25: Basics of Radiation Physics

Basics of Radiation Physics

Ravikiran Ongole

Pioneers in Dental Radiology

Wilhelm Conrad Röentgen (1845–1923)

Wilhelm Röentgen, the physicist from Germany is considered the father of diagnostic radiology. Röentgen discovered X-rays in 1895.

Personal life and early years

Wilhelm was born to a German father Friedrich Conrad Röentgen and Dutch mother Charlotte Constanze on March 27th, 1845 in the small town of Lennep in Rhineland. When Röentgen was 16 years old he enrolled in Utrecht Technical School, Netherlands. In 1868, he obtained a diploma in mechanical engineering from the Polytechnic School in Zurich. Under the tutelage of AEE Kundt, Wilhelm studied the properties of gases and obtained a doctoral degree in 1869. After obtaining his PhD, he worked as Kundt’s assistant at the University of Würzburg and later elevated to the post of an associate professor in theoretical physics. Wilhelm married Anna Ludwig in 1872. She was the daughter of an inn-keeper and 6 years elder to him. His wife died in 1919, following a prolonged illness and Wilhelm died due to intestinal cancer at the age of 73 years on February 10th, 1923. They were buried in Giessen.

Recognition and awards

The University of Würzburg appointed Röentgen as professor of physics in 1888. Just 6 years later in 1894, he was chosen as the Rector of the same university. After serving the University of Würzburg for 6 years as Rector, he took over as Director of a new physical institute in the University of Munich. For his outstanding work, Röentgen was awarded an honorary MD degree by the University of Würzburg. He was awarded the Rumford Gold Medal from the Royal Society (1896) and a gold medal from the Franklin Institute of Philadelphia. He was honored with the first Nobel Prize in Physics in 1901. The International Union of Pure and Applied Chemistry (IUPAC) in honor of Röentgen, named element number 111 as roentgenium (Rg) in 2004.

Publications on X-rays

1. ‘On a New Kind of Rays, A Preliminary Communication’. Journal of Würzburg Physical-Medical Society, December 28, 1985.

2. ‘On a New Kind of Rays, Continued’. Journal of Würzburg Physical-Medical Society, March 9, 1896.

3. ‘Further Observations on a New Kind of Rays’. Journal of Prussian Academy of Science, March 10, 1897.

William Herbert Rollins (1852–1929)

William Herbert Rollins was an American scientist and dentist. He was a pioneer in radiation protection and is known as the father of radiation protection. It is believed that he had published over 200 scientific articles regarding the hazards of radiation. Rollins, although a practicing dentist, also had a medical degree from Harvard Medical School. He called X-rays ‘X-light’ and documented them extensively in 1904. He is called the ‘Forgotten Man’ of dentistry. William Rollins proposed the use of filters to remove the low energy X-rays from the primary beam and introduced collimation. He recommended a long targetfilm distance to improve image quality. He pioneered the sandwiching of the X-ray film between two intensifying screens to increase the film speed. Dr Rollins advocated the need to determine a safe and harmless dose of radiation. In 1901, he advocated the use of leaded glasses for radiation personnel and a lead shield to cover all areas on the patient’s body that were not being imaged. Rollins also felt the need to construct a lead hood that would cover the X-ray tube head.

Howard Riley Raper (1887–1978)

In 1909, Dr Howard Raper, was the first to introduce radiology as a subject in the dental school. He also had three other ‘firsts’ to his credit—first Professor of Radiology, first academician to teach dental radiology and published the first textbook dealing with oral radiology titled Elementary and Dental Radiography, in 1913. In 1917, he proposed the first model of angle meter used with a chart of vertical angles for various teeth to avoid distortion. In 1925, in co-operation with Eastman Kodak Company, Dr Raper developed the bitewing technique for the detection of interproximal caries.

Weston A Price (1870–1948)

Weston Andrew Valleau Price was a dentist known primarily for his theories on the relationship between nutrition, dental health, and physical health. Dr Price, in 1897, a founding member of the American Roentgen Ray Society, designed and patented lead-lined gloves for protection against X-ray burns, but placed his innovation in the public domain instead of commanding fees from users. In 1900, Price designed a celluloid-based dental film. In 1904, he proposed two techniques for film positioning in the oral cavity, namely, the paralleling technique and the bisecting angle technique.

Edmund C Kells (1856–1928)

Edmund Kells was born in New Orleans, Louisiana, to a dentist Charles E Kells. He became a dentist, researcher, and inventor. His experiments caused the loss of most of his left arm. In 1899, he set up the first X-ray laboratory (The New Orleans X-Ray Laboratory) for radiographs and fluoroscopic examinations. He demonstrated the radiograph of chest and hip, a bullet in the head and the measurement of a root canal. He hired the first acknowledged dental assistant—Malvina Cuera, before which, his wife used to help him to mix materials and take the X-rays. In 1986, Edmund Kells and Brown Ayres devised a technique for radiographing the teeth and jaws. Dr Kells, in Dental Cosmos, mentioned the importance of keeping the film and object at right angles to the source using a film holder. In 1903, he introduced processing tanks and time-temperature processing. In 1909, Kells cut, wrapped and used rolltype photographic film.

