25Mg Reaction Research Articles

Analysis of astrophysical 26Mg(n,γ)27Mg reaction via the asymptotic normalization coefficient method

The [Formula: see text] reaction plays a crucial role in the process of nucleosynthesis in stars. It occurs primarily in massive stars during their late evolutionary stages or during explosive events like supernovae. This paper focuses on investigating discrepancies in the ANC values of the [Formula: see text] reaction by analyzing experimental angular distributions of [Formula: see text] using the DWBA, ADWA and CDCC methods for both ground and first excited states. We then use a mirror nucleus procedure to extract information on the ANCs of the ground state [Formula: see text] reaction. The Hauser–Feshbach formalism of the statistical Compound Nucleus (CN) model was applied in this study to perform a compound-nucleus analysis of the [Formula: see text] reaction. The [Formula: see text] reaction has almost fulfilled the condition of peripherality, which is necessary for understanding the magnitude of the direct reaction contribution. ANCs for the [Formula: see text] virtual decay system were obtained. Moreover, according to charge symmetry of mirror nuclei, the square of proton ANC for a [Formula: see text] is determined and comparison between the values of the presented ANCs.

Search for 22Na in novae supported by a novel method for measuring femtosecond nuclear lifetimes

Classical novae are thermonuclear explosions in stellar binary systems, and important sources of 26Al and 22Na. While γ rays from the decay of the former radioisotope have been observed throughout the Galaxy, 22Na remains untraceable. Its half-life (2.6 yr) would allow the observation of its 1.275 MeV γ-ray line from a cosmic source. However, the prediction of such an observation requires good knowledge of its nucleosynthesis. The 22Na(p, γ)23Mg reaction remains the only source of large uncertainty about the amount of 22Na ejected. Its rate is dominated by a single resonance on the short-lived state at 7785.0(7) keV in 23Mg. Here, we propose a combined analysis of particle-particle correlations and velocity-difference profiles to measure femtosecond nuclear lifetimes. The application of this method to the study of the 23Mg states, places strong limits on the amount of 22Na produced in novae and constrains its detectability with future space-borne observatories.

A comprehensive analysis of 26Mg(3H,2H)27Mg reaction at 36 MeV

The angular distribution of the 26Mg(3H,2H)27Mg reaction at 36 MeV incident energy is reanalyzed by using the distorted wave Born approximation (DWBA) method. Four forms of the optical model potentials such as temperature dependent and temperature independent density distributions, different nuclear potentials, and different nucleon-nucleon interactionsare used to determine the effect on the 26Mg(3H,2H)27Mg transfer reaction of the entrance channel. These analyses display the similarities and differences of all the approaches which are discussed in this work, and provide alternative density, alternative nuclear potential and alternative nucleon-nucleon interactions.

Search for Weak Side Branches in the Electromagnetic Decay Paths of the 6526-keV 10+ Isomer in 54Fe

High-spin nuclear isomers in N≈Z nuclei between doubly magic 40Ca and 56Ni provide an excellent testing ground for the nuclear shell model and questions related to isospin symmetry breaking in the vicinity of the proton drip line. The purpose of the present study is to investigate the possibility of weak electromagnetic decay branches along the decay paths of the 6526-keV 10+ isomer in 54Fe. The isomer was strongly populated by means of the fusion-evaporation reaction 24Mg(36Ar,α2p)54mFe. The Gammasphere array was used to detect γ-ray cascades emitted from the isomeric state. By means of γγγ coincidences, weak non-yrast decay branches can be discriminated, with the isomer’s half-life confirmed at T1/2=363(4) ns. The yrast 61+→21+ E4 cross-over transition was interrogated. The observations are compared with shell-model calculations.

Differential cross–section measurements and R-Matrix calculations for proton elastic scattering on natMg in the energy range Ep,lab = 2.70–4.25 MeV, suitable for EBS

In the current work the first coherent set of differential cross section values for the natMg(p,p0)natMg elastic scattering covering the Ep,lab = 2700–4250 keV energy range is presented for 6 backscattering detection angles (120°, 130°, 140°, 150°, 160° and 170°). R-Matrix calculations were implemented using the AZURE 2.0 code [1] in an attempt to reproduce the obtained experimental data, whilst taking into account the 24Mg(p,p1)24Mg reaction channel. Both results are suitable for EBS and other IBA applications and, furthermore, they form a basis for a future expansion of the current SigmaCalc [2] evaluation, once more experimental data become available. The measurements were performed in the 5.5 MV TN11 HV Tandem Accelerator and the high precision goniometer of N.C.S.R. ‘Demokritos’, Athens, Greece. The experimental and data analysis procedures are presented in detail, along with the process behind the implementation of the R-Matrix calculations.

