Beta-decay

In j8 decay, a nucleus emits an electron or a positron and is transformed into a new element. In addition to the electron or the positron, a neutral particle with rest mass zero is also emitted. There are two types of decay, and 

Historically, the name /8 particle has been given to electrons that are emitted by nuclei undergoing beta decay. The antineutrino (P) is a neutral particle with rest mass so small that it is taken equal to zero. 

Equations 3.50 and 3.53 show that three particles, the nucleus, the electron, and the antineutrino, share the energy Qp, and their total momentum is zero. 

There is an infinite number of combinations of kinetic energies and momenta that satisfy these two equations and as a result, the energy spectrum of the betas is continuous. 

the energy of the nucleus, T, f, is much smaller than either T -or 71 because the nuclear mass is huge compared to that of the electron or the antineutrino. For all practical purposes, Tm can be neglected and Eq. 3.53 takes the form 

In beta decay, the atomic number of the element increases by one, but the mass number does not change. Because its atomic number changes, the identity of the element changes. 

Note the same conservation laws that we observed for alpha decay the sum of the subscripts is the same on each side, and the sum of the superscripts is the same on each side. 

Nuclides with an excess of neutrons experience P decay. In the nucleus a neutron is converted into a proton, an electron and an electron antineutrino, as indicated in Table 5.1. The atomic number increases by one unit, whereas the mass number does not change (second displacement law of Soddy and Fajans). The energy of the decay process can again be calculated by comparison of the masses according to Einstein  

Nuclides with an excess of protons exhibit P decay. A proton in the nucleus is converted into a neutron, a positron and an electron neutrino, as indicated in Table 5.1. The atomic number decreases by one unit, and the mass number remains unchanged. As in the case of P decay, the energy of the decay process is obtained by eq. (5.10). But because now Z2 — Zi — 1, it follows that  

This means that y decay can occur only if M is at least two electron masses higher than M2  

Taking into account the formation of electron neutrinos in addition to the emission of electrons and positrons, respectively, the following equations are valid for p and P decay. 

P jp(nucleus) on(nucleus)-I--I-o c Electron capture is described by the following equation  

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. 

Beta-plus In beta-plus decay, a proton in the nucleus decays into a neutron, a positron ( Je), and a tiny, weakly interacting pcirticle called a neutrino (v). This decay decreases the atomic number by 1. The mass number, however, does not change. Both protons and neutrons cire nucleons (pcirticles in the nucleus), after all, each contributing 1 atomic mass unit. The general pattern of beta-plus decay is shown here  

Beta-minus Beta-minus decay essentially mirrors beta-plus decay. A neutron converts into a proton, emitting an electron and an anftneutrino (which has the same symbol as a neutrino except for the line on top). Particle and antiparticle pairs such as neutrinos and antineutrinos are a complicated physics topic, so we ll keep it basic here by saying that a neutrino and an antineutrino would annihilate one another if they ever touched, but they re otherwise very similar. Again, the mass number remains the same after decay because the number of nucleons remains the same. However, the atomic number increases by 1 because the number of protons increases by 1  

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  

Gamma-ray emission is not, strictly speaking a decay process it is a de-excitation of the nucleus. I will now explain each of these decay modes and will show, in particular, how gamma emission frequently appears as a by-product of alpha or beta decay, being one way in which residual excitation energy is dissipated 

The dominant form of radioactive decay is movement down the hillside directly to the valley bottom. This is 

The decay of Co is an example of or negatron decay (negatron = negatively charged beta particle). All nuclides unstable to (3 decay are on the neutron rich side of stability. (On the Karlsruhe chart, these are coloured blue.) The decay process addresses that instability. An example of (3 decay is  

A beta particle, (3 , is an electron in all respects it is identical to any other electron. Following on from Section 1.1, the sum of the masses of the Ni plus the mass of the (3 , and i , the anti-neutrino, are less than the mass of Co. That mass difference drives the decay and appears as energy of the decay products. What happens during the decay process is that a neutron is converted to a proton within the nucleus. In that way the atomic number increases by one and the nuclide drops down the side of the valley to a more stable condition. A fact not often realized is that the neutron itself is radioactive when it is not bound within a nucleus. A free neutron has a half-life of only 10.2 min and decays by beta emission  

That process is essentially the conversion process happening within the nucleus. 

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The Hamiltonian considered above, which connmites with E, involves the electromagnetic forces between the nuclei and electrons. However, there is another force between particles, the weak interaction force, that is not invariant to inversion. The weak charged current mteraction force is responsible for the beta decay of nuclei, and the related weak neutral current interaction force has an effect in atomic and molecular systems. If we include this force between the nuclei and electrons in the molecular Hamiltonian (as we should because of electroweak unification) then the Hamiltonian will not conuuiite with , and states of opposite parity will be mixed. However, the effect of the weak neutral current interaction force is mcredibly small (and it is a very short range force), although its effect has been detected in extremely precise experiments on atoms (see, for... 

Fm and heavier isotopes can be produced by intense neutron irradiation of lower elements, such as plutonium, using a process of successive neutron capture interspersed with beta decays until these mass numbers and atomic numbers are reached. 

