11.01.06
Radiation Part Due
Hope everyone had a nice Halloween yesterday. I saw the party animals prancing around last night, and even found that Snow White has a nasty habit of smoking. She must not have noticed me watching her light up, but now I know her deep dark secret. . .
So back on track, I’d like to continue with the topic of radiation. Radiation has likely existed since the beginning of creation. So really, the history of radiation mainly deals with the “discovery” of it. Wilhelm Röntgen, a German physicist, March 27, 1845-February 10, 1923, is known to have discovered radiation (or as he called it–x-ray) in 1895. In 1895 he was studying the phenomena accompanying the passage of an electric current through a gas of extremely low pressure. This study involving cathode-ray tubes, lead him to the discovery of different kinds of rays. With his experiments with cathode-ray tubes, he noticed that as the tube began to glow the crystals of barium platino cyanide scattered on the table began to give off light when the tube glowed. Further tests showed that paper, wood, aluminum and some other materials were transparent to these strange rays. Even at a distance of 2 meters, the rays were still penetrating a wooden door. Roentgen believed these rays were invisible electro-magnetic rays, which under certain conditions could stimulate certain materials to fluorescence. He exposed various things to these strange new rays, among them his weight box, a wire coil in a box and many different materials. He found that lead glass is permeable to light but not to these rays, while wood stopped the light, but the rays passed through it. He found that it affected photographic plates, and, since it did not noticeably exhibit any properties of light, such as reflection or refraction, he mistakenly thought the rays were unrelated to light.
Roentgen found that he could see the image of the bones in his hand when he held it between the tube and the screen. He eventually discovered that he could capture such images on film. A subsequent study he performed with these newly discovered rays resulted in the picture to the right, of Rudolph Albert von Kölliker’s hand. It is also said that Roentgen presented an x-ray of his wife’s hand, which impressed the public. However, it’s not clear to me, if the x-rayed hand on the right truly belongs to Rudolph Albert von Kolliker, or Roentgen’s wife. The net seems to have this same picture for the discription of both. Notice the circular dark spot that appears to be a ring. Nevertheless, this discovery enabled man to look inside the human body for the first time. Roentgen called the phenomenon X-radiation, though it also became known as Rontgen radiation. The “x” referred to “unknown.”
In 1896, soon after the discovery of x-ray, Henri Becquerel, a French physicist, 1852-1908, was using naturally fluorescent minerals to study the properties of x-rays. He wanted to know if some glow-in-the-dark crystals he had emitted x-ray. Becquerel gathered crystals of potassium uranyl sulfate that had been exposed to bright sunlight. These crystals have the ability to glow in the dark after they have been exposed to sunlight. He exposed potassium uranyl sulfate to sunlight and then placed it on photographic plates wrapped in black paper. The results of his photographic plates revealed images that were strong and clear, proving that the uranium emitted radiation without an external source of energy such as the sun. Becquerel had discovered radioactivity. But, at this point it was still unknown where the rays came from. From this Becquerel concluded that potassium uranyl sulfate emits some kind of penetrating rays, and caused him to wonder what kind of rays were coming out of the crystals. The crystals constantly gave off energetic rays depsite being melted, dissolved, and recrystallized. Physical radiation units, which measures the activity of the radiation source, became called the “becquerel”(Bq) in an SI unit. A radiation source with an activity of one becquerel has one disintegration per second.
In 1898, Marie Sklodowska Curie, 1867-1934, and her husband, Pierre, 1859-1906 (both scientists in France), discovered another element that seemed to defy the law of energy conservation–polonium and radium. They coined the word “radioactivity” to describe the spontaneous emission of the penetrating rays. It was the Curies who concluded that radioactivity is an atomic property that does not depend on how the atoms are chemically bonded. In 1912, the Curie standard was made. The quantity and unit for radioactivity would be called “Curie” in memory of Pierre Curie. One curie is the number of disintegrations per second in a one-gram sample of radium; one curie is 3.7 x 10^10 becquerel (Bq).
Ernest Rutherford, an English physicist, 1871-1937, is known to have invented the language which is used to describe the concepts of the atom and the phenomenon of radioactivity. It was Rutherford who coined the terms alpha, beta, and gamma rays to classify various forms of “rays” which were poorly understood at his time (alpha and beta rays are particle beams, while gamma rays are a form of high-energy electromagnetic radiation. He also observed that the intensity of radioactivity fell off with time, and named the halving time the “half-life. Particles named and characterized by him include the alpha particle, beta particle, and proton. It was Rutherford’s research that proposed the atom was “nuclear.”
Ernest Rutherford and Marie Curie were awarded the Nobel Prize in Physics in 1903. Rutherford received the Nobel Prize in 1908 in chemistry for this discovery of the half-life of radioactivity.
To be continued in the next post on radiation. Toodles!
Marlakins 
