Alpha Decay Rates Research Articles

α decay in intense laser fields: Calculations using realistic nuclear potentials

We calculate the effect of intense laser fields on nuclear alpha decay processes, using realistic and quantitative nuclear potentials. We show that alpha decay rates can indeed be modified by strong laser fields to some finite extent. We also predict that alpha decays with lower decay energies are relatively easier to be modified than those with higher decay energies, due to longer tunneling paths for the laser field to act on. Furthermore, we predict that modifications to angle-resolved penetrability are easier to achieve than modifications to angle-integrated penetrability.

Measuring the Signs of 1Hα Chemical Shift Differences Between Ground and Excited Protein States by Off-Resonance Spin-Lock R1ρ NMR Spectroscopy

Analysis of Carr-Purcell-Meiboom-Gill (CPMG) relaxation dispersion NMR profiles provides the kinetics and thermodynamics of millisecond-time-scale exchange processes involving the interconversion of populated ground and invisible excited states. In addition, the absolute values of chemical shift differences between NMR probes in the exchanging states, |Delta omega|, are also extracted. Herein, we present a simple experiment for obtaining the sign of (1)H(alpha) Delta omega values by measuring off-resonance (1)H(alpha) decay rates, R(1rho), using weak proton spin-lock fields. A pair of R(1rho) values is measured with a spin-lock field applied |Delta omega| downfield and upfield of the major-state peak. In many cases, these two relaxation rates differ substantially, with the larger one corresponding to the case where the spin-lock field coincides with the resonance frequency of the probe in the minor state. The utility of the methodology is demonstrated first on a system involving protein ligand exchange and subsequently on an SH3 domain exchanging between a folded state and its on-pathway folding intermediate. With this experiment, it thus becomes possible to determine (1)H(alpha) chemical shifts of the invisible excited state, which can be used as powerful restraints in defining the structural properties of these elusive conformers.

Relative longevity of odd-N nuclei in the heavy actinide region

It is shown that, contrary to the normal feature witnessed all across the periodic table that even–even nuclei are more abundant/longer-lived than their odd-A neighbours, many odd-mass heavy nuclei are seen to be much longer-lived than their even–even neighbours. In the trans-plutonium domain of even-Z actinides, all the predominantly alpha-decaying odd-N nuclei are longer-lived than their even-mass neighbours. Similar behaviour is observed for heavy odd-Z actinides as well. A semi-empirical criterion is stated to determine the relative longevity of the odd-N and even-N nuclei. This feature is sought to be explained by examining the respective alpha decay rates. A detailed discussion of α-decays of the β-stable curium (Z = 96) isotopic chain is presented to illustrate this phenomenon. Correspondence with a similar occurrence in spontaneously fissioning nuclei is briefly pointed out.

Alpha-decay rates of Yb and Gd in solar-neutrino detectors

The α-decay rates for the nuclides 168,170,171,172,173,174,176Yb and 148,150,152,154Gd have been estimated from transmission probabilities in a systematic α-nucleus potential and from an improved fit to α-decay rates in the rare-earth mass region. Whereas α-decay of 152Gd in natural gadolinium is a severe obstacle for the use of gadolinium as a low-energy solar-neutrino detector, we show that α-decay does not contribute significantly to the background in a ytterbium detector. An extremely long α-decay lifetime of 168Yb is obtained from calculation, which may be close to the sensitivity limit in a low-background solar-neutrino detector.

Proton, alpha and cluster decay rates for nuclei with [formula omitted] and [formula omitted

For studying the rates of radioactive nuclei in various decay chains we propose an approach unifying the advantages of the superfluid model for nucleon clustering and of the classical model for resonance tunneling in many-particle systems. We discuss the theoretical bases and numerical approach for decay rate predictions for some highly unstable proton rich trans-tin nuclei. Information on structure and nuclear mass of some exotic nuclei not yet experimentally accessible have also been obtained from a detailed analysis of the p, α and cluster decay rates. It is shown that the Casten-type rate systematics works very well in various schemes of valence nucleon numbers revealing similar decay properties for the nuclei with the same numbers of valence protons and neutrons above the 100 50Sn 50 and 208 82Pb 126 magic cores.

Induced swelling in radiation damaged ZrSiO 4

A hydrothermal gelation method was used to prepare phase pure polycrystalline ZrSiO 4 which was sintered to 95% theoretical density. Actinide doped samples containing 10 wt% 238Pu were prepared by an analogous procedure and incurred bulk radiation damage through internal alpha-decay processes. Undoped samples were subjected to external irradiation from 5.5 MeV alpha sources, and from a 60Co gamma source. Actinide doped ZrSiO 4 exhibits dose dependent swelling caused by displacement processes leading to ingrowth of amorphous regions. Bulk density and XRD measurements, as a function of dose, showed first order exponential ingrowth behavior similar to that observed in other actinide doped materials. Results are compared with reported data for naturally damaged crystals subjected to significantly lower alpha decay rates. No significant dose rate dependence on damage ingrowth has been observed. Kinetic models for the observed dose dependent swelling are proposed and rate constants for damage ingrowth in synthetic and natural crystals are compared. To study localized damage induced by both external alpha and gamma irradiation, vibrational Raman measurements were obtained for several accumulated doses. Results indicate that the initial stage of damage ingrowth is confined to the silicate sublattice. Vibrational results will be discussed in terms of microstructural changes which result from irradiation.

