Perspectives from above and beyond the proton drip-line

This paper will review the dramatic increase in our knowledge of one and two proton unbound nuclei [1] such as recoil decay tagging [2] are revealing unique insights into the structure of nuclei beyond the proton drip-line. These studies of excited states provide complementary information to proton radioactivity studies, particularly regarding the role of deformation [3]. Radioactive beams are being used to study two-proton unbound resonances and to study explosive nuclear astrophysical reactions in the region of the proton drip-line.     

A gamma-ray signature of energetic sources of cosmic-ray nuclei

Astrophysical sources of nuclei are expected to produce a broad spectrum of isotopes, many of which are unstable. An unstable nucleus can beta-decay outside the source into a single-electron ion. Heavy one-electron ions, thus formed, can be excited in their interactions with cosmic microwave background photons, in which case they relax to the ground state with the emission of a gamma ray. Repetitive cycles of excitation and gamma-ray emission can produce an observable feature in the gamma-ray spectrum with a maximum around 8 GeV (for iron). We find that the observed spectrum of Centaurus A is consistent with a substantial flux of nuclei accelerated to 0.1 EeV. A characteristic 5-10 GeV (iron) shoulder in the gamma-ray spectra of various sources can help identify astrophysical accelerators of nuclei or set upper limits on nuclear acceleration.     

爆发性核合成与核结构

讨论了天体物理环境中爆发性核合成及其与核结构的紧密关系.用反射不对称壳模型计算了远离稳定线丰中子核148Ba的低能八极转动带,结果与实验很好符合.展示了其应用于不稳定核低能态计算的有效性 ,以及在核天体物理研究中的应用前景.The explosive nucleosynthesis in the astrophysical environment and its close link to nuclear structure are discussed. The low lying octupole bands for neutron rich nucleus 148 Ba far from the stability line have been calculated by the reflection asymmetric shell model and the results are in good agreement with the experimental data, presenting the capability of the model for calculations of the low lying states of unstable nuclei as well as the foreground of application in nuclear astrophysics.     

Creation of localized optical waves that Do not obey the radiation condition at infinity

X-ray bursts have been suggested as a possible site for the astrophysical rp-process. The time scale for the process is governed by beta-decay half-lives of several even-even N = Z waiting point nuclei, in particular, N = Z = 40 80Zr. A 4.1(+0.8/-0.6)-s beta(+)/EC half-life for 80Zr was determined by observing delayed 84-keV gamma rays depopulating a T(1/2) = 4-&mgr;s isomer at 312 keV in the daughter 80Y. As this half-life is lower than many previously predicted values, the calculated excessive production of A = 80 nuclides in astrophysical x-ray burst scenarios is reduced, and less extreme conditions are necessary for the production of heavier nuclides.     

Astrophysical Rates for ¹²N(p,)¹³O Direct Capture Reaction

The proton capture on the unstable nuclei plays a very important role in nucleonsynthesis. The ¹²N(p,)¹³O reaction rates at the energies of astrophysical interest are estimated with the spectroscopic factor and asymptotic normalization coefficient methods. The present results show that the ¹²N(p,)¹³O reaction may play an important role in x-ray bursts.     

Density functional theory for reactions of astrophysical interest

For astrophysical processes nuclear reactions close to the particle emission threshold are of particular importance. As representative examples we investigate pairing resonances and new low-energy multipole modes in light and heavy exotic nuclei with a large charge asymmetry. As a common theoretical background, density functional theory and Fermi Liquid Theory are used. In particular, we consider the spectroscopy particle unstable systems, carrying the properties of open quantum systems. Results for the continuum spectroscopy of ¹⁰Li, the neutron-rich carbon isotopes, and the electromagnetic response of Sn-isotopes ¹³⁸Ba are presented.     

Challenge towards muonic atom formation with unstable nuclei

X-ray spectroscopy of muonic atoms is an important tool to obtain information on the nuclear charge distribution of nuclei. It has been successfully used for many years to study stable isotopes in condensed or gaseous states. A new method has been proposed to extend muonic atom X-ray spectroscopy to the use of radioactive isotope beams to form muonic atoms with unstable nuclei. This new method allows studies of the nuclear properties and nuclear sizes of unstable atoms by means of the muonic X-ray method at facilities where both negative muon and radioactive nuclear beams would be available. Progress of a feasibility study at RIKEN-RAL muon facility is also reported. Received: 1 May 2001 / Accepted: 4 December 2001     

