Search

We have measured angular distributions of differential cross sections and analyzing powers ( A y ) of the reaction p p → d π + at six incident proton energies between 1.3 and 2.4 GeV. They confirm the rapid variations at √ s = 2.65 GeV suggested by earlier experiments. Deviations from a monotonic behavior are also found in the excitation functions of the differential cross section at t = 0 or where Θ π + (c.m.) = 0°. Structures clearly appear at √ s = 2.4 and 2.65 GeV, in some coefficients of the associated Legendre function expansions of A y .

Experimental results on the study of the n p → pp π − reaction performed with a 4π solid angle detector are presented. Full kinematics is measured event by event. Measured analysing powers are compared to the results of a calculation including the ΔN intermediate state and realistic non-resonant amplitudes.

The study of inelastic channels induced by the nucleon-nucleon (NN) system has a two-fold interest: first, this elementary process has to be understood in itself, for example through the isobar model mechanism, second, its knowledge is necessary to interpret more complicated reactions induced by a nucleon probe with nuclei; for example, any microscopic calculation of the (n,p) charge exchange reaction in the Δ region requires the knowledge of np and nn→NNπ+ in this region of the phase space. Thus, the study of the one-pion production channel in NN interaction must be undertaken as carefully as the study of the elastic channel to be able to treat all channels on the same footing in a global description of these elementary hadronic processes. In the energy region ranging up to the GeV, a large body of data already exists. Extensive studies of proton-proton and neutron-proton elastic scattering involving complete determination of amplitudes from the measurement of spin observables by using polarized beams and targets, have been made. Many data have been obtained also for the pp→dπ+ and the pp→pnπ+ inelastic reactions, both proceeding through a mechanism dominated by the existence of an intermediate NΔ state, as can be seen from the success of the various approaches using such an isobar model1.

Inelastic scattering of 340 MeV and 480 MeV α-particles has been measured on 58 Ni, 116 Sn and 208 Pb up to 60 MeV excitation energy. Consistent background subtraction and multipole analysis has provided the repartition of multipole strength for all three nuclei. The so-obtained response functions show the already known low-energy giant resonances in a detailed way, as well as new giant resonances at high energy.

Experiments currently done at SATURNE (Saclay) with a free polarized neutron beam are described. These are measurements for the np system of elastic and inelastic cross sections and analysing powers, and of Δσ T and Δσ L .

Seven differential cross sections of the reaction $p+d\ensuremath{\rightarrow}^{3}\mathrm{He}+\ensuremath{\gamma}$ have been measured at ${T}_{p}=450 \mathrm{and} 550$ MeV between 52\ifmmode^\circ\else\textdegree\fi{} and 92\ifmmode^\circ\else\textdegree\fi{} (${\ensuremath{\theta}}_{\ensuremath{\gamma}}$ c.m.). $^{3}\mathrm{He}$'s were analyzed by the SPES I spectrometer in coincidence with photons detected by Cherenkov counters. The results are about twice the cross sections of the inverse reaction measured recently by Hegerath et al. and by Argan et al. The data are consistent, however, with the $\ensuremath{\gamma}+^{3}\mathrm{He}\ensuremath{\rightleftarrows}p+d$ data of Heusch et al.

First results for the (d,p) reaction on /sup 6/Li, /sup 9/Be, and /sup 16/O are presented for a scattering energy T/sub d/=698 MeV at momentum transfers 2< or =q< or =5 fm/sup -1/. Simple distorted-wave Born-approximation and rescattering calculations stress the need for a more comprehensive analysis by explicitly including both the stripping amplitude and mesonic degrees of freedom.

Cross sections for the /sup 12/C(p,p') reaction leading to the 1/sup +/ states at 15.1 MeV(T = 1) and 12.7 MeV(T = 0) were measured at a bombarding energy of 402 MeV. These data, covering a range of momentum transfer q from 0.45 to 2.65 fm/sup -1/ (0.6 --3.7m/sub ..pi../) provide a test of the effects, precursor to a pion condensate, predicted to be important for the T = 1 state near q = 2--3m/sub ..pi../. The cross sections for the two 1/sup +/ states are very similar fro large q, perhaps indicating that the precursor effects are small.

