Exploring the manifestation and nature of a dineutron in two-neutron emission using a dynamical dineutron model

NASA Astrophysics Data System (ADS)

Grigorenko, L. V.; Vaagen, J. S.; Zhukov, M. V.

2018-03-01

Emission of two neutrons or two protons in reactions and decays is often discussed in terms of "dineutron" or "diproton" emission. The discussion often leans intuitively on something described by Migdal-Watson approximation. In this work we propose a way to formalize situations of dineutron emission. It is demonstrated that properly formally defined dineutron emission may reveal properties which are drastically different from those traditionally expected, and properties which are actually observed in three-body decays.

Differential cross section for the 16O( t, p)18O reaction and determination of the size of the two-neutron periphery in the 18O nucleus

NASA Astrophysics Data System (ADS)

Galanina, L. I.; Zelenskaya, N. S.

2017-09-01

Within the theoretical formalism that combines a four-body problem with themultiparticle shell model, it is shown that the cross section for the dineuteron-stripping mechanism is consistent with the experimental angular distribution of protons from the 16O( t, p)18O reaction. This makes it possible to find the wave function for the relative motion of the dineutron and 16O and to obtain thereby the probability density W( r) for the dineutron in 18O, the nn-16O interaction potential, and the root-mean-square distance 〈 L〉 nn between the dineutron and 16O. The respective calculations reveal that, at r ≈ 8 fm, the dineutron probability density and a rather deep nn-16O potential become negligible, which leads to the absence of a dineuntron periphery in 18O. It seems that one can explain this fact by a rather large value (12.19 MeV) of the dineutron binding energy in this nucleus. Thus, the 18O nucleus is quite compact an object, despite the excess of two neutrons, and has a neutron skin rather than a periphery.

Strongly Interacting Multi-component Fermions: From Ultracold Atomic Fermi Gas to Asymmetric Nuclear Matter in Neutron Stars

NASA Astrophysics Data System (ADS)

Tajima, Hiroyuki; Hatsuda, Tetsuo; Ohashi, Yoji

2018-03-01

We investigate an asymmetric nuclear matter consisting of protons and neutrons with spin degrees of freedom (σ = ↑, ↓). By generalizing the Nozières and Schmitt-Rink theory for two-component Fermi gases to the four-component case, we analyze the critical temperature T c of the superfluid phase transition. Although the pure neutron matter exhibits the dineutron condensation in the low-density region, the superfluid instability toward the deuteron condensation is found to take place as the proton fraction increases. We clarify the mechanism of the competition between the deuteron condensation and dineutron condensation. Our results would serve for understanding the properties of asymmetric nuclear matter realized in the interior of neutron stars.

Structure of the spatial periphery of the {sup 11}Li and {sup 11}Be isobars

DOE Office of Scientific and Technical Information (OSTI.GOV)

Galanina, L. I., E-mail: galan-lidiya@mail.ru; Zelenskaya, N. S.

2016-07-15

On the basis of the shell model with an extended basis, the structure of {sup 9}Li-{sup 9}Be to {sup 11}Li-{sup 11}Be nuclei is examined with allowance for the competition of {sup jj} coupling and Majorana exchange forces via considering the sequential addition of neutrons, and the respective wave functions are determined. A formalism for calculating the spectroscopic factor for a dineutron and for individual neutrons in nuclei whose wave functions incorporate the mixing of shell configurations is developed. The reactions {sup 9}Li(t, p){sup 11}Li and {sup 9}Be(t, p){sup 11}Be treated with allowance for the mechanisms of dineutron stripping and amore » sequential transfer of two neutrons are considered as an indicator of the proposed structure of lithium and berylliumisotopes. The parameters of the optical potentials, the wave functions for the bound states of transferred particles, and the interaction potentials corresponding to them are determined from a comparison of the theoretical angular distribution of protons from the reaction {sup 9}Be(t, p){sup 11}Be with its experimental counterpart. It is shown that a dineutron periphery of size about 6.4 fm is present in the {sup 11}Li nucleus and that a single-neutron periphery of size about 8 fm is present in the {sup 11}Be nucleus.« less

Big bang nucleosynthesis: The strong nuclear force meets the weak anthropic principle

NASA Astrophysics Data System (ADS)

MacDonald, J.; Mullan, D. J.

