Laboratory Angles Research Articles

Triton and alpha-particle production in neutron-induced reactions on carbon at En=42.5, 62.7, and 72.8 MeV.

Double-differential cross sections for fast neutron-induced triton and alpha-particle production on carbon are reported at three incident neutron energies: 42.5, 62.7, and 72.8 MeV, complementing our previous results for proton and deuteron emissions. Angular distributions were measured at laboratory angles between 20\ifmmode^\circ\else\textdegree\fi{} and 160\ifmmode^\circ\else\textdegree\fi{} in steps of 10\ifmmode^\circ\else\textdegree\fi{}. Procedures for data taking and data reduction are described. Results for double-differential, energy-differential, and total cross sections are presented. The measurements are compared to existing data and to nuclear model calculations which include preequilibrium and equilibrium decay mechanisms. \textcopyright{} 1996 The American Physical Society.

15N(d,α 0) 13C cross section and angular distribution measurements for ion beam analysis

Motivated by the ion beam analytical possibilities for exploiting 15N(d,α 0) 13C, we have measured the cross section of this reaction at deuteron energies from 400 keV to 2 MeV for laboratory angles of 135 and 150°, and from 400 keV to 1.6 MeV at 90°. Angular distributions from 85 to 160° have been measured at energies of 850, 972, 1100, 1200, and 1400 keV. Our results differ significantly from earlier measurements, which also disagree substantially amongst themselves.

Inclusive positive pion photoproduction.

Inclusive ${\mathrm{\ensuremath{\pi}}}^{+}$ photoproduction below the \ensuremath{\Delta}(1232) resonance has been measured from H, C, Ca, Sn, and Pb at laboratory angles of 51\ifmmode^\circ\else\textdegree\fi{}, 81\ifmmode^\circ\else\textdegree\fi{}, 109\ifmmode^\circ\else\textdegree\fi{}, and 141\ifmmode^\circ\else\textdegree\fi{} using tagged photons and \ensuremath{\Delta}E-E plastic scintillator telescopes with 17-MeV thresholds. Particle identification involved both the determination of differential energy loss and the detection of the ${\mathrm{\ensuremath{\mu}}}^{+}$ from the ${\mathrm{\ensuremath{\pi}}}^{+}$ decay. Double differential cross sections, angular distributions, and total cross sections were obtained for four incident photon energy bins centered at 184, 194, 204, and 213 MeV. Comparisons are made to both theoretical predictions and previous data sets. Ratios of nuclear cross sections to those obtained from the proton are extracted, and the features of these ratios are discussed. \textcopyright{} 1996 The American Physical Society.

Small angle neutron-neutron correlation functions for the 16O+27Al reaction at 220 MeV

Abstract Small angle correlations between two neutrons emitted at a laboratory angle near 45° from the 16 O+ 27 Al reaction at 220 MeV have been measured. The results show a positive correlation peak centered near a relative momentum of 7.5 MeV/ c . However, when restrictions are placed on the total momentum of the two-neutron system, the strength of the correlation function is found to be dependent on the total momentum of the two-neutron system. A possible anti-correlation is observed at low relative momentum for low total momentum pairs.

Measurement of the electric and magnetic polarizabilities of the proton.

The Compton scattering cross section on the proton has been measured at laboratory angles of 90\ifmmode^\circ\else\textdegree\fi{} and 135\ifmmode^\circ\else\textdegree\fi{} using tagged photons in the energy range 70--100 MeV and simultaneously using untagged photons in the range 100--148 MeV. With the aid of dispersion relations, these cross sections were used to extract the electric and magnetic polarizabilities, \ensuremath{\alpha}\ifmmode\bar\else\textasciimacron\fi{} and \ensuremath{\beta}\ifmmode\bar\else\textasciimacron\fi{} respectively, of the proton. We find \ensuremath{\alpha}\ifmmode\bar\else\textasciimacron\fi{}+\ensuremath{\beta}\ifmmode\bar\else\textasciimacron\fi{}=(15.0 \ifmmode\pm\else\textpm\fi{}2.9\ifmmode\pm\else\textpm\fi{}1.1\ifmmode\pm\else\textpm\fi{}0.4)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}4}$ ${\mathrm{fm}}^{3}$, in agreement with a model-independent dispersion sum rule, and \ensuremath{\alpha}\ifmmode\bar\else\textasciimacron\fi{} -\ensuremath{\beta}\ifmmode\bar\else\textasciimacron\fi{} =(10.8\ifmmode\pm\else\textpm\fi{}1.1\ifmmode\pm\else\textpm\fi{}1.4\ifmmode\pm\else\textpm\fi{}1.0)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}4}$ ${\mathrm{fm}}^{3}$, where the errors shown are statistical, systematic, and model-dependent, respectively. A comparison with previous experiments is given and global values for the polarizabilities are extracted.

