43_decay - Lesson 43: Alpha, Beta, & Gamma Decay The...

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The late 1800s and early 1900s were a period of intense research into the new “nuclear” realm of physics. In 1896 Henri Becquerel found that a sample of uranium he was doing experiments with had a special property. After he was done with a series of experiments using the uranium, he put it into a drawer with a photographic plate. A photographic plate is a piece of glass covered in chemicals. It was used as the “film” in old style cameras. Becquerel was surprised to find out later that the uranium had caused the plate to be fogged up, as if it had been exposed to light. He correctly assumed that the uranium was emitting radiation similar to visible light. He was even able to show that a magnetic field seemed to change the direction that this invisible radiation traveled. Shortly after this, Marie and Pierre Curie isolated two other radioactive elements, polonium and radium. No matter what physical or chemical stresses they placed on these elements, they continued to emit radiation just like the uranium that Becquerel had used. Since nothing they did could stop the radioactivity, they believed that the radioactivity must come from deep within the atom, in what we would today call the nucleus. We now know that radioactivity actually results from the decay (disintegration) of an unstable nucleus. This process fundamentally changes the nucleus of the element itself. The radiation that we measure is evidence of events happening inside the nucleus. In many cases this will actually result in the element changing to a different element, a process called transmutation . The reason these decays happen is because they result in more stable nuclei. Ernest Rutherford and others started studying the radiation that was emitted by these elements. He found three distinct forms of radiation, originally divided up based on their ability to pass through certain materials and their deflection in magnetic fields. .. Alpha ( α ): could barely pass through a single sheet of paper. Deflected as a positive particle in a magnetic field. Beta ( β ): can pass through about 3mm of aluminum. Deflected as a negative particle in a magnetic field. * Gamma ( γ ): can pass through several centimetres of LEAD! Not deflected in a magnetic field. 5/26/2010 © studyphysics.ca Page 1 of 7 / Section 16.2 Illustration 1: An early camera with photographic plates. Did You Know? In 1934 Marie Curie died of leukemia from years of exposure to radioactive elements. She received two Nobel Prizes, in Physics and Chemistry. The element polonium that she helped discover is named after her homeland, Poland. * Because of our modern understanding of what can happen in decays, we will have to examine two different kinds of beta decay later.
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Alpha Decay The reason the alpha radiation has such a hard time even passing through a piece of paper is because it is not a form of EMR like we might expect. It is actually the nuclei of a helium atom
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43_decay - Lesson 43: Alpha, Beta, & Gamma Decay The...

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