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Absolute differential cross sections for elastic p 4 He, p 6 He and p 8 He small-angle scattering were measured in inverse kinematics with secondary 4,6,8 He-beams at an energy near 0.7 GeV / u. The experiment was performed using beams from the heavy-ion synchrotron SIS and the fragment separator FRS of GSI Darmstadt. The hydrogen-filled ionization chamber IKAR served simultaneously as a gas target and a detector for the recoil protons. Projectile scattering angles were measured with multi-wire tracking detectors. For proton scattering from the neutron-rich isotopes 6 He and 8 He, differential elastic-scattering cross sections d σ/ d t were deduced in the range 0.002⩽|t|⩽0.05 (GeV /c ) 2 of the four-momentum transfer squared t . For elastic p 4 He scattering, the data obtained in the t -range 0.002⩽|t|⩽0.02 (GeV /c ) 2 supplement the results from an earlier work performed in direct kinematics. From the differential cross sections the integral elastic-scattering cross sections σ el , the total cross sections σ tot , and the total reaction cross sections σ r for the proton–nucleus strong interaction were evaluated. The data obtained on d σ/ d t allow the radial matter distributions in the 6 He and 8 He nuclei to be determined and the corresponding root-mean-square matter radii to be deduced.

A Glauber based analysis of the experimental cross sections for small-angle elastic p 6,8He scattering at 0.7 GeV has been performed. The radii and radial shape of the 6He and 8He nuclei have been determined using phenomenological nuclear density distributions with two free parameters. The deduced shapes of the 6He and 8He nuclear matter radial distributions conform with the concept that both nuclei consist of an α-particle core and a significant neutron halo. The accuracy of the theoretical analysis of the elastic-scattering cross-section data is discussed, and possible sources of systematic uncertainty related to some basic limitations in the applied method are outlined. The experimental p 6,8He elastic-scattering cross sections have also been utilized for probing the matter density distributions resulting from various nuclear microscopic models. Besides, the sensitivity of the total p 6,8He reaction cross sections to the size of the 6He and 8He nuclei has been considered.

The charge-exchange contribution can dominate the energy-loss straggling of partially stripped heavy ions depending on the charge-changing cross sections and the partial stopping powers. We have studied the energy-loss straggling of few-electron uranium ions in different solids in the energy range of (200–1000) MeV/u. Our experimental data are compared with a new model taking into account realistic screening for relativistic scattering of target electrons at close impacts to derive partial stopping powers. Screening of the projectile nucleus by inner-shell electrons reduces the charge-exchange straggling compared to that pertaining to a point-like charge distribution.

A novel method for direct, high precision mass measurements of relativistic exotic nuclei has been successfully applied in the storage ring ESR at GSI. The nuclei of interest were produced by projectile fragmentation of 930 MeV / u bismuth ions, separated in-flight by the fragment separator FRS, stored and cooled in the ESR. The mass values have been deduced from the revolution frequencies of the coasting cooled ions. We have measured 104 new mass values with a precision of about 100 keV and a resolving power of 3.5×10 5 for the neutron-deficient isotopes of the elements 57≤Z≤84 . This paper presents the experimental method, the mass evaluation and a table of the experimental mass values.

mitted along a ^110& axis of a 120-mm-thick Si crystal. The emerging charge state distribution FC(qout) for well-channeled ions is governed mainly by electron impact ionization ~EII!. The corresponding EII cross sections were obtained by fitting the experimental FC(qout) with Monte Carlo simulations. For M shell ionization, they were found to be twice larger than those given by the binary encounter dipole approximation. The measured energy loss spectra were also compared to Monte Carlo simulations. The mean values and widths of these spectra increase with qout , reflecting the increase of the stopping power S with increasing transverse energy E’ . The measured stopping for channeled ions with frozen charge state 731 and for nonchanneled ions with charge state close to 901 is in good agreement with theoretical estimates. Owing to the very high ion velocity, there is a significant contribution (25%) to the stopping from Si-L shell excitation even for the best channeled ions. The width and the asymmetrical shape ~skewness m) of the energy-loss spectra depend strongly on qout(m.0 for very well-channeled ions, m,0 for poorly channeled ions!. For well-channeled ions, energy-loss spectra were reproduced by Monte Carlo simulations with the S(E’) curve extracted from fitting the mean energy losses. @S1050-2947~99!01604-2#

The effective root-mean-square ( rms ) matter radii of A Na ( A =20–23,25–32) were deduced from the measured interaction cross sections by a Glauber-type calculation. The presence of a neutron skin is suggested for neutron-rich Na isotopes. An application to the nuclear equation of state (EOS) is discussed.

