Coulomb Dissociation Experiments Research Articles

The 59Fe (n,γ) 60Fe Cross Section from the Surrogate Ratio Method and Its Effect on the 60Fe Nucleosynthesis

Abstract The long-lived 60Fe (with a half-life of 2.62 Myr) is a crucial diagnostic of active nucleosynthesis in the Milky Way galaxy and in supernovae near the solar system. The neutron-capture reaction 59Fe(n,γ)60Fe on 59Fe (half-life = 44.5 days) is the key reaction for the production of 60Fe in massive stars. This reaction cross section has been previously constrained by the Coulomb dissociation experiment, which offered partial constraint on the E1 γ-ray strength function but a negligible constraint on the M1 and E2 components. In this work, for the first time, we use the surrogate ratio method to experimentally determine the 59Fe(n,γ)60Fe cross sections in which all the components are included. We derived a Maxwellian-averaged cross section of 27.5 ± 3.5 mb at kT = 30 keV and 13.4 ± 1.7 mb at kT = 90 keV, roughly 10%–20% higher than previous estimates. We analyzed the impact of our new reaction rates in nucleosynthesis models of massive stars and found that uncertainties in the production of 60Fe from the 59Fe(n,γ)60Fe rate are at most 25%. We conclude that stellar physics uncertainties now play a major role in the accurate evaluation of the stellar production of 60Fe.

Microscopic investigation of the Li8(n,γ)Li9 reaction

The $^8$Li($n,\gamma$)$^9$Li reaction plays an important role in several astrophysics scenarios. It cannot be measured directly and indirect experiments have so far provided only cross section limits. Theoretical predictions differ by an order of magnitude. In this work we study the properties of $^9$Li bound states and low-lying resonances and calculate the $^8$Li($n,\gamma$)$^9$Li cross section within the no-core shell model with continuum (NCSMC) with chiral nucleon-nucleon and three-nucleon interactions as the only input. The NCSMC is an ab initio method applicable to light nuclei that provides a unified description of bound and scattering states well suited to calculate low-energy nuclear scattering and reactions. Our calculations reproduce the experimentally known bound states as well as the lowest $5/2^-$ resonance of $^9$Li. We predict a $3/2^-$ spin-parity assignment for the resonance observed at 5.38 MeV. In addition to the a very narrow $7/2^-$ resonance corresponding presumably to the experimental 6.43 MeV state, we find several other broad low-lying resonances. Our calculated $^8$Li($n,\gamma$)$^9$Li cross section is within the limits derived from the 1998 National Superconducting Cyclotron Laboratory Coulomb-dissociation experiment [Phys. Rev. C {\bf 57}, 959 (1998)]. However, it is higher than cross sections obtained in recent phenomenological studies. It is dominated by a direct E1 capture to the ground state with a resonant contribution at $\sim0.2$ MeV due to E2/M1 radiation enhanced by the $5/2^-$ resonance.

Borromean Feshbach resonance in $^{11}$Li studied via $^{11}$Li($p$,$p'$)

Abstract A dipole resonance of $^{11}$Li is found by a $^9$Li + $n$ + $n$ three-body model analysis with the complex-scaling method. The resonance can be interpreted as a bound state in the $^{10}$Li + $n$ system, i.e., a Feshbach resonance in the $^9$Li + $n$ + $n$ system. As a characteristic feature of the Feshbach resonance of $^{11}$Li, the $^{10}$Li + $n$ threshold is open above the $^{9}$Li + $n$ + $n$ one, which reflects a distinctive property of the Borromean system. A microscopic four-body reaction calculation for the $^{11}$Li($p$,$p'$) reaction at 6 MeV/nucleon is performed by taking into account the resonant and nonresonant continuum states of the three-body system. The calculation of angular distributions of the elastic and inelastic scattering as well as the energy spectrum reproduced a recent experimental result. Furthermore, the $E1$ strength distribution from a Coulomb dissociation experiment was also reproduced in this framework. This means that the existence of the Borromean Feshbach resonance may consistently answer a long-standing open question of an excited state of $^{11}$Li.

