Radioactive Material:
When an unstable Isotopes is decaying or disintegrating, tiny particles traveling at high speeds are emitted and / or energy in the form of waves is given off.
All radiation comes from the nucleus of the atoms.
The following particles and energies are released from the radioactive atom.
Author: Micro NDT
Radioactive Material:
When these excess neutron do not upset the balance of the nucleus. Then this new isotope is said to be “ Stable”
When these excess neutrons do upset the balance of the nucleus this isotope is unstable and will disintegrated or decay in to a more stable form.
Unstable Atoms are said to be radioactive.
Some radioactive isotopes are found in nature such as radium and uranium.
Radioactive Material:
Many isotopes of the various elements occur in natural but artificial isotopes are now common. Artificial isotopes are created by Bombarding an element with an excess of neutrons. This is done in a nuclear reactor where the atomic fission process gives off large numbers of free neutrons.
Identification of Elements:
Atomic Number or Z number is the number of protons in the nucleus of the atom and is used for identifying basic elements. Therefore an atom of beryllium with 4 protons would have a “Z” number of 4.
Basic elements may also be identified by their weight.
Mass number or “A” number is combination of protons and Neutrons. ( Heavy Parts of the Atom)
Each atom is then assigned a number equal to the total number of protons and neutrons in the nucleus. As shown below the beryllium atom has a “Z” number of 4 and an “A” number of 9.
Structure of Atom:
All Atoms are composed of three basic particles.
1. Proton : Has a positive charge and is relatively heavy.
2. Neutron : About the same size and weight as the proton but has no electrical charge.
3. Electron : Very light particle about 1/1840 of the weight of a proton it has a negative charge.
The number of the particle determines the kind of atoms it is.
There are over 100 different kind of atoms know and they are called elements and given a name oxygen, copper and lead and some common element.
Element or combinations of elements ( Molecules) from all the things we see every day living.
For example there are billions of atoms in the tips of a pencil with over 99.99 % of each atoms being empty space.
A very simple atom is that of the element Helium.
Factor Affecting Film Definition:
Film Graininess also affects the definition of the radiography while large grain films are often used to reduce exposure time, the small grain films provide the best definition
Radiography Sensitivity:
Sensitivity of radiography is a function of the “ Contrast “ and the “ Definition “ of the radiography. Contrast is the comparison between film densities for different areas of the radiography .
Sensitivity of radio graph is a function of the “ Contrast “ and the “ Definition “ of the radiography. Contrast is the comparison between film densities for different areas of the radiography
Properties Of X-Ray & Gamma Rays:
The formation of an image on the film depends upon the amount of radiation received by different section of the film. As below. A discontinuity such as a void represents a thickness difference in the specimen and will appear as a dark spot on the developed film.
Definition in Radiography:
Definition is the line of demarcation between area of different densities. If the image is clear and sharp the radiography us said to have good definition as shown below.
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.
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