Sample records for dineutrons

  1. Dineutron formation and breaking in $^8$He

    Kobayashi, Fumiharu


    We discuss the correlation of the spin-singlet two-neutron pair, the dineutron correlation, in the ground and excited $0^+$ states of $^8$He by using a method to describe the dineutron correlation in neutron-rich nuclei, the dineutron condensate wave function. The shell-model configuration and the dineutron configuration compete with each other in the ground state of $^8$He. We compare the ground state structure of $^8$He with that of $^6$He and suggest that the dineutron correlation is weaker in the ground state of $^8$He than $^6$He. We also suggest the possibility of the dineutron condensation in an excited $0^+$ state of $^8$He. In addition, we investigate the formation mechanism of the dineutron condensation in $^8$He by using a newly developed framework, $\\alpha$ and dineutron condensate wave function, and conclude that the attraction from the core is essential for the formation of the dineutron condensation.

  2. Experimental Evidence of a Bonded Dineutron Existence

    Kadenko, I M


    Experimental observation of 159Tb(n,2n) reaction product was performed with application of the activation technique. Tb specimen of natural composition was irradiated with (d,d) neutrons of 5.39 and 7 MeV energy at the AMANDE neutron generating facility with 15 month break. Several instrumental spectra of Tb specimen were measured with HPGe spectrometer in 1.5 years after last irradiation. An unexpected 944.2 keV {\\gamma}-ray peak was observed. Other {\\gamma}-ray lines of 158Gd as the daughter nucleus due to 158Tb EC and \\b{eta}+- decay were identified as well. A bonded dineutron emission with the binding energy (Bdn) within limitations 1.3 MeV < Bdn < 2.8 MeV is evidenced by the energy of incident neutrons and by 158Tb presence in output channel.

  3. First Observation of Ground State Dineutron Decay: Be16

    Spyrou, A.; Kohley, Z.; Baumann, T.; Bazin, D.; Brown, B. A.; Christian, G.; Deyoung, P. A.; Finck, J. E.; Frank, N.; Lunderberg, E.; Mosby, S.; Peters, W. A.; Schiller, A.; Smith, J. K.; Snyder, J.; Strongman, M. J.; Thoennessen, M.; Volya, A.


    We report on the first observation of dineutron emission in the decay of Be16. A single-proton knockout reaction from a 53MeV/u B17 beam was used to populate the ground state of Be16. Be16 is bound with respect to the emission of one neutron and unbound to two-neutron emission. The dineutron character of the decay is evidenced by a small emission angle between the two neutrons. The two-neutron separation energy of Be16 was measured to be 1.35(10) MeV, in good agreement with shell model calculations, using standard interactions for this mass region.

  4. Analysis of the effect of core structure upon dineutron correlation using antisymmetrized molecular dynamics

    Kobayashi, Fumiharu


    We extend the method of antisymmetrized molecular dynamics to investigate dineutron correlation. We apply this method to $^{10}$Be as an example and investigate the motion of two neutrons around a largely deformed $^8$Be core by analyzing the two-neutron overlap function around the core. We show that the core structure plays an important role in dineutron formation and expansion from the core and that the present framework is effective for the studies of dineutron correlation.

  5. Are there good probes for the di-neutron correlation in light neutron-rich nuclei?

    Hagino, K


    The di-neutron correlation is a spatial correlation with which two valence neutrons are located at a similar position inside a nucleus. We discuss possible experimental probes for the di-neutron correlation. This includes the Coulomb breakup and the pair transfer reactions of neutron-rich nuclei, and the direct two-neutron decays of nuclei beyond the neutron drip-line.

  6. Constraints on a possible dineutron state from pionless EFT

    H.-W. Hammer


    Full Text Available We investigate the sensitivity of the three-nucleon system to changes in the neutron–neutron scattering length to next-to-leading order in the pionless effective field theory, focusing on the triton–3He binding energy difference and neutron–deuteron elastic scattering. Due to the appearance of a proton–deuteron three-body counterterm at this order, the triton–3He binding energy difference remains consistent with the experimental value even for large positive neutron–neutron scattering lengths while the elastic neutron–deuteron scattering phase shifts are insensitive. We conclude that a bound dineutron cannot be excluded to next-to-leading order in pionless EFT.

