below: Stripping Coefficients alpha = 1.28 beta = 1.41 gamma = 0.81 Sensitivities Potassium = 1.47 cps/% Uranium = 0.09 cps/ppm Thorium = 0.054 cps/ppm

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APPENDIX B WARRANTY AND REPAIR Warranty All Scintrex equipment, with the exception of consumable items, is warranted against defects in materials and workmanship for a period of one year from the date of shipment from our plant. Should any defects become evident under normal use during this warranty period, Scintrex will make the necessary repairs free of charge. This warranty does not cover damage due to misuse or accident and may be voided if the instrument console is opened or tampered with by persons not authorized by Scintrex Limited. To validate the warranty, the warranty card supplied with the instrument must be returned to Scintrex within 30 days of shipment from our plant. Repair When to Ship the Unit Please do not ship your instrument for repair until you have communicated the nature of the problem to our Customer Service Department by facsimile, telephone, or letter, etc. Our Customer Service Department may suggest certain simple tests or steps for you to do which may solve your problem without shipping the instrument back for repair. If the problem cannot be resolved, our personnel will request that you send the instrument to our plant for necessary repairs. Description of Problem When you describe the problem, include the following information: • the symptoms of the problem • how the problem started

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• if it is constantly present, intermittent or repeatable • if constant, under what conditions it occurs • a printout of measurement data demonstrating the problem • the initial constants that were used with the instrument Please mention the instrument serial number in all communications regarding equipment leased or purchased from Scintrex. How to Ship the Unit No instrument will be accepted for repair unless it is shipped prepaid. After repair it will be returned collect. Ensure that you unplug the battery from the unit and send it with the instrument. In the case of a short battery life or possible battery problems, the charger should also be returned for diagnosis/repair. Instrument shipped for repair from outside Canada should be addressed to: Scintrex Limited c/o DANZAS Customs Brokers 1600 Drew Road, Mississauga, Ontario, Canada L5S 1S5 (Attn: Deborah Perotta) Tel: 905-405-9300 Scintrex instruments are manufactured in Canada. Consequently, there is no customer duty payable in Canada. It is advisable to state on customs documents: Canadian Goods Returned to Canada For Repair Shipments should be made by air in the original shipping case to minimize the possibility of damage in transit. Within Canada, ship by air directly to: Scintrex Limited 222 Snidercroft Road Concord, Ontario, L4K 1B5