Alpha decay amplification in superdeformed nuclei: An important new mechanism of nuclear de-excitation at high angular momenta

Alpha decay rates of superdeformed nuclei are predicted to exhibit up to hundredfold emission rate amplifications when transmission coefficients are calculated taking cognizance of deformation rather than for spherical nuclei. For the reaction 40Ar + 109Ag it is shown that several heretofore unexplained experimental observations can be understood by this potentially new de-excitation mechanism.

On the theoretical absolute alpha decay rates

It is shown that the largely disputed discrepancy between theoretical and experimental absolute alpha decay rates can be diminished by a factor between 5 and 40 if one accurately takes into account the internal structure of the alpha particle in treating the average interaction problem.

Theoretical Alpha-Decay Rates for the Actinide Region

Theoretical Alpha-Decay Rates for the Actinide Region

On alpha-decay rates in heavy nuclei

The alpha-decay rates in heavy nuclei are analyzed by a method in which the decay rates are factored into one-body widths and spectroscopic factors. It is shown that the discrepancy between the absolute values of the experimental alpha-decay rates and those calculated with the nuclear shell model has mainly resided in the incorrect assessment of the one-body widths and that it can be largely removed by a more direct treatment of the average interaction between the alpha particle and the residual nucleus.

On the magnitude of alpha-decay rates

It is shown that the discrepancy between the absolute magnitude of alpha-decay rates observed in heavy nuclei and the corresponding rates calculated with the nuclear shell model can be largely removed by a direct treatment of the average interaction between the alpha-particle and the residual nucleus.

Alpha decay to vibrational levels in deformed odd-mass nuclei

The influence of the residual interaction between quasi-particles and phonons on alpha-decay rates in deformed odd-mass nuclei is analysed. The decay constant is given explicitly. The hindrance factors (HF) for two intrinsic states and their rotational bands in 237Np and 239Np are computed. It is shown that the mixture of the β-vibrational state and the quasi-particle state corresponding to favoured transitions lowers very much the hindrance factors.

Alpha Reduced Widths of Even-Mass Polonium Nuclei

An attempt is made to obtain the alpha decay rates of even-mass polonium nuclei as a product of two factors: (a) the probability of occurrence of an alpha cluster in a surface well, and (b) the decay rate when an alpha cluster is already formed there. From a comparison with the empirical values, it seems that our method for calculating the decay rates is valid. It is shown that the break in alpha reduced width on going from ${\mathrm{Po}}^{210}$ to ${\mathrm{Po}}^{212}$ can be interpreted as due to a break in the well width. It is suggested that the nuclear surface of ${\mathrm{Pb}}^{206}$ is considerably more diffuse than that of doubly magic ${\mathrm{Pb}}^{208}$. It is also pointed out that our method gives a larger probability of finding an alpha cluster for ${\mathrm{Po}}^{210}$ than for ${\mathrm{Po}}^{212}$, whereas the Mang theory leads to the opposite result---a larger probability for ${\mathrm{Po}}^{212}$.

Nonlocal potential barrier and the perey-effect in alpha decay

Abstract It is shown that nonlocality in the alpha-nucleus potential increases the barrier penetrability. The range of nonlocality of the alpha-nucleus potential is estimated by comparing experimental and theoretical alpha decay rates.

Barrier penetrabilities and the alpha-nucleus potential

Arguments are given, that the discrepancy in the absolute value of the theoretical alpha-decay rates can be explained by using the correct alpha-nucleus potential and accurate method for calculating the barrier penetrabilities.

Effect of pairing correlations on the alpha decay rates

Alpha decay theory is formulated within the framework of the superfluid model. Effects of superconductive pairing correlations on alpha decay absolute probabilities and on hindrance factors are investigated. Improved agreement between theory and data is obtained. (L.N.N.)

Alpha-decay hindrance-factor calculations

The hindrances factor, F, in alpha decay is defined in terms of constants A and B which are empirically determined for each element. The determination of A and B by fitting even-even alpha-decay rates is discussed. Using these values, hindrance factors for all known alpha groups of alpha emitters with greater than 128 neutrons and 83 protons have been calculated. The results are divided into four groups corresponding to odd-odd, odd-even, even-odd, and excited states of even-even alpha emitters. Hindrance factor distributions are presented in histogram form.

Alpha-Radioactivity in the 82-Neutron Region

In a survey for alpha-activity among cyclotron produced neutron deficient nuclides of the elements below lead, alpha-activity was detected in a number of rare earth nuclides with atomic number greater than 62, that of samarium, and in a gold and a mercury nuclide. A detailed study of the alpha-active nuclides of europium, gadolinium, terbium, and dysprosium was made.The relationship between alpha-decay rates and energies in the rare earth region is examined. Calculations of the "effective nuclear radius for alpha-particles" were made using five different alpha-decay rate formulas.The trends of the rare earth alpha-decay energies are discussed, particularly with respect to the discontinuity in neutron binding energies at the closed shell of 82 neutrons.