Multiparticle emission in the interactions of hadrons with complex nuclei at incident momenta from 2 to 4 GeV/c

The charged secondary particles emitted in inelastic reactions of 4 GeV/cπ⁺ and π^? with the nuclei Be, Cu and Ta are thoroughly studied in their multiplicities, particle correlations and the distributions of kinematical variables, with the 1 m hydrogen bubble chamber into which the three nuclear target plates were installed. The numbers of charged secondaries emitted in the π^?(2.3 GeV/c), π⁺(2 GeV/c) and p(4 GeV/c) reactions are also investigated. From these data, characteristic features of the multiplication process of secondaries in nuclear matter are clarified. The experimental results are compared with the calculation of an intra-nuclear cascade model which takes into account the process of pion absorption by two-nucleon clusters in the nucleus. It is found that the experimental results on the properties of charged secondaries are consistently explained by the model. The model can also give an account of the experimental finding that fairly high momentum protons are emitted from the heavier nuclei into the backward hemisphere in the lab system.     

The reactive two-body part of the pion-nucleus optical potential

We calculate the reactive component of the two-body contribution to the pion-nucleus optical potential from a two-nucleon pion absorption mechanism that predicts the total cross section and angular distributions for π⁺d → pp very well. At threshold the calculated absorptive parts explain most of the values obtained from pionic atom level widths, whereas the dispersive parts, which are very sensitive to wave function correlations are considerably more attractive than what the conventional phenomenological parameters would suggest.     

The (γ, p0) reactions in the giant dipole resonance region of 51V and 52Cr nuclei

The differential cross sections at 90° for the ⁵¹V(e, p₀)⁵⁰Ti and ⁵²Cr(e, p₀ + p₁)⁵¹V reactions have been measured over the giant dipole resonance region. These cross sections were used to obtain the differential cross sections of the ⁵¹V(γ, p₀)⁵⁰Ti and ⁵²Cr(γ, p₀ + p₁)⁵¹V reactions. The results show two peaks that appear at the same energies as the main peaks of the (γ, n) and (γ, p) cross section for both nuclei. The angular distributions of protons from the (e, p) reaction have also been measured at several points of the incident electron energy. The coefficients A₂ obtained by fitting with a series of Legendre polynomials, W(θ) = 1 + A₁P₁(cos θ)+A₂P₂(cos θ), varies with excitation energy. These results are discussed in terms of the direct-semidirect process considering isospin effects in the giant dipole resonance.     

A systematic study of (n,d), (n,n' p) and (n,pn) reactions at 14.7 MeV

Cross sections for [(n, d) + (n, n′p) + (n, pn)] reactions induced by 14.7 ± 0.3 MeV neutrons on ⁴⁴Ca, ⁴⁹Ti, ⁵⁰Cr, ^{67, 68}Zn, ⁹²Zr and ^{97, 98}Mo have been measured by the activation technique using enriched isotopes as target materials, modern radiochemical separations and high-resolution counting methods. A brief summary of the literature data and our own earlier measurements is given. Our activation data are generally in agreement with those deduced from emitted charged particle characterisation. Some systematic trends in the activation cross-section data were analysed. Similar to other (n, charged particle) reactions, the [(n, d) + (n, n′p) + (n, pn)] reaction cross section decreases as a function of (N?Z)/A; the data, however, fall on two curves, one for nuclei with neutron separation energies (S_n higher than the proton separation energies (S_p) and the other for nuclei with S_n < S_p. For nuclei with S_n ? S_p the (n, n′p) process is very important. Detailed Hauser-Feshbach calculations show that in general contributions of statistical processes to the (n, d) reaction cross section are very small.     

Photoemission of protons from4He in theΔ-resonance region

High resolution proton energy spectra from the⁴He(γ,p) reaction have been measured with tagged photons in the range E_γ = 130?525 MeV using the large Mainz NaI(T1) spectrometer atΘ _p ^lab =37.1°. Three separate reaction channels were identified, viz.⁴He(γ,p)t two-body breakup,⁴He photodisintegration via two-nucleon photon absorption processes and the quasifree pion production channel. Differential cross sections are presented for each of these channels as a function of photon energy. The sum of the two-nucleon photon absorption and the quasifree pion production differential cross sections, in the CM system, resembles that of the corresponding free-nucleon differential cross section when Fermi motion is taken into account.     

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).     

