MFCM094: Basic Concepts of Radiation Hazard.pdf

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extracted text: PAPER- I
BASIC CONCEPTS OF RADIATION HAZARD
The radiation you hear about and which can affect
your health, is more properly called IONISING RADIATION. This
radiation is made of particles, or rays, which have enough
energy to break up the chemicals they hit. They do this by
smashing the electrical ’’ hooks " which hold the chemical
together. 1he bits of the chemical with their electrical kyooks

dangling around are called IONS. This gives us the name ionising
Radiation.
" In order to understand nuclear technology and its
impact on human health, three atomic level events must be
understood : fissioning, activation and ionisation. Fissioning
i.e. the splitting of uranium or plutonium atom, is responsible
for producing radioactive fission fragments and activation
products. These in turn cause the ionisation of normal atoms 9
leading to a chain of microscopic events we may eventually
observe as a cancer d< ath orjdeformed child.

Fissioning :
Radioactive fission products are produced in nuclear
reactors. They are variant forms of the ordinary chemicals
which are the building blocks of all material and living things.
Prior to 1943, radioactive forms of these chemicals were present
in only trace quantities in South Africa, where it appears that
a small nuclear fission reaction occurred spontaneously hundreds
of thousands of years ago.
When a Uranium atom is split or fissioned, it does
not always split in the same, place. The two pieces called
fragments, are chemical of lower atomic weight than uranium.
Each fragment^ receives part of the nuclear and part of
electrons of the origional large uranium atom. More than
so different possible fission products are formed, each
having the chemical properties usually associated with theirstructure, but having the added capability of releasing
ionising radiation. X-Rays, alpha particles, beta particles,
gamma rays ( like X-Rays ) or neutrons can be released by
these created chemicals. All these can cause "ionisation "
i.e. knocking an electron out of its normal orbit around
the nucleus of an atom, they produce two 'ions ', the negativdy
charged electron and the rest of the atom which now has a
net positive electric charge.

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The Atomic structure of fission fragments is
unstable; for example , a nucleus may be proportionately
heavier than usual due to inclusion of extra neutron. The
atom will at sometime release the "extra " particle and return
to a natural, low energy, more stable form, Every such release
of energy is explosion on the microscopic level.
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The violence of the fissioning process is such that
it can also yield what are called as activation products i.e.
it can cause already existing chemicals in the air, water or
other nearby materials to absorb energy, change their structure
slightly and become radioactive.As these high energy forms of
natural material eventually return to their normal stable state,
they can also release ionising radiation. About 300 different
radioactive chemicals are created with each fissioning. It takes
hundreds of thousands of years for all the newly formed
radioactive chemicals to return to stable form.
In a nuclear power plant the fissioning takes, place
inside the zirconium or magnesium alloy cladding which encloses
the fuel rods. Most of the fission fragments are trapped
’ within the rods. However the activation products can be formed'
in the surrounding air, water,pipes and contaiment building.
The nuclear plant itself becomes ■'unusable with time and must
eventually be dismatled and isolated as radioactive waste.

After fissioning, the fuel rods are said to be
.” Spent ” . The‘y contain the greatest concentration of -.radio
activity of any material on -the planet earth, many thousand
times the concentration in granite or even in uranium waste.
The spent fuel rods contain gamma radiation emitters, similar
to X-Ray emitters so they must not only be isolated from the
biosphere, but they must also be shielded with water and
thick lead wall, Direct human exposure to spent fuel rods
means certain death.
In reprocessing, spent fuel rods are broken open
and the outer cladding is disolved in nitric acid, the plutonium
is-separated out for use in nuclear weapons or fuel in nuclear
• breeder or mixed oxide, nuclear reactor, ^he remaining^ highly
radioactive debsis is stored as liquid in large .carbon or
■ ' stinless steel drums, awaiting .solidification and burial in
permanent repository. Waste of lower radioactivity is buried
in dirt trenches or as in Windscale (Sella field) in Englandpiped out to-sea. The spent nuclear, fuel rods and liquid
reprocessing waste are called ’ high level radioactive
waste *. It has to be kept secure for thousands of yearsessentially forever. Lower level waste may be equally longlived,
but it is less concentrated.
In all nuclear reactions, some radioactive
mate'rial- namely the chemically inert or so called•1 noble*
gases, radioactive canbon, water, iodine and small particu
lates of plutonium an.1 other transuranics ( i.e. chemicals of
higher atomic number than uranium ) is immediately added to

