$^{12}$C fusion reactions are among the most important in stellar evolution since they determine the destiny of massive stars. Over the past fifty years, massive efforts have been done to measure these reactions at low energies. However, existing data present several discrepancies between sets and large uncertainties specially at the lowest energies. Factors such as beam/environmental...
When stars approach the red giant branch, a deep convective envelope develops and the products of the CNO cycle appear at the stellar surface. In particular, the $\rm^{17}O$ is enhanced in RGB and AGB stars. Then, spectroscopic analyses of O isotopic ratios of these stars provide a powerful tool to investigate the efficiency of deep mixing processes, such as those powered by convective...
The presence of ${\rm ^{26}Al}$ (T$_{1/2}$=1.04 Myr) in the interstellar medium has been strongly debated through the years: its 1.809 MeV $\gamma$-ray line has been appointed as a tracer of the recent nucleosynthesis in our galaxy, and its presence have been found spread along Galactic plane. Observations support the idea that this isotope can been formed through nucleosynthesis in massive...
Facility for Research in Experimental Nuclear Astrophysics (FRENA), an upcoming tandem accelerator facility at Saha Institute of Nuclear Physics, Kolkata, India. This is a low energy (0.2-3 MV) high current facility primarily designed for nuclear astrophysical studies. Most of the astrophysical reactions have very low cross-sections with large error bars[1]. So the background studies in this...
Binding energies, proton-neutron paring and α-like quartetting in proton-rich nuclei
close to N=Z line
N. Sandulescu
National Institute of Physics annd Nuclear Engineering, 76900 Magurele-Bucharest, Romania
The modelling of nucleosynthesis processes triggered by rapid proton capture requires accurate predictions for the binding energies of...
Stellar explosions such as novae, supernovae, and X-ray bursts involve thermonuclear reactions on rare isotopes. Interpretation of observations such as the light curves from X-ray bursts, elemental abundances, or $\gamma$-rays from nuclear decay as well as predictions of nucleosynthesis are notably impacted by large uncertainties in the nuclear reaction rates. Many of these reactions either...
The NeuLAND (New Large-Area Neutron Detector) plastic scintillator based time of flight detector for 0.2-1.6 GeV neutrons is currently under construction at the Facility for Antiproton and Ion Research (FAIR), Darmstadt, Germany. In its final configuration, NeuLAND will consist of 3,000 2.7 m long plastic scintillator bars that are read out on each end by fast timing photomultipliers. Here,...
The subject of massive star explosions driven by a first-order hadron-quark matter phase transition has gained increasing attention in the community, e.g., providing a novel path to the existence of massive pulsars of 2 solar masses at birth [1] and the creation of ejected r-process material in these explosive events [2]. However, no final conclusions can yet be drawn from these results about...
Over the last decades huge efforts were made to determine the $^{12}$C($\alpha,\gamma$)$^{16}$O cross section, as it is key to understand the evolution of stars. Using direct methods with stable targets and a low-energy ion beam poses significant challenges to the experimental setup and data analysis. Center-of-mass energies down to 1 MeV were reached with sometimes large uncertainties of up...
For direct cross section measurements in nuclear astrophysics, in addition to suitable ion beams and detectors, also highly pure and stable targets are needed. Here, using a gas jet as a target offer an attractive approach that combines high stability even under significant beam load with excellent purity. Such a target is currently under construction at the Felsenkeller underground ion...
The $^{19}$F(p,$\alpha$)$^{16}$O reaction is important for understanding the fluorine abundance in the outer layers of asymptotic giant branch (AGB) stars and it might also play a role in hydrogen-deficient post-AGB star nucleosynthesis. Up to now, theoretical models overproduce F abundances in AGB stars with respect to the observed values, thus calling for further investigation of the...
A recent sensitivity study has shown that the 35K(p,γ)36Ca reaction is one of the ten (p,γ) reaction rates that could significantly impact the shape of the calculated X-ray burst light curve [1]. Its reaction rate used up to now in type I X-ray burst calculations was estimated using an old measurement for the mass of 36Ca and theoretical predictions for the partial decay widths of the first 2+...