On the kinematics of (e, e′p) reactions

The problem of interpreting experimental data on quasielastic electron scattering on nuclei in A(e, e′p)(A?1) reactions is considered. It is shown that the existing discrepancies in experimental data on the reaction ⁴He(e, e′p)T are associated with the fact that the residual-nucleus momentum p _m as determined from the law of energy-momentum conservation cannot be treated as that which is equal to the momentum p of the primary intranuclear nucleon. Under the assumption that the momentum transferred from the electron to the intranuclear nucleon is redistributed during the divergence of the products of the (e, e′p) reaction in question, the method for extracting p is modified by introducing a kinematical correction, whereby the situation is considerably improved. For a first approximation, the correction can be evaluated on the basis of data on A(e, e′) inclusive reactions. The argument behind this evaluation is illustrated by considering the example of the reaction ⁴He(e, e′p)T.     

On the electrodisintegration of nuclei

The kinematical dependences of cross sections for the electrodisintegration of nuclei that is induced by high-energy electrons is studied within the shell model of the nucleus. It is proposed to identify the quantum numbers of nuclear shells by a method that involves the subtraction of quasielastic peaks. The effect of Coulomb resonances and quasireal photons on the formation of angular and energy distributions of electrons and protons in A(e, e′p)(A ? 1) reactions is explored. The phenomenon of quasielastic-peak shift and broadening is interpreted.     

Model dependence of the (π−, nn) reaction

The recoil momentum distribution for the (π^?, nn) reaction on ⁶Li is calculated using the one- and two-nucleon absorption interactions and the α-d cluster model for ⁶Li. It is found that the shapes of the distribution calculated with the two interactions do not differ much. Its magnitude, however, can differ substantially, depending upon the parameter of the correlation function in the one-nucleon model. From this and the comparison with the available experimental data it is argued that the two-nucleon model can be used to make a relative study of the correlations in nuclei, in addition to its utility for studying two-hole states in nuclei and the advantage of an easier formalism.     

Deuteron structure and diffractive deuteron-nucleus interaction

A nonrelativistic deuteron wave function involving the D-wave state and having a correct asymptotic behavior is constructed on the basis of the experimentally measured deuteron charge form factor G _C(q) and deuteron structure function A(q). The differential cross section for elastic deuteron-nucleus scattering is calculated by using this wave function and is found to agree with experimental data at an energy of 110 MeV. Integrated cross sections for various processes involving deuteron-nucleus interactions are also calculated. The distribution in the emission angle of the center of mass of the neutron-proton system produced in the diffractive dissociation of 110-MeV deuterons in the field of ²⁰⁸Pb nuclei is obtained.     

Taking into Account the Centre-of-Mass Correlations in the Cross Sections for Elastic Scattering of Intermediate Energy Protons on the Exotic Nuclei <Superscript>6</Superscript>He and <Superscript>8</Superscript>He

We calculate the differential cross sections for proton elastic scattering on the exotic halo nuclei ⁶He and ⁸He at energies around ~0.7 GeV at the momentum transfers squared up to 0.30 (GeV/c)² and investigate the influence of the nucleon centre-of-mass correlations on the calculated cross sections. In particular, we show that the approximate account of the centre-of-mass correlations used previously considerably overestimates the cross sections at high values of the momentum transfer.     

HighP ∧ hadron production off nuclei at 70 GeV

Invariant cross sections for hadron production (π^±,K ^± ,p and \(\bar p\) ) by protons off C, Al, Cu, Sn and Pb nuclei have been measured at 70 GeV for theP _∧ range from 1 up to 4.65 GeV/c. TheA-dependence of the invariant cross section is not described by the exponentialA ^α(P _∧), which points to the presence of secondary hadron absorption in nuclei.     

Investigations of Few-Nucleon System Dynamics in Medium Energy Domain

Precise and large set of cross sections, vector A _x , A _y and tensor A _xx , A _xy , A _yy analyzing powers for the ¹ H(d, pp)n breakup reactions were measured at 100 and 130 MeV deuteron beam energies with the use of the SALAD and BINA detectors at KVI and Germanium Wall setup at FZ-Jülich. Results are compared with various theoretical approaches which model the three-nucleon (3N) system dynamics. The calculations are based on different two-nucleon (2N) potentials which can be combined with models of the three-nucleon force (3NF) and other pieces of the dynamics can also be included like the Coulomb interaction and relativistic effects. The cross sections data reveal seizable 3NF and Coulomb force influence. In case of analyzing powers very low sensitivity to the effects was found and the data are well describe by 2N models only. At 130 MeV for A _xy serious disagreements appear when 3NF models are included into calculations.     