Direct measurements of (p, \gamma) cross-sections at astrophysical energies using radioactive beams and the Daresbury Recoil Separator

There are a number of astrophysical environments in which the path of nucleosynthesis proceeds through proton-rich nuclei. These nuclei have traditionally not been available as beams, and thus proton-capture reactions on these nuclei could only be studied indirectly. At the Holifield Radioactive Ion Beam Facility (HRIBF), some of the first direct measurements of (p, $ \gamma$ ) cross-sections on radioactive beams have been made. The Daresbury Recoil Separator (DRS) has been used to separate the recoils of interest from the unreacted primary beam and identify them in an isobutane-filled ionization counter. First data from ¹⁷F (p, $ \gamma$ ¹⁸Ne and ⁷Be (p, $ \gamma$ ⁸B measurements are presented.     

Direct mass measurements of exotic nuclei

The present status and recent results from direct mass measurements of exotic nuclei are presented. ISOL, in-flight, and combined facilities provide a wide variety of nuclides far-off stability covering a wide range of half-lives down to the sub-millisecond region. Modern direct mass measurements are carried out using frequency and time-of-flight techniques. The obtained accurate mass data point to nuclear-structure phenomena and serve as a basis for astrophysical and weak-interaction studies. Received: 21 March 2002 / Accepted: 16 May 2002 / Published online: 31 October 2002 RID="a" ID="a"e-mail: c.scheidenberger@gsi.de     

天体演化过程中CNO核子辐射俘获反应

C和N核的质子辐射俘获反应对恒星平稳H燃烧阶段的能量产生和元素核合成起重要作用, C, N和O 核的中子辐射俘获是原初核合成和AGB星核合成的关键反应, 精确测定它们天体物理反应率有重要意义。 除13N(p, γ)14O和16N(n, γ)17N等不稳定核的核子辐射俘获反应外, 国际上已完成了其中若干反应的直接测量工作。 但12C(p, γ)13N, 13C(p, γ)14N和15N(p, γ)16O等CNO循环关键反应的实验测量还没有达到天体物理感兴趣的能区。 13C(n, γ)14C,15N(n, γ)16N和18O(n, γ)19O等中子辐射俘获反应测量的能量跨度较大, 截面仍存在较大的不确定性。 介绍了这些反应的研究进展, 并讨论了间接测量这些反应的方法和可行性。 The proton radiative capture reactions of C and N nuclei are important for the energy production and nucleosynthesis in the CNO cycle, and the neutron radiative capture reactions of C, N and O nuclei are key reactions for the inhomogeneous Big Bang nucleosynthesis as well as for the neutron induced CNO cycle in AGB stars. So far, most of these reactions have been measured except some reactions of the unstable nuclei, such as 13N(p, γ)14O and 16N(n, γ)17N. While the direct measured reactions, such as the  12C(p, γ)13N, 13C(p, γ)14N and 15N(p, γ)16O key reactions in CNO cycle, have not reached down to the stellar energies. In addition, the large uncertainties still exist in the measured neutron capture reactions such as 13C(n, γ)14C,15N(n, γ)16N and 18O(n, γ)19O. Thus it is significant to determine their astrophysical reaction rates via the indirect measurements. In this paper, the research status and feasibility of the indirect measurements for these reactions are discussed.     

Astrophysical constraints on particle properties

I summarize some astrophysical phenomenon like gamma ray bursters, astrophysical proof of the existence of blackholes, Active galactic nuclei — as high energy neutrino sources, and some unsolved issues in supernova. I touch on the aspects where novel particle properties (like neutrino mass and magnetic moment) are invoked to understand the astronomical observations.     

Pro duction of Exotic Nuclei in Low-Energy Multi-Nucleon Transfer Reactions

Multinucleon transfer processes in low-energy heavy ion collisions open a new field of research in nuclear physics, namely, production and studying properties of heavy neutron rich nuclei. This not-yet-explored area of the nuclear map is extremely important for understanding the astrophysical nucleosynthesis and the origin of heavy elements. Beams of very heavy U-like ions are needed to produce new long-living isotopes of transfermium and superheavy elements located very close to the island of stability.The calculated cross sections are high enough to perform the experiments at available accelerators.Beams of medium-mass ions (such as 136Xe, 192Os, 198Pt) can be used for the production of neutron rich nuclei located along the neutron closed shell N = 126 (the last waiting point) having the largest impact on the astrophysical r-process. The Low-energy multinucleon transfer reactions is a very efficient tool also for the production and spectroscopic study of light exotic nuclei. The corresponding cross sections are 2 or 3 orders of magnitude larger as compared with high energy fragmentation reactions.     