Recent results of mass measurements of exotic heavy nuclei using Schottky mass spectrometry are reported. The investigated nuclei were produced and separated by the fragment separator FRS, injected, stored and cooled in the experimental storage ring ESR. Their masses were determined from the frequency analysis of the beam noise. In the present experiment the masses of more than 150 proton-rich nuclei in the mass region A ∼- 200 have been determined for the first time. Representative results are given for proton-separation energies and shell corrections. For some elements the proton drip line can be determined.

The effective root-mean-square (rms) matter radii of ANa (A = 20–23, 25–32) and AMg (A = 20, 22, 23, 27, 29–32) have been deduced from the measured interaction cross sections using a Glauber-type calculation. It was found that the increase of rms matter radii in Na isotopes is primarily a consequence of the increase of rms neutron radii. A correlation between the radii, corrected for quadrupole deformation, and the Fermi-energy difference was observed for both Na and Mg isotopes. This correlation can be explained by a model that assumes the valence nucleons are responsible for the changes in nuclear radii. The presence of a neutron skin is suggested for neutron-rich Na and Mg isotopes. An application to the nuclear equation of state (EOS) is discussed.

High-precision mass measurements of proton-rich isotopes in the range of 60{le}Z{le}84 were performed using the novel technique of Schottky spectrometry. Projectile fragments produced by {sup 209}Bi ions at 930{ital A} MeV were separated with the magnetic spectrometer FRS and stored and cooled in the experimental storage ring (ESR). A typical mass resolving power of 350000 and a precision of 100keV were achieved in the region A{approx}200 . Masses of members of {alpha} chains linked by precise Q{sub {alpha}} values but not yet connected to the known masses were determined. In this way it is concluded that {sup 201}Fr and {sup 197}At are proton unbound. {copyright} {ital 1997} {ital The American Physical Society}

The interaction cross sections (σI) of ANa (A = 20–23, 25–32) and AMg (A = 20, 22–25, 27, 29–33) on carbon target have been measured at a beam energy of around 950 A MeV. The effective root-mean-square matter radii of these isotopes were deduced from σI by a Glauber-type calculation. Combining the isotope-shift data with the present Na data the radii of neutrons have been compared with those of protons for the first time along a chain of stable and unstable isotopes. A monotonic increase in the neutron skin thickness has been observed as the neutron number increases in Na isotopes. The Mg data are also consistent with the claim that the formation of a neutron/proton skin is a universal feature in β-unstable nuclei.

Differential cross sections for p- ${}^{6}\mathrm{He}$ and p- ${}^{8}\mathrm{He}$ elastic scattering have been measured in inverse kinematics at small momentum transfers up to $|t|\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.05(\mathrm{GeV}/c{)}^{2}$ and projectile energies of about 700 MeV/nucleon. Nuclear matter densities deduced from the data are consistent with the concept that ${}^{6}\mathrm{He}$ and ${}^{8}\mathrm{He}$ nuclei have an $\ensuremath{\alpha}$-like core and a significant neutron skin. The rms radii of the nuclear matter distributions were determined to be ${R}_{m}$ ${(}^{6}\mathrm{He})\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}2.30\ifmmode\pm\else\textpm\fi{}0.07\mathrm{fm}$ and ${R}_{m}$ ${(}^{8}\mathrm{He})\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}2.45\ifmmode\pm\else\textpm\fi{}0.07\mathrm{fm}$.

