Positron A positively

Nuclei that have too many protons relative to their number of neutrons correct this situation in either of two ways. They either capture one of their Is electrons or they emit a positron (a positively charged particle with the same mass as an electron). Either process effectively changes a proton to a neutron within the nucleus. 

Of course, Feynman was right once again. To us oversized humans, the quantum mechanical world of the very small seems weird. However, quantum mechanics beautifully explains the behavior of atoms and predicts many oddities that have turned out to be true. Using quantum mechanics, many properties of atoms can be calculated. For example, chemists can now predict the shape of a molecule when atoms combine (molecules will be explored in more detail in Chapter 6). Another success was the prediction of the existence of a never-detected particle called the positron, a positively charged electron. Years after the prediction was made, experimental physicists discovered the particle. 

Positron A positively charged particle of mass equal to an electron. Positrons are created either by the radioactive decay of unstable nuclei or by collision with photons. 

Emission of an a-particle produces a new nucleus with a reduction in atomic number by two and in mass number by four. When a nucleus emits a /3-particle, the atomic number of the new nucleus increases by one (over that of the decaying nucleus), but the mass numbers are unchanged. Some radioactive nuclei do not increase in atomic number in decay, but decrease by one unit of mass number due to the emission of a positron (a positively charged /3 ray). Eor example, in /3 decay with electron emission, is converted to yN, whereas in positron f3 decay, uNa is converted to i a. An alternative process to f3 decay involves the absorption of an orbital electron by the nucleus in a process known as electron capture, which results in a decrease in the atomic number of the product nucleus, for example, Wu decaying to Pt. Gamma-ray decay results in no change in either mass number or atomic number. 

Positron. A positively charged atomic particle with the same mass as an electron. 

Those isotopes with too few neutrons (red dots below the band of stability) decay as well, but in a manner that increases the number of neutrons relative to the number of protons. One way this can happen is by emission of a type of subatomic particle discovered in 1932, a positron— a positively chained electron, e. For example, the decay of nitrogen-13, an isotope with too few neutrons, is by positron emission. 

Positron discovered (Carl D. Anderson) Anderson discovers the positron, a positive electron and an element of antimatter. 

Another relatively recent technique, in its own way as strange as Mossbauer spectrometry, is positron annihilation spectrometry. Positrons are positive electrons (antimatter), spectacularly predicted by the theoretical physicist Dirac in the 1920s and discovered in cloud chambers some years later. Some currently available radioisotopes emit positrons, so these particles arc now routine tools. High-energy positrons are injected into a crystal and very quickly become thermalised by... 

Similar to beta decay is positron emission, where tlie parent emits a positively cliargcd electron. Positron emission is commonly called betapositive decay. Tliis decay scheme occurs when tlie neutron to proton ratio is too low and alpha emission is not energetically possible. Tlie positively charged electron, or positron, will travel at higli speeds until it interacts with an electron. Upon contact, each of tlie particles will disappear and two gamma rays will... 

Since Rutherford s work, scientists have identified other types of nuclear radiation. Some consist of rapidly moving particles, such as neutrons or protons. Others consist of rapidly moving antiparticles, particles with a mass equal to that of one of the subatomic particles but with an opposite charge. For example, the positron has the same mass as an electron but a positive charge it is denoted 3 or f e. When an antiparticle encounters its corresponding particle, both particles are annihilated and completely converted into energy. Table 17.1 summarizes the properties of particles commonly found in nuclear radiation. 

Positron The antiparticle of an electron. It is a particle with mass of an electron hut with a positive electric charge of the same magnitude as the electron s negative charge. 

Annihilation (Positron-Electron)—An interaction between a positive and a negative electron in which they both disappear their rest mass, being converted into electromagnetic radiation (called annihilation radiation) with two 0.51 MeV gamma photons emitted at an angle of 180° to each other. 

Electron—A stable elementary particle having an electric charge equal to 1.60210xl0 19 C (Coulombs) and a rest mass equal to 9.1091xl0 31 kg. A positron is a positively charged "electron" (see Positron). 

Ans. /3 is a high-energy electron. +/3 is a positron—a particle with the same properties as the electron except for the sign of its charge, which is positive. 

Cyclotrons and accelerators are sources of charged particles (i.e., protons, deuterons, a particles, etc.), and the radionuclides produced are generally proton rich and decay by positron emission and/or electron capture. A positive ion beam is eventually extracted from the cyclotron, regardless of whether positive or negative ions were accelerated. The isotope of interest is separated from the target for use in chemical syntheses. Accelerator- or cyclotron-produced radioisotopes tend to be the most expensive as only one radionuclide is produced at a time. 

Beta (+) or positron emission ( J>+) This type of decay occurs when a nucleus has a greater number of protons than neutrons. In this process, a proton is converted into a neutron by emitting a positive particle known as a (11 particle or positron. The positron is a particle having the mass of an electron but carrying a positive charge. It is sometimes called the antielectron and shown as e+. The reaction can be shown as... 

A positron is a positively charged electron (fJ>, or °+fi). It is annihilated by interaction with normal electrons, once it has lost most of its ejection energy. Its emission leaves the parent nucleus unchanged in mass, but decreased in charge by one ... 

A positron is essentially an electron that has a positive charge instead of a negative one. It is represented as J/3 or ye. Positron emission results from the conversion of a proton to a neutron and a positron ... 

Positron emission, in which a positron, +°e, a particle having the same mass as an electron but a positive charge, is emitted from the nucleus. This is due to a proton converting into a neutron and the positron. 

Conversely, nuclei that contain an excess of protons undergo proton to neutron transition with the emission of a positively charged beta particle known as a positron Q8+) and with the reduction of the atomic number by one. A positron has only a very short existence, combining immediately with an electron of a nearby atom. The two particles disintegrate in the process with the emission of two gamma rays, e.g. 

When Dirac completed work on his theory in 1928, it was a notable success. Among other things, it explained electron spin, which turned out to be a relativistic effect, rather than something analogous to the spin of a macroscopic object like a top. But the theory also made what seemed to be a very strange prediction. If Dirac s theory was correct, then there had to exist particles that had properties like the electron, but that carried a positive rather than a negative charge. At the time, such particles, called positrons, had never been observed. 

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