Search

The exclusive 2H( 3He, t)2p reaction has been studied at 2 GeV for energy transfers up to 500 MeV and triton angles up to 3.4°. The protons were measured in the large acceptance magnetic detector DIOGENE, in coincidence with the forward tritons detected in a dedicated magnetic arm. The energy transfer spectra extend well above the pion threshold. However, in the region of Δ excitation, the yield is less than 10% of the inclusive 2H( 3He, t) cross-section, which indicates the small contribution of the ΔN ↦ NN process. The angular distributions of the two protons in their center of mass have been analysed as a function of energy transfer and triton angle and a Legendre polynomial decomposition has been achieved. These data have been compared to a model based on a coupled-channel approach for describing the NN and NΔ systems.

The inclusive 2(3He,t) reaction has been studied at 2 GeV for energy transfers up to 500 MeV and scattering angles from 0.250 up to 40. Data are well reproduced by a model based on a coupled-channel approach for describing the NN and NΔ systems. The effect of final state interaction is important in the low energy part of the spectra. In the delta region, the cross-section is very sensitive to the effects of Δ-N interaction and ΔN → NN process. The latter has also a large influence well below the pion threshold. The calculation underestimates the experimental cross-section between the quasi-elastic and the delta peaks; this is possibly due to projectile excitation or purely mesonic exchange currents.

Peripheral collisions involving heavy ions at relativistic energies have been extensively studied for the last years. Such reactions lead to generally hot fragments [1,2], however the excitation energy is subject to large fluctuations and can reach low values [3]. The study of the energy dissipation, its coupling to other quantities such as the isospin and momentum of fragments are of interest because they carry information on the underlying mechanism, governing to a large extent production yields. Up to now this excitation energy has been essentially assessed from the effect of the evaporation stage on the N Z ratio of fragments [1,2]. We report in this contribution on a direct measurement, in coincidence with heavy fragments, of particles which mainly come from the deexcitation stage of the quasi-projectile. This type of measurement provides information not only on the mean deposited energy, but also on the excitation spectrum. The experimental results will be discussed in view of two questions: are neutron-rich isotopes produced either by fluctuations in the energy deposition (low energy tail) or by fluctuations in the decay stage for hot primary fragments? Does a Glodhaber-type mechanism [4] (recoil effects) fully accounts for the width of the longitudinal momentum spectrum?

Tensor analyzing powersiT 11,T 20,T 21 andT 22, have been measured for deuteron laboratory energiesE lab =75, 85, 95, 106, 119, 131, 144, 156, 172, and 187 MeV. The data are compared to rigorous Faddeev calculations with realistic nucleon-nucleon potentials. A generally good description of the data at all energies is obtained.

Data are presented on the 12 C ( 3 He , t π + ) reaction at 2 GeV bombarding energy. In coincidence with forward scattered tritons, pions are momentum-analysed in a large acceptance detector. For events where the target is left in its g.s. or low-lying states, the angular correlation between the momentum transfer vector and the momentum of the pion is sharply peaked at small relative angles.

The mass of the η meson has been measured through the study of the d p→ 3 He η reaction near threshold, the beam having been calibrated through comparison with three other nuclear reactions. The value obtained is m η =547.30±0.15 MeV/ c 2 , where the error bar includes both systematic and statistical effects. This is much more precise and significantly lower than the Particle Data Group average, through it is consistent with a previous counter experiment.

The excitation of theΔ resonance is observed in proton collisions on C, Nb and Pb targets at 0.8 and 1.6 GeV incident energies. The mass E0 and widthΓ of the resonance are determined from the invariant mass spectra of correlated (p, π±)-pairs in the final state of the collision: The mass E0 is smaller than that of the free resonance, however by comparing to intra-nuclear cascade calculations, this reduction is traced back to the effects of Fermi motion, NN scattering and pion reabsorption in nuclear matter.

Data for the (3He, t) reaction at 900 MeV and 2 GeV on the targets 26Mg, 40Ca, 48Ca, 54Fe, 90Zr and 208Pb are presented. A multipole decomposition for the data at 900 MeV has been made and the different distributions have been analysed. From the L = 0 cross section the Gamow-Teller strength distributions are extracted and compared with (p, n) data. The L = 1 and 2 distributions are analysed in a schematic model which describes the general systematics fairly well. The spectra at 2 GeV and Θ = 4° show for all targets a well-developed quasi-elastic peak. The A-dependence of the cross section is analysed in a simple model.

