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Showing papers in "Physical Review C in 1990"


Journal ArticleDOI
TL;DR: The formalism, the potentials, and the results of this paper may also serve as a basis and a realistic starting point for systematic relativistic nuclear structure studies as well as for the investigation of further relativism many-body corrections and of contributions of higher order.
Abstract: The formalism for the Dirac-Brueckner approach to the nuclear many-body problem is described including its basis in relativistic two-nucleon scattering. A family of relativistic meson-exchange potentials is constructed which (apart from the usual coupling terms for heavy mesons) apply the pseudovector (gradient) coupling for the interaction of pseudoscalar mesons (\ensuremath{\pi},\ensuremath{\eta}) with nucleons. These potentials describe low-energy two-nucleon scattering and the deuteron data accurately. Using these potentials, the properties of nuclear matter are calculated in the Dirac-Brueckner-Hartree-Fock approximation, in which the empirical nuclear matter saturation is explained quantitatively. The effective two-body interaction in the nuclear matter medium (G matrix) is calculated directly in the nuclear matter rest frame. Thus, cumbersome transformations between the two-nucleon center-of-mass frame and the nuclear matter rest frame are avoided. Size and nature of relativistic effects included in the present approach are examined in detail. The formalism, the potentials, and the results of this paper may also serve as a basis and a realistic starting point for systematic relativistic nuclear structure studies as well as for the investigation of further relativistic many-body corrections and of contributions of higher order.

444 citations


Journal ArticleDOI
TL;DR: Strong evidence is found for a model of the {ital E}1 strength function, which is characterized by an energy dependent spreading width of the underlying Lorentzian for the photoabsorption cross section and a nonzero, temperature dependent, limit as the transition energy tends to zero.
Abstract: The impact of models for E1 and M1 gamma-ray strength functions on the results of nuclear model calculations of total average radiation widths, radiative capture cross sections, and gamma-ray spectra has been studied. We considered strength functions that reproduce photoabsorption and/or average resonance data but significantly differ from each other at low gamma-ray energies. As the calculated quantities critically depend on the strength functions in this energy region, model calculations can be used to test the low-energy behavior of strength functions. By analyzing the $^{197}\mathrm{Au}$, $^{143}\mathrm{Nd}$, $^{105}\mathrm{Pd}$, and $^{93}\mathrm{Nd}$ neutron capture reactions we found strong evidence for a model of the E1 strength function, which is characterized by the following properties: (i) an energy dependent spreading width of the underlying Lorentzian for the photoabsorption cross section and (ii) a nonzero, temperature dependent, limit as the transition energy tends to zero. This model is founded in theoretical work by Zaretskij, Sirotkin, and Kadmenskij and represents a partial breakdown of Brink's hypothesis.

427 citations


Journal ArticleDOI
TL;DR: The extent of the island'' and the magnitude of the anomaly is explored by calculating the binding energies of 2{h bar}{omega} excitations of neutrons from the (1{ital s},0{ital d}) shell to the (0 {ital f},1 {ital p}) shell relative to the 0{hbar}{omegas} ground state.
Abstract: Further evidence for the presence of an anomaly in binding energies for the ``island of inversion'' centered at Z=11, N=21 is obtained by comparison of shell-model calculations to experiment. The calculations were done with a shell-model interaction that is applicable to nuclei with active valence nucleons in both the (1s,0d) and (0f,1p) major shells. This interaction is described in detail as are its predictions for binding energies and energy spectra of Z=8--20, N=18--25 nuclei. These calculations provide the background for the exploration of the ``island of inversion.'' The extent of the ``island'' and the magnitude of the anomaly is explored by calculating the binding energies of 2\ensuremath{\Elzxh}\ensuremath{\omega} excitations of neutrons from the (1s,0d) shell to the (0f,1p) shell relative to the 0\ensuremath{\Elzxh}\ensuremath{\omega} ground state. The reason why mixed (0+2)\ensuremath{\Elzxh}\ensuremath{\omega} calculations are not considered reliable is addressed. Truncation schemes and a weak-coupling approximation are used to extend the range of the calculations. It is found that for Z=10--12, N=20--22 (and possibly Ng22) nuclei the lowest 2\ensuremath{\Elzxh}\ensuremath{\omega} state is more bound than the 0\ensuremath{\Elzxh}\ensuremath{\omega} ground state. The role of odd n n\ensuremath{\Elzxh}\ensuremath{\omega} excitations is considered and it is found that the 1\ensuremath{\Elzxh}\ensuremath{\omega} ground state always lies below that of 3\ensuremath{\Elzxh}\ensuremath{\omega}, and for N=19, 21, and 23, the lowest 1\ensuremath{\Elzxh}\ensuremath{\omega} state is in close competition with 2\ensuremath{\Elzxh}\ensuremath{\omega} for the lowest binding energy. Collectivity is considered via E2 observables and energy spectra for the 2\ensuremath{\Elzxh}\ensuremath{\omega} ground-state bands. The reason for the existence of the ``island'' is discussed.

