Download Absorption and Biological Effects of Ionising Radiation

Absorption and Biological Effects of Ionising
Radiation
November 2001
By Professor Alek Samarin FTSE
"Between the idea and the reality
Between the motion and the act
Falls the shadow."
Thomas Stearns Eliot (1888 - 1965)
Nuclear Energy - the Source of all Life
Life on Earth can be defined in theological, metaphysical, physiological, metabolic, biochemical,
genetic, and thermodynamic terms. Of these, the thermodynamics seems to be less complicated than
the rest, at least from the scientific point of view.
The second law of thermodynamics states, that in a closed system, no process can occur, which will
result in increase of the net order (that is in decrease of the net entropy) of that system. Thus the
Universe, taken as a whole, is steadily moving towards a state of complete randomness and disorder,
as its entropy increases. This phenomenon is known as the heat death of the Universe.
Yet, living organisms are manifestly ordered and, as they develop to the higher states of complexity,
there seem to be a contravention of the second law of thermodynamics. This seeming contradiction
however is specious only at the first sight. Living systems are not closed, but rather open. Most of life
on Earth is dependant in the flow of energy from the Sun, which is utilised by plants to construct
complex molecules from simpler ones. However, the increase in order that results on Earth is more
than compensated by the decrease in order on the Sun through the thermonuclear process
responsible for the Sun's radiation. Death, which brings an ultimate extinction of all life, emanates a
final and rapid increase of entropy of each living system as the matter decomposes, and, in case of
higher living forms, as the mind ceases to exist.
If we accept the hypothesis that the Earth interior upon its formation was cool, then the subsequent
considerable increase in temperature must have been caused by disintegration of radioactive
elements in its core. Apart from this nuclear source of energy from the Earth's interior, the main flow
of energy, which sustains all life on Earth, is the radiation from the nuclear fusion process in the Sun.
At the core of the Sun lies a giant nuclear furnace, converting hydrogen to helium at the temperature
0
of approximately 15,000,000 K. Owing to this nuclear reaction, during which mass is converted to
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energy, some 3.86x10 ergs of energy is generated. This corresponds to a mass loss of about
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4,700,000 tonnes per second, or a dissipation of only about 10 of the total solar mass per year. The
energy released by this nuclear reaction is carried off from the core by gamma-ray photons and
neutrinos. This process of energy release is extremely slow. Light currently reaching the Earth from
the Sun, was generated in its core nearly 30 million years ago.
It is estimated, that there is enough fuel for this fusion reaction to continue in its present mode for at
least 7 billion years. The future evolution of the Sun is expected to be similar to that of other
comparable stars. Eventually all hydrogen will be burned up and nuclear reactions involving helium
and heavier atoms will take over. This will change the chemical composition of the Sun. It will then
increase in size and luminosity and turn into a red giant star. When the Sun will reach the peak of its
expansion as a red giant, it will extend more than 100 times its present diameter, so that both Mercury
and Venus will be engulfed within its body. The Earth may remain outside the swollen bulk of the Sun,
but the enormous heat radiating from the giant Sun will most likely vaporise it. All life forms will
certainly be annihilated and the remarkable creations of human genius, the sciences, the arts, the
marvels of engineering, and the philosophies will be no more. The entropy increase will reach its
pinnacle!
The Sun's surface viewed from the Earth is called the photosphere, where the temperature is 5,800
0
K. Most of the Sun's radiation reaching the Earth is generated at the photosphere, the radiation
below is absorbed and re-radiated, and the emission from overlaying chromosphere drops sharply, by
about factor of six every 200 kilometres. Above the chromosphere is a dim, extended halo called the
0
corona, which has a temperature of 1,000,000 K.
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Beyond the distance of some 3.5x 10 kilometres from the Sun, the corona flows outward at a speed
near the Earth of about 400 kilometres per second. This flow of charged particles is called the solar
wind. Radiation given off by the Sun represents the whole spectrum of electromagnetic waves, from
radio to X-rays. High-energy particles, such as electrons are also emitted, especially from the solar
flares. However, the main components of solar emission are visible light, ultraviolet and infrared
radiation. Solar constant - the total electromagnetic energy radiated by the Sun at all wavelengths per
2
unit time through a given area at the mean distance from the Earth is 1.37 kW per m . It is not, in fact,
truly constant, and variations of the order of 0.1% are detectable.
