Hoyle State In 12C Research Articles

Effects of Hoyle state de-excitation on νp–process nucleosynthesis and Galactic chemical evolution

The particle-induced hadronic de-excitation of the Hoyle state in 12C induced by inelastic scattering in a hot and dense plasma can enhance the triple-alpha reaction rate. This prevents the production of heavy nuclei within the neutrino-driven winds of core-collapse supernovae and raises a question as to the contribution of proton-rich neutrino-driven winds as the origin of p–nuclei in the solar-system abundances. Here we study νp-process nucleosynthesis in proton-rich neutrino-driven winds relevant to the production of Mo92,94 and Ru96,98 by considering such particle-induced de-excitation. We find that the enhanced triple-alpha reaction rate induced by proton inelastic scattering can increase the production of Mo92,94 and Ru96,98 in an energetic hypernova wind model with a massive proto-neutron star although the abundances of these p–nuclei decrease in a wind model of ordinary core-collapse supernovae. The enhancement of the triple-alpha reaction rate induced by the neutron scattering hardly affects the νp-process at low temperature. We show the new result that, contrary to the results for ordinary core-collapse supernovae, the hypernova νp-process can contribute to the Galactic chemical evolution of p–nuclei regardless of the particle-induced Hoyle state de-excitation and even enhance the solar isotopic fractions of Mo92,94 and Ru96,98.

Radiative Decay Branching Ratio of the Hoyle State in 12C via Charged Particle Coincidence Techniques

The properties of the Hoyle state in 12C (7.654 MeV, 0+) affect the rate at which carbon, one of the most abundant elements in the Universe, is forged in stars. Recent experiments reported values of its radiative decay branching ratio that are in tension, posing major implications especially in the astrophysical domain. This work reports on an almost background-free measurement of the radiative decay branching ratio of the Hoyle state that exploits charged particle coincidence techniques. The experiment adopts several methodologies to minimize the background and identify the rare signal associated with the radiative decay. Large care is devoted to having under full control two of the major sources of systematic errors in particle-coincidence experiments: the coincidence efficiency and the spurious coincidence rate. We find a radiative decay branching ratio of Γrad/Γtot = 4.2(6) · 10−4. The new finding helps to resolve the tension between recent data published in the literature.

Measurement of 12C(n,n’) reaction cross section to determine triple-alpha reaction rate in high-density environments

The reaction rate of the triple-alpha reaction can be enhanced in hot and dense environments due to the deexcitation of the Hoyle state in 12C by neutrons. The cross section of the deexcitation should be determined for the enhanced reaction rate. We plan to obtain the cross section by measuring the inverse reaction using a neutron beam around 10 MeV and an active target system. In the present paper, we report a proof-of-principle experiment using a neutron beam at 14 MeV. The obtained cross section is consistent with a previous result, demonstrating the validity of our method.

The Hoyle Family: break-up measurements to probe α-condensation in light nuclei

The ^{12}12C Hoyle state is a candidate for \alphaα-condensation, due to its large volume and \alphaα-cluster structure. This paper discusses precision break-up measurements and how they can elucidate \alphaα-condensate structures. Two experiments are discussed in detail, firstly concerning the break-up of ^{12}12C and then the decays of heavier nuclei. With more theoretical input, and increasingly complex detector setups, precision break-up measurements can, in principle, provide insight into the structures of states in \alphaα-conjugate nuclei. At present, such searches have not delivered evidence for \alphaα-condensation in ^{12}12C or ^{16}16O.

Theoretical approaches to the 3α break-up of 12C

Two recent experiments have indicated that the break-up of the 12C Hoyle state is dominated by the sequential 8Be(g.s.) + α decay channel. The rare direct 3α decay was found to contribute with a branching ratio of less than 0.047% (95% C.L.). However, the ability of experimentalists to successfully disentangle these two competing decay channels relies on accurate theoretical predictions of how they each manifest in phase space distribution of the three break-up α-particles. The following paper reviews the current theoretical approaches to calculating the break-up of the Hoyle state and introduces a semi-classical WKB approach, which adequately reproduces the results of more sophisticated calculations. It is proposed that a more accurate upper limit on this branching ratio may be obtained if these new theoretical results are taken into account when analysing experimental data.

