Reaction cross section measurements of the neutron-rich isotopes8,9,11Li at 80 MeV/nucleon

Total interaction cross sections have been measured for⁸Li on C and Pb targets, for⁹Li on C, Al, Cu, Sn and Pb targets as well as for¹¹Li on C, Sn and Pb targets. For each beam, we also used a plastic scintillator as target. The measurements with the scintillator targets are used to extract reduced nuclear radii of the lithium isotopes. These radii are then used for the calculation of the nuclear part of the total cross section for the other targets. The total electromagnetic-dissociation (EMD) cross sections have been deduced and are compared to different models. A strong target-charge-dependent EMD cross section is measured for¹¹Li reaching 2.96 _–0.82 ^+0.84 b for the Pb target. In the⁹Li case, a large EMD cross section for high-Z targets has been observed which amounts to 0.75 ± 0.45 b for the Pb target. The EMD cross sections of both,⁹Li and¹¹Li, may be understood by the giantdipole-resonance model.This work forms part of the PhD Thesis of B. Blank     

Total interaction and proton-removal cross-section measurements for the proton-rich isotopes 7Be, 8B,and 9C

In an experiment performed at the FRS of GSI, we measured total interaction cross sections for ⁷Be, ⁸B, and ⁹C, one-proton-removal cross sections for ⁸B and ⁹C as well as two-proton-removal cross sections for ⁹C on targets ranging from carbon to lead at an energy of 285 MeV/nucleon. In addition, we performed measurements at 142 MeV/nucleon for ⁸B. The experimental results are compared to different calculations. Glauber-type calculations with different model·density distributions show that, down to incident energies of about 50 MeV/nucleon, total interaction cross-section measurements with light targets are not sensitive to an extended proton distribution in ⁸B. However, at lower incident energies, a tail in the proton density distribution is needed to explain the total interaction cross sections. Total interaction cross-section measurements with high-Z targets in the present experiment show a significant increase of the cross sections due to low-lying electromagnetic strength.     

Nuclear sizes derived from high-energy reaction cross sections

An analysis has been made of reaction cross sections for negative pions on a range of nuclei in the momentum region from 20 to 60 GeV/c. Data for C, Al, Sn and Pb are analysed in terms of nuclear sizes. Assuming the neutron and proton distributions in C are identical it is found that for Pb the best agreement with experiment is obtained using neutron density distributions which have similar geometrical parameters to that of the proton distribution. The accuracy with which the neutron distribution can be determined by these experiments is considered. The analysis is also extended to similar measurements for K⁻ mesons and antiprotons.     

Projectile breakup and total reaction strengths in Li-induced reactions

Spectra and angular distributions have been measured for the light particles emitted from the reactions induced by 36 MeV ⁶Li and ⁷Li ions on targets of ¹²C, ¹³C and ²⁷Al. Some measurements were also performed at beam energies of 28 and 32 MeV. The spectra are dominated by broad peaks centered at energies corresponding to the beam velocity, a characteristic of projectile breakup. A simple breakup model roughly reproduces the shapes of the measured spectra and angular distributions. The total cross sections observed for projectile breakup average about 600 mb and are almost as large as the fusion cross sections. The ⁷Li breakup yields are somewhat larger than those for ⁶Li, the same trend that was previously observed for the Li-induced fusion cross sections on C. As a result the measured total reaction cross sections induced by ⁷Li ions are about 200 mb larger than those of ⁶Li on the same targets. This difference is not predicted by conventional optical model calculations.     

Production of residual radioactive nuclei in thin <Superscript>209</Superscript>Bi, <Superscript>nat</Superscript>Pb, <Superscript>206</Superscript>Pb, <Superscript>207</Superscript>Pb,and <Superscript>208</Superscript>Pb targets bombarded with 0.04–2.6 GeV protons

The results of the experimental measurement and numerical simulation of the cross sections for residual radioactive nuclei production in thin ²⁰⁹Bi, ^natPb, ²⁰⁶Pb, ²⁰⁷Pb, and ²⁰⁸Pb targets bombarded with protons in the energy range from 0.04 to 2.6 GeV are reported. The nuclide production cross sections were measured using γ spectrometry with a high-resolution Ge detector. The experimental data include a total of 5972 reaction cross sections at 11 proton energy values. The results are compared to the data from other laboratories reported in 80 papers. The model calculations were carried out using eight simulation code packages: LAHET, INCL4 + ABLA, CEM03, LAQGSM + GEM2, CASCADE, CASCADE-2004, CASCADO, and LAHETO. A detailed analysis of discrepancies between the measured and calculated data is presented.     