Excitation mechanisms in moderate-energy Na+-Ar collisions.

By means of differential energy-transfer measurements, excitation mechanisms in ${\mathrm{Na}}^{+}$-Ar collisions have been studied at laboratory collision energies of 50\ensuremath{\le}${\mathit{E}}_{\mathrm{lab}}$\ensuremath{\le}1500 eV. In these experiments, doubly differential cross sections have been measured over nearly the whole angular range in the center-of-mass system by simultaneously detecting both scattered and recoiled particles (${\mathrm{Na}}^{+}$, Na, ${\mathrm{Ar}}^{+}$, and Ar) at laboratory angles of 2\ifmmode^\circ\else\textdegree\fi{}\ensuremath{\le}\ensuremath{\theta}\ensuremath{\le}92\ifmmode^\circ\else\textdegree\fi{}. The ${\mathrm{Na}}^{+}$ ions and Na atoms scattered inelastically were observed at reduced angles of \ensuremath{\tau}>3.5 keV deg and collision energies of ${\mathit{E}}_{\mathrm{lab}}$>500 eV. For energies of 500${\mathit{E}}_{\mathrm{lab}}$1000 eV, the dominant inelastic signal is due to one-electron charge transfer, while for ${\mathit{E}}_{\mathrm{lab}}$>1000 eV, two-electron excitation as well as one-electron excitation were observed. The electronic transitions in the ${\mathrm{Na}}^{+}$-Ar collisions are classified into two types of excitation mechanisms. One type is the one-electron transition that takes place at internuclear distances of R${\mathit{R}}_{\mathit{C}1}$=1.07 \AA{}. The other type is the one- and two-electron transitions that occur at distances of R${\mathit{R}}_{\mathit{C}2}$=0.45 \AA{}. These critical distances ${\mathit{R}}_{\mathit{C}}$=1.07 and 0.45 \AA{} are close to \ensuremath{\Vert}${\mathit{r}}_{\mathit{i}}$\ifmmode\pm\else\textpm\fi{}${\mathit{r}}_{\mathit{j}}$\ensuremath{\Vert}=0.96 and 0.38 \AA{}, respectively, evaluated from the ionic and atomic radii.

Nuclear decay following deep inelastic scattering of 470 GeV muons.

We detected 1--10 MeV neutrons at laboratory angles from 80{degree} to 140{degree} in coincidence with 470 GeV muons deep inelastically scattered from H, D, C, Ca, and Pb targets. The neutron energy spectrum for Pb can be fitted with two components with temperature parameters of 0.7 and 5.0 MeV. The average neutron multiplicity for 40{lt}{nu}{lt}400 GeV is about 5 for Pb, and less than 2 for Ca and C. These data are consistent with a process in which the emitted hadrons do not interact with the rest of the nucleus within distances smaller than the radius of Ca, but do interact within distances on the order of the radius of Pb in the measured kinematic range. For all targets the lack of high nuclear excitation is surprising.

Pion double charge exchange on the even selenium isotopes.

Pion-induced double charge exchange (${\mathrm{\ensuremath{\pi}}}^{+}$,${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$) on $^{76,78,80,82}\mathrm{Se}$, leading to the double isobaric analog states (DIAS) and the ground states of $^{76,78,80,82}\mathrm{Kr}$, has been studied at a laboratory angle of ${5}^{0}$ and incident pion kinetic energy of 293.2 MeV. Cross sections for these transitions have been extracted, and those for the DIAS are compared to two simple models of pion double charge exchange.

The 17,18O(p, n)17,18F reaction at Ep = 35 MeV

The 17,18 O(p, n) 17,18 F reactions were studied at E p = 35 MeV. Neutron spectra were measured at laboratory angles between 0° and 140°. Results were compared with distorted-wave calculations using the shell-model wave functions. For the 17 O(p, n) reaction, cross-section magnitudes as well as the angular-distribution shapes were well described by the calculation. On the other hand, normalization factors of 0.60 were required for the spin-flip excitations observed in the 18 O(p, n) reaction leading to the ground (1 + ), 1.700 MeV (1 + ) and 2.100 MeV (2 − ) states. Possible origins of such differences were discussed.

Pion-induced single charge exchange in deuterium.