2009-08-01

Contrary to a common argument that a small increase in the strength of the strong force would lead to destruction of all hydrogen in the big bang due to binding of the diproton and the dineutron with a catastrophic impact on life as we know it, we show that provided the increase in strong force coupling constant is less than about 50% substantial amounts of hydrogen remain. The reason is that an increase in strong force strength leads to tighter binding of the deuteron, permitting nucleosynthesis to occur earlier in the big bang at higher temperature than in the standard big bang. Photodestruction of the less tightly bound diproton and dineutron delays their production to after the bulk of nucleosynthesis is complete. The decay of the diproton can, however, lead to relatively large abundances of deuterium.

Origin of the main r-process elements

NASA Astrophysics Data System (ADS)

Otsuki, K.; Truran, J.; Wiescher, M.; Gorres, J.; Mathews, G.; Frekers, D.; Mengoni, A.; Bartlett, A.; Tostevin, J.

2006-07-01

The r-process is supposed to be a primary process which assembles heavy nuclei from a photo-dissociated nucleon gas. Hence, the reaction flow through light elements can be important as a constraint on the conditions for the r-process. We have studied the impact of di-neutron capture and the neutron-capture of light (Z<10) elements on r-process nucleosynthesis in three different environments: neutrino-driven winds in Type II supernovae; the prompt explosion of low mass supernovae; and neutron star mergers. Although the effect of di-neutron capture is not significant for the neutrino-driven wind model or low-mass supernovae, it becomes significant in the neutron-star merger model. The neutron-capture of light elements, which has been studied extensively for neutrino-driven wind models, also impacts the other two models. We show that it may be possible to identify the astrophysical site for the main r-process if the nuclear physics uncertainties in current r-process calculations could be reduced.

ORBITING CLUSTERS IN ATOMIC NUCLEI

PubMed Central

Pauling, Linus

1969-01-01

As an alternative to their description as vibrational levels, the low excited states of even-even nuclei can be described as rotational states of a helion, dineutron, diproton, or other cluster about the rest of the nucleus, leading to reasonable values of the average distance between centers of the clusters. Some states involve rotational excitation of two or more helions or other clusters. The nature of the rotating clusters is determined by the relation of the neutron and proton numbers to the magic numbers. PMID:16591799

Two-neutron sequential decay of O 24

DOE PAGES

Jones, M. D.; Frank, N.; Baumann, T.; ...

2015-11-25

In this study, a two-neutron unbound excited state of 24O was populated through a (d,d') reaction at 83.4 MeV/nucleon. A state at E=715±110 (stat) ±45 (sys) keV with a width of Γ<2 MeV was observed above the two-neutron separation energy placing it at 7.65 ± 0.2 MeV with respect to the ground state. Three-body correlations for the decay of 24O → 22O + 2n show clear evidence for a sequential decay through an intermediate state in 23O. Neither a di-neutron nor phase-space model for the three-body breakup were able to describe these correlations.

Two-neutron sequential decay of O 24

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jones, M. D.; Frank, N.; Baumann, T.

In this study, a two-neutron unbound excited state of 24O was populated through a (d,d') reaction at 83.4 MeV/nucleon. A state at E=715±110 (stat) ±45 (sys) keV with a width of Γ<2 MeV was observed above the two-neutron separation energy placing it at 7.65 ± 0.2 MeV with respect to the ground state. Three-body correlations for the decay of 24O → 22O + 2n show clear evidence for a sequential decay through an intermediate state in 23O. Neither a di-neutron nor phase-space model for the three-body breakup were able to describe these correlations.

Investigation of the reaction d + d → {sup 2}He + {sup 2}n at the deuteron energy of 15 MeV

DOE Office of Scientific and Technical Information (OSTI.GOV)

Konobeevski, E. S., E-mail: konobeev@inr.ru; Zuyev, S. V.; Kasparov, A. A.