New high precision study on the decay width of the Hoyle state in 12C

Precise estimation of the rare direct 3α decay of the Hoyle state of 12C has been made to unveil its unusual α-cluster configurations ranging from linear 3α chain structure to diffuse Bose gas as well as Bose Einstein condensate. The present new high precision, nearly zero background experimental study with 1.6×105 Hoyle events has converged on the upper limit for direct decay at ∼0.019% with 95% confidence limit, which is more than a factor of 2 lower than the limit obtained in the previous studies.

Searching for states analogous to the C12 Hoyle state in heavier nuclei using the thick target inverse kinematics technique

Identification of alpha cluster states analogous to the 12C Hoyle state in heavier alpha- conjugate nuclei can provide tests of the existence of alpha condensates in nuclei. Such states are predicted for 16O, 20Ne, 24Mg, 28Si etc. at excitation energies slightly above the multi-alpha particle decay threshold, but have not yet been experimentally identified. The Thick Target Inverse Kinematics (TTIK) technique can be used to study the breakup of excited self-conjugate nuclei into many alpha particles. The reaction 20Ne+{\alpha} was studied using a 20Ne beam at 12 MeV/nucleon from the K150 cyclotron at Texas A&M University. The TTIK method was used to study both single {\alpha}-particle emission and multiple {\alpha}-particle decays. Events with alpha multiplicity up to four were analyzed. The analysis of the three {\alpha} - particle emission data allowed the identification of the Hoyle state and other 12C excited states decaying into three alpha particles. The results are shown and compared with other data available in the literature. Although the statistics for events with alpha multiplicity four is low, the data show a structure at about 15.2 MeV that could indicate the existence in 16O of a state analogous to the 12C Hoyle state. This structure is confirmed by the re-analysis of alpha multiplicity four events from a previous experiment performed at 9.7 MeV/nucleon with a similar setup but lower granularity. Moreover, the reconstructed excitation energy of 24Mg for these events peaks at around 34 MeV, very close to the predicted excitation energy for an excited state analogous to the 12C Hoyle state in 24Mg.

The α-decay of the Hoyle state in 12C: a new high-precision investigation

The αdecay path of the Hoyle state in 12C (Ex = 7:654MeV) represents one ofthe most challenging questions of modern nuclear physics. Its knowledge can help in theunderstanding of cluster configurations in light nuclei and the possible existence of Bose-Einstein condensates in nuclei. In stars, it is involved in the so-called 3αprocess, wherethe 12C nucleosynthesis occurs. We studied the 14N(d; α2)12C(7:654) reaction at 10:5MeVincident energy to probe its direct decay component. We found, with a precision higherof a factor 5 than any other previous experiment, an almost total absence of direct decaysby-passing the ground state of 8Be. From our analysis, a new upper limit of such decayis found at 0:043% (95% C.L.). Astrophysical 3α process reaction rate calculations haveto be accordingly revised.

The cluster states in light nuclei

The differential cross-sections of the elastic and inelastic α +11B scattering was measured at E(α) = 29 MeV. The analysis of the data by Modified Diffraction Model (MDM) showed that the root-mean- square (RMS) radius of the 11B state 3/2-, E* = 8.56 MeV is ~ 0.5 fm larger than that of the ground state. It is found that the radius of 3/2- (8.56 MeV) state in the 11B nucleus is close to the radii of the Hoyle state in 12C.