A new type of deuteron polarimeter to work in the energy range 120 < Ed < 250 MeV has been designed, constructed, and calibrated. The figure of merit (√ϵTkq) has been determined for various polarization components from the calibration data.

EI SEP PHASE ACC; The paper describes the spectrometric system “SPES4–$\pi$” used at the National Laboratory Saturne (CE Saclay, France) for the exclusive study of the baryon resonance excitation in inelastic α and d scattering on the proton, as well as coherent pion production in charge exchange reactions. The system consists of the magnetic spectrometer SPES4 and two wide-aperture position-sensitive detector arrays, equipped with wire chambers and scintillator hodoscopes, installed around a large-gap C-shape dipole magnet.

Energy dissipation is studied in 200 MeV/u 84Kr-induced reactions. Two experiments were performed at the SATURNE facility with the SPES4 spectrometer. Projectile-like fragments were measured for both the 84Kr+197Au and 84Kr+59Co systems. In the latter case light charged particles emitted in the forward direction were detected in coincidence with PLF. From the projectile-like fragment isotopic distributions one can estimate that the mean excitation energy value per abraded nucleon deposited in primary fragments is quite large (20–30 MeV). However, the excitation energy distribution is very broad: the neutron-rich nuclei come from weakly excited neutron-rich primary fragments. The mean velocity loss of projectile-like fragments with respect to the projectile velocity as well as the correlation between the proton coincidence rate and the projectile-like fragments momentum also claim for a dissipative mechanism.

Using a magnetic spectrometer, a precision measurement of N/Z distributions and fragment velocity distributions was performed at 0.6° and 1.5° in peripheral collisions of 200 MeV / nucleon 84Kr on a gold target. The data are compared with both the participant-spectator model and the intranuclear cascade model. It is shown that the primary fragments underwent substantial excitation, which cannot be accomodated with the cold fragmentation.

Charged pions and light nuclei ({ital p}, {ital d}, {ital t}, {sup 3}He, and {sup 4}He) have been measured in the interaction of proton beams with C, Nb, and Pb targets at 0.8 and 1.6 GeV incident energies, using a large solid angle detector. From slices on the multiplicity of protonlike particles (free protons and protons bound in light fragments), the events have been sorted out into two classes corresponding to more peripheral and more central collisions. For each class of events, the mean value and the dispersion of the {pi}{sup +} and {pi}{sup {minus}} multiplicity distributions have been studied as a function of target mass and incident energy. Comparisons to the Liege intranuclear cascade predictions exhibit some discrepancies which are discussed.

Data are presented for the (/sup 3/He, t) reaction at energies of 600 MeV, 1.2 GeV, and 2 GeV on targets /sup nat/C, /sup 54/Fe, and /sup 89/Y. The low--excitation-energy regions of the spectra are dominated by isospin-spin excitations. Cross-section calculations in distorted-wave impulse approximation with parameters from NN data account reasonably well for the data. At 2-GeV bombarding energy a strong excitation of the ..delta.. resonance is observed for all targets.

Excitation of the Δ resonance has been observed for the first time in a heavy ion reaction. The strength of the Δ signal depends on the projectile nuclear structure. In the same incident energy range, about 900 MeV per nucleon, we observe — a strong Δ excitation in 27 Al( 20 Ne, 20 F) and 27 Al( 20 Ne, 20 Na), — a weak Δ in 12 C( 14 N, 14 C) and — nearly no Δ excitation in ( 12 C, 12 B) and ( 12 C, 12 N) whatever the target is among a sample of nuclei from 12 C to 89 Y.

Angular distributions have been measured at 66 MeV for the /sup 16/O(..pi../sup +/,p)/sup 15/O reaction leading to the (p/sub 3///sub 2/)/sup -1/ hole state at 6.18 MeV and the (p/sub 1///sub 2/)/sup -1/ hole ground state of /sup 15/O. The ratio of the two differential cross sections lies between 6 and 13 over the whole measured angular range. A comparison is made with preliminary calculations of Miller. At 45/sup 0/ and 105/sup 0/ a measurement has also been performed on the reaction /sup 16/O(..pi../sup -/,p)/sup 15/C at the same incident energy.

