Stability of (3)He(2)(4)He(n) and (3)He(3)(4)He(n) L=0 clusters

We have studied the stability of mixed (3)He/(4)He clusters in L=0 states by the diffusion Monte Carlo method, employing the Tang-Toennies-Yiu He-He potential. The clusters (3)He(4)He(N) and (3)He(2)(4)He(N) are stable for N>1. The lighter atoms tend to move to the surface of the cluster. The minimum number of 4He atoms able to bind three 3He atoms in a L=0 state is nine. Two of three fermionic helium atoms stay on the surface, while the third one penetrates into the cluster.     

Large-space cluster model calculations for the 3He(3He,2p)4He and 3H(3H,2n)4He reactions

The ³He(³He,2p)⁴He and ³H(³H,2n)su4He reactions are studied in a microscopic cluster model. We search for resonances in the ³He+³He and ⁴He + p + p channels using methods that treat the two- and three-body resonance asymptotics correctly. Our results show that the existence of a low-energy resonance or virtual state, which could influence the ⁷Be and ⁸B solar neutrino fluxes, is rather unlikely. Our calculated ³He(³He,2p)⁴He and ³H(³H,2n)⁴He cross sections are in a good general agreement with the experimental data.     

Determination of the cluster spectroscopic factor of the 10.3 MeV state in 12Be

From an inelastic excitation and breakup experiment with a ¹²Be beam at 29 MeV/u, a large ⁴He+⁸He cluster decay width of 1.1(2) MeV is determined for a state at an excitation energy of 10.3 MeV and with a spin parity of 0+. By using the R-matrix analysis, a cluster spectroscopic factor of 0.53(10) is extracted from the cluster partial width, providing a strong support for the clustering structure in ¹²Be. A specially designed zero-degree telescope played an essential role in the present experiment and has been demonstrated to be a promising tool in future studies of the molecular-like resonances near the cluster separation threshold.     

Bubble formation and decay in 3He and 4He clusters

The energy transfer in 3He and 4He clusters electronically excited by monochromatic synchrotron radiation is investigated by luminescence spectroscopy. Depending on the cluster size and the isotopic constitution, either sharp, broadened, or shifted emission bands of single He molecules are observed. The spectral features show that He molecules emit light either within a bubble inside the cluster or in the vacuum after desorption from the cluster. From the luminescence intensity, the cluster diameter, and the radiative lifetime, an average velocity of approximately 7 m/s of bubbles in 4He clusters could be deduced. In the nonsuperfluid 3He clusters this velocity was observed to be significantly lower.     

Microscopic calculation of the 3He(α,γ)7Be and 3H(α,γ)7Li capture cross sections using realistic interactions

The radiative capture cross sections for the 3He(α,γ)7Be and 3H(α,γ)7Li reactions are calculated in the fully microscopic fermionic molecular dynamics approach using a realistic effective interaction that reproduces the nucleon-nucleon scattering data. At large distances bound and scattering states are described by antisymmetrized products of 4He and 3He/3H ground states. At short distances the many-body Hilbert space is extended with additional many-body wave functions needed to represent polarized clusters and shell-model-like configurations. Properties of the bound states are described well, as are the scattering phase shifts. The calculated S factor for the 3He(α,γ)7Be reaction agrees very well with recent experimental data in both absolute normalization and energy dependence. In the case of the 3H(α,γ)7Li reaction the calculated S factor is larger than available experimental data by about 15%.     

First-principles study of helium clustering at initial stage in ThO_2

The clustering behavior of helium atoms in thorium dioxide has been investigated by first-principles calculations. The results show that He atoms tend to form a cluster around an octahedral interstitial site(OIS). As the concentration of He atoms in ThO_2 increases, the strain induced by the He atoms increases and the octahedral interstitial site is not large enough to accommodate a large cluster, such as a He hexamer. We considered three different Schottky defect(SD) configurations(SD_1, SD_2, and SD_3). When He atoms are located in the SD sites, the strain induced by the He atoms is released and the incorporation and binding energies decrease. The He trimer is the most stable cluster in SD_1. Large He clusters, such as a He hexamer, are also stable in the SDs.     