413 citations


Journal ArticleDOI
TL;DR: The predictive power of the global Dirac optical model fits to elastic proton scattering data from heavy nuclear targets at energies between 65 and 1040 MeV is tested for both interpolation and extrapolation.
Abstract: We present global Dirac optical model fits to elastic proton scattering data from heavy nuclear targets at energies between 65 and 1040 MeV. Such optical potentials provide critical input for a wide variety of nuclear reactions. The energy and mass number dependence of the parameters in the Lorentz four-vector and scalar potentials of Dirac phenomenology are given. The characteristic features of the potentials are discussed and the predictive power of the global approach presented here is tested for both interpolation and extrapolation.

212 citations


Journal ArticleDOI
TL;DR: Two-pion correlation functions are calculated from a dynamical string model situation and from a Bjorken-scaling solution and the effects of hadronic decays and final-state Coulomb and strong interactions are included.
Abstract: We calculate two-pion correlation functions from a dynamical string model situation and from a Bjorken-scaling solution. The effects of hadronic decays and final-state Coulomb and strong interactions are included. Correlation functions are shown to depend strongly on both the total transverse momenta and the direction of the relative momentum of the pairs.

164 citations


Journal ArticleDOI
TL;DR: A simple closed-form analytic expression for the heavy-ion reactionCross section, involving nuclear densities of colliding ions and the nucleon-nucleon cross section, has been obtained within the framework of the Glauber model modified for the Coulomb field effect.
Abstract: A simple closed-form analytic expression for the heavy-ion reaction cross section, involving nuclear densities of colliding ions and the nucleon-nucleon cross section, has been obtained within the framework of the Glauber model modified for the Coulomb field effect. Reaction cross sections for a large number of heavy-ion systems have been predicted reasonably well over an energy range beginning with the Coulomb barrier to a few GeV/nucleon.

161 citations


Journal ArticleDOI
TL;DR: The mass changing cross sections measured are found to agree with earlier cross section measurements using energetic protons incident on targets composed of heavier elements to within \ensuremath{\sim}2% in cases where a comparison can be made.
Abstract: This is the first in a series of papers describing the results of a systematic study of total, elemental, and isotopic cross sections measured in hydrogen, helium, and carbon targets. These fragmentation studies are based on measurements using 42 beams of 12 separate nuclei from $^{12}\mathrm{C}$ to $^{58}\mathrm{Ni}$. This has resulted in the measurement of more than 100 secondary elemental cross sections and over 300 secondary isotopic cross sections in addition to the total charge changing and mass changing cross sections reported in this paper. These measurements have been made at energies from 300 to 1700 MeV/nucleon and include ten separate energies for $^{56}\mathrm{Fe}$, for example. The measurements have been made with the objective of interpreting the production of secondary nuclei during cosmic-ray propagation in the galaxy in order to better estimate the source elemental and isotopic composition of cosmic rays. At the same time they provide a valuable data base for nuclear physics and the understanding of peripheral interactions of energetic heavy nuclei. In the work reported in this paper \ensuremath{\sim}100 total charge changing and mass changing cross sections have been measured for various targets and energies. The mass changing cross sections we measure are found to agree with earlier cross section measurements using energetic protons incident on targets composed of heavier elements to within \ensuremath{\sim}2% in cases where a comparison can be made. The systematics of this new data set are described and a new, more accurate cross section formula is presented and discussed.

156 citations


Journal ArticleDOI
TL;DR: Calculations of the yield of intermediate mass fragments are made with the expanding-evaporating source model and compared with data and the consequences of distributions in excitation energy, on the observation of multifragmentation, are discussed.
Abstract: The process of rapid massive cluster formation at low densities is associated with the process of {ital multifragmentation}. This phenomenon is studied by comparing the free energy for internally formed clusters with the free energy of the homogeneous system. The importance of considering {ital two} freeze-out conditions (entropy-freeze-out and force-freeze-out) in the dynamics leading to multifragmentation is discussed. Calculations of the yield of intermediate mass fragments are made with the expanding-evaporating source model and compared with data. The consequences of distributions in excitation energy, on the observation of multifragmentation, are discussed.