Differential cross sections have been measured for p+d\ensuremath{\rightarrow}\ensuremath{\gamma}${+}^{3}$He at ${T}_{\mathrm{p}}$(lab)=300, 350, 400, 425, 450, 470, and 500 MeV for ${\mathrm{theta}}_{\ensuremath{\gamma}}$(c.m.) near 60\ifmmode^\circ\else\textdegree\fi{} and 90\ifmmode^\circ\else\textdegree\fi{}. Measurements were also made for d+p\ensuremath{\rightarrow}\ensuremath{\gamma}${+}^{3}$He at ${T}_{\mathrm{d}}$=376 MeV for ${\mathrm{theta}}_{\ensuremath{\gamma}}$(c.m.)=84\ifmmode^\circ\else\textdegree\fi{}, 98\ifmmode^\circ\else\textdegree\fi{}, and 113\ifmmode^\circ\else\textdegree\fi{}, and at ${T}_{\mathrm{d}}$=600 MeV for ${\mathrm{theta}}_{\ensuremath{\gamma}}$=96\ifmmode^\circ\else\textdegree\fi{} and 105\ifmmode^\circ\else\textdegree\fi{}. Our results are in agreement with those of the inverse reaction, \ensuremath{\gamma}${+}^{3}$He\ensuremath{\rightarrow}p+d of Sober et al., as is expected from time-reversal invariance. Our data agree with the latest results of Cameron et al. The older radiative capture measurements of Heusch et al. and the photodisintegration measurements made at other laboratories differ significantly from our results. Our data are compared with three theoretical models; the one proposed by Maximon and Prats comes closest to describing the data.

The reactions p p →π − X and p d → pX earch for narrow baryonium states in the mass region between 1.6 and 2.0 GeV/c2. No such state has been observed. In the first reaction the upper limit for the production of narrow baryonium states is 8μb/sr for a 3 standard deviation signal with 4 MeV/c2 width. In the second reaction this limit is 10 μb/sr. The second reaction is rather insensitive for observation of baryonium states as it is dominated by quasi-free contributions.

The positive pion prodution through the 6 Li(p, π + ) reaction at 600 MeV has been studied using the high-resolution magnetic spectrometer SPES I. Differential cross sections have been measured from 5° to 35° lab . The 6 Li(p, π + ) reaction feeds preferentially the 4.63 MeV 7 2 − level of 7 Li. The results of a calculation based on two- and three-nucleon diagrams with π and ρ exchange between the projectile and a bound nucleon are also presented.

The elastic and inelastic scattering of α-particles to the lowest 2 + , 3 − and 0 + levels of 12 C is measured at an energy of 1.37 GeV. The impulse approximation using various models for the nucleon-α interaction leads to a fair agreement with experiment. It is shown that the cross sections are sensitive to the detailed description of this interaction. The best results are obtained using the free t -matrix for the scattering of a nucleon by 4 He at the same incident energy per particle (340 MeV).

We present differential cross sections for p+ d → 3He + π0 at Tp = 300, 350, 400, 425, 450, 470 and 500 MeV, and for p + d → 3H + π+ at 500 MeV, mostly near θπ (c.m.) = 48° and 98°. The ratio dσ(pd → 3H π+)/dσ(pd → 3Heπ0) for identical four momentum transfer at 500 MeV is found to be 2.21 ± 0.17 to 2.57 ± 0.34, depending on angle. The dependence of the invariant matrix element squared |M|2 on the relativistic invariants t and s is examined; for a given value of t, |M|2 is almost independent of s for Tp between 350 and 800 MeV.

Differential cross sections of elastic and inelastic scattering of 1.37 GeV α-particles from 40, 42, 44, 48Ca have been measured. The angular distributions show that the scattering process is quite diffractive. Glauber's nucleus-nucleus scattering theory for elastic scattering has been examined in two approximate ways. The method in which the projectile is assumed not to be excited internally in the course of multiple scattering, reproduces reasonably well the experimental angular distributions. The trend of the root-mean-square radii of the neutron densities of the four calcium isotopes has been found to be in agreement with the recent results from proton scattering measurements at 1.04 GeV.

