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LA-UR-12-24875. Canberra NetCAM, Dynamic Radiation Source and CAM Alarm Modeling . James T. Voss Jonathan A. Hudston Tom McLean RP-2 Group Los Alamos National Laboratory Los Alamos, NM, 87545. Presented at 2012 HPIC Meeting, UNM-LA, Los Alamos, NM September 24-26 2012.

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canberra netcam dynamic radiation source and cam alarm modeling


Canberra NetCAM, Dynamic Radiation Source and CAM Alarm Modeling

James T. Voss

Jonathan A. Hudston

Tom McLean

RP-2 Group

Los Alamos National Laboratory

Los Alamos, NM, 87545

Presented at 2012 HPIC Meeting,

UNM-LA, Los Alamos, NM

September 24-26 2012

introduction outline
Introduction: Outline
  • Introduction
    • Evaluation recap
    • Evaluation update
    • Suggested areas for future improvement
  • Current NetCAM performance
    • Alarm algorithms and set points
      • Alarm modeling
    • Dynamic radiation source testing
  • Conclusions
  • Canberra NetCAM evaluation began 9/2008 at LANL
    • Selected as candidate for continuous air monitor at the RLUOB facility
    • Perceived advantages of NetCAM dongle over ASM1000
      • Cost ($3.5 K cheaper than ASM1000)
      • Networking capability (built-in web browser)
      • Peak-shape fitting algorithm included
  • Immediate problems found with:
    • Hardware
    • Firmware
    • User interface
    • Intra and Inter-communications
    • Documentation incomplete
  • Spent next 3.5 years resolving these issues
  • NetCAM dongle
    • Up to 8 CAM heads can be connected
      • but 1:1 configuration selected for RLUOB
    • RS-232 output to PC ( terminal emulator) console program
    • RJ-45 ethernet connections (unit has built-in web browser)
    • Remote monitoring using RadHawk (RadNet-compliant) listener
    • Has wireless capability too ( not used at LANL)
  • AS1700 CAM head
    • 1700 mm2 PIPs detector
    • Efficiency of ~32% for electroplated distributed 239Pu source
    • Flow rates ~ 2cfm
    • Original firmware: version 1.10 (now have 2.4)
canberra netcam
Canberra NetCAM
  • Panel PC functions as local display (runs embedded Win XP)
  • Dongle configuration
    • 2 RJ-45 ports
    • RS-485 (to CAM head)
    • RS-232 for console connection
recent issues and resolutions
Recent issues and resolutions
  • Power supplies for Panel PC and NetCAM dongle not UL-listed
    • Also leakage voltage of >30v AC measured on dongle
    • Resolved using quality power supplies
  • Sigma-based DAC-h alarm limit not correctly calculated
    • Issue fixed by Canberra
  • Acute false alarm rate abnormally high
    • Issue identified through modeling of NetCAM performance (discussed later)
    • Issue fixed by Canberra
canberra netcam1
Canberra NetCAM
  • Extensive list of required fixes satisfactorily completed earlier this year
    • Now offers reliable, robust operation
    • Able to automatically reboot to restore normal operation
    • Couples low detection limits with low false alarm probability
  • Acceptance test passed 7/2012
    • Alarm response tests (acute and chronic)
    • Performance tests
    • Reliability tests
  • 54 NetCAM units delivered to RLUOB facility in 8/2012
    • Additional 13 units purchased as spares
future netcam improvements
Future NetCAM improvements
  • Revise calculation of sigma-based DAC-h alarm limit i.e. :
    • Net TRU counts = Gross counts – sum of tail contributions
    • Variance in Net counts = Gross counts + sum of tail contributions
  • Modify automatic energy calibration scheme
    • Currently too restrictive and unable to locate or track 7.69 MeV peak
  • Modify performance test algorithm
    • Currently takes >7 minutes whereas ASM1000 took ~ 2 minutes
  • Allow user to select chronic analysis update frequency
    • Currently fixed at 4 minute intervals
netcam alarm algorithms acute alarm
NetCAM alarm algorithms: acute alarm
  • Acute alarm solely resides with the Alpha-Sentry CAM head
    • Based on a user-set count interval (6 - 60 seconds)
    • Counts in TRU region (2.8 - 5.8 MeV by default) and Rn region (5.8 - 6.0 MeV by default) summed
    • Alarm sounds if following conditions satisfied