138 citations


Journal ArticleDOI
TL;DR: A relativistic nuclear mean field model is developed involving nucleons coupled to effective scalar and vector fields that yields a compression modulus of 225 MeV and an effective nucleon mass=0.85.
Abstract: A relativistic nuclear mean field model is developed involving nucleons coupled to effective scalar and vector fields. It differs slightly from the usual Walecka model in the form of the coupling of the nucleon to the scalar meson. We calculate the equation of state for symmetric nuclear matter at zero temperature. The model, which has no arbitrary parameters, once we fit the empirical density and energy of nuclear matter, yields a compression modulus of 225 MeV and an effective nucleon mass=0.85.

131 citations


Journal ArticleDOI
TL;DR: It is observed that to first order, the mass fractions for each isotope are essentially independent of energy, which indicates that the energy dependence of the isotopic cross sections is essentially the same as for the charge changing cross sections.
Abstract: In this paper, the third in a series of papers, we discuss isotopic fragmentation cross sections measured in hydrogen, helium, and carbon targets. Over 300 of these cross sections have been measured in 24 separate runs using 12 charges from $^{12}\mathrm{C}$ to $^{58}\mathrm{Ni}$. Most of these isotope cross sections were measured at an energy \ensuremath{\sim}600 MeV/nucleon, however, some measurements of the $^{56}\mathrm{Fe}$ fragmentation are available at an energy \ensuremath{\gtrsim}1 GeV/nucleon. We observe, comparing both these data and other data, that to first order, the mass fractions for each isotope are essentially independent of energy. This indicates that the energy dependence of the isotopic cross sections is essentially the same as for the charge changing cross sections. It is also observed that the isotopic mass fractions and the width of the mass distributions for each charge are essentially independent of the H, He, and C targets involved. These systematics greatly simplify the construction of a semiempirical formula to describe these cross sections. New isotopic cross sections are presented for a number of interesting reactions, $^{12}$C\ensuremath{\rightarrow}Be, $^{16}$O\ensuremath{\rightarrow}N, $^{27}$Al\ensuremath{\rightarrow}Na, and $^{56}\mathrm{Fe}$ into Mn and Ar among others. A large body of new data on proton and neutron stripping reactions are also presented and discussed.

125 citations


Journal ArticleDOI
TL;DR: It is suggested that multi-lambda hypernuclei could be produced in high-energy heavy ions and observed in secondary noncharge-changing reactions and the equation of state of lambda matter and the possibility of pure lambda droplets are discussed.
Abstract: Within a relativistic mean-field theory (RMFT) experimental data on the single-particle spectra of lambda hypernuclei are well reproduced. It is shown that the coupling constants cannot be fixed unambiguously from the single-particle spectra. The stability and structure of multi-lambda hypernuclei is explored on the basis of the RMFT using the coupling constants as determined from the observed single lambda hypernuclear levels. It is predicted that multistrange nuclei exhibit an enhanced interaction radius, which further increases in the case of finite temperatures. We suggest that multi-lambda hypernuclei could be produced in high-energy heavy ions and observed in secondary noncharge-changing reactions. The equation of state of lambda matter and the possibility of pure lambda droplets are also discussed.

Journal ArticleDOI
TL;DR: The new near-target residues provide significant new insight into the variation of the cross sections of products near in mass to the target (or projectile) and are compared to the internuclear-cascade model of these reactions.
Abstract: Target residues from the reaction of 2.6 GeV protons with gold and thorium nuclei have been studied with radiochemical techniques. Chemical separations were used to enhance the sensitivity for detecting target residues in the near-target region. These data are compared to a new empirical parametrization of the mass and charge yields of fragmentation, or spallation, products based on a comprehensive analysis of data in the literature. Data include results from both projectile and target fragmentation studies. The new near-target residues provide significant new insight into the variation of the cross sections of products near in mass to the target (or projectile). The results of this study and the empirical description are compared to the internuclear-cascade model of these reactions.

