Laboratory Angles Research Articles

Photodissociation of o-bromotoluene at 266 nm

The photodissociation of o-bromotoluene at 266 nm has been investigated using the universal crossed laser–molecular beam technique. The angle-resolved time-of-flight (TOF) spectra corresponding to Br photofragment are measured at different lab angles. The observed translational energy distribution and anisotropy parameters of the Br photofragment indicate that o-bromotoluene dissociates via two channels. In the first channel, the anisotropy parameter β is determined to be 0.5±0.2 and the average translational energy is only 9% of the available energy. In the other photofragmentation channel, β is determined to be −0.4±0.2 and 44% of the available energy is assigned to translational energy. Possible mechanisms are discussed.

Measurement of the $pp$ analyzing power in the vicinity of 2.20 GeV

The pp elastic scattering analyzing power was measured in small energy steps in the vicinity of the accelerator depolarizing resonance \(\gamma G= 6 \) at 2.202 GeV. A vertically polarized proton beam was extracted from SATURNE II at energies above the resonance and passed through different copper degraders. The beam was focused on the beam line polarimeter CH\(_2\) target. Its halo was removed by four powerful magnets. Measurements at degraded energies were complemented by data obtained with the directly extracted polarized beam outside the resonance region. Analyzing power results at fixed laboratory angles are compared with existing data in the region under discussion, with polynomial fits from 1.6 to 3.5 GeV, and with phase shift analysis predictions.

Neutron Yields from 155 MeV/Nucleon Carbon and Helium Stopping in Aluminum

Neutron fluences have been measured from 155 MeV/nucleon 4He and 12C ions stopping in an Al target at laboratory angles between 10 and 160 deg. The resultant spectra were integrated over angle and energy above 10 MeV to produce total neutron yields. Comparison of the two systems shows that approximately two times as many neutrons are produced from 155 MeV/nucleon 4He stopping in Al and 155 MeV/nucleon 12C stopping in Al. Using an energy-dependent geometric cross-section formula to calculate the expected number of primary nuclear interactions shows that the 12C + Al system has, within uncertainties, the same number of neutrons per interaction (0.99 ± 0.03) as does the 4He + Al system (1.02 ± 0.04), despite the fact that 12C has three times as many neutrons as does 4He. Energy and angular distributions for both systems are also reported. No major differences can be seen between the two systems in those distributions, except for the overall magnitude. Where possible, the 4He + Al spectra are compared with previously measured spectra from 160 and 177.5 MeV/nucleon 4He interactions in a variety of stopping targets. The reported spectra are consistent with previously measured spectra. The data were acquired to provide data applicable to problems dealing with the determination of the radiation risk to humans engaged in long-term missions in space; however, the data are also of interest for issues related to the determination of the radiation environment in high-altitude flight, with shielding at high-energy heavy-ion accelerators and with doses delivered outside tumor sites treated with high-energy hadronic beams.

EXPERIMENTAL CROSS SECTIONS FOR LIGHT-CHARGED PARTICLE PRODUCTION INDUCED BY NEUTRONS WITH ENERGIES BETWEEN 25 AND 65 MeV INCIDENT ON OXYGEN

Experimental double-differential cross sections (d2ς/dΩdE) for fast neutron-induced proton, deuteron, triton, and alpha-particle production on oxygen are reported at several incident neutron energies between 25 and 65 MeV for outgoing particle energies above the experimental energy detection thresholds. Angular distributions were measured at laboratory angles between 20° and 160°. Reliable extrapolated spectra are obtained at very forward (2.5° and 10°) and at very backward (170° and 177.5°) angles. Based on these experimental data, energy-differential (dς/dE), angle-differential (dς/dΩ), and total cross sections (ςT) are reported for each detected particle.

Measurements of R= σL/ σT for 0.03< x

Measurements were made at SLAC of the cross section for scattering 29 GeV electrons from carbon at a laboratory angle of 4.5°, corresponding to 0.03< x<0.1 and 1.3< Q 2<2.7 GeV 2. Values of R= σ L / σ T were extracted in this kinematic range by comparing these data to cross sections measured at a higher beam energy by the NMC collaboration. The results are in reasonable agreement with pQCD calculations and with extrapolations of the R1990 parameterization of previous data. A new fit is made including these data and other recent results.

