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A 1910 paper [38] by Geiger, The Scattering of the α-Particles by Matter, describes an experiment to measure how the most probable angle through which an alpha particle is deflected varies with the material it passes through, the thickness of the material, and the velocity of the alpha particles. He constructed an airtight glass tube from ...
When infrared light of these frequencies strikes an object, the energy is reflected or transmitted. If the object is transparent, then the light waves are passed on to neighboring atoms through the bulk of the material and re-emitted on the opposite side of the object. Such frequencies of light waves are said to be transmitted. [10] [11]
Alpha (α) radiation consists of a fast-moving helium-4 (4 He) nucleus and is stopped by a sheet of paper. Beta ( β ) radiation, consisting of electrons , is halted by an aluminium plate. Gamma ( γ ) radiation, consisting of energetic photons , is eventually absorbed as it penetrates a dense material.
An opaque object is neither transparent (allowing all light to pass through) nor translucent (allowing some light to pass through). When light strikes an interface between two substances, in general, some may be reflected, some absorbed, some scattered, and the rest transmitted (also see refraction).
This suggested that alpha radiation is not a form of light but made of particles that lose kinetic energy as they pass through barriers. In 1902, Rutherford found that he could deflect alpha rays with a magnetic field and an electric field, showing that alpha radiation is composed of electrically charged particles.
One type had short penetration (it was stopped by paper) and a positive charge, which Rutherford named alpha rays. The other was more penetrating (able to expose film through paper but not metal) and had a negative charge, and this type Rutherford named beta. This was the radiation that had been first detected by Becquerel from uranium salts.
In order to detect trapped antihydrogen, ALPHA also includes a 'silicon vertex detector': a cylindrical detector composed of three layers of silicon strips. Each strip acts as a detector for the charged particles passing through. By recording how the strips are excited, ALPHA can reconstruct the traces of particles traveling through the detector.
If one places between the phosphorescent substance and the paper a piece of money or a metal screen pierced with a cut-out design, one sees the image of these objects appear on the negative ... One must conclude from these experiments that the phosphorescent substance in question emits rays which pass through the opaque paper and reduce silver ...