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the air, water and land of the biosphere. In the long range,
all tie longlived radioactive material, even that now stored
and trapped, will mix with the biosphere unless each generation
repackages it. Ouib planet earth is designed to recycle every
thing*
The radioactive chemical which escapes to the
biosphere can combine with one another or with stable chemicals
to form molecules which may be soluble or insoluble in water:;
which may be solids, liquids or gases at ordinary temperature
and pressure, which may be able to enter into biochemical
reactions or be biologically inert. The radioactive materials
may be external to the body and still give off destructive
penetrating radiation. They may also be taken into the body
with air, food & water or through an open wound, becoming
even more, dangerous as they release their energy in close
proximity to living cells and delicate body organs. They may
remain near the place of entry into the body or travel in the
blood stream or lymph fluid. They can be incorporated into tiss
ue or bone. They may remairjin the body for minutes or hours
or a lifetime. In nuclear Jedicine for example, radioactive
tracer chemical are deliberately chosen among those quickly
excreted by the body* Most of the radioactive partic-.les
decay into other radioactive " daughter 11 products which may
have very different physical, chemical or radiological
properties from the parent radioactive chemical. The /average
number of such radioactive daughters of fission products
produced before a stable chemical form is reached) is four.
Besides their ability, to give off ionising
radiation, many, of the radioactive particles are bilogically
toxic for other reasons. Radioactive lead, a daughter product
of the radon gas Released by uranium mining is a cause of
lead poisoning and brain damage. Plutonium is biologically
and chemically attracted to bone as radioactive chemical
radium. Plutonium cUumps oh the surface of the bone, delivering
a concentrated dose of alpha radiation to surrounding cells,
whereas radium diffuses homogeniously in bone and thus has a
lesser, localised cell damage effect.-This makes plutonium
because of its concentration, much more biological toxic than
a comparable amount of radium.
The cellular damage caused by internally deposited
radioactive particles becomes manifest as a health effect
related to the particular organ damaged. The body of^en mistake/
these dangerous substances for ordinary substances that it
needs. These radioisotopes stay in the body and continue to
give off harmful radiation internally. For example radio
nuclides lodged in the bones can damage bonemarrow or cause

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bone cancers or leukaemia, while radionuclides lodged in
lungs can cause respiratory diseases. It has been found that
even very low level of radiation can cause a rise in death,
particularly in babies. Strangely the deaths are mainly from
common diseases like pneumonia and measels, not cancer. Could
it be that the fragile immune system of the body which fights
diseases, is being damaged. In this way, man made .radiation
mimics natural radiation and-causes the ageing or breakdown
process to be accelerated.

Radw^tAva_±artic_les jmdJAvwg^
X-Rays and gamma rays are photons i.e. high energy
light waves. When emitted by a source,for example, radium or
cobalt, located outside the body,they easily pass through
the body, hence they are usually called penetrating radiation.
Because X-rays are penetrating, they can be used in diagnostic
medicine to image human bones or human organs made opaque by
ail dye.