  7. How to determine a dineutron correlation in Borromean nuclei via a quasi-free knockout ($p,pn$) reaction?

    Kikuchi, Yuma; Kubota, Yuki; Sasano, Masaki; Uesaka, Tomohiro


    The quasi-free neutron knockout reaction on $^6$He is investigated to discuss the dineutron correlation in the ground state. In the present work, the momentum distributions of the two emitted neutrons are calculated with the $\\alpha$~+~$n$~+~$n$ three-body model and the simple reaction model, and the effects of the knockout process via the $^5$He resonance and the target dependence in the momentum distributions are discussed. From the calculation, it is found that a clear signature of the dineutron correlation can be obtained by choosing the kinematical condition to exclude the process via the $^5$He resonance, while the inclusion of the $^5$He resonance drastically changes the momentum distributions. It is also shown to be important to use the proton target in the quantitative discussion on the dineutron correlation by the knockout reaction. In addition to theoretical arguments, a possible experimental setup to determine the dineutron correlation via the quasi-free knockout reaction is considered.

  8. Dinucleon correlation of $^9$Li, $^{10}$Be, and $^{9,10}$C

    Kobayashi, Fumiharu


    We study the dinucleon (dineutron and diproton) correlation of the ground states of $^9$Li, $^{10}$Be, and $^{9,10}$C. We assume an $\\alpha+t$ core for $^9$Li, an $\\alpha+\\alpha$ core for $^{10}$Be and $^{10}$C, and an $\\alpha+^3$He core for $^9$C, and investigate the effect of core structure changes on the degree of dineutron formation and spatial expansion from the core. For $^9$Li, $t$ cluster breaking in the core significantly enhances the dineutron component inside the nuclei. Moreover, its component markedly depends on the strength of the spin-orbit interaction since a dineutron is fragile and dissociates readily due to the spin-orbit interaction. Compared with $^9$Li, the dineutron of $^{10}$Be dissociates largely due to the stronger spin-orbit attraction from the $\\alpha+\\alpha$ core than the $\\alpha+t$ core. We also investigate diproton features in $^{9,10}$C, the mirror nuclei of $^9$Li and $^{10}$Be, respectively, and compare them with the dineutron features of $^9$Li and $^{10}$Be. No qualitative ...

  9. Exploring the neutron dripline two neutrons at a time: The first observations of the 26O and 16Be ground state resonances

    Kohley, Z; Lunderberg, E; DeYoung, P A; Attanayake, H; Bauman, T; Bazin, D; Brown, B A; Christian, G; Divaratne, D; Grimes, S M; Haagsma, A; Finck, J E; Frank, N; Luther, B; Mosby, S; Nagi, T; Peaslee, G F; Peters, W A; Schiller, A; Smith, J K; Snyder, J; Strongman, M J; Thoennessen, M; Volya, A


    The two-neutron unbound ground state resonances of $^{26}$O and $^{16}$Be were populated using one-proton knockout reactions from $^{27}$F and $^{17}$B beams. A coincidence measurement of 3-body system (fragment + n + n) allowed for the decay energy of the unbound nuclei to be reconstructed. A low energy resonance, $<$ 200 keV, was observed for the first time in the $^{24}$O + n + n system and assigned to the ground state of $^{26}$O. The $^{16}$Be ground state resonance was observed at 1.35 MeV. The 3-body correlations of the $^{14}$Be + n + n system were compared to simulations of a phase-space, sequential, and dineutron decay. The strong correlations in the n-n system from the experimental data could only be reproduced by the dineutron decay simulation providing the first evidence for a dineutron-like decay.

  10. Low-energy theorems for nucleon-nucleon scattering at Mπ=450 MeV

    Baru, V.; Epelbaum, E.; Filin, A. A.


    We apply the low-energy theorems to analyze the recent lattice QCD results for the two-nucleon system at a pion mass of Mπ≃450 MeV obtained by the NPLQCD Collaboration. We find that the binding energies of the deuteron and dineutron are inconsistent with the low-energy behavior of the corresponding phase shifts within the quoted uncertainties and vice versa. Using the binding energies of the deuteron and dineutron as input, we employ the low-energy theorems to predict the phase shifts and extract the scattering length and the effective range in the S31 and S10 channels. Our results for these quantities are consistent with those obtained by the NPLQCD Collaboration from effective field theory analyses but are in conflict with their determination based on the effective-range approximation.