Journal ArticleDOI
TL;DR: In this article, the authors measured differential cross sections for the D-wave reaction at 11 deuteron bombarding energies from 20 to 117 keV, with an additional scale error of 1.3%.
Abstract: We have measured differential cross sections for the $^{2}\mathrm{H}$(d,p${)}^{3}$H and $^{2}\mathrm{H}$(d,n${)}^{3}$He reactions at 11 deuteron bombarding energies from 20 to 117 keV. The differential data are accurate to 2.0% (relative) over most of the energy range, with an additional scale error of 1.3%. Integrated cross sections are derived with total errors generally about 1.5%. The results are compared with other measurements and with an existing R-matrix analysis. We find a larger D-wave reaction amplitude than previously reported. Formulas for the cross sections and reactivities are given.

Journal ArticleDOI
TL;DR: This simple model predicts the polarization of neutrons in a fully polarized {sup 3}He target to be 87%, while protons should have a slight residual polarization of {minus}2.7% and works very well for quasielastic electron scattering.
Abstract: Simple formulas for the neutron and proton polarizations in polarized $^{3}\mathrm{He}$ targets are derived assuming (1) quasielastic final states; (2) no final-state interactions; (3) no meson-exchange currents; (4) large momentum transfers; (5) factorizability of $^{3}\mathrm{He}$ SU(4) response-function components. Numerical results from a wide variety of bound-state solutions of the Faddeev equations are presented. It is found that this simple model predicts the polarization of neutrons in a fully polarized $^{3}\mathrm{He}$ target to be 87%, while protons should have a slight residual polarization of -2.7%. Numerical studies show that this model works very well for quasielastic electron scattering.

Journal ArticleDOI
TL;DR: An important systematic in the data is a regular decrease in the elemental cross sections into a particular charge, {ital Z}{sub {ital f}}, with increasing charge change at a constant energy, which has important implications for constructing an empirical formula to describe these cross sections.
Abstract: In this paper we describe individual elemental cross sections. Over 100 of these cross sections have been measured by studying the fragmentation of beams of 12 charges ranging from $^{12}\mathrm{C}$ to $^{58}\mathrm{Ni}$ in hydrogen, helium, and carbon targets. The energies of the beams ranged from \ensuremath{\sim}300 to 1700 MeV/nucleon. The relative cross sections in hydrogen, helium, and carbon targets are examined as a function of both beam charge and energy. Limits are placed on the energy region in which the concept of factorization or scaling of cross sections for different beam charges and targets applies. The approach of these elemental cross sections to the asymptotic high-energy values is examined as a function of the beam charge and the charge change. The systematics of the energy dependence of these cross sections is also described in terms of the beam charge and the charge change. Another important systematic in our data is a regular decrease in the elemental cross sections into a particular charge, ${Z}_{f}$, with increasing charge change at a constant energy. It is found that this regular behavior of the cross sections follows a simple exponential law in the charge change, ${Z}_{B}$-${Z}_{f}$. This has important implications for constructing an empirical formula to describe these cross sections, as well as having theoretical implications.

Journal ArticleDOI
TL;DR: It is found that streamer chamber data can be fitted by Boltzmann-Uehling-Uhlenbeck calculations with a momentum-dependent potential that closely models realistic nuclear matter interactions and yields an equation of state with {ital K}=215 MeV.
Abstract: We investigate the generation of transverse momentum in high-energy heavy-ion collisions and its relation to the nuclear equation of state. We find that streamer chamber data can be fitted by Boltzmann-Uehling-Uhlenbeck calculations with a momentum-dependent potential that closely models realistic nuclear matter interactions and yields an equation of state with {ital K}=215 MeV.

Journal ArticleDOI
TL;DR: This formula, which is considerably simpler than earlier semiempirical formulations, is able to predict the cross sections in hydrogen for {ital Z}=4--28, {ital A}=7--60 nuclei above to an accuracy of 10% or better---a substantial improvement over earlier formulations.
Abstract: In this paper we describe a new formula for calculating the partial cross sections for the production of secondary fragments with energy \ensuremath{\gtrsim}200 MeV/nucleon in hydrogen targets. This formula and the systematics of these cross sections are based on fragmentation studies using 42 beams of 12 separate nuclei between Z=6 and 28. This has resulted in the measurement of more than 100 secondary elemental cross sections and over 300 secondary isotopic cross sections. The systematics of these cross sections allow us to write the cross section formula as a product of three essentially independent terms, one which describes the elemental cross sections, another the isotopic cross sections, and a third term describing the energy dependence. Overall, this formula, which is considerably simpler than earlier semiempirical formulations, is able to predict the cross sections in hydrogen for Z=4--28, A=7--60 nuclei above \ensuremath{\sim}200 MeV/nucleon to an accuracy \ensuremath{\sim}10% or better---a substantial improvement over earlier formulations.