It is possible to prepare very heavy elements in thermonuclear explosions, owing to the very intense, although brief (order of a microsecond), neutron flux furnished by the explosion (3,13). Einsteinium and fermium were first produced in this way they were discovered in the fallout materials from the first thermonuclear explosion (the "Mike" shot) staged in the Pacific in November 1952. It is possible that elements having atomic numbers greater than 100 would have been found had the debris been examined very soon after the explosion. The preparative process involved is multiple neutron capture in the uranium in the device, which is followed by a sequence of beta decays. Eor example, the synthesis of EM in the Mike explosion was via the production of from followed by a long chain of short-Hved beta decays,... 

IT = isomeric transition, EC = electron capture, l3 = positron emission, and j3 = beta decay. 

Figure 1 Chart showing the decay chain of the U-Th decay series isotopes. Vertical arrows define alpha (a) decays while beta (/ ) decays are illustrated by diagonal arrows...

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... 

Beryllium difiuoride, dipole in, 293 Berzelius, Jons, 30 Bessemer converter, 404 Beta decay, 417 Bela particle, 417 Bicarbonate ion, 184 Bidentaie. 395 Billiard ball analogy, 6, 18 and kinetic energy, 114 Billiard ball collision, conservation of energy in, 114 Binding energy, 121, 418 Biochemistry, 421 Bismuth, oxidation numbers, 414 Blast furnace, 404 Bohr, Niels, 259 Boiling point, 67 elevation, 325 normal, 68... 

Americium grows in the plutonium-239 from the beta decay of plutonium-241. 

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-... 

The study of the radiochemical reactions of arsenic atoms in benzene solution was carried further by comparing the product spectra of neutron irradiated ASCI3 solutions and GeC solutions which have undergone beta decay. The product spectra were found to be remarkably similar, especially when considered only as to the number of As-0... 

The most detailed studies of the results of beta decay in organometallic compounds concern Pb(CH3)4. The nuclide used is which decays... 

In the last column of Table 7.1, the most popular radioactive precursor nuclide is given together with the nuclear decay process (EC = electron capture, = beta decay) feeding the Mossbauer excited nuclear level. 

Ra decays by low energy beta decay to the short-lived Ac (with a... 

Luo et al. (2000) used a somewhat different method for determining the partitioning of Ra by noting that Rn is produced by the total amount of Ra both in solution and on surfaces (and so equal to (1 + K226Ra)( Ra)w) as well as by recoil. " Ra is produced similarly by Ra (through the beta decay of Th) from within the minerals and from the surface. Combining the respective equations (by assuming that the recoil rates for... 

Identification of the isotope 239Np, which is generated by slow-neutron bombardment of 238U and subsequent beta decay. 

Light-silver-colored element generated from a plutonium isotope (241Pu) by beta decay. Never detected in nature. Chemically similar to Europium. A few tons have been produced throughout the world through regeneration of fuel rods. Americium is a good source of alpha rays. Hence it is suitable to measure thicknesses, as a detector in smoke alarms, and for the activation analysis of the tiniest amounts of substances. 

Silvery, artificial element generated by beta decay from a plutonium isotope (239Pu). Chemically similar to gadolinium. Like Eu and Gd, Am and Cm are difficult to separate. It can be produced in kilogram amounts. The most common isotope is 244Cm with a half-life of 18.1 years. Is used for thermoelectric nuclide batteries in satellites and pacemakers. It is strongly radioactive and hence also suitable for material analysis. 

Two of these isotopes, carbon-12, the most abundant, and carbon-13 are stable. Carbon-14, on the other hand, is an unstable radioactive isotope, also known as radiocarbon, which decays by the beta decay process a beta particle is emitted from the decaying atomic nucleus and the carbon-14 atom is transformed into an isotope of another element, nitrogen-14, N-14 for short (chemical symbol 14N), the most common isotope of nitrogen ... 

Perturbation theory was applied to the ionization of atoms accompanying alpha and beta decay soon after the advent of quantum theory (Migdal, 1941). Migdal concluded that the probability for... 

Migdal, A., Ionization of Atoms Accompanying Alpha and Beta Decay, J. of Phvs. IV 449-453 (1941). 

Radon-222, a decay product of the naturally occuring radioactive element uranium-238, emanates from soil and masonry materials and is released from coal-fired power plants. Even though Rn-222 is an inert gas, its decay products are chemically active. Rn-222 has a a half-life of 3.825 days and undergoes four succesive alpha and/or beta decays to Po-218 (RaA), Pb-214 (RaB), Bi-214 (RaC), and Po-214 (RaC ). These four decay products have short half-lifes and thus decay to 22.3 year Pb-210 (RaD). The radioactive decays products of Rn-222 have a tendency to attach to ambient aerosol particles. The size of the resulting radioactive particle depends on the available aerosol. The attachment of these radionuclides to small, respirable particles is an important mechanism for the retention of activity in air and the transport to people. 

The central wire, made of a neutron-absorbing material, absorbs a neutron and undergoes beta decay. 

As more beta decays occur, the remaining atoms cause the wire to become more positively charged. 

He is present in natural gases with a concentration of MO-7 of that of 4He and 1(T6 of the helium in the atmosphere. The separation is very expensive. Hence 3He is instead obtained as by-product of tritium production in nuclear reactors. Tritium in fact produces, by beta decay (the half life is 12.26 years), 3He the separation of 3He is obtained through a diffusion process. 

Neutrinoless double-beta decay and other rare decays studied using massive calorimeters. 

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