Photodisintegration Cross Section Research Articles

Doublet 1/2+ resonances of B9 in the complex scaling method

We try to resolve the longstanding controversy over the low-lying $1/{2}^{+}$ state in $^{9}\mathrm{B}$. Experimentally, the energies for this state show a gap between various measurements done by different groups and some of them reported that the existence of the state is unclear. The situation is similar in the theoretical calculations. We study the existence and structure of the $^{9}\mathrm{B}(1/{2}^{+}$) state based on our previous method for the $\ensuremath{\alpha}+\ensuremath{\alpha}+N$ cluster model with the complex scaling method that well explains the measured photodisintegration cross section for the $^{9}\mathrm{Be}(1/{2}^{+})$. We find two resonances at the energies of ${E}_{1}^{\mathrm{res}}=1.81$ MeV with a decay width $\mathrm{\ensuremath{\Gamma}}=1.98$ MeV and ${E}_{2}^{\mathrm{res}}=2.38$ MeV, $\mathrm{\ensuremath{\Gamma}}=1.81$ MeV in $^{9}\mathrm{B}$. The charge radii and the three-body channel configurations are calculated to see the properties of two resonances. We also calculate the level density of two resonances, which indicates the difficulty to distinguish them in the energy distribution.

Photodisintegration cross section of deuteron

The peak produced by the M1 and E1 transition strengths for the photodisintegration cross section of deuteron is calculated in the complex scaling method and the origin of the peak of the M1 strength near threshold energy is discussed.

Secondary neutrino and gamma-ray fluxes from SimProp and CRPropa

The interactions of ultra-high energy cosmic rays (UHECRs) with background photons in extragalactic space generate high-energy neutrinos and photons. Simulating UHECR propagation requires assumptions about physical quantities such as the spectrum of the extragalactic background light (EBL) and photodisintegration cross sections. These assumptions, as well as the approximations used in the codes, may influence the computed predictions both of cosmic-ray spectra and composition, and of cosmogenic neutrino and photon fluxes. Following up on our previous work where we studied the resulting uncertainties on cosmic-ray simulations, here we quantify those on neutrinos and photons, using the Monte Carlo codes CRPropa and SimProp in various source scenarios. We discuss the results in the light of the constraining power of the neutrino and photon spectra on the origin of the UHECRs. We show that cosmogenic neutrino fluxes are more sensitive to the parametrization of the EBL than UHECR spectra, whereas the overall cosmogenic gamma-ray production rates are relatively independent on details of the propagation. We also find large differences between neutrino fluxes predicted by the latest released versions of CRPropa and SimProp, and discuss their causes and possible improvements in future versions of the codes.

Local chiral interactions and magnetic structure of few-nucleon systems

The magnetic form factors of $^2$H, $^3$H, and $^3$He, deuteron photodisintegration cross sections at low energies, and deuteron threshold electrodisintegration cross sections at backward angles in a wide range of momentum transfers, are calculated with the chiral two-nucleon (and three-nucleon) interactions including $\Delta$ intermediate states that have recently been constructed in configuration space. The $A\,$=$\,$3 wave functions are obtained from hyperspherical-harmonics solutions of the Schr\"odinger equation. The electromagnetic current includes one- and two-body terms, the latter induced by one- and two-pion exchange (OPE and TPE, respectively) mechanisms and contact interactions. The contributions associated with $\Delta$ intermediate states are only retained at the OPE level, and are neglected in TPE loop (tree-level) corrections to two-body (three-body) current operators. Expressions for these currents are derived and regularized in configuration space for consistency with the interactions. The low-energy constants that enter the contact few-nucleon systems. The predicted form factors and deuteron electrodisintegration cross section are in excellent agreement with experiment for momentum transfers up to 2--3 fm$^{-1}$. However, the experimental values for the deuteron photodisintegration cross section are consistently underestimated by theory, unless use is made of the Siegert form of the electric dipole transition operator. A complete analysis of the results is provided, including the clarification of the origin of the aforementioned discrepancy.