An experimental setup for studying the reaction d + d → {sup 2}He + {sup 2}n is described, and the first preliminary results of measurements at a deuteron energy of 15 MeV are presented. The experiment was aimed at determining the energies of quasibound singlet states of two-nucleon systems (nn and pp), these energies being important features of nucleon–nucleon (NN) interaction. The measurements in question were performed at a deuteron beamfrom the U-120 cyclotron of the Skobeltsyn Institute ofNuclear Physics (Moscow State University). Two protons and one of the neutrons fromthe breakup of the dineutron system were detected in themore » experiment. A simulation of the reaction in question and preliminary experimental results reveal the possibility of determining the energy of quasibound singlet states on the basis of the form of the energy spectra of particles originating from their breakup.« less

Halo-induced large enhancement of soft dipole excitation of 11Li observed via proton inelastic scattering

NASA Astrophysics Data System (ADS)

Tanaka, J.; Kanungo, R.; Alcorta, M.; Aoi, N.; Bidaman, H.; Burbadge, C.; Christian, G.; Cruz, S.; Davids, B.; Diaz Varela, A.; Even, J.; Hackman, G.; Harakeh, M. N.; Henderson, J.; Ishimoto, S.; Kaur, S.; Keefe, M.; Krücken, R.; Leach, K. G.; Lighthall, J.; Padilla Rodal, E.; Randhawa, J. S.; Ruotsalainen, P.; Sanetullaev, A.; Smith, J. K.; Workman, O.; Tanihata, I.

2017-11-01

Proton inelastic scattering off a neutron halo nucleus, 11Li, has been studied in inverse kinematics at the IRIS facility at TRIUMF. The aim was to establish a soft dipole resonance and to obtain its dipole strength. Using a high quality 66 MeV 11Li beam, a strongly populated excited state in 11Li was observed at Ex = 0.80 ± 0.02 MeV with a width of Γ = 1.15 ± 0.06 MeV. A DWBA (distorted-wave Born approximation) analysis of the measured differential cross section with isoscalar macroscopic form factors leads us to conclude that this observed state is excited in an electric dipole (E1) transition. Under the assumption of isoscalar E1 transitions, the strength is evaluated to be extremely large amounting to 30 ∼ 296 Weisskopf units, exhausting 2.2% ∼ 21% of the isoscalar E1 energy-weighted sum rule (EWSR) value. The large observed strength originates from the halo and is consistent with the simple di-neutron model of 11Li halo.

Ground-state properties of H 5 from the He 6 ( d , He 3 ) H 5 reaction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wuosmaa, A. H.; Bedoor, S.; Brown, K. W.

2017-01-01

We have studied the ground state of the unbound, very neutron-rich isotope of hydrogen 5H, using the 6He(d,3He)5H reaction in inverse kinematics at a bombarding energy of E(6He)=55A MeV. The present results suggest a ground-state resonance energy ER=2.4±0.3 MeV above the 3H+2n threshold, with an intrinsic width of Γ=5.3±0.4 MeV in the 5H system. Both the resonance energy and width are higher than those reported in some, but not all previous studies of 5H. The previously unreported 6He(d,t)5Heg.s. reaction is observed in the same measurement, providing a check on the understanding of the response of the apparatus. The data aremore » compared to expectations from direct two-neutron and dineutron decay. The possibility of excited states of 5H populated in this reaction is discussed using different calculations of the 6He→5H+p spectroscopic overlaps from shell-model and ab initio nuclear-structure calculations.« less

Changes in the structure of nuclei between the magic neutron numbers 50 and 82 as indicated by a rotating-cluster analysis of the energy values of the first 2+ excited states of isotopes of cadmium, tin, and tellurium

