SabreASC

Operation Manual

B L A D E W E R X

SabreASC Operations Manual

SabreASC Operations Manual

Documentation version 4.0 29 August 2007

Copyright Notice

Copyright 2004-2007, Bladewerx LLC. All Rights Reserved.

Any technical documentation that is made available by Bladewerx LLC is the copyrighted work of Bladewerx LLC and is owned by Bladewerx LLC.

NO WARRANTY. The technical documentation is being delivered to you AS-IS and Bladewerx LLC makes no warranty as to its accuracy or use.. Any use of the technical

documentation or the information contained therein is at the risk of the user. Documentation may contain technical or other inaccuracies or typographical errors. Bladewerx reserves the

right to make changes without prior notice. No part of this publication may be copied without the express written permission of Bladewerx LLC, 103 Rio Rancho Dr N.E. Suite C4, Rio

Rancho, New Mexico 87124.

Trademarks

Bladewerx, the Bladewerx logo, SabreASC and SabreMCA are trademarks of Bladewerx LLC. Microsoft, Window, ActiveSync and the Windows logo are registered trademarks of Microsoft

Corporation.

SabreASC Operations Manual .......................................................................................................................................................... i

GETTING STARTED ........................................................................................................................................................................... 4

WHAT IS A SABREASC? ....................................................................................................................................................................... 4 THE PARTS OF THE SABREASC ............................................................................................................................................................ 4 INSTALL THE SABREASC ASSISTANT SOFTWARE ................................................................................................................................ 5 INSTALL THE AC ADAPTER AND THE COMMUNICATION CABLE .......................................................................................................... 5 QUICK START BASICS .......................................................................................................................................................................... 5

CALIBRATION .................................................................................................................................................................................... 8

PASSWORD SECURITY .......................................................................................................................................................................... 9 ENERGY CALIBRATION ........................................................................................................................................................................ 9

MCA Calibration ............................................................................................................................................................................. 9 Peak Location / Energy Calibration ................................................................................................................................................ 9

EFFICIENCY CALIBRATION ................................................................................................................................................................. 11

CONFIGURATION ............................................................................................................................................................................ 13

INSTRUMENT OPTIONS DIALOG ......................................................................................................................................................... 14 General Tab ................................................................................................................................................................................... 14 Isotope Tab .................................................................................................................................................................................... 16 Changing the Isotopes Table ......................................................................................................................................................... 17 Calibration Tab ............................................................................................................................................................................. 17

SPECTRUM PANE PROPERTIES ............................................................................................................................................................ 18 STRIP CHART PANE PROPERTIES ........................................................................................................................................................ 19 CONFIGURATION FILES ...................................................................................................................................................................... 20

PERFORMING A SAMPLE COUNT ............................................................................................................................................... 21

SAMPLE DATA/ACTIVITY REPORTING ..................................................................................................................................... 25

DISPLAYING AND LOGGING READINGS .............................................................................................................................................. 25 DISPLAYING AND LOGGING SPECTRUMS ............................................................................................................................................ 28 IMPORTING THE DATA INTO MICROSOFT EXCEL ................................................................................................................................ 29

THEORY OF OPERATION .............................................................................................................................................................. 30

MULTI-CHANNEL ANALYZER ............................................................................................................................................................. 30 CALCULATIONS.................................................................................................................................................................................. 31

Uncertainties in Peak Counts ........................................................................................................................................................ 31 Calculation of the Detection Limit ................................................................................................................................................. 31 Activity Calculation Method .......................................................................................................................................................... 32

ISOTOPE MATCHING........................................................................................................................................................................... 32

SABREASC STATUS CONDITIONS ............................................................................................................................................... 33

SPECIFICATIONS ............................................................................................................................................................................. 34

Table of Contents

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4

Getting Started

What is a SabreASC?

The Bladewerx SabreASCTM is a field-deployable alpha sample counter that provides high-sensitivity alpha activity determinations on filters or swipes with real time compensation for radon-daughter background. Samples no longer need to be stored for several days for radon daughters to decay before being able to assess non-background alpha activity, and SabreASC is easily calibrated to most alpha-emitting isotopes of interest. Throughout this manual, the sample displays and text refer to Pu-239 as the isotope of interest. However, the isotope of interest is user selectable and your unit may therefore indicate some other isotope or isotopes (up to two isotopes of interest, in addition to the normal radon daughters, can be simultaneously measured.

The Parts of the SabreASC

Your package should include the SabreASC sample counter assembly, an AC Adapter, a serial communication cable, and Software CD containing the SabreASC Assistant software and documentation.