Radioactivity and Ionising Radiation
Radioactivity is a spontaneous alteration of the nuclei of radioactive atoms, accompanied by the
emission of radiation - a radiant energy in the form of particles or waves. It is the property exhibited by
the radioactive isotopes of stable elements and all isotopes of radioactive elements, and can be
natural or induced. Radioactivity establishes equilibrium in parts of the nuclei of unstable radioactive
substances, which ultimately leads to the formation of stable arrangements of nucleons (protons and
neutrons) - that is to a stable, non-radioactive element. This process is most frequently accomplished
by the emission of alpha particles (helium nuclei), beta particles (electrons and positrons), or gamma
radiation (electromagnetic waves of very high frequency). The instability of the particle arrangements
in the nucleus of a radioactive atom, expressed as the ratio of neutrons to protons or the total number
of both, determines the length of the half-lives of the isotopes in that atom, which can range from
fraction of a second to billions of years. All isotopes of relative atomic mass 210 and greater are
radioactive.
Ionising radiation knocks electrons from atoms during its passage, thereby changing their physical
state and causing the atoms to become electrically charged, or ionised. The presence of such ions in
living tissues has the potential to disrupt normal biological processes. Therefore one objective in
measuring ionising radiation is to determine what the ionisation is doing in human cells, yet another
unit is needed to measure how much energy has been deposited in a tissue (the amount of ionisation
depends on the amount of energy stored). Thus, it is measured in various units. The oldest unit, the
roentgen (R), represents the amount of radiation which is required to produce 1 electrostatic unit of
charge in 1 cubic centimetre of air under standard conditions of pressure temperature and humidity.
The principal units for expressing the dose of radiation absorbed in a living tissue are the gray (Gy; 1
Gy = 1 joule of radiation energy absorbed per kilogram of tissue), and rad (1 rad = 100 ergs per gram
of tissue, or 0.01 Gy).
In order to normalise doses of different types of radiation in terms of relative biological effectiveness
(RBE) the sievert (Sv) and the rem (1 Sv = 100 rem) are used.
Since particulate radiations tend to cause greater injury for a given dose than do the gamma rays, the
dose equivalent of a given type of radiation expressed as sievert, is the dose of the radiation
expressed in gray multiplied by a quality factor that is based on the RBE of the radiation. Hence, with
some degree of approximation, it can be stated that one sievert is that amount of radiation, which is
-1
roughly equivalent in biological effectiveness to one gray of gamma rays (i.e. 1 Sv = 1 J kg ). In
practice, the milligray (mGy; 1 MGy = 1/1000 Gy) and millisievert (mSv; 1 mSv = 1/1000 Sv) are
generally used for measurement of the most common intensities of radiation.
To measure radioactivity, that is the number of atoms undergoing radioactive decay, we must
determine how many atoms decay per unit time. It was found that in one gram of radium some
37,000,000,000 atoms undergo radioactive decay every second. This quantity, appropriately enough,
was called one curie (Ci). Again, in practice the millicurie, (mCi; 1 mCi - 1/1000 Ci) or even smaller
unites, i.e. microcurie (mCi, or one millionth of curie) are commonly used. Another unit for measuring
radioactivity is becquerel (Bq). One becquerel is that quantity of a radioactive element in which there
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is one atomic disintegration per second. Thus, 1 Bq = 2.7 x 10 Ci.
In summary:
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•
•
•
•
The measure of ionisation in air or the unit of exposure is one roentgen, replaced in the
International System of Units (IS) by the coulomb/kilogram.
The measure of energy deposition in tissue, or the unit of absorption dose is rad. The rad can
apply to all types of tissue. It was chosen because in most cases one roentgen in air is just
about equal to one rad in tissue. In SI units rad is replaced by gray (Gy).
The dose equivalent is measured in rems. The rem is equal to the number of rads multiplied
by the appropriate modifying factor. In radiation protection profession, it is called the quality
factor (QF) and it ranges from 1 (for X-rays and gamma radiation) up to 20 (for some high
energy particles). Thus rem = rad x QF. In SI units rem is replaced by sievert (Sv). One Joule
of beta or gamma radiation absorbed per kilogram of tissue has 1 Sv of biological effect; 1
J/kg of alpha radiation has 20 Sv effect, and 1 J/kg of neutrons has 10 Sv effect.
The measure of radioactivity: - curie (Ci) was replaced in SI units by becquerel (Bq).
