Alpha a Radiation

When an atom emits an alpha particle, it becomes a lighter atom. We represent this process with a nuclear equation, an equation that represents the changes that occur during radioactivity and other nuclear processes. For example, the nuclear equation for the alpha decay of uranium-238 is  

The original atom is called the parent nuclide, and the products are called the daughter nuclides. When an element emits an alpha particle, the number of protons in its nucleus changes, transforming it into a different element. In this case, uranium-238 becomes thorium-234. Unlike a chemical reaction, in which elements retain their identity, a nuclear reaction often changes the identity of the elements involved. Like a chemical equation, however, nuclear equations must be balanced. 

The sum of the atomic numbers on both sides of a nuclear equation must be equal, and the sum of the mass numbers on both sides must also be equal. 

The identity and S5mibol of the daughter nuclide of any alpha decay can be deduced from the mass and atomic numbers of the parent nuclide. During alpha decay, the mass number decreases by 4 and the atomic nimiber decreases by 2. For example, to write a nuclear equation for the alpha decay of Th-232, we begin with the S5mibol for Th-232 on the left side of the equation and the symbol for an alpha particle on the right side. 

We can deduce the mass number and atomic number of the unknown daughter nuclide because the equation must be balanced. 

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Radioactivity is the spontaneous emission of radiation from an unstable nucleus. Alpha (a) radiation consists of helium nuclei, small particles containing two protons and two neutrons (fHe). Beta (p) radiation consists of electrons ( e), and gamma (y) radiation consists of high-energy photons that have no mass. Positron emission is the conversion of a proton in the nucleus into a neutron plus an ejected positron, e or /3+, a particle that has the same mass as an electron but an opposite charge. Electron capture is the capture of an inner-shell electron by a proton in the nucleus. The process is accompanied by the emission of y rays and results in the conversion of a proton in the nucleus into a neutron. Every element in the periodic table has at least one radioactive isotope, or radioisotope. Radioactive decay is characterized kinetically by a first-order decay constant and by a half-life, h/2, the time required for the... 

Alpha (a) radiation is attracted towards the cathode or negative pole. This is because it is made up of positive particles. Beta O) radiation, on the other hand, is attracted towards the positive pole, or anode, because it is made up of negative particles. 

Alpha (a) radiation occurs when an unstable nucleus emits a small piece of itself consisting of 2 protons and 2 neutrons (A Figure 17.4). Since 2 protons and 2 neutrons are identical to a helium-4 nucleus, the S5mibol for an alpha (a) particle is identical to the S5mibol for helium-4. 

Human Cytogenetic Dosimetry A Dose-Response Relationship for Alpha Particle Radiation from Am-241, Health Physics 37 279-289 (1979). 

Beryllium is an excellent source of alpha particles, which are the nuclei of helium atoms. Alpha particles (radiation) are not very penetrating. These particles travel only a few inches in air and can be stopped by a sheet of cardboard. Alpha particles are produced in cyclotrons (atom smashers) and are used to bombard the nuclei of other elements to study their characteristics. 

Radium is extremely radioactive. It glows in the dark with a faint bluish light. Radiums radioisotopes undergo a series of four decay processes each decay process ends with a stable isotope of lead. Radium-223 decays to Pb-207 radium-224 and radium-228decay to Pb-208 radium-226 decays to Pb-206 and radium-225 decays to Pb-209. During the decay processes three types of radiation—alpha (a), beta ((5), and gamma (y)—are emitted. 

The magnitude of AV is measured most conveniently by placing an air electrode (a radiation emitter Po210 [alpha-emitter]), near the surface (ca. millimeter in air), connected to an impedance electrometer. This is required since resistance in air is very high, but it is appreciably reduced by the radiation electrode. However, proper isolation is essential for the data to be reliable. 

Protactinium is a very dangerous substance to work with. It is highly toxic and presents a radiation hazard (alpha emitter). The Pa-231 isotope is a long-lived alpha-emitter which is not excreted out readily. Exposure can cause cancer. 

It is important to consider the type of radiation with respect to whether a radiation source is external or internal to the body. External alpha, and to some extent beta radiation, are not as hazardous as external gamma radiation. Clothing or the outer layer of the skin will stop alpha radiation. Beta... 

Frank, S. M., Barber, T. L. et al. 2002. Alpha-decay radiation damage study of a glass-bonded sodalite ceramic waste form. Materials Research Society Symposium Proceedings, 713, 487-494. 

Scientists have known since 1896 that many nuclides are radioactive—that is, they spontaneously emit radiation. Early studies of radioactive nuclei, or radionuclides, by the New Zealand physicist Ernest Rutherford in 1897 showed that there are three common types of radiation with markedly different properties alpha (a), beta (f3), and gamma (y) radiation, named after the first three letters of the Greek alphabet. 

Senzer N, Mani S, Rosemurgy A, Nemunaitis J, et al. 204. TNFerade biologic, an adenovector with a radiation-inducible promoter, carrying the human tumor necrosis factor alpha gene A phase I study in patients with solid tumors. J Clin Oncol. 22 592-601. 

Carrier or Tracer Addition. To quantify the purified final sample that will be measured by a radiation detection instrument (as compared to a mass spectrometer), a carrier or tracer is added to the sample. The carrier usually is the same element as the radioanalyte ( isotopic carrier ) and is standardized, typically at 5-20 mg/mL concentration. The carrier serves two purposes to provide macro quantities so that certain chemical steps (such as precipitation) may be performed on the sample, and to determine the chemical yield, usually by weight. A tracer serves only to determine the chemical yield of the process its nanogram quantities or less, comparable to the radioanalyte in the sample, prevent use as carrier. The tracer is measured by its characteristic radiation at the same time as the radioanalyte. An advantage in alpha-particle spectral analysis is that the activity of the analyte can be calculated from the activity of the tracer without knowledge of the detector counting efficiency, as discussed below. 

While Thomson and others were busy studying electrical phenomena, Henri Becquerel discovered a new phenomenon—radiation. (We will discuss radiation in more detail in Chapter 5.) The study of this new type of high-energy emission from materials was the principal focus of Ernest Rutherford. Rutherford s initial work discovered two new types of particles associated with the high-energy emissions, the alpha (a) particle and the beta ((3). These are now known to be a helium nucleus and an electron, respectively (more on this in Chapter 5). 

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