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. . . High energy gamma rays, which easily penetrate
bone, would be unsuitable for such medical usage because
film will be uniform?.y exposed. No radiation remains in the
body after an X-Ray picture is taken. It is like light passing
through a window. The damage it may.have caused on the way
through, however, remains.
Some radioactive substances give off beta particles,
or electrons, as they release energy and seek a stable atomic
stage. These are negatively charged particles, namely electrons,
which can penetrate skin but cannot penetrate through the whole
body as do X-rays and gamma rays.
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Microscopic nuclear explosions of some radio
active chemicals release high energy alpha particles. An
. alpha particle, the nucleus of a helium atom, is a positively
charged particles ( two uncharged neutrons and two charged
protons ). It is larger in size than beta particle, like a
cannon- ball relative to bullet, having correspondingly less
penetrating power but more impact. Alpha particles can be
stopped by human skin, but they may damage the skin in,.the
process. Both alpha and beta particles penetrate cell membranes
more easily than they penetrate skin. Hence ingesting, inhaling
or absorbing radioactive chemicals capable of emitting alpha
or beta particles and thereby placing them inside delicate
body parts such as the lungs, heart, brain or kidneys, always
posj.es serious threat to human health. Plutonium is an alpha
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emitter, and no quantity has been found to be too small
to induce lung cancer in animals. The skin of course can stop
alpha or beta radiation inside the body tissue from escaping
outwards and damaging . It is impossible to detect these
particles with most whole body ’’ counters " such as are
used in hospitals and nuclear installations. These counters
can only detect X-Rays and gamma rays emitted from within the
body.
Splitting a uranium aiem also releases neutrons,
which act like microscopically small bullets. Neutrons ar ■
about one fourth the size of alpha particl'es and have almost
2000 times the mass of an electron. If there are other
fissionable atoms nearby ( uranium 235 or plutonium 239, for
example ) these neutron projectiles may strike them, causing
them to split and to release- more neutrons. This process is
called a chain reaction. It takes place spontaneously when
fissionable material is sufficiently concentrated iee.. forms
a critical/.In a typical atom tbombjfissioning is very rapid..
In a nuclear reactor, water gas or the control rods function
to slow down or to absorb neutrons and control.the chain
reaction.

Neutrons escaping from the fission reaction
can penetrate the human body. They are among the most
biologically destructive of the fission products, ^hey
have-a short range, however, and in the■absence of fissionable
material they will quickly be absorbed by non radioactivematerials. Some of these latter become radioactive in the
process, as iyas noted earilier and are called activation
products.

Effect on Living,Cell ; The chaotic state induced within
a living cell when it is exposed to ionising radiation has
been graphically described by Dr. Karl Z. Morgan as a
"madman loose in library ", The effect of cell exposure to
these microscopic explosions with the resultant sudden
influx of random energy and ionisation may be either cell
death or cell alteration.lt can be temporary and permanent.
It can leave the cell unable to produce ( or replace ) itself.
Radiation damage can cause the cell to produce a slightly
different hormone or ^thzyme, still leaving it able to
reproduce other cells capable of generating this same
altered hormone or Enzyme*. In time there may be millions
of such altered cells. This mechanism called biological
magnification,can cause some of the chronic diseases and

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changes we usually associate with old age. One possible
to n
speciiic nu-t-rfrtion could be the destructions of the cell's
mechanism for resting which normally causes it to cease
reproductive activities after cell division. This causes
runaway proliferation of cells in one place, which, if not
destroyed will form tumour, either benign or malignant.
The abnormal proliferation of white blood cells is oharacteristic of leukaemia; red blood cells proliferation results
in polycythemia vara.

If the radiation damage occurs in germs cells, the
sperms or' oizum, it can cause defective offspring. The
defective offspring will inturn produce defective sperms or
ova, and the genetic 'mistake 1 will be passed on to all
succeding generations, reducing their quality of life until
•the family line terminates in sterlisation and/or death. A
blighted or abnormal embryomic growth can result in what
is called as hydatidifcrm mole instead of a baby. .
Exposura to radiation is also known to reduce
fertility i.e. women become unable to conceive or give birth.

Radiation can damage an embryo or foetus causing
teratogenic damage.
The complete molecules making up living organisms are
composed of long stands of atoms forming proteins, carbo
hydrates and fats. They are held together by chemical bonds
involving shared electrons.If the % ionising radiation
displaces one of the electrons in a chemical bond, it can
cause the chain of.s atoms to break apart, spleitting the .
long molecule into fragments, or changing itsshape by
elongation..This is an ungluing of the complex chemical
bonds so carefully structured to support and perpetuate
life.- The gradual breakdown of these molecular bounds
destroys the template^ used by the body to make DNA and
-RiVA or causes abnormal cell division.
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Measuring .Radiation

Glossary :

1. Alpha particle - An electrically charged (+)
particle emitted from the nucleus of some radio- .
active chemicals of plutonium. In contains 2
protons and 2 neutrons, and is largest of the
two atomic particles emitted by radioactive
chemicals. It can cause ionisation.

