User Manual DOSEman
Contents
1. Dose DOSE 4 1 pSv 12 The dose value shown on the display is based on the Radon exposure meaning the product of Radon average concentration and total sample time The Equilibrium Factor as well as the Dose Conversion Coefficient adjusted by the user set up are included in the calculation procedure The determination of average Radon concentration is depending on the chosen calculation mode fast slow Stop sample and turn off the device If the button was locked the measurement can be cancelled by the PC software only The software also allows to switch off the instrument after the download of the acquired data In case of unlocked button the DOSEman can be switched off also by pressing the button for approx five Seconds The acquired data remains in the memory and may be loaded again after switching on the unit Please note that a repeated keystroke starts a new sample if the button is unlocked and the sum spectrum of the last measurement series will be lost immediately The related time distribution will be overwritten if the first integration interval has been completed If the battery voltage drops below the defined minimum level the instrument switches off automatically The data are stored non volatile so that it is possible to read them after recharging Alert states Alert states are indicated by a blinking light an acoustic signal and a display output Two alert states are implemented Low Battery Alarm becomes2. only a statistical fluctuation The test is very simple Define a confidence level with respect to your needs and look at the statistical error bands of the two points of interest If the error bands do not overlap each other the change in the Radon concentration is significant otherwise it can be or not can be Example 1 Reading 1 1500 Bq m 10 gt error band 1350 1650 Bq m Reading 2 1300 Bq m 13 gt error band 1131 1469 Bq m The upper limit of the error band of the reading 2 is higher than the lower limit of the error band of reading 1 Because the true value could be placed within 1350 Bq m and 1469 Bq m the variation of both readings is not statistical significant Example 2 Reading 1 1500 Bq m 10 gt error band 1350 1650 Bq m Reading 2 1000 Bq m 15 gt error band 850 1150 Bq m The error bands of the readings do not overlap each other Therefore a statistical significant concentration change is given Two arbitrary points of a measurement series may be considered using this test It is not necessary that the points are direct neighbours Detection Limit The term Detection Limit defines the smallest value of the Radon concentration which delivers a non zero reading of the instrument within a given integration interval at least 1 decay per interval Because of the statistical behaviour a related confidence interval has to be stated Why is it necessary to know
3. within the range from 663 Bq m 780 Bq m 15 to 897 Bq m 780 Bq m 15 Error Prediction The relative statistical error E for a chosen confidence interval of k Sigma can be predicted from the number of detected counts N by the equation E 100 k V N N The simple consequence is The higher the number of counts the higher is the accuracy of the measurement From the opposite point of view one could ask How many counts have to detect to achieve a predefined uncertainty Two items will affect the number of counted decays The sensitivity of the instrument at the one hand side and the time period used for counting process integration interval on the other hand While the sensitivity is an instrument specific constant the integration interval may be expanded to the maximum acceptable value for the desired time resolution of a measurement series The relationship between the measured Radon concentration Cr and the number of counts N within an integration interval T is Cr N T S whereby S represents the Sensitivity of the instrument given in the unit cts min kBq m The sensitivity using the slow mode is double as high as in the fast mode see chapter Theory of Operation and whenever the required response time is more than 2 hours the slow mode should be selected For the following examples a fast mode sensitivity of 0 18 cts min kBq m shall assumed while the slow mode sensitivity shall be 0 32 cts
4. 9 TECHNICAL DATA 3 gesdisicsn anta eaaa a E E eaa EE E EE S 10 Manual_DOSEman_EN_05 03 07 doc Page 2 General Information Important Hint The determination of the activity concentration of Radon is always a radiometric measurement meaning a counting experiment This causes a number of specific circumstances which have to take in consideration by the one who is carrying out this task Only the knowledge of those particularities allows the correct set up of a test and avoids misinterpretations of the achieved results Please read carefully the next chapters Theory of Operation and Statistical Error to become familiar with this kind of radiometric measurements Theory of Operation The Radon gas diffuses through the front side membrane into a high voltage biased measurement chamber The Radon Rn 222 gas concentration will be measured by the short living daughter products generated by the Radon decay inside this chamber Directly after the decay the remaining Po 218 nuclei becomes charged positively for a short period because some shell electrons are scattered away by the emitted alpha particle Those ions are collected by the electrical field forces on the surface of a semiconductor detector The number of collected Po 218 ions is proportional to the Radon gas concentration inside the chamber Po 218 itself decays with a half life time of only 3 05 Minutes and about 50 particles emitted towards the detector surface of