SabreASC is comprised of a solid metal base plate with interchangeable filter/sample holder that provides for repeatable sample geometry coupled to an electronics assembly that houses the solid-state detector, detector power supply, amplifier, and SabreMCA multi-channel analyzer. A rugged parallelogram hinge moves the detector in and out of position over the sample and protects the detector face, keeping it parallel to lower plate and out of harm’s way.

The SabreASC Assistant software is a PC-compatible Windows-based program that provides complete instrument control, calibration, data analysis, and data logging capabilities. It is a high performance package with the capability for doing spectrum analysis and quantifying alpha activity against a background of radon-daughter interference. The user interface is highly simplified by

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point and drag thresholds and peak locators on the spectral display during calibration and automatic count time determination based on user-defined action level, real time limit of detection determination, and activity level.

Install the SabreASC Assistant Software

The SabreASC Assistant software runs only on a Windows equipped PC-compatible computer with a spare serial communication port (DB-9 connector). Insert the Software CD into the PC and, if the installation does not automatically start, double click on the Setup program stored there to automatically create an appropriate folder on the hard drive and install the executable program files. The SabreASC is controlled entirely from this software. The only control on the sample counter assembly itself is the power on/off switch located on its rear panel.

Install the AC Adapter and the Communication Cable

Connect one end of the provided cable to one of the serial communication ports on the PC and to the DB-9 connector on the rear panel of the sample counter electronics housing. For PCs with more than one serial port, note the port number when connecting the cable.

Plug the AC adapter into a 115 VAC wall socket and then into the power connector on the rear panel of the sample counter electronics housing. The SabreASC has a green LED on the front panel that indicates whether the unit is connected to power and the rear panel on/off switch is in the on position.

Quick Start Basics

Make sure the sample counter is connected to power and to the PC and that the power switch is in the on position.

Start the SabreASC Assistant software by clicking the icon on the Windows desktop.

While the software is configured with default parameters on startup, configuration and calibration must be performed prior to putting the unit into service counting actual samples. Please refer to following sections in this manual for details on how to select appropriate parameters and to calibrate the instrument.

The software provides three “panes” that indicate status and provide data and control. Each pane can be resized by using the cursor to drag and release at the pane boundaries. The upper left pane contains status and data readings, the upper right pane the alpha energy spectrum, and the lower pane displays a real time strip chart representation of the analysis results.

NOTE: All configuration and calibration parameters can be accessed by

double clicking within the pane of interest to call up a dialog box and/or

through the pull down menus at the top of the page. Menu items may be

“grayed” out and not accessible if you are not logged in at the proper

security level through the “File--Login” menu. The SabreASC Assistant

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software stores configuration and calibration parameters for the sample

counter on the PC hard drive. These parameters are used for any sample

counter that is connected to the PC. If a different SabreASC is connected to

a PC that was previously calibrated to a different SabreASC, the

configuration and calibration parameters MUST be reset or erroneous

readings will result.

To open the sample counter, place your four fingers on top of the case and with your thumb lift upward on the release lever located in the center of the front panel allowing the upper assembly to move to its rear position. The hinges are spring loaded so that the detector/electronics housing automatically moves out of the way to expose the sample holder. Place the sample in the circular sample recess milled in the base plate.

CAUTION: The sample holder is reversible and interchangeable. Make sure

you have the proper sample holder for the sample you are using. Any

samples placed in the sample holder MUST NOT protrude above the surface

of the bottom plate. Catastrophic detector damage will result if the sample

counter is closed with anything protruding from the sample recess above

the surface of the base plate. Always make certain that the area between

the detector housing and the bottom plate is clear before closing the sample

counter. Never touch the face of the detector! Besides the potential for

damaging the light-tight detector surface, the buildup of oils on the face will

degrade the spectral performance of the detector.

To close the sample counter, Place your four fingers on top of the case, pull upward on the release lever with your thumb, pull the case forward to the closed position and release the release lever making sure the latch clicks shut.

Start a sample count by pressing the space bar, or by clicking on the start count button in the control/status pane, or by using the pull down menu. A menu will pop up to allow you to identify the sample prior to starting the count. A sample ID which ends in a digit automatically increments. For air samples, the date/time stamp, run time and volume information should be filled in. The inherent alpha background for the solid-state detector is extremely low, so a source is needed in order to see anything interesting. A filter paper that has had air drawn through it for several hours makes a good “test” source, as does a plated source with the isotope-of-interest.