Rotational excitation of the Hoyle state in 12C

12C is synthesised in stars by fusion of three α particles. This process occurs through a resonance in the 12C nucleus, famously known as the Hoyle state. In this state, the 12C nucleus exists as a cluster of α particles. The state is the band-head for a rotational band with the 2+ rotational excitation predicted in the energy region 9 - 11 MeV. This rotational excitation can affect the triple-α process reaction rate by more than an order of magnitude at high temperatures (109 K). Depending on the energy of the resonance, the knowledge of the state can also help determine the structure of the Hoyle state. In the work presented here, the state of interest is populated by beta decay of radioactive 12N ion beam delivered by the IGISOL facility at JYFL, Jyväskylä.

Investigation of the Hoyle state in12C with a new hodoscope detector

The state in12C (7.654MeV, the Hoyle state) is important for the understanding of clustering phenomena in nuclei. The pronounced cluster nature of this state allows the triple-α process in stars with a reaction rate regulated by its structure properties. To precisely estimate the direct component in the 3α decay mechanism of the Hoyle state, we developed a new experiment using the14N(d,α)12C reaction at 10.5MeV. An anti-coincidence telescope was used to identify the α ejectiles leading the residual12C in the Hoyle state, while its decays in 3α were studied by means of a new hodoscope of silicon detectors, superOSCAR, placed in kinematical coincidence to fully reconstruct the events. Details of the experiment and preliminary results are discussed in the text.

Alpha-Particle Condensate Structure of the Hoyle State: where do we stand?

The present understanding of the structure of the Hoyle state in12C is reviewd. It is pointed out that a crucial test of any theory is the good reproduction of the experimental results for the inelastic form factor from ground to the Hoyle state. The performances of the so-called THSR wavwe function are outlined confirming the α particle condensation hypothesis proposed 15 years back in [1].

Clustering effects in fusion evaporation reactions with light even-even N=Z nuclei

In the recent years, cluster structures have been evidenced in many ground and excited states of light nuclei [1, 2]. In the currently experimental campaign, the NUCL-EX collaboration has measured the12C+12C and14N+10B reactions at 95 MeV and 80 MeV respectively. The experimental data corresponding to complete fusion of target and projectile into an excited24Mg nucleus was compared to the results of a pure statistical model [3, 4]. In addition, data from12C+12C have been analyzed to investigate the decay of the Hoyle state of12C* [12] obtained as an intermediate step in the 6α decay channel of the24Mg* formed in central events.

Quartet condensation in Fermi-systems. The Hoyle state in the 12C nucleus and life on earth

The possibility that a four component Fermi gas with attractive interaction can form a quartet condensate at low density is pointed out. It is discussed that for quartets only the Bose-Einstein Condensatio (BEC) phase exists and that the analogue to the weak coupling long coherence BCS phase of pairing is absent. Precurser phenomena in finite nuclei are presented. For instance, the present understanding of the structure of the Hoyle state in 12C being the gateway for Carbon production in the universe is reviewed. It is pointed out that a crucial test of any theory is the good reproduction of the experimental results for the inelastic form factor from ground to the Hoyle state. The performances of the so-called THSR wavwe function are outlined confirming the α particle condensation hypothesis proposed 15 years back in [1].

Colloquium: Status ofα-particle condensate structure of the Hoyle state

The present understanding of the structure of the Hoyle state in 12C is reviewed. Most of the theoretical approaches to the Hoyle state are shortly summarized. The corresponding results are analyzed with respect to whether they give evidence to the alpha particle condensation structure of the Hoyle state (and other Hoyle-like states in heavier self-conjugate nuclei) or not.

Nuclear states with anomalously large radius (size isomers)

Methods of determination of the nuclear excited state radii are discussed together with the recently obtained data on the states of some light nuclei having abnormally large radii (size isomers). It is shown that such states include excited neutron-halo states in 9Be, 11Be, and 13C and some alpha-cluster states in 12C, 11B, and 13C. Among the latter ones, there is the well-known Hoyle state in 12C—the structure of this state exhibit rudimentary features of alpha-particle states.