5. active if the battery capacity drops below 10 of the nominal value To prevent an automatic turn off in case of complete discharging the battery should recharged immediately Manual_DOSEman_EN_05 03 07 doc Page 8 Low Batt Dose Alarm becomes active if the calculated dose value exceeds the pre set limit DOSE ALARM After confirming the alert message by pressing the button the dosimeter turns back to the normal display mode In the right upper edge of the display appears either a bell or a battery symbol dependent on the kind of alert Instrument set up All set up parameters can be changed by PC software only Beside the integration interval and the Radon calculation mode also the Equilibrium Factor the Dose Conversion Factor and the dose limit may be adjusted To assign the acquired data correctly to a person or location some codes are programmable which appear later on within any data protocol or export file Unintended manipulations can be avoided by locking the push button The activation of the internal buzzer forces the DOSEman to give a short audible signal at each keystroke Please refer to the software manual for more information Battery and Charger The internal rechargeable battery allows an autonomous operation of approx 12 days To ensure optimal performance two things should be attended The battery must not be stored over long times in the discharged state Please recharge the instrument after each measur
6. all decays will be registered by the detector The equilibrium between the Radon decay rate and the Po 218 detector activity is given after about 5 half life times say 15 Minutes This time span defines the minimum achievable response time to a Radon concentration step Now the decay chain is continued by the both beta emitters Pb 214 and Bi 214 followed by another alpha emitter the Po 214 That means each Po 218 decay causes one more detectable decay by the Po 214 which is delayed about 3 hours because of the superposed half life times of those nuclides The emission energies of Po 218 and Po 214 are different and therefore it is possible to separate both nuclides from each other by alpha spectroscopy In case of the DOSEman we have the particularity that also the Radon gas itself gives an non negligible contribution to the measurement Because of the small chamber the distance between detector and any position inside the chamber is short and the probability that an alpha particle emitted by the Radon decay will hit the detector is quite high The Radon decays are immediately present and will not cause any response delay Therefore it is possible to include this signal additionally for the Radon calculation The DOSEman offers two calculation modes for the Radon concentration one Slow includes both Rn 222 and Po 218 as well as the Po 214 decays and the other one includes Rn 222 and Po 218 only Fast The advantage of the Fast mode is the q
7. min kBq m The first question could be What an integration interval T have to set to get a statistical uncertainty less than 20 at a confidence level of 10 if the expected Radon concentration is 1000 Bq m A 10 error of 20 requires 25 counts 100 1 V 25 25 20 Using the fast mode the integration interval can calculated by T fast N Crn S 25 cts 1 KBq m 0 18 cts min kBq m 139 min Because the required interval is longer than 2 hours the slow mode is the better choice leading to the following result T slow N Cr S 25 cts 1 kKBq m 0 32 cts min kBq m 78 min Manual_DOSEman_EN_05 03 07 doc Page 4 That looks pretty but makes no sense because of the longer response time So we will set the interval to 120 Minutes and ask for the statistical error in this case N slow Crn T S 1 kBq m 120 min 0 32 cts min Bq m 38 cts E 10 100 1 V N N 100 1 V 38 38 16 2 Now one could say 68 3 is not sure enough want to choose 2o confidence interval to get a more trustable result E 2c 100 2 V N N 100 2 V 38 38 32 4 For interpretation look at the begin of this chapter Is an observed concentration change statistical signifcant or not If you have a look at the acquired time distribution you will see variations of the concentration from point to point The question is now Is it a real change in the Radon concentration or
