Neutron-rich

Neutron-rich lanthanide isotopes occur in the fission of uranium or plutonium and ate separated during the reprocessing of nuclear fuel wastes (see Nuclearreactors). Lanthanide isotopes can be produced by neutron bombardment, by radioactive decay of neighboring atoms, and by nuclear reactions in accelerators where the rate earths ate bombarded with charged particles. The rare-earth content of solid samples can be determined by neutron... 

Proton capture processes by heavy nuclei have already been briefly mentioned in several of the preceding sections. The (p,y) reaction can also be invoked to explain the presence of a number of proton-rich isotopes of lower abundance than those of nearby normal and neutron-rich isotopes (Fig. 1.5). Such isotopes would also result from expulsion of a neutron by a y-ray, i.e. (y,n). Such processes may again be associated with supernovae activity on a very short time scale. With the exceptions of " ln and " Sn, all of the 36 isotopes thought to be produced in this way have even atomic mass numbers the lightest is Se... 

If, before it decays, Li is struck by a prevalent " He nucleus then "B can be formed ("Li 4-" He -> "B 4- n) and this will survive longer than in a proton-rich environment ("B 4 p -> 3" He). Other neutron-rich species could also be synthesized and survive in greater numbers than would... 

We can use Fig. 17.13 to predict the type of disintegration that a radioactive nuclide is likely to undergo. Nuclei that lie above the band of stability are neutron rich they have a high proportion of neutrons. These nuclei tend to decay in such a way that the final n/p ratio is closer to that found in the band of stability. For example, a l4C nucleus can reach a more stable state by ejecting a (3 particle, which reduces the n/p ratio as a result of the conversion of a neutron into a proton (Fig. 17.15) ... 

FIGURE 17.15 Three different ways of reaching the band of stability- (black). Nuclei that are neutron rich (blue region) tend to convert neutrons into protons by P emission nuclei that are proton rich (red) tend to reach stability (black) by emitting a positron, capturing an electron, or emitting a proton. 

The pattern of nuclear stability can be used to predict the likely mode of radioactive decay neutron-rich nuclei tend to reduce their neutron count proton-rich nuclei tend to reduce their proton count. In general, only heavy nuclides emit a particles. 

B (c) tsCs is neutron rich (in the blue band) and there-... 

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 silver white, shiny, metal-like semiconductor is considered a semimetal. The atomic weight is greater than that of the following neighbor (iodine), because tellurium isotopes are neutron-rich (compare Ar/K). Its main use is in alloys, as the addition of small amounts considerably improves properties such as hardness and corrosion resistance. New applications of tellurium include optoelectronics (lasers), electrical resistors, thermoelectric elements (a current gives rise to a temperature gradient), photocopier drums, infrared cameras, and solar cells. Tellurium accelerates the vulcanization of rubber. 

Reactors are sources of neutrons, and thus most reactor-produced radionuclides are neutron-rich ft emitters. Reactor-produced radionuclides are of relatively low specific activity if the target nucleus is the same element as the product radionuclide, because the target and the product cannot then be chemically separated. 

The a-process Could the low [a/Fe] and low [Y/Eu] ratios in dSph stars be related by the a-process The a-process (or a-rich freeze out) occurs when a neutron-rich, a-rich gas is out of nuclear statistical equilibrium and is thought to be important in the formation of 44Ca (Woosley Weaver 1995), 48Ti (Naka-... 

The magic numbers which impart stability to a nucleus are 2, 8, 20, 28, 50, 82 or 122. The isotope, 39K, has a magic number equal to its number of neutrons, so it is probably stable. The others have a larger neutron-to-proton ratio, making them neutron-rich nuclei, so 40K and 41K might be expected to decay by beta emission. In fact, both 39K and 41K are stable, and 40K does decay by beta emission. 

A separate neutron capture process is needed for neutron-rich nuclides by-passed by the s-process and for species above 209Bi. A possible path for this rapid or r-process is shown in Fig. 6.9. 

Neutron-rich lanthanide isotopes, 14 635 Neutrons, 21 290 Nevirapine, 18 722... 

In principle the density dependence of the SE at higher densities (and further away from N = Z) can be probed by means of heavy-ion reactions using neutron rich radioactive beams. In ref. [35] possible observable effects from the isovector field are considered in terms of the RMF model. Of particular... 

In a simplistic and conservative picture the core of a neutron star is modeled as a uniform fluid of neutron rich nuclear matter in equilibrium with respect to the weak interaction (/3-stable nuclear matter). However, due to the large value of the stellar central density and to the rapid increase of the nucleon chemical potentials with density, hyperons (A, E, E°, E+, E and E° particles) are expected to appear in the inner core of the star. Other exotic phases of hadronic matter such as a Bose-Einstein condensate of negative pion (7r ) or negative kaon (K ) could be present in the inner part of the star. 

Isotopes that are neutron-rich, that have too many neutrons or not enough protons, lie above the belt of stability and tend to undergo beta emission because that decay mode converts a neutron into a proton. 

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 fate of stars also depends on the presence of a companion. Other violent episodes known as Novae or type la supemovae result from the accretion of materials from a partner star. Supemovae of type I are thought to be responsible for most of the production of the neutron-rich isotopes of the iron group (Woosley et al. 1995 Hoflich et al. 1998). One of the key parameters in stellar evolution, and consequently the nucleosynthetic outcome, is the metallicity, defined as the proportion of elements heavier than He. 

The nucleosynthetic sources for Ti isotopes are very similar to those of the isotopes of Ca, and Ti requires a neutron-rich zone to be produced in significant amoimts. In addition to the nonlinear effects, absolute isotopic compositions have been measured in a number of samples using double spike techniques (Niederer et al. 1985). Mass dependent fractionation effects are rarely resolved and are small, below 1 %o/amu except in one sample, where it reaches 1.3 %o/amu. In general the fractionation is in favor of the heavy isotopes partial condensation or evaporation may explain of this observation. 

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