The dose that will accumulate over a given period (say, 50 years) from exposure to a given
source of radiation is called the committed dose, or commitment.
Natural or Background Radiation
All inanimate entities and living beings on Earth are completely and incessantly submerged in a sea
or radiation, some of which is ionising, and some is not. Apart from radiation from the Sun, there are
cosmic rays, which are streams of positively charged nuclei (protons), mainly of hydrogen. Cosmic
rays may also consist of electrons, gamma rays, pions and muons. Naturally occurring radioactive
materials are present in the Earth's crust and in the interior. There are radioactive gases in the air,
which we breathe. All the items in our household, all buildings and structures around us, sand
beaches and grass on which we walk and rest, and even the food and drink, which we consume, are
radioactive to a certain degree. Our bodies are no exception, and do contain tiny amounts of
radioactive isotopes of potassium-40, and carbon-14. Around 38,000 atoms of potassium-40 and 1,
200 of carbon-14 explode in human body each second. It is estimated that the total number of
radioactive explosions in a human body from all of the above sources is of the order of 60,000 per
second. However, whatever damage is inflicted on human cells by these radioactive isotopes, it must
be considered as part of the natural aging process in humans.
The typical annual exposures to natural or to the background radiation, originating from various
sources are:
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•
Cosmic rays at sea level: - 0.20 to 0.40 mSv; at 3,000 metres above sea level: - 0.80 to 1.20
mSv; at 12,000 metres: - 28 mSv (an altitude of a commercial jet aircraft).
Food and drink: - approximately 0.35 mSv, mostly from naturally occurring radioactive
potassium-40 and polonium-210. Some foods are more radioactive than others.
Terrestrial radiation: - an average of 1.35 mSv can be taken as a guide, but it can vary with
the geographic locations, due to the differences in the content of potassium-40, radium,
thorium and uranium in the Earth's crust. This average can be reduced by 20% for those who
live in a tent, increased by 10% if one sunbakes on the radioactive beach sands, and
increased by 100% if all the doors and windows in a house are always shut.
"Man-made" radiation, viz: - technologically generated (e.g. burning of fossil fuels) results in
0.04 mSv, nuclear power stations contribute some 0.002 mSv, and another 0.04 mSv is a
result of nuclear explosions and global fallout; seemingly innocent activity of wearing radioluminous watches daily adds another 0.01 mSv .
•
Medical exposures can vary considerably. Radiopharmaceuticals contribute some 0.14 mSv,
diagnostics 0.78 mSv; approximately 0.25 mSv can be taken as a typical average dose, but
some radiation exposures (such as cobalt-60 treatment for cancer) can increase this dose up
to as much as 125 mSv in some extreme cases.
For occupational exposures, the recommended annual limit (sum of external and internal exposures,
but excluding medical exposures) is 50 mSv. Recommended limit for a maximum cumulative
exposure (committed dose) is 10 mSv times age.
Industrial Sources of Ionising Radiation
For the majority of people who are not directly involved with nuclear technology or nuclear weaponry,
the exposure to the "man-made" (including medical) radiation is limited to the levels from the
background sources, listed above. However, for the minority of population working in industries
directly or indirectly associated with uranium mining, nuclear fuel processing, fission reactors, particle
accelerators (van de Graaff, linear accelerators, cyclotrons, betatrons, synchrocyclotrons and
synchrotrons), and with nuclear medicine, etc., the levels of exposure can be dangerously high.
Special protection measures, including radiation shielding, are introduced if the emission levels are
considered a serious health hazard. The risks, of course, are even greater in instances of nuclear
warfare, as the detailed study of the Japanese atomic-bomb survivors from Hiroshima and Nagasaki
has shown.
The main types of "man-made" ionising radiation, from which special protection measures may be
required, are: •
Alpha radiation consists of positively charged particles (helium nuclei, with 2 protons and 2
neutrons), emitted by the atoms of radioactive elements, such as radium, plutonium and
uranium. The process of alpha decay transforms one element into another, decreasing the
atomic mass (or nuclear number) by four. Because of their large mass alpha particles have
short range of only a few centimetres in air. Alpha radiations may only penetrate as deep as
the surface of the skin. However, if alpha-emitting substances are taken into the body along
with food or drink, or by inhalation, they can expose the internal tissues directly to alpha
radiation, which has strong ionising effect, and is capable of damaging living cells, thus
representing a considerable health hazard.
