PHYSICAL AND BIOLOGICAL EFFECTS OF NUCLEAR

RADIATIONIntesar Zalloum

Atheer Shamisti Dujana Kamal

Supervisor:Dr. Othman ZalloumAssociate Professor

WHAT IS NUCLEAR RADIATION?• Nuclear radiation arises from hundreds of different kinds of unstable

atoms. While many exist in nature, the majority are created in nuclear reactions. Ionizing radiation which can damage living tissue is emitted as the unstable atoms (radionuclides) change ('decay') spontaneously to become different kinds of atoms.

• The principal kinds of ionizing radiation are:

• Alpha particles• Beta particles• Gamma rays• X-rays• Cosmic radiation• Neutrons 

SOURCE OF RADIATIONSources of Exposure:

• Humans are being continuously exposed to radiations, both ionizing as well as non-ionizing.

• The major sources of exposure are of two types: natural and artificial.

• Natural radiations are universal in the sense that the entire population, in all parts of the world, is exposed to them to a larger or smaller extent throughout life, while the artificial exposure affects only a small part of the population only for a certain time period of their life.

The above chart is taken from the National Council on Radiation Protection and Measurements (NCRP) Report No. 93, Ionizing Radiation Exposure of the Population of the United States, 1987.

NATURAL SOURCESCosmic Radiation: The term cosmic rays or cosmic radiation refers to primary energetic particles of

extraterrestrial origin that enter the earth’s atmosphere, and to the secondary radiations produced by their interactions with the atmosphere.

Cosmogenic Nuclides

NATURAL SOURCE Terrestrial Radiation:

• The dose from terrestrial sources also varies in different parts of the world.

• Locations with higher concentrations of uranium and thorium in their soil have higher dose levels.

• The major isotopes of concern for terrestrial radiation are uranium and the decay products of uranium, such as thorium, radium, and radon.

• Uranium and thorium each initiate a chain of radioactive progeny, which are nearly always found in the presence of the parent nuclides.

Radioactive Decay in Thorium and Uranium Series

• Although many of the daughter radio nuclides are short-lived, they are distributed in the environment because they are continually being forming from long-lived precursors.

NATURAL SOURCESInternal Radiation

• Its a number of naturally occurring radio nuclides within our bodies.

• The major one that produces penetrating gamma radiation that can escape from the body is a radioactive isotope of potassium, called potassium-40.

• This radionuclide has been around since the birth of the earth and is present as a tiny fraction of all the potassium in nature.

• There are many other radio nuclides in the human body, but these either are present at lower levels than 40K (for example, 238U, 232Th, and their decay products) or they do not emit gamma rays that can escape the body (for example, 14C and 87Rb).

TYPES OF ARTIFICIAL RADIATION• Radiation used in medical applications is the largest source of man-made

radiation that people in the industrialized countries are exposed to.

• The majority of this exposure is from diagnostic X-rays, which are used by physicians to determine the extent of disease or physical injury.

• In the field of nuclear medicine, radioactive compounds called radiopharmaceuticals are also used to support diagnoses, while a further source of radiation exposure is radiation therapy.

• Although all people are exposed to natural sources of radiation, there are two distinct groups exposed to man-made radiation sources.

HOW DOES IONIZING RADIATION INTER THE BODY?

• X-rays and gamma rays can pass directly through the body when it is exposed to an irradiating source such as an x-ray machine. Alpha and beta particles do not penetrate very far into the body but radioactive materials that emit alpha, beta or gamma radiation can be taken into the body alone or with other materials which have become contaminated in the following ways:

1. In the air or mixed with the dust in the air.2. Dissolved in water.3. Mixed with soil on the ground through fertilizers and absorbed by plants

that we may eat.4. By consumption of plants and animals that have become contaminated.

RADIATION UNITS• There are four different but interrelated units for measuring radioactivity,

exposure, absorbed dose, and dose equivalent with both common British units and international metric units in use.

