ST350 Radiation Counter
Contents
1. SPECTECH ST350 Radiation Counter Operating and Service Manual November 1994 Spectrum Techniques Page 1 Model ST350 RADIATION COUNTER The ST350 Radiation Counter brings new dimensions to Nuclear Science instruction and Health Physics training By incorporating a specialized microcontroller many of the features previously found only in multiple products are now combined in a single inexpensive instrument The classical nuclear scaler function has now been extended to include a timer preset counter digital ratemeter with alarm computer interface and a battery option for field applications When constant counting statistics are required the preset count mode can be extremely useful and the digital ratemeter is ideal for contamination survey work An alarm level may be set to any pre selected value and if the count rate exceeds this level the audible alarm is sounded warning of a high activity condition High voltage is fully variable from O to 1200 volts allowing operation with many types of GM tubes The supply is fully regulated and controlled by the processor for digital accuracy and readout on the display Extra large LED s are used for the digital display for clear visual readout under widely differing ambient light conditions with leading zero suppression for clarity Classroom demonstrations and nuclear experiments may now be run directly from an IBM PC compatible computer using the on line serial DATALINK b2. Input 7 5 volt DC at 500mA from AC line charger Specify 110 120 220 240 VAC at time of order Battery option requires installation of 4 x C size NiCd rechargeable batteries not supplied 12 in W x 8 in H x 4 5 in D ST350 Radiation Counter PC emulation software DOS program runs on most IBM compatible PC s including CGA EGA VGA SVGA and Hercules graphics systems Real time display of simulated analog ratemeter with auto ranging digital ratemeter in CPM or CPS count elapsed time preset count preset time high voltagesetting acquisition time and run number Data is loaded into spreadsheet compatible files for transfer Bi directional LABLINK offers full control of all functions including preset count preset time countrate in CPM or CPS alarm level high voltage start stop reset and data transfer Requires EGA or VGA graphics All operations may be run directly from the computer with spreadsheet compatibility Page 3 Operation CAUTION Never operate the ST350 Radiation Counter with the GM probe discon nected Dangerous voltages can exist at the probe connector so ensure the instru ment is in the OFF position and the high voltage is set to zero before disconnect ing or reconnecting the GM probe General The ST350 Radiation Counter may be operated with or without the optional rechargeable batteries installed by connecting the AC power supply charger module supplied If batteries are installed it
3. may be necessary to supply an initial overnight charge before operating away from the power source A LOW BATTery indicator is included to alert the operator before the batteries become fully exhausted and the instrument ceases to function If this indicator is illuminated discontinue use until the unit has been reconnected to the charger To maintain good battery life and condition rechargeable batteries should be discharged and fully recharged periodically Detectors Geiger Mueller tubes produce electrical pulses when ionizing radiation events occur within their sensitive volume For proper operation these detectors should be run at a predetermined operating voltage specified by the manufac turer or derived empirically To improve sensitivity to alpha and beta particle radiation many GM tubes have extremely thin entrance windows which require considerable care in handling Do not remove protective caps unless necessary and never touch the window The ST350 is designed to accommodate many types of GM probes and includes a fully adjustable high voltage power supply to cover a wide range of applications The high voltage level may be displayed on the digital readout by moving the FUNCTION switch to the HIGH VOLTAGE position Adjustments to the high voltage may now be made using the UP DOWN buttons in 25 volt increments Page 4 Operating Modes and Controls Each mode may be selected by the DISPLAY FUNCTION switch DISPLAY OFF Turns off