Recent measurement of coherent π0 photoproduction on Pb lead to a most accurate determination of the neutron skin, constraining nuclear matter Equation of State (EoS) at around ρ~1ρ0. A natural next step is elucidating the nuclear EoS at higher densities to tune our understanding of the most violent process in the Universe - neutron stars mergers. It was demonstrated that at densities above...
The nuclear fission of very neuron-rich nuclei is essential for the termination of the r-process flow on the nuclear chart and the determination of the final abundances. Nevertheless, most of the available fission data for neutron-rich nuclei are based on theory predictions mostly by phenomenological treatments. In this study, we calculated a series of nuclear fission distribution for...
Nuclei in the $^{135}$I region have been identified as a possible bottleneck for the i process. Nuclear properties such as the Maxwellian-averaged cross section are indispensable tools when trying to explain nucleosynthetic processes, but the instability of the region prevents us from carrying out direct measurements. In order to investigate it, we propose an indirect approach.
At the Oslo...
In spite of decades of research, many observed nuclear abundances remain that can not be reproduced by p-process nucleosynthesis calculations [1].
This is mainly due to the lack of constraints for the involved nuclear physics models.
Previous studies have shown that key reactions affecting the abundance of the p-nucleus $^{168}$Yb are the $^{164,166}$Yb($\alpha, \gamma$) reactions and that...
The neutron activation method is well-suited to investigate neutron-capture
cross sections relevant for the main s-process component. Neutrons can be pro-
duced via the $^7$Li(p,n) reaction with proton energies of 1912 keV at e.g. Van de
Graaf accelerators, which results in a Maxwellian spectrum of neutrons corre-
sponding to a temperature of k$_\text{B}$T = 25 keV. This mimicks the...
The 3He(α,γ)7Be reaction plays a role in two distinct astrophysical scenarios, solar fusion processes as well as the Big Bang nucleosynthesis. The astrophysical S-factor of this reaction has been studied several times for energies above 0.3MeV and once for energies between 0.1MeV and 0.2MeV, but never directly for energies below 0.1MeV. The energies in between and below the measured range are...
Cross section measurements of ${}^{12,13}\mathrm{C}(\mathrm{p},\gamma){}^{13,14}\mathrm{N}$ have been performed at the Laboratory for Underground Nuclear Astrophysics (LUNA), where the low-background environment and high beam currents of the $400\,\mathrm{kV}$ accelerator allowed to obtain cross section data for these reactions at lower energies and with smaller statistical uncertainties than...
To calculate the reaction rate in the neutron capture processes it is common to work with the Maxwellian Average Cross Section (MACS), defined as the reaction rate scaled by the most probable neutron velocity of the Maxwell-Boltzmann distribution. For the s-process mainly, the MACS directly describes the reaction rate inside the stars, for a given temperature and neutron density. Hence, the...
$^{12}C(\alpha,\gamma)^{16}O$ has been, and still is, one of the central topic in nuclear astrophysics.\
Reason for this is that stellar models are very sensitive to the ratio $^{12}C/^{16}O$ produced by the helium buring stage. Knowing the value of the $^{12}C(\alpha,\gamma)^{16}O$ S-factor at the energy of astrophysical interest ($E_0\sim$ 300 keV) to a precision better than 10\% would...
Multinucleon-transfer (MNT) reactions have gained a lot of attention in the last decade following the theoretical prediction of larger than expected production cross sections for heavy neutron-rich nuclei [1] playing a key role in the astrophysical rapid neutron capture process (r process) [2]. At the Ion Guide Isotope Separator On-Line (IGISOL) facility [3] in the JYFL Accelerator Laboratory,...
Short-lived radionuclides, i.e. radioactive isotopes with half-lives of less than 100 Ma, were present as primordial isotopes in the proto-solar cloud and during the formation of our solar system. The origin of specific short-lived radionuclides is still a matter of dispute. Because of their comparatively short half-lives, these isotopes are no longer present in cosmic samples today, but are...