Quantity Old Unit New Unit Equivalence

Activity Curie (Ci) Becquerel (Bq) = 1

dps

1 Ci = 3.7x1010 Bq

Exposure Roentgen (R) Coulomb/kg (C/kg) 1 R = 2.58 x 10-4 C/kg

Absorbed

Dose

Radiation absorbed dose (rad) =

100 erg/gm

Gray (Gy) = 1 J/kg 1 Gy = 100 rad

Dose

Equivalent

Roentgen equivalent man (rem) Sievert (Sv) = 1 J/kg 1 Sv = 100 rem

STOCHASTIC EFFECTS OF RADIATION• The term stochastic means ‘random’ and implies that low levels of radiation

exposure are not certain to produce an effect.

• Stochastic effects are usually associated with low levels of radiation exposure over a long period of time (e.g. years).  

• They are effects that occur without a threshold level of dose and whose probability is proportional to the dose and whose severity is independent of the dose.

DETERMINISTIC EFFECTS OF RADIATION• Deterministic effects are usually associated with high levels of radiation

exposure over a short period of time (fractions of a second to tens of days).

• Deterministic effects have two characteristic features: 

• There is a threshold radiation dose, below which the deterministic effects are not observed;

• The severity of the deterministic effect increases with the magnitude of the radiation dose

• Acute Radiation Syndrome (ARS) or radiation sickness is an acute illness caused by irradiation of the entire body (or most of the body) by a high dose of penetrating radiation in a very short period of time (usually a matter of minutes).

INTRODUCTION TO THE BIOLOGICAL EFFECTS OF RADIATION

• Radiation which is absorbed in a cell has the potential to impact a variety of critical targets, the most important of which is the DNA.

• Evidence indicates that damage to the DNA is what causes cell death, mutation, and cancer.

• The mechanism by which the damage occurs can happen either by direct action or indirect action.

I. Direct Action

• Direct action can be visualized as a “direct hit” by the radiation on the DNA, and thus is a fairly uncommon occurrence due to the small size of the target; the diameter of the DNA helix is only about 2 nm.

• In a direct action, radiation may impact the DNA directly, causing ionizations which physically break one or both of the sugar phosphate backbones or break the base pairs of the DNA.

II. Indirect Action

• In an indirect action, the radiation interacts with non-critical target atoms or molecules, usually water.

• This results in the production of free radicals, which are atoms or molecules that have an unpaired electron and thus are highly reactive due to the presence of unpaired electrons on the molecule.

• Free radicals may form compounds, such as hydrogen peroxide, which could initiate harmful chemical reactions within the cells.

SINGLE STRAND BREAKS• These breaks occur when the chemical links between two nucleotide

bases in one strand of DNA become damaged, causing a break in one strand of the double helix.

• During a double-stranded break, nucleotides on both strands of the double helix become damaged and break apart, completely separating a strand of DNA.

DOUBLE STRAND BREAKS

• These events can lead to the creation of tumour cells if, for example, the deleted chromosomal region encodes a tumour suppressor or if an amplified region encodes a protein with cancer potential.

• If the genetic code is damaged and the cell does not undergo apoptosis (cell suicide), the mutation may be passed on during cell division, perhaps leading to a cancer or other mutation. In some cases a mutation may remain dormant for years and perhaps forever.

DNA MUTATIONS AND REPAIR• When such breaks occur, DNA usually repairs itself through a process

called excision. The base-excision process has four steps:

1. DNA glycosylase removes the damaged base.

2. AP endonuclease cleaves the DNA backbone and removes the deoxyribose sugar and the phosphate group.

3. DNA polymerase adds new nucleotides in the gap.

4. The gap is sealed by DNA ligase.

• There are two basic types of mutations:

1. Substitutions — this is the replacement of one base by another. There are two types of base substitutions: 

• transitions —involve the replacement of one purine with the other purine, (adenine and thymine), or the replacement of one pyrimidine with the other pyrimidine (cytosine and guanine)

• transversions — replacement of a purine with a pyrimidine or vice versa

2. Mutations — these change the reading frame of a gene (the triplet code). There are two types of frameshift mutations: 

• Insertions — as the name implies, these involve the insertion of one or more extra nucleotides into a DNA chain

• Deletions — these result from the loss of one or more nucleotides from a DNA chain

MEDICAL EFFECTS OF IONIZING RADIATION• Certain body parts are more specifically affected by exposure to different

types of radiation sources. Several factors are involved in determining the potential health effects of exposure to radiation. These include:

• The amount of energy deposited in the body

• The ability of the radiation to harm human tissue

• The organs are affected

• The most important factor is the amount of energy actually deposited in your body.

