3. Explain in brief - Goldstein's experiment which led to the discovery of the proton and - Lord Rutherford's experiment which led to the discovery of the atomic nucleus.
Answers
DISCOVERY OF PROTON
.The concept of a hydrogen-like particle as a constituent of other atoms was developed over a long period. As early as 1815, William Prout proposed that all atoms are composed of hydrogen atoms (which he called "protyles"), based on a simplistic interpretation of early values of atomic weights (see Prout's hypothesis), which was disproved when more accurate values were measured.
Ernest Rutherford at the first Solvay Conference, 1911
Proton detected in an isopropanol cloud chamber
In 1886, Eugen Goldstein discovered canal rays (also known as anode rays) and showed that they were positively charged particles (ions) produced from gases. However, since particles from different gases had different values of charge-to-mass ratio (e/m), they could not be identified with a single particle, unlike the negative electrons discovered by J. J. Thomson. Wilhelm Wien in 1898 identified the hydrogen ion as the particle with the highest charge-to-mass ratio in ionized gases.[13]
Following the discovery of the atomic nucleus by Ernest Rutherford in 1911, Antonius van den Broek proposed that the place of each element in the periodic table (its atomic number) is equal to its nuclear charge. This was confirmed experimentally by Henry Moseley in 1913 using X-ray spectra.
In 1917 (in experiments reported in 1919 and 1925), Rutherford proved that the hydrogen nucleus is present in other nuclei, a result usually described as the discovery of protons.[14] These experiments began after Rutherford had noticed that, when alpha particles were shot into air (mostly nitrogen), his scintillation detectors showed the signatures of typical hydrogen nuclei as a product. After experimentation Rutherford traced the reaction to the nitrogen in air and found that when alpha particles were introduced into pure nitrogen gas, the effect was larger. In 1919 Rutherford assumed that the alpha particle knocked a proton out of nitrogen, turning it into carbon. After observing Blackett's cloud chamber images in 1925, Rutherford realized that the opposite was the case: after capture of the alpha particle, a proton is ejected, so that heavy oxygen, not carbon, is the end result i.e. Z is not decremented but incremented. This was the first reported nuclear reaction, 14N + α → 17O + p. Depending on one's perspective, either 1919 or 1925 may be regarded as the moment when the proton was 'discovered'.
However, Rutherford also had in mind the word protyle as used by Prout. Rutherford spoke at the British Association for the Advancement of Science at its Cardiff meeting beginning 24 August 1920.[15] Rutherford was asked by Oliver Lodge for a new name for the positive hydrogen nucleus to avoid confusion with the neutral hydrogen atom. He initially suggested both proton and prouton (after Prout).[16] Rutherford later reported that the meeting had accepted his suggestion that the hydrogen nucleus be named the "proton", following Prout's word "protyle".[17] The first use of the word "proton" in the scientific literature appeared in 1920.[18]
Recent research has shown that thunderstorms can produce protons with energies of up to several tens of MeV.[19][20]
Protons are routinely used for accelerators for proton therapy or various particle physics experiments, with the most powerful example being the Large Hadron Collider.
In a July 2017 paper, researchers measured the mass of a proton to be 1.007276466583+15
−29 atomic mass units (the values after the number being the statistical and systematic uncertainties, respectively), which is lower than measurements from the CODATA 2014 value by three standard deviations.
DISCOVERY OF NUCLEUS
he nucleus was discovered in 1911, as a result of Ernest Rutherford's efforts to test Thomson's "plum pudding model" of the atom.[9] The electron had already been discovered by J.J. Thomson himself. Knowing that atoms are electrically neutral, J.J.Thomson postulated that there must be a positive charge as well. In his plum pudding model, Thomson suggested that an atom consisted of negative electrons randomly scattered within a sphere of positive charge. Ernest Rutherford later devised an experiment with his research partner Hans Geiger and with help of Ernest Marsden, that involved the deflection of alpha particles (helium nuclei) directed at a thin sheet of metal foil. He reasoned that if J.J Thomson's model were correct, the positively charged alpha particles would easily pass through the foil with very little deviation in their paths, as the foil should act as electrically neutral if the negative and positive charges are so intimately mixed as to make it appear neutral. To his surprise, many of the particles were deflected at very large angles. Because the mass of an alpha particle is about 8000 times that of an electron, it became apparent that a very strong force must be present if it could deflect the massive and fast moving alpha particles..
I read in class 2 I don't know who is Rutherford