C. Samour's research while affiliated with Université Paris-Sud 11 and other places

Publications (73)

Article
The cross section for exclusive [pi][sup +] electroproduction on the proton has been measured near threshold for the first time at two different values of the virtual photon polarization ([var epsilon][similar to]0.2 and [var epsilon][similar to]0.7). Using the low energy theorem for this reaction we deduce the axial and pseudoscalar weak form fact...
Article
We have studied the reaction: π−p→ne+e− at rest, i.e. inverse pion electroproduction at threshold, using the pion and a magnetic pair spectrometer at the Saclay Linear Accelerator. With 30 000 analyzed events, we proceed for the first time to the separation between the transverse and the longitudinal parts of the process, leading to model-independe...
Article
We have studied the π0 Dalitz decay π0 → γe+e− using the pion beam and a magnetic pair spectrometer at the Saclay Linear Accelerator. A shape analysis of the (e+e−) invariant mass squared x, carried out on 32 000 events, gives a direct measurement of the π0 electromagnetic transition form factor squared |F(x)|2, and of its slope parameter a in the...
Article
We present a detailed analysis of the low transfer data for the (ΔT = 1, 0+ ↔ 1+) transition in the A = 12 system. From the experimental observables obtained in electron scattering, in β-decay and in μ− capture, we deduce the experimental form factors of the weak and electromagnetic nuclear currents. The theoretical values of these form factors are...
Article
The purpose of this note is to point out the merits of macroscopic polarization signals, known as Hanle signals, generated with stopped polarized muons.
Article
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Article
We show that any deviation from the closed-core hypothesis for 16O(0+, g.s.) may strongly affect the theoretical ratio of the transition probabilities for the two inverse processes: muon-capture) and (beta-decay). As a consequence, the possible evidence for exchange currents in this transition must be reexamined. Preliminary calculations do not exc...
Article
Using the short pulses of a linac a measurement has been performed of partial μ--capture rates in 16O leading to the O- and 1- bound excited states of 16N. The experimental O+-->O- transition rate supports the assumption of a large mesonic exchange effect in the time part of the weak axial current. NUCLEAR REACTIONS Muon capture 16O(μ,ν)16N. Measur...
Article
A calculation is made of exchange current corrections for partial capture rates of muons in12C,16O,32S and40Ca nuclei. One-pion exchange is taken into account. Adler-Dothan's results are used to obtain the weak pion production amplitude. The nuclear states are described in the Tamm-Dancoff approximation. It is found that the corrections are very er...
Article
It is shown that a particularly large mesonic exchange effect is to be expected for the two inverse processes muon-capture and β-decay concerning the transitions between the 16O(O+) ground state and the 16N(OO−) exited state. It arises from a strong correction to the time part of the axial weak current. It is found that presently available experime...
Article
The helicity, h−, of μ− in π-decay has been determined as positive (h−⩾+0.90) from the average polarization, Pav≡〈JB·sμ〉, of 12B produced in the reaction. We obtain also dynamical information on μ-capture: (i) the weak magnetism form factor, μ=4.5±1.1, and (ii) the sum of the induced pseudoscalar (gp) and the 2nd class induced tensor (gT) couplings...
Article
The reactions 6Li(e,e'α) and 6Li(e,e'd) have been studied at T0 ~ 520 MeV and q ~ 1.4 fm-1, by coincidence measurements. The angular dependence of the cross sections is interpreted in the plane wave impulse approximation to obtain the momentum distribution of α-particle and deuteron clusters in 6Li. The amount of clustering of 6Li is also discussed...
Article
The average polarization of 12B produced by the capture of polarized muons in 12C has been measured using recoil implantation techniques. From the result we deduce the average polarization of the 12B ground state 12B(0) corresponding to the 12C --> 12B(0) Gamow-Teller reaction: Jmu(0) = 0.43 +/- 0.10. The sizeable deviation of this polarization fro...
Article
Le facteur de forme élastique de 208Pb a été mesuré pour des électrons incidents de 400 et 600 MeV et analysé à l'aide de la méthode des déphasages dans un domaine de transfert compris entre 0,5 et 4,3 fm-2.
Article
Gamma-ray spectra of radiative neutron capture have been studied in some nuclei with the Saclay linear accelerator using the time-of-flight method and a Ge(Li) detector. Level schemes from neutron resonances allow the assignment of spin values in a few cases. This study puts in evidence M1 transitions in 35Cl + n. New levels not previously observed...
Article
Experiments on some nuclei have been performed with the Saclay linear accelerator using the time-of-flight method. The investigated energy range is 9–113 keV for Cl, 200–31000 eV for Cu, 20–1000 eV for Ba and 3–740 eV for Nd. The spin value is assigned to most of the resonances. Strength function values against the spin value and the mass number A...
