TM372B User`s Manual
Contents
1. 4 Figure 2 4 Registering a Count When the batteries are starting to run low the three decimal points in the center of the display will flash see Figure 2 5 When the batteries are charging the three decimal points in the center of the display will be illuminated see Figure 2 6 1 Low Battery Indicator Figure 2 5 Low Battery Indicator Charging Indicator Figure 2 6 Charging Indicator 2 5 Batteries The instrument is equipped with 5 size AA NiMH rechargeable batteries located inside the instrument These batteries should not need to be replaced during normal operation When the terminal voltage of the batteries drops below a certain threshold the three low battery indicator lights will flash see Figure 2 5 The instrument will continue to function for one or two hours after this level is reached without deterioration of performance permitting the operator to conclude his her tests Once depleted the batteries will need to be charged for 16 hours to restore full charge To charge the batteries plug the supplied charger into an electrical outlet Only the charger supplied with the instrument should be used remove the cover from the charger jack and insert the end of the charger see Figure 2 1 for the location of the charger jack When the batteries are charging the three center decimal points should be illuminated see Figure 2 6 If the charger is plugged in before the batteries become low the device will not charge2. the batteries until they do become low The device will automatically stop charging after 16 hours have elapsed Chapter 3 Operation This section describes the operation of the TM372B and the calibration of the instrument for counting radioactivity in a prepared sample For information on preparation of samples or interpretation of results see ref erence section 5 1 3 1 Inserting the Sample To insert a sample in the 2 piece holder remove the sample holder assembly from the tray A hole in the tray facilitates this Reinstall the base piece with its smaller diameter located in the hole in the tray Center the filter sample on the base surface place the ring over the top with the smooth surface facing up and close the sample tray It is not usually necessary to switch the instrument off when changing samples Some light may be reflected into the detector area when the tray is open but the light seal will be restored when the tray is fully closed The effectiveness of this seal may be checked from time to time by counting for a period of time when no source or sample is installed in the instrument A light leak will show up by causing many counts to be registered Note however that the proper sensitivity settings must be established beforehand A light leak should not be confused with luminescence of the detector after exposure to light or the background noise counts that may be 1 count per minute or less 3 2 Counting After inse
3. aged or become contaminated with radioactivity from the sample Routine efficiency tests should indicate if the surface of the alpha detector has been scratched or damaged High background readings will indicate surface contamination 4 2 Circuit Functions The TM372B is basically a Scintillation counter The circuits used perform the following functions The photomultiplier tube converts the light flashes scintilla tions from the detector into electrical pulses These pulses are amplified and sent to a comparator The comparator compares the pulses to a fixed reference voltage If the amplitude of a pulse is greater than the reference voltage an output pulse will be generated The pulses generated by the comparator are counted by the microcontroller The microcontroller and related circuits handle pulse counting timing low battery detection and display functions The high voltage circuit is essentially a charge pump which converts the low voltage supply provided by the regulator into a high voltage supply suitable for driving the photomultiplier tube The supply is adjustable from about 450 to 1000 volts 12 Chapter 5 Reference 5 1 Reference Radiation Protection in Uranium Mines ANSI N 13 8 1973 Available from The American National Standards Institute Inc 1430 Broadway New York New York 10018 This is a very useful reference in itself but it also includes an extensive list of related papers 13
