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The nuclear periphery was studied by using antiprotons. Two experimental methods were applied: analysis of the antiproton annihilation residues one mass unit lighter than the target mass by nuclear spectroscopy and the measurement of strong interaction effects on antiprotonic level widths and shifts. 26 isotopes from a wide range of mass numbers (40

Fusion barrier distributions for the 20 Ne + 112,116,118 Sn systems have been extracted from quasi-elastic scattering cross sections measured at the Warsaw HIL Cyclotron. Results are compared to coupled-channels calculations performed with the CCFULL code. The overall widths of the distributions are reproduced on taking account of the low-lying collective states of the target and projectile but some puzzling discrepancies in their shapes remain to be explained.

The nuclear capture of antiprotons from atomic states is studied. New measurements of level shifts and widths of deuterium are analysed and compared with similar results obtained in heavy nuclei. Some properties of antiproton nucleus interactions are outlined, a comparison of cold and total capture modes is done.

Two different methods were employed by the collaboration PS209 at LEAR (CERN) to investigate the nucleon density at the outer nuclear periphery. The first one was the comparison of the yield of (N − 1) nuclei and (Z − 1) nuclei produced by antiproton annihilation on a nucleus with mass number A (here N and Z denote the neutron and proton number of the nucleus, respectively); the second one is the measurement of widths and shifts of the last observable transitions in antiprotonic atoms. Earlier studies of (A−1) production were extended by measurements of short-lived isotopes (lifetimes down to a few seconds). More than thirty widths and twenty shifts were extracted from the antiprotonic x-ray data. The results fit nicely into the systematics established recently by C.J. Batty, E. Friedman, and A. Gal [Nucl. Phys. A592, 487 (1995)]. Pronounced isotope effects were found for some of the investigated elements.

The antiprotonic x-ray cascade in ${}^{172}\mathrm{Yb}$ and ${}^{176}\mathrm{Yb}$ was studied and the widths and shifts of the levels which are affected by the strong interaction were deduced. A large number of transitions up to $\ensuremath{\Delta}n=5$ could be observed. This opened the possibility to determine for the first time also the widths of noncircular orbits. In ${}^{172}\mathrm{Yb}$ and ${}^{176}\mathrm{Yb}$ four level shifts and seven level widths were measured in each case. The widths are slightly increasing from ${}^{172}\mathrm{Yb}$ to ${}^{176}\mathrm{Yb}$ whereas the shifts stay roughly constant. The experimental intensities of the transitions are compared with results from calculations of the antiproton cascade. Using a Fermi distribution for the nucleon densities the neutron diffuseness parameter was deduced to be for ${}^{172}\mathrm{Yb} (0.58\ifmmode\pm\else\textpm\fi{}0.04) \mathrm{fm}$ larger than the proton diffuseness parameter. For ${}^{176}\mathrm{Yb}$ this value is $(0.71\ifmmode\pm\else\textpm\fi{}0.04) \mathrm{fm}.$

Nuclear periphery was studied using antiprotons. Two experimental methods were applied: analysis of the antiproton annihilation residues one mass unit lighter than the target mass by nuclear spectroscopy and the measurement of strong interaction effects on antiprotonic X-rays. Isotopes from a wide range of mass number (40

We demonstrate a new method for the investigation of the neutron to proton density ratio at the nuclear surface. The method relies on the radiochemical determination of some residual nuclei after the annihilation of stopped antiprotons. A clear neutron halo effect has been observed with the 232 Th target.

Antiprotonic X rays were used to investigate the nuclear matter densities. Neutron densities in 26 isotopes were determined using this method. The information on the nuclear matter density at relatively large radii was then converted to rms radii by the use of a two‐parameter Fermi‐function profile. The obtained systematics of differences of the neutron and proton rms radii is in a fair agreement with theoretical calculations and results of other experimental methods.

Using the Warsaw cyclotron beam we have determined barrier distributions from the quasielastic scattering of ${}^{16}\mathrm{O}$ on ${}^{116,119}\mathrm{Sn}$ targets. They turned out to be similar in both systems. To improve the signal/noise ratio, digital filters were applied in the data analysis procedure and are discussed in detail. Experimental results were compared with coupled-channels calculations performed using the FRESCO code. Reasonable agreement between experiment and theory was obtained but some disagreements remain.

Two kinds of experiments using an antiproton beam were performed to investigate the nuclear periphery: the on-line measurement of antiprotonic X-rays and the off-line determination of the yield of annihilation products with mass number one unit smaller than the target mass. The neutron-to-proton density ratios as well as the differences of root-mean-square (rms) radii of neutron and proton distributions were determined for a number of stable isotopes. To this end both the neutron and the proton density distributions were assumed to have the form of a two-parameter Fermi distribution. The differences of rms radii are caused mostly by an increase in the neutron diffuseness and not in half-density radius. The results agree with corresponding data derived by other methods and with theoretical predictions.