Article
Values of the total radiative width Lambdagamma have been measured for about 50 nuclei. Experiments have been performed with the Saclay linear accelerator using the time-of-flight method. For some nuclei, Lambdagamma is not constant from resonance to resonance. It is shown that variation of Lambdagamma is due to the strong intensity of favoured tra...
Article
Experiments on silver, thulium and platinum have been performed with the Saclay linear accelerator using the time-of-flight method. Resonance parameters are given for resonances detected in the 4 eV-830 eV energy range and spin value is assigned to most of the levels. The strength function dependence against neutron energy and spin value (J = 1 or...
Article
Experiments on gold have been performed with the Saclay linear accelerator using the time-of-flight method. Resonance parameters are given for 69 resonances, the spin value being assigned to 57 ones: 32 J = 2, 25 J = 1. Taking into account the previous results in the energy range 10–1000 eV, the strength function dependence against neutron energy a...
Article
The direct capture process has been studied in analysing the variation of relative intensity with neutron energy for several transitions in gold and cobalt. For the 6245 keV transition in 197Au+n and the 7490 keV transition in 59Co+n, the experimental data are consistent with the existence of a direct capture process. The cross section for such a p...
Article
The possible correlation in 184W between two partial radiative widths relative to transitions to near-lying energy states has been investigated with the Saclay linear accelerator using the time-of-flight method and a Ge(Li) detector. The spectra for 13 resonance with spin and parity 1− were analysed. The data agree with no appreciable correlation b...
Article
The total neutron cross sections of Cl, 51V, 89Y, Zr, La, 141Pr and 209Bi have been measured. Experimental data were fitted with a multi-level formula to obtain the individual resonance parameters. Values of the strength functions S0 and S1 and of the scattering lengths R' are obtained and compared with optical-model calculations.
Article
The statistical properties of the partial radiation widths in 196Pt have been studied with the Saclay linear accelerator using the time-of-flight method and a Ge(Li) detector. The spectra for 22 resonances with spin and parity 1- were analysed, and a sample of 66 transitions was obtained. The result of such a study confirms the validity of the Port...
Article
Gamma-ray spectra of radiative neutron capture have been studied in several tin isotopes with the Saclay linear accelerator using the time-of-flight method and a Ge(Li) detector. The intensity of 13 E1 transitions and 12 M1 transitions has been evaluated. This study has shown that strong M1 transitions are on the average only five times less intens...
Article
Des expériences de capture radiative de neutrons de résonance ont permis de montrer que la distribution des largeurs radiatives partielles suivait une loi en χ2 à un degré de liberté et de préciser les schémas des états excités de quelques noyaux lourds (Pt, W et Sn), en particulier du noyau sphérique pair-pair 196Pt, pour lequel un nouveau schéma...
Article
The total neutron cross sections of 55Mn and 59Co have been measured up to energies respectively equal to 80 keV and 500 keV. Experimental data were fitted with multi-level formulae by shape analysis; resonance parameters are given for 55Mn up to 80 keV and for 59Co up to 120 keV. For 55Mn, the s-wave strength function S0 is found to equal to (4.08...
Article
The gamma-ray spectrum from the beta decay of 196Au has been studied with high resolution. The data together with earlier (n, gamma) (d, p) and (d, d') results are combined to yield a new level scheme for 196Pt.
Article
The neutron strength function of cobalt has been measured for neutron energies between 0 and 500 keV. Intermediate structure in the form of oscillators with widths of about 40 keV is observed.
Article
Experiments on gold have been performed with the Saclay linear accelerator using the time-of-flight method. Resonance parameters are given for 63 resonances in the energy range 10–1000 eV. Spin assignment methods are described and discussed. The J value is found for 40 resonances in combining total capture and transmission experiments. A convenient...
Article
The correct knowledge of the detector response is the main difficulty for analyzing experimental data. A simple shape is obtained with an annular cristal operating in coincidence or anti-coincidence with a central cristal 4″ × 6″. Merits of this detector are discussed and results are presented. A program is described to find intensities of differen...
Article
Experiments on niobium have been performed with the Saclay linear accelerator using the time-of-flight method. The resonance parameters were investigated in the energy range from 30 to 4000 eV. Transmission experiments allowed identification of the p wave neutron resonances above a few hundred eV, and for the low-energy range, identification was pe...
Article
The total neutron cross section has been investigated for natural bromine from 100 eV up to 200 eV. Resonance parameters and spin valies are given for many levels. As in neighbouring nuclei (As75, Ga) the strength function for the spin value J = 2 is twice that for J = 1. This strength function dependence is discussed for different nuclei investiga...