Coulomb dissociation ofN20,21

Neutron-rich light nuclei and their reactions play an important role for the creation of chemical elements. Here, data from a Coulomb dissociation experiment on $^{20,21}$N are reported. Relativistic $^{20,21}$N ions impinged on a lead target and the Coulomb dissociation cross section was determined in a kinematically complete experiment. Using the detailed balance theorem, the $^{19}\mathrm{N}(\mathrm{n},\gamma)^{20}\mathrm{N}$ and $^{20}\mathrm{N}(\mathrm{n},\gamma)^{21}\mathrm{N}$ excitation functions and thermonuclear reaction rates have been determined. The $^{19}\mathrm{N}(\mathrm{n},\gamma)^{20}\mathrm{N}$ rate is up to a factor of 5 higher at $T<1$\,GK with respect to previous theoretical calculations, leading to a 10\,\% decrease in the predicted fluorine abundance.

Comment on “Structure effects in theN15(n,γ)N16radiative capture reaction from the Coulomb dissociation ofN16”

In their recent study Neelam, Shubhchintak, and Chatterjee have claimed that ``it would certainly be useful to perform a Coulomb dissociation experiment to find the low-energy capture cross section for the reaction'' $^{15}\mathrm{N}$($n,\ensuremath{\gamma}$)$^{16}\mathrm{N}$. However, it is obvious that a Coulomb dissociation experiment cannot constrain this capture cross section because the dominating branchings of the capture reaction lead to excited states in $^{16}\mathrm{N}$, which do not contribute in a Coulomb dissociation experiment. An estimate of the total $^{15}\mathrm{N}$($n,\ensuremath{\gamma}$)$^{16}\mathrm{N}$ cross section from Coulomb dissociation of $^{16}\mathrm{N}$ requires a precise knowledge of the $\ensuremath{\gamma}$-ray branchings in the capture reaction. Surprisingly, the calculation of Neelam, Shubhchintak, and Chatterjee predicts a strongly energy-dependent ground-state branching of the order of 0.05% to 0.6% at energies between 100 and 500 keV, which is almost 2 orders of magnitude below calculations in the direct capture model. Additionally, this calculation of Neelam, Shubhchintak, and Chatterjee deviates significantly from the expected energy dependence for $p$-wave capture.

Properties of Lithium-11 and Carbon-22 at leading order in halo effective field theory

We study the $^{11}\mathrm{Li}$ and $^{22}\mathrm{C}$ nuclei at leading order (LO) in halo effective field theory (Halo EFT). Using the value of the $^{22}\mathrm{C}$ rms matter radius deduced in Ref. [1] as an input in a LO calculation, we simultaneously constrained the values of the two-neutron (2$n$) separation energy of $^{22}\mathrm{C}$ and the virtual-state energy of the $^{20}\mathrm{C}-$neutron system (hereafter denoted $^{21}$C). The 1$-\sigma$ uncertainty of the input rms matter radius datum, along with the theory error estimated from the anticipated size of the higher-order terms in the Halo EFT expansion, gave an upper bound of about 100 keV for the 2$n$ separation energy. We also study the electric dipole excitation of 2$n$ halo nuclei to a continuum state of two neutrons and the core at LO in Halo EFT. We first compare our results with the $^{11}\mathrm{Li}$ data from a Coulomb dissociation experiment and obtain good agreement within the theoretical uncertainty of a LO calculation. We then obtain the low-energy spectrum of $B(E1)$ of this transition at several different values of the 2$n$ separation energy of $^{22}\mathrm{C}$ and the virtual-state energy of $^{21}\mathrm{C}$. Our predictions can be compared to the outcome of an ongoing experiment on the Coulomb dissociation of $^{22}\mathrm{C}$ to obtain tighter constraints on the two- and three-body energies in the $^{22}\mathrm{C}$ system.