Journal ArticleDOI
TL;DR: Author(s): Gutbrod, H.H; Kampert, K.H.; Kolb, B.
Abstract: Squeeze-out, a component of the collective flow of nuclear matter, is the preferential emission of particles out of the reaction plane. Using the sphericity method the out-of-plane/in-plane ratio of the kinetic energy flow has been analyzed as a function of multiplicity and beam energy for Ca+Ca, Nb+Nb, and Au+Au collisions measured with the Plastic Ball detector at the Bevalac. Also, azimuthal distribution of the particles around the flow axis are presented together with the extracted out-of-plane/in-plane ratios. Finally, the rapidity dependence of the out-of-plane/in-plane ratio has been investigated with a new method using the transverse momentum components of the particles.

Journal ArticleDOI
TL;DR: A thorough analysis of the existing differential cross section data up to 1.4 GeV shows the Orsay data to be internally inconsistent, and a rather simple reaction mechanism with the extracted main kaon-hyperon-nucleon coupling constants in agreement with the SU(3) predictions is proposed.
Abstract: The process {gamma}{ital p}{r arrow}{ital K}{sup +}{Lambda} is studied in a phenomenological approach. A thorough analysis of the existing differential cross section data up to 1.4 GeV, taking into account the systematic uncertainties, shows the Orsay data to be internally inconsistent. Removing this data set from the data base results in a rather simple reaction mechanism with the extracted main kaon-hyperon-nucleon coupling constants in agreement with the SU(3) predictions. Employing a diagrammatic model, the differential and total cross section, {Lambda}-polarization, and polarized target data are well reproduced. Predictions for other single and double polarization observables and suggestions for new measurements are presented. Applying crossing symmetry, the reaction is related to the radiative {ital K}{sup {minus}} capture process, and a comparison with the measured branching ratio is made.

Journal ArticleDOI
TL;DR: The observed differences in the subbarrier fusion cross sections for the {sup 90}Zr and {sup 93}Nb nuclei have led us to question the view that excursions of the strong nuclear force due to collective motions of the colliding nuclei are the primary enhancement mechanisms for the observed heavy-ion subbarriers fusionCross sections.
Abstract: Measurements of the fusion cross sections in the barrier and subbarrier regions are presented for the four heavy-ion systems $^{46,50}\mathrm{Ti}$${+}^{90}$Zr${,}^{93}$Nb. The measured cross sections varied from 0.04 to 400 mb. The evaporation residues were detected by the use of a velocity filter. Procedures are described for extracting fusion cross sections from such measurements. The observed differences in the subbarrier fusion cross sections for the $^{90}\mathrm{Zr}$ and $^{93}\mathrm{Nb}$ nuclei, both of which have small collectivity, have led us to question the view that excursions of the strong nuclear force due to collective motions of the colliding nuclei are the primary enhancement mechanisms for the observed heavy-ion subbarrier fusion cross sections.A simple formula is presented, based on a flat distribution of barriers, which is applied to the near-barrier region (10--200 mb). This formula states that the quantity (\ensuremath{\sigma}E${)}^{1/2}$ vs E is linear in the near-barrier region with a zero intercept defining a threshold energy for fusion. These threshold values reflect variations in the binding energies of the valence neutrons. We also point out that the far-subbarrier region (10 mb) shows large variations in fusion cross sections and that these variations reflect differences in the collectivities of the colliding nuclei (especially noticeable differences are seen between permanently deformed nuclei and ``vibrational'' nuclei). These systematics of heavy-ion subbarier fusion suggest that neck formation is playing an important role. The barrier for neutron transfer vanishes at distances typically 1.5 fm beyond the typical barrier distance and this distance could vary with the binding energy of the valence neutrons. The presence of neutrons in the region between the nuclei could promote neck formation which provides a force strong enough to overcome the Coulomb force. The collective properties of the colliding nuclei are then interpreted as a modulation of the threshold for neck formation and thereby reflect the large observed differences in the far-subbarrier cross sections. Formulas are presented for ${\mathrm{\ensuremath{\sigma}}}_{\mathit{L}}$ which result from a flat distribution of barriers. These formulas predict a broad bell-shaped spin distribution and are compared to the measured distribution in the subbarrier region for the system $^{64}\mathrm{Ni}$${+}^{100}$Mo.

