Division of Compensation Analysis and Support

Dose Conversion Factors for Radon WLM DCAS-TIB-011 Rev. 05 

Effective Date: 06/28/2018

Supersedes: Rev 04

Subject Expert(s): David Allen 

Document Owner 

Approval: Signature on file

David Allen, Document Owner

Approval Date: 06/27/2018

Approval: Signature on file_________________ J. W. Neton, Associate Director for ScienceApproval Date: 06/28/2018
Document No. DCAS-TIB-011 Revision No. 05 Effective Date: 06/28/2018 Page 2 of 13

 

1BPUBLICATION RECORD

EFFECTIVE 

DATE

REVISION

NUMBER DESCRIPTION

03/16/2005 00 New document to provide a basis for the conversion factor.

04/15/2005 01 Correction factors added for ET1 and ET2 regions 

01/13/2006 02 Correction factors added for ET1 and ET2 regions for Radon 222 

01/04/2008 03 Correction factors added for Radon 219 and calculation errors 

corrected. Minor editorial changes to text. 

05/01/2013 04 Added conversion factor for Radon 222 lung dose

03/26/2018 05-A Added conversion factors for organs outside the respiratory tract. 

Minor editorial changes to text. Changes to document format. 

Changed title to better match content

05/23/2018 05-B Incorporated NIOSH comments

06/27/2018 05-C Incorporated additional NIOSH comments
Document No. DCAS-TIB-011 Revision No. 05 Effective Date: 06/28/2018 Page 3 of 13

 

TABLE OF CONTENTS

SECTION TITLE PAGE

1.0 Introduction .............................................................................................................................. 4

1.1 Purpose........................................................................................................................ 4

2.0 Background.............................................................................................................................. 4

3.0 Working Level Definition........................................................................................................... 4

4.0 Calculation Method .................................................................................................................. 5

4.1 Absorption rate ............................................................................................................. 5

4.2 Particle size.................................................................................................................. 5

5.0 Radon-222 ............................................................................................................................... 6

5.1 Unattached Fraction ..................................................................................................... 6

5.2 Equilibrium.................................................................................................................... 7

5.3 Radon-222 Results....................................................................................................... 7

6.0 Radon-220 ............................................................................................................................... 7

6.1 Unattached Fraction ..................................................................................................... 8

6.2 Equilibrium.................................................................................................................... 8

6.3 Radon-220 Results....................................................................................................... 9

7.0 Radon-219 ............................................................................................................................. 10

7.1 Unattached Fraction ................................................................................................... 10

7.2 Equilibrium.................................................................................................................. 10

7.3 Radon-219 Results..................................................................................................... 10

8.0 Dose to Organs Outside the Respiratory Tract....................................................................... 11

8.1 Model Parameters ...................................................................................................... 11

8.2 Organ Dose Conversion Factor Results ..................................................................... 11

References ........................................................................................................................................ 13

LIST OF TABLES

TABLE TITLE PAGE

Table 5-1. Equilibrium Factors for Radon 222..................................................................................... 7

Table 5-2. Dose Conversion Factors for Radon 222. .......................................................................... 7

Table 6-1. Dose Conversion Factors for Radon 220. .......................................................................... 9

Table 7-1. Dose Conversion Factors for Radon 219. ........................................................................ 11

Table 8-1. Dose Conversion Factors for Organs outside the Respiratory Tract................................. 12
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1.0 INTRODUCTION

Technical information bulletins (TIBs) are not official determinations made by the National Institute for 

Occupational Safety and Health (NIOSH) but are rather general working documents that provide 

historical background information and guidance to assist in the preparation of dose reconstructions at 

particular sites or categories of sites. They will be revised in the event additional relevant information 

is obtained about the affected site(s). TIBs may be used to assist NIOSH staff in the completion of 

individual dose reconstructions.