We perform microscopic Molecular Dynamics simulations to study crystallization in the outer crust of Neutron Stars (NSs). We study the energetics and pressure in the electron screened nuclear system using a consistent nuclear population in the inner and outer crust under the approximation of one the component plasma (OCP) and multicomponent plasma (MCP) assuming some nuclear species...
Neutron-induced charged particle reactions (n, p) and (n, α), especially on unstable proton-rich isotopes, play an important role in understanding explosive astrophysical scenarios and interpreting their remnants. In a recent publication [1], a novel approach is described to study experimental cross-sections of (n, p) and (n, α) reactions at explosive stellar temperatures for various nuclei...
The $^3$He($\alpha$,$\gamma$)$^7$Be nuclear reaction has been investigated in several times before [1]. The importance of this reaction is manifested in two astrophysical scenarios. It plays a role in the nucleosynthesis of the Big Bang (BBN) through the production of lithium and is also a branching reaction in the solar p-p chain. The astrophysically relevant energy range of this reaction in...
Black holes have ignited thought-provoking ideas for decades because of their peculiar origin of existence and very nature. Once only thought to be merely a mathematical curiosity, black holes have now become an integral part of Astrophysics and Astronomy that devour copious amounts of matter. Given the advancement from the first speculation to the latest research, an up-to-date review report...
The impression of mean field and spectator matter has been studied through the collision geometry dependence of reduced flow and elliptical flow in heavy-ion collisions (HICs) at intermediate energies using Isospin-dependent Quantum Molecular Dynamics (IQMD) model for the reaction of $^{50}_{20}$Ca+$^{50}_{20}$Ca and $^{197}_{79}$Au+$^{197}_{79}$Au at incident energy between 50 MeV/nucleon and...
Several reactions of light nuclei require a better understanding in Nuclear Astrophysics. The most relevant one is 12C(α,γ)16O. The reason for this is both, the unmitigated importance of the reaction, and the complexity of its cross section at the relevant energies of static helium burning (300 keV) which uncertainty is still undesirably large. As there is no state of natural parity to serve...
Big Bang Nucleosynthesis (BBN) accounts for the cosmic origin of the lightest elements, and deuterium (D/H) plays a key role in probing the physics of the early universe. The simplicity of BBN theory allows for few-percent-level precision of D/H prediction, which is not normally possible in nuclear astrophysics. Under such precision, the comparison between predicted and observed primordial D/H...
Bardeen–Cooper–Schrieffer theory explains how the heat capacity of the superfluid vanishes when the temperature approaches zero. Various mechanisms may suppress the pairing gap in the superfluid, leading to an increased heat capacity. In turn, this may translate to changing the cooling rate and the thermal evolution of neutron stars. The presence of a vortex in a superfluid neutron matter will...
The existence of most of the stable very neutron deficient nuclei - the $p$ nuclei - cannot be explained via neutron-capture reactions. Therefore, at least one other process has to exist in order to describe their origin, the $\gamma$ process. Since most photodisintegration reactions involved in the process are not directly accessible, reliable statistical model calculations are needed to...
The $^{17}$O(n,$\alpha$)$^{14}$C reaction is considered in astrophysical codes for its role in the astrophysically relevant "s(slow)-process" since it could act as a possible “neutron-poison” for the neutron induced nucleosynthesis thus influencing the final stellar abundances of some elements such as Fe, Ni or Sr. Thus, its reaction rate must be known in the energy region of interest for...
Muon are the subatomic particles. with very high speed(2.9*10^8).with this speed it can travel a distance of 456meters.But the muon formed in the atmosphere travel the distance of 15 km whish is shown by research.
This phenomenon is called muon paradox if we can differentiate between these special muon (of muon paradox which undergoes in time dilation and length contraction) and normal muon...
Observed supermassive black holes in the early universe have several proposed formation channels, in part because most of these channels are difficult to probe. One of the more promising channels, the directly collapse of a supermassive star, has several possible probes including the explosion of a helium supermassive star triggered by a general relativistic instability. We develop a...
