TOPIC 11: Activation Analysis
Let’s look at Activation Analysis.
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Typical Density Gauges
Contain Radioactive Material as a Radiation Source
Usually Cs-137 from 30 mCi to 5 Ci
Emit penetrating gamma radiation
Detects changing density of flow material
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We can perform Activation Analysis through continuous elemental analysis gauges. These gauges contain radioactive CF-252 (a natural neutron emitter) or a tritium activation device which emits neutrons when activated.
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Cf-252 Characteristics
- Emits gammas and neutrons
- Is a transuranic
- Shielding is of low “Z” materials
- Dose has higher LET
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Cf-252 Operating Principle
Process materials absorb the neutrons.
The absorption changes the element and creates a prompt gamma from the product which characterizes the material.
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Gauges with Cf-252 Additional Concerns
- Higher LET dose
- Work performed only by manufacturer
- Inventory/leak tests more frequent
- Requires additional secure location for storage
- AU must be USDOT HAZMAT trained for Cf-252
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Gauges with Cf-252 Additional Requirements
- Specific license only
- Company personnel remain outside of restricted area, unless properly trained to do work inside of the restricted area to maintain ALARA
- USDOT HAZMAT required for shipping Cf-252
- Leak testing every 6 months
- Requires a designated and licensed storage area for replacement sources
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Here is an Example of housing for Cf-252 sources. This unit can be placed inside a fenced area where the exposure rate is less than 2 mR/hr.
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Gauges with Cf-252
GM to Neutron Meter
GM measures in mR/hour
BF3 measures thermal (slowed) neutrons expressed in mrem/hour
Ratio of emissions is generally 3 neutrons to 1 gammas
Add together to get total dose rate
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Additional tasks for holders of Cf-252:
Secured storage area
EXAMPLE: Highest gamma reading at 1 meter is 0.8 mR/hour.
Remember, for gammas, the ratio is 1 mR/hr for 1 mrem/hr
0.8 mR/hr becomes 0.8 mrem/hr (gamma)
0.8 X 3 = 2.4 mrem/hour (neutron).
Total TI is: 0.8 + 2.4 = 3.2 (Yellow III)