The differences between neutron and proton density distributions at large nuclear radii in stable nuclei were determined. Two experimental methods were applied: nuclear spectroscopy analysis of the antiproton annihilation residues one mass unit lighter than the target mass and the measurements of strong-interaction effects on antiprotonic x rays. Assuming the validity of two-parameter Fermi neutron and proton distributions at these large radii, the conclusions are that the two experiments are consistent with each other and that for neutron rich nuclei it is mostly the neutron diffuseness which increases and not the half-density radius. The obtained neutron and proton rms radii differences are in agreement with previous results.

The importance of geometrical effects in the A dependence of many observables regarding antiproton annihilation on nuclei is expected on theoretical grounds. The cases of the charged pion multiplicity and of the frequency of the so-called single nucleon events are examined. In the first case, the respective roles of surface diffuseness, partial nuclear opacity, and pion absorption mechanism are examined. The possibility of extracting from comparison with experiment the average location of the annihilation site is critically discussed. The obtained values are in agreement with current theoretical estimates.

The neutron-to-proton density ratio at the nuclear periphery was determined for six targets from the yield of nuclei with mass ${(A}_{t}\ensuremath{-}1)$ generated by antiproton annihilation on targets with mass number ${A}_{t}.$ A new setup allowed us to measure this yield for nuclei with half-lives down to 6 s. The experiment confirmed the negative correlation between the peripheral neutron-to-proton density ratio and the neutron binding energy, which had been previously found. Results of Hartree-Fock-Bogoliubov and relativistic Hartree-Bogoliubov calculations show good agreement for a large number of nuclei. By comparing the measured values with those derived from Hartree-Fock-Bogoliubov calculations, the ratio R of the imaginary parts of the effective scattering lengths of antiprotons on bound neutrons and protons was deduced to be $\mathcal{R}=0.69(4).$ For the first time yields of several excited states of some ${(A}_{t}\ensuremath{-}1)$ nuclei have been investigated.

Thirteen targets with mass numbers from 58 to 238 were irradiated with the antiproton beam from the Low Energy Antiproton Ring facility at CERN leading to the formation of antiprotonic atoms of these heavy elements. The antiproton capture at the end of an atomic cascade results in the production of more or less excited residual nuclei. The targets were selected with the criterion that both reaction products with one nucleon less than the proton and neutron number of the target be radioactive. The yield of these radioactive products after stopped-antiproton annihilation was determined using gamma-ray spectroscopy techniques. This yield is related to the proton and neutron density in the target nucleus at a radial distance corresponding to the antiproton annihilation site. The experimental data clearly indicate the existence of a neutron-rich nuclear periphery, a "neutron halo", strongly correlated with the target neutron separation energy Bn and observed for targets with Bn < 10 MeV. For two-target nuclei 106Cd and 144Sm, with larger neutron binding energies, a proton-rich nuclear periphery was observed. Most of the experimental data are in reasonable agreement with calculations based on current antiproton-nucleus and pion-nucleus interaction potentials and on nuclear densities deduced with the help of the Hartree-Fock-Bogoliubov approach. This approach was, however, unable to account for the 106Cd and 144Sm results., Latex (RevTeX,aps style), 13 pages + 12 Postscript figures

Some results inferred from a program devoted to the study of the nuclear periphery using antiprotonic atoms are presented.

A new method to study the nuclear periphery using antiproton annihilation was applied to nine isotopes with mass numbers between 58 and 238. The method makes use of the detection of the radioactive annihilation products one unit lower in mass number than the target. A clear neutron halo effect, strongly correlated with the neutron binding energy, was observed in some nuclei. The experimental results are in qualitative agreement with calculations of proton and neutron densities at the nuclear periphery based on either a simple asymptotic density model or a more complex Hartree-Fock approach.

The search for and study of high spin isomers produced by 12C, 14N and 16O induced reactions on targets close to N = 82 has been performed. The observed isomers were identified unambiguously by a detailed study of the excitation functions, delayed gamma-ray multiplicity and multiparametric gamma-gamma coincidences. The isomers with the highest spin above the ground state were observed in 152Er and 151Ho nuclei.

The average transferred linear momentum in nuclear reactions induced by 3 He, 4 He, 14 N, and 20 Ne projectiles on Co, Cu and Ag targets was determined by thick-target-thick-catcher recoil range techniques for bombarding energies between 10 A MeV and 90 A MeV. A comparison with results obtained from fission fragment angular correlations indicates a strong target mass dependence of the linear momentum transfer.

