Two-proton radioactivity of exotic nuclei beyond proton drip-line

To search for new candidates of the true and simultaneous two-proton(2 p) radioactivity, the 2 p decay energies(Q2 p) are extracted by the Weizs?cker–Skyrme-4(WS4) model, the finite-range droplet model(FRDM), the Koura–Tachibana–Uno–Yamada(KTUY) model and the Hartree–Fock–Bogoliubov mean-field model with the BSk29 Skyrme interaction(HFB29). Then, the 2 p radioactivity half-lives are calculated within the generalized liquid drop model by inputting the four types of Q2 pvalues. By the energy and half-life constraints, it is found that the probable 2 p decay candidates are the nuclei beyond the proton-drip line in the region of Z≤50 based on the WS4 and KTUY mass models. For the FRDM mass model, the probable 2 p decay candidates are found in the region of Z≤44. However, the 2p-decaying candidates are predicted in the region of Z≤58 by the HFB29 mass model. It means that the probable 2 p decay candidates of Z50 are only predicted by the HFB29 mass model. Finally, the competition between the true 2p radioactivity and α-decay for the nuclei above the N=Z=50 shell closures is discussed. It is shown that ~(101)Te,~(111)Ba and ~(114)Ce prefer to 2p radioactivity and the dominant decay mode of ~(107)Xe and ~(116)Ce is α-decay.     

Heavy-particle radioactivity of superheavy nuclei

The concept of heavy-particle radioactivity (HPR) is changed to allow emitted particles with Z(e) > 28 from parents with Z > 110 and daughter around (208)Pb. Calculations for superheavy (SH) nuclei with Z = 104-124 are showing a trend toward shorter half-lives and larger branching ratio relative to α decay for heavier SHs. It is possible to find regions in which HPR is stronger than alpha decay. The new mass table AME11 and the theoretical KTUY05 and FRDM95 masses are used to determine the released energy. For 124 we found isotopes with half-lives in the range of ns to ps.     

Self-consistent description of proton radioactivity

Proton radioactivity from spherical nuclei is described by a fully self-consistent calculation based on relativistic density functionals derived from meson exchange and point coupling models. The experimental data are well reproduced and a strong evidence of the effects of configuration mixing is found for nuclei away from the N=82 magic number.     

New experimental results in proton radioactivity

A review of experimental data obtained recently on proton-radioactive nuclei is presented. The highlights include the observation of fine structure in proton emission, for the decays of ¹³¹Eu, ¹⁴⁵Tm and ¹⁴⁶Tm, and the studies of the excited states in proton-emitting nuclei. The observation limits are extended to few nanobarns cross-sections ( ¹⁴⁰Ho, ¹⁶⁴Ir and ¹³⁰Eu) and few microsecond half-lives (e.g., ¹⁴⁵Tm). Measured decay properties for thirty-nine proton-emitting ground and isomeric states contributed to the understanding of nuclear masses and evolution of single-particle states at and beyond the proton drip line. Experimental results have stimulated new theoretical approaches to proton emission and the structure of unbound narrow resonance states. Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"e-mail: rykaczew@phy.ornl.gov     

Systematics of half-lives for proton radioactivity

Half-life measurements for both ground-state and isomeric transitions in proton radioactivity are systematized by using a semiempirical, one-parameter model based on tunneling through a potential barrier, where the centrifugal and overlapping effects are taken into account within the spherical nucleus approximation. This approach, which has been successfully applied to alpha decay cases covering ∼ 30 orders of magnitude in half-life, has shown, in addition, very adequate at fitting all existing data on partial half-life, T _1/2p , of proton emission from nuclei. Nearly 70 measured half-life values have been analysed, and the data could be described by two straight lines relating the pure Coulomb contribution to half-life with the quantity (Z _d is the atomic number of the daughter nucleus, μ₀ is the reduced mass, and Q _p is the total nuclear energy available for decay). These straight lines are shown to correspond to different degrees of deformation, namely, very prolate ( δ ≳ 0.1 , and other shaped ( δ ≲ 0.1 parent nuclei. The goodness in reproducing the data attained in the present systematics allows for half-life predictions for a few possible cases of proton radioactivity not yet experimentally accessed.     

Cluster preformation in heavy nuclei and radioactivity half-lives

Various cluster radioactivities of heavy nuclei have been investigated by using the unified fission model (UFM). The cluster preformation factors have been extracted by employing the UFM connected with the experimental half-lives, and the relationship of preformation probability between the cluster and -particle has been discussed in detail. In addition, the cluster preformation probability has been studied in the framework of statistical physics. Some useful predictions on the cluster emission half-lives are provided for future experiments.     

A formula for half-life of proton radioactivity

We present a formula for proton radioactivity half-lives of spherical proton emitters with the inclusion of the spectroscopic factor. The coefficients in the formula are calibrated with the available experimental data. As an input to calculate the half-life, the spectroscopic factor that characterizes the important information on nuclear structure should be obtained with a nuclear many-body approach. This formula is found to work quite well, and in better agreement with experimental measurements than other theoretical models. Therefore, it can be used as a powerful tool in the investigation of proton emission, in particular for experimentalists.     