In this document, the word “facility” is used as a general term for an area, building, or group of 

buildings that served a specific purpose at a site. It does not necessarily connote an “atomic weapons 

employer facility” or a “Department of Energy (DOE) facility” as defined in the Energy Employees 

Occupational Illness Compensation Program Act of 2000 [42 U.S.C. § 7384l(5) and (12)].

1.1 PURPOSE

This Technical Information Bulletin provides the conversion factors for calculating organ dose from 

Rn-222, Rn-220 and Rn-219 decay products measured in working level months (WLM). 

2.0 BACKGROUND

The Interactive RadioEpidemiological Program (IREP) is used to determine the Probability of 

Causation (POC) that a cancer was caused by occupationally related radiation exposure. Annual 

radiation dose is the normal IREP input but in the case of Rn-222, a direct exposure model is also 

included for lung cancers. The exposure model was based on studies performed at uranium mines 

and thus applies to Rn-222 and its associated decay products. Rn-220 (also known as thoron) and 

Rn-219 (also known as actinon) decay products have characteristics that are sufficiently different from 

Rn-222 so that the exposure model is not applicable to Rn-220 and Rn-219. However, decay 

products of these two isotopes are often measured in units of working levels. This requires the 

development of a conversion factor to express Rn-220 and Rn-219 working level exposures in terms 

of lung dose in rem. For completeness, conversion factors for all organs for Rn-222, Rn-220 and Rn219 have been included.

3.0 WORKING LEVEL DEFINITION

The majority of dose received from radon is actually derived from energy emitted by the decay 

products rather than the gas itself. Because of this, the dose per unit radon gas activity is greatly 

dependent on the state of equilibrium of the decay products. To better describe the hazard 

associated with radon, worker exposure has historically been expressed in terms of the decay product 

activity. The unit developed for this is the Working Level. A Working Level is described as the amount 

of short lived radon decay products in one liter of air that will ultimately decay with 1.3E5 MeV of alpha 

energy. 

When the decay chain reaches 100% equilibrium, one Working Level is equivalent to approximately 

100 pCi/L of Rn-222, 7.5 pCi/L of Rn-220 or 162 pCi/L of Rn-219. While this is a significant 

difference in the gas concentrations, by definition of the working level, the decay products will 

ultimately emit the same amount of alpha energy. This, however, does not lead to the same lung 

dose. This is caused largely by the difference in the half-lives of the decay products. Since Rn-220 

products have longer half-lives, the body has longer to transport the activity from one compartment to 

another and thus deliver dose to different areas of the lung. 
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Since the working level is an air concentration, it is analogous to an exposure rate. To describe 

exposure, the unit working level month (WLM) is normally used. A WLM is described as the exposure 

equivalent to breathing one WL for 170 hours (one working month).

4.0 CALCULATION METHOD

The ICRP publication 66 (ICRP 1994) lung model was used to determine the proper conversion factor 

of dose per WLM for each isotope of radon. Each isotope of radon decays to several decay products 

creating a decay chain. Since most of the decay products are relatively short lived, all will decay in 

hours or days and most of that energy will be absorbed in the body. Therefore, the dose from the 

inhalation of a particular isotope is related most closely to the number of atoms inhaled from each 

isotope rather than activity inhaled. 

Some of the isotopes have a branching ratio. That is the isotope decays to one isotope some 

percentage of the time and to a different isotope the rest of the time. To simplify the calculations, 

branching ratios representing less than 1% of the decays are ignored.

The LNet and LNth compartments were determined but not listed in the respiratory dose sections. 

Due to the fact that there is no direct deposition in the lymph nodes and the short half-life of the radon 

progeny, no significant dose is received by the lymph nodes. The progeny undergoes significant 

decay before any of the material can reach the lymph nodes. LNet and LNth doses are included in 

section 8.