4. e bottom of the instrument into which a sample holder may be placed The sample holders can accommodate membrane filter samples of 25mm 37mm or 47mm diameter The following sections describe the device itself as well as the procedures re quired to determine detector efficiency and measure the activity of a sample 1 2 Specifications ALPHA COUNTING DETECTOR PHOTOMULTIPLIER BATTERY SUPPLY BATTERY LIFE per charge BATTERY CHARGER TIME BASE HIGH VOLTAGE DIMENSIONS WEIGHT 2 50mm diameter zinc sulphide open foil B38B01W Five size AA NiMH rechargeable batteries Aproximately 35 hours depending on number of digits displayed 9V 660mA externally connected charger CSA approved 16 hours charging time Batteries should be charged once a month if left idle Only use the charger supplied with this instrument Crystal controlled clock oscillator Nominally 450 1000V Adjustable Basic instrument 21 6 cm 8 5 w x 10 8 cm 4 25 d x 19 cm 7 5 h With leather case 24 8 cm 9 75 w x 11 4 cm 4 5 d x 20 3 cm 8 h Basic instrument 2 2 kg 5 lbs With leather case 3 2 kg 7 lbs Chapter 2 Components 2 1 Controls and Display An overview of the front face plate controls is given in Figure 2 1 Environmental Instruments Canada Inc http www eic nu Model TM372B Sample Counter HV ON CHARGING LOW BATTERS LOW BATTERY 2 3 00 6 9 0 0 9 6 CHARGER 5 Figure 2 1 Fro
5. nt Plate Controls 1 Main Display Start Button Stop Button Ae WwW N Toggle Button 5 Timer Button aD On Off Button Charger Jack and Cover al Main Display A five digit L E D display where the gross counts or the elapsed time is displayed An overview is given in section 2 4 Start Button This button begins the count from zero The display shows the number of counts until either the pre set time is reached or the stop button is pressed Stop Button Stops the count Toggle Button Used to briefly toggle the display to show either the pre set time that the user has entered or the time remaining on the count depending on whether or not the device is counting at the moment the button is pressed Timer Button Used to enter a time for which the TM372B will count On Off Button Turns the device on or off NOTE This button must be held for two seconds in order to turn the power off Charger Jack and Cover The TM372B runs off of internal rechargeable bat teries The batteries may be recharged by connecting the supplied charger to this jack See section 2 5 for more information 2 2 Sample Tray The sample tray is located on the back of the device near the bottom The sample is held in the sample holder which drops into the recess in the sample tray To count a sample withdraw the tray insert the sample as outlined in section 3 1 close the tray and start the counting cycle 2 3 Sample Holder
6. nvironmental E Instruments Canada Inc TM372B Sample Counter User s Manual Environmental Instruments Canada Inc http www eic nu Contents 1 Overview of Device 1 1 Introduction iss a anos ey a ee a A ds 1 2 Bp c f t tions 4 2 4 eek e Doe PG at da ee at 2 Components 2 1 Controls and Display 0 0 0 0 ai a hN 2 2 spam ple Tray 8 26 4 se sok de p a GBR LMR Bolg Que kw eda pes 23 Sample Holdets x cee Sh ES RE AE ee ee eA a 2 4 Display Overview oii a eh Ba GR ee ee E e 250r Batteries Zajas Panes e Kae last o g j m ey 3 Operation 3 1 Inserting the Sample Bed Counting kiai g pertan ar taas LG ie Bed atskan ai 3 3 Calculating Detector Efficiency a 3 4 Daily Source Check 2 aa 3 5 Counting an Unknown Sample la 3 6 Resetting the Device a 4 Detector 4 1 Internal Detector V aa 4 2 Circuit Functions ais ees a Ao es ee eu 5 Reference 5 1 Reference aa Insert checkout sheet and plateau here Set footers on checkout sheets to read DN and aie Chapter 1 Overview of Device 1 1 Introduction The TM372B is an ALPHA counter equipped with a foil type open zinc sulphide detector This type of detector is inexpensive readily obtainable and is easily replaced The instrument uses a photomultiplier tube to count the number of scintillations from the alpha particles that strike the zinc sulphide A sample tray opens near th
7. play Indicator The Timer count mode has an upper display limit of 167 x 10 counts Once this limit has been reached the display will read 167 x 10 and no further counts will be registered 3 3 Calculating Detector Efficiency This procedure should be carried out once per year or as required by local reg ulations With the standard source properly placed in the sample tray count for a sufficiently long period of time to obtain at least 10 000 counts and then convert this to counts per minute C P M By knowing the disintegrations per minute D P M of the standard source the detection efficiency may be calculated d U 100 x C P M determined above o detection ef ficiency T PM as given for standard This figure will vary slightly with the detector but a typical value is approxi mately 43 The efficiency achieved is not as important as the accuracy and reproducibility of the efficiency value This value will remain constant as long as the instrument settings are not changed or the detector damaged 3 4 Daily Source Check This procedure should be carried out at the beginning of each working day Insert the check source into the sample changer Count for 1 to 3 minutes The result 10 should be within 20 of the nominal value of the source Remove the source from the sample changer IMMEDIATELY after doing the source check 3 5 Counting an Unknown Sample The unknown sample may now be inserted in the 2 piece holde