Systematic calculations of cluster radioactivity half-lives in trans-lead nuclei

In the present work, based on the Wentzel-Kramers-Brillouin (WKB) theory, considering the cluster preformation probability (\begin{document}$ P_{c} $\end{document}), we systematically investigate the cluster radioactivity half-lives of 22 trans-lead nuclei ranging from ²²¹Fr to ²⁴²Cm. When the mass number of the emitted cluster \begin{document}$ A_{c} $\end{document} \begin{document}$ < $\end{document} 28, \begin{document}$P_{c} $\end{document} is obtained by the exponential relationship of \begin{document}$ P_{c} $\end{document} to the α decay preformation probability (\begin{document}$ P_{\alpha} $\end{document}) proposed by R. Blendowskeis \begin{document}$ et $\end{document} \begin{document}$ al. $\end{document} [Phys. Rev. Lett. 61, 1930 (1988)], while \begin{document}$ P_{\alpha} $\end{document} is calculated through the cluster-formation model (CFM). When \begin{document}$ A_{c} $\end{document} \begin{document}$ \ge $\end{document} 28, \begin{document}$ P_{c} $\end{document} is calculated through the charge-number dependence of \begin{document}$ P_{c} $\end{document} on the decay products proposed by Ren \begin{document}$ et $\end{document} \begin{document}$ al. $\end{document} [Phys. Rev. C 70, 034304 (2004)]. The half-lives of cluster radioactivity have been calculated by the density-dependent cluster model [Phys. Rev. C 70, 034304 (2004)] and by the unified formula of half-lives for alpha decay and cluster radioactivity [Phys. Rev. C 78, 044310 (2008)]. For comparison, a universal decay law (UDL) proposed by Qi \begin{document}$ et $\end{document} \begin{document}$ al. $\end{document} [Phys. Rev. C 80, 044326 (2009)], a semi-empirical model for both α decay and cluster radioactivity proposed by Santhosh [J. Phys. G: Nucl. Part. Phys. 35, 085102 (2008)], and a unified formula of half-lives for alpha decay and cluster radioactivity [Phys. Rev. C 78, 044310 (2008)] are also used. The calculated results of our work, Ni's formula , and the UDL can well reproduce the experimental data and are better than those of Santhosh's model. In addition, we extend this model to predict the half-lives for 51 nuclei, whose cluster radioactivity is energetically allowed or observed but not yet quantified in NUBASE2020.     

On the excitation of isovector dipole strength by inelastic proton scattering in the giant resonance region in light nuclei

A detailed comparison between inelastic α and p scattering in the giant resonance region of ^{24, 26}Mg, ²⁸Si and ⁴⁰Ca shows that there is no evidence for ΔT = 1, E1 excitation in the (p, p′) spectra. This is consistent with DWBA calculations using a recently obtained isovector interaction potential.     

Neutron and proton distribution in nuclei

We calculate the energy gap for deformed nuclei using the gap equation which appears in the Migdal theory of finite Fermi systems with pair correlations. To obtain good agreement with experiment for nuclei with neutron excess, it is necessary to choose differently the forms of the density dependent residual interaction for the protons and neutrons because of the difference between their density distributions. The distributions we get are in good agreement with experiment as well as with other theoretical predictions. We also show which approximations are required to reduce the general gap equation to the special Migdal equation.     

Neutron and proton densities in nuclei

A simple expression for nuclear densities which incorporates the correct asymptotic and central behaviour, gives quite accurate values for rms radii and surface thicknesses. It also brings out some important nuclear properties, (i) global constancy of neutron densities, (ii) equality of half-density radiiR for neutrons and protons, (iii) near constancy ofRN ^?1/3, (iv) larger surface thickness and rms radius for neutrons (v) shell effects on charge density.     

Investigation of proton radioactivity with the effective liquid drop model

Proton radioactivity has been investigated using the effective liquid drop model with varying mass asymmetry shapes and effective inertial coefficients. An effective nuclear radius constant formula replaces the old empirical one in the calculations. The theoretical half-lives are in good agreement with the available experimental data. All the deviations between the calculated logarithmic half-lives and the experimental values are less than 0.8.The root-mean-square(rms) deviation is 0.523. Predictions for the half-lives of proton radioactivity are made for elements across the periodic table. From the theoretical results, there are 11 candidate nuclei for proton radioactivity in the region Z <51. In the region Z >83, no nuclei are suggested as probable candidate nuclei for proton radioactivity within the selected range of half-lives studied.     

Evaluation of radioactivity induced by patient-specific devices in proton therapy

Journal of the Korean Physical Society - Estimating the radioactivity induced by patient-specific devices installed near the patient skin is important, because patients are directly exposed during...     

High-energy proton scattering on nuclei

We have studied high-energy proton scattering on Be, C, Cu and Pb targets using a single-arm spectrometer. The projectile momenta were 19 and 24 GeV/c, the square of the four-momentum transfer varied from t = 0.1 to t = 4.4 GeV². We have recorded momentum distributions of scattered protons in the high-momentum range. An application of multiple-scattering theory yielded agreement of calculation and experimental results to within a ± 30% uncertainty of the former.     

低能质子回旋加速器内部束流测量探头的感生放射性

 为满足回旋加速器内部束流测量探头产生低放射性的要求,通过理论分析和蒙特卡罗模拟方法,研究了11 MeV,50 μA质子束轰击铜探头产生的感生放射性,得到各种感生放射性核素的饱和放射性活度,并对结果进行了比较。分析结果表明,采用软件FLUKA进行蒙特卡罗模拟,核反应考虑完全,可同时计算不同照射时间下的直接和间接感生放射性,计算结果准确。应用该方法,质子束轰击不同测量探头产生的感生放射性可以得到详细和准确的分析和预测。     

低能质子回旋加速器内部束流测量探头的感生放射性

为满足回旋加速器内部束流测量探头产生低放射性的要求,通过理论分析和蒙特卡罗模拟方法,研究了11 MeV,50 μA质子束轰击铜探头产生的感生放射性,得到各种感生放射性核素的饱和放射性活度,并对结果进行了比较。分析结果表明,采用软件FLUKA进行蒙特卡罗模拟,核反应考虑完全,可同时计算不同照射时间下的直接和间接感生放射性,计算结果准确。应用该方法,质子束轰击不同测量探头产生的感生放射性可以得到详细和准确的分析和预测。