We report the measurement of the differential cross section for $^{2}\mathrm{H}$(${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$,${\mathrm{\ensuremath{\pi}}}^{0}$) for laboratory angles 0\ifmmode^\circ\else\textdegree\fi{}--145\ifmmode^\circ\else\textdegree\fi{}, at incident pion energies of 164, 263, and 371 MeV. A Faddeev calculation at 164 MeV incorporating Pauli-blocking and multiple-scattering effects describes those data well. At the two higher energies the $^{2}\mathrm{H}$(${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$,${\mathrm{\ensuremath{\pi}}}^{0}$) cross section is essentially identical to the $^{1}\mathrm{H}$(${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$,${\mathrm{\ensuremath{\pi}}}^{0}$) cross section, except at forward angles where the former is suppressed by the Pauli principle. This experiment was the first to make use of a major component of the Neutral Meson Spectrometer at the Los Alamos National Laboratory.

Proton and deuteron production in neutron-induced reactions on carbon at En=42.5, 62.7, and 72.8 MeV.

Double-differential cross sections for proton and deuteron production in fast neutron induced reactions on carbon are reported for three incident neutron energies: 42.5, 62.7, and 72.8 MeV. Angular distributions were measured at laboratory angles between 20\ifmmode^\circ\else\textdegree\fi{} and 160\ifmmode^\circ\else\textdegree\fi{}. Procedures for data taking and data reduction are presented. Energy-differential cross sections and total cross sections are also reported. Experimental cross sections are compared with existing data and with theoretical calculations in the frame of the intranuclear cascade model.

Mass dependence of antiproton production in nucleus-nucleus collisions at 3.65 GeV/nucleon

Antiproton production cross-sections have been measured for p+C, C+C, C+Cu and C+Pb collisions at 3.65 GeV/nucleon.\(\bar p\) laboratory momentum and angle are 0.8 GeV/c and 24°. The target mass dependence parameter is found to be 0.43±0.1. A strong increase in antiproton yield is observed from p+C, d+C to C+C collisions. Projectile mass parameter is 1.2±0.2 for d+C to C+C. The construction and calibration of APAKI, an annihilation detector for\(\bar p\) identification, are also described.

The high precision measurement of 208Pb+ 208Pb Mott scattering at energies under the Coulomb barrier: the observation of new atomic effects

In a high precision experiment, Mott scattering of the 208Pb+ 208Pb and elastic scattering of the 208Pb+ 238U systems was measured at 6 energies near the Coulomb barrier with kinematic coincidences for angle pairs at θ lab =30°, 60°. The relative laboratory angle between scattered and recoiling nuclei, measured with an absolute precision of 0.003° provides a measurement of the reaction kinematics and the energy loss in the reaction. The binding energy of internal shells of the quasiatioms formed during the collision can be measured in this way.

Kerma values deduced from neutron-induced charged-particle spectra of carbon from 40 to 75 MeV

The double-differential cross-sections for the 12C(n,px), 12C(n,dx), 12C(n,tx) and 12C(n, alpha x) reactions have been measured at three incident neutron energies, 42.5, 62.7 and 72.8 MeV, at laboratory angles between 20 degrees and 160 degrees . From these measurements, the energy-differential cross-sections have been determined and consequently the partial and total kerma values. Results of the experimental double-differential and energy-differential cross-sections at the three incident neutron energies are presented. The deduced kerma values are compared with previous measurements and theoretical predictions.

Charge separation reaction dynamics from pepipico using a position‐sensitive detector

AbstractThe combination of a position‐sensitive detector with the photoelectron–photoion–photoion coincidence (PEPIPICO) technique allows complete determination of the laboratory momenta and angles of ions in coincidence. The technique yields angular distributions of fragment ions, high resolution kinetic energy distributions for two‐body reactions and Newton diagrams for three‐body dication dissociation. The reactions SF→F++SF+F2 and cyclo‐C4F→CF+C2F+CF are shown to follow sequential mechanisms as determined previously. The technique's potential for elucidating more complex reactions is illustrated for SO→O++S++O and CF3I2+→CF+I++F, which show variations in mechanism as a function of total kinetic energy release.

Electron bombardment induced fragmentation of size selected neutral (D2O) n clusters

The fragmentation behaviour of size selected neutral (D2O) n clusters withn≦4 after ionization with 70 eV electrons is subject of this work. Size selection by scattering the cluster beam from a He target beam in combination with a quadrupole mass filter and time resolved measurements at specific laboratory angles enables us to determine the neutral precursor masses of the detected ions. The measured fragment pattern is dominated by deuterated ions of the form (D2O) n−x D+ withx≧1. The dimer fragmentation which leads with a probability of 62.5% to the D3O+ ion and with 37.5% to D2O+ can be explained by fast intracluster ion-molecule reactions of charged monomer fragments reacting with the partner molecule. For larger clusters the fragmentation process can be rationalised by the creation of an initially highly excited D3O+ (D2O) x complex which is stabilized by evaporating additional monomer units with the main fragment channel (D2O)D+ forn=3 and (D2O)2D+ forn=4. With increasing cluster size an increasing tendency of evaporation of more than one water monomer unit has been observed.

