Date post: | 03-Apr-2018 |
Category: |
Documents |
Upload: | john-w-holland |
View: | 217 times |
Download: | 0 times |
of 16
7/28/2019 PDF 4.4 External Radiation Standards
1/16
A Look at NuclearScience and Technology
Larry Foulke
Radiation and Realism
4.4 External Radiation Standards
Hormesis
7/28/2019 PDF 4.4 External Radiation Standards
2/16
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.
7/28/2019 PDF 4.4 External Radiation Standards
3/16
Nuclear Engineering Program
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
7/28/2019 PDF 4.4 External Radiation Standards
4/16
Nuclear Engineering Program
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
7/28/2019 PDF 4.4 External Radiation Standards
5/16
Nuclear Engineering Program
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?
7/28/2019 PDF 4.4 External Radiation Standards
6/16
Nuclear Engineering Program
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
7/28/2019 PDF 4.4 External Radiation Standards
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
7/28/2019 PDF 4.4 External Radiation Standards
8/16
7/28/2019 PDF 4.4 External Radiation Standards
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?
7/28/2019 PDF 4.4 External Radiation Standards
10/16
Nuclear Engineering Program
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?
7/28/2019 PDF 4.4 External Radiation Standards
11/16
Dose (Sv)
Relative
riskofcancer
0.1
Dose Response Curve
Linea
rHigh Dose Range: Linear
Low Dose Range: any curve allowed
Hiroshima /
Nagasakidata
7/28/2019 PDF 4.4 External Radiation Standards
12/16
Nuclear Engineering Program
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
7/28/2019 PDF 4.4 External Radiation Standards
13/16
Human Health Effects of Radiation Dose
3.7 mSv Above 1 Sv
Image Source: See Note 2
100
mSv
7/28/2019 PDF 4.4 External Radiation Standards
14/16
Nuclear Engineering Program
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
7/28/2019 PDF 4.4 External Radiation Standards
15/16
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
7/28/2019 PDF 4.4 External Radiation Standards
16/16
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