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RADON FILM-BADGES BY RADIATORSWITH NANOHOLES VERSUS EXISTING
PASSIVE MONITORS
L. TommasinoTHL, Via Cassia 1727, 00123 Roma, Italy
Rn atoms are nanoparticles .4 nm wide for entering nanoholes with .4 nm aperture
Rn nanoparticles move through nanoholes in liquids and solids (Eyring, 1936)
Rn-monitors by diffusion chambers
Absorber Thickness Part. Coeff. α
CR-39 1 mm 0.06
Polycarbonate 0.3 mm 8
Holder-plastics 3 mm 0.5-0.75
(From More and Hubbard, 1997)
(From Pressianov and others)
LIQUID–LIKE POLYMERS (T>Tg)(Rubber, polyethylene)Transient nanoholes
GLASS–LIKE POLYMERS (T< Tg)(Polycarbonate) Frozen nanoholes
THERMOSETS-(CR-39)
Frozen nanoholes as sorptive sites
Diffusion by molecular-induced jumps
EQUILIBRIUM SAMPLING:
Fast Rn-absorption time
Equilibrium time (Barrer, 1939): T=d2/6D
d the film thickness D the diffusivity
For a 300-μm-thick PC-film (CD)T=~ 30 days
Non-equilibrium sampling
For a PC-film thickness < 50 μmT < 5 hours
Equilibrium sampling
CR-60 absorptive radiatorswith bulk-distributed nanoholes for:
- obtaining compact and easy-to-deploy radon film-badges - increasing the response linearity of passive monitors
-measuring soil-radon under equilibrium conditions-measuring radon directly in water.
CR-60 Definition respectively for:- having a radon-diffusion length of about 60 μm at environmental temperature
- being a Carbonate Radiator (CR) with a solubility of 60 ± 20 (i.e. in the range 40-80)-degrading maximum alpha-particle energy by a 64 μm-thick film
- having a film-thickness not greater than 60 μm.
CR-60 Characteristics depend on: - the polymer structure and morphology
- the manufacturing processes - the shelf-life
- the thermal history, etc.
Radiator
(facing CR-39)
Thickness
(µm)
Response[Tracks.m3/
(cm2. kBq.h)
Metal ----------- 0.010±0.002
CR-60 (1 Makrofol N; Low solubility, S=40)
20 0.20 ± 0.02
CR-60 (2 Makrofol N) 40 0.34 ± 0.04
CR-60 (3 Makrofol N) 60 0.45 ± 0.05
CR-60 (4 Makrofol N) 80 0.42 ± 0.06
Two responses in one monitor
Response Tracks.m3/
(cm2.kBq.h)
Passive chambers 2.8 ± 0.7 (with CR-39)
CR-60 (20 µm Makrofol N) 0.2 ± 0.03
Two Radiators
PE Bag CR-39
Radon film badge for in-soil and in-water measurements
Large tubes are conducive to errors (Tanner, 1991)
Different volumes-Same responses
α
(T)
[C]Rn
[C]Rn
[CRn]water =α (T) [CRn]air
For large exposure measurements:
Film-badges by absortpive radiators with bulk-enclosed nanoholes
For low exposure measurements of one week or less:
Film-badges by adsortpive radiators with surface-distributed nanoholes
ADSORPTION
Non-equilibrium sampling-activated-charcoals
Equilibrium sampling-solid layers with surface-distributed
nanoholes having very large surface to volume ratio.
CR-2000 adsorptive radiatorswith surface-distributed nanoholes for:
- measuring indoor radon-exposures for one week or less.
CR-2000 Definition:-equilibrium Rn-adsorption of radon up to a concentration
2000 times of that present in the surrounding air.
CR-2000 Characteristics depend on:- the manufacturing processes
- the shelf-life - the storage environment
Sampler Response Tracks.m3/(cm2.kBq.h)
- CR-2000 (Adsorptive radiator) 20 ± 4
-Passive chambers 2.8 ± 0.7 (with CR-39)
Uniquely-compact radon-film-badges with absorptive- and/or adsorptive-
radiators for:
- indoor measurements for days, months, and years
- using as a back-up monitor
- correct soil-measurements
- direct-in-water measurements
CR-0 bags for storing all types of monitors prior to and after
the exposure are:
- radon-proof bags
-radon-free bags
-bags sealable by pressure-type devices
CR-60, CR-2000, CR-0 available through a centralised distribution because of the:
- need of custom-made radiators with desired characteristics
- large cost of minimum-orders consisting of stocks up to 1000 kg
- difficulty in handling and storing large volumes of materials in suitable low-radon environments
Luigi Tommasino
THL, Via Cassia 172700123 Roma, Italy