Understanding the cosmic abundance of 22Na: Lifetime measurements in 23Mg

Simulations of explosive nucleosynthesis in novae predict the production of 22Na, a key astronomical observable to constrain nova models. Its gamma-ray line at 1.275 MeV has not yet been observed by the gamma-ray space telescopes. The 20Ne/22Ne ratio in presolar grains, a possible tool to identify nova grains, also depends on 22Na produced. Uncertainties on its yield in classical novae currently originate from the rate of the 22Na(p, γ)23Mg reaction. At peak novae temperatures, this reaction is dominated by a resonance at ER=0.204 MeV, corresponding to the Ex=7.785 MeV excited state in 23Mg. The resonance strengths measured so far disagree by one order of magnitude. An experiment has been performed at GANIL to measure the lifetime and the proton branching ratio of this key state, with a femtosecond resolution for the former. The reactions populating states in 23Mg have been studied with a high resolution detection set-up, i.e. the particle VAMOS, SPIDER and gamma tracking AGATA spectrometers, allowing the measurements of lifetimes and proton branchings. We present here a comparison between experimental results and shell-model calculations, that allowed us to assign the spin and parity of the key state. Rather small values obtained for reduced M1 matrix elements, M(M1) ≲ 0.5 µN, and proton spectroscopic factors, C2Sp<10−2, seem to be beyond the accuracy of the shell model. With the reevaluated 22Na(p, γ)23Mg rate, the 22Na detectability limit and its observation frequency from novae are found promising for the future space telescopes.

S-process Nuclear Reaction Rates

In stars the 13C(α, n)16O and 22Ne(α, n)25Mg reactions are the two main sources of neutrons for the so-called slow neutron capture process (s-process), which is one of the main mechanisms for the stellar synthesis of heavy elements. About 13C(α, n)16O, in despite of many efforts in measuring its cross section at the lower energies, only high uncertainty data above the s-process Gamow window (150 keV < Ecm < 230 keV) were available, due mostly to the difficulties on suppress the natural background. Indeed, only recently the LUNA collaboration performed high precision underground measurements of the reaction cross section inside the Gamow window, improving the accuracy of its extrapolation at the lower energies. Again due to natural background, only upper limits for the 22Ne(α, n)25Mg reaction cross section are currently known in the s-process Gamow window (450 keV < Ecm < 750 keV). For this, the ERC founded project SHADES (Unina/INFN) aims to perform high precision and high sensitivity measurements of the 22Ne(α, n)25Mg reaction cross section down to the neutron threshold. A sensitivity improvement of at least two orders of magnitude over the state of the art is expected thanks to the low natural background environment of the INFN-LNGS laboratory in Italy, the high beam current of the new LUNAMV accelerator and the Beam Induced Background events suppression performed by SHADES hybrid detectors array. In this paper I will present the LUNA efforts to estimate nuclear reaction rates for 13C(α, n)16O, with a focus on the R-Matrix analysis performed with the code AZURE2 to extrapolate nuclear reaction rates at stellar energies and the estimate of their uncertainty through Monte Carlo methods. I will also present an overview of the SHADES project to measure 22Ne(α, n)25Mg in the Gamow window and the first results on the setup commissioning.

RIB induced reactions: Studying astrophysical reactions with low-energy RI beam at CRIB

Astrophysical reactions involving radioactive isotopes (RI) often play an important role in high-temperature stellar environments. The experimental studies on the reaction rates for those are still limited mainly due to the technical difficulties in producing high-quality RI beams. A direct measurement of those reactions would be still challenging in many cases, however, we can make a reliable evaluation of the reaction rates by an indirect method or by studying the resonance prorerties. Here we ntroduce recent examples of experimental studies on such RI-involving astrophysical reactions, performed at Center for Nuclear Study, the University of Tokyo, using the low-energy RI beam separator CRIB. One is for the neutron-induced destruction reactions of 7Be in the Big-Bang nucleosynthesis, and the other is the study on the 22Mg(α, p) reaction relevant in X-ray bursts, which was performed with the resonant scattering method from the inverse reaction channel.