4.1 ABSORPTION RATE

The rate material is absorbed from the lungs to the bloodstream is an important parameter. The ICRP 

66 (ICRP 1994) lung model defines three default categories for particulate lung absorption. These 

defaults are to be used unless more specific information is known about the situation at hand. In the 

case of radon decay products, a number of references are available indicating an absorption half-life 

of approximately 10 hours. Marsh and Birchall (Marsh 1994) describe an evaluation while Nikezic 

(Nikezic 2002) lists four separate references to this value. Therefore, the 10 hour half-life is used in 

this calculation for each of the isotopes of radon.

4.2 PARTICLE SIZE

The particle size of the inhaled material is another important parameter for these calculations. The 

ICRP recommends a default particle size of 5 micron for a working environment and 1 micron for 

members of the public exposed to environmental releases. In both cases, these particle sizes are the 

median of a lognormal distribution of particle sizes. The default geometric standard deviation (GSD) 

is 2.5, the default density is 3 g/cc and the default shape factor is 1.5. This calculation uses all of 

these defaults with the exception of the particle size and GSD. GSD is calculated based on particle 

size using equation 16 of ICRP publication 66 (ICRP 1994). 

The particle size distribution affects the regional deposition of the aerosol in the lungs. This size is 

greatly affected by the unattached fraction. The fraction that is attached to other particulates can 

exhibit the aerodynamic characteristics of the larger particle to which it is attached. The unattached 

fraction, on the other hand, represents very small particles produced from the noble gas (radon). 

Nikezic et. al. (Nikezic 2002) indicated a particle size distribution for the attached fraction of 0.2 

micron with a GSD of 2.35 while the unattached fraction was 0.0015 micron with a GSD of 1.1. 
Document No. DCAS-TIB-011 Revision No. 05 Effective Date: 06/28/2018 Page 6 of 13

 

Porstendorfer (Porstendorfer 2001) indicated particle sizes for various environments. The unattached 

median particle sizes ranged from 0.00013 micron to 0.0013 micron with GSDs ranging from 1.1 to 

1.3. For the attached fraction, the major contribution (~86%) exhibited median particle sizes of 0.33 

micron for outdoor air and 0.217 micron for indoor air. Most of the remaining distribution exhibited a 

median size of ~0.040 micron. The GSD for these distributions varied from 1.5 to 2.2. 

Birchall and James (Birchall 1994) indicated that the available data of attached aerosol size in 

underground uranium mines indicates a particle size between 0.15 micron and 0.5 micron with Samet 

et. al. (Samet 1991) considering the best estimate to be 0.25 micron. 

ICRP 32 (ICRP 1981) indicates the value between 0.2 and 0.3 micron. 

Based on the references above, for each of the isotopes of radon, these calculations will use a 

median particle size of 0.25 micron for the attached fraction. A size of 0.0015 micron will be used for 

the unattached fraction.

Two additional important parameters are the unattached fraction and the degree of equilibrium 

between members of the decay chain. These parameters vary with the different radon isotopes and 

will be discussed in the sections specific to each isotopes.

5.0 RADON-222

Rn-222 is historically known as Radon. The decay chain for Rn-222 and its short lived decay 

products is shown below.

Rn-222 3.8235 day Alpha decay 

Po-218 3.10 min Alpha decay

Pb-214 27 min Beta decay

Bi-214 19.9 min Beta decay

Po-214 163.7 μsec Alpha decay

(GE 1989)

The half-life of Po-214 is very short and thus will represent only a small number of atoms inhaled. 

Therefore, to simplify calculations, inhaled Po-214 will be ignored. Also, for dose calculations, it will 

be assumed that each decay of Bi-214 will include one decay of Po-214.

A direct risk-based Rn-222 exposure model is available for lung cancer cases in NIOSH-IREP. 

However the chronic lymphocytic leukemia (CLL) model requires the calculation of a lung dose from 

all sources including Rn-222. Table 5-2 provides the conversion factor but it should only be used for 

CLL dose calculations. This direct exposure model should continue to be used for Rn-222 exposures 

for lung cases. 

The Po-214 decay was not modeled separately. The energy emitted from this decay was added to 

the Bi-214 decays. This is due to the very short half-life of Po-214 (approximately 0.16 msec).