As counts are received from the detector, data will be displayed in all three panes and updated in real time:

The elapsed time, gross alpha activity, net reading and error in the upper left control/status pane. Note that the error is shown in dpm at the 1 sigma level.

The energy spectrum and “curve fit” in the upper right spectrum pane.

The strip chart in the lower pane with pens for the Pu-239 (or other isotope as selected by the user) reading, the LD (level of detection), and the user selected action level.

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As the count progresses, you’ll typically see a highly fluctuating Pu-239 reading that eventually settles down as the measurement accuracy improves. Depending on the configuration settings, the LD line may be off scale high. As the count progresses and statistics improve, the LD line will continuously trend lower towards the action level line.

The count is automatically terminated by reaching the max count time parameter or when the LD reaches the action level and the Pu-239 reading is below the action level or when the Pu-239 reading is above the action level with a user specified error term (more on this in later sections). The count can also be terminated by pressing the escape key, by using the stop count button in the control/status pane, or by using the pull down menu.

The SabreASC is a powerful and flexible alpha-counting system. Please read the rest of this manual to garner a clear understanding of the various configuration and calibration settings prior to putting it into service.

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Calibration

To maintain accurate measurements of the isotope-of-interest, the SabreASC must be calibrated periodically. The purpose of calibration is to insure that the peak-fitting algorithm knows where in the spectrum to expect the radon progeny and isotope-of-interest peaks. The peak-fitting algorithm will fail (causing a periodic “BEEP”) and the instrument will fail to make accurate measurements if the peaks do not appear in the expected locations.

NOTE: Because of variations in filter media or sample material or

methods, as well as differences in sample position with respect to the

detector (i.e. detector spacing), a calibration is typically applicable to a

specific sample configuration. Switching between swipes and filters

may require calibration adjustments. The SabreASC makes this easy by

allowing the user to create several different configuration profiles and

then selecting the proper one to use that matches the current sample

type. The MCA settings (gain, threshold, offset, and scale) are MCA

dependent and are saved in the MCA and are not saved in the

configuration files on disk. The configuration files save values such as

efficiency, peak locations, count termination criteria, etc.

The calibration functions are accessed from the Calibration item on the pull down menu. There are two steps to calibrating the SabreASC: energy calibration and efficiency calibration. The energy calibration step should always be performed before the efficiency calibration.

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Password Security

The SabreASC has three levels of security accessed through the User Login menu. The User Login menu is located on the File menu. Selecting Login pulls up the User Login dialog box.

If a user is not logged in, he is at the lowest security level and able to perform sample counts, but not to change the configuration or calibration parameters. The second level of security is the Configuration level. At this level, the user is allowed to select different configuration profiles to match the sample type. The highest level of security is the Calibration level. At this level, the user may calibrate the instrument and create different configuration profiles. The default passwords are:

calib for the calibration level password

config for the configuration level password

You must be logged in at the appropriate level in order to change the passwords. Logging in under the config password will allow you to change the password for that level. Logging in under the calib password will allow you to change the password for both levels. Once they are changed, the default passwords will no longer work.

Energy Calibration

To begin the energy calibration, access the routine from the pull down menu. The Energy Calibration dialog will be displayed showing the energy calibration settings and a window of the spectrum.

MCA Calibration

In most cases, the default values for Gain, Offset, Threshold and Scale will not need to be changed. See the Theory of Operation section for more information on these parameters.

Peak Location / Energy Calibration

The peak location calibration consists of using a radon-daughter loaded filter paper to perform a 2-point calibration using the Bi-212 and the Po-214 peaks to establish the channel versus energy

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calibration linear response curve. This requires a filter that has had air drawn through it for several hours thus accumulating radon daughters on the filter. The filter doesn’t need any kind of specific activity calibration for this step. Begin the calibration by opening the sample counter and placing the radon-daughter loaded filter paper under the detector, closing the sample counter, and allowing the peaks to build up. Clicking on the Reset Spectrum button resets and restarts the accumulation of the spectrum.

Drag the Po-214 peak locator line over the largest peak in the spectrum and the Bi-212 peak locator line over the next peak to the left. Move the line by click-and-holding the cursor on the line, then dragging the line to the new location and releasing the mouse button. Once the Bi-212 and Po-214 peak locator lines are in the correct positions, energy calibration is complete and you can remove the filter.

NOTE: Some filter media may provide poor resolution of the Bi-212 peak

and/or the peak may not show up well at low radon levels. If this is the

case, then set the Po-214 to the appropriate channel and set the Bi-212

peak locator line 50 channels lower. For a typical calibration with the

MCA settings shown above, PeakCH(Bi-212) = PeakCH(Po-214) – 50.