PubMed Central

Pauling, Linus

1981-01-01

Values of R, the radius of rotation of the rotating cluster, are calculated from the observed values of the energy of the lowest 2+ states of the even isotopes of 48Cd, 50Sn, and 52Te with the assumption that the cluster is α, p2, and α, respectively. R shows a maximum at ≈N = 58, a minimum at ≈N = 62, and a second maximum at ≈N = 70. The increase to the first maximum is interpreted as resulting from the overcrowding of spherons (alphas and tritons) in the mantle (outer layer) of the nuclei, causing the cluster to change from rotating in the mantle to skimming over its surface; the decrease to the minimum results from the addition of three dineutrons to the core, expanding the mantle and permitting the rotating cluster to begin to drop back into it; and the increase to the second maximum results from the overcrowding of the larger mantle surrounding the core containing the semi-magic number 14 of neutrons rather than the magic number 8 for N = 50. The decrease after the second maximum results from the further increase in the number of core neutrons to 20, corresponding to the magic number 82. Some additional evidence for the change to an intermediate structure between N = 50 and N = 82 is also discussed. PMID:16593084

Three-body model for the two-neutron emission of Be 16 [Three-body model for the two-neutron decay of 16Be

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lovell, A. E.; Nunes, F. M.; Thompson, I. J.

While diproton emission was first theorized in 1960 and first measured in 2002, it was first observed only in 2012. The measurement of 14Be in coincidence with two neutrons suggests that 16Be does decay through the simultaneous emission of two strongly correlated neutrons. In this study, we construct a full three-body model of 16Be (as 14Be + n + n) in order to investigate its configuration in the continuum and, in particular, the structure of its ground state. Here, in order to describe the three-body system, effective n – 14Be potentials were constructed, constrained by the experimental information on 15Be.more » The hyperspherical R-matrix method was used to solve the three-body scattering problem, and the resonance energy of 16Be was extracted from a phase-shift analysis. As a result, in order to reproduce the experimental resonance energy of 16Be within this three-body model, a three-body interaction was needed. For extracting the width of the ground state of 16Be, we use the full width at half maximum of the derivative of the three-body eigenphase shifts and the width of the three-body elastic scattering cross section. In conclusion, our results confirm a dineutron structure for 16Be, dependent on the internal structure of the subsystem 15Be.« less

Two nucleon systems at m π ~ 450 MeV from lattice QCD

DOE PAGES

Orginos, Kostas; Parreño, Assumpta; Savage, Martin J.; ...

2015-12-23

Nucleon-nucleon systems are studied with lattice quantum chromodynamics at a pion mass ofmore » $$m_\\pi\\sim 450~{\\rm MeV}$$ in three spatial volumes using $$n_f=2+1$$ flavors of light quarks. At the quark masses employed in this work, the deuteron binding energy is calculated to be $$B_d = 14.4^{+3.2}_{-2.6} ~{\\rm MeV}$$, while the dineutron is bound by $$B_{nn} = 12.5^{+3.0}_{-5.0}~{\\rm MeV}$$. Over the range of energies that are studied, the S-wave scattering phase shifts calculated in the 1S0 and 3S1-3D1 channels are found to be similar to those in nature, and indicate repulsive short-range components of the interactions, consistent with phenomenological nucleon-nucleon interactions. In both channels, the phase shifts are determined at three energies that lie within the radius of convergence of the effective range expansion, allowing for constraints to be placed on the inverse scattering lengths and effective ranges. Thus, the extracted phase shifts allow for matching to nuclear effective field theories, from which low energy counterterms are extracted and issues of convergence are investigated. As part of the analysis, a detailed investigation of the single hadron sector is performed, enabling a precise determination of the violation of the Gell-Mann–Okubo mass relation.« less

Three-body model for the two-neutron emission of Be 16 [Three-body model for the two-neutron decay of 16Be

DOE PAGES

Lovell, A. E.; Nunes, F. M.; Thompson, I. J.