Differential cross sections for elastic and reactive collisions between Na and multiple photon excited SF 6

Differential cross sections for collisions of Na and SF 6 from beam experiments are presented. The SF 6 is vibrationally excited to the 5 v 3 level with a CO 2 laser. Enhancement of reactive scattering is detected for different energies (0.25 eV, 1.04 eV and 2.70 eV) and at laboratory angles between 10 and 75 deg. The amount of elastically scattered Na from excited SF 6 always decreases in comparison with ground state scattering. The experiments show that the reaction is more efficient if vibrational energy is put into SF 6 as compared with exciting Na electronically.

Angular distribution of delta electrons emitted in collisions of 1.0-MeV/u Fq+ (q=4,6,8,9) with molecular hydrogen.

The angular distribution, as well as the energy distribution of \ensuremath{\delta} electrons produced in collisions of 1.0-MeV/u ${\mathrm{F}}^{\mathit{q}+}$ (q=4,6,8,9) ions with molecular hydrogen, have been studied for laboratory observation angles (${\mathrm{\ensuremath{\theta}}}_{\mathit{L}}$) from 0\ifmmode^\circ\else\textdegree\fi{} to 70\ifmmode^\circ\else\textdegree\fi{} with respect to the beam direction. The measurements are in fair agreement with the impulse approximation calculations which use the quantal elastic electron-ion differential scattering cross sections folded with the Compton profile of the target electrons. We observe that the energy of the centroid of the binary-encounter-electron (BEE) peak is projectile charge state, q, and laboratory angle, ${\mathrm{\ensuremath{\theta}}}_{\mathit{L}}$, dependent. Moreover, at 0\ifmmode^\circ\else\textdegree\fi{}, an enhancement of the ratio of the observed double differential cross section for nonbare projectiles to that for the bare ion projectiles, \ensuremath{\sigma}(q+)/\ensuremath{\sigma}(9+), is observed, contrary to the ${\mathit{q}}^{2}$ scaling predicted by a first Born calculation for ionization. This ratio \ensuremath{\sigma}(q+)/\ensuremath{\sigma}(9+) decreases nonotonically with increasing ${\mathrm{\ensuremath{\theta}}}_{\mathit{L}}$, and becomes smaller than one for ${\mathrm{\ensuremath{\theta}}}_{\mathit{L}}$\ensuremath{\ge}30\ifmmode^\circ\else\textdegree\fi{}.

The relativistic transport model description of subthreshold kaon production in heavy-ion collisions

The relativistic transport model, in which the nucleon effective mass is connected to the scalar field while its energy is shifted by the vector potential, is extended to include the kaon degree of freedom. We further take into account the medium modification of the kaon mass due to explicit chiral symmetry breaking. Both the propagation of kaons in the mean-field potential and the kaon-baryon elastic scattering are explicitly treated in our study. We find that the attractive kaon scalar mean-field potential in the dense matter leads to an enhanced kaon yield in heavy-ion collisions at energies of about 1 GeV/nucleon that are below the threshold for kaon production from the nucleon-nucleon interaction in free space. The final-state kaon-baryon scattering is seen to affect significantly the kaon momentum spectra, leading to an enhanced yield of kaons with large momenta or at large laboratory angles. With a soft nuclear equation of state and including the attractive kaon scalar potential, the calculated kaon energy spectra agree with the preliminary data on subthreshold kaon production from the heavy-ion synchrotron at GSI.

Measurements and analysis of neutron elastic scattering at 65 MeV.

Elastic scattering cross sections for 65 MeV neutrons have been measured for natural targets of C, Si, Ca, Fe, Sn, and Pb at laboratory angles from 6\ifmmode^\circ\else\textdegree\fi{} to 45\ifmmode^\circ\else\textdegree\fi{}. A unique, compact detection system consisting of a ${\mathrm{CH}}_{2}$ (proton) converter and large-acceptance, wire-chamber-based, recoil-proton telescope is utilized for the measurements. The data is compared with macroscopic optical model potentials derived from proton scattering. In addition, comparisons with the microscopic optical model potentials, those of Jeukenne-Lejeune-Mahaux and Yamaguchi-Nagata-Matsuda, give a very good fit to the data.