  11. Study of n-n correlations in d + 2H --> p + p + n + n reaction

    Konobeevsky, E; Mordovskoy, M; Zuyev, S; Lebedev, V; Spassky, A


    A kinematically complete measurement of the four-body breakup reaction d+2H-->2ps+2ns --> p +p +n +n has been performed at 15 MeV deuteron beam of the SINP MSU. The two protons and neutron were detected at angles close to those of emission of 2ps and 2ns systems. The energy of singlet dineutron state was determined by comparing experimental TOF spectrum of breakup neutrons with simulated spectra depending on this energy. A low value Enn = 0.076 +/- 0.006 keV obtained by fitting procedure apparently indicates an effective enhancement of nn-interaction in the intermediate state of studied reaction.

  12. Light Nuclei and Hypernuclei from Quantum Chromodynamics in the Limit of SU(3) Flavor Symmetry

    Beane, S R; Cohen, S D; Detmold, W; Lin, H W; Luu, T C; Orginos, K; Parreno, A; Savage, M J; Walker-Loud, A


    The binding energies of a range of nuclei and hypernuclei with atomic number A <= 4 and strangeness |s| <= 2, including the deuteron, di-neutron, H-dibaryon, 3He, Lambda 3He, Lambda 4He, and Lambda Lambda 4He, are calculated in the limit of flavor-SU(3) symmetry at the physical strange quark mass with quantum chromodynamics (without electromagnetic interactions). The nuclear states are extracted from Lattice QCD calculations performed with n_f=3 dynamical light quarks using an isotropic clover discretization of the quark-action in three lattice volumes of spatial extent L ~ 3.4 fm, 4.5 fm and 6.7 fm, and with a single lattice spacing b ~ 0.145 fm.

  13. Two neutron decay from the $2_1^+$ state of $^6$He

    Kikuchi, Yuma; Minomo, Kosho; Ogata, Kazuyuki


    Decay mode of the $2_1^+$ resonant state of $^6$He populated by the $^6$He breakup reaction by $^{12}$C at 240 MeV/nucleon is investigated. The continuum-discretized coupled-channels method is adopted to describe the formation of the $2_1^+$ state, whereas its decay is described by the complex-scaled solutions of the Lippmann-Schwinger equation. From analysis of invariant mass spectra with respect to the $\\alpha$-$n$ and $n$-$n$ subsystems, coexistence of two decay modes is found. One is the simultaneous decay of two neutrons correlating with each other and the other is the emission of two neutrons to the opposite directions. The latter is found to be free from the final state interaction and suggests existence of a di-neutron in the $2_1^+$ state of $^6$He.

  14. Coulomb breakup effects on the elastic cross section of $^6$He+$^{209}$Bi scattering near Coulomb barrier energies

    Matsumoto, T; Iseri, Y; Kamimura, M; Ogata, K; Yahiro, M


    We accurately analyze the $^6$He+$^{209}$Bi scattering at 19 and 22.5 MeV near the Coulomb barrier energy, using the continuum-discretized coupled-channels method (CDCC) based on the $n$+$n$+$^4$He+$^{209}$Bi four-body model. The three-body breakup continuum of $^6$He is discretized by diagonalizing the internal Hamiltonian of $^6$He in a space spanned by the Gaussian basis functions. The calculated elastic and total reaction cross sections are in good agreement with the experimental data, while the CDCC calculation based on the di-neutron model of $^6$He, i.e., the $^2n$+$^{4}$He+$^{209}$Bi three-body model, does not reproduce the data.

  15. Structure of the spatial periphery of the isotopes {sup 9,11}Li

    Galanina, L. I., E-mail:; Zelenskaya, N. S. [Moscow State University, Skobeltsyn Institute of Nuclear Physics (Russian Federation)


    The cross sections for the (t, p) reactions on the lithium isotopes {sup 9,11}Li were calculated within a theoretical approach based on employing integral equations of the four-body problem in the Alt—Grassberger-Sandhas formalism and the multiparticle shell model. This made it possible to determine the wave functions for the relative motion of various clusters and the nuclear core and to calculate, on their basis, the root-mean-square radii of nuclei of the isotopes {sup 9,11}Li and the spatial structure of their neutron periphery. It is shown that the {sup 9}Li nucleus has virtually no neutron halo. The {sup 11}Li nucleus is a Borromean halo nucleus. The two-neutron periphery of this nucleus manifests itself in both spatial configurations, a dineutron and a cigar one, the respective root-mean-square radii being large (about 6.5 to 6.9 fm)