4. the digital display to conserve power Mainly used when operating on internal battery power The ST350 continues to operate in the last mode selected COUNTS This is the normal operating mode where the display registers the number of radiation events detected by the GM tube Before starting a count a preset count value or preset time may be entered using the UP DOWN buttons If this feature is selected once started the unit will continue to count until the preset count or preset time level is reached Preset count mode can be very useful when constant counting statistics are required TIME If the operator wishes to count radiation events for a predetermined time select this position and with the unit in the STOP mode enter the required counting time in seconds using the UP DOWN buttons When a preset time is entered the preset count mode is reset and disabled RATEMETER This mode provides a digital display of the instantaneous count rate It can be very useful for survey applications particularly when used in conjunction with the ALARM feature ALARM SET An alarm level in counts per second may be preloaded into the ST350 Whenever the incoming count rate exceeds this level an audible alarm will sound To select this feature set the FUNCTION switch to ALARM SET and enter the required level using the UP DOWN buttons The ST350 may now be set to other modes with the alarm level retained HIGH VOLTAGE This position of the function switch di
5. time is reached by pressing the STOP button and continued with the COUNT button Once the preset time is reached the counter will stop accumulating data At this point it is only necessary to press COUNT to restart the next cycle as the preset will automatically be restored and the count register reset to zero Using the preset count mode is similar to the preset time Set the function switch to COUNTS and load the preset count value with the UP DOWN buttons and press COUNT to start accumulating events The acquisition time or the event register may be selected for display using the function switch The STOP button may be used to interrupt a count without losing current data Once the preset value has been reached counting will stop automatically To recycle simply press COUNT In the RATEMETER mode CPS or CPM may be selected using the UP DOWN buttons Convenient indicator lights show the currently selected mode to assist operation An ACTIVITY indicator is also included which monitors incoming events independent of the selected mode even in the stopped condition Page 6 GM Plateau The correct operating voltage for the Geiger Mueller tube may be determined experimentally using a small radioactive source such as Cs 137 or Co 60 A properly functioning tube will exhibit a plateau effect where the counting rate remains nearly constant over a range of applied voltage Place the radioactive source close to the window of the GM probe and slo
6. 1 Di L1 i 100uH 5V CHARGER IN WP3 WP2 MC3405P 5 C2 C3 C4 C5 c6 c32 E 7 R1 1 4 1 4 4 4700UF 120K U14 B Ed LR1720R LR1720R LR1720R LR1720R WP4 MAX641 WP5 e C 1 O WP6 B i L anp Gase 2N3906 ap 2N3906 2N3906 2N3906 2N3906 ey R4 PN E R6 NY ER D4 2K COUNT 5V a 1 U3 TX DATA 6 CO DS6 DS5 DS4 DS3 DS1 WP8 C10 2 1 CTS a Ci R a 1 c D ae WP9 14 THIN 11 TXD RXDATA C Pp 7 TIN 10 CTS Wei peat ie RxD wey R16 s C a Max232 2 RTS NMI U11 aj R17 5V co 10K RESET BKG 4 5 GATE NMI 5V 5 wp18 e ore Ea E e S pues Eai 1 2K MODEO COUNT Ge MODEO 2 MODE1 S1 R21 Se PAS GC AT SAT f BUZZER LARM KO wone A Pa ae S e R79 BKG a AD7 AA 13 ALARM GND CLED 7 ADE AS C13 BESET DS6 PB6 AD5 A6 pE y D55 PB5 ADA A7 PB4 WP17 10UF DS4 Gen AD3 ABS 5V GATE DS3 PB2 AD2 AB9 2 PBI AB10 51 COUNT GND ds ABI 35 PC7 CO1 ABI2 Ani sw2 PC6 CO0 11 ADO Ser 2 U6 A GND 3 dee 12 ADI ABI5 3 o 1 STP 1 2 1 PC3 TVINT2 Ge E Ee TP1 AD 5V SW3 S TP E ADS END e 7406 TP2 4 os 18 AD6 GND 5 2 1 AD7 a o RES JP3 E we 74LS138 3 O SW4 SN74HC4024N i S 2 5V HE 5V ae 510 SW5 C14 GND dis R32 4 ALE Bra do E Ei ADO 2 AO ADO AD1 5 Al AD1 SW6 R35 AD2 6 A2 AD2 AD A AD sid R33 GND Gen E Ad AD 1K AD5 15 A5 AD5 AD6 16 A6 AD6 GND R37 AD7 19 A7 AD7 y 3o 74LS373 74LS374 PN Bo a NY R39 o gois R38 Dio R45 10 CLED 11 oo c 1K O ze COUNTS C W R41 8 740