Cross sections of large-angle hadron production in proton-nucleus and pion-nucleus interactions

We report on double-differential inclusive cross sections of the production of secondary protons and charged pions (in interactions with thin stationary targets made of Be, C, Cu, Sn, Ta, and Pb) of proton and pion beams with momentum from ±3 to ±15 GeV/c.     

Measurement of (n,p) cross sections on isotopes of Cd,Sn and Te for 14 MeV neutrons

For several isotopes of Cd, Sn and Te, cross sections for the (n, p) process have been measured by activation relative to ²⁷Al(n, α)²⁴Na. As target materials, natural Cd, Sn and TeO₂ of high purity have been used. Measurements were carried out by γ-detection using a Ge(Li) detector. For measuring short-lived activities, a pneumatic tube system was used. The neutron energy was 14.6±0.2 MeV for all activations. The results obtained for the total (n, p) cross sections show decreasing values with increasing number of neutrons for a given proton number. This trend obviously follows the behaviour of the difference of the proton and neutron separation energies, determining the competition between proton and neutron emission.     

A dependence of the cross sections for the cumulative production of pions and protons in proton-nucleus and nucleus-nucleus interactions

The behavior of the inclusive cross sections for the cumulative production of π ^± mesons and protons in pA, DA, and ⁴HeA interactions is studied versus the atomic mass number of fragmenting nuclei. The primary-beam momenta were 4.5 GeV/c per nucleon. Secondary pions and protons were recorded with a fixed momentum of 0.5 GeV/c at an angle of 120°. Specifically, the experiment explored the fragmentation of D, He, ⁶Li, ⁷Li, C, Si, ⁵⁸Ni, ⁶⁴Ni, ⁶⁴Zn, ¹¹⁴Sn, ¹²⁴Sn, and Pb nuclei. The energy spectra of π ⁺ and π ^? mesons and protons with momenta in the range 0.3–0.7 GeV/c (the emission angle being 120°) were measured in an 8.9-GeV/c proton beam for Ni, Zn, and Sn isotopes. The special features in the behavior of the cross sections are found and discussed, and a comparison is drawn with the results of other studies.     

Formation of close-to-target products in reactions induced by <Superscript>12</Superscript>C ions on tin isotopes at the energy of 2.2 GeV per nucleon

Cross sections for charge-exchange reactions induced by the interaction between ¹²C ions of energy E_{¹² C} = 2.2E_{^{12} C} = 2.2 GeV per nucleon and tin targets enriched in the isotopes ^118,120,124Sn were measured by the induced-activity method. The cross sections for products whose charge numbers were in excess of the target charge number (Sb and Te) were determined. The shape of the isotope distribution of Sb products was indicative of the evaporative character of neutron emission in the formation of final-state products. The dependence of cross sections for charge-exchange reactions on the nucleonic composition of the target was considered. The contribution of electromagnetic excitation to the cross section for the reaction ¹²⁴Sn(¹²C, x)¹²⁴Sn was estimated.     

Study of the one-neutron transfer reactions induced by polarized 7Li ON 26Mg and 120Sn

Angular distributions of the cross sections and analyzing powers up to third rank have been measured for the one-neutron transfer reactions ²⁶Mg(⁷Li,⁶Li)²⁷Mg, ¹²⁰Sn(⁷Li,⁶Li)¹²¹Sn and ¹²⁰Sn(⁷Li, ⁸Li)¹²⁹Sn initiated by polarized ⁷Li ions of 44 MeV. Third-rank analyzing power has been measured for the first time in transfer reactions. Coupled-channels calculations in which the ground and first excited states of ⁷Li are coupled together by collective interactions and one-neutron transfers are calculated in exact finite range explain the experimental data for low-lying states in final nuclei. Extracted spectroscopic factors are in good agreement with those obtained from other one-neutron transfer reactions on the same targets.     