Altitude WILL affect where the peaks show up. If the Po-214 peak is not

with a few channels of 220, adjust the MCA offset setting. Note that you

must change the offset by intervals of 8, i.e., the only legitimate offset

settings are …64, 72, 80, 88, 96… Lowering the offset moves the peaks

to the right. Increasing the offset moves the peaks to the left.

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Click the OK button to exit the energy calibration dialog. All the peak locations for peak fitting are saved on the PC and the MCA settings are saved on the SabreMCA. To discard any changes, click Cancel.

Efficiency Calibration

To begin the efficiency calibration, access the routine from the pull down menu. The Efficiency Calibration dialog will be displayed showing the current efficiency.

To perform the efficiency calibration, a calibrated Pu-239 source (or other isotope of interest) with traceable activity should be used. A source of at least 10,000 dpm should be used for the calibration.

Enter the source activity in dpm into the Activity in DPM edit field.

Now, place the source in the sample counter, making sure that the surface of the source is as close as possible to the position of the surface of the intended samples, and close it.

NOTE: The curve fit to a calibration source will not initially line up precisely

with the spectrum from the calibration source. This is ok as the peak fitting

algorithm automatically determines the peak location once adequate counts

from the source are in the spectrum and calculates efficiency based on the

area under the peak. Peak locations for the same isotope almost always

differ between a plated source and the actual filter paper. The energy

calibration is performed off an actual filter paper and will provide the most

accurate results.

Tap the Start Calibration button to start the measurement. The routine will compare the gross count rate and source activity and display the Net CPM and calculated 4-Pi Efficiency. When the count completes, the final calculated efficiency is displayed. Depending on the source quality and active area, an efficiency between 23 and 28% should be expected for Pu-239.

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Repeat the calibration if desired or remove the source and click the OK button. The Efficiency Calibration dialog will close, saving the new setting.

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Configuration

The SabreASC Assistant program provides several dialogs to allow configuration of the instrument’s operation. These dialogs are accessed through the pull down menus at the top of the screen and/or by double clicking in the appropriate pane. The basic configuration settings are accessed from the Monitor pull-down menu and all several settings:

The instrument options include the basic operating mode settings

The General tab is used to set the count time mode, either fixed count time mode or automatic count time mode.

The Isotope tab is used to configure what isotope(s) you want to measure. The basic configuration is to measure for a single isotope (such as Pu-239) and automatically compensate for any radon daughters by mathematically fitting a spectrum curve to the radon daughter peaks. An alternate isotope of interest can also be specified and the SabreASC will measure and report on both isotopes. The alternate isotope can be specified as “Match”, which means that the SabreASC will look for any unknown peaks and attempt to match them to one of the isotopes stored in the file “isotopes.csv”. This file is editable by the user.

The Calibration tab is used to specify the maximum calendar days between energy calibrations.

The spectrum pane dialog is used to set the display parameters for the spectrum pane.

The strip chart pane dialog is used to set the display parameters for the strip chart pane.

Additionally, the configuration settings (which include the calibration settings) can be saved on disk as different configuration files.

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Instrument Options Dialog

The SabreASC Instrument Options dialog is accessed from the Monitor menu.

General Tab

Com Port— This pull-down list provides for the selection of which PC serial com port the SabreASC is connected to. Default is COM1.

Count Termination—These parameters control when the count cycle is automatically terminated. There are two modes of operation, either fixed count time or automatic count time. If the automatic mode is selected, then

the count cycle will terminate when the Detection Limit LD is below the Action Level and the Pu-239 reading is below the action level by more than its error term OR

the count cycle will terminate when the LD is below the Action Level and the Pu-239 reading is above the action level and has an error calculated for the Pu-239 reading that is better than the ±% value entered on this screen. The reading error is shown in the status/data pane at the one sigma level and the ±% error is calculated as the one sigma error divided by the reading. The default is 10%.

In either case, the count time must exceed the minimum count time specified before the count will terminate. Regardless of these two conditions, the count will terminate once the count time reaches the maximum count time entered on this screen.

Default is both conditions enabled. Cannot be edited.

Count for at least:—This parameter selects the minimum count time, the sample count will always last at least this long. The default is 10 seconds.

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but not more than—This parameter selects the maximum count time, after which the count cycle is automatically terminated, regardless of any other conditions. The default is 300 minutes.