Excitation function and angular distribution for the 14N(α,p) 17O reaction

The cross sections for 14N(α,p) 17O reactions at lab angle 165° and incident energies between 5.5 and 7.5 MeV were measured. Angular distribution of protons for an incident energy of 6.576 MeV, which is the energy of the resonance peak of the excitation function of the reaction 14N(α,p) 17O is presented. Finally, two examples for detecting nitrogen with this reaction are given.

Coherent π0 photo-production on 4He at intermediate energies with polarized photons

The reaction 4 He( γ,π 0) 4 He has been studied with the LEGS tagged, polarized gamma-ray beam. Data are presented at laboratory angles of 31°, 45°, 72.5°, 90°, 110° and 130° for incoming photon energies of 206, 219, 232, 245, 259, 274, 289, 306 and 322 MeV. The unpolarized cross sections are compared with the Δ-hole theoretical model results available in literature. The measured photon beam asymmetry is −1 as expected from conservation of angular momentum and parity.

Experimental double-differential cross sections and derived kerma factors for oxygen at incident neutron energies from reaction thresholds to 65 MeV

The double-differential cross sections (energy spectra) for the (n, px), (n, dx), (n, tx) and (n, x) reactions on oxygen have been measured for nine incident neutron energies in the range 25 to 65 MeV at lab angles between and in steps of . From these measurements, the energy differential cross sections have been determined and consequently the partial and total kerma factors. Based on the obtained experimental partial kerma factors in the incident neutron energy range 25-65 MeV, a procedure is proposed for the extrapolation of these values to the reaction threshold energy of each measured reaction channel. Results of the experimental double-differential, energy differential and total cross sections are presented. The deduced partial and total kerma factors of the present work are compared with results of previous measurements and theoretical predictions.

Measurements of Double-Differential Neutron Emission Cross Sections of 6Li, 7Li and 9Be for 11.5 MeV and 18.0 MeV Neutrons

Double-differential neutron emission cross sections (DDXs) of 6Li, 7Li and 9Be were measured for 18.0 MeV and 11.5 MeV incident neutrons produced by the T(d, n) and 15N(d, n) reactions respectively, using the Tohoku University Dynamitron time-of-flight (TOF) spectrometer. The data were obtained at 13 laboratory angles, and angular-differential cross sections (ADXs) of elastic and inelastic scattering neutrons were derived from the DDXs. For 11.5 MeV neutrons, we obtained the neutron emission spectra over the secondary neutron energies by newly employing the double TOF method as well as the conventional one. In the measurements at 18.0 MeV, we achieved better energy resolution than in our previous studies by using a neutron detector that has a larger solid angle and a thinner tritium target. The experimental results of DDXs and ADXs were compared with our previous results and the evaluated data given in JENDL-3.2, JENDL Fusion File and ENDF/B-VI. It is found that the JENDL data reproduce the experimental ones very well.

Light charged particle emission induced by neutrons with energies between 25 and 65 MeV on oxygen. II. Tritons and alpha-particles

Double-differential cross sections for fast neutron induced triton and alpha-particle production on oxygen, are reported at seven incident neutron energies between 30 and 65 MeV. Angular distributions were measured at laboratory angles between 20 degrees and 160 degrees. Energy-differential, angle-differential and total cross sections are reported. Experimental cross sections are compared with existing experimental data and with theoretical model calculations.

The dynamics of hydrogen abstraction reactions: Crossed-beam reaction Cl+n-C5H12→C5H11+HCl

We present a crossed molecular beam study of the dynamics of the metathesis reaction Cl+n-C5H12→HCl+C5H11 at a collision energy of 16.8 kcal/mol. The experiments were conducted on the Chemical Dynamics Beamline at the Advanced Light Source, using tunable undulator radiation to effect soft ionization of the pentyl radical product. Laboratory angular distributions and time-of-flight spectra at many laboratory angles were used to obtain the center-of-mass translational energy and angular distributions. These distributions were found to be strongly coupled, with the forward scattered pentyl radical formed extremely cold, while the backscattered radicals were formed leaving nearly 15 kcal/mol in internal energy in the products. These results are contrasted with recent studies on the analogous reaction with propane, suggesting in this case direct involvement of the carbon skeleton in the collision process.

