Download Ionizing radiation as a factor of environment

Ionizing radiation as a factor of environment.
Problem of contamination of environment by
radionuclide. Hygienic setting of ionizing
radiations norms as basis of radiation
protection.
Author:
Lototska O.V
1
THE PLAN
Introduction
1. Sources of radiation exposure.
2. Ionizing radiation and radioactivity.
3. Radiation quantities and unit.
4. Biological manifestations of radiation
exposure.
5. Principles of radiation protection.
6. The concepts of "maximum permissible
dose" and "dose limit“
Conclusions
The Chernobyl accident occurred on April 26, 1986 at
the Chernobyl nuclear power plant in Pripyat, Ukraine
It is regarded as the worst accident in the history of nuclear power
There are two types of radiation exposure: One is internal
exposure from radioactive material taken into the body; the
other is external exposure from radiation sources outside
the body.
Internal exposure
can continue if the
radioactive
material remains
in the body. In
contrast, external
exposure will not
occur again once
radiation
has
penetrated
the
body,
if
no
additional
radiation reaches
the body.
Components of Environmental
Radiation
Naturally occurring sources
•
cosmic radiation originating in outer
space and reaching the earth's surface
after reacting with, and being partially
absorbed by, the earth's atmosphere;
30 millirem/year
2.
terrestrial radiation coming from
natural radioisotopes present in the
earth's crust; 30 millirem/year
3. radiation from natural radioisotopes that have
been accumulated in the body as a result of the
consumption of food and water and the inhalation
of air containing such radioisotopes.
40 millirem/year
Man-made radiation
1. radiation to patients from the
medical uses of radiation
2.
radiation to
exposed persons
occupationally
3. radiation from "fallout" from
nuclear tests
4. radiation from other
forms of radioactive
contamination
5. radiation from radioactive consumer
goods and from electronic devices.
Radiation Source
Radiation Amount
(mrem/year)
Cigarette smoking (1 pack/day)
1300
Radon in homes
200
Medical x-rays and pharmaceuticals
53
Direct exposure from naturally occurring
radioactivity in soil
30
Cosmic radiation
30
Continental round trip by air
5
Building materials
3.6
Examples of radiation doses from common
medical procedures are:
• chest x-ray (14 x 17 inch area) - 15 mrem,
• dental x-ray (3 inch diameter area) - 300 mrem,
• spinal x-ray (14 x 17 inch area) - 300 mrem,
Ionizing radiation and
radioactivity
"Radiation" is generally defined as the
process of emitting energy as waves or particles,
and the energy thus radiated.
Ionizing radiations include all electromagnetic
and particulate radiations that are capable of
producing ions, either directly or indirectly,
during their passage through matter.
What is the difference between radiation and radioactivity?
Radioactivity is the property or capacity of radioactive materials to
emit radiation. Radiation means particle beams carrying energy emitted
from radioactive materials (radioactive isotopes). To put in an analogy, a
flashlight is a radioactive material and the light from a flashlight is
radiation.
Ionizing radiations
protons
alpha particles
gamma rays
X-ray
beta particles
(electrons)
Corpuscular
radiations
electromagnetic
radiations
Alpha radiation is simply helium nuclei, that is, each particle
consists of two protons and two neutrons. Because the nuclei have
no electrons, they have a +2 charge.
Beta radiation consists of electrons. They have negative
charges. Because they are energetic and have no rest mass, they can
be more of a potential health threat than alpha radiation.
Gamma radiation is closely related to X-rays. Like light,
gamma radiation consists of photons. Gamma rays are extremely
energetic and potentially dangerous.
Other types of particulate radiations
include neutrons, protons and deuterons
Protons
and
deuterons are usually
produced in high-energy
particle
accelerators
used in high energy
physics research work
and are not commonly
encountered in medical
applications.
Neutrons may come into more common usage in
departments of radiology as the techniques of neutron
radiography and radiation therapy are developed.
Although
neutrons
do
not
produce
ionization
themselves, they may do so indirectly. They can also be
absorbed by the nuclei of stable atoms to produce
another isotope of that atom. If the nucleus of the new
atom is unstable, the atom will be a radioactive isotope.
RADIATION QUANTITIES AND UNIT
Four of the most important quantities to
be defined are:
Activity
Exposure (X)
Absorbed dose (D)
Dose equivalent (H)
Activity:
The nuclei of atoms may be unstable as a result of too much
mass, too much energy, or both. Such atoms are said to be
radioactive. We can define radioactivity as a process of nuclear
transformation, resulting in a new nucleus and the emission of
particles and/or electromagnetic energy from the nucleus. The
emitted radiation consists of particles and/or electromagnetic
rays carrying a certain amount of energy.
