Flashcards in Monitoring Deck (24)
What is a TLD?
LiF crystal, x-rays create ions which are then trapped (by doping element) and released by applying heat
No. electron and light is directly proportional to dose (supra lin at high dose)
Clear with high temp
Range: 10uGy to 1Gy
What is OSL?
Optically stimulated luminescence
Crystalline material, electron traps -> readout via laser like TLD
Can be reread mult times before annealing
10uSv to 10Gy
What is DIS?
Direct ion storage
Similar to DR but also contains an ion chamber to improve dosimetry
Ion-gate, charge liberated in the chamber is collected at the gate. Can store a long term record.
30uGy to 5Gy
Other dosimetry methods
Real time dosim (DIS for interventional)
Quartz fibre: charge fibre moves over a scale dep on charge. Prev used by emergency services
EPD: Electronic personal dosim GM tech, gives realtime int dose
Blood tests: after acute expo
Looks for breaks and dicentrics in DNA
Why is monitoring required?
Required by IRR17
Classified workers must be monitored
Most exposed workers (in healthcare) are not classified
Personal monitoring provides ongoing confirmation that each worker’s status remains appropriate
What are examples fluoro staff doses?
Rad practitioner: 0.6mSv
Risk from of accidental whole body expo: low
What are example cardiology staff doses?
0.25-0.31,Sv per year
Consequence of expo: med
IRR2017 monitoring requirements
- Need an Approved dosimetry service; systematic dose assessment and recording
- Individual monitoring where possible or otherwise
- Retain records (to 75 years or 50 years after assessment)
- Provide radiation passbooks
- Approved by HSE
- Approve dosimetry service
- Follows written procedures
- Reported doses traceable to primary standards
- external testing and inspection
- Dose audits
- Investigate unexp results
- retains records securely
- Report to ADS
What is an ADS ?
- requests estimated doses from the employer
- contains special entries
- makes special entries in the record
- retains details of investigations
Reg22 IRR - est doses and special entries
Employer monitoring duties
Takes advice from RPA
Determines what/who/how to monitor
Estab inv. levels
Monitors badge/PPE use
Liases with ADS, regulators, other employers
How is Hp10 derived?
Whole body measure
Dose at depth of 10mm to ICRU sphere
Measure air-kerma in standard phantom
Issues with Hp10
Significant underestimate due to orientation:
Front badge, radiation from rear
Back badge, radiation from front
Consider field conditions
Shielded dosimeter underestimates dose (~20%)
Unshielded collar badge overestimates dose (x20?)
If critical use two badges
under apron (trunk) badge
over apron (collar) badge
Issues with Hp(0.07)
Tip of finger difficult to monitor
Underestimates extremity doses factor 4-5 for Tc99m
Eye dose - water phantom under standard conditions, used tld
How to measure surface contamination
Surface contamination measurements; floors, work surfaces and skin; slow sweep of entire areas to find maximum levels; routine check against derived working limits consider area and background
What is a wipe test?
Test surfaces and storage containers for leaks
Swap areas and measure with a device such as a well counter.
What are the issues with wipe testing?
No immediate result
Portion removed (assume 10%?)
How to estimate surface contamination
Review local limits
Consider transfer routes
Averaging area 1000cm2 Floors, 300cm2 1cm2 Skin
Typical values for public areas (MDG Notes)
30Bqcm-2 Tc-99m, C-14, S-35, Ga-67,I-123, I-125
300Bqcm-2 H-3, Cr-57
What is environmental monitoring?
how is it carried out short/long term?
A requirement of the regulations; outside x-rays rooms, radio-pharmacies, LINAC rooms, etc.
Short term: Instantaneous dose rate gives quick indication
For long term review integrated dose (TLD badge or similar, 2 months) which incorporates workload.
What are the measures of enviromental doserate
IDR instaneous dose rate
TADR Time average dose rate (avr over 8hr)
TADR2000 av over work year x occupancy factor
How is radon monitored?
Passive and active devices, sample basements over 2 months against a derived limit of 400 Bq m-3
What is RIMNET?
RIMNET – Monitoring environmental GAMMA background using standard GM equipment (mSv/yr)