Journal ArticleDOI
TL;DR: In this paper, the spins and moments of strontium isotopes with A=78 to A=98 and A=100 were extracted from the collinear fast beam laser spectroscopy data and compared with predictions of the droplet model and Hartree-Fock-plus-BCS calculations.
Abstract: Hyperfine structures and isotope shifts of strontium isotopes with A=78 to A=98 and A=100 were measured by collinear fast beam laser spectroscopy. Nuclear spins, moments and changes in mean square charge radii are extracted from the data. The spins and moments of most of the odd isotopes are explained in the framework of the single particle model. The changes in mean square charge radii are compared with predictions of the droplet model and of Hartree-Fock-plus-BCS calculations. For the isotopes in the transitional regions below and above the N=50 shell closure, the inclusion of quadrupole zero point motion in the Droplet model describes part of the observed shell effect. An additional change in the surface region of the charge distribution at spherical shape is suggested by the microscopic model. Furthermore, we propose that the isotopes $^{78}\mathrm{Sr}$ and $^{80}\mathrm{Sr}$ may show an unusual shape-sharing structure, with different mean deformations in the ground and ${2}_{1}^{+}$ excited states.

Journal ArticleDOI
TL;DR: In this paper, the authors presented a multi-energy phase shift analysis of all partial wave data below 350 MeV, where the long-range potential consisting of the improved Coulomb potential (including the magnetic moment interaction), the vacuum polarization potential, and the tail of the one-pion exchange potential was considered.
Abstract: As a continuation of our 0--30 MeV analysis we present a multienergy phase shift analysis of all {ital pp} scattering data below {ital T}{sub lab}=350 MeV. In the description of all partial waves we take exactly into account the long-range potential consisting of the improved Coulomb potential (including the magnetic moment interaction), the vacuum polarization potential, and the tail of the one-pion-exchange potential. To describe the short-range interaction in the lower partial waves we use a {ital P}-matrix parametrization. The intermediate partial waves are treated either by optimal mapping techniques or by using the Nijmegen soft-core potential. The latter gives a better description of the data. The final data set comprises 1626 scattering observables. The best fit to this final data set results in {chi}{sup 2}/{ital N}{sub df}=1.117, where {ital N}{sub df}=1576 is the number of degrees of freedom. The {ital pp}{pi}{sup 0} pseudovector coupling constant is determined to be {ital f}{sub 0}{sup 2}=(74.9{plus minus}0.7){times}10{sup {minus}3}. Single-energy phase shifts and errors are also given.

Journal Article
TL;DR: Caracterisation de la nouvelle phase ''1222'' as discussed by the authors : Une transition supraconductrice de 25 K est mesuree pour echantillon homogene de composition (Eu 3/4 Ce 1/4 ) 2 (Sr 7/8 Eu 1/8 ) 2
Abstract: Caracterisation de la nouvelle phase «1222». Une transition supraconductrice de 25 K est mesuree pour echantillon homogene de composition (Eu 3/4 Ce 1/4 ) 2 (Sr 7/8 Eu 1/8 ) 2 Cu 2 O z . C'est le 1er supraconducteur de structure «1222»

Journal ArticleDOI
TL;DR: An attempt has been made to synthesize the extremely neutron-rich isotope {sup 26}O in the nuclear reaction 44 MeV/nucleon {sup 48}Ca+Ta, and the previously unobserved isotopes {sup 32}Ne was found to be particle stable and the isotope{sup 31}Ne particle unstable.
Abstract: An attempt has been made to synthesize the extremely neutron-rich isotope $^{26}\mathrm{O}$ in the nuclear reaction 44 MeV/nucleon $^{48}\mathrm{Ca}$+n/rTa. Use was made of magnetic separation and identification methods including time-of-flight and \ensuremath{\Delta}E,E measurements. The $^{26}\mathrm{O}$ nucleus appears to be unstable against particle emission since no events attributable to the $^{26}\mathrm{O}$ nucleus were observed at a level one order of magnitude lower than that predicted from the extrapolated yields. The previously unobserved isotope $^{32}\mathrm{Ne}$ was found to be particle stable and the isotope $^{31}\mathrm{Ne}$ particle unstable. Neutron-separation energies calculated with different models are tabulated.