Study of the 12C +16 O fusion reaction in carbon burning via the Trojan Horse Method

12C +12 C is the main reaction during core and shell carbon burning in massive stars, however, at temperatures higher than 109K when most of the carbon is depleted and its abundance is lower than 16O, the 12C +16 O fusion can also become relevant. Moreover, 12C +16 O reaction can ignite also in the scenario of explosive carbon burning. The astrophysical energy region of interest thus ranges from 3 to 7.2 MeV in the center-of-mass frame. There are various measurements of the cross-section available in the literature, however, they all stop around 4 MeV, making extrapolation necessary at lower energies. To try to solve this uncertainty and corroborate direct measurement the Trojan Horse Method was applied to three-body processes 16O(14N, α24Mg)2H and 16O(14N, p27Al)2H to study the 16O(12C, α)24Mg and 16O(12C, p)27Al reactions.

The 12C +16 O fusion reaction in carbon burning: Study at energies of astrophysical interest using the Trojan Horse Method

The carbon-burning process in massive stars mainly occurs via the 12C +12 C. However, at temperatures higher than 109K and considering the increased abundance of 16O produced during the later stages of the heliumburning,the 12C+16O fusion can also become relevant. Moreover, 12C+16O also plays a role in the scenario of explosive carbon burning. Thus, the astrophysical energy region of interest ranges from 3 to 7.2 MeV in the center-of-mass frame. However, the various measurements of the cross-section available in the literature stop around 4 MeV, making extrapolation necessary. To solve this uncertainty and corroborate direct measurement we applied the Trojan Horse Method to three-body processes 16O(14N, α24Mg)2H and 16O(14N, p27Al)2H to study the 12C(16O, α)24Mg and 12C(16O, p)27Al reactions in their entire energy region of astrophysical interest. In this contribution, after briefly describing the method used, the experiment and the preliminary phases of the data analysis will be presented and discussed.

A New Reaction Rate of the 27Al(p/α)24Mg Reaction Based on Indirect Measurements at Astrophysical Energies and Implications for 27Al Yields of Intermediate-mass Stars

The abundance of 26Al carries a special role in astrophysics, since it probes active nucleosynthesis in the Milky Way and constrains the Galactic core-collapse supernovae rate. It is estimated through the detection of the 1809 keV γ-line and from the superabundance of 26Mg in comparison with the most abundant Mg isotope (A = 24) in meteorites. For this reason, high precision is necessary also in the investigation of the stable 27Al and 24Mg isotopes. Moreover, these nuclei enter the so-called MgAl cycle, playing an important role in the production of Al and Mg. Recently, high-resolution stellar surveys have shown that the Mg–Al anticorrelation in red-giant stars in globular clusters may hide the existence of multiple stellar populations, and that the relative abundances of Mg isotopes may not be correlated with Al. The common thread running through these astrophysical scenarios is the 27Al(p,α)24Mg reaction, which is the main 27Al destruction channel and directly correlates its abundance with the 24Mg one. Since available reaction rates show large uncertainties owing to the vanishingly small cross section at astrophysical energies, we have applied the Trojan Horse Method to deduce the reaction rate with no need of extrapolation. The indirect measurement made it possible to assess the contribution of the 84 keV resonance and to lower upper limits on the strength of nearby resonances. In intermediate-mass AGB stars experiencing hot bottom burning, a sizeable increase in surface aluminum abundance is observed at the lowest masses, while 24Mg is essentially unaffected by the change in the reaction rate.

Development of the multi-purpose Cologne Compact Differential Plunger (CoCoDiff) for the measurement of nuclear level lifetimes with the Recoil Distance Doppler-shift method

A new 3-foil plunger device, the Cologne Compact Differential (CoCoDiff) plunger has been built and commissioned. Due to its compact size, it can be used together with many different spectrometers and auxiliary detectors. As a commissioning experiment, level lifetimes of the 21+ and the 41+ excited states of 50Cr have been measured, using the Differential Decay Curve method (DDCM). A derivation is given on how this method can be applied to a differential plunger measurement, in order to measure distances for lifetimes from two different regions of sensitivity at the same time. The commissioning experiment took place at the Cologne FN tandem accelerator, using the reaction 24Mg(32S,4p2n)50Cr. Lifetimes, deduced from this measurement, agree well with literature values from earlier measurements.

