Recoil Technique Research Articles

Cross sections and recoil properties ofRb83,84,86formed by 0.6-21 GeVH1reactions with targets of Y to U

Cross sections for the formation of rubidium isotopes 83, 84, and 86 have been determined for targets from yttrium to uranium irradiated by protons of 0.6, 10.5, and 21 GeV. The recoil technique, using thick targets and thick collectors, combined with a mathematical formalism based on the two step model, permits the determination of some characteristics of the nuclear reactions, i.e., the range $R$, the mean momentum $〈P〉$ of the observed products, and the excitation energy ${E}^{*}$ of the residual nucleus after cascade. For the three Rb isotopes at 0.6 GeV, the mean momenta fall into three groups depending on the nature of the targets: (a) less than 30 ${(\mathrm{MeV}\mathrm{u})}^{\mathrm{\textonehalf{}}}$ for Y, Nb, and Ag but proportional to $\ensuremath{\Delta}A$, the difference between the target and product masses, (b) about 40 to 55 ${(\mathrm{MeV}\mathrm{u})}^{\mathrm{\textonehalf{}}}$ for the rare earths, and (c) from 55 to 120 ${(\mathrm{MeV}\mathrm{u})}^{\mathrm{\textonehalf{}}}$ for Ta to U. For 0.6, 10.5, and 21 GeV protons, the mean momenta are all practically the same as for the first two groups of targets. On the contrary, for $^{83}\mathrm{Rb}$ and $^{84}\mathrm{Rb}$ formed in targets Ta to U, the momenta decrease decidedly between 0.6 and 10.5 GeV. The mean momentum of $^{86}\mathrm{Rb}$ formed in Th and U seems almost the same at 10.5 and 0.6 GeV. The excitation energies ${E}^{*}$ are very similar for 0.6, 10.5, and 21 GeV protons for all nuclear reactions where the mean momentum depends only slightly on ${E}_{p}$. However, the apparent value of ${E}^{*}$ diminishes for targets showing a decrease of mean momentum at 10.5 and 21 GeV. A semi-empirical test, based on the mean squared momentum $〈{{m}_{i}}^{2}{{v}_{i}}^{2}〉$ per evaporated nucleon, allows the production of Rb from Y, Nb, and Ag to be interpreted as spallation. Comparison of the experimental momenta or kinetic energies $〈T〉$ with values $\overline{E}$ calculated from the liquid drop model suggests binary fission at medium energies for the production of all three isotopes from targets of Ta to U with 0.6 GeV protons. The same conclusion is reached for the production of $^{86}\mathrm{Rb}$ from Th and U for all incident energies employed. Reactions showing anomalous behavior of ${E}^{*}$ not explicable by the fission or simple spallation could result from a high energy mechanism.NUCLEAR REACTIONS $^{83}\mathrm{Rb}$, $^{84}\mathrm{Rb}$, $^{86}\mathrm{Rb}$ in 13 targets (Y to U), 0.6-10.5-21 GeV ${E}_{p}$. Measured cross sections $\ensuremath{\sigma}$ and thick target-thick collectors recoil properties. Derived deposition energy ${E}^{*}$, kinetic energy $T$ and momentum per emitted nucleon.

Precise Measurements of the Elastic n-d Differential Cross Section at Low Energy

A recoil technique to measure the n-d/n-p differential cross section ratio is discussed. The method has been used to obtain an n-d cross section of 231.2±1.9 mb/sr at 180° and En.lab=8.05 MeV. The error is a quadratic combination of uncertainties from a large number of sources including counting statistics. The present lack of knowledge of the reference n-p differential cross section contributes approximately a further uncertainty of 1.5 mb/sr. A Monte Carlo program was used to calculate the average scattering angle and a correction factor to transfer the experimental numbers to an n-d cross section at 180°.

Scattering of Low-Energy Electrons by Excited Sodium Atoms Using a Photon and Electron Atomic Beam Recoil Technique

A new method for measuring cross sections for the scattering of electrons by laser-excited atoms is described. It is a generalization of the atomic-beam recoil technique, taking advantage of the recoil of atoms during resonant photon interactions to spatially separate excited from nonexcited atoms. A preliminary value for the total cross section for the scattering of electrons by the 3/sup 2/P/sub 3///sub 2/(m/sub F/=3) state of sodium at 4.4 eV is presented. (AIP)

Differential spin exchange in the elastic scattering of low-energy electrons by rubidium

The atomic-beam recoil technique has been used to obtain the ratio of spin-flip to full differential cross sections for the elastic scattering of electrons by rubidium at 0.80, 1.10, and 1.40 eV. Data are presented for a range of angles between 30degree and 180degree at each of these energies. These measurements were partly motivated by the expectation that relativistic effects, particularly the spin-orbit interaction, will be significant in electron scattering by the heavier alkali metals, even at low energies. In this context, we show how our measurements are related to the relativistic scattering amplitudes recently discussed by Burke and Mitchell for one-electron atoms. These experiments were performed at intermediate magnetic fields, where the nuclear and valence electron magnetic moments are not fully decoupled. The necessary corrections are discussed and taken into account. (AIP)