7. 6 od x2 7406 1 NY C17 O O R40 PA w E 2 4576 1K lt lt 47pF R42 56 10K R43 1K O 36 WP20 WP23 E 10K K 2 6 1 ES 5V GND 1K sw1 ND E R46 LI S WP21 WP22 47pF 5V e O Ro 2K C19 1 1 D22 GND GND 01 1000V INSTALL FOR 350W ONLY GE Gs R19 f C21 01 1000V 1N4148 1M 3 9K ACTIVITY C20 2K WP11 1 C34 01 1000V INSTALL FOR 350W ONLY D12 SES e 1 a WP12 470pF 2000V OND 5 C22 R50 Ge WP13 3 E Ze DIS D14 a DIS D16 a D7 C25A C25B C25C 1M R51 GND A 1 P2 S2 1 E XFORMER Q SES 470pF 2000V 47K R80 R53 mig 100 Qs C23 01 1000V C24 01 1000V 22M D18 R73 s 01 1000V ws 1N4148 1N4148 R57 E R59 5V R60 MPSA13 B V 5 1K Go WP15 1M R62 GM TUBE ele R66 GND E E 22M Res 1 LM555CHC pas A C R75 R77 C27 C28 or U14 D R64 R65 We 10K 1K 1k D20 D21 GND GND 01 01 E 7 22M 22M Ee R61 1N4148 1N4148 Can 1 D24 5V 15V E MPSA64 MC3405P 001 qm Je WP19 1N4148 10uF GND E 2N3904 Si MC3405P o 10 E C31 1N4148 U14 C DACCS R70 1 00K D23 R76 ST 350 COUNTER GND w R82 Size Number R78 R63 Dez 1 00K 19 GND ow cow 5V Ai G03501 10K 4 22K 1 00K 7 Date 8 16 95 REV4 08 01 00 Drawn by R S S GND C29 GND Filename ST350 S01 Sheet 1 of DO Bl oo 4 o CJ SD F 4
8. Before commencing a count ensure the high voltage is set to the correct value by accessing the PRESETS menu bar and selecting the HIGH VOLTAGE function Others presets such as TIME and COUNT may also be set through this menu As with the RADEM software most operations may be accessed through the menu bar and are intuitive Several different VIEW modes are possible including ratemeter and counter timer with CPM or CPS selection RT Link Disabied Counts Preset Time 0 Elapsed Time 0 00 Voltage 0 Preset Count 0 Count H Runs 0 For performing plateau measurements the high voltage may be set to increase automatically at the completion of each count and the data stored in the Data File Use the MODE menu to select this feature The contents of the Data File may be stored as a TSV file on disk using the FILE menu and can be imported directly into many common spreadsheets for subsequent manipulation and analysis Use the spreadsheet to perform statistical analysis and produce graphical presentations of the data Manufactured by Spectrum Techniques Inc 106 Union Valley Road Oak Ridge TN 37830 USA Tel 865 482 9937 Fax 865 483 0473 www spectrumtechniques com sales spectrumtechniques com Sek C32 R3 SA Fe WP4 CC 0 O O G D1 R44 C8 ES C1 ol Cem rn y TE Or 9 TP3 TP2 TPI L aL D a o O 9 C23 C19 D14 C21 GND LM7805CTB E as ower owltc WP1 U
9. T_P keyboard command Page 10 Page 11 Applications Maintenance In its basic configuration battery operation audible alarm and the ability to interchange GM probes allows the ST350 to be used for a variety of CAUTION applications some of which are listed below Dangerous voltages can exist inside the ST350 from the high voltage power supply Surface contamination measurement Before removing the cover ensure the instrument is in the OFF position and the Personnel monitoring high voltage is set to zero Only qualified technicians should attempt any repairs Plotting a GM plateau Your ST350 has been built with care using quality parts and should not Radiation background measurement require any routine service In the unlikely event of a malfunction the unit may be returned to the factory for repair We will gladly supply a cost estimate if the Natural radioactivity warranty period has expired Battery installation is straightforward and involves removing the rear GM resolving time cover which is held in place by four screws Ensure the instrument is in the OFF position and the high voltage set to zero Replacement requires standard Detector efficiency C size Nickel Cadmium batteries preferably with a 2000 mAh rating Radiation absorption studies A complete list of parts is included for your convenience Please contact our customer service department for pricing and availability In many Backscattering instances substitute parts may be u
10. ate COM port Choose a COM port COML COM2 Your system will now be configured for 9600 Baud data transfer and ready for use Software Emulator The ST350 software emulator greatly expands the capability of the counter by providing large screen displays combined with multi mode operation Three basic modes are included Pla td Have ee Digital Ratemeter Scaler Operation of the software is straightforward and requires little explanation The analog ratemeter mode provides a large screen display of the instrument meter which can be very useful for classroom demonstrations of basic radioactivity Use the spacebar to switch the display between CPM and CPS and the up down arrows to change the range For more precise readings the digital ratemeter mode may be preferred for some measurements When operating in the scaler mode all radiation events detected by the GM tube will be recorded during the pre selected time Use F1 to initialize the PRESET TIME mode and enter the required counting time in seconds Entering zero or blank will allow the unit to operate in a manual mode The scaler is started and stopped using the return key and the elapsed counting time is displayed in seconds Page 9 At the completion of a preset time the counting data together with elapsed time and the computer time of day clock is automatically stored in a data file which is displayed on the screen as a table A new count may be restarted by simpl