Single neutron transfer on 23Ne and its relevance for the pathway of nucleosynthesis in astrophysical X-ray bursts

We present new experimental measurements of resonance strengths in the astrophysical 23Al(p,γ)24Si reaction, constraining the pathway of nucleosynthesis beyond 22Mg in X-ray burster scenarios. Specifically, we have performed the first measurement of the (d,p) reaction using a radioactive beam of 23Ne to explore levels in 24Ne, the mirror analog of 24Si. Four strong single-particle states were observed and corresponding neutron spectroscopic factors were extracted with a precision of ∼20%. Using these spectroscopic factors, together with mirror state identifications, we have reduced uncertainties in the strength of the key ℓ = 0 resonance at Er = 157 keV, in the astrophysical 23Al(p,γ) reaction, by a factor of 4. Our results show that the 22Mg(p,γ)23Al(p,γ) pathway dominates over the competing 22Mg(α,p) reaction in all but the most energetic X-ray burster events (T>0.85 GK), significantly affecting energy production and the preservation of hydrogen fuel.

Neutron-Driven Nucleosynthesis in Stellar Plasma

A large uncertainty for the slow neutron capture nucleosynthesis (s-process) models is caused by the amount of neutrons available to the process itself. This quantity is strongly affected by the 13C(α,n)16O, and 22Ne(α,n)25Mg reaction cross sections, whose measurements at energies corresponding to the s-process thermal conditions (∼102 keV) are mainly hampered by the Coulomb barrier. For this reason, indirect approaches could offer a complementary way of investigation and, among these, the Trojan Horse Method (THM) has been applied to determine these cross sections overcoming the Coulomb barrier. With this approach, a low-energy binary reaction cross section can be obtained selecting the quasi-free contribution from a suitable three-body reaction cross section, taking advantage of the cluster structure of proper nuclei.

Exploring the astrophysical energy range of the 27Al[formula omitted]Mg reaction: A new recommended reaction rate

The 26Al abundance holds a special role in present-day astrophysics, since it is a probe of active nucleosynthesis in the Galaxy and a valuable constraint of Galactic core-collapse supernovae rate. It is estimated through the detection of the 1809-keV γ-line of the daughter 26Mg and from the superabundance of 26Mg in comparison with the most abundant 24Mg isotope in meteorites. Accurate knowledge of the reaction rates involving 26Al, its stable counterpart 27Al and 24Mg is then mandatory. Moreover, these nuclei enter the MgAl cycle playing an important role in the production of Al and Mg isotopes. Recently, high-resolution stellar surveys have shown that the Mg-Al anti-correlation in red giants of globular clusters may hide the existence of multiple stellar populations, and that the relative abundances of Mg isotopes may not show correlation with Al.The common thread running through these astrophysical scenarios is the 27Al(p,α)24Mg reaction, which is the main 27Al destruction channel and directly correlates its abundance with the 24Mg one. Since available reaction rates show an order of magnitude uncertainty owing to the vanishingly small cross section at astrophysical energies, we have applied the Trojan Horse Method to deduce the reaction rate with no need of extrapolation. The indirect measurement made it possible to assess the contribution of the 84-keV resonance and to lower the upper limits on the strength of nearby resonances, with potential important impact for astrophysics. In particular, modifications in the 27Al and 24Mg abundances up to ∼30% are predicted for intermediate mass stars.

First direct limit on the 395 keV resonance of the 22Ne(α, γ)26Mg reaction

The 22Ne(α, γ)26Mg reaction (Q = 10614.74 keV) competes with the 22Ne(α, n)25Mg reaction (Q = −478.34 keV) which is the main source of neutrons for the s-process in low-mass Asymptotic Giant Branch and massive stars. The cross sections of these reactions are crucial to fix the cross over temperature at which (α, n) rate exceeds the (α, γ) one. Moreover, the uncertainty on the 22Ne(α, γ)26Mg reaction rate affects also the nucleosynthesis of isotopes between 26Mg and 31P in intermediate-mass stars. At lower temperatures (T < 300 MK) where the (α, γ) channel is dominant, the rate of the 22Ne(α, γ)26Mg reaction is influenced by several resonances. The present study focuses on the Eα = 395 keV resonance which so far have been studied only indirectly leading to a wide range of possible values for its resonance strength (10−15 −10−9 eV). The experiment has been completed at LUNA using the intense alpha beam of the LUNA 400 kV accelerator and a windowless differential-pumped gas target combined with a high efficiency BGO detector. Experimental details and preliminary results will be shown.

