Simulation of the d + 3 H →3 He + 2 n; 2 n → n + n Reaction

Results of a simulation of setups intended to search for excited states of few-nucleon systems decaying into two clusters are presented.     

Setup for studying quasi-free neutron-neutron scattering in the energy range of 20–60 MeV

A setup installed on the RADEX neutron beam channel (Institute for Nuclear Research, Russian Academy of Sciences) and designed to study quasi-free nn scattering in the n + d → p + n + n reaction is described. The setup is a two-arm time-of-flight spectrometer composed of scintillation neutron hodoscope (in the left arm), a scintillation neutron detector (in the right arm), and an active scintillation deuterated target for detecting protons. Secondary neutrons are detected at angles corresponding to the kinematic conditions of quasi-free nn scattering. Events are selected at low energies of the outgoing proton spectator. It is shown that data on neutron-neutron quasi-free scattering can be obtained in a wide range of primary-neutron energies.     

Study of the structure of neutron halo using neutron transfer reaction

To estimate the probability of two-neutron configurations in halo nuclei, we propose an experimental method of studying neutron-neutron correlations at periphery of such nuclei by measuring two-neutron transfer reaction. The experimental study of ⁶He + A ↦ ⁴He + B for various targets is performed using ⁶He beam of Flerov Laboratory of Nuclear Reactions (JINR, Dubna) at energy of about 15 MeV/u and technique of nuclear photoemulsions. Searching for events of two-nucleon transfer reaction and their processing is performed using the PAVICOM-setup at P.N. Lebedev Physical Institute.     

Data on Neutron–Neutron Scattering Length from the Reaction $$\boldsymbol{n+^{2}\textrm{H}\to n+n+p}$$ at $$\boldsymbol{E_{n}=60}$$ MeV

Physics of Atomic Nuclei - The $${}^{1}S_{0}$$ neutron–neutron ( $$nn$$ ) scattering length was measured in the neutron–deuteron ( $$nd$$ ) breakup reaction at an energy of 60 MeV. The...     

New evidence for supernarrow dibaryons production in pd interactions

The analysis of new experimental data, obtained at the Proton Linear Accelerator of INR, with the aim to search for supernarrow dibaryons in the pd↦ppX ₁ and pd↦pdX ₂ reactions is presented. Narrow peaks with an experimental width of 5 MeV at masses of 1904±2, 1926±2, and 1942±2 MeV have been observed in missing mass M _pX1 spectra. In the missing mass M _X1 spectra, the peaks at M _X1 = 966±2, 986±2, and 1003±2 MeV have been found. The analysis of the data obtained leads to the conclusion that the observed peaks in M _pX1 spectra are most likely supernarrow dibaryons, the decay of which into two nucleons is forbidden by the Pauli exclusion principle. An alternative interpretation of the spectra by assuming a decay of the supernarrow dibaryons in “exotic baryon states” with masses M _X1 is discussed. Received: 22 October 2001 / Accepted: 15 November 2001     

Investigating neutron-neutron and proton-proton correlations in few-nucleon systems in reactions with two nucleons in the final state

The great disagreement between theory and experiment observed in nd and pd interactions indicates that investigations of mechanisms for various processes in few-nucleon systems should be continued. It is planned to investigate the reactions d + ³H → ³He + (nn) and ³He + d → ³H + (pp) in order to study nn and pp correlations in ³He and ³H nuclei. Test measurements of the d + ²H → ²He + (nn) reaction, performed with the deuteron beam at the Institute of Nuclear Physics, confirm that it is methodologically possible to perform the planned experiments.     

Reaction <Emphasis Type="Italic">d</Emphasis> + <Superscript>2</Superscript>H → <Superscript>3</Superscript>He + <Emphasis Type="Italic">n</Emphasis> as a source of quasi-monoenergetic neutrons for studying the properties of neutron detectors

The responses of two liquid scintillators to neutron irradiation are investigated. Monoenergetic neutrons are obtained in the reaction d + ²H → ³He + n in different configurations of a coincidence experiment involving the detection of both neutrons and the ³He nucleus. In the experiment, the 15 MeV deuteron beam from the U-120 accelerator at the Skobeltsyn Institute of Nuclear Physics, Moscow State University, hits a target of deuterated polyethylene, and the secondary neutrons obtained in the reaction irradiate the EJ-301 and EJ-315 liquid scintillators under study.     

Low-Energy Parameters of Neutron–Neutron Interaction: Analysis of Data Obtained in <Emphasis Type="Italic">nd</Emphasis> and <Emphasis Type="Italic">dd</Emphasis> Breakup Reactions

Data obtained in recent years for the neutron–neutron scattering length in nd and dd breakup reactions are analyzed. Serious discrepancies between experimental data from different studies may be explained by the effect of three-nucleon forces depending on the velocity of separation of a neutron–neutron pair and a charged fragment. It is shown that the data under analysis can be approximated by a smooth curve representing the dependence of the scattering length on the parameter R, which determines the fragment-separation distance after a fixed time. This dependence makes it possible to obtain the scatteringlength value for R→∞—that is, in the absence of the effect of three-nucleon forces.     

Measurements of the two-neutron transfer reaction induced by a 6He radioactive beam

To estimate the probability of two-neutron configuration in halo nuclei, an experimental method for studying neutron-neutron correlations at the periphery of such nuclei by measuring the two-neutron transfer reaction is proposed. Experimental investigation of the ⁶He + A → ⁴He + B reaction was performed using a 60-MeV ⁶He radioactive beam at the Flerov Laboratory of Nuclear Reactions (Joint Institute for Nuclear Research, Dubna); the technique of nuclear photoemulsions was applied. Search for events of the two-nucleon transfer reaction was performed at the PAVIKOM setup (Lebedev Physical Institute, Russian Academy of Sciences).     

Determination of the 1S0 neutron-neutron scattering length in the nd breakup reaction at energies in the range En = 40?60 MeV

The first results are obtained in a kinematically complete experiment devoted to measuring the n + d → p + n + n reaction yield at energies in the range E _n = 40−60 MeV and various angles of divergence of two neutrons (Δθ = 4°, 6°, and 8°) in the geometry of neutron-neutron final-state interaction. The ¹ S ₀ neutron-neutron scattering length a _nn is determined by comparing the experimental energy dependence of the reaction yield with the results of a simulation in the Watson-Migdal approximation, which depend on a _nn . For E _n = 40 MeV and Δθ = 6° (the best statistics in the experiment), the value a _nn = −17.9 ± 1.0 fm was obtained. A further improvement of the experimental accuracy will make it possible to remove the existing disagreement of the results from different experiments.