Sensitivity of cross sections for elastic nucleus-nucleus scattering to halo nucleus density distributions

In order to clear up the sensitivity of the nucleus-nucleus scattering to the nuclear matter distributions in exotic halo nuclei, we have calculated differential cross sections for elastic scattering of the ⁶He and ¹¹Li nuclei on several nuclear targets at the energy of 0.8 GeV/nucleon with different assumed nuclear density distributions in ⁶He and ¹¹Li.     

Fusion cross sections for 10,11B+12C at sub-Coulomb energies

Total fusion cross sections for the ¹⁰B + ¹²C and ¹¹B + ¹²C reactions have been determined over a 5 MeV (c.m.) energy range extending to ≈ 3 MeV below the Coulomb barrier. Absolute γ-ray yields for specific transitions in the de-excitation of the heavy products following compound nucleus decay were measured using a Ge(Li) detector. Statistical model calculations of the decay modes of the compound nucleus have been used to deduce, from the γ-ray data, cross sections for single proton, neutron and α-particle emission, and to determine total cross sections for compound nucleus formation. No evidence has been found for sub-Coulomb resonances in either reaction. The total reaction cross sections are compared with optical model calculations using different parameter sets and the observed trend in the very low energy cross sections is discussed relative to other reactions in the same mass region.     

Total charge-changing cross sections for neutron-deficient isotopes from58Ni fragmentation

At the projectile-fragment separator FRS of GSI, relativistic secondary beams of about 520 MeV/nucleon were produced by fragmentation of a primary beam of⁵⁸Ni at 650 MeV/nucleon in a beryllium target. By means of aΔE—Bρ—TOF measurement, the fragments have been identified and their charge-changing probabilities in targets of CH₂, C, Al, and Pb have been determined. We describe the results for the total charge-changing cross sections in this first paper, whereas a second article deals with the partial charge-changing cross sections. At the drip line, the measured charge-changing cross sections exhaust close to 100% of the total interaction cross sections as calculated with semiempirical models. The measurements at the proton drip line with low-Z targets indicate that only a very small increase of the cross sections may be observed, whereas the measurements with a lead target show that no significant increase of the total charge-changing cross sections is present which would be a hint for low-lying dipole strength. Our experimental data are compared to Glauber-type calculations.     

η production in nuclei by protons at Tp≦ 1 GeV

The reactionpA →η X has been measured on⁶Li, C and Cu targets at a proton energy of 0.9 GeV at the SATURNE accelerator. The doubly differential cross sections at T_p=0.9 GeV together with data at T_p=1 GeV, previously presented [1], are analysed in the frame of a recent folding model [3].     

Proton hole states excited by monoenergetic gamma quanta

Earlier work has shown how information about the giant dipole resonance and proton hole states can be inferred from high resolution photoproton spectra obtained in irradiation with the 17.62 MeV gamma quanta produced by the⁷Li(p, γ)⁸Be-reaction. To exploit this method the high energy photoproton spectra from⁴⁵Sc,⁵¹V,⁵⁹Co,⁵⁸Ni,⁶³Cu and natural nickel have been measured with 60–120 keV resolution. The absolute cross sections for transitions to levels in the daughter nucleus have been determined. The results are compared with a simple model assuming a semidirect reaction proceeding via a dipole doorway state. Good correlation is found between the cross sections and the spectroscopic factors measured in proton pick-up reactions. Comparison with the total photoproton cross section for⁵⁸Ni indicates, however, that the majority of protons are emitted at lower energies from more complicated states.     