We have succeeded in measuring at 0\ifmmode^\circ\else\textdegree\fi{} and small angles the energy spectra for the (d,2p${[\mathrm{}}^{1}$${S}_{0}$]) reaction (with the two protons in the singlet S state) at 650 MeV and 2 GeV. It is demonstrated that the reaction is a one-step process that can be used to study isospin-spin excitations. The \ensuremath{\Delta} excitation is very clearly observed. A shift down in energy of the \ensuremath{\Delta} peak from the proton to the $^{12}\mathrm{C}$ target is observed. The experiments are performed with a tensor polarized beam and the tensor analyzing power for the p(${d}_{\mathrm{pol}}$,${\mathrm{}}^{2}$He)n reaction at 2 GeV is given.

An experimental study of the 3 He( γ , π + ) 3 H reaction has been performed in the region of the Δ 1236 resonance between 227 MeV and 453 MeV. The experiment shows two main features: at fixed four-momentum transfer q 2 , the resonance is shifted towards lower energies, this shift increasing with q 2 ; at a fixed angle, but variable q 2 , the minimum of the charge form factor observed in the elastic scattering of electrons on 3 He does not appear. Recent calculations explain partly these two effects. This experiment might be used as part of a test of time-reversal invariance in the electromagnetic interaction of hadrons.

Data are presented for the p(3He,t)Δ++ reaction at 2.0, 2.3 and 1.5 GeV. The reaction specifically excites the Δ++ with very little yield outside the resonance. The data are analysed as one pion exchange and the hadronic form factor for the 3He−1 system is extracted and compared with the magnetic form factor from electron scattering.

The reaction $^{6}\mathrm{Li}(p, {\ensuremath{\Delta}}^{++})^{6}\mathrm{He}$ has been studied at 1.04 GeV for transferred momenta ranging from 0.11 to 0.35 ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^{2}$. An exponential decrease of the cross section is observed. A Glauber-type calculation is presented. The possibility of extracting information on ${\ensuremath{\sigma}}_{\ensuremath{\Delta}N}$ and ${\ensuremath{\alpha}}_{\ensuremath{\Delta}N}$ is discussed.

An apparatus which has been used to study the 3 He( γ , π + ) 3 H reaction around the 3-3 resonance is presented. The beam arrangement and the target are described. A magnetic spectrometer, followed by a wire chamber, analysed the momentum of the outgoing pions and defined their emission angle. The tritons emerging from the target are detected in coincidence with the pions by two methods: a telescope of thin plastic scintillators inside the vacuum of the scattering chamber for a triton energy below 40 MeV; or a magnetic spectrometer followed by a series of plastic scintillators for larger energies.

Momentum spectra of projectile fragments from 1.1 A GeV20Ne interactions with a Fe target have been measured with associated charged-particle multiplicity of participant nucleons. We also measured fragment absorption by introducing a Fe absorber. We searched for enhanced anomalous fragment production for fragments of charge 6≦Z≦ 10 as a function of multiplicity. To the possible exception of18Ne, a negative result is reported.

The complete angular distribution and the forward-backward asymmetry have been measured for the reaction α+d → t+ 3 He at 55 MeV (c.m.). Validity of the isospin concept requires this angular distribution to show up a forward-backward symmetry, following a theorem by Barshay and Temmer. Important asymmetries have been observed previously at lower energies. At 55 MeV a small but significant angle dependent asymmetry appears, which is, however, only about half the one observed at 27 MeV (c.m.). A calculation of the Coulomb effects in a DWBA analysis seems to account for this asymmetry. Other possible effects are also discussed.

Spin structure and cross section data for Δ production in the (n, p-like reaction (d, 2p[1S0]) on p, d and 12C targets are presented. At laboratory kinetic energies 2 GeV and 1.6 GeV, and forward scattering angles, we find dominance of spin transverse over spin longitudinal cross section for free Δ production. On the nucleus 12C we find significant enhancement of the transverse dominance, and a large downwards shift in the peak position of the laboratory energy transfer associated with the production of the Δ.

Results on the Δ excitation by heavy ion charge exchange are presented. 900 MeV per nucleon 12C, 16O, 20Ne and 1100 MeV per nucleon 12C have been used. The Δ excitation strength depends on the projectile — ejectile nature and on the incident energy. The role of the target mass is also discussed. The peak for the Δ in nuclei is energy shifted from the free Δ peak.

