Beta decay, forms

Figure 8.3 Fission processes. The uranium nucleus can split in many ways, of which two are shown here. Since fission fragments tend to be heavier with neutrons than stable isotopes of the same element, they each begin a sequence of beta decays, forming elements from virtually every group across the periodic table, including transition elements.

Because the path of the s process is blocked by isotopes that undergo rapid beta decay, it cannot produce neutron-rich isotopes or elements beyond Bi, the heaviest stable element. These elements can be created by the r process, which is believed to occur in cataclysmic stellar explosions such as supemovae. In the r process the neutron flux is so high that the interaction hme between nuclei and neutrons is shorter that the beta decay lifetime of the isotopes of interest. The s process chain stops at the first unstable isotope of an element because there is time for the isotope to decay, forming a new element. In the r process, the reaction rate with neutrons is shorter than beta decay times and very neutron-rich and highly unstable isotopes are created that ultimately beta decay to form stable elements. The paths of the r process are shown in Fig. 2-3. The r process can produce neutron-rich isotopes such as Xe and Xe that cannot be reached in the s process chain (Fig. 2-3). 

The other form taken by molecule syntheses in the present context is that of synthesis of novel molecules which had not previously been known , or in any case are prepared only for the study of these molecules themselves. Here we refer to the synthesis of such molecules as Tc(C6Hg)2 - Rh(C5Hs)2 and others, all by beta decay of a pre-... 

All isotopes of plutonium are radioactive. The two isotopes that have found the most uses are Pu-238 and Pu-239. Pu-238 is produced by bombarding U-238 with deuterons in a cyclotron, creating neptunium-238 and two free neutrons. Np-238 has a half-life of about two days, and through beta decay it transmutates into plutonium-238. There are six allotropic metallic crystal forms of plutonium. They all have differing chemical and physical properties. The alpha (a) aUotrope is the only one that exists at normal room temperatures and pressures. The alpha allotrope of metallic plutonium is a silvery color that becomes yellowish as it oxidizes in air. AH the other allotropic forms exist at high temperatures. 

Neutron bombardment converts thorium-232 to its isotope of mass 233. The thorium-233 formed undergoes two successive beta decays to form uranium-233, a fissionable material, similar to uranium-235 and plutonium-239. 

Fermi realized this meant that, if uranium, the heaviest known element, was irradiated with neutrons, it might decay to form a previously unknown transuranic element. Uranium has an atomic number of 92 beta decay would convert it to element 93 , anew member of the Periodic Table. 

They are formed by a kind of reverse beta decay a proton becomes a neutron. In order to do so, it must shed its positive charge, and this happens by the emission of. positively charged version of the electron the positron, which is the antimatter sibling of the electron. ... 

Another form of three-dimensional imaging of internal organs, called positron emission tomography (PET) scanning, exploits a less common form of beta decay. Most beta decays involve the emission of electrons from the nucleus as a neutron decays into an electron and a proton. But the reverse can happen too a proton can decay into a neutron (see page 106). The positive charge is borne away by a positron, which will soon collide with an electron. Their mutual annihilation produces a gamma ray. 

The second type of decay, called beta decay (fi decay), comes in three forms, termed beta-plus, beta-minus, and electron capture. All three involve emission or capture of an electron or a positron (a pcirticle with the tiny mass of an electron but with a positive chcirge), and all three also change the atomic number of the daughter atom. 

Electron capture The final form of beta decay, electron capture, occurs when an inner electron — one in an orbital closest to the atomic nucleus — is captured by an atomic proton (see Chapter 4 for info on orbitals). By capturing the electron, the proton converts into a neutron and emits a neutrino. Here again, the atomic number decreases by 1 ... 

Ne-b V. Electron capture is a form of beta decay that results in the atomic number... 

Any of the foregoing conditions may be achieved when the nucleus contains an even number of both protons and neutrons, or an even number of one and ail odd number of the oilier. Since Ihere is an excess of neutrons over protons for all but the lowest atomic number elements, in the odd-odd situation there is a deficiency of protons necessary to complete the two-proton-two-neutron quartets. It might be expected that these could be provided by the production of protons via beta decay. However, there exist only four stable nuclei of odd-odd composition, whereas there are 108 such nuclei in the even-odd form and 162 in the even-even series. It will be seen that the order of stability, and presumably the binding energy per nucleon, from greatest to smallest, seems to be even-even, even-odd, odd-odd. 

The prompt neutrons emitted in fission are available for fission in other nuclei - hence the chain reaction. The fission fragments formed initially are rich in neutrons. For example the heaviest stable isotopes of krypton and barium are 86Kr and 138Ba. Excess neutrons are emitted from the fission fragments as delayed neutrons or converted to protons by beta decays. For example... 

Plutonium is a man-made element, and only infinitesimal traces occur naturally. It melts at 641°C and boils at 3330°C. 239Pu is formed in nuclear reactors by neutron capture in 238U, followed by two successive beta decays (Fig. 5.1). Further neutron captures lead to 240Pu and 241 Pu. 238Pu is formed from 239Pu by (n,2n) reactions, or from 235U by three successive neutron captures and two beta decays. Table 5.1 shows the half-lives, alpha and X-ray energies of the principal Pu isotopes. 

The conversion of muonium (y+e ) to its antiatom antimuonium (y e+) would be an example of a muon number violating process,2 and like neutrinoless double beta decay would involve ALe=2. The M-M system also bears some relation to the K°-K7r system, since the neutral atoms M and M are degenerate in the absence of an interaction which couples them. In Table III a four-Fermion Hamiltonian term coupling M and M is postulated, and the probability that M formed at time t=0 will decay from the M mode is given. Present experimental limits22 23 for the coupling constant G are indicated and are larger than the Fermi constant Gp. 

Beta-decay of 125antimony in pentaphenyl antimony formed tetraphenyl 125tellurium in 60% yield7,8. 

The correct answer is (C). Beta decay occurs when a neutron breaks down to form a proton and a beta particle (electron). This will cause the atomic number to increase by one, and the mass number remains constant. In the first beta decay, lead-214 becomes bismuth-214. The second beta decay converts bismuth-214 to polonium-214,... 

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