A new precise value of the absolute , , transition frequency in

The absolute frequency of the optical electric-dipole transition between the metastable 1 s 2 s 3 S1, F =5/2 and the short-lived 1 s 2 p 3 P2, F =7/2 hyperfine structure sublevels of the helium-like ion in its rest frame was determined by combining Doppler-free saturation spectroscopy and laser heterodyning. One of two cw single-mode dye lasers was locked to the calibrated w-component of the [R(85) 26-0]-line in the (B-X)-system of the -molecule at MHz. While crossing two counterpropagating beams of the other laser perpendicularly (lab angle ) with a low-velocity ion beam and tuning its frequency over the transition under study, the distance of the Lamb-dip center frequency from was obtained by mixing both laser frequencies with an avalanche diode and registering their beat frequency at about 4 GHz with a quartz-stabilized high-frequency counter. The Lamb-dip position was measured for different ion velocities (in units of the velocity of light) in the range of . The parameters and of the relativistic Doppler formula were extracted via a fit to the experimental data set , providing MHz and . This result of differs noticeably from MHz, measured by another group in a collinear-beam configuration at an ion beam propagating with .

Light charged particle production in neutron-induced reactions on aluminum atEn=62.7MeV

Double-differential cross sections for $62.7\ifmmode\pm\else\textpm\fi{}1.0$ MeV neutron-induced light charged particle $(p$, $d$, $t$, and $\ensuremath{\alpha})$ production on aluminum are reported. 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 production cross sections are presented. The measurements are compared to existing proton-induced data and to nuclear model calculations which include preequilibrium and equilibrium decay mechanisms. Agreement with the model calculations is good for all ejectile types except for deuterons, where pickup processes are overestimated. The neutron-induced data presented are shown to be in good agreement with experimental proton-induced data for charge-symmetric reaction channels. For the proton emission channel the approximate factor of two between the two emission spectrum measurements is explained.

The pp elastic scattering analyzing power measured with the polarized beam and the unpolarized target between 1.98 and 2.80 GeV

A polarized proton beam extracted from SATURNE II was scattered on an unpolarized CH 2 target. The angular distribution of the beam analyzing power A oono was measured at large angles from 1.98 to 2.8 GeV and at 0.80 GeV nominal beam kinetic energy. The same observable was determined at the fixed mean laboratory angle of 13.9° in the same energy range. Both measurements are by-products of an experiment measuring the spin correlation parameter A oon .

Accelerator‐based boron neutron capture therapy

Boron neutron capture therapy (BNCT) is a promising therapy modality for cancer. Clinical trials are under way. BNCT works by a selective loading of tumor cells with and subsequent irradiation of the tumor with thermal neutrons. The reaction is induced which releases 2.3 MeV of energy. In accelerator‐based BNCT, neutrons for this therapy are produced using particle induced reactions. Three reactions, =2.5 MeV, =3.0–4.0 MeV, and =2.6 MeV were investigated. Complete data for the reaction were not previously available. Therefore, 28 thick target neutron spectra were measured, on an absolute basis, using time‐of‐flight techniques. Proton energies of 3.0, 3.4, 3.7, and 4.0 MeV and laboratory angles of 0°–145° were used. The accuracy of the data was confirmed by measuring a different reaction. Monte Carlo techniques were used to design therapy beams. Using and therapy times of 12–25 and 27–60 min, respectively, were predicted (tumor depth 2–6 cm, 15 RBE‐Gy total tumor dose, 10 kW accelerator beam power, 30 ppm boron tumor concentration). The total tumor dose includes four components [fast neutron, thermal neutron, gamma, and which are estimated by using energy‐dependent fluence‐to‐kerma conversion factors. Using and a 1 mA beam current, nearly equivalent therapy beam parameters were predicted with 4.0 and 3.7 MeV protons. For equivalent accelerator beam power, 3.7 MeV protons would produce higher dose rates. Using resulted in lower dose rates. Facility shielding is presented.

