CAM2: and why Lab Impex bought a licence

Morgan Jones AWE

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What is a CAM and what does it do?

CAM = Continuous Air Monitor Machining radioactive materials risks dust

entering external atmosphere and being inhaled Pump air at 40 litres/minute Trap dust on standard 25mm diameter filter 239Pu and 235U are α emitters (5.2MeV, 4.4MeV) Thin silicon detector 4.5mm away, opposite filter

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Penetration of radiation

CAMs exist to warn of potential biological damage due to inhalation of radioactive airborne dust particles. Damage is proportional to energy deposited per unit path length:

α: Stopped by sheet of paper or epidermis β: Stopped by 3mm of aluminium or Perspex/Lucite γ: Quite hard to stop, inches of lead may not be enough

Thus, although an alpha emitter may be innocuous externally, ingestion or inhalation is very dangerous.

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AWE outline design specification

Primarily α detection, but β detection added at commercial request

Send robust signals down existing cabling Retain AWE’s familiar interface; minimise new

bells & whistles Make the hardware modular, use generic

components, keep it simple Radon…

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CAMs live or die by radon…

Typical radon daughter α spectrum(6/6.08MeV, 7.69MeV, 8.78MeV)

0

20

40

60

80

100

2 3 4 5 6 7 8 9 10

Energy (MeV)

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But peak proportions change with time

Radon daughter peak channel count against time(Started at 09:00 Monday 3/8/09)

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100

1,000

0 24 48 72 96

Elapsed time (hours)

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t ra

te (

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er

ho

ur)

6.00/6.08MeV Po218/Bi212

7.69MeV Po214

8.78MeV Po212

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Outline radon compensation requirement

256 channel spectrometry. Original AWE CAM used Regions Of Interest with radon algorithm tailored to each building (to match proportions of U and Th series in the building materials)

Automated curve fitting – one size fits all Keep the algorithm simple Assembler rather than high-level language

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Exponential curve fitting

Traditional curve fitted radon daughter α spectrum

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40

80

120

160

2 3 4 5 6 7 8 9Energy (MeV)

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Curve fitting

Curves caused by random alpha path lengths across that 4.5mm air gap

Traditional technique fits and strips all three daughter peaks sequentially starting from highest energy

But air gap compensation allows all three peaks to use the same value of exponential, enabling a single curve fit

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Release detection

Traditional technique subtracts all three peaks and treats entire residual as release – very sensitive to curve fitting errors

AWE technique tests for statistical anomalies – automatically ALARP*, and resistant to radon jumps caused by opening doors

* As Low As Reasonably Practicable

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Release detection (from early type test)

Detection of 239Pu against radon background

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5

10

15

20

25

30

35

2.8 3.2 3.6 4.0 4.4 4.8 5.2 5.6

Energy (MeV)

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Measured

Release

Curve fit

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Summary

Drop-in replacement for existing AWE CAM (500 ordered in March 2012)

One size fits all Statistical release detection confers enhanced

immunity to abrupt radon changes

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Why Lab Impex bought a licence…

UK Patent 1011982.4 (filed July 2010) covers:

Air gap compensation and consequent simplified curve fitting

Channel by channel statistical testing Adjacent channel testing