SHORT-TERM EFFECTS OF RADIATION • The short term effects of radiation are called Radiation Sickness and

include:

• Bone marrow is the spongy tissue inside some of our bones. It contains immature cells, called stem cells. The stem cells can develop into the red blood cells that carry oxygen through your body, the white blood cells that fight infections, and the platelets that help with blood clotting. A bone marrow disease causes problems with the stem cells or how they develop.

• Gastrointestinal syndrome causes destruction in the lining of the gastrointestinal tract. GI tract lining is a semi permeable membrane that absorbs nutrients and acts as a barrier to toxins. Damage will allow the wrong substances to seep through into the bloodstream.

• Central nervous system syndrome is an effect seen at very high radiation doses in which the central nervous system undergoes irreparable damage.

LONG TERM EFFECTS OF RADIATION• The long-term effects of radiation occur several decades after the explosion .

These effects include:

1. Blood Disorders

• This causes a deficiency in red blood cells

2. Cataracts• There was an increase in cataract (A clouding of the lens of the eye)

rate of the survivors at Hiroshima and Nagasaki.• 2 gray of gamma rays cause cloudiness in a few percent• 6-7 gray can seriously impair vision and cause cataracts

3. Tumors• Cancer induction is the most significant long term risk of exposure

to a nuclear explosion. Approximately 1 out of every 80 people exposed to 1 gray will die from cancer and 1 in 40 people will get cancer. Different types of cancer take different times for them to appear.

4. Keloids• Keloids is an area of irregular fibrous tissue formed at the site of a

scar or injury. Beginning in early 1946, scar tissue covering apparently healed burns began to swell and grow abnormally.

NUCLEAR EXPLOSIONS• Nuclear explosions produce both immediate and delayed destructive

effects.

• Blast, thermal radiation, and prompt ionizing radiation cause significant destruction within seconds or minutes of a nuclear explosion.

• The delayed effects, such as radioactive fallout and other environmental effects, inflict damage over an extended period ranging from hours to years.

THE ENERGY FROM A NUCLEAR EXPLOSION• One of the fundamental differences between a nuclear and a

conventional explosion is that nuclear explosions can be many thousands (or millions) of times more powerful than the largest conventional explosion.

• Both types of weapons rely on the destructive force of the blast or shock wave.

• However, the temperatures reached in a nuclear explosion are very much higher than in a conventional explosion, and a large proportion of the energy in a nuclear explosion is emitted in the form of light and heat, generally referred to as thermal energy.

• This energy is capable of causing skin burns and of starting fires at considerable distances.

• Nuclear explosions are also accompanied by various forms of radiation, lasting a few seconds to remaining dangerous over an extended period of time.

• When an explosion occurs, a sudden release of energy takes place along with a rapid expansion of gas in the region of the explosion occurs which causes shock waves and other blast effects.

• The energy of a nuclear explosion is released in the form of a blast wave, thermal radiation (heat) and nuclear radiation.

• For nuclear weapons in the kiloton range, the energy is divided in various forms, roughly as 50% blast and 35% thermal.

• The remaining 15% of the energy is released as various type of nuclear radiation.

BLAST EFFECTS• Most damage comes from the explosive blast. The shock wave of air

radiates outward, producing sudden changes in air pressure that can crush objects, and high winds that can knock objects down.

• In general, large buildings are destroyed by the change in air pressure, while people and objects such as trees and utility poles are destroyed by the wind.

• The magnitude of the blast effect is related to the height of the burst above ground level.

• For any given distance from the center of the explosion, there is an optimum burst height that will produce the greatest change in air pressure, called overpressure. 

• Blast effects are usually measured by the amount of overpressure, the pressure in excess of the normal atmospheric value.