Testing fundamental physics with astrophysical transients

Explosive astrophysical transients at cosmological distances can be used to place precision tests of the basic assumptions of relativity theory, such as Lorentz invariance, the photon zero-mass hypothesis, and the weak equivalence principle (WEP). Signatures of Lorentz invariance violations (LIV) include vacuum dispersion and vacuum birefringence. Sensitive searches for LIV using astrophysical sources such as gamma-ray bursts, active galactic nuclei, and pulsars are discussed. The most direct consequence of a nonzero photon rest mass is a frequency dependence in the velocity of light propagating in vacuum. A detailed representation of how to obtain a combined severe limit on the photon mass using fast radio bursts at different redshifts through the dispersion method is presented. The accuracy of the WEP has been well tested based on the Shapiro time delay of astrophysical messengers traveling through a gravitational field. Some caveats of Shapiro delay tests are discussed. In this article, we review and update the status of astrophysical tests of fundamental physics.     

Mass prediction of proton-rich nuclides with the Coulomb displacement energies in the relativistic point-coupling model

The masses,one-and two-proton separation energies of proton-rich nuclei with Z = 20-55,are computed using the measured masses of mirror neutron-rich nuclei and the Coulomb displacement energies calculated from the relativistic point-coupling model.The implications for the proton drip lines,candidates for two-proton emitters,as well as the impact on the astrophysical rp-process are discussed.     

Magnetorotational-type instability in Couette-Taylor flow of a viscoelastic polymer liquid

We describe an instability of viscoelastic Couette-Taylor flow that is directly analogous to the magnetorotational instability (MRI) in astrophysical magnetohydrodynamics, with polymer molecules playing the role of magnetic field lines. By determining the conditions required for the onset of instability and the properties of the preferred modes, we distinguish it from the centrifugal and elastic instabilities studied previously. Experimental demonstration and investigation should be much easier for the viscoelastic instability than for the MRI in a liquid metal. The analogy holds with the case of a predominantly toroidal magnetic field such as is expected in an accretion disk, and it may be possible to access a turbulent regime in which many modes are unstable.     

Neutron-induced reaction rates for the <Emphasis Type="Italic">r</Emphasis>-process

Neutron-induced reaction rates for the formation of heavy and superheavy nuclei in the astrophysical r-process are presented. Neutron-induced reactions, including fission and neutron capture, at astrophysical temperatures are treated within the framework of the statistical model and calculated for targets with the atomic number 84 < Z < 118, using different mass and fission barrier predictions. The dependence of heavy element yields from nuclear explosions on the target nuclei, nuclear reactions, and nuclear models is discussed.     

Calculation of astrophysical reaction rate of 82Ge(n,γ)83Ge

The neutron capture reaction on a neutron-rich near closed-shell nucleus 82Ge may play an important role in the r-process following the fallout from nuclear statistical equilibrium in core-collapse supernovae.By carrying out a DWBA analysis for the experimental angular distribution of 82Ge(d, p)83Ge reaction we obtain the single particle spectroscopic factors, S2,5/2 and S0,1/2 for the ground and first excited states of 83Ge=82Ge(⊕)n, respectively. And then these spectroscopic factors are used to calculate the direct capture cross sections for the 82Ge(n, γ)83Ge reaction at energies of astrophysical interest. The optical potential for neutron scattering on unstable nucleus 82Ge is not known experimentally. We employed a real folding potential which was calculated by using the proper 82Ge density distribution and an effective nucleon-nucleon force DDM3Y.The neutron capture reactions on neutron-rich closed-shell nuclei are expected to be dominated by the direct capture to bound states. We will show that the direct capture rates on these nuclei are sensitive to the structure of the low-lying states.     

A quantum long time energy red shift: a contribution to varying <Emphasis Type="Italic">α</Emphasis> theories

By analyzing the survival probability amplitude of an unstable state we show that the energy corrections to this state in the long (t→∞) and relatively short (lifetime of the state) time regions are different. It is shown that in the considered model the above corrections decrease to zero as t→∞. It is hypothesized that this property could be detected by analyzing the spectra of distant astrophysical objects. The above property of unstable states may influence the measured values of possible deviations of the fine structure constant α as well as other astrophysical and cosmological parameters.