We have studied (p, p) reactions on 12 C , 63 Cu, and 209 Bi to search for possible nuclear states formed ny antiprotons and nuclei. The experiments used the 180 MeV antiproton beam from LEAR, and the high-resolution magnetic spectrometer, SPES II, to detect the outgoing protons. No evidence of antiproton-nucleus states was found. The gross features of the proton spectra are reasonably well described by intranuclear cascade model calculations, which consider proton emission following antiproton annihilations in the target nucleus.

Elastic and inelastic scattering of 1.044 GeV protons have been studied on isotopically enriched even 40, 42, 44, 48 Ca isotopes and 48 Ti. A spin independent Glauber theory analysis of the elastic scattering allowed the extraction of neutron and nuclear matter densities for these targets.

The 3He(3He, π+)6 Li reaction has been studied as a function of energy using the 3He beam at SATURNE. Cross sections for the 6Li ground state (1+) and 2.18 MeV (3+) levels have been obtained at 350,420,500 and 600 MeV incident energies at angles θπ(lab) = 15° and 40°. These results are compared with two theoretical predictions.

Negative-pion production leading to discrete excitation levels of the residual nucleus has been investigated on /sup 9/Be and /sup 12/C targets with 613-MeV protons. On the first seen spectra of /sup 13/O a strong excited peak is observed at 2.82 minus-or-plus 0.24 MeV in excitation energy. The resulting cross sections are found to be far below previously published theoretical predictions.

Using negative kaons of momenta 400 and 450 MeV/c, Σ hypernuclear states have been produced in (K−, π−) and (K−, π+) reactions on 12C. The observed states are interpreted as the recoilless production of Σ particles on carbon. The upper limit for the widths of these states is estimated to be 5 MeV, independent of the charge of the Σ particle.

The knock-out reaction A( p , p)X has been used to search for narrow p -nucleus states. The experiment was performed using the 600 MeV/ c antiproton beam at LEAR and the high-resolution and large-acceptance magnetic spectrometer SPES II. The A -dependence of the annihilation-induced proton spectra has been studied on 2 H, 6 Li, 12 C, 63 Cu, 208 Pb and 209 Bi. The quasi-free elastic p p scattering observed in the lighter targets, and the comparison with the free p p scattering, also observed in this experiment, determine an effective proton number N eff for 1s- and 1p-shell protons. No evidence for narrow bound or resonant p -nucleus states could be found. Upper limits for their production are one order of magnitude lower than certain theoretical predictions, but consistent with the properties of the p -nucleus interaction, as established from recent elastic and inelastic scattering as well as from studies of antiprotonic atoms.

Proton-induced pion production at intermediate energies, leaving the final nucleus in discrete, resolved states, has been measured at the Saclay Synchrotron Saturne I, using the high resolution spectrometer facility SPES I. The (p, π+) reaction has been investigated on 9Be at proton energies of 410 and 605 MeV, and on 10B at incident energies of 320,410, 483 and 605 MeV. These data are presented and analysed in a coherent way, together with previous results at intermediate energies, by means of a pion exchange model. It is found that all the characteristic features of the data are reproduced satisfactorily.

The ( 3 He, d) reaction was studied on all stable Zr isotopes. Twenty-three unbound analog states in the Nb isotopes were populated. The observed cross sections were analyzed using two different methods for DWBA calculations of stripping to unbound analog states. The deduced proton spectroscopic factors are compared to the neutron spectroscopic factors obtained for the parent states from the (d, p) reaction studies. The agreement is generally good, except for the 97 Zr- 97 Nb isotope pair. The difference in the sensitivity to the transferred angular momentum between the (d, p) reaction and the ( 3 He, d) reaction to the analog states is discussed. The good agreement leads us to conclude that the ( 3 He, d) reaction to analog states may be used in nuclear spectroscopy for the study of levels in the parent states which are populated through large angular momentum transfer.