•
Beta radiation consists of electrons and electron-antineutrino particles, also emitted from an
atom in the process of radioactive decay. During beta decay a proton in the nucleus changes
into a neutron, thereby increasing the atomic number by one, while the mass number stays
the same. The mass lost in the change is converted into kinetic energy of the beta particle.
Beta particles do not exist in the nucleus. They are created during the process of beta decay
disintegration, when a neutron converts to a proton to emit an electron. They are more
penetrating than alpha particles, and can travel several metres in air. Beta particles are less
ionising than alpha particles, but due to their greater penetrating ability, they can damage
some external tissues directly.
•
Gamma rays are a form of high-energy electromagnetic radiation, similar to X-rays, but of
shorter wavelength, emitted by the nuclei of radioactive substances during decay or by
interactions of high-energy electrons with matter. Gamma rays are stopped only by direct
collision with an atom and therefore are very penetrating. They can pass right through a
human body, and affect tissues, such as bone marrow. However, their ionising effect (dose
equivalent) is less than that for alpha radiation by a factor of 20. Gamma radiation is used to
kill bacteria and other microorganisms, to sterilize medical instruments and to change
molecular structure of plastics to modify their properties (for example, to improve their
resistance to heat and abrasion).
•
X-rays are a form of electromagnetic radiation, commonly used in medical or dental
examinations, usually with a lesser penetrating power than gamma rays. They are emitted by
bombardment of a tungsten target with high-energy electrons. Television sets, especially
colour, emit soft X-rays and therefore are shielded with a special glass to greatly reduce the
risk of radiation exposure.
•
Neutrons are uncharged subatomic particles with the mass approximately equal to that of
proton. They are contained in the nucleus of every atom, except for hydrogen. Although
stable in nuclei, isolated neutrons decay by b-emission into protons, with a half-life of 11.6
minutes. They induce ionisation only indirectly in atoms, which they strike, but in this way can
inflict some damage in the body tissues. Solitary mobile neutrons travelling at various speeds
originate from fission reactions, such as take place in the nuclear power plants, and can be
very penetrating. An efficient shielding against neutrons can be provided by water or by
materials in which water is chemically bound, or physically adsorbed.
In the aftermath of the Chernobyl nuclear power plant explosion on April 26, 1986, some 50 million
curies of the more volatile radioactive substances escaped. Although this represents only a few per
cent of the total inventory of the nuclear reactor core, it is estimated that up to 20% of the radioiodine
and about 12% of the radio-caesium, originally contained in the core, were emitted into the
atmosphere. The authorities used a relatively large radiation dose of 75 millisieverts as a criterion for
evacuation of more than 135,000 people beyond the original 30-kilometre zone around the damaged
reactor. The dose was later reduced to 50 millisieverts, which is ten times the limit set in most parts of
the world on the basis of recommendations of the International Commission on Radiological
Protection.
As a result of radioactive fallout in Western Europe, up to 200,000 becquerels of caesium per square
kilometre of soil were recorded near Stockholm. The radioactivity level in reindeer, in the northern
parts of Norway, Sweden and Finland, had risen from an average of about 6,600 becquerels per
kilogramme of meat to more than 42,000 Bq/kg. However, the official views in many European
countries of what were acceptable levels of radiation have changed considerably after Chernobyl. The
UK set an upper limit for the sale and consumption of food of 1,000 Bq/kg. Norway, as a concession
to deer herders, set a limit of 6,000 Bq/kg.
In the USA, the personal radiation limit remained unchanged at 0.25 mSv, and in the USSR, a new
limit of 50 mSv was approved by the Government.
Biological Effects of Ionising Radiation
The basis of all biological material is the cell. There are 50 trillion of these in a human body. A cell
consists of a wall, cytoplasm and nucleus. Food and oxygen are taken in from the blood through the
cell wall and are chemically processed in the cytoplasm to serve various metabolic functions. The
information needed to control the activities of the cell and the process of mitosis (or cell division), is
contained in the DNA molecules of the gens composing the chromosomes.
Now let us consider the effect of radiation on the cell. Of all the ionising radiation types, gamma rays
and neutrons are especially penetrating. The ionising radiation passing through the cell can inflict the
following damage:
1. It can cause the death of a cell due to either loss of respiratory ability or due to severe
2.
mutilation of the chromosomes. Apart from the loss of chromosomes per se, this damage can
lead to an alteration of the genetic blueprint, so that incorrect information is passed on to the
future generation of cells.