11. ctor resolving time is unknown it may be determined experimentally using two radioactive sources Maintaining constant counting geometry is important throughout the experiment A special source split into two halves is available for making the measurement but good results may be obtained by careful positioning of two standard check sources With the high voltage correctly set for the GM tube position the two sources a b side by side to obtain a count rate of at least 10 000 CPM Accurately record the countrate as R a b Remove source b and record the count rate as R a Carefully replace source b to its original position remove source a and record the count rate of source b as Rw The resolving time is given by R a by R a b The resolving time of the ST350 RADIATION COUNTER is very short and is not a significant factor compared to that of the GM tube Page 8 Serial Data Link Your ST350 Radiation Counter contains a unique Data Link making it possible to connect the instrument to a personal computer for recording events Data transfers are via a RS 232C serial link and requires connection through a standard 9 pin cable to the computer COM 1 or COM 2 port The ST350 RADEM Emulation Software may be run directly from the floppy disk supplied or copied onto a hard drive if preferred To run the software enter the command line RADEM EXE The program will self configure to the graphics system in use Select the appropri
12. sed providing they meet or exceed the original specifications Inverse square law Isotope half life Radiation properties Counting statistics Low level environmental measurements of naturally occurring radioactivity may be performed more effectively by surrounding the detector assembly with 1 2 of lead This will have the effect of reducing the detector background thus improving the lower limit of detection Page 12 LabLink Communication Software Your ST350 Radiation Counter is supplied with a computer communication and control software package named LabLink Command and data transfers are via the standard RS 232C serial port and requires connection to the computer COM 1 or COM 2 port LabLink transfers full control of the ST350 to the computer system and when operating in this mode the function switch must be set to the REMOTE position and all front panel controls will be inoperative To run LabLink insert the program disk supplied into drive A type A LABLINK and the following screen will appear k Select COM port Serial Link Disabled k ST 350 Radiation Counter Help Help On Help How To Run a Plateau Automatic Counting Manual Count ing Operating the ST 350 Commands File menu commands Mode menu commands Presets menu commands View menu commands res E TE OU apsed ET 0 00 Sg Voltage U Preset Count 0 Count 0 CPS O Runs 0 Page 13
13. splays the value of the high voltage setting for the GM tube The high voltage may be adjusted in 25 volt increments using the UP DOWN buttons between 0 and 1200 volts REMOTE The REMOTE feature is used with the optional LABLINK com puter control software In this mode all front panel control is transferred to the computer screen The LED indicators and numerical display will continue to show mode information being selected by the computer When using the standard RADEM emulator software supplied with the ST350 the function switch may be set to any position Page 5 Operation Basic operation of the model ST350 Radiation Counter is straightfor ward and intuitive First set the high voltage to the recommended value for the GM tube using the HIGH VOLTAGE function and the PRESETS buttons If no other presets are required return the function switch to the COUNT position Operation may now be controlled with the START STOP and RESET buttons Setting the function switch to COUNTS will display the number of radiation events detected by the GM tube or selecting TIME will display the acquisition time in seconds To count for a preset time select TIME on the function switch and enter the required counting time in seconds using the UP DOWN buttons Once set this time will remain until changed with the PRESET Set the function switch to COUNTS press RESET and start the count with the COUNT button The count may be interrupted before the preset
