GENERAL INFORMATION ON THE STRUCTURE OF MATTER, X-RAY PRODUCTIONS AND PROPERTIES
INTRODUCTION :
Wilhelm Conrad Röntgen discovered electromagnetic rays in 1895 which he called: X-Rays.
The X-ray is an electromagnetic wave produced by the deceleration of electrons outside the atomic nucleus.
CONSTITUTION OF THE MATTER:
Matter is made up of atoms. The atom itself is made up of:
a (+) (positively) charged nucleus composed of elementary particles, the main ones being: positively charged protons (electric charge) and neutrons, which have a neutral charge. Protons and neutrons have the same mass, and the sum of their masses represents the mass of the nucleus, which is close to that of the atom.
(-) (negatively) charged electrons, which have a mass 1850 times lower than neutrons and protons.
The atom therefore reproduces a solar system with the central nucleus charged + around which the electrons gravitate in peripheral orbits.
The atom is electrically neutral, because the number of protons is equal to the number of electrons.
We define by: A: the mass number = number (protons + neutrons) = number of nucleons
Z: atomic number = number of electrons
A – Z = number of neutrons
X-RAYS:
X-rays are electromagnetic radiations
They are made up of “photons” which are small particles without an electrical charge, carrying a quantity of energy E.
They are characterized by:
-a wavelength λ
-its frequency F
-his energy E
-its intensity I
-its propagation speed v or c
X-RAY PRODUCTION
X-rays are produced in an X-ray tube (Coolidge tube) which is a vacuum tube containing a filament heated by a low voltage and an anode brought to a high positive voltage.
X-rays are photons that are emitted if a beam of accelerated electrons hits a material target: nuclei and electrons. These two interactions are of two types: Braking & Collision.
a) Braking: interaction between incident electron beams and nuclei giving rise to braking radiation which is a continuous energy spectrum: X-ray tube.
b) Collision: interaction between incident electron (ei) and medium electron (em). This gives rise to characteristic radiation (characteristic line spectrum of the target).
PROPERTIES OF X-RAYS
There are some properties of X-rays that must be known to understand the medical application of X-rays.
1-RX is able to penetrate and cross the human body. During this crossing the beam undergoes a weakening which corresponds to ABSORPTION.
ABSORPTION depends on:
* the thickness of the region crossed. It is all the more important as the thickness is important.
* of the nature of the absorbing body. It increases with the atomic number of the absorbing elements.
* of the wavelength. It varies in the same direction as the wavelength.
– Long wavelength radiation is very absorbable and therefore not very penetrating: it is a SOFT RADIATION, of low energy.
– Short wavelength radiation is poorly absorbable and therefore very penetrating: it is HARD RADIATION, with high energy.
2-Diffusion: X-rays produce secondary radiation in the bodies they pass through. This radiation is essentially composed of diffused radiation which is all the more important as the irradiated volume is large and the KV used are high. This radiation occurs in all directions and represents parasitic radiation which will attenuate the contrast of the image of the shot.
3-They cause the illumination of certain mineral salts (scopy or brightness amplifier and reinforcing screens).
4-They cause the photographic emulsions in the image to darken.
5-They spread in a straight line and in all directions.
6-RX have biological effects:
a-At the molecular level:
-DNA damage by direct effect or by free radicals
-chromosomal abnormalities
– alteration of the permeability of the cell membrane.
-modification of enzymatic activity.
-cell death
-neoplastic transformation
b-Pathological effects in humans:
-The skin:
medium to high dose: erythema; desquamation; blistering; alopecia.
Late: dermal atrophy, vascular lesions, necrosis, cancer
-the eye: posterior subcapsular radio-induced cataract (1-10 years)
-Gonads: testicles and ovaries: sterility
– Bones: radionecrosis – Fracture of the neck of the femur
-Lung: retractile sd (radiation lung)
-Kidney: radionephritis responsible for renal failure.
-Liver: progressive hepatitis.
-Feto-embryonic effects: especially embryogenesis
-Genetic effects: mutation by alteration of the chromosome
Hematopoietic tissue:
¨¨¨low doses: slight decrease in precursor elements with recovery (1st week)
¨¨medium or high doses: significant cellular depletion with recovery (long + incomplete)
7-Optical properties:
a-reflection
Change of direction of the incident ray at a reflecting surface.
The angle of reflection is equal to the angle of incidence.
Intensity of reflected R < incident R
b-refraction:
Bending of an incident ray at the interface between two media of different speed or density
c-Diffraction:
This is the behavior of waves when they encounter an obstacle or an opening
CONCLUSION
X-rays are radiations with characteristics (wavelength-intensity-energy-frequency).
X-rays are produced by the X-ray tube.
They undergo the phenomena (absorption-diffusion-ionization)
X-rays can be extremely dangerous in high doses, they are used daily to treat patients .
GENERAL INFORMATION ON THE STRUCTURE OF MATTER, X-RAY PRODUCTIONS AND PROPERTIES
Early cavities in children need to be treated promptly.
Dental veneers cover imperfections such as stains or cracks.
Misaligned teeth can cause difficulty chewing.
Dental implants provide a stable solution to replace missing teeth.
Antiseptic mouthwashes reduce bacteria that cause bad breath.
Decayed baby teeth can affect the health of permanent teeth.
A soft-bristled toothbrush preserves enamel and gums.