Friedrich Otto Walkhoff (1860–1934)

Friedrich Otto Walkhoff was a Berlin dentist, a pioneer of dental X-ray diagnostics and a dedicated fighter for civil interests of dentists. It was barely 14 days after the announcement of the discovery of roentgen rays that Walkhoff wrapped a photographic glass plate in a routinely used rubber dam material and held it with his teeth. He then laid still on the floor for an X-ray exposure that lasted a full 25 minutes. This was considered the first dental radiograph. A year later, he managed to take extraoral radiographs with an exposure time of 30 minutes.

Gordon Fitzgerald (1907–1981)

In the 1940s, Dr Fitzgerald designed the long cone for the dental X-ray machine. He published four papers on long cone technique in the Journal of American Dental Association between 1947 and 1950.

Frank Van Woert (1856–1927)

Dr Frank Van Woert is credited for his work on the use of films, film holders and processing of films. He was the first to use films as image receptors which were developed by Kodak. He also engineered a metallic holder which could be used to hold films. His other inventions include the daylight film processing tank, an improved angle meter for bisecting angle technique and an automated exposure timer switch.

Franklin W McCormack

Franklin McCormack, an American medical X-ray technician, employed paralleling technique principles in intraoral radiography. He wrapped the film with a black paper and used a flat metal plate to make the film packet rigid. He was also known for using bite blocks and hemostat as film holders to stabilize the film in the mouth.

Readers are encouraged to visit the website of the roentgen museum for more information on the chronology of events in origin of radiology (http://www.roentgenmuseum.de).

Films and Processing of Films

1896:	The exposure time varied between 5 and 15 minutes and the processing time varied between 30 and 60 minutes
1913:	Hand-wrapped, moisture-proof, dental packet containing two films
1919:	First machine-wrapped dental X-ray film packet called Regular film (Kodak) with emulsion on only one side
1920:	Film hangers were introduced
Early 1920s:	Cellulose nitrate as base, emitted poisonous gases on burning
1924:	Radia-tized film (Kodak) with double side emulsion
1924:	Non-flammable cellulose triacetate film base
1940:	Ultra speed (improved Radia-tized film) doubled the film speed of the 1924 film
Early 1960s:	Polyester film base
1980s:	Ektaspeed film introduced by Kodak

Fundamentals of Radiation Physics

Radiation

Radiation is the transmission of energy through space and matter. There are two basic forms of radiation, namely, particulate radiation and electromagnetic radiation.

Particulate Radiation

Particulate radiation consists of a stream of atomic or subatomic particles that transmit kinetic energy by means of their small masses moving at very high velocities. They may carry a positive charge (alpha particles), negative charge (beta particles) or no charge (neutrons). Examples of particulate radiation are alpha rays, beta rays and cathode rays.

Electromagnetic Radiation

There are two concepts to understand electromagnetic radiation, namely, classical theory and modern quantum theory. According to the classical theory, the flow of energy at the universal speed of light through free space or through a material medium is in the form of the electric and magnetic fields that make up electromagnetic waves such as radio waves, visible light, and gamma rays. In such a wave, time-varying electric and magnetic fields are mutually linked with each other at right angles and perpendicular to the direction of motion (Figure 1).

Figure 1 Electromagnetic spectrum

In terms of the modern quantum theory, electromagnetic radiation is the flow of photons (also called light quanta) through space. Photons are packets of energy (hν) that always move with the universal speed of light. The symbol h is Planck’s constant, while the value of ν is the same as that of the frequency of the electromagnetic wave of classical theory. The spectrum of frequencies of electromagnetic radiation extends from very low values over the range of radio waves, television waves, and microwaves to visible light and beyond to the substantially higher values of ultraviolet light, X-rays, and gamma rays.

Ionizing and Non-ionizing Radiation

Radiation has a wide range of energies that form the electromagnetic spectrum (Figure 2). The spectrum has two major divisions:

Figure 2 Various energy levels of the electromagnetic spectrum

1. Non-ionizing radiation

2. Ionizing radiation.

Radiation that has enough energy to move around atoms in a molecule or cause them to vibrate, but not enough to remove electrons, is referred to as ‘non-ionizing radiation’. Examples of this kind of radiation include radio waves, infrared, ultraviolet, visible radiation and microwaves.

Radiation that falls within the ‘ionizing radiation’ range has enough energy to remove tightly bound electrons from atoms, thus creating ions.

Production of X-rays

X-ray photons are produced within the X-ray tube by accelerating electrons with a high voltage and allowing them to collide with a metal target. This collision results in the production of X-rays by two basic mechanisms: Bremsstrahlung radiation and characteristic radiation.

Bremsstrahlung radiation is the major source of X-ray photons from the X-ray tube. Char/>

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