Photodisintegration cross sections for resonant states and virtual states

The $s$-wave photodisintegration cross sections observed just above the neutron breakup threshold energy are calculated for resonant and virtual states by using a complex-scaled two-body model, which simulates the $^{9}\mathrm{Be}$ nucleus with a $^{8}\mathrm{Be}+n\phantom{\rule{4pt}{0ex}}s$-wave channel. We investigate the differences between behaviors of the resonance and virtual states in the photodisintegration cross sections near threshold energy in detail. It is shown that, in the present two-body model, resonant states very near the threshold energy produce a peak structure in the photodisintegration cross section that is similar that of the virtual state.

Neutron capture rates of C18

Background: Small changes in reaction rates due to neutron capture, $\ensuremath{\alpha}$ capture, and $\ensuremath{\beta}$ decay by exotic nuclei in the low and medium mass region can direct the $r$-process path in different ways, thereby affecting the abundance pattern. In this context, it is important to find the most abundant carbon isotope closer to the neutron drip line. It was postulated that the $(n,\ensuremath{\gamma})$ reaction network will be broken at the $^{18}\mathrm{C}$ isotope and follow the $^{18}\mathrm{C}(\ensuremath{\alpha},n)^{21}\mathrm{O}$ reaction path [Terasawa et al., Astrophys. J. 562, 470 (2001)].Purpose: In this paper, we calculate the radiative capture cross section of $^{18}\mathrm{C}(n,\ensuremath{\gamma})^{19}\mathrm{C}$, taking into consideration the halo character of $^{19}\mathrm{C}$. Eventually, we calculate the reaction rate for the same reaction and compare it with Hauser-Feshbach estimates of $(n,\ensuremath{\gamma})$ and $(\ensuremath{\alpha},n)$ to determine the abundance pattern of carbon isotopes.Method: We compute the relative energy spectrum for elastic Coulomb breakup of $^{19}\mathrm{C}$ on a Pb target at a beam energy of 67 MeV/u using the finite-range distorted-wave Born approximation (FRDWBA) theory. We use the principle of detailed balance to calculate the radiative capture cross section from the photo disintegration cross section, and subsequently we calculate the reaction rate.Results: We report the $^{18}\mathrm{C}(n,\ensuremath{\gamma})^{19}\mathrm{C}$ capture cross section as a function of relative energy. Estimation of the energy range contributing to the reaction rates is done by calculating the integrand of the reaction rate expression. A comparison of the $^{18}\mathrm{C}(n,\ensuremath{\gamma})^{19}\mathrm{C}$ with $^{18}\mathrm{C}(\ensuremath{\alpha},n)^{21}\mathrm{O}$ (extracted from the Hauser-Feshbach estimates) shows the domination of the neutron radiative capture reaction in the relevant temperature range ${T}_{9}=0.1--4$.Conclusion: The radiative capture cross section of $^{18}\mathrm{C}$ calculated using FRDWBA theory agrees well with the experimental data, whereas the statistical model calculation lies orders of magnitude lower. We conclude that at equilibrium temperature of ${T}_{9}=0.62$, the $^{18}\mathrm{C}(n,\ensuremath{\gamma})^{19}\mathrm{C}$ reaction rate is orders of magnitude higher than that of the $^{18}\mathrm{C}(\ensuremath{\alpha},n)^{21}\mathrm{O}$ reaction, thereby pushing the carbon isotope abundance towards the neutron drip line.

Photoneutron reaction cross section measurements on Mo94 and Zr90 relevant to the p -process nucleosynthesis

The photodisintegration cross sections for the 94Mo({\gamma},n) and 90Zr({\gamma},n) reactions have been experimentally investigated with quasi-monochromatic photon beams at the High Intensity {\gamma}-ray Source (HI{\gamma}S) facility of the Triangle Universities Nuclear Laboratory (TUNL). The energy dependence of the photoneutron reaction cross sections was measured with high precision from the respective neutron emission thresholds up to 13.5 MeV. These measurements contribute to a broader investigation of nuclear reactions relevant to the understanding of the p-process nucleosynthesis. The results are compared with the predictions of Hauser-Feshbach statistical model calculations using two different models for the dipole {\gamma}-ray strength function. The resulting 94Mo({\gamma},n) and 90Zr({\gamma},n) photoneutron stellar reaction rates as a function of temperature in the typical range of interest for the p-process nucleosynthesis show how sensitive the photoneutron stellar reaction rate can be to the experimental data in the vicinity of the neutron threshold.

