Radiography –introduction for ndt

•Electromagnetic radiation (photon), of shorter wavelength than ultraviolet radiation. Produced by

bombardment of atoms by high-quntum-energy particles. Radiation wavelength is from 10-11 m

•A device for generating X-rays by accelerating electrons from a filament to strike a metal target

(anode).

An image storage medium consisting of a transparent base, usually coated on both sides with a radiation

sensitive emulsion.

History of Radiography

• X-rays were discovered in 1895 by Wilhelm Conrad Roentgen (1845-1923)

Nature of Penetrating Radiation

Properties of X-Rays and Gamma Rays• They are not detected by human senses (cannot be seen,

heard, felt, etc.).• They travel in straight lines at the speed of light.• Their paths cannot be changed by electrical or magnetic

fields.• They can be diffracted to a small degree at interfaces between

two different materials.• They pass through matter until they have a chance encounter

with an atomic particle.• Their degree of penetration depends on their energy and the

matter they are traveling through.• They have enough energy to ionize matter and can damage or

destroy living cells. •

Bremsstrahlung Radiation

Bremsstrahlung Radiation• from German "bremsen" to brake, and "Strahlung" radiation"). Electromagnetic radiation produced by the deceleration of a charged particle. In an X-ray tube this is the radiation that is emitted when electrons are suddenly "braked" when they collide with the target after being emitted from the cathode. Bremsstrahlung is characterised as a continuous spectrum with a peak that shifts to higher intensities and towards higher frequency energies with increasing voltage potential. Increasing voltage past the threshold value required for characteristic radiation does not shift the spike to a shorter wavelength but does increase their intensity. For a given applied voltage X-ray intensity is zero up to a certain wavelength termed the short-wavelength limit (SWL). There is no abrupt limit on the long wavelength side of the curve. As the voltage is increased the SWL and the position of the peak bremsstrahlung moves to the left and the intensity at all wavelengths increase. At some critical voltage that is dependent on the target material, characteristic radiation (c.v.) is emitted. These are characterised by "spikes" is energy that rise up out of the continuous background.

K-shell Emission Radiation

Bremsstrahlung Radiation

1.The abrupt acceleration of the charged particles (electrons) produces Bremsstrahlung photons.

2The K-shell is the lowest energy state of an atom3. A tungsten electron of higher energy (from an

outer shell) can fall into the K-shell. 4. The energy lost by the falling electron shows up

in an emitted x-ray photon. Meanwhile, higher energy electrons fall into the vacated energy state in the outer shell, and so on

• Gamma-raysA nucleus which is in an excited state may emit one or more photons (packets of electromagnetic radiation) of discrete energies. The emission of gamma rays does not alter the number of protons or neutrons in the nucleus but instead has the effect of moving the nucleus from a higher to a lower energy state (unstable to stable). Gamma ray emission frequently follows beta decay, alpha decay, and other nuclear decay processes.

. Half-life

• . Half-life is defined as the time required for the activity of any particular radionuclide to decrease to one-half of its initial value.

excitation and ionization

• 1.The various types of penetrating radiation impart their energy to matter primarily through excitation and ionization of orbital electrons

• The term "excitation" is used to describe an interaction where electrons acquire energy from a passing charged particle but are not removed completely from their atom.

ionization"

• Excited electrons may subsequently emit energy in the form of x-rays during the process of returning to a lower energy state. The term "ionization" refers to the complete removal of an electron from an atom following the transfer of energy from a passing charged particle. In describing the intensity of ionization, the term "specific ionization" is often used. This is defined as the number of ion pairs formed per unit path length for a given type of radiation.

The intensity of the influence at any given radius (r) is the source strength divided by the area of the sphere.

atteunation

• attenuation

the intensity of photons

• Where: I = the intensity of photons transmitted across some distance x I0 = the initial intensity of photons s = a proportionality constant that reflects the total probability of a photon being scattered or absorbed µ = the linear attenuation coefficient x = distance traveled

Discuss why X-rays are important and how we use them.

• Dentists, doctors, NDE inspectors, and airport personal are just some examples of people who use X-rays in their jobs. X-rays can be used to "look inside" an object and to locate defects in materials.

RADIOGRAPHS AND PHOTOGRAPHS

• In photography, reflected light rays from the object expose the film to produce an image.

• In radiography, X-rays that pass through the object expose the film to produce an image.

• Differences in the types and amounts of the materials that the X-rays must travel through are responsible for the details of the radiographic image.

THE DISCOVERY OF RADIOACTIVITY

• When the nucleus of an element decays or disintegrates radiation is emitted, and this kind of element is called a radioactive element.

• Minerals that glow when sunlight is exposed on them are called fluorescent minerals.