Energy-loss straggling measurements performed at the high-momentum-resolution magnetic spectrometer fragment separator with bare and highly charged {sub 8}O, {sub 54}Xe, {sub 79}Au, and {sub 92}U ions with specific kinetic energies (700{endash}1000)MeV/u are reported. The results are in good agreement with rigorous calculations recently reported by Lindhard and So/rensen and reveal systematic deviations from the well-known relativistic Bohr formula, which was obtained within the framework of the first-order Born approximation. {copyright} {ital 1996 The American Physical Society.}

High-energy interaction cross sections of A = 20 nuclei (20N, 20O, 20F, 20Ne, 20Na, 20Mg) on carbon were measured with accuracies of ≈ 1%. The nuclear matter r.m.s. radii derived from the measured cross sections show an irregular dependence on isospin projection. The largest difference in radii, which amounts to approximately 0.2 fm, has been obtained for the mirror nuclei 20O and 20Mg. The influence of nuclear deformation and binding energy on the radii is discussed. By evaluating the difference in r.m.s. radii of neutron and proton distributions, evidence has been found for the existence of a proton skin for 20Mg and of a neutron skin for 20N.

As part of a comprehensive study of uranium fragmentation at relativistic energies at the GSI projectile fragment separator, FRS, inclusive neutron-removal cross sections have been measured for several xn channels at projectile energies of 600 and 950 A MeV. The electromagnetic cross sections agree surprisingly well with a semiclassical calculation based on measured photonuclear cross sections and do not require an extra enhancement of the two-phonon giant dipole excitation as concluded from similar measurements with 197Au.

A possibility of using the Cherenkov technique to measure the average energy of collimated relativistic nuclear 79Au beams is investigated in the article for specific beam—radiator interaction (strong deceleration, fragmentation) produces a considerable effect of the spreading of the Cherenkov one. Two Cherenkov methods — achromatic (E, α) and combined (“combi”) — were employed for this purpose. At an energy about 1 GeV/u the accuracy of measurement by the “combi” method was ± 1.4 MeV/u. The accuracy of measurement by the (E, α) method was ±0.9 MeV/u at the energy EAu≈640 MeV/u. These results turned out to be in good agreement with initial EAu0 data from the SIS accelerator with allowances made for energy losses over the beam line (the maximum discrepancy was ≤0.4%). With all the set of these data, the direction condition was for the first time checked for VChR from heavy nuclei. It is shown to be fulfilled to an accuracy above ±5′ in the angle range 27°

The interaction cross sections $({\ensuremath{\sigma}}_{I})$ of ${}^{A}\mathrm{Na}$ isotopes $(A\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}20--23,25--32)$ on a carbon target have been measured at $950A\mathrm{MeV}$. The effective root-mean-square matter radii of these isotopes were deduced from ${\ensuremath{\sigma}}_{I}$ by a Glauber-type calculation. By combining the isotope-shift data with the present data the radii of neutrons have been compared with those of protons for the first time along a chain of stable and unstable isotopes. A monotonic increase in the neutron skin thickness has been observed as the neutron number increases in Na isotopes.

Resonant transfer and excitation in highly charged uranium ions has been investigated by applying the X-ray/particle coincidence technique. This complete detection method for the RTE process in combination with the large L-shell fine structure splitting in uranium allows, for the first time, an L-subshell differential as well as angular differential study of the excitation and radiative stabilization of different intermediate electronic states. Measured L-subshell differential cross sections for the KLL-RTE in U 90+ →C collisions compare well with full relativistic calculations. For the radiative stabilization of the KL 1 2 L 3 2 intermediate states a significant anisotropy was found.

As part of a comprehensive study of uranium fragmentation at relativistic energies at the GSI projectile fragment separator, FRS, inclusive neutron-removal cross sections have been measured for severalxn channels at projectile energies of 600 and 950A MeV using targets of Al, Cu and Pb. The variation of the experimental cross sections with target nuclear charge is used to disentangle nuclear and electromagnetic contributions. The electromagnetic cross sections agree surprisingly well with a simple harmonic oscillator calculation of giant dipole resonances based on measured photonuclear cross sections and do not require an extra enhancement of the two-phonon giant dipole excitation as concluded from similar measurements with197Au.