  16. The lightest neutral hypernuclei with strangeness -1 and -2

    Richard, Jean-Marc; Zhao, Qiang


    Our current knowledge of the baryon--baryon interaction suggests that the dineutron $(n,n)$ and its strange analogue $(\\Lambda,n)$ are unstable. In contrast, the situation is more favourable for the strange three-body system $(n,n,\\Lambda)$, and even better for the four-body system $T=(n,n,\\Lambda,\\Lambda)$ with strangeness $-2$, which is likely to be stable under spontaneous dissociation. This new nucleus could be produced and identified in central deuteron--deuteron collisions via reaction $d+d\\to T+K^++K^+$, and the tetrabaryon $T$ could play an important role in catalysing the formation of a strange core in neutron stars.

  17. Estimation of the breakup cross sections in $^6$He+$^{12}$C reaction within high-energy approximation and microscopic optical potential

    Zemlyanaya, E V; Lukyanov, K V


    The breakup cross sections in the reaction $^6$He+$^{12}$C are calculated at about 40 MeV/nucleon using the high-energy approximation (HEA) and with the help of microscopic optical potentials (OP) of interaction with the target nucleus $^{12}$C of the projectile nucleus fragments $^4$He and 2n. Considering the di-neutron $h$=2n as a single particle the relative motion $h\\alpha$ wave function is estimated so that to explain both the separation energy of $h$ in $^6$He and the rms radius of the latter. The stripping and absorbtion total cross sections are calculated and their sum is compared with the total reaction cross section obtained within a double-folding microscopic OP for the $^6$He+$^{12}$C scattering. It is concluded that the breakup cross sections contribute in about 50% of the total reaction cross section.

  18. First observation of $^{13}$Li ground state

    Kohley, Z; DeYoung, P A; Volya, A; Baumann, T; Bazin, D; Christian, G; Cooper, N L; Frank, N; Gade, A; Hall, C; Hinnefeld, J; Luther, B; Mosby, S; Peters, W A; Smith, J K; Snyder, J; Spyrou, A; Thoennessen, M


    The ground state of neutron-rich unbound $^{13}$Li was observed for the first time in a one-proton removal reaction from $^{14}$Be at a beam energy of 53.6 MeV/u. The $^{13}$Li ground state was reconstructed from $^{11}$Li and two neutrons giving a resonance energy of 120$^{+60}_{-80}$ keV. All events involving single and double neutron interactions in the Modular Neutron Array (MoNA) were analyzed, simulated, and fitted self-consistently. The three-body ($^{11}$Li+$n+n$) correlations within Jacobi coordinates showed strong dineutron characteristics. The decay energy spectrum of the intermediate $^{12}$Li system ($^{11}$Li+$n$) was described with an s-wave scattering length of greater than -4 fm, which is a smaller absolute value than reported in a previous measurement.

  19. Recent results from MoNA-LISA

    Spyrou, Artemisia


    Studies of the nuclear properties of nuclei close and even beyond the limits of stability have revealed exotic modes of decay and new structural characteristics. The MoNA-LISA array is used at the National Superconducting Cyclotron Laboratory at Michigan State University to study nuclei along the neutron dripline. In a typical experiment, a radioactive beam is employed to produce the neutron-unbound state of interest. This state/resonance immediately decay into a neutron, which is detected by MoNA-LISA and a remaining charged nucleus detected by the sweeper magnet detector suite. In this talk, new exciting findings from recent MoNA-LISA experiments will be presented. These include the first observation of a dineutron decay from ^16Be, the exploration of the ``south shore'' of the Island of Inversion and the first evidence of the decay of the troubling nucleus ^26O.