8. Page 1 User Manual DOSEman Version 03 2007 SARAD GmbH Tel 0351 6580712 Wiesbadener Stra e 10 FAX 0351 6580718 01159 Dresden e mail support sarad de GERMANY Internet www sarad de CONTENT GENERAL INFORMATION sssssessssoesseesssossssossscssscosssosessossscossoossssosssoesssossssesssossssossssesssose 2 IMPORTANT EIN Toses erered enaa eie a aaae A AEE ssvvenveuddesaccedusseveassecagecdveesseasderaccteveusds 2 THEORY OF OPERATION 66 oscopsictaicenations anana aE AAA EAEE EA AEREAS EANAN AEA 2 STATISTICAL ERROR FOR NON MATHEMATICIANS ssseeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeees 2 Error Predicti h ssessrerisisa reiese rn ea nnana EER ERS EREET E EEEE ETER IEE 3 Is an observed concentration change statistical signifcant or not cccccccceeeseeeeeeeeeeees 4 Detection Limit srice ner insine a eas A a A AES aa iSS 4 THE INSTRUMENT scssssssswssacsssvsnnesscensseccceascensswceaessceccsesesensceecdsennstceensuseeeniceckaewenusiseenesstvees 6 OPERA ON aeea rea E a E a E aaanmeastaunenanede 6 Starting ICUS UII ica intrinatarniamadhlakeonensenkRiano Gone aaa 6 Stop sample and turn off the device cccscccccsssscccccessnscecesssneecesusnececesenceecensenacesessnneesenes 7 Instrument set up ogo eid credited eases eco nd ace pod easel tales ba ekg tana einbeebes 8 Battery and CHAISE cgi ne i a in a EE E E E E TA 8 Communication with the DC iu ccroieinrmundersinsoreiipnsaveemydnadewueonseenuaesesaseon tena teenmnnres
9. ailable IrDA interface integrated in the PC is not possible The infrared adapter has to be connected to the USB port The PC software handles the adapter as a serial port COM To link the adapter to any COM port a driver is necessary which can be found on the program disc in the subdirectory DRIVER After plugging the connector into the USB port Windows will automatically start the hardware installation assistant The port number is commonly assigned by Windows during the installation The port number has to be between COM1 and COMO otherwise the software will not be able to access the adapter In the normal case the first free number following the last physical available port for example COM3 or COM5 is chosen The Windows device manager within the Windows control panel can be used for reassignment if it is necessary To read the data or to change the set up the DOSEman has to be placed on the top of the infrared adapter with the bottom panel down IR transmitter window This guarantees a safely connection and no other instrument in the surrounding will be affected Manual_DOSEman_EN_05 03 07 doc Page 10 Technical data Measurement range Response time Sensitivity 0 4 MBq m 12 120 Minutes to 95 of the final value fast slow mode 0 18 0 32 Counts Minute 1000 Bq m fast slow mode 20 statistical error 10 200 Bq m within 8 hours slow mode 10 statistical error 106 200 Bq m within 24 hours slow mod
10. e 16 statistical error 106 1000 Bq m within 2 hours slow mode Sample interval Memory Power supply Instrument control Display Dimensions weight Interface Software 1 255 Minutes adjustable by software 720 data records non volatile and sum spectrum Internal rechargeable battery for 12 days permanent operation approx 2 hours recharge time Single push button Optical and audible alert LCD 3 lines x 12 characters Info concentration exposure and dose available with SI or US units 115 x 57 x 32 mm 250 g Infrared special IR USB adapter is required Data transfer set up and instrument control by Radon Vision software Manual_DOSEman_EN_05 03 07 doc
11. ement From time to time the battery should be discharged and recharged by the maintenance function of the charger unit button next to the LED To charge the battery the charger has to be plugged to the mains power line firstly After that the cable can be connected to the charge receptacle of the DOSEman The red LED lamp will blink for a few Seconds battery check and afterwards light permanently At the end of the recharging process the LED lamp switches from red to green light If the maintenance button of the charger was pressed the battery will be discharged firstly the LED lamp blinks during this process and after that the charging process will be started automatically The charger is not a power supply for permanent operation of the DOSEman The connection between the battery and charger is released by the charge controller if the full battery capacity is reached If the DOSEman shall operated permanently please contact the manufacturer to talk about the modifications required for your application Manual_DOSEman_EN_05 03 07 doc Page 9 ATTENTION The poles of the battery are directly connected to the charge receptacle of the instrument Do not connect any external power supply or shortcut the contacts This will cause a heavy damage of the instrument and a strong heat emission Communication with the PC The data communication between PC and DOSEman is realised by a special infrared adapter The usage of a possibly av