The unit of
measure
for
energy is the joule
(noted J).
Another unit of
measure, the eV electronvolt,
is
more practical.
The activity of a radioactive source is defined as the
rate at which the isotope decays. Radioactivity may be
thought of as the volume of radiation produced in a given
amount of time.
The unit of measure for activity, in
SI, is disintegrations per second. To
honour
the
discoverer
of
radioactivity (Henri Becquerel,
1896), the unit of activity
(disintegrations per second) was
named the Becquerel and the
notation used is Bq .
Historically, another unit
was used - the Curie - noted
Ci. It was named after
Marie Curie, the discoverer
of Radium, and other
radionuclides.
One curie (or 1 Ci)
is the activity of 1 gram of
pure Radium. This activity
is
equal
to
3.7x1010
disintegrations per second,
or 3.7x1010 Bq.
Radiation Units
Coloumb / kg (C/kg) =
roentgen (R)
1 gray (Gy) = 100
rad
1 sievert (SV)
= 100 rem
Quality factor is a modifying factor that is introduced
to take into account the different degrees of biological
effect that can result following exposure to the same
absorbed doses of different types of radiation.
The Q factors for several types of radiation.
Type of Radiation
Rad
Q Factor
Rem
X-Ray
Gamma Ray
Beta Particles
1
1
1
1
1
1
1
1
1
Thermal Neutrons
1
5
5
Fast Neutrons
1
10
10
Alpha Particles
1
20
20
Exposure
X
Absorbed
Dose (D )
Equivalent
Dose H
Radiation
type
x-rays and
all ionizing
gamma rays radiations
Media in
which
measured
Effect
measured
Unit
Air
Any medium Biological
system
Ionization
Deposited
energy
rad
Biological
effect
rem
Gray
Joule / kg
SI unit
Roentgen
(R)
Coloumb /
kg
all ionizing
radiations
Biological Effects
The biological effect of ionizing radiation
Can lead to:
The occurrence of particular health effects from
exposure to ionizing radiation is a complicated
function of numerous factors including:
•Type of radiation involved.
•Size of dose received.
•Rate the dose is received.
•Part of the body exposed.
•The age of the individual.
•Biological differences.
Object
Characteristic
of effects
Biologic effects of ionizing radiation
Deterministic
effects
Somatic
Acute
radiation sickness
chronic
radiation sickness
Stochastic effects
Somato-stochastic
skin and
tissue burns
alopecia
ray cataract
clinical registered
frustration of hemopoesis
cancerogenic effect
teratogenic effect
temporary or
constant sterility
Genetic
genetic mutation
Chromosomal
aberration
Somatic effects
 The early effects are normally observed within a few days or
weeks of exposure;
the late effects are observed after a period ranging from a few
months to years.
Relationship between Exposure Dose and
Acute Radiation Effect in adult humans
A latent period supervenes after initial symptoms of malaise,
loss of appetite and fatigue. The length of this period is
roughly inversely proportional to the radiation dose received.
The end of the latent period is followed by the onset of
the illness:
early lethality,
destruction of bone marrow,
damage to the gastrointestinal tract associated with diarrhea and
hemorrhage,
central nervous system symptoms,
Epilation (loss of hair),
dermatitis,
sterility.
Pathological acute effects arise after exposure to doses hundreds of
times greater than those likely to be received from environmental
contamination, except in major accidents.
Deterministic
effects
have a clear relationship
between the exposure and
the effect. In addition, the
magnitude of the effect is
directly proportional to the
size of the dose. These
effects will often be evident
within hours or days.
Stochastic
effects
are
those that occur by chance and
consist primarily of cancer and
genetic
effects.
Stochastic
effects often show up years
after exposure. As the dose to
an individual increases, the
probability that cancer or a
genetic effect will occur also
increases.
Late effect
Cancer is any malignant
growth or tumor caused by
abnormal and uncontrolled cell
division.
Cataracts - a clouding of
the lens of the eye
Leukemia
Leukemia is a cancer of the early blood-forming cells.
Usually, the leukemia is a cancer of the white blood cells, but
leukemia can involve other blood cell types as well. Leukemia
starts in the bone marrow and then spreads to the blood.
From there it can go to the
lymph nodes, spleen, liver, central
nervous system (the brain and
spinal cord), testes (testicles), or
other organs. Leukemia is among
the
most
likely
forms
of
malignancy
resulting
from
overexposure
to
total
body
radiation. Chronic lymphocytic
leukemia does not appear to be
related to radiation exposure.
Genetic effects
If the information that is jumbled is in a germ cell that
subsequently is fertilized, then the new individual may carry a
genetic defect, or a mutation. Such a mutation is often called a
point mutation, since it results from damage to one point on a
gene.
