Values Of Total Cross Sections Research Articles

Pion absorption in3He at 100, 120, and 145 MeV

π+ true absorption cross-section on3He has been measured at 100, 120, and 145 MeV. The maximal total cross-section values of the reaction π+3He→ppp turn out to be 10, 16, and 19 mb, respectively. About 16% of the cross-section corresponds to three-nucleon absorption. The measured angular distribution as a function of the opening angle between the two fast protons has been fitted with the Legendre polynomial expansionA0+A2P2(cos θ). The values of the coefficients turn out to beA0=(1.7±0.5) mb/sr, andA2=(1.4±0.5) mb/sr, in agreement with the values obtained in the study of the pion absorption on deuteron.

Bidimensional fit to 2H( gamma,p)n cross-section values between 20 and 440 MeV.

All the $^{2}$H(\ensuremath{\gamma},p)n data in the energy range 20--440 MeV have been fitted to a simple phenomenological function. All differential cross-section data were used: The bremsstrahlung data were normalized to the total cross-section values obtained by fitting data provided by monochromatic photon beams. The results obtained give a good representation of the experimental points.

Semiempirical relationship for the total cross section for electron scattering in atoms and molecules

Total cross section values for electrons scattered by atoms and molecules can be obtained by adding the total inelastic cross section to the total differential elastic cross section. We compare these values with experimental values for nitrogen and carbon dioxide. For methane, we compare with experimental values from positron scattering. The agreement is excellent for nitrogen between 40 and 1500 eV and for carbon dioxide between 100 and 500 eV.

Photoelectric cross-sections for Cd and In at 22.2, 59.6 and 88.8 keV

The total photon interaction cross-sections for Cd and In at photon energies of 22.2, 59.6 and 88.8 keV have been measured. The photoelectric cross-sections at these energies have been deduced by subtracting the scattering cross-sections (coherent plus incoherent) from the measured values of total interaction cross-sections. The results have been compared with corresponding theoretical values in the literature.

Interaction of energetic uranium ions with 165Ho, 184W, 197Au, and 209Bi targets

Mica Track Detectors have been used in 2π -geometry for studying the interaction of 238 U-ions with 165 Ho, 184 W, 197 Au, and 209 Bi targets at 2380 MeV. The distributions of the angles versus the elastic differential cross-section relative to the Rutherford cross-section were analysed using (a) Generalized Fresnel Model and (b) Parameterized S-Matrix Method. Quarter-point angles were obtained and were used to compute the values of the reaction parameters. Values of inelastic total reaction cross-sections were obtained by counting the three-,four-, and five-, prong events alongwith the two prong inelastic events as observed in the 2π -geometry.

Electron production in proton collisions: total cross sections

Existing data on the ionization of neutral atoms and molecules by proton impact are reviewed, and electron production cross-section data are collected. The three major experimental methods are discussed and possible sources of error identified. Some theoretical cross sections are discussed, and well-established methods of relating them to measured cross sections are reviewed. A mathematical equation is fitted to the weighted experimental data for each target, and these fits are adjusted to be consistent with appropriate theoretical calculations and with electron impact and photoionization data. Recommended values of total cross sections for proton-impact ionization are given.

A comparison of charged current cross sections and structure functions for neutrino and antineutrino beams on hydrogen and neon

Using BEBC equipped with a hydrogen-filled neon-surrounded track-sensitive target, the charged current cross sections and structure functions of hydrogen and neon targets traversed by the same neutrinos and antineutrinos are compared directly. The measured total cross-section ratios between hydrogen and neon allow precise total cross-section values for hydrogen to be inferred. Using this normalization, the ν and ν hydrogen data are combined and the quark distributions in free nucleons, parametrised as functions of ξ, are extracted. This free-nucleon parametrisation is then compared directly with the neon data in order to measure nuclear effects such as those recently reported by the EMC collaboration. Only small effects are seen, in excellent agreement with recent SLAC data in a more similar A and q 2 range.

Assessment of Neutron Cross Sections for Titanium with Neutron Spectrum in Titanium Pile

The measurement of angular neutron spectrum in a quasi-spherical pile of Ti was carried out by the linac time-of-flight method for the assessment of neutron cross sections for Ti in the energy range from a few keV to a few MeV. The measured spectrum in the pile is generally in good agreement with the calculated one from ENDF/B-IV (MAT = 1,286 for Ti) except in the energy range from about 60 keV to a few 100 keV, where the calculation gives considerably lower neutron flux than the measurement. In order to investigate the cause of this discrepancy between the measured and calculated spectra, the total cross sections for Ti were measured by the transmission method. The results give larger values of total cross sections for Ti by about 30% than ENDF/B-IV below 200 keV, and smaller values by about 10% above 200 keV. These results were ensured at 55 and 147 keV by the measurement using a Si-filtered neutron beam. The calculation based on the measured cross sections shows better agreement with the measured spectrum than that based on ENDF/B-IV. The discrepancy is still observed around 100 keV. The sensitivity analysis shows the importance of cross sections above 1 MeV and elastic cross sections in the resonance energy region to solve the disagreement between the measured spectrum and the calculated one.

