scholarly journals Bakerian Lecture: Nuclear constitution of atoms

1920 ◽  
Vol 97 (686) ◽  
pp. 374-400 ◽  
Keyword(s):  
Large Mass ◽  
Atomic Weight ◽  
Single Atom ◽  
Central Field ◽  
X Rays ◽  
Hyperbolic Orbit ◽  
Series Of Experiments ◽  
Charged Nucleus ◽  
Positively Charged ◽  
Α Particles

Introduction .—The conception of the nuclear constitution of atoms arose initially from attempts to account for the scattering of α-particles through large angles in traversing thin sheets of matter. Taking into account the large mass and velocity of the α-particles, these large deflexions were very remarkable, and indicated that very intense electric or magnetic fields exist within the atom. To account for these results, it was found necessary to assume that the atom consists of a charged massive nucleus of dimensions very small compared with the ordinarily accepted magnitude of the diameter of the atom. This positively charged nucleus contains most of the mass of the atom, and is surrounded at a distance by a distribution of negative electrons equal in number to the resultant positive charge on the nucleus. Under these conditions, a very intense electric field exists close to the nucleus, and the large deflexion of the α-particle in an encounter with a single atom happens when the particle passes close to the nucleus. Assuming that the electric forces between the α-particle and the nucleus varied according to an inverse square law in the region close to the nucleus, the writer worked out the relations connecting the number of α-particles scattered through any angle with the charge on the nucleus and the energy of the α-particle. Under the central field of force, the α-particle describes a hyperbolic orbit round the nucleus, and the magnitude of the deflection depends on the closeness of approach to the nucleus. From the data of scattering of α-particles then available, it was deduced that the resultant charge on the nucleus was about ½ A e , where A is the atomic weight and e the fundamental unit of charge. Geiger and Marsden made an elaborate series of experiments to test the correctness of the theory, and confirmed the main conclusions. They found the nucleus charge was about ½ A e , but, from the nature of the experiments, it was difficult to fix the actual value within about 20 per cent. C. G. Darwin worked out completely the deflexion of the α-particle and of the nucleus, taking into account the mass of the latter, and showed that the scattering experiments of Geiger and Marsden could not be reconciled with any law of central force, except the inverse square. The nuclear constitution of the atom was thus very strongly supported by the experiments on scattering of α-rays. Since the atom is electrically neutral, the number of external electrons surrounding the nucleus must be equal to the number of units of resultant charge on the nucleus. It should be noted that, from the consideration of the scattering of X-rays by light elements, Barkla had shown, in 1911, that the number of electrons was equal to about half the atomic weight. This was deduced from the theory of scattering of Sir J. J. Thomson, in which it was assumed that each of the external electrons in an atom acted as an independent scattering unit.

Henry Moseley, X-ray spectroscopy and the periodic table

2020 ◽  
Vol 378 (2180) ◽  
pp. 20190302 ◽  
Author(s):  
Russell G. Egdell ◽  
Elizabeth Bruton
Keyword(s):  
Periodic Table ◽  
Chemical Elements ◽  
Atomic Weight ◽  
X Rays ◽  
Radioactive Elements ◽  
Theme Issue ◽  
X Ray ◽  
Series Of Experiments ◽  
Radiological Characterization

Just over 100 years ago, Henry Moseley carried out a systematic series of experiments which showed that the frequencies of the X-rays emitted from an elemental target under bombardment by cathode rays were characteristic of that element and could be used to identify the charge on its atomic nucleus. This led to a reorganization of the periodic table, with chemical elements now arranged on the basis of atomic number Z rather than atomic weight A, as had been the case in previous tables, including those developed by Mendeleev. Moseley also showed that there were four ‘missing elements’ before gold. With further measurements up to uranium Z = 92, the Swedish physicist Manne Siegbahn identified two more missing elements. This paper provides an introduction to Moseley and his experiments and then traces attempts to ‘discover’ missing elements by X-ray spectroscopy. There were two successes with hafnium (Z = 72) and rhenium (Z = 75), but many blind alleys and episodes of self-deception when dealing with elements 43, 61, 85 and 87. These all turned out to be radioactive, with extremely small natural abundances: all required synthesis by a nuclear reaction, with radiological characterization in the first instance. Finally, the paper moves on to consider the role of X-ray spectroscopy in exploring the periodic table beyond uranium. Although the discovery of artificial radioactive elements with Z > 92 again depended on nucleosynthesis and radiological characterization, measurement of the frequencies or energies of characteristic X-rays remains the ultimate goal in proving the existence of an element. This article is part of the theme issue ‘Mendeleev and the periodic table’.