If fixed count time is selected, then the count time in minutes is entered and used by the SabreASC.

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Isotope Tab

Primary—This pull-down list provides for the selection of isotope of interest. This selection affects only the isotope-of-interest and not the measurement of radon daughters, which are always monitored. The list of isotopes on the pull-down menu is determined by the contents of the file “isotopes.csv”. The reading for this isotope is shown in the status/data pane. Default Primary is Pu-239.

Alternate—This pull-down list provides for the selection of an additional isotope of interest. The list of isotopes on the pull-down menu is determined by the contents of the file “isotopes.csv”. The alternate isotope can be specified as “Match”, which means that the SabreASC will look for any unknown peaks and attempt to match them to one of the isotopes stored in the file “isotopes.csv”. The reading for this isotope is shown in the status/data pane if an isotope or “Match” is selected. Default Alternate is None.

Action Level—This parameter is the “Action Level” used in the automatic count cycle termination logic. If the alternate isotope is “None” then the action level is compared to the only the reading from the primary isotope. If the alternate isotope is match or any of the list of isotopes on the pull-down menu, then the action level is compared to the SUM of the readings from the primary and alternate isotopes. Default is 25 dpm.

Det. Limit Confidence—This parameter selects the confidence level used in the detection limit, LD calculation. Default is 95.3%.

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Changing the Isotopes Table

The isotopes included on the Primary and Alternate isotopes pull-down menus come from a disk file named “isotopes.csv”. An example is shown below:

Isotope keV Halflife

Cm244 5805 5.72E+08

Am241 5486 1.36E+10

Pu238 5499 2.77E+09

Pu239 5150 7.62E+11

U234 4776 7.72E+12

U235 4396 2.22E+16

U238 4196 2.22E+16

This table also controls what isotopes the software searches for if the isotope “Match” mode is enabled. This file can be edited by simply double clicking on the file name from Windows File Explorer (the files are normally stored in the “\Program Files\Bladewerx\SabreASC\” folder). Note that energy is always in keV and the Halflife is in seconds. After making changes, you must be sure to save the file as a comma delimited (CSV) file type. DO NOT CHANGE THE NAME.

Calibration Tab

This allows the user to determine the calibration interval. The unit will post an out of calibration message on the screen if the current date is beyond the calculated calibration expiration date.

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Spectrum Pane Properties

To access the settings for the spectrum display, double-click inside the spectrum pane and the following dialog will display:

X Axis—This selection box selects the units used for the horizontal x-axis. If keV or MeV is selected, the channel to energy conversion is determined by where the Bi-212 and Po-214 peak locator lines on the energy spectrum are set. Default is MeV.

Y Axis—This selection box selects either linear or log scale for the vertical Y-axis display. Default is linear.

Spectrum Type—This selection box selects the type of graphing used for the data. Default is Line Graph with a marker size of 3.

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Strip Chart Pane Properties

To access the settings for the strip chart display, double-click inside the strip chart pane and the following dialog will display:

Max Y Scale—This parameter selects max scale for the vertical Y-axis of the Strip Chart in dpm. Default is 100 dpm.

Pen Width—This parameter selects the pin width for the strip chart pens in pixels (approximate). Default is 2 pixels.

Reference—This parameter is automatically set to equal the Action Level in dpm and results in a red straight line on the strip chart against which the Pu-239 reading and MDA pens can be compared. It cannot be edited on this screen.

Min Y Scale—This parameter selects min scale for the vertical Y-axis of the Strip chart in dpm. Default is 0 dpm.

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Configuration Files

All of the configuration settings are stored in a configuration file (note that the MCA settings are saved by the MCA itself and are not a part of the configuration file). The user may create and maintain multiple configuration files. The default configuration file is named “default.cfg”. Configuration file management is via the File pull-down menu.

To create a new configuration file with all default values, use the New command.

To open an existing configuration file and load the parameters stored there, use the Open command.

The user can save the current parameters to the current configuration file using the Save command.

To save the current parameters under a new configuration filename use the Save As command.

NOTE: Configuration settings are saved to the disk file ONLY upon user

command. Whenever you change configuration settings, you must use

one of the commands on the file pull-down menu to update the

configuration file on disk or create a new one. When you exit the

SabreASC Assistant program you will be prompted as to whether or not

you want to save changes to the configuration file.

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Performing a Sample Count

To open the sample counter, place your four fingers on top of the case, pull upward on the release lever located in the center of the front panel with your thumb, and move the upper assembly to its rear position. The hinges are spring loaded so that the detector/electronics housing automatically moves out of the way to expose the sample holder. Place the sample in the circular sample recess milled in the base plate.