  20. Nuclear Sturcture Along the Neutron Dripline: MoNa-LISA and the dinueutron system

    Spyou, Artemis [Michigan State Univeristy


    Nuclei with extreme neutron-to-proton ratios were found to present different structures from what was known for the stable ones. With the current facilities we can now study nuclei that lie even beyond the neutron drip line. At the National Superconducting Cyclotron Laboratory at Michigan State University we use the MoNA/Sweeper setup to perform such studies of neutron unbound nuclei. In a typical experiment, a radioactive beam is employed to produce the nucleus of interest. This unbound nucleus immediately decays into a neutron and a remaining charged fragment, both of which are detected and used to reconstruct the original nucleus and study its properties. In this Colloquium, new exciting findings from recent experiments will be presented. These include the first observation of a dineutron decay from 16Be, the exploration of the “south shore” of the Island of Inversion and the first evidence of the decay of the troubling nucleus 26O.

  1. Two-neutron decay of excited states of 11Li

    Smith, Jenna; MoNA Collaboration


    One prominent example of a Borromean nucleus is the two-neutron halo nucleus, 11Li. All excited states of this nucleus are unbound to two-neutron decay. Many theories propose that the two valence neutrons exhibit dineutron behavior in the ground state, but it is unclear what effect such a structure would have on the decay of the excited states. We have recently completed an experiment designed to study the decay of one of these excited states. Unbound 11Li was populated via a two-proton knockout from 13B. The two emitted neutrons were detected with the Modular Neutron Array (MoNA) and the Large-area multi-Institutional Scintillator Array (LISA) in coincidence with the daughter fragment, 9Li. Preliminary results will be discussed.

  2. Relativistic description of BCS-BEC crossover in nuclear matter

    Sun, Bao Yuan; Toki, Hiroshi; Meng, Jie


    We study theoretically the di-neutron spatial correlations and the crossover from superfluidity of neutron Cooper pairs in the S10 pairing channel to Bose-Einstein condensation (BEC) of di-neutron pairs for both symmetric and neutron matter in the microscopic relativistic pairing theory. We take the bare nucleon-nucleon interaction Bonn-B in the particle-particle channel and the effective interaction PK1 of the relativistic mean-field approach in the particle-hole channel. It is found that the spatial structure of neutron Cooper pair wave function evolves continuously from BCS-type to BEC-type as density decreases. We see a strong concentration of the probability density revealed for the neutron pairs in the fairly small relative distance around 1.5 fm and the neutron Fermi momentum kFn ∈ [ 0.6 , 1.0 ] fm-1. However, from the effective chemical potential and the quasiparticle excitation spectrum, there is no evidence for the appearance of a true BEC state of neutron pairs at any density. The most BEC-like state may appear at kFn ∼ 0.2 fm-1 by examining the density correlation function. From the coherence length and the probability distribution of neutron Cooper pairs as well as the ratio between the neutron pairing gap and the kinetic energy at the Fermi surface, some features of the BCS-BEC crossover are seen in the density regions, 0.05 fm-1

  3. Three-body correlations in the ground-state decay of 26O

    Kohley, Z; Christian, G; DeYoung, P A; Finck, J E; Frank, N; Luther, B; Lunderberg, E; Jones, M; Mosby, S; Smith, J K; Spyrou, A; Thoennessen, M


    Background: Theoretical calculations have shown that the energy and angular correlations in the three-body decay of the two-neutron unbound O26 can provide information on the ground-state wave function, which has been predicted to have a dineutron configuration and 2n halo structure. Purpose: To use the experimentally measured three-body correlations to gain insight into the properties of O26, including the decay mechanism and ground-state resonance energy. Method: O26 was produced in a one-proton knockout reaction from F27 and the O24+n+n decay products were measured using the MoNA-Sweeper setup. The three-body correlations from the O26 ground-state resonance decay were extracted. The experimental results were compared to Monte Carlo simulations in which the resonance energy and decay mechanism were varied. Results: The measured three-body correlations were well reproduced by the Monte Carlo simulations but were not sensitive to the decay mechanism due to the experimental resolutions. However, the three-body...