Alpha-Particle Exposure Induces Mainly Unstable Complex Chromosome Aberrations which do not Contribute to Radiation-Associated Cytogenetic Risk

2021 ◽  
Author(s):  
C. Hartel ◽  
E. Nasonova ◽  
S. Ritter ◽  
T. Friedrich
Keyword(s):  
Ex Vivo ◽  
Human Peripheral Blood ◽  
Mitotic Cell ◽  
Peripheral Blood Lymphocytes ◽  
Small Scale ◽  
X Rays ◽  
Carcinogenic Effect ◽  
High Let Radiation ◽  
High Let ◽  
Α Particles

The mechanism underlying the carcinogenic potential of α radiation is not fully understood, considering that cell inactivation (e.g., mitotic cell death) as a main consequence of exposure efficiently counteracts the spreading of heritable DNA damage. The aim of this study is to improve our understanding of the effectiveness of α particles in inducing different types of chromosomal aberrations, to determine the respective values of the relative biological effectiveness (RBE) and to interpret the results with respect to exposure risk. Human peripheral blood lymphocytes (PBLs) from a single donor were exposed ex vivo to doses of 0–6 Gy X rays or 0–2 Gy α particles. Cells were harvested at two different times after irradiation to account for the mitotic delay of heavily damaged cells, which is known to occur after exposure to high-LET radiation (including α particles). Analysis of the kinetics of cells reaching first or second (and higher) mitosis after irradiation and aberration data obtained by the multiplex fluorescence in situ hybridization (mFISH) technique are used to determine of the cytogenetic risk, i.e., the probability for transmissible aberrations in surviving lymphocytes. The analysis shows that the cytogenetic risk after α exposure is lower than after X rays. This indicates that the actually observed higher carcinogenic effect of α radiation is likely to stem from small scale mutations that are induced effectively by high-LET radiation but cannot be resolved by mFISH analysis.

scholarly journals The orbits of a charged particle round an electric and magnetic nucleus

1915 ◽  
Vol 91 (628) ◽  
pp. 273-290
Keyword(s):  
Charged Particle ◽  
Hydrogen Atom ◽  
Magnetic Moment ◽  
Equatorial Plane ◽  
Central Mass ◽  
Magnetic Nucleus ◽  
Chief Interest ◽  
Revolving Body ◽  
Charged Nucleus ◽  
Positively Charged

The following communication is formally a complement to one published in the 'Proceedings' of the Society on "The Effect of the Magneton on the Scattering of α-Rays." In the present paper the more general case of a central positively charged nucleus possessing mass and a magnetic moment is considered. The case is treated as if the mass of the nucleus is so large compared with that of the revolving particle that it may be regarded as fixed. It is, therefore, not directly applicable when the revolving body is an α-particle except in cases where the central mass is large compared with that of the hydrogen atom. It is shown later what modification is needed when the motion of the nucleus is not large enough to affect its magnetic quality. The former paper was suggested by certain theories relating to the scattering of α and β-particles by matter. In the present, however, the chief interest lies in the discussion of the nature and properties of the various orbits, more especially of such as do not extend to infinity, or as they may be called "local orbits." In both cases the motion in the equatorial plane of the magneton alone is considered.

scholarly journals Evaluation the Safety and Security Procedures used In X-ray Clinics in Al-Harthiya-Baghdad

2021 ◽  
Vol 2114 (1) ◽  
pp. 012009
Author(s):  
Thuraya A. Abdul Hussian ◽  
Anwar kh. Farman
Keyword(s):  
Ionizing Radiation ◽  
X Rays ◽  
X Ray ◽  
Beta Particles ◽  
Medical Clinics ◽  
Γ Rays ◽  
Health Laws ◽  
Different Sources ◽  
Α Particles ◽  
Security Procedures