5.1 UNATTACHED FRACTION

Rn-222 decay products are normally electrically charged. This causes the products to quickly attach 

to particles normally in the air. This greatly affects the aerodynamic characteristics of these particles 

which in turn affects the deposition of the particles in the lungs. While the unattached fraction is not 

specifically a parameter of the ICRP 66 lung model, the aerodynamic parameters are. 
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The unattached fractions used were 18%, 2.1%, and 0.07% for Po-218, Pb-214, and Bi-214 

respectively. This was taken from a formula in NCRP Report 78 (NCRP 1984) that equates 

unattached fractions to dust particle concentrations in the air. The particle concentration used was 

1x10

4

particles per cm

3

, which equates to an overall unattached fraction of 8%. This fraction is the 

same reported by Nikezic et. al. (Nikezic 2002) for indoor air. By comparison, Birchall and James

(Birchall 1994) reported an unattached fraction of 1% for mine air. The dose conversion factor was 

determined to be higher for higher unattached fractions. Since the dust concentration is difficult to 

determine and the difference is not large (~15%) the 8% assumption was used. This should be an 

overestimate for most work sites. 

5.2 EQUILIBRIUM

The equilibrium of the various Rn-222 progeny also affects the conversion factor. However, this also 

affects the number of working levels the activity in the air will represent. These tend to be competing 

factors and cause the effect on this conversion factor to be relatively small. Three equilibrium 

fractions were investigated. Two from NCRP Report 78 (NCRP 1984) and the third from Domanski

(Domanski 1979). The factors along with the associated overall equilibrium factor are shown in the 

table below. 

Table 5-1. Equilibrium Factors for Radon 222.

NCRP 78 outdoor NCRP 78 indoor Domanski

Po-218 0.9 0.5 0.656

Pb-214 0.7 0.3 0.446

Bi-214 0.7 0.2 0.259

Overall 0.72 0.28 0.40

The highest conversion factor for the ET2 compartment was produced by the NCRP 78 outdoor 

factors. Given the small difference in factors, these fractions will be used as a slightly favorable 

assumption for all values of equilibrium.

5.3 RADON-222 RESULTS

As a result of these parameters, the Rn-222 conversion factors are listed in the table below. 

Table 5-2. Dose Conversion Factors for Radon 222.

Conversion Factor 

(Rem/WLM)

ET1 compartment 1793

ET2 compartment 6.09

Lungsa 15.69

a. Direct exposure model in NIOSH-IREP should be used for lung cases. The lung conversion factor should only be 

used for CLL cases.

6.0 RADON-220

Rn-220 is historically known as Thoron. The decay chain for Rn-220 and its short lived decay 

products is shown below.
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Rn-220 55.6 sec Alpha decay 

Po-216 0.15 sec Alpha decay

Pb-212 10.64 hours Beta decay

Bi-212 60.6 min Alpha decay (36%), Beta decay (64%)

Po-212 304 nsec Alpha decay

Tl-208 3 min Beta decay 

(GE 1989)

The half-life of Po-216 and Po-212 are very short and thus will represent only a small number of 

atoms inhaled. Also, Tl-208 has a relatively short half-life but more importantly is a beta emitter. As 

such, it does not contribute to the working level calculation and represents an insignificant dose 

compared to other isotopes in the chain. Therefore, to simplify calculations, inhaled Po-216, Po-212 

and Tl-208 will be ignored. For dose calculations, it will be assumed that each decay of Bi-212 will 

include one decay of Po-212 (64% of the time) and one decay of Tl-208 the remaining 36% of the 

time.

6.1 UNATTACHED FRACTION

Birchall and James (Birchall 1994) used an unattached fraction of 1% based on a report by Samet et. 

al. (Samet 1991) Nikezic et. al. (Nikezic 2002) used 8% apparently based on the same report. The 

largest difference appears to be that Birchall and James attempted to describe typical mine air while 

Nikezic attempted to describe typical household air. It should also be noted that both reports were 

describing Rn-222 decay products. The unattached fraction of Rn-220 decay products can be 

different due to the greatly different half-lives of the products. The Rn-220 products have longer halflives and thus a longer period of time for the attachment to occur. 