4He fragmentation induced by 46–400 GeV Protons

Inclusivep, d and³He cross sections have been obtained using experimental data on p⁴He collisions over an incident proton energy range of 46-400 GeV. Considering the slopes of spectra, the effective nuclear temperature has been found to be T₀=11 MeV, which is in good agreement with experimental results for lower energies and heavier targets. The shape of the³He inclusive spectrum suggests the existence of two different³He production mechanisms. The experimental³He cross section is compared with theoretical predictions assuming fragment formation as a result of the spectator and cluster knockout mechanisms. The⁴He→³He +n vertex constant has been found to be G²=10.9±0.2 fm.     

Reaction matrix calculation of 4He including Δ degrees of freedom

The effects of the Δ(3-3) resonance components on the binding energy of ⁴He are studied within the framework of reaction matrix theory. In this approach, the Δ -configurations in ⁴He are introduced in terms of the NΔ transition potential by solving the reaction matrix equation and thus it goes beyond perturbation theory with the NΔ transition potential. Not only the two-body cluster energy but also the three-body cluster energy containing Δ-configurations are calculated.     

Frequency metrology of helium around 1083 nm and determination of the nuclear charge radius

We measure the absolute frequency of seven out of the nine allowed transitions between the 2 (3)S and 2 (3)P hyperfine manifolds in a metastable (3)He beam by using an optical frequency comb synthesizer-assisted spectrometer. The relative uncertainty of our measurements ranges from 1×10(-11) to 5×10(-12), which is, to our knowledge, the most precise result for any optical ^{3}He transition to date. The resulting 2 (3)P-2 (3)S centroid frequency is 276,702,827,204.8(2.4) kHz. Comparing this value with the known result for the (4)He centroid and performing ab initio QED calculations of the (4)He-(3)He isotope shift, we extract the difference of the squared nuclear charge radii δr(2) of (3)He and (4)He. Our result for δr(2)=1.074(3) fm(2) disagrees by about 4σ with the recent determination [R. van Rooij et al., Science 333, 196 (2011)].     

Lowest order constrained variational method applied to liquid $^\mathsf{3}$He

The energy of normal liquid ³He is obtained using the lowest order constrained variational (LOCV) method. In order to test the convergence of the cluster expansion series, the three-body cluster energy is calculated, with the LOCV correlation functions, and by imposing the normalization constraint on the two-body distribution function which includes three-body cluster correlations (LOCVE). It is shown that the normalization constraint plays an important role in keeping the higher cluster terms small. The resulting LOCVE calculation for the ground state energy of liquid ³He is compared with the available experimental data and the prediction from different theoretical techniques.Received: 26 May 2003, Published online: 30 January 2004PACS: 61.20.Gy Theory and models of liquid structure - 61.20.Ne Structure of simple liquids - 67.55.-s Normal phase of liquid ³He     

First measurement of kaonic helium-3 X-rays

The first observation of the kaonic (3)He 3d→2p transition was made, using slow K- mesons stopped in a gaseous (3)He target. The kaonic atom X-rays were detected with large-area silicon drift detectors using the timing information of the K+K- pairs of ?-meson decays produced by the DAΦNE e+e- collider. The strong interaction shift of the kaonic (3)He 2p state was determined to be -2±2(stat)±4(syst) eV.     

Direct observation of the ... 4+-to-2+ ... [corrected] gamma transition in 8Be

Electromagnetic transition rates provide an important test for nuclear structure models. The nucleus 8Be exhibits a pronounced alpha-cluster structure and is a building block for more complex cluster nuclei. Here we report on the first observation of the gamma transition between the 4(+) and 2(+) states of 8Be in the 4He+4He reaction. The measured on-resonance cross section of 165+/-54 nb leads to a B(E2) of25+/-8e(2) fm(4), in good agreement with alpha-cluster models and sophisticated ab initio structure calculations.     

Electron detachment spectroscopic study on carbon and silicon cluster anions

The electron detachment of mass-selected carbon and silicon cluster anions was studied using different ion-source conditions. Ultraviolet photoelectron spectra of medium-sized carbon cluster anions were measured using a laser vaporization source with different fluences. On systematic inspection, the series of spectra showed 4n-periodicity in their electron affinity, which is consistent with the predicted ring-form structure. For silicon cluster anions, resonance-enhanced multiphoton electron detachment spectra were measured. The role of the carrier gases He, N₂ and CO₂ is discussed.     