$^{19}$F (p,$\alpha$) reaction is one of the crucial reactions in the CNO Cycle. It has the utmost importance in the astrophysical region particularly below the Coulomb barrier [1]. In an astrophysical scenario, the importance astrophysical S-factor is crucial for the understanding of discrepancies in fluorine nucleosynthesis [2-4] and the contribution of direct or resonance at such low...
Around half of the elemental abundances heavier than iron are created via the rapid neutron capture process (r-process). For nuclear masses $A>100$, there are two main peaks in the r-process abundances, located at $A\sim 130$ and $A\sim 195$. These peaks are associated with neutron shell closures. In contrast, the rare-earth peak (REP) is a small - but clear - peak around mass $A=160$,...
As the slowest reaction in the carbon-nitrogen cycle of hydrogen burning, the $^{14}$N($p,\gamma$)$^{15}$O reaction modulates the rate of energy generation in stars in the cycle and thus determines the time spent on the main sequence. Astrophysical challenges, such as the age determination of globular clusters or the solar-abundance problem can be targeted by improving the precision on the...
The isospin dependent nuclear saturation property has a salient role to play in understanding the matter behaviour at high density regimes. Very recently an improved value of neutron skin thickness of $^{208}\text{Pb}$ was reported in Lead Radius EXperiment-II (PREX-2) to be $R_{\text{skin}}=R_n - R_p=(0.283\pm 0.071)$ fm which corresponds to high estimations of nuclear symmetry energy...
The nucleosynthesis of elements heavier than iron in stars is one of the most relevant topics in nuclear astrophysics. The neutron-capture processes made most of the abundances of heavy elements in the solar system, but they are not able to make a number of rare proton-rich stable isotopes (p-nuclei) lying on the left side of the stability valley. The $\gamma$-process, i.e. a chain of...
Carbon burning is a fundamental process for the advanced stages of a massive star ($ M> 8M_\odot $) evolution. It mainly occurs through the $^{12}C+^{12}C$ fusion, however at temperatures higher than $ 10^9 K $ the $^{12}C+^{16}O $ fusion can become prevalent due to the increased abundance of $ ^ {16} O $ in the ashes of the helium burning. The $ ^{12}C + ^{16} O $ reaction also plays a role...
Present nuclear reaction network computations for astrophysical simulations involve many different types of rates, including neutron-capture reactions of interest for the modeling of heavy-element nucleosynthesis. While for many of them we still have to rely on theoretical calculations, an increasing number of experimentally-determined cross sections have now become available. In this...
Nucleosynthesis by the rapid neutron-capture process (r-process) produces elements heavier than iron via neutron-rich nuclides, observed in the solar system and stars with various metallicities. In the r-process, fission plays a fundamental role by recycling the matter during neutron irradiation and by shaping the final r-abundance distribution. Nevertheless, most of the fission data available...
We show the impact on AGB stellar nucleosynthesis of the maxwellian averaged capture cross sections determined at n_TOF over the past 20 years. We developed an automated procedure to derive MACSs from evaluated data libraries, which are subsequently used as input to stellar models computed by means of the FUNS code.
In this contribution, we present a number of s-process abundances obtained...
The nuclear fission of very neuron-rich nuclei is essential in the r-process for the termination of nucleosynthesis flows and the final abundances. Nevertheless, most of the available fission data for the r-process simulations are based on phenomenological calculations. In the present study, we investigate the theoretical uncertainty of nuclear fission related to the r-process. Focusing on the...
It has long been postulated that the onset of electron captures in degenerate high-density ONe cores of super-AGB stars would trigger a supernova, resulting in a collapse into a neutron star (NS). New models of these so-called electron capture supernovae (ECSNe) suggest that while the full collapse to a NS is still a possibility, the energy release by the electron-capture reactions can also...
Two significant anomalies have been recently observed in the emission of electron-positron
pairs in the 7Li(p,e− e+)8Be and 3H(p,e− e+)4He reactions [1, 2]. These anomalies have
been interpreted as the signature of the existence of a boson (hereafter referred to as X17)
of mass M_X17 = 16.8 MeV that could be a mediator of a fifth force, characterised by a
strong coupling suppression of...