2017-03-10

While diproton emission was first theorized in 1960 and first measured in 2002, it was first observed only in 2012. The measurement of 14Be in coincidence with two neutrons suggests that 16Be does decay through the simultaneous emission of two strongly correlated neutrons. In this study, we construct a full three-body model of 16Be (as 14Be + n + n) in order to investigate its configuration in the continuum and, in particular, the structure of its ground state. Here, in order to describe the three-body system, effective n – 14Be potentials were constructed, constrained by the experimental information on 15Be.more » The hyperspherical R-matrix method was used to solve the three-body scattering problem, and the resonance energy of 16Be was extracted from a phase-shift analysis. As a result, in order to reproduce the experimental resonance energy of 16Be within this three-body model, a three-body interaction was needed. For extracting the width of the ground state of 16Be, we use the full width at half maximum of the derivative of the three-body eigenphase shifts and the width of the three-body elastic scattering cross section. In conclusion, our results confirm a dineutron structure for 16Be, dependent on the internal structure of the subsystem 15Be.« less

Existence of diproton-like particles in 3+1 lattice QCD with two flavors and strong coupling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Faria da Veiga, Paulo A.; O'Carroll, Michael; Neto, A. Francisco

2011-02-01

Starting from quarks, gluons, and their dynamics, we consider the existence of two-baryon bound states of total isospin I=1 in an imaginary-time formulation of a strongly coupled 3+1-dimensional SU(3){sub c} lattice QCD with two flavors and 4x4 spin matrices, defined using the Wilson action. For a small hopping parameter {kappa}>0 and a much smaller gauge coupling 0<{beta}<<{kappa}<<1 (heavy quarks and large glueball mass), using a ladder approximation to a lattice Bethe-Salpeter equation, diproton-like bound states are found in the I=1 isospin sector, with asymptotic masses -6ln{kappa} and binding energies of order {kappa}{sup 2}. By isospin symmetry, for each diproton theremore » is also a dineutron bound state with the same mass and binding energy. The dominant two-baryon interaction is an energy-independent spatial range-one potential with an O({kappa}{sup 2}) strength. There is also an attraction arising from gauge field correlations associated with six overlapping bonds, but it is subdominant. The overall range-one potential results from a quark-antiquark exchange with no meson exchange interpretation (wrong spin indices). The repulsive or attractive nature of the interaction does depend on the isospin and spin of the two-baryon states. A novel representation in term of permanents is obtained for the spin, isospin interaction between the baryons, which is valid for any isospin sector.« less

Neutron-neutron quasifree scattering in nd breakup at 10 MeV

NASA Astrophysics Data System (ADS)

Malone, R. C.; Crowe, B.; Crowell, A. S.; Cumberbatch, L. C.; Esterline, J. H.; Fallin, B. A.; Friesen, F. Q. L.; Han, Z.; Howell, C. R.; Markoff, D.; Ticehurst, D.; Tornow, W.; Witała, H.

2016-03-01

The neutron-deuteron (nd) breakup reaction provides a rich environment for testing theoretical models of the neutron-neutron (nn) interaction. Current theoretical predictions based on rigorous ab-initio calculations agree well with most experimental data for this system, but there remain a few notable discrepancies. The cross section for nn quasifree (QFS) scattering is one such anomaly. Two recent experiments reported cross sections for this particular nd breakup configuration that exceed theoretical calculations by almost 20% at incident neutron energies of 26 and 25 MeV [1, 2]. The theoretical values can be brought into agreement with these results by increasing the strength of the 1S0 nn potential matrix element by roughly 10%. However, this modification of the nn effective range parameter and/or the 1S0 scattering length causes substantial charge-symmetry breaking in the nucleon-nucleon force and suggests the possibility of a weakly bound di-neutron state [3]. We are conducting new measurements of the cross section for nn QFS in nd breakup. The measurements are performed at incident neutron beam energies below 20 MeV. The neutron beam is produced via the 2H(d, n)3He reaction. The target is a deuterated plastic cylinder. Our measurements utilize time-of-flight techniques with a pulsed neutron beam and detection of the two emitted neutrons in coincidence. A description of our initial measurements at 10 MeV for a single scattering angle will be presented along with preliminary results. Also, plans for measurements at other energies with broad angular coverage will be discussed.

Two-nucleon emitters within a pseudostate method: The case of 6Be and 16Be

NASA Astrophysics Data System (ADS)

Casal, J.