Resonant transfer and excitation (RTE) followed by X-ray emission in highly charged uranium ions colliding with carbon atoms has been investigated by applying the X-ray-particle-coincidence technique. This renders possible a subshell differential investigation of the population and radiative stabilization of different excited intermediate states. Preliminary results for the measured RTE excitation function for U 90+ → C collisions are presented.

Total cross sections for radiative double electron capture (RDEC) in collisions of fast highly charged ions with light target atoms were estimated. The applied method is based on the principle of detailed balance using the cross sections for the double photoionization process. Preliminary results of a dedicated RDEC experiment aiming at the observation of photons with twice the single REC photon energy, associated with double charge exchange, are discussed. Additionally, results of complementary measurements of double capture (without photon registration) by fully stripped U ions in collisions with C atoms at 295 MeV/u are presented. Here, a surprisingly enhanced cross section for double electron capture is found in accordance with observations reported in the literature.

Nuclear matter distributions of the neutron-rich nuclei 6 He and 8 He were studied via proton-nucleus scattering in inverse kinematics using the recoil detector IKAR. The differential cross sections for p 4 He and p 8 He elastic scattering were measured with un uncertainty of ±2% for the absolute normalization for proton recoil energies from 1 to 20 MeV. The experimental techniques and the data analysis are described and first Glauber calculations presented. Data analysis is still in progress so only preliminary results are given.

In the fragmentation of 500 MeV/u46Ti the spin alignment of43mSc (I=19/2−, T1/2=473 ns) fragments was observed by the Time Dependent Perturbed Angular Distribution (TDPAD) method. The measurement was performed for different cuts in the longitudinal momentum distribution. A positive spin alignment of about 35% was observed in the center and a negative alignment of about 15% in the wing of the distribution. For the different cuts the relative production of the 19/2− state was measured. In the wing of the distribution the isomeric ratio N(19/2−)/total43Sc is about 15 times larger than in the center. The results of this pilot experiment are discussed in the frame of a shell-model.

The SIS accelerator facilities at GSI in combination with a magnetic spectrometer allow the direct measurement of stopping powers for relativistic heavy ions up to uranium with high precision for the first time. Here, we report our representative results obtained for projectiles up to xenon in the energy range from 700 to 1000 MeV/u. Systematic deviations from the Bethe stopping-power theory are observed, whereas the data are in good agreement with theory once Mott and Bloch corrections and the Fermi density effect are included.

Relativistic heavy-ion collisions of few-electron projectiles ranging from argon up to uranium have been investigated in solid and gaseous media. Electron-loss and electron-capture cross sections, charge-state distributions, as well as energy loss and energy deposition have been measured and are compared with theoretical predictions. Especially fully-ionized heavy projectiles represent a unique possibility to test atomic-collision theories.

Low-energy fission of neutron-deficient actinium, thorium, protactinium and uranium isotopes has been investigated using a new experimental technique. The isotopes were produced as secondary beams by projectile fragmentation from a 950 A MeV 238U primary beam. Their fission was induced by electromagnetic excitation and nuclear reactions in a lead and in a plastic target at energies between 510 A MeV and 150 A MeV. The transition from symmetric fission is shown to take place around N = 138.

To determine the behaviour of time-of-flight mass analyzers containing rotationally symmetric electrostatic lenses and mirrors, transfer matrices up to third and fifth order have been determined. For this purpose the distribution of the electrostatic potential is calculated from the geometry and the potentials of the electrodes and a reference particle is traced through this distribution using differential algebra. By varying some parameters specific elements of the transfer matrix or of combinations thereof can be minimized by numerical multiparameter fits thus obtaining for instance energy-independent transversal and/or longitudinal focusing to first and/or second order.

Using the method of surface charges, the fringing field of electrostatic quadrupole lenses is investigated and the result is compared to measured field maps of magnetic quadrupoles of low flux densities. For different field clamp geometries third-order fringing-field integrals are calculated.