A Proton Recoil Scintillation Technique for Estimating Neutron Energy Spectra

The proton recoil technique using plastic scintillators is employed to measure fast-neutron spectra. Associated gamma-ray background is eliminated by using various thicknesses of thin scintillators. The method, based on different ranges of electrons and protons in the detector material, is shown to be useful for measuring neutron spectra over an extended energy region. Four scintillator thicknesses are chosen to cover the neutron energy from 1 to 18 MeV, based on practically 100 percent transmission of Compton-edge electrons. The pulse-height spectra from different detectors are mixed to give a pulse-height spectrum of the ''combined'' detector. A general purpose unfolding code is developed to unfold the combined pulse-height spectrum using a combined response matrix that results from the mixing of the calculated (Monte Carlo) response functions for the individual detectors. The neutron spectra of different ($alpha$,n) sources and of $sup 252$Cf spontaneous fission are measured and compared with published data. The technique developed, although used only for a neutron energy up to 14 MeV, can be applied in practice to higher energies.

The combination of the gas jet recoil technique with the fast chemical on-line separation system SISAK

The fast chemical on-line separation system SISAK has been connected to a gas jet recoil transport arrangement. Pure fractions of short-lived La, Ce and Pr nuclides have been isolated from complex mixtures of reaction products obtained by thermal-neutron-induced fission of 235U.

Hydrogen abstraction reactions by atomic fluorine. III. Temperature dependence of the intermolecular kinetic isotope effect for the thermal F+H2 reaction

The intermolecular kinetic isotope effect for the title reaction has been investigated using a moderated nuclear recoil technique. The following Arrhenius temperature dependence was obtained: kH2/kD2 = (1.04±0.06)exp[(382±35)/RT]. This result is in quantitative agreement with an independent study based upon a discharge flow reactor method. The advantages and limitations of the nuclear recoil procedure are considered, and relevant literature results are critically reviewed.

Scattering of alkali halides by electrons. II. CsCl

Scattering of CsCl by 0.47–15.7 eV electrons has been measured using the molecular beam recoil technique. Center of mass differential cross section models are adjusted to the scattering after transformation to apparatus space. Absolute total cross sections, approximately equal to the first Born approximation point dipole prediction at 15.7 eV, fall to one-fourth of the theory at 0.47 eV. Momentum transfer cross sections are dramatically smaller than the theory at low energies.

Scattering of alkali halides by electrons. III. KI

Scattering of KI by 0.81–15.7 eV electrons has been observed using the molecular beam recoil technique. Center of mass cross section models are adjusted to fit the apparatus space scattering pattern. Absolute total cross sections agree at high energies with the first Born approximation and are a factor of 4 smaller at the lowest energy. At low energies the momentum transfer cross sections are an order of magnitude below theory. The measured cross sections are nominally identical to those measured in CsCl.

Scattering of alkali halides by electrons. I. CsF

The scattering of CsF by 0.69–6.81 eV electrons has been measured with the molecular beam recoil technique. A novel kinematic analysis is used to fit center of mass differential cross section models to the data. Absolute total cross sections determined in this fashion are a factor of 2 smaller than first Born approximation predictions at low energies. Absolute momentum transfer cross sections are an order of magnitude smaller than theory.

Absolute measurements of total cross sections for electron scattering by Na2 and K2 (0.5–50 eV)

Absolute measurements have been made of total cross sections for the scattering of electrons by sodium and potassium diatomic molecules, over the electron energy range 0.5–50 eV, at temperatures of 405 and 335 °C, respectively, using the molecular beam recoil technique. We find the molecular cross sections to lie about 60% and 33% above the respective sodium and potassium atomic cross sections above 2 eV. The measured sodium and potassium molecular total cross sections range from 305 and 430 Å2, respectively, at 0.5 eV and 85 and 97 Å2, respectively, at 50 eV. The over-all uncertainty in the sodium dimer results is at most 16%, and in the potassium dimer results is at most 20%.

Short-LivedαEmitters of Thorium: New IsotopesTh218−220

The $\ensuremath{\alpha}$-decay energies and half-lives of three new thorium isotopes, $^{218\ensuremath{-}220}\mathrm{Th}$, have been measured by a simple recoil technique. The observed $\ensuremath{\alpha}$-decay widths are in qualitative agreement with Mang's shell-model theory.

Addition of singlet and triplet silylene to buta-1,3-diene

Formation of high-energy silicon atoms by the nuclear recoil technique in the presence of buta-1,3-diene gives rise to silylene consisting of 80% triplet and 20% singlet; both configurations add to buta-1,3-diene to give silacyclopent-3-ene.

Scattering of CsF by Electrons

Absolute differential and total cross sections for the scattering of CsF by 0.6- to 6.5- eV electrons have been measured using the molecular-beam recoil technique. The first-Born-approximation differential cross section is used as the theoretical model to fit the data. The experimental differential cross sections rise more sharply near 0\ifmmode^\circ\else\textdegree\fi{} than predicted. Total cross sections derived from our measurements are a factor of 1.5 to 4 smaller than the first-approximation results.