Level properties of 185Ir were investigated by in-beam γ-spectroscopy using (α, 4n) and (α, 6n) reactions with E, ranging from 41 to 77 MeV. A well-developed system of levels built on the h 9 2 Subshell is excited. A band built on the 11 2 − isomeric state is also observed. In distinction from heavier Ir isotopes, only a single positive parity band is developed to high-spin states. Two isomers with T 1 2 = 120 ns and 40 ns are found for excitation energies above 2.2 MeV. The experimental results are discussed in terms of rotational models including the Coriolis coupling and providing for a stable triaxial shape of the 185Ir nucleus.

Excitation functions and projected recoil ranges for radioactive nuclei produced in the /sup 6/Li bombardment of /sup 54/Fe an /sup 56/Fe targets over 10 to 100 MeV energy range have been measured using the activation technique. At 55 and 85 MeV differential ranges have also been measured for the /sup 56/Fe target. Using the in-beam gamma-ray technique production cross sections for many residual nuclei were measured for the /sup 6/Li + /sup 56/Fe system for a /sup 6/Li energy range of 55 to 94 MeV. Close to 90% of the optical model reaction cross section is observed over the entire energy range. About 80% of the observed cross section corresponds to statistical evaporation of the compound nucleus. Above about 30 MeV /sup 6/Li energy /sup 56/Fe(/sup 6/Li,..cap alpha..)/sup 58/Co* transfer process can explain the observed behavior of recoil ranges. It contributes about 300 mb to the production of various nuclei reached through evaporation decay of /sup 58/Co*. Pre-equilibrium nucleon emission appears to be noticeable above 60 MeV and contributes 100 mb to the production process at 80 MeV. A reasonable account of the observed cross section for various product nuclei is given by the predictions of the fusion-evaporation model. Inmore » its fusion characteristics /sup 6/Li projectile appears to behave very much like other light heavy ions.« less

The lifetime of the first excited state in Ir 189 was determined by the time-to-pulse-height conversion technique to be 12.5±1.0 ns. The B (M1) and B (E2) values were compared with those for similar transitions in other Ir and Au isotopes. The experimental data are consistent with the supposition that the main part of the wave function of the first excited state of these nuclei has a collective character.

Short-lived isotopes of argon, krypton, silver, cadmium, tin, iodine, xenon, platinum, gold, mercury, polonium, radon and francium have been studied by the on-line isotope separator technique. Nuclear decey data are presented.

An enriched 192Os target was bombarded with protons of energy 12 to 24 MeV and deuterons of energy 19 to 28 MeV. The levels characteristics of the transitional 191Ir nucleus were investigated. Both positive and negative parity level systems observed in this nucleus show a close similarity to those observed in lighter Ir isotopes. The description of the positive parity states in terms of the Nilsson model with the Coriolis coupling and the h 11 2 system in terms of a model assuming the coupling of the odd nucleon to the rigid triaxial core are discussed. A 5.5±0.7 s isomer with excitation energy exceeding 2 MeV was identified.

A natural gold target was irradiated with the antiproton beam from the Low Energy Antiproton Ring at CERN. Antiprotons of 200 MeV/c momentum were stopped in a thick target, products of their annihilations on Au nuclei were detected using the off-line gamma-ray spectroscopy method. In total, yields for 114 residual nuclei were determined, providing a data set to deduce the complete mass and charge distribution of all products with A > 20 from a fitting procedure. The contribution of evaporation and fission decay modes to the total reaction cross section as well as the mean mass loss were estimated. The fission probability for Au absorbing antiprotons at rest was determined to be equal to (3.8+-0.5)%, in good agreement with an estimation derived using other techniques. The mass-charge yield distribution was compared with the results obtained for proton and pion induced gold fragmentation. On the average, the energy released in pbar annihilation is similar to that introduced by ~ 1 GeV protons. However, compared to proton bombardment products, the yield distribution of antiproton absorption residues in the N-Z plane is clearly distinct. The data for antiprotons exhibit also a substantial influence of odd-even and shell effects., 14 pages, 9 figures, Revtex 4, to be published in Physical Review C

The x-ray cascade from antiprotonic atoms was studied for 106Cd, 116Cd, 112Sn, 116Sn, 120Sn, and 124Sn. Widths and shifts of the levels due to strong interaction were deduced. Isotopic effects in the Cd and Sn isotopes are clearly seen. The results are used to investigate the nucleon density in the nuclear periphery. The deduced neutron distributions are compared with the results of the previously introduced radiochemical method and with HFB calculations.