Journal ArticleDOI
TL;DR: A simple method is proposed for determining the impact parameter in relativistic nucleus-nucleus collisions by Assuming a monotonous correlation between multiplicity and impact parameter, the multiplicity dependence of the measured cross section is interpreted as an impact-parameter dependent of the geometrical reaction cross section.
Abstract: A simple method is proposed for determining the impact parameter in relativistic nucleus-nucleus collisions. Assuming a monotonous correlation between multiplicity and impact parameter, the multiplicity dependence of the measured cross section is interpreted as an impact-parameter dependence of the geometrical reaction cross section. The reliability of this method is checked to be excellent within the framework of the intranuclear cascade model. Its application to data analysis at lower and higher energies is suggested.

Journal ArticleDOI
TL;DR: The mean mass losses observed for fragments that have lost a few protons show that typically many neutrons are lost with each proton, producing fragment nuclei that must be highly proton rich, and consequently very unstable.
Abstract: Relativistic iron, lanthanum, holmium, and gold projectile nuclei with several different energies have been fragmented in targets of polyethylene, carbon, aluminum, copper, and lead. Our detectors cleanly resolve the individual charges of the heaviest of these fragments and provide some limited information on the masses. We have measured 1256 elemental partial cross sections for the production of fragments from interactions in these target materials. Values have been derived for another 417 cross sections in a hydrogen medium. These cross sections depend on the energy and mass of the projectile nuclei as well as on the nature of the target. Total charge-changing cross sections were also found, but only in a composite target, and have been shown to be weakly dependent on energy. The mean mass losses observed for fragments that have lost a few protons show that typically many neutrons are lost with each proton, producing fragment nuclei that must be highly proton rich, and consequently very unstable. The cross sections for charge pickup on heavy targets show a rapid increase with decreasing energy, particularly for the heaviest targets. The systematics of the dependencies of the partial cross sections will be discussed in a companion paper.

Journal ArticleDOI
TL;DR: Various contributions to the average binding energy per nucleon are investigated in the framework of Brueckner's expansion; particular attention is paid to the dependence of the calculated binding energy upon the choice of the auxiliary'' potential which is added to and subtracted from the Hamiltonian before performing the expansion.
Abstract: A separable representation of the Paris interaction is used as input for the investigation of various nuclear matter properties. The faithfulness of the separable representation is checked by comparison with results previously obtained from the original Paris interaction. Calculations are performed for four different values of the Fermi momentum, namely ${\mathit{k}}_{\mathit{F}}$=1.10, 1.36, 1.55, and 1.75 ${\mathrm{fm}}^{\mathrm{\ensuremath{-}}1}$. One evaluates the contributions to the quasiparticle potential energy that are of first, second, and third order in the reaction matrix. The momentum distribution n(k) in the correlated ground state is calculated up to second order in the reaction matrix. For 0k2 ${\mathrm{fm}}^{\mathrm{\ensuremath{-}}1}$, it mainly depends upon the ratio k/${\mathit{k}}_{\mathit{F}}$; in the domain 2k4.5 ${\mathrm{fm}}^{\mathrm{\ensuremath{-}}1}$, it is accurately reproduced by the expression 1/7${\mathit{k}}_{\mathit{F}}^{5}$${\mathit{e}}^{\mathrm{\ensuremath{-}}1.6\mathit{k}}$, with k and ${\mathit{k}}_{\mathit{F}}$ in units of ${\mathrm{fm}}^{\mathrm{\ensuremath{-}}1}$. The quasiparticle strength at the Fermi surface is calculated, as well as the mean-square deviation of the one-body density matrix from that of the unperturbed Fermi sea: This quantity gives an estimate of the minimum value of the norm of the difference between the one-body density matrix of a correlated nucleus and that associated with any Slater determinant. The average kinetic energy per nucleon is evaluated. Various contributions to the average binding energy per nucleon are investigated in the framework of Brueckner's expansion; particular attention is paid to the dependence of the calculated binding energy upon the choice of the ``auxiliary'' potential which is added to and subtracted from the Hamiltonian before performing the expansion. One also evaluates diagrams that are characteristic of the difference between the Green's function and the Brueckner hole-line expansions. The fulfillment of the Hugenholtz--Van Hove theorem is studied.