Production cross sections of more than 270 isotopes ranging from Z = 59 to Z = 82 were measured in the reaction 208Pb(1 GeV A)+Cu. The method of identifying the projectile fragments and evaluating the production cross sections is described. The experimental data are compared with a modern version of the abrasion-ablation model and with the empirical parameterization EPAX. Apart from deviations in the details they both show an overall good agreement. The cross sections of those fragments which are produced by the removal of protons only test the lower part of the excitation energy distribution. For the first time, the four-proton removal channel could be observed.

Break-up of secondary Li-11 ion beams (280 MeV/nucleon) on C and Pb targets into Li-9 and neutrons is studied experimentally. Cross sections and neutron multiplicity distributions are obtained, characterizing different reaction mechanisms. Invariant-mass spectroscopy for Li-11 and Li-10 is performed. The E1 strength distribution, deduced from electromagnetic excitation of Li-11 up to an excitation energy of 4 MeV comprises similar to 8% of the Thomas-Reiche-Kuhn energy-weighted sumrule strength. Two low-lying resonance-like structures are observed for Li-10 at decay energies of 0.21(5) and 0.62(10) MeV, the former one carrying 26(10)% of the strength and likely to be associated with an s-wave neutron decay. A strong di-neutron correlation in Li-11 can be discarded. Calculations in a quasi-particle RPA approach are compared with the experimental results for Li-10 and Li-11. (C) 1997 Elsevier Science B.V.

Neutron and He-6 momentum distributions from He-8 break-up reactions in a C target have been measured at 240 MeV/u. The two-neutron removal cross section was found to be sigma(-2n) = 0.27 +/- 0.03 b. The nature of the momentum distributions is interpreted in some simple reaction scenarios.

Secondary beams from fragmentation of $^{58}\mathrm{Ni}$ have been produced with energies of $(200\ensuremath{-}220)A$ MeV, separated with a fragment separator and injected into a storage-cooler ring for half-life measurements. The relative momentum spread $\frac{\ensuremath{\Delta}p}{p}\ensuremath{\approx}1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$ (FWHM) which we achieved allowed us to resolve the ground and isomeric states of cooled $^{52}\mathrm{Mn}$ and $^{53}\mathrm{Fe}$ nuclei in the measured mass spectra. The circulating beams were fully ionized, which rendered it possible to measure pure ${\ensuremath{\beta}}^{+}$ branches for $^{52g}\mathrm{Fe}$ and $^{53g}\mathrm{Fe}$ and the sum of pure ${\ensuremath{\beta}}^{+}$ and $\ensuremath{\gamma}$ branches in the decay of the isomers $^{52m}\mathrm{Mn}$ and $^{53m}\mathrm{Fe}$.

7 pages, 3 figures, 1 table., Transverse and longitudinal momentum distributions of 9Li fragments from 11Li break-up reactions in C, Al and Pb targets have been measured at 280 MeV/u. The two-neutron removal cross-section was measured to be σ(−2n) = 0.26 ± 0.02 b for the carbon target, σ(−2n) = 0.47 ± 0.08 b for the aluminum target and σ(−2n) = 1.9 ± 0.4 b for the lead target. No significant difference is observed between the narrow widths (FWHM ≈ 47 MeV/c) of the transverse and longitudinal momentum distributions of the 9Li fragments. The physical implications of this are discussed., This work was supported by the German Federal Minister for Research and Technology (BMFT) under Contracts 06 DA 641 I, 06 BO 103 and 06 MZ 106 and by GSI via Hochschulzusammenarbeitsvereinbarungen under Contracts DA RICK, BO FRE, F ELE, Mz KRD and partly supported by the Polish Committee of Scientific Research under Contract PB 1158/P3/92/02 and CICYT under contract AEN92-078%CO2-02 (MJGB).

Neutron angular distributions from violent break-up reactions of Li-11 and Be-11 have been measured at 28 MeV/u and 280 MeV/u and at 41 MeV/u and 460 MeV/u, respectively. The derived neutron momentum distributions show a narrow component in transverse momentum that is within uncertainties independent of beam energy and target charge. This component is suggested to be simply related to the momentum distribution of the loosely bound halo neutron(s) in the projectiles.