Yamasaki et. al. (Yamasaki 1995) performed a theoretical calculation that showed the unattached 

fraction for Rn-220 decay products to be approximately 1.6% for indoor air. 

Porstendorfer (Porstendorfer 2001) demonstrated that the unattached fraction depends on the 

concentration of particulates in the air. He also showed that the unattached fraction of Rn-220 decay 

products is smaller than that of Rn-222 decay products. His values match well with each of the 

references above; therefore, this calculation will use a value of 2%. It is likely that the dust 

concentration in a work environment is higher than in a dwelling and thus the unattached fraction 

should be lower for the work environment. Therefore, when Yamasaki’s value of 1.6% is considered, 

the 2% unattached fraction should be slightly high for a standard work environment. This can be 

shown to be a slight overestimate of dose conversion factors but with the percentages so low, it 

appears to be reasonable.

6.2 EQUILIBRIUM

The last major factor to consider is the state of equilibrium exhibited by the decay chain inhaled. 

The decay chain of Rn-220 is shown below. 

Rn-220 55.6 sec Alpha decay 

Po-216 0.15 sec Alpha decay

Pb-212 10.64 hours Beta decay

Bi-212 60.6 min Alpha decay (36%), Beta decay (64%)

Po-212 304 nsec Alpha decay

Tl-208 3 min Beta decay 

(GE 1989)
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When the chain is in 100% equilibrium, the activity of each generation is equal. However, the 

number of atoms required to reach this equilibrium activity varies depending on the half-life. Since the 

working level is defined by the ultimate energy released, it is affected by the number of atoms more 

than the total activity in a mixture. The alpha energy is emitted only by Po-216 and essentially Bi-212. 

In reality Bi-212 emits an alpha only 36% of the time but the other 64% of the time it emits a beta 

then an alpha almost immediately through the decay of Po-212 (304 nsec half-life). The average 

alpha energy released by a Bi-212 decay is then 7.8 MeV (6.07 Mev * 0.36 + 8.785 MeV 

* 0.64). Since Po-216 ultimately decays by two alphas (Po-216 and Bi-212) the alpha energy 

released per Po-216 atom is 14.6 MeV. Pb-212 and Bi-212 both decay with an effective alpha 

energy of 7.8 MeV. Po-212 decays with an energy of 8.785 MeV and Tl208 decays by beta decay 

only. 

The largest number of atoms associated with the chain in equilibrium are Pb-212 and Bi-212 due to 

the relatively long half-lives. The remaining nuclides contribute little to the WL measurement or the 

lung dose. Therefore, in order to simplify the calculations, dose from inhaled Po-216, Po-212 and Tl208 will be ignored. Also, for each Bi-212 decay, it is assumed there is an immediate decay of Po212 64% of the time and Tl-208 the remaining 36% of the time. 

Since Pb-212 has a half-life approximately 10 times larger than Bi-212, the number of Pb-212 atoms 

in a 100% equilibrium mixture is approximately 10 times that of Bi-212. This causes Pb-212 to be the 

primary contributor to the WL measurement regardless of the degree of equilibrium. On the other 

hand, Pb-212 atoms inhaled have more time to be removed from the lungs prior to emitting all energy 

that will ultimately be emitted by the remainder of the decay chain. Therefore, while the amount of 

Pb-212 in air drives the WL measurement, the amount of Bi-212 in air is a large contributor to lung 

dose. This causes the degree of equilibrium to be an important parameter. A good measurement of 

this degree of disequilibrium is the ratio of Bi-212 to Pb-212. 

The degree of equilibrium depends entirely on the circumstances surrounding the production and 

movement of the Rn-220 gas in the breathing zone. This cannot be easily predetermined but a range 

of likely values can. 