Structure effects in theN15(n,γ)N16radiative capture reaction from the Coulomb dissociation ofN16

Purpose : The aim of this paper is to calculate the $^{15}$N($n, \gamma$)$^{16}$N radiative capture cross section and its subsequent reaction rate by an indirect method and in that process investigate the effects of spectroscopic factors of different levels of $^{16}$N to the cross section. Method : A fully quantum mechanical Coulomb breakup theory under the aegis of post-form distorted wave Born approximation is used to calculate the Coulomb breakup of $^{16}$N on Pb at 100 MeV/u. This is then related to the photodisintegration cross section of $^{16}$N($\gamma, n$)$^{15}$N and subsequently invoking the principle of detailed balance, the $^{15}$N($n, \gamma$)$^{16}$N capture cross section is calculated. Results : The non-resonant capture cross section is calculated with spectroscopic factors from the shell model and those extracted (including uncertainties) from two recent experiments. The data seems to favor a more single particle nature for the low-lying states of $^{16}$N. The total neutron capture rate is also calculated by summing up non-resonant and resonant (significant only at temperatures greater than 1 GK) contributions and comparison is made with other charged particle capture rates. In the typical temperature range of $0.1-1.2$ GK, almost all the contribution to the reaction rate comes from capture cross sections below 0.25 MeV. Conclusion : We have attempted to resolve the discrepancy in the spectroscopic factors of low-lying $^{16}$N levels and conclude that it would certainly be useful to perform a Coulomb dissociation experiment to find the low energy capture cross section for the reaction, especially below 0.25 MeV.

Coulomb Dissociation of 27P

In this work the astrophysical 26Si(p,γ)27P reaction is studied using the Coulomb dissociation technique. We performed a 27P Coulomb Dissociation experiment at GSI, Darmstadt (28 May-5 June 2007) using the ALADIN-LAND setup which allows complete-kinematic studies. A secondary 27P beam at 498 AMeV impinging a 515mg/cm2 Pb target was used. The relative energy of the outgoing system (26Si+p) is measured obtaining the resonant states of the 27P. Preliminary results show four resonant states measured at 0.36±0.07, 0.88±0.09, 1.5±0.2, 2.3±0.3 MeV and evidence of a higher state at around 3.1 MeV. The preliminary total cross section obtained for relative energies between 0 and 3 MeV has been measured and yields 55±7 mb.

Coulomb dissociation of 8B and 6Li

The analysis of high-energy Coulomb dissociation experiments with 8B and 6Li beams in order to extract low-energy S factors of the 7Be(p,γ)8B and 4He(d,γ)6Li radiative capture reactions relies on a precise knowledge of the reaction mechanism. A comparison of various experimental cross sections with predictions from theory allows us to identify the relevant ingredients that are necessary for a successful theoretical description. The cases of 8B and 6Li Coulomb breakup show substantial differences related to the structure of the nuclei.

Photodissociation of neutron deficient nuclei

The knowledge of the cross sections for photodissociation reactions like e.g. (γ, n) of neutron deficient nuclei is of crucial interest for network calculations predicting the abundances of the so-called p nuclei. However, only single cross sections have been measured up to now, i.e., one has to rely nearly fully on theoretical predictions. While the cross sections of stable isotopes are accessible by experiments using real photons, the bulk of the involved reactions starts from unstable nuclei. Coulomb dissociation (CD) experiments in inverse kinematics might be a key to expand the experimental database for p-process network calculations. The approach to test the accuracy of the CD method is explained.

Can the neutron-capture cross sections be measured with Coulomb dissociation?

In this paper we present first results from a 8Li electromagnetic neutron-breakup experiment. Specific reactions studied were Pb(8Li,7Li+n)Pb and C(8Li,7Li+n)C at 41 MeV/nucleon beam energy. This is an effort to compare the results of a Coulomb dissociation experiment with the well determined (n, γ) reaction cross sections at astrophysical energies. The angular dependence of the cross section above 7 degree, which is the grazing angle of 8Li-Pb system, is similar in shape for lead and carbon and approximately proportional to A 2/3 in magnitude indicating that the nuclear dissociation is the main component in this region. At very forward angles the angular distributions differ significantly and the electromagnetic dissociation dominates for the lead, although the nuclear contribution is not negligible.