8. r assembly as de scribed in section 3 1 Enter a suitable pre set time for example 3 minutes and note the counts ac cumulated during the time period Divide by the counting time to convert this to C P M By knowing the detection efficiency a D P M figure for the unknown may be obtained 100 x C P M of unknown PETA OU i detection ef ficiency Due to the random nature of radiation a steady or constant rate of detection is not possible The rate of occurrence will vary from the average by an amount equal to the square root of the counts 65 of the time Therefore a count of 100 will be accurate to 10 counts or 10 a count of 1000 will be accurate to 33 counts or 3 and a count of 10 000 will give a 1 accuracy 3 6 Resetting the Device If for any reason the device becomes unresponsive the following should be done to reset it 1 Unscrew the cap on the charger jack Insert the reset key into the charger jack Wait 10 seconds OR until the display goes black Remove the reset key Turn power back on ok Wh If the device is still unresponsive contact Environmental Instruments Canada for further assistance 11 Chapter 4 Detector 4 1 Internal Detector Do not work in an area where bare fluorescent tubes without plastic cover are used Exposing the ZnS detector to UV light will cause the background reading to be elevated for about a day Detectors will need to be changed if they are dam
9. rting a sample into the sample tray and if you have not already done so turn the device on by pressing the ON OFF button To enter the time you would like to count for press the TIMER button enter the time in mmm ss format using the number pad then press the TIMER button again If you made a mistake you may repeat this same procedure to enter a new time The maximum time that you may enter is 999 59 To start the count press the START button An LED beside the digit on the far left of the display will illuminate indicating that the device is counting The count stops when either the preset time has elapsed or the STOP button is pressed By default the gross counts are shown on the main display but to briefly display the elapsed time press the TOGGLE button The display will change to show the time remaining in mmm ss format for a few seconds before automatically switching back to display the gross counts This button may also be used before the count has started or after the count has finished to display the pre set time that has been entered An overview of the display is shown in Figure 3 1 HV ON TOGGLE HV ON DOLO IL TEG i Ci 71 IZ El _ Li LI II Device Counting Remaining Time HV ON ZI LI ZI L TOGGLE ZIVI men Li Li TL Ll _ I LILI Count Stopped Figure 3 1 Counting Dis
10. s Three 2 part sample holders are supplied with the TM372B for membrane filter samples of 25 mm 37 mm and 47 mm diameter Alpha emitting calibration sources are calibrated for either 27 or 47 geometry and the active diameter is usually less than the diameter of the disc When the membrane filter sample is inserted in the 2 piece holder assembly it is secured around the edge masking a portion of the filter from alpha particle activity The region that is masked is a ring of about 1 mm thickness around the outside edge of the sample This means for example that the active area of a 25 mm diameter sample would be the area within a 23 mm diameter This however will not adversely affect the activity reading because the outer edge is essentially inactive 2 4 Display Overview The display shows either the gross number of counts or time in mmm ss format For how to change between the two displays see section section 3 2 While counting a value will be displayed using either five digits or three digits and an exponent For numbers less than 100 000 five digits are used see Fig ure 2 2 For numbers greater than 99 999 three digits and an exponent are used see Figure 2 3 Figure 2 2 An example of the display reading 19864 Figure 2 3 An example of the display reading 123 x 104 When the device detects an alpha particle an LED at the top of the display will briefly illuminate to show that it has registered a count as shown in Figure 2
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