ICRP 32 (ICRP 1981) indicates this ratio (Bi-212 to Pb-212) is between 20% and 80%. Pillai and Paul

(Pillai 1999) indicate the ratio is between 11% and 37% in a monazite mine and 24% to 84% in open 

air. This calculation will use 80% as a default value but also provide values for a range of equilibrium 

values. This will allow the most appropriate value to be used for the particular circumstances. 

6.3 RADON-220 RESULTS

The ICRP 66 lung model was solved using the assumptions described above. Under the default 

assumptions used in this report, a dose of 6.20 rem to the lungs will be assigned per WLM of Rn-220 

decay products inhaled. Similarly, the default doses to the ET1 region will be 943.83 rem and 0.45 

rem to ET2. This value should be considered to be received entirely in the year the material was 

inhaled. 

The values for different degrees of equilibrium were also calculated and are provided in the table 

below. The degree of equilibrium is specified by the ratio of Bi-212 activity to Pb-212 activity. These 

values can be used if information for the specific situation is available.

Table 6-1. Dose Conversion Factors for Radon 220. 
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% Equilibrium 

(Bi212/Pb-212)

Lung dose (rem) 

per WLM

ET1 dose (rem) per 

WLM

ET2 dose (rem) per 

WLM

20% 5.77 913.92 0.23

40% 5.92 924.25 0.31

60% 6.06 934.21 0.38

80% 6.20 943.83 0.45

7.0 RADON-219

Rn-219 is historically known as Actinon. The decay chain for Rn-219 and its short lived decay 

products is shown below.

Rn-219 3.96 sec Alpha decay 

Po-215 1.78 msec Alpha decay

Pb-211 36.1 min Beta decay

Bi-211 2.14 min Alpha decay

Tl-207 4.77 min Beta decay 

The half-life of Po-215 is very short and thus will represent only a small number of atoms inhaled. As 

such, it represents an insignificant dose compared to other isotopes in the chain. Therefore, to 

simplify calculations, inhaled Po-215 will be ignored. 

7.1 UNATTACHED FRACTION

No specific information was found for the unattached fraction of Rn-219. This fraction appears to be 

related to the time the particles have to attach to dust particles and so is related to the half-life. The 

first decay product of Rn-219 is Po-215 which has a half-life of 1.7 microseconds. This implies there 

is little time for it to attach to dust particles before it decays and so the unattached fraction is 

considered to be 100%. 

For Rn-222, the first decay product (Po-218) is assigned an unattached fraction of 18% due to its 

short half-life of 3.05 minutes. Its progeny (Pb-214) has a half-life of 26.8 minutes leading to an 

unattached fraction of 2.1%. The progeny of Rn-220 are assigned an unattached fraction of 2% due 

to a longer half-life (10.64 hrs for Pb-212). It appears there is little change in the unattached fraction 

once the half-life of the progeny reaches a particular value. Since the second decay product of Rn219 is Pb-211 with a half-life longer than Pb-214, an unattached fraction of 2% will be assigned to the 

second and subsequent decay products of Rn-219.

7.2 EQUILIBRIUM

The equilibrium of the Rn-219 progeny has little effect on the conversion factor. The initial progeny 

(Po-215) has a very short half-life and therefore represents very few atoms in one working level. The 

next progeny (Pb-211) drives the composition of progeny in a working level. This decays to Bi-211 

which has a 2.13 minute half-life then to Po-211 which has a 0.516 sec half-life. Given the short halflives of the progeny produced after Pb-211, it is reasonable to assume they are in 100% equilibrium 

with Pb-211.

7.3 RADON-219 RESULTS

As a result of these parameters, the Rn-219 conversion factors are listed in the table below. 
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Table 7-1. Dose Conversion Factors for Radon 219.