Most
geneticists
believe that the majority
of such mutations in
man are undesirable or
harmful.
In addition to point
mutations,
genetic
damage
can
arise
through chromosomal
aberrations.
Nonstochastic (Acute) Effects
Nonstochastic effects have a clear relationship between the
exposure and the effect. In addition, the magnitude of the effect is
directly proportional to the size of the dose. Nonstochastic effects
typically result when very large dosages of radiation are received in
a short amount of time. These effects will often be evident within
hours or days. Examples of nonstochastic effects include erythema
(skin reddening), skin and tissue burns, cataract formation, sterility,
radiation sickness and death.
Critical organs
the particular organs or
tissues that are critical
because of the damage
they may suffer is the
essential simplifying step.
For example, in the case of
radioisotopes of iodine,
the critical organ is the
thyroid,
since
the
concentration of such
isotopes
in
it,
and
therefore
the
dose
received, is far greater
than for any other organ.
For general irradiation of the whole body, the critical
organs and tissues are
the gonads (fertility, hereditary effects),
the haematopoietic organs,
the bone marrow (leukemia),
the eye (cataracts).
PRINCIPLES OF RADIATION
PROTECTION
Rods for Internal Radiation
External Radiation of a Tumor
The physical protection against external radiation is based on the
following three principles:
•distance from the source of radiation (distance),
•limitation of the time of irradiation (time),
•absorption of radiation (shielding).
Shortening the time of exposure, increasing distance from a
radiation source and shielding are the basic countermeasures (or
protective measures) to reduce doses from external exposure.
To reduce doses from intake of radioactive
substances, the following basic countermeasures can be
considered:
shortening time of exposure to contaminants;
preventing surface contamination;
preventing inhalation of radioactive materials in air;
preventing ingestion of contaminated foodstuffs and
drinking water.
The duration of exposure
during fluoroscopy can be
minimized
by
the
fluoroscopist
by
using
image
hold
technique,
intermittent beam on-off
imaging, and avoiding long
static imaging.
The picture above demonstrates how image hold techniques can be
useful in decreasing radiation exposure to the patient during dynamic
fluoroscopic imaging procedures. The high resolution of modern
monitors allows the physician to make observations not easily seen with
archaic imaging equipment. It can be seen in this picture that an ERCP
procedure is being done; this imaging department uses two monitors in
their fluoro room, one for dynamic imaging the other for last image hold.
Distance is the most effective means of radiation protection
I1/l2 =(D2/D1)2
Area "A" is smaller and the radiation is more concentrated than in
an equal area "A1" which is some distance from "A." Each square
A1 is the same size as "A" but only 1/4 the number of photons
occupies it because of the divergence of the radiation with
increasing distance.
The use of shielding as a cardinal principle of radiation protection
Secondary barriers
are designed for
protection from
scatter radiation.
This picture demonstrates the
protective curtain to be at least
0.25 mm Pb equivalency. It should
not be routinely removed for
fluoroscopic procedures (white
arrow).
The curtain will protect the technologist
and radiologist from a significant amount of
scatter radiation.
mobile shields
Thyroid shields used to help
reduce exposure to the thyroid
gland
during
fluoroscopy
exams. Lead aprons used to
protect from scatter radiation
can protect up to 80% of the
active blood forming organs in
the body.
Lead gloves are used to protect the
worker when a potential for exposure
to the hands may occur.
Shielding requirements according to NCRP
recommendation are:
• Lead aprons - 0.5 mm lead equivalency
• Lead gloves, protective curtain, thyroid
shield – 0.25 mm lead equivalency
• Thyroid shields – 0.25 mm lead
equivalency
Protection from radiation :

Avoid unusual exposure to radiation.

Protective devices such as gloves, goggles and lead sheets
must be used by persons working in radiology department.

Workers must wear a film badge which shows accumulated
exposure to radiation since last time the instrument was
charged.

Regular medical check- up.

Standards laid down by International Commission on
Radiological Protection (ICRP), International Atomic Energy
Agency (IAEA) and W.H.O. must be followed.
This picture is of a
canister
used
to
transport radioisotopes
for PET imaging, and the
syringe
holder
for
protection during dose
administration.
Some radiology departments equip their exterior room door
with a light indicator (right & left picture) to warn nursing,
patient transport, and others, that the room is energized, and
no one should enter the room at this time.
Radiation dosimeters are important for people working with
radioactive isotopes, as in analytical research laboratories, in
nuclear medical applications, in medical X-ray imaging, in
nuclear power-stations or in non-destructive testing of
materials by ionizing radiation. They need to known their
received radiation dose and need to be warned when threshold
values become exceeded.