Experimental studies on astrophysical reactions at the low-energy RI beam separator CRIB

Experimental studies on astrophysical reactions involving radioactive isotopes (RI) often accompany technical challenges. Studies on such nuclear reactions have been conducted at the low-energy RI beam separator CRIB, operated by Center for Nuclear Study, the University of Tokyo. We discuss two cases of astrophysical reaction studies at CRIB; one is for the 7Be+n reactions which may affect the primordial 7Li abundance in the Big-Bang nucleosynthesis, and the other is for the 22Mg(α, p) reaction relevantin X-raybursts.

The polarization sensitivity of GRETINA

Compton polarimeters have played an important role in the study of nuclear structure physics, but have often been limited in their applications because of relatively low γ-ray detection efficiency. With the advent of γ-ray tracking detector arrays, which feature nearly 4π solid angle coverage and the ability to identify the location of Compton-scattering events to within a few millimeters, this limitation can be overcome. Here we present a characterization of the performance of the Gamma Ray Energy Tracking In-beam Nuclear Array (GRETINA) as a Compton polarimeter using the 24Mg(p,p′) reaction at 2.45 MeV proton energy. We also discuss a new capability added to the simulation package UCGretina to simulate the emission of polarized photons, and compare it to the measured data. Finally, we use these simulations to predict the performance of the Gamma Ray Energy Tracking Array (GRETA).

Evaluation the nonlinear response function of a HPGe detector for 59 keV to 10.7 MeV gamma-rays using a Monte Carlo simulation and comparison with experimental data

Modeling of High Purity Germanium (HPGe) detector on a wide energy range is important in gamma-ray spectroscopy. The precisely modeled detector can be used for proton-induced prompt gamma-ray spectroscopy. In this work, we used both the gamma-rays of calibration sources and prompt gamma-rays emitted in proton capture reactions to model a coaxial p-type HPGe detector using Geant4 Monte Carlo simulation for the gamma-ray energy range of 59–10764 keV. The calibration sources were 137Cs, 241Am, 60Co, 152Eu, and 133Ba, while the prompt gamma-rays were due to the gamma-ray cascades following the 27Al(p,γ)28Si reaction capture at the resonant energies of 992, 1317 and 2483 keV, as well as the 23Na(p,γ)24Mg reaction capture at the resonant energies of 1417 and 1395 keV. According to the results obtained, the presented simulated and experimental spectra show a good agreement. In addition, the mean and maximum relative deviations between experimental and simulated efficiencies corresponding to 27 major peaks are smaller than 5% and 15%, respectively.

Non-Resonant Reaction Rates of 13C(α,n)16O and 22Ne(α,n)25Mg reactions in AGB Stars

Both 13C 16O and 22Ne 25Mg reactions perform a cosmic role in the production of neutrons in AGB stars, which significantly contributes to the nucleosynthesis via the s-process. The astrophysical S-factor for both reactions has been calculated in this research, utilizing EMPIRE code and depending on two parameter sets for the optical potential: McFadden and Satchler (MFS), and Avrigeanu and Hodgson (AH) for the non-resonant region of the spectrum, and over a temperature range . The extrapolated S-factor at zero energy is derived to be and for 13C 16O, and for 22Ne 25Mg from using MFS and AH parameter sets respectively, and they show a reasonable agreement with the most recommended value. The differences in the S-factor, S(E), values obtained from these two adopted parameters set, were attributed to the variations of the real potential term's diffuseness parameter that affecting the reaction cross section, hence S-factor, and specifically at low energy region. Moreover, the present results imply an influential enhancement of the rates by the electron shielding effect at the low-temperature region in which 13C 16O reaction activated, and especially on 22Ne 25Mg reaction. In addition, for both adopted reactions and overall selected temperature range, the reaction rates using values based on MFS showed acceptable results with other previous compilations and reference libraries. While that obtained from AH exceed all other compilations even though the resonance contributions are currently unconsidered.