April 2008
David Baltz
Chief Technologist
Bladewerx LLC
Rio Rancho, New Mexico
`
Accurate measurement of occupational dose
due to radon progeny is affected by several
factors:
◦
◦
◦
◦
`
Radon gas concentration (222Rn and
Air exchange rates
Particulate sizing
Plate-out
220Rn)
The decay chain is involved, with short-lived
daughters, and the possibility of
resuspension of longer-lived radionuclides
222Rn
5.30 MeV α
218Po
210Po
3.05 min
6.03 MeV α
214Pb
26.8 min
138 d
4.19 min
210Bi
206Pb
5.01 d
700 keV β
214Bi
19.9 min
1.5 MeV β
214Po
164 µs
7.69 MeV α
206Tl
210Pb
22.3 y
stable
220Rn
216Po
0.15 s
208Tl
6.78 MeV α
212Pb
10.6 h
6.05 MeV α
36%
3.05 min
208Pb
212Bi
330 keV β
1.78 MeV β
stable
60.6 min
64%
2.25 MeV β
212Po
304 ns
8.78 MeV α
`
Working Level:
`
EPA action level:
◦ A unit of measurement of the concentration of radon decay
products Polonium-218 through Polonium-214. One WL is equal
to 100 pCi/l of radon in equilibrium with its decay products and
will release 1.3x105 MeV of potential alpha energy per liter of air.
[EPA-402-R95-013]
◦ Any combination of short-lived radon decay products in one liter
of air that will result in the ultimate emission of 1.3 x 105 MeV of
potential alpha energy. This number was chosen because it is
approximately the alpha energy released from the decay products
in equilibrium with 100 pCi of Ra-222. Exposures are measured in
working level months (WLM). [EPA 402-R-92-004, July 1992
(revised)]
◦ 4 pCi/L (0.02 WL when the equilibrium ratio is 0.5). [EPA 402-R92-004, July 1992 (revised)]
`
Working Level (WL)
mWL = 27.8C A + 137C B + 100.8CC
x Where, CA, CB, CC are the airborne concentrations in Bq/liter of 218Po,
214Pb,
`
and
214Po
respectively.
SI Unit (J/m³)
x WL=20.8 µJ/m³
`
The total concentration of radon decay products (RDPs)
present divided by the concentration that would exist if
the RDPs were in radioactive equilibrium with the radon
gas concentration which is present. At equilibrium (i.e., at
an equilibrium ratio of 1.0), 1 WL of RDPs would be
present when the radon concentration was 100 pCi/L. The
ratio is never 1.0 in a house. Due to ventilation and plateout, the RDPs never reach equilibrium in a house
environment. A commonly assumed equilibrium ratio is
0.5 (i.e., the progeny are halfway toward equilibrium), in
which case 1 WL corresponds to 200 pCi/L. However,
equilibrium ratios vary with time and location, and ratios
of 0.3 to 0.7 are commonly observed. Large buildings,
including schools, often contain equilibrium ratios less
than 0.5.
`
`
`
Determine 218Po, 214Po and 212Po
concentrations from alpha spectroscopy
Estimate the 214Pb and 212Bi concentrations
Derive the PAEC from the cumulative ultimate
energy yields of each constituent. This
method is independent of equilibrium.
PAEC
Time
GoF
Equil
MDC
Counts
Po212
Po214
Pb214
Po218
Po210
Vol(m³)
(µJ/m³)
2/14/2008 12:04
0
0.4
0.0001
0.3246
0.04
0.0001
0
0
0
0.1011
0.0317
2/14/2008 12:05 0.006
0.395
0
0.3947
0.04
0
0
0
0
0
0.034
2/14/2008 12:06 0.008
0.416
0.0407
1.7605
16.86
0.0003
0.0081
0.0036
0.0287 222.8894
0.0398
2/14/2008 12:07 0.003
0.434
0.5521
6.8068
288.34
0.027
0.186
0.2084
0.1307 358.5219
0.0455
2/14/2008 12:08 0.002
0.44
1.0148
9.3984
643
0.234
0.1819
0.4159
0.1831 -31.8544
0.0515
2/14/2008 12:09 0.002
0.437
0.6387
5.4236
816.92
0
0.1583
0.296
0.1843 182.7724
0.0572
2/14/2008 12:10 0.002
0.431
0.5498
3.433
965.78
0
0.1456
0.2364
0.1677 283.4974
0.063
2/14/2008 12:11 0.002
0.426
0.5485
2.5326
1161.94
0
0.1459
0.2403
0.1623 430.0032
0.0687
2/14/2008 12:12 0.002
0.424
0.6276
1.885
1493.43
0
0.1452
0.303
0.1794 368.8723
0.0747
2/14/2008 12:13 0.002
0.425
0.7848
1.3379
2057.58
0
0.1404
0.4153
0.2291 200.3005
0.0805
2/14/2008 12:14 0.002
0.419
0.7367
1.0762
2198.71
0
0.1031
0.4035
0.2301 217.1998
0.0865
2/14/2008 12:15 0.001
0.409
0.7313
0.8132
2582.04
0.0878
0.1072
0.3049
0.2313 220.6257
0.0923
2/14/2008 12:16 0.001
0.412
1.2805
1.5934
3040.98
0.1221
0.2187
0.533
0.4067 344.6761
0.0581
2/14/2008 12:17 0.001
0.409
1.5716
2.6423
3374.47
0.0715
0.2534
0.8144
0.4323 457.4076
0.0583
2/14/2008 12:18 0.001
0.402
1.4478
2.3289
3463.17
0.0838
0.2135
0.6812
0.4693 395.0992
0.0582
2/14/2008 12:19 0.001
0.394
1.4832
2.1397
3922.89
0.0574
0.2888
0.6304
0.5066 248.6751
0.0582
2/14/2008 12:20 0.001
0.388
1.67
2.1122
4341.83
0.0357
0.3541
0.7453
0.5349
67.7591
0.0583
2/14/2008 12:21 0.001
0.383
1.7424
2.0328
4648.34
0.0019
0.3711
0.8005
0.5689 -36.3518
0.0584
2/14/2008 12:22 0.001
0.374
1.5951
1.8988
4711.33
0
0.3786
0.655
0.5616 120.6342
0.0582
2/14/2008 12:23 0.001
0.366
1.6056
1.8959
4935.2
0.009
0.4422
0.5877
0.5667
36.2629
0.0583
2/14/2008 12:24 0.001
0.362
1.8178
1.7991
5198.78
-0.1216
0.4943
0.7504
0.5731
-4.7949
0.0582
2/14/2008 12:25 0.001
0.359
1.8064
1.8146
5320.87
-0.112
0.4747
0.7603
0.5714 -94.7044
0.0583
2/14/2008 12:26 0.001
0.35
1.5686
1.6446
5567.55
-0.0967
0.4671
0.5092
0.5924 -109.047
0.0584
2/14/2008 12:27 0.001
0.346
1.7476
1.7567
5780.64
-0.0745
0.5588
0.6003
0.5885 -214.605
0.0584
Bladewerx LLC
4135 Jackie Rd SE #108
Rio Rancho, New Mexico 87124
www.bladewerx.com