Guide Particles and Nuclei

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Atomic particles
Contents:
  1. What Is an Atom?
  2. Translators
  3. Physics of Particles and Nuclei | NCBS

FAQ Policy. About this Textbook This well-known introductory textbook gives a uniform presentation of nuclear and particle physics from an experimental point of view. Show all. Nuclear Stability Pages Povh, Bogdan et al. Scattering Pages Povh, Bogdan et al. Quarkonia Pages Povh, Bogdan et al. Mesons Pages Povh, Bogdan et al. Baryons Pages Povh, Bogdan et al. Nuclear Thermodynamics Pages Povh, Bogdan et al. Show next xx. Journal catalogue: by title by subject by publisher. Open Access: What is Open Access?

Why Open Access? Open Access licenses How to publish your article. Impact Factor. Read online version. Matveev Publisher: Pleiades Publishing, Ltd. This experimental ansatz is the basis of modern nuclear and parti- cle physics. Systematic studies of nuclei became possible by the late thirties with the availability of modern particle accelerators.

But the fundamental building blocks of atoms - the electron, proton and neutron - were detected beforehand. A pre-condition for these discoveries were important technical developments in vacuum techniques and in particle detection. Before we turn to the global properties of nuclei from a modern viewpoint, we will briefly discuss these historical experiments. The first building block of the atom to be identified was the electron.

In Thomson was able to produce electrons as beams of free particles in discharge tubes. By deflecting them in electric and magnetic fields, he could determine their velocity and the ratio of their mass and charge. The results turned out to be independent of the kind of cathode and gas used. He had in other words found a universal constituent of matter. He then measured the charge of the electron independently — using a method that was in significantly refined by Millikan the drop method — this of course also fixed the electron mass.

The atomic nucleus. Subsequently, different models of the atom were dis- cussed, one of them being the model of Thomson. In this model, the electrons, 12 2 Global Properties of Nuclei and an equivalent number of positively charged particles are uniformly dis- tributed throughout the atom. The resulting atom is electrically neutral. Rutherford, Geiger and Marsden succeeded in disproving this picture. In their famous experiments, where they scattered a-particles off heavy atoms, they were able to show that the positively charged particles are closely packed together.

They reached this conclusion from the angular distribution of the scattered a-particles.


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The angular distribution showed a-particle scattering at large scattering angles which was incompatible with a homogeneous charge distribution. The explanation of the scattering data was a central Coulomb field caused by a massive, positively charged nucleus. The method of extract- ing the properties of the scattering potential from the angular distribution of the scattered projectiles is still of great importance in nuclear and particle physics, and we will encounter it repeatedly in the following chapters.

These experiments established the existence of the atom as a positively charged, small, massive nucleus with negatively charged electrons orbiting it. The proton. Rutherford also bombarded light nuclei with a-particles which themselves were identified as ionised helium atoms.

What Is an Atom?

In these reactions, he was looking for a conversion of elements, i. While bombarding nitrogen with a-particles, he observed positively charged particles with an unusually long range, which must have been ejected from the atom as well. From this he concluded that the nitrogen atom had been destroyed in these reactions, and a light constituent of the nucleus had been ejected.

He had already discovered similar long-ranged particles when bombarding hydrogen. From this he concluded that these particles were hydrogen nuclei which, therefore, had to be constituents of nitrogen as well. The hydrogen nucleus could therefore be regarded as an elementary constituent of atomic nuclei. Rutherford also assumed that it would be possible to disintegrate additional atomic nuclei by using a-particles with higher energies than those available to him. He so paved the way for modern nuclear physics. The neutron. The neutron was also detected by bombarding nuclei with a-particles.

Translators

The development of ionisation and cloud chambers significantly simplified the detection of charged particles, but did not help here. Neutral particles could only be detected indirectly. Chadwick in found an ap- propriate experimental approach. He used the irradiation of beryllium with a-particles from a polonium source, and thereby established the neutron as a fundamental constituent of nuclei. Chadwick arranged for this neutral radiation to collide with hy- drogen, helium and nitrogen, and measured the recoil energies of these nuclei in a ionisation chamber.

He deduced from the laws of collision that the mass of the neutral radiation particle was similar to that of the proton. Nuclear force and binding. With these discoveries, the building blocks of the atom had been found. The development of ion sources and mass spec- trographs now permitted the investigation of the forces binding the nuclear constituents, i. These forces were evidently much stronger than the electromagnetic forces holding the atom together, since atomic nuclei could only be broken up by bombarding them with highly energetic a-particles.

An Introduction to the Physical Concepts

The binding energy of a system gives information about its binding and stability. This energy is the difference between the mass of a system and the sum of the masses of its constituents. The mass defect is of fundamental importance in the study of strongly interacting bound systems. We will therefore describe nuclear masses and their systematics in this chapter at some length.

The atomic number Z gives the number of protons in the nucleus. In a neutral atom, there are Z electrons, which balance the charge of the nucleus, in the electron cloud. The atomic number of a given nucleus determines its chemical properties. The classical method of determining the charge of the nucleus is the mea- surement of the characteristic X-rays of the atom to be studied.

Physics - Particles - Unstable Nuclei

For this purpose the atom is excited by electrons, protons or synchrotron radiation. Nowadays, the detection of these characteristic X-rays is used to identify elements in material analysis. Atoms are electrically neutral, which shows the equality of the absolute values of the positive charge of the proton and the negative charge of the electron. In addition to the Z protons, N neutrons are found in the nucleus. Different combinations of Z and N or Z and A are called nuclides. The binding energy B is usually determined from atomic masses [AM93] , since they can be measured to a considerably higher precision than nuclear masses.

The conversion factor into SI units is 1. In nuclear physics, nuclides are denoted by ' 4 X, X being the chemical symbol of the element. Determining masses from mass spectroscopy. The binding energy of an atomic nucleus can be calculated if the atomic mass is accurately known. At the start of the 20th century, the method of mass spectrometry was developed for precision determinations of atomic masses and nucleon binding energies. From these, its mass can be determined.

Physics of Particles and Nuclei | NCBS

This is how most mass spectrometers work. While the radius of curvature te of the ionic path in an electrical sector field is proportional to the energy: M 2. Doubly focusing mass spectrometer [Br64]. For clarity, only the trajectories of particles at the edges of the beam are drawn 1 and 2.