The first excited 1/2+ state in 9Be and 9B

Nuclear states observed around threshold energies provide us with interesting problems associated withthe nuclear cluster structure [1, 2, 3, 4]. The first excited Jπ = 1/2+ state of 9Be [5], which is an α+ α + nBorromean nucleus, is one of the typical examples in light nuclei. This state of 9Be has been observed as asharp peak above the 8Be + n threshold energy in the photo-disintegration cross section of γ+9Be→ α + α+ n [6, 7]. The strength of the peak has a strong influence on the reaction rate of the 9Be synthesis. Weperformed the calculations using an α + α + n three-body model [8, 9] and the complex scaling method(CSM), which well reproduces the observed photo-disintegration cross section. However, the resultindicates that the 1/2+ state shows the s-wave virtual-state character of 8Be+n. In addition to this problem,we discuss a mirror state problem of the first excite 1/2+ state in 9B.

Photo-disintegration of He4 on the cosmic microwave background is less severe than earlier thought

We thoroughly study the photo-disintegration of $^4$He on the cosmic microwave background using the most recent cross-section data both from the inclusive measurement observing the analog of the giant dipole resonance in $^4$He through the charge-exchange spin-flip $^4$He ($^7$Li,$^7$Be) reaction and from measurements of exclusive two-body and three-body processes: $^4{\rm He} \, (\gamma,p)\, ^3{\rm H}$, $^4{\rm He} \, (\gamma,n) \, ^3{\rm He}$, and $^4$He $(\gamma, pn)$ $^2$H. We show that the present-day (redshift $z=0$) mean free path of ultra-relativistic (Lorentz factor $\sim 10^{10}$) helium nuclei increases by more that $15\%$ with respect to previous estimates adopted as benchmarks for Monte Carlo simulation codes of ultrahigh-energy cosmic ray propagation. This implies that the physical survival probability of $^4$He nuclei would be larger than predicted by existing event generators. For example, for $E \sim 10^{10.8}~{\rm GeV}$ and a propagation distance of 3.5 Mpc, the $^4$He intensity would be $35\%$ larger than the output of CRPropa 3 program and $42\%$ larger than the output of SimProp v2r4 program. We provide new parametrizations for the two-body and three-body photo-disintegration cross-sections of $^4$He, $^3$He, tritium, and deuterium.

Electromagnetic reactions from coupled-cluster theory

We review recent results for electromagnetic reactions and related sum rules in light and medium-mass nuclei obtained from coupled-cluster theory. In particular, we highlight our recent computations of the photodisintegration cross section of 40Ca and of the electric dipole polarizability for oxygen and calcium isotopes. We also provide new results for the Coulomb sum rule for 4He and 16O. For 4He we perform a thorough comparison of coupled-cluster theory with exact hyperspherical harmonics.

Virtual-state character of the two-body system in the complex scaling method

In association with the property of the $1/{2}^{+}$ state observed just above the $^{8}\mathrm{Be}({0}^{+})+n$ threshold energy in $^{9}\mathrm{Be}$, we investigate the photodisintegration cross section of an $s$ state in a simple schematic two-body model using the complex scaling method. The photodisintegration cross section, continuum level density, scattering phase shifts, and scattering length are discussed in relation with the virtual state. These scattering observables show strong divergences when a virtual state is located near the physical scattering region.

Photodisintegration cross section of9Be up to Eγ = 16 MeV in the α + α + n three-body model

We investigate the photodisintegration cross section (PDXS) of9Be in low and higher energy regions by using the α + α + n three-body model and the complex scaling method (CSM). The calculated photodisinegration cross section of well reproduces the recent experimental data, and shows that the transitions into the8Be(2+) + n states dominate the cross section in the energy region of 6 ≤Eγ ≥ 16 MeV.

A Virtual State in a Two-Body System Using the Complex Scaling Method

In association with the property of the 1/2+ state observed just above the 8Be(0+)+n threshold energy in 9Be, we investigate the photo-disintegration cross section of an s-state in a schematic two-body system using the complex scaling method.

The first unbound states of mirror 9Be and 9B nuclei

The structures of the first excited states of mirror 9 Be and 9 B nuclei are studied by using the α + α + N three-body model and the complex scaling method. The resonance energy with a decay width of the 1/2 + state of 9 B is calculated by taking into account the consistency with photodisintegration cross sections of 9 Be into the 1/2 + state. We also compare the results with the measured data and other theories.