CAUTION: The sample holder is reversible and interchangeable. One side is

deeper and accepts Planchets, while the other side is shallow and accepts

filters and swipes. Make sure you have the proper sample holder for the

sample you are using. Any samples placed in the sample holder MUST NOT

protrude above the surface of the bottom plate. Catastrophic detector

damage will result if the sample counter is closed with anything protruding

from the sample recess above the surface of the base plate. Always make

certain that the area between the detector housing and the bottom plate is

clear before closing the sample counter. Never touch the face of the

detector! Besides the potential for damaging the light-tight detector

surface, the buildup of oils on the face will degrade the spectral

performance of the detector.

To close the sample counter, Place your four fingers on top of the case, pull upward on the release lever with your thumb, pull the case forward to the closed position and release the release lever making sure the latch clicks shut.

Start a sample count by pressing the space bar, or by clicking on the start count button in the control/status pane, or by using the pull down menu. A menu will pop up to allow you to identify the sample prior to starting the count.

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The sample ID automatically increments if it ends with a digit. For air samples the collection date/time stamps, run time and sample volume fields should be filled in. Run time, Volume, Location, and Purpose are only used as identifying entries in the data log file. If a Volume is entered (total air volume through the filter), then the software calculates the average concentration in dpm/m3 and adds it to the log file.

As counts are received from the detector, data will be displayed in all three panes and updated in real time:

The elapsed time, gross alpha activity, net reading and error in the upper left control/status pane. Note that the error is shown in dpm at the 1-sigma level.

The energy spectrum and “curve fit” in the upper right spectrum pane. The display shows the current spectrum from channel 0 through channel 255. The vertical scale adjusts automatically to display the highest peak.

The strip chart in the lower pane with pens for the Pu-239 (or other isotope as selected by the user) reading, the LD (level of detection), and the user selected action level.

As the count progresses, you’ll typically see a highly fluctuating net reading that eventually settles down as its accuracy improves. Depending on the configuration settings, the LD line may be off scale high. As the count progresses and statistics improve, the LD line will continuously trend lower towards the action level line. If the activity of the radon progeny is not too excessive, the LD will eventually dip below the Action Level. In unusually high radon situations, the LD may not reach the sensitivity represented by the Action Level requiring the Action Level to be raised or the sample do be decayed for some period of time.

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Depending upon the configuration settings, the count is automatically terminated when

1. The LD is less than the Action Level and the Pu-239 reading is below the Action Level by an amount at least equal to its error term. In this case the status becomes CLEAN.

2. OR the LD is less than the Action Level and the Pu-239 reading is above the Action Level and the Pu-239 reading has an error less than the user-defined error tolerance. In this case, the status becomes ABOVE LIMIT.

3. OR the Maximum Count time is reached.

4. OR the user manually terminates the count cycle by pressing the escape key, by using the stop count button in the control/status pane, or by using the pull down menu. In this case, the status will indicate CANCELLED.

If the SabreASC is operated in the fixed count time mode, then the count will not terminated until the user selected count time has elapsed.

CAUTION: The SabreASC Assistant software stores configuration and

calibration parameters for the sample counter on the PC hard drive. These

parameters are used for any sample counter that is connected to the PC. If

a SabreASC is connected to the PC that was previously calibrated to a

different SabreASC, the configuration and calibration parameters MUST be

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reset or erroneous readings will result. Save calibration and configuration

information for each SabreASC in a separate *.CFG config file.

If an alternate isotope of interest has been enabled (refer to the Isotopes tab on the Instrument Options menu), then the alternate isotope of interest (or “match” if the user has enabled the matching option) reading will show up on the display along with a reading for the sum of the primary and alternate isotopes of interest. When an alternate isotope is enabled, the automatic count termination logic operates on SumIoI (sum Isotopes of Interest) value and its error term.

When a count is completed, the user may print a report of the count results by selecting File-

Print.

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Sample Data/Activity Reporting

Printing the Sample Analysis

The SabreASC Assistant compiles a sample analysis report at the completion of each count. This report may be printed through the File—Print… menu item.

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An example of the Sample Analysis is reproduced below and lists the results of the count, as well as the collection information and SabreASC calibration data.

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Displaying and Logging Readings

The SabreASC Assistant displays readings on a continual basis during a count cycle. At the end of the count cycle, the readings are logged onto the hard drive and stored in a file named SabreASC_log.csv, or other file name that the user can specify. To start a new log and specify a new log file name, access the File pull-down menu and use the Start New Log command.

