If one observes the DC current output of an ion chamber, or photo-multiplier
tube, one will notice that the current output follows square root relationship
to the input radiation.
Part 1: Interpolating the Curves
In studying health, we frequently test using very high doses then
interpolate linearly to make assumptions about lower exposures.
There is no easy and ethical means of measuring all exposure levels.
So we interpolate from available data.
But the real effect might not follow the cause linearly. This will
lead to very poor estimates.
With radiation, some things are considered logarithmic rather than
linear. Both the linear model and the logarithmic model may be inaccurate
for predicting the effects of low exposures to radiation.
Over a range of about a decade and a half the square root curve
follows closely to the log curve which is normally used to plot
Might this imply that the square root curve would be a better choice
for plotting radiation, or even a better model for understanding
the effects of radiation?
Related pages at this site
||So why does current have a square root relation
to radiation? The answer shows up in communication theory and simple circuit
theory. Radiation produces a random series of ionizations that a detector
reads as electrical pulses. A communication theory text will show that random
impulse noise has a power spectrum that contains a DC part. From circuit
theory, power has a known relationship to current:
P= I2R or I = sqrt(P/R).
Current from the detector acts as the square root of the incoming power
or radiation intensity.
This all seems to raise a few questions:
- Since power has a square relationship to both the ionization pulses
in and the current out, would using square root curves be a more natural
model for radiation metering?
- Which is the best model for the impact of radiation for any given
material such as living tissues: number of ionizations, power absorbed,
current generated, power within a certain spectrum range or, other?
Without knowing the answer to the second question, valid interpolations
from large doses to small doses of radiation can not be made. Our models
for the health impacts of low level radiation may be contain significant
errors. Which model is best for interpolations? For circuits, the square
root model is the best. But what model is best for living flesh? To answer
that we must determine how the energy is absorbed by the flesh.
The discussion above only considers possible nonlinear effects of the
radiation. No consideration is given to the probable nonlinear characteristics
of human flesh and other absorbing materials.
Since I first made the observation that radiation has nonlinear characteristics
I have read two sets of articles regarding the health effects of radiation.
- Research done on cells in laboratory environments show greater damage
resulting from low level radiation than the "linear no threshold
model" would imply.
- Research done on living organisms, including human epidemiological
studies, that show that low level radiation may be non-harmful, and
|This page was motivated when I observed that the
current from a radiation detector followed a square root curve. Traditional
meters use logarithmic scales. I wondered why the standard had not
been made square root the natural output of the detector. I also wondered
whether the effects of radiation also followed the square root curve.
See more considerations below in Part 2.
Part 2: What are the Sources of the Non-linearities
In many branches of science we reduce complex multidimensional concepts
to simple linear measurements. This makes measurement and communication
easier, but removes critical information. Unfortunately, this reduction
may remove the very information that we actually want to know. Radiation
is composed of many dimensions. Each of these dimensions may have nonlinear
aspects. We will briefly review these major dimensions.
Many Types of Radiation
We use the words radiation and radioactivity to cover a broad range
of emissions. Usually, we use the term radiation to mean ionizing
radiation, but sometimes we use the term to refer to electromagnetic
radiation. Each type of radiation has its own distinct energy and
way of interacting. We frequently use the same sensors to detect
the presence of many of them. But, each can have a different impact
on living tissue.
||ionized helium nucleus
||Will not penetrate skin, but will ionize the first
molecule it encounters.
||fast moving electrons
||Can penetrate a little and ionize molecules they
|| high energy electromagnetic radiation
||Highly penetrating, may ionize or pass right through
with minimal effect
||Can enter and alter atomic nuclei
||Very reactive. Will alter, transmute first matter
||radioactive elements - atoms that emit alpha,
beta, or gamma rays
||Have both chemical and radiation effects.
||Includes microwaves, radiowaves, and light
Many Dimensions of Effects
Just as there a many types of radiation, radiation can have many
different effects on materials such as living tissues. Each of these
effects will have different health impacts with quite different
- Heating: Radiation will heat the tissues that absorb
it. A large dose will cause burning. A mild dose some heating.
