Singlet Deuteron, Dineutron and Neutral Nuclei

The existence of the dineutron was predicted over 70 years ago. At present, a number of experimental works confirm this assumption. By virtue of the principle of isotopic invariance, a singlet deuteron must also exist. The possibility of describing the neutron-proton interaction in the state at low energies as the excitation of a quasi-stationary level (singlet deuteron) lying below the deuteron decay threshold is discussed. The position, neutron and radiative widths of the level are determined by the scattering length, the effective radius, and the cross section for the radiative capture of neutrons by protons. Experiments to search for this level are discussed. The discovery of the singlet deuteron would be confirmation of the existence of the dineutron

Precision Measurement of the n-3He Incoherent Scattering Length Using Neutron Interferometry

We report the first measurement of the low-energy neutron-$^3$He incoherent scattering length using neutron interferometry: $b_i' = (-2.512\pm 0.012{statistical}\pm0.014{systematic})$ fm. This is in good agreement with a recent calculation using the AV18+3N potential. The neutron-$^3$He scattering lengths are important for testing and developing nuclear potential models that include three nucleon forces, effective field theories for few-body nuclear systems, and neutron scattering measurements of quantum excitations in liquid helium. This work demonstrates the first use of a polarized nuclear target in a neutron interferometer.Comment: 4 figure

Nuclear Reaction Network for Primordial Nucleosynthesis: a detailed analysis of rates, uncertainties and light nuclei yields

We analyze in details the standard Primordial Nucleosynthesis scenario. In particular we discuss the key theoretical issues which are involved in a detailed prediction of light nuclide abundances, as the weak reaction rates, neutrino decoupling and nuclear rate modeling. We also perform a new analysis of available data on the main nuclear processes entering the nucleosynthesis reaction network, with particular stress on their uncertainties as well as on their role in determining the corresponding uncertainties on light nuclide theoretical estimates. The current status of theoretical versus experimental results for 2H, 3He, 4He and 7Li is then discussed using the determination of the baryon density as obtained from Cosmic Microwave Background anisotropies.Comment: LaTeX, 83 pages, 30 .pdf figures. Some typos in the units of R-functions in appendix D and relative plots fixe

An Accurate Redetermination of the 118Sn^{118}Sn Binding Energy

The energy of wellknown strong {gamma}line from {{^198}Au}, the "gold standard", has been modified in the light of new adjustments in the fundamental constants and the value of 411.80176(12) keV was determined which is 0.29 eV lower than the latest 1999 value. An energy calibration procedure for determining the neutron binding energy, {B_n}, from complicated {(n , gamma)}spectra has been developed. A mathematically simple minimization function consisting only of terms having as parameters the coefficients of the energy calibration curve (polynomial) is used. A priori information about the relationships among the energies of different peaks on the spectrum is taking into account by a Monte Carlo simulation. The procedure was used in obtaining of {B_n} for {{^118}Sn} and {{^64}Cu}. The {gamma}ray spectrum from thermal neutron radiative capture by {{^117}Sn} has been measured on the IBR2 pulsed reactor. {gamma}rays were detected by a 72 cm^3 HPGedetector. {B_n} for {{^64}Cu} was obtained from two {gamma}spectra. One spectrum was measured on the IBR2 by the same detector. The other spectrum was measured with a pair spectrometer at the Brookhaven High Flux Beam Reactor. From these two spectra {B_n} for {{^64}Cu} was determined equal to 7915.52(8) keV. The mean value of two the most precise results of the {B_n} for {{^118}Sn} was determined to be 9326.35(9) keV. The {B_n} for {{^57}Fe} was determined to be 7646.08(9) keV