The reactions 95, 97 Mo(p, d) 94, 96 Mo were studied at a proton energy of 26 MeV. Angular distributions were measured from 11° to 40° and compared with distorted-wave Born approximation calculations; l -values and spectroscopic factors were extracted for the low-lying states of 94 Mo and 96 Mo. The angular distributions of these states have a characteristic l = 2 shape. The ratios of the summed spectroscopic factors to the 0 + , 2 + and 4 + states are in good agreement with the (2 d 5 2 ) n neutron configurations. The 2 + strength is strongly fractionated in both 94 Mo and 96 Mo. The 4 + strength in 94 Mo is split among two states, whereas in 96 Mo it is concentrated in the second 4 + state.

The nuclear structure of 50 Sc is investigated through the 48 Ca( 3 He, p) 50 Sc reaction using 3 He ions accelerated to 18.5 MeV in a cyclotron and semiconductor detectors. Data are obtained on the excitation energies and the spins and parities of a large number of levels in 50 Sc up to 6.62 MeV. The experimental data are compared with DWBA calculations using various wave functions obtained in the framework of the shell model with different degrees of sophistication as to the orbits considered. A reasonable agreement is obtained up to 3.5 MeV excitation energy in 50 Sc for the most complex wave functions. Above 3.5 MeV, the results indicate the existence of strong L = 2 transitions in the ( 3 He, p) reaction, which are not explained by current models, and also a new and previously unidentified collective mode of excitation in 50 Sc.

We have studied levels in $^{58}\mathrm{Ni}$ up to 10 MeV excitation energy through the ($\ensuremath{\alpha},{\ensuremath{\alpha}}^{\ensuremath{'}}$) reaction at 30 MeV and found surprising overall agreement between the observed spectra and those from $\ensuremath{\alpha}$-transfer reactions.

A systematic study of collective states excited in 44 MeV α-particle inelastic scattering by nuclei near closed shells with 28 neutrons, 20, 28, 50 and 82 protons is presented. The nuclei studied are 40Ca, 46, 48, 50Ti, 52Cr, 54, 56, 58Fe 58, 60, 62, 64Ni, 112, 114, 116, 118, 120, 122, 124Sn and 208Pb. The theoretical analysis has been performed with the Austern-Blair model. The deformation lengths and transition probabilities obtained are compared with several experimental and theoretical data. A discussion of the two-phonon states is given.

The doubly odd nuclei 48 Sc, 50 V, 52 Mn and 54 Co have been studied by the charge exchange reaction ( 3 He, t) on 48 Ca, 50 Ti, 52 Cr and 54 Fe enriched targets. In addition to the analogue state of the target ground state, we observed a great number of low-lying energy levels, especially those which can be described by the [( f 7 2 ) p ( f 7 2 ) n −1 ] configuration. For these levels we got angular distributions from 10° to 70° c.m. We observed that these angular distributions show a typical pattern for each value of the total transferred angular momentum J as shown by levels of 48 Sc, 52 Mn and 54 Co for which spins are already known. This property allowed us to propose J -values for the more excited levels. Thus, most of the components of the [( f 7 2 ) p ( f 7 2 ) n −1 ] multiplet have been identified in 48 Sc, 50 V and 52 Mn. For 48 Sc, angular distributions are practically identical at 18.5 and 30.2 MeV. It seems that the ( 3 He, t) reaction at 30.2 MeV on N = 28 targets proceeds through an apparently quite simple mechanism.

ABS>The plausibility of interpreting the inelastic scattering of alpha particles by the odd nuclei Cu/sup 63/ and Cu/sup 65/ in terms of the coupling of a 3/2- proton to the nuclei Ni/sup 62/ and Ni/sup 64/ respectively is examined. It is assumed that there is a non-negligible interaction between the outside proton and the even Ni nucleus. The interpretation is based on a comparison of inelastic alpha scattering by the four nuclei under consideration. (T.F.H.)

Nous avons etudie simultanement les etats de neutron de 55Fe et les etats de proton T> et T< de 55Co. On donne les resultats concernant les principaux niveaux ƒ1/2, p3/2, p1/2, ƒ5/2 et g9/2 avec les facteurs spectroscopiques relatifs tires d'une analyse en ondes deformees.

