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Hindrance factor

The decays of the odd A nuclei are referred to as hindered decays, and a hindrance factor may be defined as the ratio of the measured partial half-life for a given a transition to the half-life that would be calculated from the simple one-body theory applied to even-even nuclides. [Pg.192]

In general, these hindrances for odd A nuclei may be divided into five classes  [Pg.193]

If the hindrance factor is between 1 and 4, the transition is called a favored transition. In such decays, the emitted a particle is assembled from two low-lying pairs of nucleons in the parent nucleus, leaving the odd nucleon in its initial orbital. [Pg.193]

To form an a particle within a nucleus, two protons and two neutrons must come together with their spins coupled to zero and with zero orbital angular momentum relative to the center of mass of the a particle. These four nucleons are likely to come from the highest occupied levels of the nucleus. In odd A nuclei, because of the odd particle and the difficulty of getting a partner for it, one pah of nucleons is drawn from a lower lying level, causing the daughter nucleus to be formed in an excited state. [Pg.193]

A hindrance factor of 4-10 indicates a mixing or favorable overlap between the initial and final nuclear states involved in the transition. [Pg.193]


In the two polyisoprene isomers, the length of the repeat unit and the steric hindrance factor vary oppositely for the two isomers. The greater end-to-end distance in the trans isomer is the dominant influence on the order of 1q values. [Pg.62]

Johnson et al. [186] measured diffusion of fluorescein-labeled macromolecules in agarose gels. Their data agreed well with Eq. (85), which combined the hydrodynamic effects with the steric hindrance factors. Gibbs and Johnson [131] measured diffusion of proteins and smaller molecules in polyacrylamide gels using pulsed-field gradient NMR methods and found their data to fit the stretched exponential form... [Pg.584]

The polymerization sites at the molecule s exterior are likely to experience more fruitful collisions than sites on the interior. To account for such complex phenomena, an additional separable function was introduced to simulate steric hindrance factors at the molecular level. An arbitrary, but continuous, exponential function was selected. The resulting rate constant that yields a good fit of experimental population density distributions is... [Pg.285]

Meunier and coworkers investigated the degradation of arteflene using manganese(II) TPP as a heme model. They were able to spin-trap the secondary C-centred radical with the piperidyl radical (TEMPO) and the adduct 64c was fully characterized following acetylation of the crude reaction mixture (Scheme 20). An arteflene-heme adduct was not observed and the authors suggest that this is attributable to steric hindrance factors. However, this could be further evidence that endoperoxide antimalarials do not target heme. [Pg.1306]

Hindrance factors of >1000 indicate that the transition involves a parity change and a spin flip, that is, the spin projections of the initial and final states are antiparallel, which requires substantial reorganization of the nucleon in the parent when the a is emitted. [Pg.193]

Figure 4. The a-decay schemes of 190 192>19lBi the assigned spins are only tentative but are linked to each other by the multipolarity of the y transitions and by a branches with hindrance factors (HF) around unity. The dashed y transitions are observed but uncertainty exists because of doublet structure and the missed y transitions (indicated by e). Figure 4. The a-decay schemes of 190 192>19lBi the assigned spins are only tentative but are linked to each other by the multipolarity of the y transitions and by a branches with hindrance factors (HF) around unity. The dashed y transitions are observed but uncertainty exists because of doublet structure and the missed y transitions (indicated by e).
Z18Ra corresponding to 8% of the El molecular sum rule [8] In Z °Ra an enhanced ground state alpha particle decay width is already known and the systematics of the Ra isotopes suggest a decrease in the alpha hindrance factors for the 1 and 3 states--as predicted by the cluster model. [Pg.284]

S. Towner, "A Mass Dependence in Hindrance Factors for Favoured Gamow-Teller Transitions", to be published. [Pg.443]

Still another DA receptor model, based on the study of aporphines, takes chirality factors into consideration. This model suggested by Neumeyer (16, 96) postulates an obstruction or "obstacle" on the receptor that precludes appropriate interaction of aporphines in the 6aJ> configuration with the receptor. This model, in common with many others, also takes into account OH binding sites, conformational aspects, steric hindrance factors, and N-substitution with the observation as noted elsewhere (e.g., 97), that N-substitution with groups as large as propyl may provide supplemental binding to favor D-2 receptor interaction. As the asymmetric center of apomophine is located on the carbon ct to the N, whereas in I-III it is located on the ben-... [Pg.237]