12. on Limit 63 2 1 95 3 99 75 6 Example Determination of the detection limit of the DOSEman using the Slow Mode and an integration interval of 120 Minutes The confidence interval shall be 95 that means in about 95 from 100 intervals a no zero reading should appear Required mean value number of counts from the table N 3 Calculating the detection limit by formula C N T S 3cts 120 min 0 32 cts min kBq m 0 078 kBq m 78 Bq m The detection limit in this case is 78 Bq m Manual_DOSEman_EN_05 03 07 doc Page 6 The instrument Operation Starting a measurement The instrument is switched on by pressing the front side push button On the display appears WELCOME Please push button If the button was locked in the set up before the display will show WELCOME Please check in Changing user parameters and access to the device set up is possible only during this state of operation stand by The measurement can be started by pressing the button once again If the button is locked the software has to be used to start the sample The data of the last measurement series will remain in the memory as long as the first integration interval of the new sample is not yet finished If a measurement was started unintentionally the instrument can be stopped by the time to read the data Please note that the sum spectrum is lost from the moment of starting During a r
13. the Detection Limit If the set integration interval is short and the Radon concentration low the expected true value of the number of detected decays may be around or less than 1 Because of the statistical variations intervals without any detected decay will appear frequently The most extreme situation would be a measurement series with a lot of zero intervals and only one interval with one detected decay because a decay can not be split Manual_DOSEman_EN_05 03 07 doc Page 5 When calculating the Radon concentration by the given formula the concentration value for the interval with the one count is much to high while all other values show zero Then all intervals have to be averaged to get a usable result This procedure is nothing else than to create an integration interval long enough to meet the Detection limit for the applied Radon concentration To avoid zero readings set the integration interval with respect to the lowest expected concentration level during the measurement The mean true value of the number of decays during an integration interval in case of a Radon concentration in the surrounding of the detection limit is less than 16 and therefore the statistical fluctuations have to be derived from the Poisson distribution The stated confidence interval gives the probability that the detected number of decays within the interval is not zero Confidence Interval Required Mean Value for N at the Detecti
14. uick response to concentration changes while the Slow mode gives a sensitivity approx 40 higher than in the fast mode The higher sensitivity reduces the statistical error of a measurement which depends on the number of counted decay events only The user should select the calculation mode carefully with respect to the application specific requirements see next chapter Statistical Error for non mathematicians The radioactive decay is a statistical process That means even if the Radon concentration is constant over the time the number of decays N counted within several intervals of the same period will be different N will vary around the mean value of all considered intervals Manual_DOSEman_EN_05 03 07 doc Page 3 Considering an infinite number of intervals would lead to an average which one indicates the true result of N For a single interval the value of N will be either below or above the true value This observed deviation is covered by the term Statistical Error Therefore each serious measurement contains beside the calculated Radon value the error band for a stated confidence interval The commonly used confidence intervals are 1 2 or 3 Sigma c which refer to a likelihood of 68 3 95 45 and 99 73 For example the correct interpretation of a measured Radon concentration of 780 Bq m with a Statistical 1o error of 15 is The real true Radon concentration lies with a likelihood of 68 3
15. unning sample four different display pages can be toggled by the push button Info page 15 45 uve OOE aly SAMPLES 34 In the upper line the actual time and a symbol to indicate the remaining battery capacity are shown Some other symbols are displayed depending on the actual settings o Key symbol if the button was locked o Symbolised S if the slow mode was chosen for the Radon calculation o Bell symbol if any alert was detected within the running measurement series The second row contains the information about the pre set integration interval T and the time t elapsed since the begin of the recent interval in Minutes The lower line shows the number of samples already stored in the memory Actual Radon concentration RADON 634 Bq m3 24 The Radon concentration will be calculated at the end of each integration interval In addition to the concentration value the statistical error is given in the lower line Before finishing the Manual_DOSEman_EN_05 03 07 doc Page 7 first interval or if no decay was detected within the last integration interval the values are replaced by bars Radon average concentration Rn Avg 670 Bq m3 12 The average concentration is derived from all counts detected from the begin of the actual measurement series The calculation depends on like the actual value calculation the actual setting of the Radon calculation mode fast or slow see chapter Theory of Operation
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