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All subsequent log data will go into this new file. To revert to an existing log file, use the Open Existing Log command and all subsequent log data will go into the selected file. This file can be viewed by simply double clicking on the file name from Windows File Explorer (the files are normally stored in the “My Documents” folder). An example log file is shown below (the one wide table has been broken up into three):

Index SampleID Location Purpose Description Volume (M³) Runtime (hr) Collected

1 3 Filter 0 0 2/16/2006 10:39:23 AM

2 4 Filter 0 0 2/16/2006 11:00:32 AM

3 5 Filter 0 0 2/16/2006 11:03:55 AM

4 7 6 6 Filter 0 0 2/16/2006 11:07:43 AM

Isotope1 Net DPM MDA Error pCi/M³ MDC Isotope2 Net DPM MDA Error pCi/M³ MDC

Pu239 13.6 11.2 6.8 0 0

Pu239 14.7 10.7 6.5 0 0 Match 0.9 15.9 6.4 0 0

Pu239 8.7 24.3 14.8 0 0 Match 0.9 36.1 14.6 0 0

Pu239 29.9 4.8 2.9 0 0 Match 6.3 7 2.8 0 0

Total Net DPM MDA Error pCi/M³ MDC Gross DPM Count Time Result Date

350.6 00:03:10 CLEAN 2/16/2006 10:42:35 AM

SumIoI 15.6 19.2 15 0 0 254 00:03:21 CANCELLED 2/16/2006 11:03:55 AM

SumIoI 9.6 43.5 34.1 0 0 218.4 00:01:28 CANCELLED 2/16/2006 11:05:26 AM

SumIoI 36.1 8.5 6.7 0 0 217.4 00:07:34 CANCELLED 2/16/2006 11:15:20 AM

Displaying and Logging Spectrums

The SabreASC Assistant displays spectral data in the spectrum pane on a continual basis during a count cycle. The user can save spectrum data to the hard disk at any time by using the file pull-down menu. The file names are of the format Spectrum_xxx.csv, where the xxx in the file name is equal to the sample ID, or the user can specify a different name when performing the save. To save the current spectrum, access the Save Spectrum command from the file pull-down menu. This file can be viewed by simply double clicking on the file name from Windows File Explorer (the files are normally stored in the “My Documents” folder).

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Importing the data into Microsoft Excel

Log files and spectrum files are in Comma-Separated-Variable (*.csv) format and can be opened and viewed directly from Microsoft Excel by simply double-clicking on the file.

A more convenient method for viewing different sessions of SabreASC files is to open a blank Excel spreadsheet and select Data—Get External Data—Import Text File…

Next, select the SabreASC log file and import it at cell A1. The data can now be graphed and analyzed. Save the spreadsheet to preserve the link to the imported data.

To examine the SabreASC data from a different session it is only necessary to open the previously saved spreadsheet, then select Data—Refresh Data and select the new log file.

Disk files can be found using Windows File Explorer (the files are normally stored in the “My Documents” folder).

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Theory of Operation

Multi-channel Analyzer

Internally, the SabreMCA utilizes a 1024-Channel discriminator, whose output can be translated to the 256-channel MCA output through four configuration settings. The four fields at the top of the screen, Gain, Thresh, Offset and Scale, control the translation of the SabreMCA discriminator output and affect the location, width, spacing and offset of isotope peaks on the 256-channel spectrum. These values are stored permanently on the SabreMCA board and in most cases do not need to be changed from the factory settings. Changing any of the four values will result in new values being permanently stored on the board.

Gain—(Range 1 to 31) This value controls the amplitude of pulses coming from the detector. Increasing the gain broadens isotope peaks, shifts them to the right, and spreads individual peaks further apart. As the Gain is increased, the peak(s) can be shifted completely off the right end of the spectrum display. Shifting to the next Scale will bring the peaks back into view on the spectrum. Default Gain is 24.

Thresh—(Range 1 to 31) This value controls the amplitude threshold that pulses must exceed to be measured. It should be set just above the level where the amplifier noise is first observed. Default Threshold is 0 (i.e. disabled).

NOTE: As Gain is increased, the noise amplitude will increase proportionally,

requiring a compensating increase in Threshold level.

Scale—(Range 0 to 2) This value controls the binning or compression of the 1024-channel discriminator output into the 256-channel spectrum value. A value of zero results in no compression. A value of one does 2::1 compression, binning 512 channels of the discriminator output into 256 spectrum channels. A value of two does 4::1 compression,

SECTION

6

31

binning all 1024 channels of the discriminator output into 256 spectrum channels. Default Scale is 1.