For odd nuclei, partial a and spontaneous fission half-lives calculated by R. Smolanczuk and A. Sobiczewski [55] have to be multiphed by a factor of 10 and 1000, respectively, thus making provisions for the odd particle hindrance factors. However, we have to keep in mind that fission hindrance factors show a wide distribution from 101 to 105, which is mainly a result of the specific levels occupied by the odd nucleon. For odd-odd nuclei, the fission hindrance factors from both the odd proton and the odd neutron are multiphed. For odd and odd-odd nuclei, the island character of a emitters disappears and for nuclei with neutron numbers 150 to 160 a-decay prevails down to rutherfordium and beyond. In the allegorical representation where the stability of SHEs is seen as an island in a sea of instability, see Chapter 8, even-even nuclei portray the situation at high-tide and odd nuclei at low-tide, when the island is connected to the mainland. [Pg.18]

Table 6 shows experimental values of conformational parameters for the Kuhn segment, A= /nl0 (where 10 is the structural unit length), hindrance factor of rotation around the single bond, cr=(/)l/2, and constants of the Mark-Kuhn-Hauvink equation, K(f [ri]/Mm, at different temperatures. [Pg.228]

Average ratios and standard deviations of permeability coefficients reported by Peck et al. (1994) determined from 11 HEM samples. "Ratios based upon free aqueous diffusion coefficients corrected by diffusional hindrance factors that were calculated from Eq. 6 for each permeant based upon an Rp of 21 A. [Pg.281]

The basis for comparing the ratios of the free diffusion coefficients and permeability coefficients was the assumption that hindrance considerations could be ignored. In the instance that this assumption is valid (i.e., the case of large pore dimensions relative to solute radii), the free diffusion coefficients are a reasonable approximation to the diffusion coefficients of the solutes in the membrane. In the instance that hindrance considerations are not negligible, due to pore dimensions that lead to diffusion-restricting hydrodynamic interactions between the solute and the membrane, the diffusion coefficient of the solute in the membrane is a function of both the solute parameters and the properties of the membrane. In this case, the effective diffusion coefficient can be approximated by the product of the free diffusion coefficient and a diffusional hindrance factor, HQC) (Deen, 1987) ... [Pg.282]

Fig. 2. The relationship between the first-order rate constant (k) for hydrolysis and the steric hindrance factor (F) for dipeptides of the type X-glycine. From Muramatu et al. (1963a,b). Fig. 2. The relationship between the first-order rate constant (k) for hydrolysis and the steric hindrance factor (F) for dipeptides of the type X-glycine. From Muramatu et al. (1963a,b).
The high temperature reactors like VHTR holds the promise to be applied various chemical processes that need high temperature, especially for coal processes, to produce hydrocarbons and hydrogen. However, in high temperature reactors, due to material limitation at present, the pressure of chemical process should be in the same range as the primary coolant pressure, which may be a hindrance factor in some processes. [Pg.22]

Here H(r, r ) is a steric hindrance factor (see following text) and x9 is the standard chemical potential of an ion of type i inside the pore. We use a previously obtained estimate (13)... [Pg.453]

Note that only pores with r > rs participate, because the hindrance factor is zero for r = rs (eq 11). The net number of molecules transported across the membrane is the time integral of Ns over the duration of the simulation and is a quantity that should be measurable for different experimental conditions, particularly different pulse magnitudes, durations, and shapes. The terms... [Pg.456]

But the polymer chain will probably have an effective diameter which is 1.5 to 2 times that for a compact molecule of the same molecular weight. This will reduce the bulk diffusivity and also decrease the hindrance factor. [Pg.459]


See other pages where Hindrance factor is mentioned: [Pg.53]    [Pg.180]    [Pg.275]    [Pg.220]    [Pg.192]    [Pg.197]    [Pg.308]    [Pg.202]    [Pg.209]    [Pg.263]    [Pg.265]    [Pg.265]    [Pg.266]    [Pg.281]    [Pg.282]    [Pg.199]    [Pg.233]    [Pg.28]    [Pg.535]    [Pg.283]    [Pg.48]    [Pg.2208]    [Pg.147]    [Pg.457]    [Pg.2192]    [Pg.459]   
See also in sourсe #XX -- [ Pg.192 ]




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