Differential Cross Sections with Spin Analysis for4S122−4P12,322Excitation of Potassium by Electrons

The atomic-beam recoil technique has been used to obtain the ratio of spin-flip to full differential cross sections, for $4^{2}S_{\frac{1}{2}}\ensuremath{-}4^{2}P_{\frac{1}{2},\frac{3}{2}}$ excitation in potassium by electrons. Data are presented at energies of from 3 to 10 eV, and for electron scattering angles of from $\ensuremath{\theta}\ensuremath{\approx}0\ifmmode^\circ\else\textdegree\fi{} \mathrm{to} 20\ifmmode^\circ\else\textdegree\fi{}$, in 5-deg intervals. Additional data at $\ensuremath{\theta}\ensuremath{\approx}0\ifmmode^\circ\else\textdegree\fi{}$, for energies from threshold to 20 eV, are also presented. Appropriate scattering amplitudes are calculated using the Born, Ochkur, and close-coupling approximations, and comparison with our experiments is made. Exchange is necessary to account for the $\ensuremath{\theta}\ensuremath{\approx}0\ifmmode^\circ\else\textdegree\fi{}$ data; the close-coupling results are in fair agreement with all of the angular data, while the Ochkur approximation gives good agreement at very small angles.

Absolute Total Cross Sections for the Scattering of Low-Energy Electrons by Rubidium, Cesium, and Potassium

Using the atom-beam recoil technique, absolute total cross sections were measured for the scattering of electrons in the energy range 0.3-9 eV by potassium, rubidium, and cesium. The results of these measurements are in substantial disagreement with the experimental values of Brode, obtained more than 40 years ago. On the other hand, our potassium cross sections agree extremely well with the recent calculations of Karule, and Karule and Peterkop, as well as with the experimental values of Collins et al. For cesium and rubidium, the existing theoretical calculations are not in as good agreement with our results as in the case of potassium.

Nuclear decay properties of light einsteinium isotopes

The light einsteinium isotopes 248Es, 249Es, 250Es and 251Es were synthesized by irradiating a 249Bk target with 3He and 4He ions. Because of the short half-life of 248Es, it was necessary to characterize this isotope by using the recoil technique, whereas the other isotopes were chemically purified before their properties were determined. The half-lives of the above nucleides were found to be 28 ± 5 min, 1.7 ± 0.1 h, 8.3 ± 0.2 h and 33 ± 1 h, respectively. A new isomer of 250Es was discovered and its half-life was determined to be 2.1 ± 0.2 h. The energies of the main α groups for 248Es, 249Es and 251Es were observed to be 6.87 ± 0.01, 6.770 ± 0.005 and 6.488 ± 0.005 MeV, respectively. The α/K X-rays ratio for 249Es was found to be 0.007 ± 0.001 and the value for 251Es was 0.008±0.002. Several gamma rays associated with the electron-capture decay of the einsteinium isotopes were observed. On the basis of the present investigation the ground states of 249Es and 251Es have been assigned to the Nilsson states 7 2 +(633↑) and 3 2 − (521↑) , respectively.

Electron-Alkali-Metal Inelastic Recoil Experiments with Spin Analysis: Experimental Method and the Small-Angle Behavior of the4S122→4P12,322Excitation of Potassium

The use of the atom-beam recoil technique in the study of differential inelastic electron-atom collisions with spin analysis is discussed. The general theory of the experimental method is presented. It is shown how to relate the observable $R$, the fractional depolarization of a polarized atom beam, to the several direct and exchange scattering amplitudes. A linear momentum-transfer analysis, required to connect the atomic and electron scattering angles, is also given. Some observations of the change of spin state of potassium, resulting from small-angle excitations of $4^{2}S_{\frac{1}{2}}\ensuremath{\rightarrow}4^{2}P_{\frac{1}{2},\frac{3}{2}}$ transitions are discussed, and are related to the threshold laws.

Beam Studies of the Energy Dependence of Hot-Hydrogen-Atom Reactions with Cyclohexane

Beam studies of the energy dependence of hydrogen-atom-molecule reactions having appreciable thresholds are reported. Such investigations spanning the entire chemical range promise to be of importance in understanding the dynamics of reactive collisions. This work examines the interactions with solid cyclohexane of tritium ion beams, both T+ and T2+, having controlled energy between 1–200 eV. These ions undergo efficient charge transfer at the surface of the target to form hot tritium atoms of similar velocity. Labeled products are formed by hot-atom reactions, and their yields are measured by radio–gas chromatography. At high energies (≥ 30 eV), absolute yields for T+ beams are close to those found by the nuclear recoil technique. With T2+, high-energy yields are about 20% lower; this apparently corresponding to the fraction of ions forming unreactive T2 upon charge exchange. At lower energies, yields decline. The threshold for the T for H replacement is at 1.5 ± 0.5 eV. Hexenes and hexanes appear to result from processes in which a C–C as well as a C–H bond is ruptured. The threshold for such double displacement is at 4.5 ± 0.5 eV. Provided certain rather drastic assumptions are made, the energy dependence of the yields can be used to derive approximate excitation functions.

Recoil technique and its possible use in activation analysis

Recoil technique and its possible use in activation analysis