Fragment emission from the mass-symmetric reactions58Fe,58Ni+58Fe,58NiatEbeam=30 MeV/nucleon

The mass-symmetric reactions ${}^{58}{\mathrm{F}\mathrm{e},}^{58}{\mathrm{Ni}\mathrm{}+}^{58}{\mathrm{F}\mathrm{e},}^{58}\mathrm{Ni}$ were studied at a beam energy of ${E}_{\mathrm{beam}}=30 \mathrm{M}\mathrm{e}\mathrm{V}/\mathrm{n}\mathrm{u}\mathrm{c}\mathrm{l}\mathrm{e}\mathrm{o}\mathrm{n}$ in order to investigate the isospin dependence of fragment emission. Ratios of inclusive yields of isotopic fragments from hydrogen through nitrogen were extracted as a function of laboratory angle. A moving source analysis of the data indicates that at laboratory angles around $40\ifmmode^\circ\else\textdegree\fi{}$ the yield of intermediate mass fragments (IMF's) beyond $Z=3$ is predominantly from a midrapidity source. The angular dependence of the relative yields of isotopes beyond $Z=3$ indicates that the IMF's at more central angles originate from a source which is more neutron deficient than the source responsible for fragments emitted at forward angles. The charge distributions and kinetic energy spectra of the IMF's at various laboratory angles were well reproduced by calculations employing a quantum molecular-dynamics code followed by a statistical multifragmentation model for generating fragments. The calculations indicate that the measured IMF's originate mainly from a single source. The isotopic composition of the emitted fragments is, however, not reproduced by the same calculation. The measured isotopic and isobaric ratios indicate an emitting source that is more neutron rich in comparison to the source predicted by model calculations.

α-particle emission as a probe of dynamical deformations

We have measured alpha-particle spectra at different laboratory angles from the fusion reaction Si-28+V-51 at 140 MeV. These spectra deviate at higher energies from the statistical model calculations using rotating liquid drop model values of the moment of inertia. In order to explain the experimental spectra, changes were required in the moments of inertia corresponding to deformation, which suggests dynamical effects on the deexcitation process for charged-particle emission. The comparison of decay times with formation times implies that light charged particles are preferentially emitted prior to the full relaxation of the compound nucleus. Statistical models and dynamical calculations have been employed in an attempt to interpret the experimental data. The results were compared with the Si-28+Al-27 system studied earlier in order to understand the symmetric and asymmetric entrance channel effects in the formation of the compound system.

Revised cross sections of the 32S(d,p) 33S reactions

The differential cross sections of the 32S(d,p) 33S nuclear reactions have been measured at a laboratory angle of 150° for incident ion energies between 1.0 and 2.7 MeV. Two different experimental methods were used, one using a thin CdS film and the other using a thick ZnS target. The resulting cross sections are compared to previously published data and the 32S(d,p 0) 33S and 32S(d,p 1) 33S cross sections are also compared directly to the Rutherford cross section. Some applications of the cross sections are discussed.

Elastic scattering cross sections for the analysis of helium by 1H backscattering and hydrogen by 4He ERD

Elastic scattering cross sections for the analysis of helium by proton backscattering have been determined in the energy region 1.6–2.7 MeV. The measurements were performed at laboratory angles of 110°–160°. For the analysis of hydrogen by elastic recoil detection (ERD), the scattering cross sections for 1H recoils by 4He ion bombardment for energies 6.4–10.8 MeV at recoil angles of 28°-8° have been calculated by kinematically reversing the backscattering process. The helium target was prepared by implanting 60 keV 4He ions into a thin tantalum foil. The helium concentration in the target was determined by 10 MeV 28Si ion transmission ERD analysis. The obtained systematic cross section data are compared with the scarce literature values available.

Measured Correlated Motion of Three Massive Coulomb Interacting Particles

We have measured the correlated center-of-mass (c.m.) motion and energy sharing of the three massive Coulomb-interacting particles ${\mathrm{H}}^{+}+{\mathrm{H}}^{+}+{\mathrm{H}}^{\ensuremath{-}}$ with total energy of a few eV. We measured in time coincidence the lab frame energy and angle of all three particles produced from excited 4 keV ${\mathrm{H}}_{3}^{\phantom{\rule{0ex}{0ex}}+}$ formed in collisions with He. For each triple coincidence, we found the c.m. energy of each particle and the c.m. correlation angle between the two ${\mathrm{H}}^{+}$. The c.m. energy data, displayed on a Dalitz plot, reveals the high degree of correlated motion of the three massive charged particles.