Radiation Protection Standards.
The concept of "tolerance dose"
Exposure Limits
Concern over the biological effect of ionizing
1)
2)
radiation began shortly after the discovery of X-rays
in 1895. Over the years, numerous recommendations
regarding occupational exposure limits have been
developed by the International Commission on
Radiological Protection (ICRP) and other radiation
protection groups. In general, the guidelines
established for radiation exposure have had two
principle objectives:
to prevent acute exposure; and
to limit chronic exposure to "acceptable" levels.
MAXIMUM PERMISSIBLE DOSES AND DOSE LIMITS'
Organ or tissue
Maximum
permissible dose for
adults exposed in
the course of their
work
Dose limits for
members of the
public
(average
for groups of
individuals)
Whole body (in case of 5 rem in a year
uniform irradiation),
0.5 rem in a year
Skin, bone and thyroid
30 rem in a year
3 rem in a year3
Other single organs
15 rem in a year
1.5 rem in a year
Hands and forearms; feet 75 rem in a year
and ankles
7.5 rem in a year
The shallow-dose equivalent is the
external dose to the skin of the wholebody or extremities from an external
source of ionizing radiation. This value
is the dose equivalent at a tissue depth
of 0.007 cm averaged over and area of
10 cm2.
The lens dose equivalent is the dose
equivalent to the lens of the eye from
an external source of ionizing radiation.
This value is the dose equivalent at a
tissue depth of 0.3 cm.
The deep-dose equivalent is the
whole-body dose from an external
source of ionizing radiation. This value
is the dose equivalent at a tissue depth
of 1 cm.
The total effective dose equivalent is
the dose equivalent to the whole-body.
Declared Pregnant Workers and Minors
Because of the increased health risks to the rapidly
developing embryo and fetus, pregnant women can receive
no more than 0.5 rem during the entire gestation period. This
is 10% of the dose limit that normally applies to radiation
workers. Persons under the age of 18 years are also limited
to 0.5rem/year.
Non-radiation Workers and the Public
The dose limit to non-radiation workers and members of
the public are two percent of the annual occupational dose
limit. Therefore, a non-radiation worker can receive a
whole body dose of no more that 0.1 rem/year from
industrial ionizing radiation. This exposure would be in
addition to the 0.3 rem/year from natural background
radiation and the 0.05 rem/year from man-made sources
such as medical x-rays.
According to " Norms of radiating safety of
Ukraine " all population divided on three categories
A
- persons from among the personnel
which constantly or temporarily work
directly with sources of ionization
radiations;
- persons from among the personnel which
directly do not work with sources ionization
radiations, but in connection with an arrangement of
workplaces in rooms and on industrial platforms of
objects with radio-nuclear technologies may receive
an additional irradiation;
B
C - all other population
Categories of
population
Maximum permissible dose for groups of
critical organs
1 group
1 group
1 group
A
5
15
30
B
0,5
1,5
3,0
C
RADIATION MONITORING
DEVICES
Survey Meters
for determine
the presence
and intensity
of radiation
Human beings cannot detect the presence of
ionizing radiation with any of their five senses,
and therefore one or another kind of instrument
must be used for this purpose. Radiation detection
instruments should be able to measure both the
type (qualitative) and amount (quantitative) of
radiation exposure. The operation of such
instruments is usually based on their response to
charged particles that are produced as radiation
interacts with and ionizes matter through which it
is passing. In general, radiation detection and
measuring instruments can be divided into two
categories, depending upon whether they are used
for personnel monitoring or area survey purposes.
Safety Controls
Since X-ray and gamma radiation are not detectable by the human
senses and the resulting damage to the body is not immediately
apparent, a variety of safety controls are used to limit exposure. The
two basic types of radiation safety controls used to provide a safe
working environment are engineered and administrative controls.
Engineered controls include shielding, interlocks, alarms, warning
signals, and material containment.
Administrative controls include postings, procedures, dosimetry,
and training.
Radiation Detectors
Instruments used for radiation
measurement fall into two broad
categories:
- rate measuring instruments and
- personal dose measuring
instruments.
Dose measuring instruments
are those that measure the
total amount of exposure
received during a measuring
period. The dose measuring
instruments, or dosimeters,
that are commonly used in
industrial radiography are
small devices which are
designed to be worn by an
individual to measure the
exposure received by the
individual.
Direct Read Pocket Dosimeter
Audible Alarm Rate
Meters and Digital
Electronic Dosimeters
Film Badges
Digital Electronic
Dosimeter
Thermoluminescent Dosimeter
Thank you
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