Abstract Radiation is a form of energy, its emitted either in the form of particles such as α-particles and β-particles (beta particles including the electron and the positron) or waves such as sunlight, X-rays and γ-rays. Radiation found everywhere around us and it comes from many different sources naturally or man-made sources. In this study a questionnaire was distributed to people working in the field of X-rays that used for a medical imaging (X-ray and CT-scan) to evaluate the extent of awareness and knowledge in estimate the damage of ionizing radiation as a result of wrong use. The questionnaire was distributed to medical clinics in Al-Harithiya in Baghdad, which it’s considered as one of the important areas in Iraq to attract and treat patients. It’s found that most of the commitment of radiography clinics by safety and security procedures. Most of the radiology clinics abide by most of the Iraqi Ministry of Health laws. However, some clinics did not implement some of the security and safety conditions

Lethality and Mutagenesis of B Lymphocyte Progenitor Cells Following Exposure to α-particles and X-rays

1994 ◽  
Vol 66 (2) ◽  
pp. 197-205 ◽  
Author(s):  
S.D. Griffiths ◽  
S.J. Marsden ◽  
E.G. Wright ◽  
M.F. Greaves ◽  
D.T. Goodhead
Keyword(s):  
Progenitor Cells ◽  
B Lymphocyte ◽  
X Rays ◽  
Α Particles

1. The fly in the cathedral

2015 ◽  
Author(s):  
Frank Close
Keyword(s):  
Internal Structure ◽  
Nuclear Physics ◽  
Positive Charge ◽  
X Rays ◽  
Ernest Rutherford ◽  
Nuclear Atom ◽  
Positively Charged

‘The fly in the cathedral’ charts the discovery of the nuclear atom and the start of modern atomic and nuclear physics. It began in 1895 with the discovery of X-rays by Wilhelm Roentgen and radioactivity by Henri Becquerel. In 1897, J.J. Thomson discovered the electron and realised they were common to all atoms, which implied that atoms have an internal structure. Negatively-charged electrons are bound to positively-charged entities within the atom, but what carries this positive charge and how is it distributed? It was Ernest Rutherford, in 1911, who announced his solution: all of an atom’s positive charge and most of its mass are contained in a compact nucleus at the centre.

Charles Glover Barkla, 1877-1944

1947 ◽  
Vol 5 (15) ◽  
pp. 341-366 ◽  
Keyword(s):  
Electromagnetic Wave ◽  
Atomic Number ◽  
Chemical Element ◽  
Three Dimensional ◽  
Atomic Weight ◽  
New Method ◽  
X Rays

The name of Barkla will always be distinguished on account of his fundamental researches on Rontgen rays. In 1905 he made the discovery that scattered X-rays are polarized, but only to a certain degree. He also established the fact that each chemical element can radiate Röntgen rays having properties characteristic of that element, and in this way he anticipated the assignment to each element of an ‘atomic number’, the number being, in general, about one-half the atomic weight. For these discoveries he was admitted a Fellow of the Society in 1912, his investigations having resulted in the most important additions to our knowledge of the Röntgen rays since their discovery. Barkla consistently adopted the electromagnetic wave or pulse theory of the nature of the rays. At the end of the year 1912, von Laue put forward his theory of the diffraction of X-rays by transmission through a crystal regarded as a three-dimensional grating, thus introducing an entirely new’ method of investigation.

DISCOVERY OF STRONGLY ENHANCED LOW ENERGY ALPHA DECAY OF A LONG-LIVED ISOMERIC STATE OBTAINED IN 16O + 197Au REACTION AT 80 MeV, PROBABLY TO SUPERDEFORMED BAND

1996 ◽  
Vol 11 (11) ◽  
pp. 861-869 ◽  
Author(s):  
A. MARINOV ◽  
S. GELBERG ◽  
D. KOLB
Keyword(s):  
Isomeric State ◽  
Alpha Decay ◽  
Low Energy ◽  
X Rays ◽  
Superdeformed Band ◽  
Calculated Probability ◽  
Γ Rays ◽  
Bombarding Energy ◽  
Α Particles ◽  
Superdeformed Nucleus

The reaction 16 O + 197 Au has been studied at a bombarding energy of 80 MeV. A group of 5.20 MeV α particles with a half-life of about 90 m has been found in coincidence with characteristic X-rays of At and with γ-rays. The γ-ray energies fit predicted energies for superdeformed band. The data are interpreted as due to formation of a long-lived isomeric state which decays by low energy α-particles to SD band. The calculated probability for decay via a barrier of a superdeformed nucleus was found to be consistent with the experimental results.

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