A background dose will cause no observable variations from normal
temperatures. For example, turning on the lights in a room cause
no observable temperature change for your body. Standing in the
bright sun will make you sweat and tan. Staying in tropical sun
can cause serious burning even with relatively short exposures.
From this example, we recognize that the health impact depends
on time. The same dose that is harmful over a short time may actually
be good for you over a longer time.
- Current generation: Radiation can create electrical currents
in the materials it hits. This is how solar cells work. It is
the basis of the discussion in part one. As shown, the effect
is known to be nonlinear. How such currents might affect living
tissues is not well studied.
- Ionization: Nuclear radiation is also called ionizing
radiation. It can ionize, break apart, molecules that it hits.
Those molecules become altered. Altered molecules in living tissues
will no longer function in the cells as they should. Each cell
contains billions of molecules. Ionizing certain molecules will
just interfere with the cell temporarily, altering others may
cause cell death, and altering DNA may cause mutations that reproduce
and spread in future cells. Some of these changes may lead to
cancer or birth defects.
- Chemical bonding: Radionuclides are chemical elements
so they can deposit in the body the same as any other chemical
or poison. This depositing can have unusual delayed effects. For
example, the thyroid absorbs iodine. When the iodine decays it
emits beta and gamma radiation. The radiation will ionize surrounding
molecules. After the decay the thyroid no longer has iodine where
it needs iodine, it now has xenon which it doesn't need. The transmutation
iodine to xenon will alter the molecules in which it was bonded.
Thus, radionuclides have both radiation and chemical impacts on
- Resonance: Tissues may absorb non-ionizing radiation
through resonance. The best known example is the microwave which
heats by vibrating molecules of water and some organic molecules.
Although resonance effects have not been highly studied there
is evidence that some electromagnetic frequencies change the speeds
at which specific biological reactions occur and may alter brain
Each of these effects is most likely nonlinear For heating a specific
dose spread out over a long time has much less impact
than the same dose over a short time. Doses do not add up. For some
of the other effects a specific dose over a long might have a greater
effect than the same dose over a short time. There is no easy means
to determine the impact of long term exposures.
Many Dimensions of Absorption
Ionizing radiation, neutrons, and radioactive elements are each
absorbed differently by different materials. Thus, the definition
of a radioactive field is not constant or easy to define. The measure
of the radioactive field is totally dependent on which material
it is passing through and what type of radiation it is. Thus, the
same radiation passing through the air in the room will be different
passing through your body (possibly higher, possibly lower), and
different as it passes through the walls, and different as it passes
Many Sources of Radiation
Radiation has many natural sources - some natural, some anthropogenic.
There is a common misconception that humans create radiation and
without humans there would be no radiation. This is not true. All
living things spend their entire lives bathed in radiation, and
always have. It is good to consider where our exposures to radiation
- Mineral deposits
- Cosmic rays
- The sun
- Wells: water wells bring various buried minerals to the surface
including radioactives such as radon.
- Coal burning power plants: coal contains uranium, thorium and
other radioactives. When coal is burned the radioactive particles
go up the chimney with the ash.
- X-rays& medical isotopes
- Nuclear weapons testing
- Nuclear power accidents (Chernobyl, Three Mile Island, Fukushima)
- Non-ionizing sources: transformers, electronic equipment, cell
phones, radio towers
From these lists we can see that much of our exposure to radiation
comes from hidden non-nuclear sources. A person living down wind
of a coal burning power plant, drinking well water, may be absorbing
more radiation than a person living near a nuclear plant. However,
the types of radiation he absorbs will be different. Thus, its not
always clear where to do epidemiological studies on radiation exposure.
Added August 2011
|Part 2 was added after I was asked
to add more depth to the discussion by people concerned about the
radiation leaks at Fukushima.