The projectile fragmentation in peripheral nuclear collisions was studied using ≈ 1 GeV·A of 208 Pb and 238 U from the SIS at GSI, impinging on a copper target. Lead and thallium isotopes from the fragmentation of 208 Pb as well as uranium and protactinium isotopes from 238 U, were selected by the fragment separator FRS. In contrast to the fragmentation of 208 Pb, the cross sections for the production of heavy fragments from 238 U are strongly reduced by fission. The measured isotopic yields may be explained quantitatively by calculations in the framework of the abrasion-ablation model, if fission is allowed to compete with particle evaporation in the deexcitation of the prefragments.

The photon angular distributions for radiative electron capture (REC) into the $j=\frac{1}{2}$ and $j=\frac{3}{2}$ $L$ subshell levels were measured and calculated for ${\mathrm{U}}^{90+}$ \ensuremath{\rightarrow} C collisions at 89 MeV/u. The experiment provides the first study of the photon angular distribution of REC into a projectile $p$ state ($j=\frac{3}{2}$) which was found to exhibit a slight backward peaking in the laboratory frame. For radiative capture to the $j=\frac{1}{2}$ states, the measured angular distribution deviates considerably from symmetry around 90\ifmmode^\circ\else\textdegree\fi{}. The results demonstrate that the usual ${sin}^{2}{\ensuremath{\theta}}_{\mathrm{lab}}$ distribution is not valid in the high-$Z$ regime.

The longitudinal momentum distribution of7Be was measured after the break-up reaction of8B in C, Al, and Pb targets at 1471 A·MeV. We observed a narrow distribution with a FWHM of (81±6) MeV/c in all targets. The experimental results indicate an extended spatial distribution of the loosely bound proton in8B, and agree with QRPA calculations.

Schottky mass spectrometry is a novel method of precision nuclear mass spectrometry based on the measurement of the revolution frequencies of ions in a storage ring. The measurements are performed by non-destructive detection and frequency analysis of the beam noise, the well-established Schottky diagnosis technique. Schottky mass spectrometry was applied for the first time at the Experimental Storage Ring ESR at GSI using electron-cooled, highly charged (mainly bare, H- and He-like) heavy ions at relativistic energies of up to 370 MeV/u. The performance of the method at the ESR is shortly reviewed and an overview of the results from our first mass measurements of radioactive neutron-deficient gold and bismuth fragments is given. Relative accuracies down to 3 × 10 −7 were achieved for the measured masses, corresponding to absolute uncertainties of 50 to 150 keV/ c 2 for these heavy isotopes (135 ≤ A ≤ 209). The typical mass resolving power of about 350 000 allows even the resolution of isomeric from ground state masses in some cases. Due to the required cooling time, the method is applicable, so far, to nuclei with half-lives of at least a few seconds.

In recent experiments using the FRS-ESR facilities at GSI we have measured the masses of 225 proton-rich nuclei in the range of 135≤A≤209. Applying the new technique of Schottky-Mass Spectrometry an accuracy of about 100 keV and a resolving power of 4 · 10 5 was achieved. Masses for cooled projectile fragments with half-lives larger than a few seconds were determined by their revolution frequencies in the ESR. Reliable predictions for the proton-drip line can be made for elements from bismuth to protactinium using the precisely measured Q α -values from literature and our new mass values for the isotopes at the ends of the corresponding α-chains.

We plan to measure masses of very shortlived exotic nuclei far from β-stability by using the Experimental Storage Ring (ESR) of the GSI as an energy isochronous Time-of-Flight (TOF) mass-spectrometer which requires a special ion-optical setting of the quadrupoles in the ESR. Via projectile fragmentation a large variety of exotic nuclei can be produced. which can be separated in flight by the Fragment Separator (FRS) prior to being injected into the ESR. A special time-pick-off-detector has been developed, which uses secondary electron emission from a thin foil, which is penetrated by the ions under investigation. This detector has been designed for use in the ESR-vacuum of 10 −11 mbar and has an intrinsic time-resolution of ≈ 85ps. Also a Time Recording System (TRS) with a time-jitter of only ≈ 50ps has been build. The TRS is capable of recording time-marks for a few ions over a large number (> 500) of turns.