• The greater the distance the greater the optimum burst height.

• As a result, a burst on the surface produces the greatest overpressure at very close ranges, but less overpressure than an air burst at somewhat longer ranges.

Variation of pressure (in excess of ambient) with distance in an ideal shock wave.

The above diagram shows the approximate radiation exposure (in Sieverts) in relation to a person’s distance from the bombsite and provides a comparison with other radiation exposures.

• A 15 kiloton weapon creates pressure created in excess of 10 Psi (pounds per square inch) with wind speeds in excess of 800 km per hour up to about a 1.2 km radius.

• Most buildings are demolished and there will be almost no survivors (much larger strategic nuclear weapons will greatly extend this radius of destruction).

• Beyond this distance, and up to about 2.5 km the pressure gradually drops to 3 Psi and the wind speed comes down to about 150 km per hour as in a severe cyclonic storm.

• There will be injuries on a large scale and some fatalities

• Human beings are quite resistant to pressure, but cannot withstand being thrown against hard objects nor to buildings falling upon them.

• Illustration of blast effects for a 15 kiloton explosion. Zones 1 and 2 correspond to the "killing field“ where the fatalities are universal.

• There are many different effects that make it difficult to provide a simple rule of thumb for assessing the magnitude of injury produced by different blast intensities. However, a general guide is given by:

Overpressure Physical Effects20 psi Heavily built concrete buildings are severely

damaged or demolished.10 psi Reinforced concrete buildings are severely

damaged or demolished.Most people are killed.

5 psi Most buildings collapse.Injuries are universal, fatalities are widespread.

3 psi Residential structures collapse.Serious injuries are common, fatalities may occur.

1 psi Window glass shattersLight injuries from fragments occur.

THERMAL RADIATION (LIGHT AND HEAT) EFFECTS

• Thermal effects hold the greatest potential for environmental damage and human destruction. 

• This is because nuclear firestorms in urban areas can create millions of tons of smoke which will rise into the stratosphere and create massive global cooling by blocking sunlight. 

• In any nuclear conflict, it is likely that this environmental catastrophe will cause more fatalities than would the initial immediate local effects of the nuclear explosion.

• The first effect of a nuclear explosion in the air is an intense flash of light, as quick as a lightning flash but a thousand times as bright.

• It is accompanied by a powerful pulse of heat radiation, sufficient to set fire to light combustible material out to a distance.

• Immediately after the flash, a "fireball" forms in the air and rises for several seconds, blindingly bright and radiating much heat.

• The visible light will produce "flashblindness" in people who are looking in the direction of the explosion.

• Flashblindness can last for several minutes, after which recovery is total.

• If the flash is focused through the lens of the eye, a permanent retinal burn will result.

• At Hiroshima and Nagasaki, there were many cases of flashblindness, but only one case of retinal burn, among the survivors.

• Skin burns result from higher intensities of light, and therefore take place closer to the point of explosion.

• First-degree, second-degree and third-degree burns can occur at distances of five miles away from the blast or more.

• Third-degree and second-degree burns will result in serious shock, and will probably prove fatal unless prompt, specialized medical care is available.

• The entire United States has facilities to treat 1,000 or 2,000 severe burn cases. A single nuclear weapon could produce more than 10,000.

• The fireball, an extremely hot and highly luminous spherical mass of air and gaseous weapon residues, occurs within less than one millionth of one second of the weapon's explosion.

• Immediately after its formation, the fireball begins to grow in size, engulfing the surrounding air. This growth is accompanied by a decrease in temperature because of the accompanying increase in mass.

• The surface of the fireball also emits large amounts of infrared, visible and ultraviolet rays in the first few seconds. This thermal radiation travels outward at the speed of light.

• As a result this is by far the most widespread of all the effects in a nuclear explosion and occurs even at distances where blast effects are minimal.

 

ACKNOWLEDGMENTS

MANY THANKS GOES TO:

• DR. OTHMAN ZALLOUM

• OUR TEACHERS

• THE DEPARTMENT OF THE APPLIED PHYSICS

• OUR PARENTS & OUR FAMILY

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