2018-03-01

Background: Since the first experimental observation, two-nucleon radioactivity has gained renewed attention since the early 2000s. The 6Be system is the lightest two-proton ground-state emitter, while 16Be was recently proposed to be the first two-neutron ground-state emitter ever observed. A proper understanding of their properties and decay modes requires a reasonable description of the three-body continuum. Purpose: Study the ground-state properties of 6Be and 16Be within a general three-body model and investigate their nucleon-nucleon correlations in the continuum. Method: The pseudostate (PS) method in hyperspherical coordinates, using the analytical transformed harmonic oscillator (THO) basis for three-body systems, is used to construct the 6Be and 16Be ground-state wave functions. These resonances are approximated as a stable PS around the known two-nucleon separation energy. Effective core-N potentials, constrained by the available experimental information on the binary subsystems 5Li and 15Be, are employed in the calculations. Results: The ground state of 16Be is found to present a strong dineutron configuration, with the valence neutrons occupying mostly an l =2 state relative to the core. The results are consistent with previous R -matrix calculations for the actual continuum. The case of 6Be shows a clear symmetry with respect to its mirror partner, the two-neutron halo 6He: The diproton configuration is dominant, and the valence protons occupy an l =1 orbit. Conclusions: The PS method is found to be a suitable tool in describing the properties of unbound core+N +N ground states. For both 16Be and 6Be, the results are consistent with previous theoretical studies and confirm the dominant dinucleon configuration. This favors the picture of a correlated two-nucleon emission.

Magnetic structure of light nuclei from lattice QCD

DOE PAGES

Chang, Emmanuel; Detmold, William; Orginos, Kostas; ...

2015-12-09

Lattice QCD with background magnetic fields is used to calculate the magnetic moments and magnetic polarizabilities of the nucleons and of light nuclei withmore » $$A\\le4$$, along with the cross-section for the $M1$ transition $$np\\rightarrow d\\gamma$$, at the flavor SU(3)-symmetric point where the pion mass is $$m_\\pi\\sim 806$$ MeV. These magnetic properties are extracted from nucleon and nuclear energies in six uniform magnetic fields of varying strengths. The magnetic moments are presented in a recent Letter. For the charged states, the extraction of the polarizability requires careful treatment of Landau levels, which enter non-trivially in the method that is employed. The nucleon polarizabilities are found to be of similar magnitude to their physical values, with $$\\beta_p=5.22(+0.66/-0.45)(0.23) \\times 10^{-4}$$ fm$^3$ and $$\\beta_n=1.253(+0.056/-0.067)(0.055) \\times 10^{-4}$$ fm$^3$, exhibiting a significant isovector component. The dineutron is bound at these heavy quark masses and its magnetic polarizability, $$\\beta_{nn}=1.872(+0.121/-0.113)(0.082) \\times 10^{-4}$$ fm$^3$ differs significantly from twice that of the neutron. A linear combination of deuteron scalar and tensor polarizabilities is determined by the energies of the $$j_z=\\pm 1$$ deuteron states, and is found to be $$\\beta_{d,\\pm 1}=4.4(+1.6/-1.5)(0.2) \\times 10^{-4}$$ fm$^3$. The magnetic polarizabilities of the three-nucleon and four-nucleon systems are found to be positive and similar in size to those of the proton, $$\\beta_{^{3}\\rm He}=5.4(+2.2/-2.1)(0.2) \\times 10^{-4}$$ fm$^3$, $$\\beta_{^{3}\\rm H}=2.6(1.7)(0.1) \\times 10^{-4}$$ fm$^3$, $$\\beta_{^{4}\\rm He}=3.4(+2.0/-1.9)(0.2) \\times 10^{-4}$$ fm$^3$. Mixing between the $$j_z=0$$ deuteron state and the spin-singlet $np$ state induced by the background magnetic field is used to extract the short-distance two-nucleon counterterm, $${\\bar L}_1$$, of the pionless effective theory for $NN$ systems (equivalent to the