Rutherford scattering experiments

FIGURE 2.5 The Rutherford scattering experiment, (a) When a beam of alpha particles is directed at a thin gold foil, most particles pass through the foil undeflected, but a small number are deflected at large angles and a few bounce back toward the particle source. 

Figure 5-4 The Rutherford scattering experiment. A narrow beam of a-particles from a radioactive source was directed at a very thin sheet of gold foil. Most of the particles passed right through the gold foil brown). Many were deflected through moderate angles shown in red). These deflections were surprising, but the 0.001% of the total that were reflected at acute angles shown in blue) were totally unexpected. Similar results were observed using foils of other metals.

In a Rutherford scattering experiment atoms of 150 keV are used to bombard a thin Ni foil having a surface density of 67 X 10 g cm. The detector subtends a solid angle of 1.12 x 10 sr and detects 4816 deuterons out of a total of 1.88 x lo incident on target. Calculate (a) the differential cross-section (in bams), (b) What is the distance between target and the solid state detector, which has a surface area of 0.2 cm ... 

The cross-section, as its name suggests, is the effective area for collision. The cross-section of a spherical target is cr = Trr. In aiming a beam of particles at a target (which is much smaller than the beam), as in the Rutherford scattering experiment, the scattering process is treated statistically in terms of the cross-section for interaction with a nucleus. 

Describe and/or interpret the Rutherford scattering experiments and the nuclear model of the atom. 

Planetary model of the atom Rutherford scattering experiments... 

How can we account for the fact that, in the Rutherford scattering experiment, some of the alpha particles were deflected from their paths through the gold foil, and some were even bounced back at various angles ... 

What major conclusions were drawn from the Rutherford scattering experiment ... 

Rusting, 45, 85, 405 Rutherford, Ernest, 244 Rutherford nuclear atom, 244 scattering experiment, 244 Rutile, 401... 

Schematic view of Rutherford s scattering experiment. When a beam of positively charged helium particles was shot at a thin gold foil, most of them passed through without much effect. Some, however, were reflected backward.

Schematic drawing of an atom, showing a central, positive nucleus surrounded by a cloud of electrons. This model of the atom is consistent with the results of Rutherford s scattering experiments.

C02-0042. Describe the scattering pattern that would have been observed in Rutherford s experiment if atoms were like chocolate chip cookies. 

Recall from Chapter 2 what Rutherford s scattering experiment demonstrated. Every atom contains a tiny central core where all the positive charge and most of the mass are concentrated. Subsequent experiments showed that while the masses of nuclei can have various values, the mass of every nucleus is at least 1800 times larger than the mass of the electron. Thus, more than 99.9% of the mass of an atom is contained in its nucleus. 

Chemists were not able to use their methods to determine the structure of the atom. The discovery of radioactivity by Henri Becquerel and the work of Marie and Pierre Curie showed, however, that heavy elements were not stable. The earlier postulate of their indivisibility could no longer be maintained. In 1906 Ernest Rutherford made the next horrorif-ic revelation his scattering experiments showed that the atom was almost empty. A tiny nuclear mass was circled by electrons at a large distance. For comparison, if the nucleus were the size of a cherry pit and were placed in the center of a football field, the electrons would be circulating in the back rows of the stadium. If the nucleus were the size of a football, the first electrons would be circling it at a distance of one kilometer. Between them would be absolute emptiness. 

Sir Ernest Rutherford (1871-1937 Nobel Prize for chemistry 1908, which as a physicist he puzzled over) was a brilliant experimentalist endowed with an equal genius of being able to interpret the results. He recognized three types of radiation (alpha, beta, and gamma). He used scattering experiments with alpha radiation, which consists of helium nuclei, to prove that the atom is almost empty. The diameter of the atomic nucleus is about 10 000 times smaller than the atom itself. Furthermore, he proved that atoms are not indivisible and that in addition to protons, there must also be neutrons present in their nucleus. With Niels Bohr he developed the core-shell model of the atom. 

A little earlier, in 1903 (Lenard 1903), Philipp Eduard Anton von Lenard (1862-1947) had carried out some scattering experiments in which he bombarded various metallic foils with high-energy cathode rays. He observed that the majority of electrons passed through the foils undeflected - from this he concluded that the majority of the volume occupied by the metallic atoms must be empty space. This idea was more fully developed by Rutherford (1911), who proposed the nuclear model of the atom which, despite much further elaboration, we still use today for the most basic explanations. 

Rutherford based his model on a refinement of von Lenard s electron scattering experiment carried out by Geiger and Marsden in 1909. They used u-particles, which were known to be much heavier than electrons (more than 7000 times heavier), instead of electrons as the shells . Using a thin gold foil, they observed that almost all the u-particles went through the foil undeflected, but approximately 1 in 20 000 was reflected back towards the radioactive source. Rutherford, in describing this experiment, is widely quoted as saying It was almost as if you fired a 15 inch shell at a piece of tissue paper and it came back and hit you, but the source of this quote is obscure. 

An estimate of die size of the proton and an understanding of the structure of the hydrogen atom resulted from two major developments in atomic physics the Rudierford scattering experiment (1911) and the Bohr model of die atom (1913). Rutherford showed that the nucleus is vanishingly small compared to the size of an atom. The radius of a proton is on the order of 10-13 centimeter as compared with atomic radii of 10-3 centimeter, Thus, the size of a hydrogen atom is determined by the radius of the electron orbits, but the mass is essentially that of the proton,... 

PROBLEM 2.2 The gold foil Rutherford used in his scattering experiment had a thickness of approximately 0.0002 in. If a single gold atom has a diameter of 2.9 X 10-8 cm, how many atoms thick was Rutherford s foil ... 

The planetary model of the atom was proposed by Rutherford in 1912 following the a particle scattering experiments of Geiger and Marsden, which showed most the mass of an atom to be concentrated in a tiny positive nucleus. The orbiting of light electrons resembles the problem of planetary motion first solved by Newton. 

This result is that used by Rutherford in his original a-scattering experiments. Note that cosec(.x) = 1 /sin(.x), cosec-is the inverse function, and... 

Rutherford published the results of these scattering experiments in mid-1909, and it seemed as if publication of the discovery of the nuclear atom would soon follow. But the plum pudding model remained the working model of the atom. Through the rest of 1909 and most of 1910, Rutherford pondered. 

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