  4. Monte Carlo calculations and experimental results of Bonner spheres systems with a new cylindrical Helium-3 proportional counter

    Müller, H; Bouassoule, T; Fernández, F; Pochat, J L; Tomas, M; Van Ryckeghem, L


    The experimental results on neutron energy spectra, integral fluences and equivalent dose measurements performed by means of a Bonner sphere system placed inside the containment building of the Vandellos II Nuclear Power Plant (Tarragona, Spain) are presented. The equivalent dose results obtained with this system are compared to those measured with different neutron area detectors (Berthold, Dineutron, Harwell). A realistic geometry model of the Bonner sphere system with a new cylindrical counter type 'F' (0,5NH1/1KI--Eurisys Mesures) and with a set of eight polyethylene moderating spheres is described in detail. The response function in fluence of this new device, to mono-energetic neutrons from thermal energy to 20 MeV, is calculated by the MCNP-4B code for each moderator sphere. The system has been calibrated at IPSN Cadarache facility for ISO Am-Be calibrated source and thermal neutron field, then the response functions were confirmed by measurements at PTB (Germany) for ISO recommended energies of mono-e...

  5. Monte Carlo calculations and experimental results of Bonner spheres systems with a new cylindrical Helium-3 proportional counter

    Muller, H.; Fernández, F.; Van Ryckeghem, L.; Alexandre, P.; Bouassoule, T.; Pochat, J.-L.; Tomas, M.


    The experimental results on neutron energy spectra, integral fluences and equivalent dose measurements performed by means of a Bonner sphere system placed inside the containment building of the Vandellòs II Nuclear Power Plant (Tarragona, Spain) are presented. The equivalent dose results obtained with this system are compared to those measured with different neutron area detectors (Berthold, Dineutron, Harwell). A realistic geometry model of the Bonner sphere system with a new cylindrical counter type "F" (0,5NH1/1KI—Eurisys Mesures) and with a set of eight polyethylene moderating spheres is described in detail. The response function in fluence of this new device, to mono-energetic neutrons from thermal energy to 20 MeV, is calculated by the MCNP-4B code for each moderator sphere. The system has been calibrated at IPSN Cadarache facility for ISO Am-Be calibrated source and thermal neutron field, then the response functions were confirmed by measurements at PTB (Germany) for ISO recommended energies of mono-energetic neutrons and with the CANEL IPSN facility which simulates realistic fields.

  6. The Magnetic Structure of Light Nuclei from Lattice QCD

    Chang, Emmanuel; Orginos, Kostas; Parreno, Assumpta; Savage, Martin J; Tiburzi, Brian C; Beane, Silas R


    Lattice QCD with background magnetic fields is used to calculate the magnetic moments and magnetic polarizabilities of the nucleons and of light nuclei with $A\\le4$, 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...

  7. Baryon Number Violating Scalar Diquarks at the LHC

    Baldes, Iason; Volkas, Raymond R


    Baryon number violating (BNV) processes are heavily constrained by experiments searching for nucleon decay and neutron-antineutron oscillations. If the baryon number violation occurs via the third generation quarks, however, we may be able to avoid the nucleon stability constraints, thus making such BNV interactions accessible at the LHC. In this paper we study a specific class of BNV extensions of the standard model (SM) involving diquark and leptoquark scalars. After an introduction to these models we study one promising extension in detail, being interested in particles with mass of O(TeV). We calculate limits on the masses and couplings from neutron-antineutron oscillations and dineutron decay for couplings to first and third generation quarks. We explore the possible consequences of such a model on the matter-antimatter asymmetry. We shall see that for models which break the global baryon minus lepton number symmetry, (B-L), the most stringent constraints come from the need to preserve a matter-antimatte...

  8. Indication of BCS-BEC crossover behavior in halo nuclei

    Hagino, K; Sagawa, H; Schuck, P


    We investigate the spatial structure of two-neutron wave function in a Borromean nucleus $^{11}$Li using a three-body model in which two valence neutrons interact with each other by a density-dependent contact force. The behavior of the neutron Cooper pair at different densities is simulated by calculating the two-neutron wave function at several distances between the core nucleus and the center of mass of the two neutrons. We find that the neutron pair wave function in $^{11}$Li has an oscillation at normal density, while it becomes a well localized single peak in the dilute density region around the nuclear surface. These features are in close analogue to the BCS-BEC crossover of the Cooper pair wave function found in the infinite nuclear matter. The present results also provide a unified picture of the di-neutron and the cigar-like configurations in Borromian nuclei as a manifestation of the BCS-BEC crossover phenomenon.