The Prototype Active-Target Time-Projection Chamber used with TwinSol radioactive-ion beams

The study of low-energy reactions with radioactive-ion beams has been greatly enhanced by the recent use of active-target detectors, which have high efficiency and low thresholds to detect low-energy charged-particle decays. Both of these features have been used in experiments with the Prototype Active-Target Time-Projection Chamber to study α-cluster structure in unstable nuclei and 3-body charged-particle decays after implantation. Predicted α-cluster structures in 14C were probed using resonant α scattering and the nature of the 3-α breakup of the 02+ Hoyle state in 12C after the beta decay of 12N and 12B was studied. These experiments used in-flight radioactive-ion beams that were produced using the dual superconducting solenoid magnets TwinSol at the University of Notre Dame. Preliminary results from these experiments as well as the development of future radioactive beams to be used in conjunction with the PAT-TPC are presented.

Analogues of the exotic Hoyle state in the 12C nucleus

Experimental data on inelastic scattering of alpha particles by the 11B, 12C, and 13C nuclei are analyzed using the modified diffraction model and the radii of these nuclei in some “abnormal” excited states are found. It is shown that the 0 2 + (7.65 MeV) Hoyle state in the 12C nucleus is the base state for a new 0 2 + –2 2 + –4 2 + rotational band (in addition to the ground-state band), in which the third member is the discovered 4 2 + (13.75 MeV) state. The radii of the 12C nucleus in the above-mentioned three states are 25–30% larger than its ground state radius. It is found that the radii of the 1/2– (8.86 MeV) state in the 13C nucleus and the 3/2– (8.56 MeV) state in the 11B nucleus are close to the radius of the Hoyle state in 12C and that a similar rotational band is based on the 8.56 MeV state. The above 13C and 11B states can be regarded as analogues of the Hoyle state. The prediction of the alpha-condensation model that a similar analogue in 11B is the 12.56 MeV state with a radius that is comparable with the nuclear radius of uranium was not confirmed.

轻核α团簇结构理论和实验研究进展

The degree of freedom of α cluster exists widely in light α conjugate nuclei, which not only plays essential roles in the synthesis of elements and abandance of elements in nuclear astrophysics but also serves as the natural laboratory to test various new many-body theories and nuclear force due to the available high precision data. This article briefly summarizes the different theoretical approaches for alpha-cluster and compares the results of 12C Hoyle state with these approaches. All the theories support the structure of Hoyle state with a more extended size compared with ground state. However, a consensus has not be reached about how α clusters stay inside Hoyle state, where several candidate states are possible, such as a condensate state, a gas or crystalline arrangements of the α-particles. Further more, we also introduce the new experimental measurements of a decay and collective excitation of rotational band. In order to pin down the existence form of a in Hoyle state, a deeper knowledge of the collective excitation of cluster is needed. The essential progress can only be possible by high combination of new data with high precision and new many-body theory, where the roles of nucleon-nucleon correlation, cluster-cluster correlation and continuum are needed to be included reasonably.

HPC-enabled Nuclear Structure Studies – Description and Applications of the Symmetry-adapted No-Core Shell Model

By exploiting symmetries that enable the accounting of vital collective correlations in nuclei, we achieve significantly reduced dimensions for equivalent ultra-large model spaces, and hence resolve the scale explosion problem in nuclear structure calculations, i.e, the explosive growth in computational resource demands with increasing number of particles and size of the spaces in which they reside. As a result, we provide – with the help of High Performance Computing (HPC) resources – first solutions for selected benchmark calculations with remarkable findings of large-deformation and low-spin dominance in low-lying nuclear states. In the framework of a complementary symmetry-adapted study, one is able, facilitated by symmetry-preserving pieces of the inter-nucleon interaction, to accommodate unprecedented shell-model spaces critical to capture the physics governing the Hoyle state in 12C, thereby addressing a 60-year-old puzzle on the emergence of cluster substructures within a no-core shell model framework. All of these findings underline the key role of symmetries in nuclear structure studies.