# Presentation: 042301

## Radon, Thoron and Their Progeny:DOE’s Proposed Internal Dosimetry Standard

- Radon, Thoron and Their Progeny:DOE’s Proposed Internal Dosimetry Standard

- April 21-23, 1998 Air Monitoring Users Group
- Savannah River Site, South Carolina

- Judith D. Foulke and Daniel J. Strom
- DOE EH-52 Office of Worker Protection Programs and Hazards Management
- Risk Analysis & Health Protection, Pacific Northwest National Laboratory
- Richland, Washington
- Work supported by the U.S. Department of Energy under
- Contract No. DE-AC06-76RLO 1830

## Overview

- Introduction
- Issues peculiar to radon, thoron, and their progeny
- Air monitoring
- Air sampling for personnel dosimetry
- Current status in the DOE
- Future directions

**Notes:**
For decades, the phrase "time, distance, and shielding" has been presented as summarizing the "basics" of radiation protection. 
Indeed, for protection from external radiation sources, these three principles are probably the most important ones on which a worker can make decisions and take actions.  

However, these principles do not address protection against intakes of radioactive materials or "ontakes" (skin contamination), other risk-limiting measures, or other important protective measures taken by governments, public health agencies, regulators, and institutional programs.
Performance standards, health education, facility engineering requirements, and administrative procedures.

Furthermore, "time, distance, and shielding" simply do not apply to many radiation protection situations, such as indoor radon.  And finally, the standard liturgy of "time, distance, and shielding" doesn't tell the worker what action to take.  For these reasons, I have chosen to separate the principles (short names) from the commandments (what to do).

## Introduction

- DOE’s Proposed Standard *Internal Dosimetry*
- December 1996
- www.doe.gov/html/techstds/tsdrafts/tsdrafts.html

## Introduction

- Radon (222Rn, 3.82 d) and thoron (220Rn, 55.6 s) are the messengers
- Short-lived progeny (decay products) are the message
- short-lived, alpha-emitting heavy metals
- 238U  ... 226Ra, 222Rn, 218Po, 214Pb, 214Bi, 214Po
- 232Th  ... 220Rn, 216Po, 212Pb, 212Bi, 212Po

## Issues peculiar to radon, thoron, and their progeny

- Is it Nature’s radon or DOE’s radon?
- History of being ignored (not a product!)
- No *practical* bioassay
- Weird quantities and units

## Weird Quantities and Units

- funky equilibrium, equilibrium factor
- unattached fraction
- potential alpha energy concentration *(PAEC)*; working level (WL)
- potential alpha energy exposure *(PAEE)*; working level month (WLM)

## Air Monitoring

- Workplace
- characterize in real time the concentrations that workers might be exposed to while in an area
- Environment
- not covered in Proposed *Internal Dosimetry Standard*
- Mature technology, many manufacturers
- Instruments measure alphas
- Usually don’t have to discriminate against Pu!

## Air Monitoring 2

- should be
- real-time monitors that
- continuously measure and display results
- for periods of one hour or less
- should be placed to measure the highest concentrations to which workers in the area are likely to be exposed

## Air Sampling for Personnel Dosimetry

- Personnel monitoring
- establish the exposure of record for workers
- a potential area for intercomparison, accreditation
- should be
- continuous instruments
- either time-averaged or real-time measurements
- placed to measure the concentrations to which workers are exposed
- individual personnel monitors needed for large gradients of concentration or equilibrium (e.g., outdoors)

## Air Sampling for Personnel Dosimetry 2

- Active devices
- pump with filter: measure progeny
- Energy discriminating:
- Si surface barrier
- CR-39 with filters
- Not energy discriminating: *PAEE *(WLM)
- Passive devices
- measure radon gas
- etched-track detectors
- charcoal

## Exposure Monitoring Thresholds for Radon and Thoron Progeny

- Two PAEE approaches
- DOE 10 CFR 835: *above* background
- 0.08 WLM/year for radon progeny
- 0.24 WLM/year for thoron progeny
- Exemption from 10 CFR 835: *including* background
- 0.4  WLM/year for radon progeny
- 1.2 WLM/year for thoron progeny

## Why PAEE?

- relevant ionizing energy is delivered to the bronchial epithelium by alpha particles
- 218Po and 214Po in the case of 222Rn
- 212Bi and 212Po in the case of 220Rn (thoron)
- decay-product aerosol often contains an unknown mixture of the various radon and/or thoron progeny

## Assessment of Intake, Exposure, and Dose

## Background

- Highly variable
- Best to measure
- Default values:

## Equilibrium Equivalent Concentration

## Equilibrium Factor, F

## Acceptable Default Equilibrium Factors for Radon (FRn)

## Assigned Respiratory Protection Factors for Rn, Tn, and Their Progeny

- What good does a respirator do?
- Noble gas goes through

## Time-Integrated Concentration, NV

## Equilibrium Equivalent Concentration, EEC

## PAEE and transitions per unit volume

## PAEE to Dose Equivalent Conversions For 222Rn Progeny

- DOE’s 10 CFR 835 (with stochastic DAC):
- 1994 ICRP (Pub. 65), 1996 IAEA SS 115 dose conversion convention:  5 mSv/WLM (= 0.5 rem/WLM)

## Converting Measurements to CEDE

- Ignore refinements based on
- particle size
- equilibrium factor
- unattached fraction
- Don’t know
- effect of respiratory protection
- worker’s breathing rate
- nose or mouth breathing

## Converting Measurements to CEDE

## Minimum Detectable Dose for a Nuclear Track Etch Radon Detector

- minimum detectable amount for time-integrated radon concentration: 30 pCi-d/L (9.59E7 transitions/m3)

## Committed Dose Equivalent to Lung and Intakes

- From CEDE to CDE: backwards!
- Intake in joules (J); exposure in WLM
- What nuclides were taken in?

## Rounding

- Rounding is biasing
- Lack of knowledge never justifies biasing what you do know
- Standards are *exact* numbers
- 1/3 WL and 3E-8 Ci/cm3 EEC differ by 11.1%
- You’re smart enough to know when to round

## Conversion Factors, slide 1

## Conversion Factors, slide 2

## Conversion Factors, slide 3

## DL and MDA

*DL* and *MDA*

- < *DL*

- < *MDA*

- Never compare data with minimum detectable amount (*MDA* = *L**D*)
- Compare data with decision level (*DL* = *L**C*)

## Current Status in the DOE

- Personnel monitoring for radon/radon progeny not done at any DOE site
- Exemptions from 10 CFR 835 at 9 sites
- Active pump samplers with crude or refined alpha spectroscopy preferred to track etch
- Active samplers are expensive, not made in USA
- Will be needed at Fernald for some operations
- By current standards, likely were needed in past

## Future Directions

- DOE may adopt ICRP/IAEA standard
- Progeny aerosol inside respirator
- poor understanding
- unattached fraction very high
- equilibrium factor very low
- Mining and milling not in DOE mission

## Conclusions

- Radon, thoron, and progeny are unique
- known human carcinogen (radon progeny)
- complex measurements
- complex dosimetry
- no *practical* bioassay
- ownership question: Nature or DOE
- Changing mission and exemptions have taken care of problem