Pre-formation Probability of 5He Cluster in Pre-equilibrium Mechanism

The possibility of 5He cluster emission has been affirmed theoretically. In order to describe the emission probability of 5He cluster, the pre-formation probability of 5He cluster in pre-equilibrium emission process is needed to be established. In terms of Iwamoto-Harada model, the theoretical formula of pre-formation probability of 5He cluster including 1p shell nucleon in pre-equilibrium mechanism has been established and calculated. In the case of low incident energies, the configuration of [1, m] for 5He cluster is the dominant part in the nuclear reaction. The calculated results indicate that pre-formation probability of configuration [1, m] for the unstable 5He cluster is much smaller than those of d, t, 3He, and 4He, i.e. the light stable composite particles, which are consisted of only 1s shell nucleons. However, it is propitious to the emission of 5He from the point of view on threshold energies, since the binding energies of 5He are generally lower than that of 3He in compound nucleus. The corresponding model formula has been given in this paper for described pre-formation probability of 5He cluster in pre-equilibrium mechanism.     

Stability of small mixed clusters of 4He and 3He atoms

The existence of small helium clusters containing a variable number of 4He and 3He atoms is studied within a variational Monte Carlo calculation employing the Aziz HFD-B(HE) pair interaction. The clusters 4He(2) support one and two 3He atoms; however, the system with three 3He atoms is metastable, and the next bound system requires at least 18 fermions. All clusters obtained by adding 3He atoms to the trimer 4He(3) and the tetramer 4He(4) are bound, but the clusters 4He(3)-3He(3,4,5) and 4He(3,4)-3He(9) are metastable. All remaining clusters with three or more bosons and any number of fermions are stable.     

Study about the Binding Energy of Light Double Hypernuclei ^6_ΛΛHe,^5_ΛΛHe,^5_ΛΛH,^4_ΛΛHe,and ^4_ΛΛH Based on Chiral SU(3) Quark Model

In the framework of the resonating group method, the binding energies of double lambda hypernuclei ^6_ΛΛHe,^5_ΛΛHe,^5_ΛΛH,^4_ΛΛHe,and ^4_ΛΛH are calculated in the chiral SU(3) quark model. In the two-cluster approximation in which a two-lambda cluster and a core nuclei are considered, one finds that the resultant binding energy of double-lambda hypernuclei ^6_ΛΛHe is in good agreement with the experimental data. It means that the chiral SU(3) quark model can well-describe the spectrum of baryon, the interactions of N-N, Y-N, and the binding energies of light lambda hpernuclei, as well as the interaction of Y-Y and the binding energy of double-lambda hypernucleus. With the same set of parameters, we calculate the binding energies of light double-lambda hypernuclei ^6_ΛΛHe,^5_ΛΛHe,^5_ΛΛH,^4_ΛΛHe,and ^4_ΛΛH and discuss the possibilities of these states.     

通过费米能区重离子碰撞产额分布来研究16O原子核的团簇结构

近几年来,原子核核内的α团簇结构引起了人们的广泛关注.本工作的目的是讨论在费米能区下重离子碰撞的碎片产额分布是否可以作为研究轻核中α团簇结构的工具.本文基于扩展的量子分子动力学输运模型(EMQD)模拟了16O具有4种不同的初始化α构型(长链型、风筝型、四方型以及正四面体型)的16O+16O反应,通过观察碎片产额多重数分...     

Astrophysical S factors of radiative 3He4He, 3H4He, and 2H4He capture

The possibility of describing the astrophysical S factors for radiative ³He⁴He capture at energies of up to 15 keV and radiative ³H⁴He and ²H⁴He capture at energies of up 5 keV is considered on the basis of the potential cluster model involving forbidden states.     

Formation Mechanism and Binding Energy for Equilateral Triangle Structure of He3+ Cluster

The formation mechanism for the equilateral triangle structure of the He3 cluster is proposed. The curveof the total energy versus the internuclear distance R for this structure has been calculated by the method of a modifiedarrangement channel quantum mechanics. The result shows that the curve has a minimal -7.81373 a.u at 1 = 1.55 a0.The binding energy of He3 with respect to He He He was calculated to be 0.1064 a.u. (about 2.89 eV). This meansthat the He3 cluster may be formed in the equilateral triangle structure stably by the interaction of He with two heliumatoms.