![]() ![]() He was studying uranium salts as part of an investigation into fluorescence. They didn't give helium nuclei, electrons and photons fancy names to make it difficult for introductory physics students they did it because they had no idea what they were looking at!īy the way, the tale of Becquerel's initial discovery is a classic. You can tell how mysterious the whole thing was by the classification scheme of the different types of radiation: alpha, beta, and gamma are simply the first three letters of the Greek alphabet. Though the Nobel committee didn't know it at the time, spontaneous radioactivity was the first observed signature of the weak nuclear force, one of the four fundamental forces of nature. Depending on the particular isotope, several types of radiation could be emitted: alpha radiation (a helium nucleus) beta radiation (an electron) gamma radiation (a photon) a neutron or two (relatively) heavy daughter nuclei, if the decay is via spontaneous nuclear fission. To do this, the unstable nucleus must jettison some of the excess material and energy this constitutes radiation. In the same way that a pencil balanced on its tip will inevitably and spontaneously fall over, an unstable nucleus will eventually spontaneously decay to a lighter nucleus (transition to a heavier nucleus would require an input of energy). Some of these are more stable than others. This was the first Nobel Physics Prize to be split between two people, and the committee consequently took pains to prove that their decision was "not only justified, but just," observing that this project represented a perfect marriage between theory and experiment.Īnswer: Its nucleus is unstable, and tends to decay to a lighter nucleus by releasing radiation.Īn element is defined by the number of protons in its nucleus different isotopes mean different numbers of neutrons in the nucleus. Nevertheless, it was very fruitful as the basis for the investigations that would eventually lead to quantum mechanics and a true understanding of emission spectra. The theory was beautiful, although we now know that it is incorrect. The field split the degeneracy, inducing a slight energy change in the different oscillations that made them just distinguishable from each other. Lorentz had been working on incorporating electrons into classical electrodynamics, and he came up with a clever explanation for the phenomenon: electrons were oscillating back and forth inside the atom, giving off light in the process, and a magnetic field disturbed their paths and changed the frequency of the light. He went to his colleague Lorentz, a theorist who was also instrumental in developing special relativity - and who had proposed these experiments himself. Zeeman observed a curious effect: a single spectral line would split into two or more closely spaced lines in the presence of a magnetic field. ![]() We now understand that the spectral lines represent the energy difference between different electron states (since a photon is emitted when an electron drops in energy), but it was a grand mystery at the time: electrons had barely been discovered, and atomic nuclei were totally unknown! The locations, widths and separations of these lines were carefully catalogued, but their origins were unknown. In the late nineteenth century, scientists measuring atomic emission spectra - the range of light emitted from a certain type of atom - realized that, instead of looking like rainbows, the spectra consisted of narrow lines at particular wavelengths that were the same for each type of atom. He was one of many working in the field it was good luck (and good experimental instincts) that got him there first.Īnswer: Two or more states share the same energy, despite being physically different. Röntgen, a German physicist, discovered the X-ray in 1895 while performing experiments with vacuum tubes. An X-ray image is all about the contrast between high-density and low-density areas, which is why images of organs can be taken if they're first injected with a relatively high-density substance like iodine. Visible light has a relatively low energy, and it doesn't take a very dense material to block it at higher energies, X-rays pass right through skin, muscle and fat, and are stopped only by higher-density objects like bones and metal. Each photon carries a distinct energy, which defines its wavelength and hence its color the full range of possible photon energies defines the electromagnetic spectrum, which runs from radio waves at the low-energy end, to the visible range that our eyes can see, all the way up to ultraviolet, X-rays, and gamma rays. Answer: An X-ray is light that is more energetic than visible light.īasically, light can be understood as being made up of particles - photons - that are nothing more than bundles of energy.
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