Coulomb dissociation experiment for explosive hydrogen burning: study of the 22Mg(p, γ)23Al reaction

By taking advantage of the high efficiency of the Coulomb dissociation method, we studied the stellar 22Mg(p, γ)23Al reaction. The radiative width Γγ of the first excited state in 23Al was determined by measuring the intermediate-energy 23Al → 22Mg + p breakup process with a lead target.

Electromagnetic strength of neutron and proton single-particle halo nuclei

Electromagnetic strength functions of halo nuclei exhibit universal features that can be described in terms of characteristic scale parameters. For a nucleus with nucleon + core structure the reduced transition probability, as determined, e.g., by Coulomb dissociation experiments, shows a typical shape that depends on the nucleon separation energy and the orbital angular momenta in the initial and final states. The sensitivity to the final-state interaction (FSI) between the nucleon and the core can be studied systematically by varying the strength of the interaction in the continuum. In the case of neutron + core nuclei analytical results for the reduced transition probabilities are obtained by introducing the effective-range expansion. The scaling with the relevant parameters is found explicitly. General trends are observed by studying several examples of neutron + core and proton + core nuclei in a single-particle model assuming Woods–Saxon potentials. Many important features of the neutron halo case can be obtained from a square-well model. Rather simple analytical formulas are found. The nucleon–core interaction in the continuum affects the determination of astrophysical S factors at zero energy in the method of asymptotic normalisation coefficients (ANC). It is also relevant for the extrapolation of radiative capture cross sections to low energies.

Coulomb dissociation of high-energy radioactive beams: the case of 8B

Coulomb dissociation of 8 B is an alternative method to measure the low-energy 7 B(p,γ) 8 B cross section. This reaction is of great current interest in the context of solar neutrinos and has been studied recently both in direct proton-capture [Phys. Rev. Lett. 86 (2001) 3985, Nucl. Phys. A 696 (2001) 219, Phys. Rev. C 68 (2003) 065803, Phys. Rev. Lett. 90 (2003) 022501] and in Coulomb-dissociation experiments [Phys. Lett. B 391 (1997) 261, Eur. Phys. J. A 3 (1998) 213, Phys. Rev. Lett. 83 (1999) 2910, Phys. Rev. C 63 (2001) 065806, Phys. Rev. Lett. 90 (2003) 232501]. The validity of the latter method has been questioned since the role of E 2 multipolarity is considered controversial. The present experiment [Phys. Rev. Lett. 90 (2003) 232501] has studied observables that could clarify the role of a possible E 2 contribution.

Dipole excited states in 11Li with complex scaling

The 1 − excitations of the three-body halo nucleus 11Li are investigated. We use adiabatic hyperspherical expansion and solve the Faddeev equations in coordinate space. The method of complex scaling is used to compute the resonance states. The Pauli forbidden states occupied by core neutrons are excluded by constructing corresponding complex scaled phase equivalent two-body potentials. We use a recently derived neutron–core interaction consistent with known structure and reaction properties of 10Li and 11Li. The computed dipole excited states with J π =1/2 +, J π =3/2 +, and J π =5/2 + have energies ranging from 0.6 to 1.0 MeV and widths between 0.15 and 0.65 MeV. We investigate the dependence of the complex energies of these states on the 10Li spectrum. The finite spin-3/2 of the core and the resulting core–neutron spin–spin interaction are important. The connection with Coulomb dissociation experiments is discussed and a need for better measurements is pointed out.