It can delay the process of mitosis, so that the normal replacement of cells in the living
organism is affected.
In the adult human, the most radiosensitive tissues are the blood-forming organs (red bone marrow),
the gonads (sex organs) and the lymphatic glands.
The biological effects on humans can be somatic, which are those that appear in the persons
irradiated, or genetic, which affect their offspring. The somatic effects may include leukaemia and
various forms of cancer. The genetic may not be evident for several generations after the irradiation
have taken place.
The acute effects of radiation occur after a singe dose received in a relatively short period of time, and
can range from nausea to death. The chronic effects of irradiation are due to relatively small
incremental doses received over a long period of time.
The biological effects of radiation also depend on a number of factors including:
1. Size of the dose received (Large doses, in excess of 6 Sv can be fatal),
2. Extend of the body irradiated (In radiotherapy only a fraction of the body tissue is irradiated.
3.
4.
The most common method is to slowly rotate the radiation source about the malignant
tumour. The beam of gamma rays, such as 60Co or 137Cs, is concentrated on the cancerous
tumour, and the irradiation of the healthy tissues is minimised, as the radiation path constantly
changes during rotation. Fortunately, some forms of damage done to the healthy cells by
radiation are reparable. For example, a single dose of 10 Sv to a mouse is fatal in all cases,
but if doses of 2 Sv are administered once per week for five consecutive weeks to give a total
of 10 Sv there are almost no ill effects),
Part of the body irradiated (Even a large dose of 2 Sv may be relatively harmless, if given to a
portion of a limb),
Type of radiation (For example, fast neutrons are about thirty times more damaging than Xrays or gamma rays to the eye, by causing cataracts).
Thus, the consequences of ionising radiation energy transfer to the surrounding material are: (i) the
material may be physically, chemically and (in case of the living tissue) biologically changed, (ii) heat
is generated, (iii) the radiation loses its energy and is finally stopped.
Radiation Shielding
It is impossible to escape the natural or background radiation. However, some common sense
measures, such as regular ventilation of buildings to reduce the concentration of radioactive gases
(radon, actinon, and thoron), which account for approximately 35% of all the natural radiation, can be
taken.
Of the "man-made" or "artificial" radiation, intensive sources do present an additional and sometimes
considerable risk to the researchers and workers, exposed to these environments. Radiation shielding
is particularly effective as a protection measure from the most penetrating forms of ionising radiation,
viz: - neutrons, gamma rays and X-rays.
The reduction in flux density (neutron flux is the number of neutrons passing through unit area per unit
time) or of power per unit area due to absorption and/or scattering is called attenuation. In nuclear
physics absorption is the capture by elements (such as present in the reactor control rods, usually
made of boron) of neutrons and c-rays produced by the fission in a reactor.
When electromagnetic radiation enters a body of matter, part of it is subjected to scattering, when it is
reflected in all directions, while another part is absorbed, as it is converted into other forms of energy.
The scattered radiation may still be effective in the same way as the original, but the absorbed portion
ceases to exist as radiation, or it is re-emitted as the secondary radiation.
The linear absorption coefficient is the natural logarithm of the ratio of incident and emerging energy
for a beam of radiation passing through the unit thickness of a medium (such as lead of concrete).
The mass absorption coefficient is defined in the same way, but for the thickness of the medium,
corresponding to unit of mass per unit area. True absorption coefficients exclude scattering losses,
while total absorption coefficients include them.
The following relationship demonstrates the exponential nature of the attenuation of radiation, such as
beta and gamma: -lqt
I = I0xbe , where I = radiation intensity through absorbing material, I0 = initial radiation intensity, b =
build-up factor dependant on the energy and collimation of the source, and on q and t.
b accounts for radiation, which has been scattered or changed in direction by interactions that do not
stop the radiation.
l = absorption coefficient, dependant on the composition of absorbing material, on the energy of
radiation and on the source detector geometry,
q = specific gravity of absorbing material, and
t = thickness of absorbing material.
The distances that gamma rays, neutrons and beta decay electrons can travel in different absorbing
material are usually given in half-lengths, i.e. the distance travelled before half are absorbed. In two
half-lengths all but one quarter are absorbed, end so on.