Article
The total neutron cross section has been investigated for natural bromine from 100 eV up to 200 eV. Resonance parameters and spin valies are given for many levels. As in neighbouring nuclei (As75, Ga) the strength function for the spin value J = 2 is twice that for J = 1. This strength function dependence is discussed for different nuclei investiga...
Article
Using the short pulses of a linac, a measurement has been performed of partial ..mu..⁻-capture rates in ¹°B, ¹²C, and ¹⁴N leading, respectively, to the bound excited states of ¹°Be, ¹²B, and ¹⁴C. These rates are deduced from the intensities of the observed de-excitation nuclear ..gamma.. rays. A theoretical discussion is given based...

Citations

... [121], but the experimental errors are rather large. An earlier experiment [122] produced a π = −0.11 ± 0.03 ± 0.08, a result whose (central) value has the opposite sign and much larger absolute magnitude. ...
... 2.4Experimentally obtained 579 eV 63 Cu resonance parameters. Each data point is taken from different references (#1 [24], #2 [25], #3 [26], #4 [27], #5 [28], and #6 [23]). The data of #6 were utilized by REFIT originally; the data of #7 are tentatively introduced to reproduce the experimental transmission dips ...
... These experiments were carried out in support to parity violation studies. Resolved resonance parameters for natural silver isotopes reported in the main evaluated data files are primarily based on experimental data of Moxon et al. [27], Garg et al. [28], Asghar et al. [29], Muradian et al. [30], de Barros et al. [31], Pattenden et al. [32], Macklin et al. [33], Mizumoto et al. [34] and Lowie et al. [26]. ...
... The 579-eV resonance parameters of 63 Cu may require being reevaluated. It should be emphasized that survey of the total cross sections of Pu and U isotopes is quite important to quantify NM. [24], #2 [25], #3 [26], #4 [27], #5 [28], and #6 [23]). The data of #6 were utilized by REFIT originally; the data of #7 are tentatively introduced to reproduce the experimental transmission dips ...
... A detailed study of the residual muon polarization for muons extracted from the πE3 beam-line and implanted in a thin aluminum (Al) target was carried out in a dedicated experiment, using the technique based on the Hanle signal [13]. The signal was deduced from the rates of decay positrons measured by three plastic scintillator telescopes, as a function of the beam momentum between 25 and 40 MeV/c. ...
... The transition was first observed in cosmic–ray data by Godfrey (1953) via the identification of the Godfrey–Tiomino cycle, i.e. µ capture on 12 C followed by β–decay of 12 B. The first investigation of the recoil polarization in the 12 C(0 + , 0) → 12 B(1 + , 0) transition was conducted by Love et al. (1959) in order to measure the µ − helicity in π − decay. The application of polarization measurements to induced currents was pioneered by Possoz et al. (1977 Possoz et al. ( , 1974) at Saclay and extended by Roesch et al. (1981a,b) and Truttman et al. (1979) at PSI. Using ingenious techniques these researchers have amassed impressive data on several polarization observables in 12 C(0 + , 0) → 12 B(1 + , 0) capture. ...
... For the level density we have mainly used the backshifted Fermi gas model, the Gilbert-Cameron model, and numerical interpolation tables, with data from RIPL2 [44]. The decay probabilities in the continuum were based on photon strength functions, while the probabilities of transitions in the discrete region below E c were determined by the branching ratios Table 9 The contribution to the thermal capture cross section σ r (without interference) and coherent scattering lengths of observed s-wave resonances using the results of transmission measurements in [49,50] and [51] and capture measurements of Mutti [47] and Domingo et al. [48]. The average radiation widths for the s-wave resonances observed in [47] and [48] are also given. ...
... 10, twenty-five prompt γ-rays were clearly observed. The 6189 and 7742 keV γ-rays have been reported by Samour [35]. Eight γ-rays have already been studied in other reac- tions [36]. ...
... The enhancement of the axial-charge NME γ 5 due to nuclear medium effects in the form of meson-exchange currents was first suggested in Refs. [323][324][325]. An enhancement of 40%-70% over the impulse-approximation value was predicted based on chiral-symmetry arguments and soft-pion theorems. ...
... Therefore a correction is necessary to obtain the interesting ground state polarization from the observed bound state polarization. Measurements of the total rate to bound states (Maier et al., 1964;Reynolds et al., 1963) and the individual rates to excited states (Budyashov et al., 1970;Giffon et al., 1981;Miller et al., 1972a;Roesch et al., 1981a) are employed to determine this correction. ...