Systematic study of8Bbreakup cross sections

Breakup cross sections of ${}^{8}\mathrm{B}$ are analyzed in a two-body structure model, with an inert ${}^{7}\mathrm{Be}$ core and a loosely bound valence proton. The nuclear induced breakup is calculated in an eikonal approximation, and Coulomb dissociation is calculated to first order. There is a strong correlation within this model between the total $E1$ strength and the one-proton removal cross section ${\ensuremath{\sigma}}_{1p}.$ Thus we find that the measured values of ${\ensuremath{\sigma}}_{1p}$ for a carbon target are consistent with the $E1$ strength extracted in recent Coulomb dissociation experiments. The predicted ${\ensuremath{\sigma}}_{1p}$ values on high-$Z$ targets are significantly larger than measured. We discuss how this discrepancy can be reduced by improving the description of Coulomb dissociation.

Detection of breakup fragments in inverse Coulomb dissociation experiments

In the framework of Coulomb dissociation experiments, performed to reconstruct the cross section of the inverse radiative capture process, the detection of breakup fragments is usually performed using separate detectors, which unavoidably are not sensitive to small relative angles. It is shown, by means of Monte Carlo simulations, that the phase-space constraints imposed by the detection geometry can bias, specially at very low relative energies, the extracted cross section, which turns out to be strongly dependent upon the assumed angular distribution of fragments in the intrinsic reference frame. A solution to the problem of the model-dependence of the response function is proposed, making use of a single three-stage detector for the identification and the relative energy measurement of the breakup fragments. A test measurement on the reaction 208Pb( 16O, 12C- α) 208Pb at 126 MeV incident energy has been performed, using a gas–Si–CsI tritelescope. The results indicate the feasibility of measuring very low relative energies in the Coulomb dissociation approach to the solution of important problems in nuclear astrophysics via the accurate determination of reaction rates at energies far below the Coulomb barrier.

Measurement ofE2Transitions in the Coulomb Dissociation of8B

In an effort to understand the implications of Coulomb dissociation experiments for the determination of the ${}^{7}\mathrm{Be}(p,\ensuremath{\gamma}{)}^{8}\mathrm{B}$ reaction rate, longitudinal momentum distributions of ${}^{7}\mathrm{Be}$ fragments produced in the Coulomb dissociation of 44 and 81 MeV/nucleon ${}^{8}\mathrm{B}$ beams on a Pb target were measured. These distributions are characterized by asymmetries interpreted as the result of interference between $E1$ and $E2$ transition amplitudes in the Coulomb breakup. When interpreted in the context of a first order perturbation theory of Coulomb dissociation that assumes a single particle ${}^{8}\mathrm{B}$ structure model, this measurement yields ${S}_{E2}/{S}_{E1}{\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}6.7}_{\ensuremath{-}1.9}^{+2.8}\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ at a fragment relative kinetic energy of 0.6 MeV.

Effects of E2 transitions in the Coulomb dissociation of 8B

We examine the Coulomb dissociation of aB in a model that has both E1 and E2 matrix elements. We find that the interference between El and E2 amplitudes produces large asymmetries in the angular and momentum distributions of the emitted protons and 7Be fragments. By measuring these asymmetries one may be able to put constraints on the E2 component and thereby improve the accuracy of the E1 strength that can be extracted from Coulomb dissociation experiments. We also investigate the effect of higher-order dynamical processes and find that they reduce the asymmetries in reactions on high-Z targets. They also reduee the effect of E2 transitions on the dissociation probability and on the peak height of the decay energy spectrum compared to predictions of first-order perturbation theory.

Double-phonon giant dipole resonances in relativistic heavy ion collisions

We report on Coulomb dissociation experiments utilizing a 208Pb-beam (641 MeV/nucleon) impinging on C, Sn, Ho, Pb and U targets. Excitation energy distributions for 208Pb are extracted from an exclusive measurement of the projectile decay products. The measured cross section is dominated for heavy targets by Coulomb excitation of giant resonance states in lead. A thorough analysis yields evidence for the excitation of the double-phonon giant dipole resonance. In contrast to earlier results obtained for other nuclei the extracted cross section for 208Pb exceeds that of theoretical predictions on the basis of a harmonic oscillator scenario only slightly by about a factor 1.3.