Conversion Factor 

(Rem/WLM)

ET1 compartment 1066

ET2 compartment 2.92

Lungs 14.66

8.0 DOSE TO ORGANS OUTSIDE THE RESPIRATORY TRACT

The previous sections of this document describe the conversion factors for the respiratory tract for Rn220, Rn-222 and Rn-219. Since the ICRP lung model is not element specific, no special treatment 

was necessary for decay products other than normal buildup and decay of radioactive isotopes. 

However, to determine dose to organs outside the respiratory tract, element specific biokinetic models 

must be used. 

Each of these three isotopes of radon first decays to an isotope of polonium followed by lead then 

bismuth. For most isotopes, the ICRP recommends assuming decay products behave the same as 

the parent isotope (shared kinetics). However for some decay chains, the decay products are 

essentially assumed to behave consistent with their own characteristic model. This is the case for the 

decay chains described in this document. Biokinetic models for these elements are not identical 

which requires some consideration as to where decays in one model enter the next model. ICRP 

publication 67 (ICRP 1993) describes the method for handling this situation with publication 71 (ICRP 

1995) Tables C-3 and C-4, providing transfer rates based on that description.

8.1 MODEL PARAMETERS

The absorption rate, particle size, unattached fractions and equilibrium factors used for the respiratory 

tract conversion factors are again used here for each isotope of radon. Only the default equilibrium 

factor of 0.8 for Rn-220 is used here since only modest differences occur in the calculated values 

using different factors. Specific effective energy (SEE) values were extracted from the computer 

program DCAL (DCAL 2006). However, it is necessary to discuss the SEE values associated with the 

“other” compartment. The “other” compartment in DCAL represents the other soft tissue compartment 

in the ICRP biokinetic models. This compartment is made up of all soft tissue not specifically 

described in the model. The mass and assigned fractions (AF) associated with this compartment vary 

depending on which organs are modeled and so they can vary depending on whether the decays 

occur as part of the ingrown or inhaled material. For that reason, the decays of an isotope in the soft 

tissue compartment are kept separate based on the original source of the inhaled material and 

multiplied by the applicable SEE. 

Dose from the radon gas itself was also considered. For Rn-222, appendix C of ICRP publication 32 

(ICRP 1981) was used to determine the dose to non-respiratory tract tissue from continuous 

inhalation of the gas. This dose was added to the dose calculated from the inhalation of the decay 

products. The half-life of Rn-222 is 3.8 days while the half-lives of Rn-220 and Rn-219 are much 

shorter (55.6 seconds and 3.96 seconds respectively). These short half-lives represent a much faster 

removal mechanism than Rn-222 and presumably a much smaller saturation concentration in the 

body tissues. Because of this, dose from the inhaled gas for these two isotopes was ignored.

8.2 ORGAN DOSE CONVERSION FACTOR RESULTS

Table 8-1 provides the calculated dose conversion factors for each radon isotope. It should be noted 

that these values are in units of mrem rather than rem used with the respiratory tract factors. Only the 

highest organ doses are provided. The remaining organs were similar enough to allow a single value 
Document No. DCAS-TIB-011 Revision No. 05 Effective Date: 06/28/2018 Page 12 of 13

 

to be presented as “all other organs”. This value represents a value that is equal to or higher than all 

the remaining organ factors.

Table 8-1. Dose Conversion Factors for Organs outside the Respiratory Tract

Organ

Rn-219 

(mrem/WLM)

Rn-220 

(mrem/WLM)

Rn-222 

(mrem/WLM)

Urinary Bladder 1.5 10 9.6

Bone surfaces 21 210 18

Stomach 8.2 10 16

Small intestine 4.2 11 12

Upper large intestine 2.4 15 10

Lower large intestine 1.5 16 - a

Colon 2.0 15 9.8

Kidney 15 240 60

Liver 4.3 58 11

Red bone marrow 3.1 27 9.9

LN(ET) 2.0 13 17

LN(TH) 1.5 9.6 9.9

All other organs 1.4 9.1 9.3

a. Value was at or below the value for all other organs so the all other organs value should be used.
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REFERENCES

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