Nuclear electron capture

An analogous SW analysis of chemically induced lifetime variations has been carried out for the nuclear electron capture (EC) for " Cr [13]. The small collection of theoretical and experimental data in table 1 discloses the urgent need for further... 

AH of the 15 plutonium isotopes Hsted in Table 3 are synthetic and radioactive (see Radioisotopes). The lighter isotopes decay mainly by K-electron capture, thereby forming neptunium isotopes. With the exception of mass numbers 237 [15411-93-5] 241 [14119-32-5] and 243, the nine intermediate isotopes, ie, 236—244, are transformed into uranium isotopes by a-decay. The heaviest plutonium isotopes tend to undergo P-decay, thereby forming americium. Detailed reviews of the nuclear properties have been pubUshed (18). 

The emission of y rays follows, in the majority of cases, what is known as P decay. In the P-decay process, a radionuclide undergoes transmutation and ejects an electron from inside the nucleus (i.e., not an orbital electron). For the purpose of simplicity, positron and electron capture modes are neglected. The resulting transmutated nucleus ends up in an excited nuclear state, which prompdy relaxes by giving offy rays. This is illustrated in Figure 2. 

Alternative symbols are given for the particles often it is sufficient to use the simplest (the one on the right). Electron capture is not nuclear radiation but is included for completeness. 

Self-Test 17.2A Identify the nuclide produced and write the nuclear equation for (a) electron capture by beryllium-7 (b) positron emission by sodium-22. 

Write the balanced nuclear equation for each of the following decays (a) p decay of actinium-228 (b) a. decay of radon-212 (c) a decay of francium-221 (d) electron capture by protacti n i um-230. 

Chemical effects of nuclear decay have been studied in Germanium through the use of Ge and Ge. Ge decays to Ga with a 275 day half-life by 100% electron capture with no y quanta emitted. Ge is a P emitter which decays to As with a 11.3 h half-life, by three jS transitions having maximum energies of 710 keV (23%), 1379 keV (35%) and 2196 keV (42%). From this are calculated maximum recoil energies of 1.7 eV, 4.5 eV and 10.2 eV, respectively. 

C22-0099. Complete the following nuclear reactions (a) positron emission from Si (b) electron capture by... 

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. 

The nuclear decay of radioactive atoms embedded in a host is known to lead to various chemical and physical after effects such as redox processes, bond rupture, and the formation of metastable states [46], A very successful way of investigating such after effects in solid material exploits the Mossbauer effect and has been termed Mossbauer Emission Spectroscopy (MES) or Mossbauer source experiments [47, 48]. For instance, the electron capture (EC) decay of Co to Fe, denoted Co(EC) Fe, in cobalt- or iron-containing compormds has been widely explored. In such MES experiments, the compormd tmder study is usually labeled with Co and then used as the Mossbauer source versus a single-line absorber material such as K4[Fe(CN)6]. The recorded spectrum yields information on the chemical state of the nucleogenic Fe at ca. 10 s, which is approximately the lifetime of the 14.4 keV metastable nuclear state of Fe after nuclear decay. 

NOE Nuclear Overhauser PDECD Pulse discharge electron-capture... 

In electron capture, the nuclear charge decreases by 1 because what happens is that a proton in the nucleus interacts with the electron to produce a neutron. 

Electron capture accomplishes the same end result as positron emission, but because the nuclear charge is low, positron emission is the expected decay mode in this case. Generally, electron capture is not a competing process unless Z 30 or so. 

The vacancy left in the low-energy K-shell will be filled by an electron from a higher level with the resultant emission of radiations of extra nuclear origin, X-rays, which are distinguished from the accompanying nuclear y radiation. It should be noted that the n p criterion is the same for both positron and electron capture processes and it is not unusual to find both occurring with different atoms of the same nuclide. 

For many of the analytical techniques discussed below, it is necessary to have a source of X-rays. There are three ways in which X-rays can be produced in an X-ray tube, by using a radioactive source, or by the use of synchrotron radiation (see Section 12.6). Radioactive sources consist of a radioactive element or compound which spontaneously produces X-rays of fixed energy, depending on the decay process characteristic of the radioactive material (see Section 10.3). Nuclear processes such as electron capture can result in X-ray (or y ray) emission. Thus many radioactive isotopes produce electromagnetic radiation in the X-ray region of the spectrum, for example 3He, 241Am, and 57Co. These sources tend to produce pure X-ray spectra (without the continuous radiation), but are of low intensity. They can be used as a source in portable X-ray devices, but can be hazardous to handle because they cannot be switched off. In contrast, synchrotron radiation provides an... 

A fourth mode of decay, which results in the nucleus reducing its proton number by one, is called electron capture, whereby a proton from the nucleus captures one of the extranuclear (orbital) electrons, converting itself into a nuclear neutron. The daughter is isobaric (same mass) with the parent, but has a proton number which is decreased by one ... 

Know that nuclear stability is best related to the neutron-to-proton ratio (n/p), which starts at about 1/1 for light isotopes and ends at about 1.5/1 for heavier isotopes with atomic numbers up to 83- All isotopes of atomic number greater than 84 are unstable and will commonly undergo alpha decay. Below atomic number 84, neutron-poor isotopes will probably undergo positron emission or electron capture, while neutron-rich isotopes will probably undergo beta emission. 

The following stage is core collapse caused by electron capture or photodisintegration of iron. According to the traditional view, collapse leads to formation of a neutron star which cools by neutrino emission and decompression of matter when it reaches nuclear density (10 g cm ). The rebound that follows generates a shock wave which is capable of reigniting a good few nuclear reactions as it moves back out across the stellar envelope. 

Theoretically, nuclear strength is enhanced by internal transmutations of protons into neutrons, under the mandate of the weak interaction, either by positron emission (p — n + e+ + v) or by electron capture (p + e n + v). However, the weak interaction is much slower than the strong interaction. The question remains as to whether it will happen inside the star, or outside, once the matter has been expelled, i.e. after the explosion. This is not just an academic question. The answer we give will determine whether or not we can corroborate explosive nucleosynthesis by observation. 

At very high temperatures, above 3 or 4 billion k, silicon is consumed so quickly that positron emission and electron capture reactions which might modify the n/p ratio are largely short-circuited. The weak interaction does not have time to convert any appreciable fraction of protons into neutrons during the brief period of thermonuclear combustion. It follows that, starting with matter that is initially dominated by nuclei containing equal numbers of neutrons and protons, such as oxygen-16 and silicon-28, the final products must conserve Z = N, unless they move away from nuclear stability beyond calcium-40, the last stable a element. 

GC = gas chromatography, Py = pyrolysis (flash or hydrous heating), MS = mass spectrometry (HR = high resolution), IRMS = isotope ratio mass spectrometry, HPLC = high-pressure liquid chromatography, EC = electron capture. Cl = chemical ionization, NMR = nuclear magnetic resonance spectrometry. X-ray = X-ray crystallography. 

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