Photodisintegration and Virtual State in the Complex Scaling Method

The photodisintegration cross section observed just above the neutron threshold energy in 9Be is discussed in the framework of an α + α + n three-cluster model and the complex scaling method. The observed cross sections shows a remarkable sharp peak, which has been discussed in association with photo-neutron reactions in nucleo-syntheses of chemical elements. It is discussed that the enhancement of the peak is understood by taking into account a virtual state but not a resonant state. The complex scaling method cannot reproduce an eigenvalue corresponding to the virtual pole, but provides us with a useful tool for investigation of the photodisintegration cross section.

Photodisintegration of9Be and the importance of the unbound 1/2+state

The photodisintegration cross section of the 9 Be(1/2 + ) state is investigated in a framework of the α + α + n three-body model. The 1/2 + state of 9 Be locates just above the three-body threshold, and the s -wave neutron property of this state is a long-standing problem. It has been a topic of quite interest in relation to the breakup mechanism of 9 Be into the 8 Be(0 + ) + n and ( α + α + n ) channels.

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.

Virtual-state character of theBe91/2+state in theBe9(γ,n)Be8reaction

We study the character of the first excited $1/{2}^{+}$ state of $^{9}\mathrm{Be}$, which is observed as a low-lying sharp peak in the cross section of $^{9}\mathrm{Be}(\ensuremath{\gamma},n)2^{4}\mathrm{He}$ just above the $^{8}\mathrm{Be}+n$ threshold. Using the $\ensuremath{\alpha}+\ensuremath{\alpha}+n$ three-body model, we describe the ground and excited unbound states of $^{9}\mathrm{Be}$ above the $\ensuremath{\alpha}+\ensuremath{\alpha}+n$ threshold. Applying the complex scaling method to the three-body model, we find no $1/{2}^{+}$ resonant solutions with the scaling angle of $\ensuremath{\theta}\ensuremath{\le}{15}^{\ensuremath{\circ}}$, while the low-lying peak in the photodisintegration cross section is reproduced in the present calculation. It is found that the $^{8}\mathrm{Be}+n$ continuum states dominate the low-lying peak in the cross section. Furthermore, using the analytical continuation of the coupling constant of the three-body interaction for the $\ensuremath{\alpha}+\ensuremath{\alpha}+n$ system, we discuss the virtual-state character of the $1/{2}^{+}$ state.

Bubble chambers for experiments in nuclear astrophysics

A bubble chamber has been developed to be used as an active target system for low energy nuclear astrophysics experiments. Adopting ideas from dark matter detection with superheated liquids, a detector system compatible with γ-ray beams has been developed. This detector alleviates some of the limitations encountered in standard measurements of the minute cross-sections of interest to stellar environments. While the astrophysically relevant nuclear reaction processes at hydrostatic burning temperatures are dominated by radiative captures, in this experimental scheme we measure the time-reversed processes. Such photodisintegrations allow us to compute the radiative capture cross-sections when transitions to excited states of the reaction products are negligible. Due to the transformation of phase space, the photodisintegration cross-sections are up to two orders of magnitude higher. The main advantage of the new target-detector system is a density several orders of magnitude higher than conventional gas targets. Also, the detector is virtually insensitive to the γ-ray beam itself, thus allowing us to detect only the products of the nuclear reaction of interest. The development and the operation as well as the advantages and disadvantages of the bubble chamber are discussed.

A resonance problem on the low-lying resonant state in the 9Be system

The photo-disintegration cross section of 9Be is investigated in a framework of the α + α + n three-body cluster model. Much interest is concentrated on the nature of the 1/2+ state of 9Be located just above the three-body threshold. The existence of this 1/2+ resonance is a long-standing problem and has been a topic of quite interest in relation to the breakup mechanism of 9Be into the 8Be(0+)+n and (α + α + n) channels. The newly measured breakup cross sections of the 1/2+ state of Ref. [1] is inconsistent with the old experimental values [2, 3]. The purpose of this study is to clarify the properties of the 1/2+ state of 9Be with the possibility of a genuine three-body (α + α + n) resonance or the two-body (8Be(0+)+n) virtual state.