A semi-classical model of multi-step direct and compound nuclear reactions

A semi-classical model of multi-step direct and compound nuclear reactions is proposed to describe the angular distributions of particles emitted from the inelastic scattering induced by a nucleon with an energy of several tens of MeV. The energy-angle correlation is exactly taken into account for the first few steps of the collision process (multi-step direct process) and the generalized master equation is employed for the following stages of collision process, using the energy-averaged kernelG(Ω → Ω′) (multicompound process). The calculations for¹⁹⁷Au(p, p′),¹²⁰Sn(p, p′) and⁹³Nb(n, n′) show that the model can rather nicely reproduce the experimental data of double-differential cross sections.     

Alpha-like four nucleon correlations in superfluid phases of atomic nuclei

α-like four-nucleon correlations are included in the structure of superfluid ground and low-lying excited states of atomic nuclei within a BCS-like approach. New metastable superfluid and normal states are predicted. These states could be associated with some of the recently discovered I^π = 0⁺ states in different regions of atomic nuclei. A new type of elementary excitations may be constructed on these metastable states in the same way as those constructed on the BCS superfluid ground states. The region of superfluid cold nuclei is enlarged due to the fact that the neutron and proton superfluidity can mutually be induced via the α-like four-nucleon ineractions. This type of correlations lead to a further enhancement of the probabilities of the favoured α-clusterization processes (such as α-decay or α-transfer reactions), two-nucleon transfer reactions and other clusterization processes such as e.g. the heavy cluster decay.     

Extended basis shell-model study of two-neutron transfer reactions

A method to calculate two-nucleon overlaps is presented. The approach is based on shell-model techniques and the effect of one and two nucleons in the continuum are included implicitly. The reactions ¹⁸O(p, t)¹⁶O and ¹⁶O(t, p)¹⁸O (ground and excited 0⁺ states) are analysed within the zero-range and finite-range DWBA framework. The differential cross sections calculated using the overlaps obtained by the present method are compared with the ones obtained by the standard well depth (WD) and Jaffe-Gerace (JG) techniques. It is shown that the WD approach yields cross sections smaller than the experimental values by an order of magnitude while the JG method predicts undue energy dependence in the cross section. Our approach removes these difficulties and is shown to be consistent with the one-nucleon transfer calculation.     

Study of the spectra of fast deuterons produced in the interaction of 670 MeV protons with nuclei

The spectra of deuterons emitted at angles of 6.5°, 9.5°, 13.5° and 16° (lab system) in the interaction of protons with the nuclei ¹H, ²H, ⁶Li, ⁷Li, C, Al, Cu, Rh and Pb have been measured in the momentum range 700–1700 MeV/c. The secondary particles were analyzed with the help of magnetic and time-of-flight spectrometers. The differential cross sections for deuteron production in the reactions p + 〈2N〉 → N + d and p + 〈N〉 → d + π have been measured for selected nuclei and angles. The effective numbers of nucleons and of two-nucleon clusters for the investigated nuclei were determined. The results obtained are discussed in terms of the dispersion theory of direct nuclear reactions.     

Compound nucleus contribution and even-odd effect for (3He,p) reactions in the Ni region

The compound nucleus contributions to the proton spectra from 8 MeV and 10 MeV ³He induced (³He, p) reactions on even-A Ni isotopes were obtained. The relative cross sections for ⁵⁸Ni/⁶⁰Ni/⁶²Ni in the high excitation region are in fair agreement with predictions of statistical theory, but the absolute cross sections in the same region are smaller than the prediction by a factor of 3 to 8, and the shapes of the measured spectra for heavier isotopes do not agree with the prediction. These discrepancies between experiment and theory are in sharp contrast to the situation in (p, p′), (p, α), (α, p) and (α, α′), where good agreement was found.The proton spectra from (³He, p) reactions on nuclei in the A = 54–68 mass range have a systematic difference in slope between even-A targets and odd-A targets; it is similar to the systematic difference found previously in (p, p′) and (α, p) reactions, but none of these is readily explainable by theory.     

Experimental results on cross sections for 7Be photoproduction on 12C, 14N,and 16O nuclei in the energy range of 40–90 MeV

The yields of A(Γ,X)⁷Be reactions induced by bremsstrahlung photons were measured at the endpoint electron energies of 40, 50, 60, 70, 80, and 90MeV. The spectra of bremsstrahlung incident to the targets used were calculated via a simulation based on the GEANT 4 code passage. The cross sections for the A(γ,X)⁷Be reactions on ¹²C, ¹⁴N, and ¹⁶O nuclei were evaluated on the basis of the measured reaction yields and the calculated bremsstrahlung spectra. The experimental cross sections for the photonuclear reactions of ⁷Be production were comparedwith their counterparts calculated on the basis of the TALYS 1.4 package. Agreement of the experimental and evaluated results was demonstrated for ¹²C nuclei and partly for ¹⁴N nuclei.