The (3He, t) reaction has been studied at intermediate energies, 600 MeV–2.3 GeV. The reaction is a single-step direct reaction, and the angular distributions are well described by DWIA calculations. At these energies the σρ component of the interaction dominates. The ratio of the isovector strengths ¦J σρ / ρ ¦ derived from the data on 13C appears to remain roughly constant in the energy range 300–700 MeV per nucleon. The triton spectra exhibit a prominent quasi-free peak. The data at momentum transfers q ⪢ 1.7 fm−1 show a shift of the peak towards smaller energy loss than observed in (e, e') experiments at corresponding four-momentum transfers. The shift becomes progressively larger with increasing q and is about 45 MeV at q = 2.5 fm−1. The shift may be caused by particle-hole correlations in the spin-longitudinal channel.

Direct α particles cross sections and angular distributions have been measured when bombarding a124Sn target with various projectiles:16O (90, 105, 125 MeV)19F (104 MeV)20Ne (112, 156 MeV). Results have been found independant of the projectile structure. In the same reactions, gamma multiplicity measurements have shown that direct α particles are emitted in collisions with intermediate impact parameters. The angular momentum is found to be about half of the valuel cr for complete fusion.

Data for the Δ excitation by the (3He,t) reaction at 2.0 GeV on various nuclei are presented together with results on 12C at 1.5 and 2.3 GeV. The Δ peak position and width are found to be target mass independent. Comparison with the p(3He,t) Δ++ reaction, however, shows a shift of the position in energy of the Δ peak. Implications of these results are discussed.

Sixfold energy spectra have been measured for the (p, pα) reaction at 157 MeV on 24Mg, 28Si, 40Ca and 58Ni around quasi-free kinematic conditions. For the three s-d shell nuclei the experiment covered a map ranging from 0 to 220 MeV/c in recoil momentum and from 0 to 20 MeV in excitation energy of the final nucleus. Recoil momentum distributions have been obtained for the 0+ ground state and the 2+ first excited state of 20Ne, 24Mg and 36Ar, and also for the states around 4.4 MeV (mainly 4+) of 36Ar. The a spectroscopic factors extracted by a DWIA analysis are about three times larger than those predicted by the SU(3) model; however, they agree quite well in relative magnitude for a number of cases. The disagreement in shape between experiment and theory observed at low recoil momentum for the 2+ states might result from another reaction mechanism. The cross sections for 58Ni are about a factor often smaller than those for 40Ca. The 58Ni(p, pα)54Fe reaction seems to lead mainly to excited states of the final nucleus.

The nn and pp final-state interaction spectra were measured at 2.5° and 7.5° in the mirror reactions 3 H(d, 3 He)2n and 3 He(d, t)2p at 83 MeV deuteron energy. The Watson-Migdal treatment does not give a good description of these spectra. Application of the comparison method of Slobodrian et al. gives a mean value for a nn of −15.5 fm, and very large values for r on : the variation of the production form factor with the relative energy of the two nucleons seems also very large. The coherent addition of a constant amplitude to the Watson-Migdal amplitude introduces only a limited number of parameters: this method gives for r on a mean value of 3.3 fm, but the values found for a nn (around −12 fm) are in general smaller than the theoretical predictions. A more rigorous theoretical treatment of these deuteron induced reactions seems necessary. Measurements have also been performed on the mirror reactions 3 H(d, t)pn, 3 He(d, 3 He)pn and 3 H(d, t) 2 H, 3 He(d, 3 He) 2 H.

The angular distribution of the elastic scattering of 166 MeV α-particles on 6Li nuclei has been measured from 3° to 175° (c.m.). The backward rise of the cross section is explained in terms of two-nucleon pick-up. The symmetry of the entrance and exit channels makes the measurement a good test of the applicability of finite-range DWBA calculations for this exchange effect. This effect is shown to become negligible for heavier nuclei like 40Ca.

On a etudie la diffusion quasi elastique (p, pt) sur 7Li ; la correlation angulaire presente la forme caracteristique d'une distribution de quantite de mouvement L ≠ 0 (2P). On compare les probabilites de groupement de nucleons ("clusterisation") de 7Li → (t + α), 6Li → (d + α) et (t + 3He). La reaction 12C(p, pd)10B a egalement ete etudiee ; les spectres en energie du noyau residuel semblent en accord avec les previsions de Balashov et al. faites dans le cadre du modele en couches en couplage intermediaire.