14. uilt into the ST350 and the standard RADEM emulation software All functions of the Radiation Counter are accessible and may be controlled from the computer including the high voltage setting for the GM tube using the optional LABLINK software The Radiation Counter PC software supplied produces computer screen displays of all functions including analog emulation of the ratemeter mode Real time data is automatically transferred to the computer and stored in spreadsheet compatible files Data analysis and graphical presentation is now possible using many common spreadsheet programs bringing new techniques to Nuclear Science education Optional batteries may be installed in the ST350 making the instrument fully portable An AC to DC line converter charger is supplied for continuous benchtop operation with or without the batteries installed Specifications Input High voltage Display Modes Audio Data Link Power Dimensions Software supplied Page 2 BNC connector Accepts standard Geiger tubes 0 to 1200 volts digitally selectable in 25 volt increments 6 decade LED in numerals Displays counts preset counts time preset time CPM CPS alarm level and high voltage Count for preset time count for preset count counts min counts sec set alarm level 0 999999 cps set high voltage 0 1200v and remote Piezo alerter if countrate exceeds preset level DB 9 male connector accepts RS 232 serial cable
15. wly increase the high voltage until radiation events just begin to be detected Now increase the voltage in 25 volt steps recording the counting rate at each increment The rate should remain fairly constant over a range of voltage and then increase rapidly as the high voltage is further raised indicating that the tube is entering the breakdown region Do not continue to operate the tube in this breakdown condition but reduce the high voltage and make a plot of the counting rate versus the applied voltage The recommended operating voltage may now be determined as the center of the plateau region GM Plateau 1 operating voltage C o u n t t a t a B00 900 1000 1100 1200 Detector Voltage Page 7 Resolving Time Geiger Mueller tube exhibit dead time effects due to the recombination time of the internal gas ions after the occurrence of an ionizing event The actual dead time depends on several factors including the active volume and shape of the detector and can range from a few microseconds for miniature tubes to over 1000 microseconds for large volume devices When making absolute measurements it is important to compensate for dead time losses at higher counting rates If the resolving time of the detector is known the true counting rate may be calculated from the measured rate using the following expression n m 1 mt where n is the true counting rate m the measured rate and t the detector resolving time If the dete
16. y pressing the return key at which time the data register and elapsed time will automatically be reset and the next run started The counting may be interrupted at any time and resumed using the return key without loss of data providing the data is not stored in the data file To store data in the manual mode stop the counting and press the space bar This action will cause the registers to reset when counting is restarted The ST350 software includes a recycle mode which can be very useful when performing radioactive decay such as half life experiments or absorption studies Use the Fl key to select the required time for each count and the F2 key to set the number of measurements Once started the ST350 will now automatically store the data at the completion of each counting sequence reset the registers and continue for the number of runs selected Data File is a unique and powerful feature of SPECTECH products Count and time data is stored in a tab separated temporary file which is displayed as a table This may be stored as a TSV file on the disk at the completion of a series of measurements The file is compatible with many popular spreadsheet programs and may be directly transferred in the spreadsheet for analysis and viewing At the end of a series of measurements use the ESC key to prompt for file storage If no filename extension is given the system will default to TSV To simply print the contents of the temporary data file use the AL
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