Proton-hole states in Bi From the Po (t, α) reaction

The ²¹⁰Po(t, α)²⁰⁹Bi reaction has been studied at 20 MeV triton energy with an overall resolution of 20 keV FWHM. Absolute cross sections were established by a comparison of the (t, α) intensities to elastic triton scattering. The three lowest single-proton states in ²⁰⁹Bi were observed and spectroscopic factors were extracted from the measured cross sections by DWBA analysis. Starting at 2.43 MeV, six levels were strongly excited. These states have large 2p-1h proton components. The spectroscopic factors were extracted by a comparison of ²¹⁰Po(t, α) cross sections to ²⁰⁸Pb(t, α)²⁰⁷T1 single-proton-hole cross sections measured previously at the same bombarding energy. The observed states and their properties were analyzed within the framework of the particle- (or hole) vibration coupling model. Surface vibrational states in ²⁰⁸Pb coupled to single protons as well as the proton pair addition modes (states in ²¹⁰Po) coupled to a proton-hole were included in the analysis.     

Production of light nuclei in the reactions of protons with separated tin isotopes

The cross sections for the production of ⁷Be, ²²Na, ²⁴Na, ²⁸Mg, ³⁸S, ³⁸Cl, and ³⁹Cl nuclei from ¹¹²Sn, ¹¹⁸Sn, ¹²⁰Sn, and ¹²⁴Sn targets irradiated with 0.6-, 1.0-, and 8.1-GeV protons were measured by the method of induced activity. In analyzing resulting data, it was established that the above nuclei are produced in the fragmentation process and that the reaction cross section is a power-law function of the mass and charge numbers of fragmentation products. A strong dependence of the reaction cross section on the nucleonic composition of the targets and of the products is observed. The measured cross sections, together with data available in the literature, are discussed within various assumptions.     

Reaction spectroscopy with even tin isotopes

The two-particle transfer reactions ^{116, 118}Sn(t, p) and the inelastic scattering of 55 MeV protons from ¹¹⁶Sn and 16 MeV protons from ^{116, 118, 120}Sn are analysed for various transitions to collective and non-collective states in the final nucleus using DWBA. Form factors have been calculated with wave functions containing two-quasiparticle excitations of neutrons in open and closed shells as well as 1p-1h transitions from closed proton shells. In the inelastic scattering, generally a Serber-type Gaussian effective interaction was inserted. The results are compared with those obtained on the assumption of two-quasiparticle excitations in a restricted configuration space only. For both types of reaction, reasonable agreement with experimental data is obtained for the angular distribution. In the (t, p) reaction the measured and calculated relative cross sections agree within a factor of two. For the inelastic scattering, apart from relative cross sections the mass dependence of the collective excitations and the influence of four-quasiparticle excitations have been examined. The transition to the collective 2⁺ level in ¹¹⁶Sn was calculated with the proton component of the wave function corrected according to electromagnetic measurements. From inelastic scattering it follows that the transitions to negative-parity states especially are not described satisfactorily by the wave functions used. Cross sections for unobserved higher excited levels have been estimated.     

Measurements ofK-shell ionization with132Xe and208Pb projectiles in the energy range of 1.4–5.9 MeV/u

Projectile and targetK-shell ionization cross sections induced by 3.6-, 4.7-, and 5.9 MeV/u¹³²Xe ions and 1.4-, 3.6-, 4.7-, and 5.9 MeV/u²⁰⁸Pb ions from the UNILAC in thin solid targets between C and U are measured. The cross sections are discussed in terms of the molecular model of innershell vacancy production in heavy ion-atom collisions. The sharing of 2p _1/2σ vacancies between theK shells of the two collision partners in these very heavy ion-atom collisions is found to deviate from the Meyerhof-Demkov formula forR≦10^?2. The measured ionization cross sections are compared with theoretical calculations for 1sσ and 2p _1/2σ excitation cross sections. AZ _UA=Z₁+Z ₂ dependence is found independent ofZ ₁/Z ₂. Outer-shell vacancy configurations measured in these close encounters are reported.     

Sensitivity of reaction cross sections to halo nucleus density distributions

In order to clear up the sensitivity of the nucleus-nucleus reaction cross sections σ _R to the nuclear matter distributions in exotic halo nuclei, we have calculated the values of σ _R for scattering of ⁶He, ¹¹Li, and ¹⁹C nuclei on several nuclear targets at the energy of 0.8 GeV/nucleon. The calculations were performed in the “rigid target” approximation to the Glauber theory, different shapes of the nuclear density distributions in ⁶He, ¹¹Li, and ¹⁹C being assumed.