Beta particle discovery

In 1899 he identified two forms of radioactivity, which he called alpha and beta particles. As we saw earlier, he deduced that alpha particles are helium nuclei. Beta particles are electrons - but, strangely, they come from the atomic nucleus, which is supposed to be composed only of protons and neutrons. Before the discovery of the neutron this led Rutherford and others to believe that the nucleus contained some protons intimately bound to electrons, which neutralized their charge. This idea became redundant when Chadwick first detected the neutron in 1932 but in fact it contains a deeper truth, because beta-particle emission is caused by the transmutation ( decay ) of a neutron into a proton and an electron. 

In spite of all the new approaches which illuminated the outer regions of the atom, the center or nucleus of the atom continued to remain a bundle of uncertainties. Something of the composition of the nuclei of a few elements was already known. This information came from a study of the spontaneous disintegration of radium and other radioactive elements, such as thorium, polonium, uranium, and radon. These elements break down of their own accord into simpler elements. Soon after the Curies discovery of radium, Rutherford and Frederick Soddy, his student and collaborator, had found that the spontaneous breaking down of radium resulted in the emission of three types of rays and particles. Radium ejected alpha particles (ionized helium atoms), beta particles (electrons), and gamma rays (similar to X-rays). In radioactive elements, at least, it was believed that the nucleus contained electrons, protons, and electrified helium particles. 

In 1911, the British physicist and Nobel laureate Ernest Rutherford (1871-1937) published the article The Scattering of Alpha and Beta Particles by Matter and the Structure of the Atom in Philosophical Magazine. In this article, Rutherford reported the results of an experiment that demonstrated that the protons and electrons in atoms are not distributed homogeneously. Instead, the protons are concentrated in a relatively tiny region Rutherford called the nucleus (from the Latin, meaning kernel ). The electrons are extranuclear electrons are located in a relatively much larger volume of space surrounding the nucleus. Rutherford s discovery of the nucleus was immediately accepted within the scientific community. However, the relationship, if any, between atomic structure and properties was still unclear. 

The discovery that positively charged particles are present in atoms came soon after the discovery of radioactivity by Henri Becquerel (1852-1908) in 1896. Radioactive elements spontaneously emit alpha particles, beta particles, and gamma rays from their nuclei (see Chapter 18). 

The study of radioactivity, beginning with Antoine-Henri Becquerel s discovery in 1896, was another problem relating to atomic structure. In fact, radioactivity was another enigma not explained by classical mechanics. Studies showed that atoms spontaneously gave off three distinct types of radiation, of which two were eventually shown to be particles of matter. The alpha particle (a) was identical to a doubly ionized helium atom, and the beta particle (/3) was identical to an electron. [The third type of radiation, gamma (y) radiation, is a form of electromagnetic radiation.] However, no known chemical process could eject particles from atoms in the manner indicated by radioactivity. 

The discovery of Lp(a) by Berg in 1962 (B6) relied on the production of rabbit antisera against beta-lipoprotein and on the selective absorption of these antisera with individual human sera. When certain human sera were used for absorption, the antisera retained precipitation capacity in radial immunodiffusion with 30-35% of individual human sera, which obviously contained a previous unknown antigen. The particle carrying the new antigen shared antigenic properties with beta-lipoprotein, but had an additional antigenic structure. This was evidenced from the only partial fusion of the precipitin bands formed between a positive human serum, the antibeta lipoprotein antiserum and the new absorbed antiserum. 

Measurement of radioactiviry, as an analytical tool became possible after the discoveries of A.H.Becquerel(uranium radiation 1896), Pi re Marie Curie (polonium radium in 1898), Sir E. Rutherford (identification of Becquerel rays as consisting of alpha-, beta and gamma-particles) and of F.Soddy(phenomenon of nuclear disintegration, in 1902)... 

Another kind of particle and another kind of interaction were discovered from a detailed study of beta radioactivity in which electrons with a continuous spectrum of energies are emitted by an unstable nucleus. The corresponding interactions could be viewed as being due to the virtual transmutation of a neutron into a proton, an electron, and a new neutral particle of vanishing mass called the neutrino. The theory provided such a successful systematization of beta decay rate data for several nuclei that the existence of the neutrino was well established more than 20 years before its experimental discovery. The beta decay interaction was very weak even compared to the electron-photon interaction. 

During the first decade of the 20th century the application of physics to chemistry once and for all established the reahty of atoms. Physicists even weighed the electrons that are now known to govern chemical properties. The discovery of radioactive particles alpha [a] and beta [P]) led to the earliest perceptions of isotopes. The remaining two natural rare earths were finally separated and identified, completing the lanthanide series of chemical elements. 

Table 1-1 gives the alpha, beta, and gamma absorption bands of some cytochromes, including cytochrome c. Whereas the alpha band of purified cytochrome c has its maximum exactly at 550 mp, the spectrum of heart mitochondria has its maximum at 551 mp. However, when the mitochondria are heated, the band position moves to 550 mp. These results suggested to Keilin and Hartree that the spectrum of heart mitochondria is the resultant of two spectra. Indeed, repeated washings of the particles led to the discovery of a thermolabile, insoluble cytochrome with a maximum alpha band at 553-554 mp. 

Further evidence of the complex structure of the atom was provided in 1896 by the discovery, by the French physicist Becquerel, of the phenomenon of radioactivity. It was found that certain elements, such as uranium, spontaneously emitted radiation at an apparently constant rate. Ernest Rutherford showed that the emissions involved two types of particle, to which he gave the names alpha (a) and beta (jS) rays. The first of these had a positive charge and a mass essentially equal to that of an atom of the element helium, while the second was found to be simply an electron. In 1903, Rutherford, in collaboration with Frederick Soddy, explained the process of radioactivity by the revolutionary hypothesis that the particle emission was a means whereby an atom of one element converted itself spontaneously into an atom of another. 

In Section 10.1, we discussed the simplest fusion reaction [Equation (10.1)] in which a beta-plus particle—that is, a positron (+i )—is a product. Other common nuclear and subnuclear particles are given in Table 10.1. Having discussed the discovery and some of the chemistry of deuterium and tritium, we are now ready to take a closer look at nuclear processes, particularly those related to hydrogen. 

The discovery of radioactivity—the emission of small energetic particles from the core of certain unstable atoms— by scientists Henri Becquerel (1852-1908) and Marie Curie (1867-1934) at the end of the nineteenth century allowed researchers to experimentally probe the structure of the atom. At the time, scientists had identified three different types of radioactivity alpha (a) particles, beta (/3) particles, and gamma (y) rays. We will discuss these and other types of radioactivity in more detail in Chapter 19. For now, just know that a particles are positively charged and that they are by far the most massive of the three. 

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