Journal ArticleDOI
TL;DR: An energy-dependent partial-wave analysis of pion photoproduction data through the second-resonance region (0--1 GeV laboratory kinetic energy) is presented and the predictions of the solutions are compared with the results of previous analyses.
Abstract: An energy-dependent partial-wave analysis of pion photoproduction data through the second-resonance region (0--1 GeV laboratory kinetic energy) is presented. A set of energy-independent analyses has also been obtained starting from the energy-dependent solution. The data set contains 9074 data for the reactions \ensuremath{\gamma}+p\ensuremath{\rightarrow}p+${\mathrm{\ensuremath{\pi}}}^{0}$, \ensuremath{\gamma}+p\ensuremath{\rightarrow}n+${\mathrm{\ensuremath{\pi}}}^{+}$, \ensuremath{\gamma}+n\ensuremath{\rightarrow}n+${\mathrm{\ensuremath{\pi}}}^{0}$, \ensuremath{\gamma}+n\ensuremath{\rightarrow}p+${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$, and the inverse reaction ${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$+p\ensuremath{\rightarrow}n+\ensuremath{\gamma} (converted to \ensuremath{\gamma}+n\ensuremath{\rightarrow}p+${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$). The predictions of our solutions are compared with the results of previous analyses. Suggestions are made for future experiments.

Journal ArticleDOI
TL;DR: Reasonable agreement is found with several different models, including those in the relativistic impulse approximation, nonrelativistic calculations that include meson-exchange currents, isobar configurations, and six-quark configurations, but all calculations are very sensitive to the choice of deuteron wave function and nucleon form factor parametrization.
Abstract: Measurements of the deuteron elastic magnetic structure function B(${\mathit{Q}}^{2}$) are reported at squared four-momentum transfer values 1.20\ensuremath{\le}${\mathit{Q}}^{2}$\ensuremath{\le}2.77 (GeV/c${)}^{2}$. Also reported are values for the proton magnetic form factor ${\mathit{G}}_{\mathit{M}\mathit{p}}$(${\mathit{Q}}^{2}$) at 11 ${\mathit{Q}}^{2}$ values between 0.49 and 1.75 (GeV/c${)}^{2}$. The data were obtained using an electron beam of 0.5 to 1.3 GeV. Electrons backscattered near 180\ifmmode^\circ\else\textdegree\fi{} were detected in coincidence with deuterons or protons recoiling near 0\ifmmode^\circ\else\textdegree\fi{} in a large solid-angle double-arm spectrometer system. The data for B(${\mathit{Q}}^{2}$) are found to decrease rapidly from ${\mathit{Q}}^{2}$=1.2 to 2 (GeV/c${)}^{2}$, and then rise to a secondary maximum around ${\mathit{Q}}^{2}$=2.5 (GeV/c${)}^{2}$. Reasonable agreement is found with several different models, including those in the relativistic impulse approximation, nonrelativistic calculations that include meson-exchange currents, isobar configurations, and six-quark configurations, and one calculation based on the Skyrme model. All calculations are very sensitive to the choice of deuteron wave function and nucleon form factor parametrization. The data for ${\mathit{G}}_{\mathit{M}\mathit{p}}$(${\mathit{Q}}^{2}$) are in good agreement with the empirical dipole fit.

Journal ArticleDOI
TL;DR: This work presents the first systematic and global analysis of nucleon-induced reactions onital A-30 systems at incident energies of 50 MeV to 1 GeV by means of a cascade-statistical approach and reexamines the model in terms of the essential physics such as Pauli principle, Fermi motion, and medium corrections.
Abstract: We present here the first systematic and global analysis of nucleon-induced reactions on {ital A}{lt}30 systems at incident energies of 50 MeV to 1 GeV by means of a cascade-statistical approach. Model simulations are tested against available data from nuclei such as C, N, O, Al, and Si. With one set of inputs provided here, most of the inclusive observables, such as the double differential spectra of light ions and heavy residual nuclei from the dominant channels, can be well reproduced. The model yields absolute cross sections and the calculations are done without any parameter adjustments. Given the success of this simple, classical approach, we reexamine the model in terms of the essential physics such as Pauli principle, Fermi motion, and medium corrections. We interpret the cascade part as a classical simulation of the intermediate multi-particle-hole configurations which dominate multistep-direct and preequilibrium reactions and provide a critical assessment of the microscopic foundation and the range of validity of the model. We also discuss possible extensions of this model to around Fermi energy.