Offset—(Range 0 to 255, Resolution 8 channels) This value shifts the 256-channel spectrum the defined number of channels to the left. It is related to the Scale setting by controlling the 256-channel window on the scaled discriminator output. If the Scale is zero, the Offset will allow the output of any consecutive 256 channels, from discriminator channel 1 to channel 512. If the Scale is one, Offset will allow the display of any 512-channels over the 1024-channel discriminator range (binned down to 256 spectrum channels). If the Scale is two, the Offset has no effect and the entire 1024-channel discriminator output is compressed 4::1 to the 256-channel spectrum. Default Offset is 80.

Calculations

Uncertainties in Peak Counts

In most ROI-based analyzers, the minimum detection limit is based on the statistical uncertainty of the background counts that fall within the region, in combination with the uncertainty of any counts in excess of the background. In the SabreASC, the Detection Limit (LD) is not directly related to the spectrum counts, but to the uncertainty in the curve fit.

When the curve fit is completed each second, values are returned which represent the counts under each isotope peak. These values are statistically distributed about the ‘true’ peak areas and have known probabilities of being within 1-sigma, 2-sigma, etc. of the true area. A characteristic of the curve fit algorithm is that in the course of solving the minimization problem, a “covariance matrix” is calculated which described the errors associated in the solution. This covariance matrix identifies, on its diagonal, the variances of each coefficient—including the peak area coefficients. In other words, the curve fit routine returns the actual variances for the peak areas so that uncertainties due to interfering isotopes (i.e. background) have already been considered.

An examination of the peak area variances confirms that when the counts due to an interfering isotope greatly outnumber the counts due to the isotope of interest, the variance of the isotope of interest increases. Likewise, when there are very few interfering counts from other isotopes, the variance begins to approach a value equal to the peak area counts.

Calculation of the Detection Limit

The variances returned from the curve fit routine represent the uncertainties on the peak counts for each isotope during the last peak-fitting. The limit of detectability variance used is a combination of the fit variance with the previously saved ‘zero-counts’ variance.

EffT

VarianceK

C

P

2

DL

Where, TC is the count time, Eff is the detector efficiency, K is the sigma factor for the user selected confidence level, and VarianceP is the variance of the fitted peak area of the isotope of interest.

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Activity Calculation Method

The curve fit function produces coefficients for each isotope that correspond to the counts under the peak. In order to calculate an activity, the counts for each peak are used. The peaks are used to determine the net count rates.

EffT

NetActivity

C

P

Where NetP is the peak count for the isotope of interest.

The error term associated with the activity determination is simply the square root of VarianceP.

Isotope Matching

The software can be configured to look for the presence of an alternate isotope of interest. When matching is enabled, the software analyzes the spectrum for the presences of any of the isotope peaks that are included in the isotopes table. It does this by evaluating “what-if” curve fits for each of the isotopes in the isotope table to determine if the potential unknown isotope from the table improves the overall spectral curve fit. The presence of unknown isotopes that do not match any in the isotopes table may produce a “poor fit” status.

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SabreASC Status Conditions

Status Description

INITIALIZING SabreASC program initialization (momentary)

READY Ready for new count cycle

ABOVE LIMIT Action Level set point has been exceeded

CLEAN Action Level set point has NOT been exceeded

INT COMM No communications with SabreMCA

POOR FIT Could not fit the spectrum with the defined isotopes

OUTOFCALIB Calibration has expired

Appendix

I

34

Specifications

Detector / Sample

Detector: Solid-state silicon (1-in. model, 450 mm² active area; 2-in. model, 2000 mm² active area).

Sample holder: One side accommodates up to 2-inch filter/swipes. The other side accommodates 2-inch planchets. Other Sample Holder configurations available.

Data Analysis

MCA: 1024-channel ADC

Peak-fitting algorithm for radon daughters and up to two additional isotopes with the capability to “Match” or identify an unknown isotope.

Max Count Rate: 600,000 cpm

4-Pi Efficiency: 25% (approx)

Physical

AC Adapter and serial RS-232 Null-Modem cable provided

Weight: 8.5 lbs (3.8 kg)

Dimensions (W x H x D): 7 x 3 x 14 in.

Temperature: 0 to 122 °F (-20 to 50°C)

Humidity: 5 to 90% (non-condensing), splash-proof electronics

Appendix

II