THE DISCOVERY OF X-RAYS

• X-rays were discovered by William Roentgen while experimenting with a cathode radiation

• . Henri Becquerel discovered the radioactive properties of uranium when he stored a piece with some film and notched an image on the film. Uranium was named a radioactive element because if gives off something that is invisible to the human eye called radiation

ATOMS AND ELEMENTS

• Marie and Pierre Curie advanced the study of radiation and discovered the radioactivematerials radium and polonium.

• An atom is the smallest particle of an element that remain identical to all other particles.

• The atoms of one element are different from those of all other element.

• Compounds are made when atoms of different elements are chemically combined together.

CHEMICAL FORMULA

• Chemical formulas are used to describe the types of atoms and their numbers in an element or compound.

• The atoms of each element are represented by one or two different letters.

• When more than one atom of a specific element is found in a molecule, a subscript is used to indicate this in the chemical formula.

• Carbon Dioxide > CO2

Sugar > C6H12O6

SUBATOMIC PARTICLES

• Subatomic particles are particles that are smaller than the atom. Protons, neutrons, and electrons are the three main subatomic particles found in an atom. Protons have a positive (+) charge. An easy way to remember this is to remember that both proton and positive start with the letter "P." Neutrons have no electrical charge. An easy way to remember this is to remember that both neutron and no electrical charge start with the letter "N

• Neutrons are all identical to each other, just as protons are.

• Atoms of a particular element must have the same number of protons but can have different numbers of neutrons.

• When an element has different variants that, while all having the same number of protons, have differing numbers of neutrons, these variants are called isotopes.

ATOMIC NUMBER AND MASS NUMBERS

• a

• An element's or isotope's atomic number tells how many protons are in its atoms.

• An element's or isotope's mass number tells how many protons and neutrons in its atoms.

• Electrons spin and rotate around the outside of the nucleus.

• As the electrons circle the nucleus they travel at certain energy levels but can "jump" between different energy levels if they gain or lose energy.

•

STABLE AND UNSTABLE ATOMS

STABLE AND UNSTABLE ATOMS

• Electromagnetic fields cause like charges to repel each other and unlike charges to attract each other.

• The protons stay together in the nucleus because the strong force opposes and overcomes the forces of repulsion from the electromagnetic field.

• Binding energy is the energy that is associated with the strong force, and this energy holds the nucleus together.

• A stable atom is an atom that has enough binding energy to hold the nucleus together permanently.

• An unstable atom does not have enough binding energy to hold the nucleus together permanently and is called a radioactive atom

RADIOACTIVITY AND RADIOISOTOPES

• Radioactivity is the release of energy and matter due to a change in the nucleus of an atom.

• Radioisotopes are isotopes that are unstable and release radiation. All isotopes are not radioisotopes.

• Transmutation occurs when a radioactive element attempts to become stabilized and transforms into a new element.

RADIOACTIVE DECAY

• As an unstable atom tries to reach a stable form, energy and matter are released from the nucleus. This spontaneous change in the nucleus is called radioactive decay.

• When there is a change in the nucleus and one element changes into another, it is called transmutation.

NUCLEAR REACTIONS

• The symbol for Uranium-238 = This shows you that Uranium has a mass number of 238 and an atomic number of 92.

Symbols are also utilized to represent alpha and beta particles.

•The symbol for an alpha particle =

The symbol for a beta particle is

The chemical symbol for a neutron =

A nuclear reaction can be described by an equation, which must be balanced.

The symbol for an atom or atomic particle includes the symbol of the element, the mass number, and the atomic number.

The mass number, which describes the number of protons and neutrons, is attached at the upper left of the symbol.

The atomic number, which describes the number of protons in the nucleus, is attached at the lower left of the symbol.

RADIOACTIVE HALF-LIFE

• The term half-life describes how long it will take for half of the atoms to decay, and is constant for a given isotope.

• The curie the unit of measure used to describe the radioactivity of radioactive material. (1C = 3.7 X 1010 disintegrations/sec)

• The disintegration of the atoms from different isotopes can produce different amounts of radiation.

RADIOACTIVE HALF-LIFE (CONTINUED

• The half-life of radioisotopes varies from seconds to billions of years.

• Carbon-dating uses the half-life of Carbon-14 to find the approximate age of an object that is 40,000 years old or younger.

• Radiographers use half-life information to make adjustments in the film exposure time due to the changes in radiation intensity that occurs as radioisotopes degrade.

half-life affect an isotope

• How does the half-life affect an isotope?• Let's look closely at how the half-life affects an

isotope. Suppose you have 10 grams of Barium-139. It has a half-life of 86 minutes. After 86 minutes, half of the atoms in the sample would have decayed into another element, Lanthanum-139. Therefore, after one half-life, you would have 5 grams of Barium-139, and 5 grams of Lanthanum-139. After another 86 minutes, half of the 5 grams of Barium-139 would decay into Lanthanum-139; you would now have 2.5 grams of Barium-139 and 7.5 grams of Lanthanum-139.

X-RAY GENERATION

• The three things needed to create x-rays are a source of electrons, a means of accelerating the electrons to high speeds, and a target for the accelerated electron to interact with.

