PDF 4.4 External Radiation Standards

7/28/2019 PDF 4.4 External Radiation Standards

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A Look at NuclearScience and Technology

Larry Foulke

Radiation and Realism

4.4 External Radiation Standards

Hormesis


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Nuclear Engineering Program

Radiation Protection Clearly massive amounts of ionizing radiation

can cause biological damage.

However, cells have advanced repair

mechanisms for this damage and can easilycope with mild to moderate exposure.

How much is too much radiation?

Government sets radiation standards that providedose limits to prevent people from receiving harmfulradiation exposure.


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Obviously, we cant set exposure limitslower than background radiation.

What is the right limit?

Use empirical data from large-dose humanexposures to quantify radiation effects

Nuclear-Weapon Effects

Accidents

Other Inadvertent Exposures High dose medical treatments

Use additional data from animal experiments

External Radiation Standards


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The 1 mSv per yr (100 mrem/yr) public dose limit is

Down in the noise

3.54.0 mSv

Avg

Avg +1 mS

2.0 mSv

1.0 mSv


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Au contraire they picked 1 mSv per year

They evidently dont believe its safe

to live in Denver, CO

Despite theVariationinNatural Background, Most

Locales in the US Are Below 6 mSv Per Year.

So where would logic dictate settingthe public dose limit? Perhaps 5 mSv?


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Universal radiation dose limits (annual)*

Occupational Public

Whole body 5 rem 0.1 rem (1 mSv)

Lens of the eye 15 rem 5 rem (50 mSv)

Other tissues 50 rem 5 rem

External Radiation Standards

*10CFR20

Special situations

25 rem Lifesaving (http://hps.org/publicinformation/ate/q3092.html)10 rem Equipment savingRemember: no observable effects below 25 rem


7/16Nuclear Engineering Program

A Range of Views Very few gene mutations lead to cancer. Most simply

leave the cell functional but unable to reproduce; in thiscase, cells die.

We encounter a range of slants on the part of authorsranging from any amount of radiation puts you at riskto the other end of the spectrum where numerousexperiments indicate stimulation of and benefit to

biological systems at low levels of ionizing radiation


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9/16Nuclear Engineering Program

Low Dose Effects

Anything below 0.25 Sv (25 rem=25,000 mrem) has noobservable effects, but what about long-term effects(cancer, genetic damage)

Hiroshima/Nagasaki data reveals a strong correlationbetween radiation dose and incidence of cancer.

There is no controversy that high radiation dose cancause cancer.

But can this correlation be extrapolated to very lowdoses of radiation?


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Low Dose Effects

Linear extrapolation of the Hiroshima/Nagasaki data tolow doses concludes there will be excess fatal cancers.

But there are NO valid studies that verify this.

Position statement #10 by Health Physics Society . . .for doses below 100 mSv (10,000 mrem) . . . risks ofhealth effects are either too small to be observed or arenon-existent

Nevertheless, theres nothing wrong with beingconservative. Right?


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Dose (Sv)

Relative

riskofcancer

0.1

Dose Response Curve

Linea

rHigh Dose Range: Linear

Low Dose Range: any curve allowed

Hiroshima /

Nagasakidata


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The BEIR-V linear no-threshold (LNT) extrapolation doesnot take credit for improved cell repair at low doses or thehormesis effect.

Hormesis is a biological process where cells react

differently to small doses of otherwise harmful toxins. The stress of low dose exposure causes cells to learn (or evolve)

to efficiently repair radiation damage.

Possible effects of hormesis for low dose radiation

Increased cell growth / fertility

Reduction in cancer incidence

Other effects, either toxic or beneficial.

Radiation standards do not take credit for hormesis.

Hormesis


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Human Health Effects of Radiation Dose

3.7 mSv Above 1 Sv

Image Source: See Note 2

100

mSv


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Are there hormetic effects?

YES: Mutation frequency decreased from Background

(When DNA repair capacities are active!)

0.05 Gy/min

MutationFreque

ncy(%)

Fruit fly; the same system to establish the linear concept in 1930s

Sham (background)

irrad

Image Source: See Note 3


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Deaths Due to Radiation ??*

CONSIDER Radioactive steel scavenged from nuclear reactor melted into rebar

Used for constructing approximately 1700 apartments units/shops inTaiwan

From 1982 to a 9-20 year period, ~ 10,000 people exposed to lowlevel radiation (average accumulated dose ~ 400 mSv)

Many still living in these apartments

CLAIM: Over 40 deaths due to cancer

BUTIn this population over this time, actual cancer deaths only 3%

of cancer deaths expected from natural causes. Hence, the argument is made that this low level radiation SAVED

many lives due to hormesis effect**

* Wikipedia, Civilian Radiation Accidents, 6-28-2009

** W.L. Chen, et. al, Effects of Cobalt-60 Exposure on Health of Taiwan Residents Suggest New Approach

Needed in Radiation Protection, Dose Response, 2007 5(1):63-75, PM C2477708


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1. Reprinted with permission from Dr. Robert L.Dixon, Wake Forest University School ofMedicine.

2. Reprinted with permission from WorldNuclear Association. Source: Presentation byAlan Waltar, World Nuclear University,

Oxford, UK, 7-11-12.

3. Reprinted with permission from Koana, et al.Radiat Res 167, 217-221 (2007).

Image Source Notes

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PDF 4.4 External Radiation Standards