- the number of counts per channel in the TRU ROI is twice that of the Rn ROI

- the number of TRU ROI counts exceeds the user-set minimum

netcam acute alarm set points
NetCAM acute alarm set points
  • Traditional LANL acute alarm set points;
    • 12 second count time
    • 80 or more TRU ROI counts required to generate an alarm
    • Default ROI boundaries used
  • Experience has shown that these settings adequately prevent false alarms but are they optimal ?
Acute alarm: Calculated 239Pu DAC-h activity at TRU count rates corresponding to 1 false alarm per year per 60 NetCAMs

* Assumptions: 2 cfm, 30% detection efficiency, DAC factor = 5E-12 μCi/cm3andenergy calibration is correct

Acute alarm: Calculated 239Pu DAC-h activity corresponding to detection probabilities of 50% and 95% per count interval

* Assumptions: 2 cfm, 30% detection efficiency, DAC factor = 5E-12 μCi/cm3

modeling of netcam alarm response
Modeling of NetCAM alarm response
  • FORTRAN program written to simulate NetCAM performance
    • Code samples background and TRU spectral distributions specified by user
    • Respective total count rates independently set by user
    • Poisson stats used for number of bkg. and TRU counts and associated energies per 6 second update frequency
    • Both contributions are summed to form an integrated spectrum
    • Performs acute and chronic alarm (Valley mode) analysis under conditions specified by user
      • analysis frequency, ROI settings, cycle time, alarm set points, etc …..
      • valley (tail-fitting) mode used for chronic analysis
        • Both true and blind man’s differential approaches are considered
netcam chronic alarm algorithms
NetCAM chronic alarm algorithms
  • Blindman’s differential approach used for NetCAM chronic analysis
    • Spectrum refreshed at end of each count cycle
  • Valley mode
    • Sequential exponential tail-fitting and subtraction of tail counts
    • Net counts in TRU ROI used to determine activity
      • recent improvements avoid non-physical net TRU cpm results
    • Uncertainty calculation incorrectly implemented by Canberra
      • grossly overestimates uncertainty in net counts
      • compensates by using a relatively small kσ factor
    • Alarm sounds when the fixed DAC-h limit and sigma-based limit are exceeded
      • an analysis every 4 minutes and at end of count cycle
  • Peaks mode
    • Not seriously considered as default analysis mode after some early problems
netcam alarm modeling conclusions
NetCAM alarm modeling: conclusions
  • Code appears to emulate NetCAM behaviour well
  • Predictions are dependent on background spectrum and count rate
  • Current number of TRU counts required for an acute alarm appears to be too conservative
  • Valley analysis mode capable of 239Pu detection limits of 2 DAC-h with negligible false alarm rates based on available Rn/Tn background data
    • Count cycle times of about 12 minutes appear optimal
    • Alarm response time can be as good or even better than true differential approach if NetCAM algorithm allowed freedom to analyze data more frequently
dynamic radiation source
Dynamic radiation source
  • Problem:
    • Evaluation of CAM heads (sensitivity, time-to-alarm)
      • Currently dependent on radioactive aerosols
      • Time intensive, expensive and requires specialized facility
  • Solution:
    • Dynamic Radiation Source (DRS)
      • Mimics the challenge of plutonium aerosol detection
introduction advantages of drs
Introduction: Advantages of DRS
  • Provides non-specialized in-house testing
  • Low cost (~2K) versus ~10K per aerosol test
  • Multiple test scenarios with various CAMs
  • Reproducibility
  • Supports iterative development of CAM analysis algorithms
  • No contamination issues
  • Rn/Tn background spectrum also present
  • Canberra NetCAM now capable of providing reliable operation and protecting workers
    • low alarm limits coupled with low false alarm probability
    • optimized alarm set points can be calculated using modeling
    • example of an ultimately successful collaboration between vendor and customer
  • Further beneficial improvements to NetCAM are readily achievable
  • DRS shown to be a useful tool in evaluating CAM chronic alarm algorithms
    • Empirical data lends support to the modeling predictions.