The (p, d) reaction at 156 MeV on nitrogen and fluorine has been studied to test a configuration mixing description of the target and residual nuclei, and the single interaction pick-up mechanism. At this energy, a simple method is used to extract the relative spectroscopic factors for a given l for the whole spectrum. The comparison has been made using spectroscopic factors calculated for nitrogen and fluorine with wave functions of Ripka and Giraud, and with the 1p wave functions of Cohen and Kurath for nitrogen. For nitrogen there is a good agreement between experimental and theoretical spectroscopic factors, especially when comparing with those calculated by Kurath where agreement is within about 20%. Such an agreement has also been obtained for other nuclei of the 1p shell. For fluoribe, the theoretical description seems qualitatively correct up to about 5 MeV excitation in 18F. Excitation of the observed higher states must be assigned to pick-up in the inner 1p shell or to the contribution of more complex configurations.

Energy spectra and angular distributions were measured with a magnetic spectrometer for the following pick-up reactions at 156 MeV: 6 Li(p, d) 5 Li; 7 Li(p, d) 6 Li; 9 Be(p, d) 8 Be; 10 B(p, d) 9 Be; 11 B(p, d) 10 B; 12 C(p, d) 11 C; 16 O(p, d) 15 O; 28 Si(p, d) 27 Si and 40 Ca(p, d) 39 Ca. It is shown that, at this energy, where the separation between levels is small compared to the energies of the incoming and outgoing particles, the PWBA without cut-off radius, although not being able to reproduce the experimental angular distributions, allows a good extraction of the relative spectroscopic factors F 2 for a given l . The F 2 values agree quite well with those calculated for 1p shell nuclei with the wave functions of Cohen and Kurath and of Boyarkina; the agreement is in general also good with the F 2 extracted by DWBA at various energies. The ratio between the absolute F 2 obtained by PWBA and the theoretical F 2 might be considered as a distortion factor, which is a function of angle θ; it appears that this factor does not vary much throughout the 1p shell. The pick-up in the inner major shell is discussed; the cross section for simple 1s pick-up decreases sharply when going from 4 He to 6 Li target nuclei; a similar effect appears for 1p pick-up between 16 O and 19 F; this behaviour, probably related to the high neutron momenta involved, is not yet well understood.

The energy spectra of the deuterons from (p,d) reaction are discussed. For /sup 40/Ca, pick-up of 1d3/2 and 2s1/2 neutrons and perhaps also of 1d5/2 neutrons is observed. For /sup 11/B and /sup 10/B one observes spectra whose general behavior is intermediate between that of /sup 12/C and /sup 9/Be. (auth)

The pp and pn final state interaction (FSI) spectra were measured in the 4 He(p, t)2p and 4 He(p, 3 He)pn reactions at 156 MeV. The Watson-Migdal treatment and the known scattering length were used to analyse the spectrum shapes at different small angles: the agreement obtained is quite good; the Watson-Migdal assumptions are indeed better satisfied for higher primary energies. Use of a modified Born approximation for the pp spectrum further improves the fit. When comparing the absolute magnitudes of the three reactions, it appears that the 4 He(p, 3 He)pn spectra should include mainly the singlet contribution. The angular distribution of the reaction 4 He(p, d) 3 He has been measured from 3° to 177° (c.m.). No evidence has been found for excited states of 3 He.

The differential cross section for the 3 He (γ, π + ) 3 H reaction has been measured at fixed values of q2 in the region of the first resonance, and at fixed θπ versus q2 up to 13 fm−2. The observed shift of the resonance towards lower energies, and the absence of a minimum near 11.6 fm−2 might be explained by recent theoretical calculations.

The D(p, γ) 3 He reaction has been studied at 156 MeV in view of obtaining information on the wave function of 3 He. The differential cross section has been measured from θ γ (lab) = 30° to 120°.

The p-n and p-p final-state interaction in the (p, 3 He) and (p, t) reactions on 4 He at 156 MeV has been measured for several t and 3 He angles and analysed in terms of the Watson-Migdal theory. Agreement is rather good for the shapes of the energy spectra, but not for their relative magnitudes. The differential cross section of 4 He+p→d+ 3 He has been measued from θ d = 4°to177° c.m.