• X-rays are produced when the free electrons cause energy to be released as they interact with the atomic particles in the target.

CHARACTERISTICS OF RADIATION

• Radiation is an electromagnetic wave that has no charge and no mass.

• X-rays and gamma-rays can be characterized by frequency, wavelength, and energy.

INTERACTION OF RADIATION AND MATTER

1. When radiation encounters a material, some of the energy will be absorbed through interactions subatomic particles.

2. More radiation will be absorbed by materials with high atomic numbers (generally more dense materials) because there are more subatomic particles to interact with the radiation.

3. Energy can never be created or destroyed; therefore, the energy does not disappear but is converted into something other form.

IONIZATION

• An ion is an atom, group of atoms, or a particle with a positive or negative charge.

• With an electron removed, the atom possesses a plus one charge, therefore it is a positive ion. Consequently, the liberated electron is a negative ion, as long as it exists by itself and does not combine with another atom.

1.The three principle level of ionization are the Photoelectric effect, the Compton Effect, and Pair-Production.

2.This process of radiation absorption is called ionization.

DEPTH OF PENETRATION OF RADIATION ENERGY

1. The more subatomic particles in a material the more quickly radiation energy will be absorbed resulting in less depth of penetration.

2. The half-value layer is the depth within a material where half of the radiation energy has been absorbed. The HVL is useful in making material comparisons.

3. Higher energy radiation will penetrate deeper into a material before it is absorbed.

RADIATION SOURCES

• Artificially produced radioisotopes are primarily used by industry because they can be produced so as to have much more radioactive energy that natural types.

• The three ways to produce radioisotopes are neutron activation, fission product separation, and charged particle bombardment.

• Elements that are atomically unstable and radioactive are called radioisotopes.

X-RAY GENERATORS

1.The three main parts to an x-ray generator setup are an x-ray tube, a high voltage power supply, and a control unit.

2.The X-ray generator provides three things that are required to produce X-rays, and they are a source of electrons, a means of acceleration, and a target for interaction.

• Radioisotopes, x-ray generation, and particle accelerators are different methods that generate radiation.

1.Devices that measure ionization are the most commonly used instruments for detecting radiation.

2.Three important words to help you minimize your exposure to radiation are time, distance, and shielding.

PRODUCING A RADIOGRAPH

• Describe how an image is produced on a radiograph.

• The making of a radiograph requires some type of recording mechanism. The most common device is film. A radiograph is actually a photographic recording produced by the passage of radiation through a subject onto a film, producing what is called a latent image of the subject.

PRODUCING A RADIOGRAPH

• A latent image is an image that has been created on the film due to the interaction of radiation with the material making up the film. This latent image is not visible to the naked eye until further processing has taken place. To make the latent image visible the film is processed by exposure to chemicals similar to that of photographic film.

DEVELOPING FILM

• An image storage medium consisting of a transparent base, usually coated on both sides with a radiation sensitive emulsion.

base

• a base for which the other materials are applied. The film base is usually made from a clear, flexible plastic such as cellulose acetate. This plastic is similar to what you might find in a wallet for holding pictures. The principle function of the base is to provide support for the emulsion. It is not sensitive to radiation, nor can it record an image.

DEVELOPING FILM

• The emulsion• The film emulsion and protective coating comprise

the other two components and are essentially made from the same material. They are applied to the film during manufacturing and usually take on a pale yellow color with a glassy appearance. Although they are made from the same material, they offer two distinct features to the film. These features are separated into the image layer of the emulsion, and the protective layer.

DEVELOPING FILM• The protective layer• The protective layer has the important function of protecting the softer

emulsion layers below.• The softer layers of the gelatin coating are technically known as the emulsion. An

emulsion holds something in suspension. It is this material in suspension that is sensitive to radiation and forms the latent image on the film. During manufacturing of the film, silver bromide is added to the solution of dissolved gelatin. When the gelatin hardens the silver bromide crystals are held in suspension throughout the emulsion. Upon exposure of the film to radiation, the silver bromide crystals become ionized in varying degrees forming the latent image. Each grain or crystal of silver bromide that has become ionized can be reduced or developed to form a grain of black metallic silver. This is what forms the visible image on the radiograph. This visible image is made up of an extremely large number of silver crystals each is individually exposed to radiation but working together as a unit to form the image.

DEVELOPING FILM

• 1. To begin the process of converting the latent image on the radiograph to a useful image we first expose the film to the developer solution.

• 2.The function of the stop bath is to quickly neutralize any excessive development of the silver crystals.

• 3. The third step in development is the fixer. Its function is to permanently fix the image on the film.

DEVELOPING FILM

• 4. Once the film has been properly developed, it is then rinsed in water and dried so that it may be visually examined.

summary

1.The three main part to radiographic film are the base, the emulsion, and the protective coating.

2.Steps in developing film include developing, stopping the developer, fixing, rinsing and drying.