  9. Spectroscopy of neutron unbound states in 24O and 23N

    Jones, Michael David

    Unbound states in 24O and 23N were populated from an 24O beam at 83.4 MeV/u via inelastic excitation and proton knockout on a liquid deuterium target. Using the MoNA-LISA-Sweeper setup, the decay of each nucleus could be fully reconstructed. The two-body decay energy of 23N exhibits two prominent peaks at E = 100 +/- 20 keV and E = 960 +/- 30 keV with respect to the neutron separation energy. However, due to the lack of gamma-ray detection, a definitive statement on the structure of 23N could not be made. Shell model calculations with the WBP and WBT interactions lead to several interpretations of the spectrum. Both a single state at 2.9 MeV in 23N, or two states at 2.9 MeV and 2.75 MeV are consistent with the shell model and data. In addition, a two-neutron unbound excited state of 24O, populated by (d,d'), was observed with a three-body excitation of E = 715 +/- 110 (stat) +/-45 (sys) keV, placing it at E = 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 were able to describe the observed correlations. This measurement constitutes the first observation of a two-neutron sequential decay through three-body energy and angular correlations, and provides valuable insight into few-body physics at the neutron dripline.

  10. Influence of neutron halo in the interaction of {sup 6}He nucleus of 35 MeV/nucleon with {sup 197}Au and {sup 238}U; Influence du halo de neutrons dans l`interaction du noyau {sup 6}He de 35 MeV/nucleon avec {sup 197}Au et {sup 238}U

    Perier, Yann [Grand Accelerateur National d`Ions Lourds (GANIL), 14 - Caen (France)


    In this study, we have attempted to answer some of the questions still open concerning neutron halo nuclei. The interest of the latter lies in their very peculiar structure. The analysis of the kinematical features of the halo nucleus fragments originating from the dissociation following the interaction with a target nucleus is an essential tool for probing this structure. We studied the {sup 6}He + Au, U at 35 A.MeV system with a new method. Simultaneous measurements of the halo nucleus core, the halo neutrons and the excitation energy deposited in the target nucleus assessed with ORION allowed us to obtain information about the formation of the {sup 5}He nucleus and about the partial validity of the sudden approximation at moderate bombarding energy. The study of the core nucleus and neutron angular distributions confirmed that it is difficult to extract information on the internal structure at the halo neutrons from their widths. The halo neutron longitudinal momentum distributions were studied. Their widths were found to increase as the impact parameter decreases. The {sup 4}He - core parallel momentum distributions were also investigated. The widths are weakly dependent on the excitation energy deposited in the target nucleus, but increase with the {sup 4}He emission angle as for the halo neutrons. The ratio between one- and two-neutron stripping cross sections seems to indicate that the two halo neutrons are strongly correlated with a large dineutron component, as ascertained by a calculation in the framework of the Serber model. (author) 84 refs., 98 figs., 17 tabs.

  11. Search for the existence of the tetra-neutron through the He{sup 8}(d,Li{sup 6})4n nuclear reaction; Recherche de l'existence eventuelle du tetraneutron via la reaction de transfert {sup 8}He(d, {sup 6}Li)4n

    Rich, E


    The He{sup 8}(d,Li{sup 6})4n reaction is studied through reverse kinematics: a radioactive beam of He{sup 8} nuclei impinges on a CD{sub 2} target. The measurement of the energy spectrum and emission angle distribution of Li{sup 6} has allowed us to determine by applying kinematics laws the excitation energy spectrum of the 4 neutrons system released in the reaction. The first chapter recalls the main features of the nucleon-nucleon interaction and reviews recent experiments on multi-neutrons. The second chapter presents the experimental setting from the production of the He{sup 8} beam at GANIL to the detection system of the reaction products via the data acquisition system. The method of the missing mass gives the mass of the 4 neutron system. The third and fourth chapters deal with the calibration of the detection system, the missing mass method is applied to the following reactions: C{sup 12}(d,Li{sup 6})Be{sup 8}, C{sup 12}(d,t)C{sup 11} and C{sup 12}(d,He{sup 3})B{sup 11}. The last chapter presents the experimental results. The analysis of the excitation energy spectrum of the 4 neutron systems shows no evidence for the existence of a bound state. We get a maximal limit of 60 {mu}b for the production cross section of a bound state. Complementary results concerning the excitation energy spectra of the di-neutron and tri-neutron released in the reactions: He{sup 8}(d,Li{sup 8})2n and He{sup 8}(d,Li{sup 7})3n are also presented. (A.C.)