Neutron An uncharged particle

The neutron, an uncharged particle with a mass slightly greater than that of a proton. 

Neutron An uncharged particle found in the nucleus of an atom. 

With the discovery, by Chadwick in 1932, of the neutron, an uncharged particle of mass closely equal to that of the proton, it was possible to provide a model for the nucleus which is essentially that accepted today. The nucleus is considered to be composed of Z protons and N neutrons, the total number of particles (>4 = N + Z) being known as the atomic mass number. The term nucleon is used to describe both types of particle in the nucleus. The nucleus of beryllium, for example, contains four protons and five neutrons, and therefore has a mass approximately nine times that of the hydrogen nucleus. 

Neutron An uncharged elementary particle with a mass slightly greater than that of the proton, and found in the nucleus of every atom heavier than hydrogen (atomic weight = 1). 

Before beginning a discussion of nuclei and their properties, we need to understand the environment in which most nuclei exist, that is, in the center of atoms. In elementary chemistry, we learn that the atom is the smallest unit a chemical element can be divided into that retains its chemical properties. As we know from our study of chemistry, the radii of atoms are approximately 1-5 x 10-10 m, or 1 -5 A. At the center of each atom we find the nucleus, a small object (r 1-10 x 10-15 m) that contains almost all the mass of the atom (Fig. 1.1). The atomic nucleus contains Z protons, where Z is the atomic number of the element under study, Z being number of protons and is thus the number of positive charges in the nucleus. The chemistry of the element is controlled by Z in that all nuclei with the same Z will have similar chemical behavior. The nucleus also contains N neutrons, where N is the neutron number. Neutrons are uncharged particles with masses approximately equal to the mass of a proton ( 1 u). Each proton has a positive charge equal to that of an electron. The overall charge of a nucleus is +Z electronic charge units. 

Let us consider what we can learn about cross sections from some general considerations. Consider the reaction of an uncharged particle (a neutron) with a nucleus as shown in Figure 10.7. The neutron makes a grazing collision with the nucleus. The impact parameter b is taken to be the sum of the radii of the projectile and target nuclei. Thus, the cross section can be written as... 

Probably the most distinguishing feature of the neutron as a surface probe is its penetrability. As an uncharged particle the... 

Proton (p) Positively charged particles found in the nucleus of an atom. Neutron (n) Uncharged particles found in the nucleus of an atom. Electron (e ) Negatively charged particles found around the nucleus of an atom (Table 1). 

The third fundamental particle, the neutron, eluded discovery until 1932. James Chadwick (1891-1974) correctly interpreted experiments on the bombardment of beryllium with high-energy a-particles. Later experiments showed that nearly all elements up to potassium, element 19, produce neutrons when they are bombarded with high-energy a-particles. The neutron is an uncharged particle with a mass slightly greater than that of the proton. 

Nemst equation—an equation describing the potential of an electrochemical half-cell neutron—an uncharged, subatomic particle found in the nucleus of an atom noble gas—Group 18 of the periodic table, characterized by their general inertness due to their complete valence shell of electrons... 

Rutherford s model explained the charged nature of matter, but it could not account for aU the atom s mass. After more than 20 years, in 1932, James Chadwick (1891-1974) discovered the neutron, an uncharged dense particle that also resides in the nucleus. 

Nuclei suitable for fusion must come near each other, where near means something like the nuclear radius of 10" cm. For positively charged nuclei to make such a close approach it requires large head-on velocities, and therefore multimillion-degree Celsius temperature. In contrast, fission can occur at normal temperatures, either spontaneously or triggered by a particle, particularly an uncharged neutron, coming near a fissionable nucleus. 

The fact that uranium is capable of undergoing a process known as fission was discovered as an indirect result of the use of neutrons as projectiles in the production of artificial radioactive isotopes. At the University of Rome, the Italian physicist Enrico Fermi bombarded many different elements with neutrons and thereby produced many new radioactive isotopes. The use of neutrons as projectiles has the distinct advantage that the collision of these uncharged particles with... 

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