For gamma rays the half-length distances for different energies of radiation are: Gamma ray energy (MeV)
.05
.2
.5
1.0
2.0
Half length in bio-tissue (mm)
35
50
80
110
150
Half length in lead (mm)
.8
.6
4
8
13
Beta decay energy (MeV)
.5
1.0
3.0
Half length in bio-tissue (mm)
.2
1
4
For beta decay electrons: -
For neutrons:- energies above 0.1 MeV - half length of about 100 mm
For heavy charged particles like protons, alpha particles, and fission fragments, all particles go the
same distance - the range - before they are stopped.
Thus, for protons: - energies of 5 MeV - the range is about 340 mm in air and 0.2 mm in solids, and
for alpha particles - energies of 5 MeV - the range is about 34 mm in air and 0.02 mm in solids.
Average range of fission fragments is 30 mm in air and 0.2 mm in solids and liquids.
Concrete is particularly useful as a radiation shield for nuclear reactors. It must contain some heavy
aggregate (steel punchings and iron shot, or natural minerals, such as ilmenite or haematite), which
are capable to slow down gamma rays and fast neutrons, and sufficient quantity of hydrogen (as
chemically bound or adsorbed water) to absorb the slow neutrons.
Conclusions
Nuclear energy - fusion reaction in stars - including our Sun is the source of all life on Earth and also
the reason for its ultimate demise, when the Sun's fusion reactor runs out of nuclear fuel and stops.
Truly, it can be said of the nuclear fusion: "I am Alpha and Omega, the beginning and the ending"
(Revelation, 1.8.).
Ionising radiation from various radioactive sources is part of our daily existence. It can be used to
enhance human life or to destroy it. The choice is ours. If only the reason can triumph over the deeply
rooted instincts of hate and aggression in human species, which seem to flourish proportional to the
technological advances in the development of weapons of mass destruction.
The question however remains: "Is ionising radiation good, or is it bad?"
In answer, I shall quote Sir Richard Francis Burton (1821 - 1890): "There is no good, there is no bad, these be the whims of mortal will;
What works me well that call I good, what harms and hurts I hold as ill.
They change with space, they shift with race, and in the veriest space of time,
Each vice has worn a virtue's crown, all good been banned as sin or crime".
References
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Bakos, G. C., "Direct Energy generation and Energy Conservation in Radiation Shielding
Facilities", Annals of Nuclear Energy, No, 28, 2000, pp 513 -518.
Leung J. K., " Application of Shielding Factors for Protection against Gamma Radiation during
a Nuclear Accident", IEEE Transactions in Nuclear Science, Vol.39, No.5, October 1992, pp
1512 - 1518.
Rockwell, T., "Our Radiation Protection Policy is a Hazard to Public Health", The Scientist,
Vol 11, No.5 March 3, 1997, p.9.
Ueki, K., and Ohashi, A., "Evaluation of Neutron Shielding Enhancement Effect due to
Structural Material", Radioact. Phys. Chem., Vol 51, Nos. 4 - 6, 1998, p.685.
General scientific and technical data in this article were verified by referring to the 5 volume
Encyclopaedia of Physics, Academy of Sciences USSR (in the Russian language), to the Van
Nostrand's Scientific Encyclopaedia, and to the Encyclopaedia Britannica Year Books of
Science and Future (1991 -2001).
For the additional information on the subject, please refer to the Uranium Information Centre
Website: http://www.uic.com.au, and to the ANSTO Website: http://www.ansto.gov.au
Professor Alek Samarin is a Private Consultant and Adviser in
Sustainable Development of Energy in Building and Construction
Industries, as well as a Professorial Fellow, Faculty of Engineering,
University of Wollongong and an Adjunct Professor, Faculty of
Science, University of Technology, Sydney.
He served (among many other committees) on the Chemical
Engineering Foundation and Warren Centre for Advanced
Engineering Committees at the University of Sydney, on the Advisory
Committee to the Division of Nuclear Physics at ANSTO, and to the
Department of Applied Physics, University of Technology, Sydney.
In the early 1970-s he worked in collaboration with (as it was then
known) Australian Atomic Energy Commission at Lucas Heights on
the R&D of polymerisation of monomer impregnated building
products, using 60Co c - radiation. In the late 1980-s his work with ANSTO included the R&D
into nuclear moisture meters. He is currently acting as an Adviser to ANSTO on the design and
construction of the radioactive shielding for the Replacement Research Reactor.
Occasional Papers are non-refereed publications prepared by Academy Fellows for
publication on the Academy web site. The views expressed in the above article are
those of the author(s) and do not necessarily represent the views of the Academy.