A study of single-particle proton strengths in odd-mass Tc isotopes was performed using the (3He, d) reaction. Angular distributions were measured from 8° to 70° and compared with calculations using the distorted-wave Born approximation. The l-values and spectroscopic factors were extracted and compared with (d, n) results. Proton configurations for the ground states of 92,94Mo and 96Mo were deduced from the analysis. Symmetry energies were extracted from the energy difference between the centroids of the T> and T< states. Various methods for DWBA calculations for unbound states are discussed.

Single neutron hole states in neutron magic N = 82 nuclei have been investigated using the (p, d) pick-up reaction on 138 Ba, 140 Ce, 142 Nd and 144 Sm with 24.55 MeV protons and about 45 keV overall energy resolution. Energy levels corresponding to the shell-model orbitals 2d 3 2 , 3s 1 2 , 1h 11 2 , 2d 5 2 and 1g 7 2 have been observed in all the residual nuclei. Absolute or relative differential cross sections measured between 15° and 80° in 5° steps have been compared with DWBA calculations. All the excitation spectra investigated show similar features characteristic of pure neutron hole states for the low-lying 3 2 + , 1 2 + and 11 2 − states and of configuration mixing above 1 MeV excitation energy for the 2d 5 2 and 1g 7 2 orbitals. For 144 Sm the polarized proton beam has been used to confirm some spin assignments. Evidence for the neutron-proton interaction effect on the location of the various orbitals is shown.

We describe an experimental study of (α, t), (α,3He) reactions at 44 MeV using a solid-state identifier, on the target nuclei 54Fe and 58, 60, 62, 64Ni. A critical study of optical-model and distorted-wave analysis has been performed. We show the complementarity of different transfer reactions, the ambiguity of the spectroscopic factors and the importance of the problem of the reaction mechanism.

The reactions 203,205 Tl(α, t) 204,206 Pb were investigated at an incident energy of 44 MeV, the reactions products being momentum analysed in a double ΔE + E particle identification system with semiconductor counters. The resulting energy resolution was 120 keV. Transitions were observed to the ground state and the lowest 2 + state of 204,206 Pb and to a number of states at higher excitation energies, starting at about 2.9 MeV in 204 Pb and about 2.6 MeV in 206 Pb. Angular distributions were measured for the triton groups corresponding to the ground and first excited states of 204 Pb. The distributions have a forward peaked shape which can be reproduced well by a DWBA calculation assuming a simple proton stripping process.

The ($sup 3$He,d) reaction on Ni isotopes was studied at 30.2 MeV bombarding energy. Twenty-six unbound analog states in Cu isotopes were populated, and the observed differential cross sections are presented. Two different distorted-wave Born-approximation methods for stripping calculations to unbound analog states were used in the analysis. Proton spectroscopic factors were deduced and compared with published neutron spectroscopic factors for the parent states. The agreement is generally good, except for the pair of isotopes $sup 62$Ni-$sup 62$Cu. The different sensitivity to the transferred angular momentum of the corresponding (d,p) and ($sup 3$He,d) reactions is discussed. The present data are compared with the results of previous studies of the ($sup 3$He,d) reaction in the A approx. 90 mass region. It is concluded again that the ($sup 3$He,d) reaction to analog states is complementary to the (d,p) reaction for the study of levels in the parent states which are populated through large angular momentum transfers. (AIP)

The angular distributions of pions produced by 3 He(p, π + ) 4 He at lab. energies of 415 and 716 MeV have been measured up to θc.m. ≈ 100°. Two simple calculations, in the framework of one-nucleon and two-nucleon mechanisms, are presented and some approximations discussed. It is concluded that more elaborate calculations involving real or virtual isobar resonances have to be done.

Elastic scattering of 1.047 GeV protons is studied on the isotopically enriched 58,60,62,64 Ni isotopes. A spin independent Glauber theory analysis allowed the extraction of nuclear matter densities for these targets.

Experimental results obtained at Saclay by alpha-particle scattering have been analysed with the Austern- Blair model. Deformation parameters δ 2 I and transition probabilities B ( I →0) are compared with other experimental data and theoretical predictions.