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2. Beta Particle - An electrically charged (-)
particle emitted from some radioactive chemicals.
It has the mass of an electron, Kryton 85, emitted
from nuclear power plants, is a strong beta emitter.
Beta particles can cause ionisation.

3. Curie - a measure of radioactivity. One curie equals
3.7 X 1O1° ruclear transformations per second.

Ci is the symbol used.
(a) Microcurie : One millionth of a curies
A -disintegrations per second)
( 3,7 x 10^

L mOi is the symbol used.
(b) Picurie : One millionth of microcurie.
(3.7 X 10" disintegrations per second)
pCi is the symbol used.

4. Dose energy imported to matter by nuclear transfor
mations ( radioactivity )

(a) Rad-= 100 ergs per-gram.
1 .GRAY.. 100 rad = 10,000 ergs per gram.
(b) Rem = radxQ where Q is a quality factor which
attempts to convert rads from different
types of-radioactivity into a common scale of
biological damage.

1 SIEVCRT = 100 rad.

5. Gamma, Ray - Short wave length electromagnetic
radiation released by some nuclear transformations.
It is similar to X-ray and will penetrate through
the human body. Iodine 131 emits gamma rays. Both
gamma rays and X-rays cause ionisation.
6. Half.life biological - time required for the body
to eliminate one half of an administered dose of
a radioactive chemical.
7. Half life physical - time required for half of a
radioactive material to undergo a nuclear trans
formation. The chemical resulting from the trans
formation may be either redioactive or nonradioactive.
8. Ionisation.- Sufficient energy is deposited in a
neutral molecule to displace an electron, thus
replacing the neutral molecule with positive and.,
negative ions.
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9. Radiation - the emission.and propagation of
energy' through space or tissue in the form of
waves. It usually refers to electromagnetic
radiation, classified by its-frequency, radio,
infrared, visible, ultraviolet,X-ray^gamms
ray. and cosmic rays.

(a) Natural background radiation- O-emission
from radioactive chemicals which are not ,
man made. These chemical include uranium,
radon, potassium, and other trace eleme
nts. They are made more hazardous
through human' activities such as mining kkj
and milling, since this makes them more
available for uptake in food, air and
water.
(b) Background radiation- included emissions,
from radioactive chemicals which occur
naturally and those which result from the
nuclear fission process. The meaning of
this term is vague.

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Permissible Leveis of Exposure - ^he US National Council
on Radiation Protection and Measurement theoretically resolved by
articulating the implicit reasoning behind subsequent radiation
protection standards development.
1.

A value judgement which reflects as it were, a measure of
psychological acceeptability to an individual -of bearing
slightly more than a normal'share of radiation induced
de fee ti ve ' ge ne s.

2.

A value judgement representing society's acceptance of
incremental damage to the population gene pool, when
weighed by total of occupationally exposed persons, or
rather those of reproductive capacity as involved in
Genetically significant Dose calculation.

3.

A value judgement derived from part experience of the
somatic effects of occupational exposure, supplimen^'d
by such biomedical and .biological experimentation and
theory as has relevance.

In short this recognises the fact that there is no safe
level of exposure to joining radiation,- and the search for
quantifying such a safe level is in vain. A permissible level,
based on a series of value judgements, must than be set, This
is essentially a trade-off of health for some 'benefit

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A permissible genetic dose ( to sperm ovum ), is that
dose ( of ionising radiation ), which if it were feceived
yearly by each person from conception to the average age of
childbearing ( taken as 30 years ), would result in an
acceptable burden to the whole population.
Complied from :

1, No Immediate Danger
Prognosis for Radioactive Earth
by Rosalie Bertell; 1985.
2. Radiation and Health by
Bob Briscoe and Dave Amis,1989
( Back ground paper for XVI Annual Meet of MFC ).

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