Ion-atom single ionisation at high and intermediate energies

The K-shell ionisation of hydrogen-like atoms in collisions with heavy projectiles is studied in two approximations: the multiple scattering approximation (MS) and the continuum distorted-wave approximation (CDW). A better evaluation of the T-matrix element in the MS approximation is carried out without neglecting the internuclear potential and a simple algebraic connection between this new calculation and the CDW is found. Furthermore, the CDW is modified to provide a better description of the binary electron-projectile collision in the entrance channel through momentum conservation. These approximations and other theoretical methods are compared with experimental results for H++Al, He2++Al, H++He+, H++H, He2++H, Li3++H and Feq++H (q=10, 22) systems. It is found that the MS approach provides better agreement with the experiments for inner-shell ionisation where the projectile charge is small, while the modified CDW gives better values for total cross sections at high projectile charges. The validity of each theoretical method is discussed in terms of the Coulomb charges.

Assessment of neutron cross sections for titanium with neutron spectrum in titanium pile.

The measurement of angular neutron spectrum in a quasi-spherical pile of Ti was carried out by the linac time-of-flight method for the assessment of neutron cross sections for Ti in the energy range from a few keV to a few MeV. The measured spectrum in the pile is generally in good agreement with the calculated one from ENDF/B-IV (MAT = 1,286 for Ti) except in the energy range from about 60 keV to a few 100 keV, where the calculation gives considerably lower neutron flux than the measurement. In order to investigate the cause of this discrepancy between the measured and calculated spectra, the total cross sections for Ti were measured by the transmission method. The results give larger values of total cross sections for Ti by about 30% than ENDF/B-IV below 200 keV, and smaller values by about 10% above 200 keV. These results were ensured at 55 and 147 keV by the measurement using a Si-filtered neutron beam. The calculation based on the measured cross sections shows better agreement with the measured spectrum than that based on ENDF/B-IV. The discrepancy is still observed around 100 keV. The sensitivity analysis shows the importance of cross sections above 1 MeV and elastic cross sections in the resonance energy region to solve the disagreement between the measured spectrum and the calculated one.

Experimental total collision cross sections in the glory region for noble gas systems

In a crossed supersonic beam apparatus measurements have been performed on the total cross section as a function of velocity in the thermal range for scattering of Ne, Ar, Kr and Xe by Ar, Kr and Xe. Apart from glory structure in the total cross section also ratios of absolute values of the non-glory total cross sections have been measured. For the analysis four quantities are introduced which are characteristic for the main aspects of total cross section data viz. the absolute value of the total cross section, the velocity dependence of the non-glory total cross section, the position of the glories and their amplitude. The four quantities are directly related to specific properties of the interaction. The various potentials proposed in the literature are tested correspondingly. The validity of combination rules for ϵ, r m and Q ngl is examined. It is demonstrated that the long range noble gas interactions do not reduce to the same form.

Computed cross section for resonant charge transfer inBa++ Ba collisions

The cross section for the resonant electron transfer process Ba/sup +/+Ba..-->..Ba+Ba/sup +/ is calculated for collision energies up to 800 keV. Energy curves for the /sup 2/..sigma../sub u//sup +/ and /sup 2/..sigma../sub g//sup +/ molecular states are first obtained using the multiconfiguration valence-bond method. The cross section is then obtained from the energy curves using the two-state impact parameter version of the perturbed stationary states method. The differential cross section is obtained using the eikonal method. Total cross-section values up to approximately 200..pi..a/sub o//sup 2/ are obtained. At low energies the total cross section exhibits rapid, strong interference oscillations of the type commonly considered to be associated with local extrema in the two-state energy difference. The differential cross-section results clearly show that impact-parameter-dependent structural details of the transfer probability are not directly observable.

Positron-helium scattering including polarization effects

An integral form of the polarized-orbital method has been employed to investigate the positron-helium collision problem. This form does not satisfy the minimum principle. A change of sign of the s-wave phaseshift occurs in the low-energy region. The zero position is obtained at an energy slightly higher than that given by variational calculations. The total elastic cross-section values below the Ps formation threshold are in qualitative agreement with experimental results as well as with the more refined theoretical findings. The Ps formation cross section for the partial wave l=1 shows a resonance-like behaviour near 20 eV. A similar feature has also been noticed by Kraidy and Fraser (1967) around 23 eV.

Total cross section measurements for the scattering of argon by aliphatic hydrocarbons

Absolute values of total cross sections have been determined for the scattering of a monoenergetic molecular beam of argon by 30 aliphatic hydrocarbons. Included are the normal paraffins, cycloparaffins, olefins, and acetylenes with from one to eight carbon atoms. Also included are two diolefins and three butene isomers. Values are reported for the cross section at a relative velocity of 555 m/s. The van der Waals coefficients from the experimental data generally are within a few percent of those calculated by the Slater–Kirkwood approximation.

Positron–Helium Scattering Cross Sections and Phase Shifts Below 19 eV: Addendum

We have extended the phase shift analysis of our positron–helium transmission experiments to determine the importance of cross correlation between the s and p wave phase shifts in a previous paper. We have found out that using Humberston's s wave phase shifts with suitably modified p and d wave phase shifts leads to as good a fit to our experimental data as Drachman's s wave phase phase shifts. Preliminary values of total cross section are given in the 19 to 27 eV energy region.

High Pressure Ionization Gauge for Calibration in the 10-7 to 10-1 Torr Range

A new concept in high pressure gauge (JHP) has been studied for use as a reference-transfer of an absolute interferometric differential manometer (MDI). Electron current I- of the JHP is divided into three components, one of which is regulated to maintain the linearity from 2.10-7 to 7.10-2 Torr for I-=5.10-5 A. The small value of the residual current, mainly due to electron impact desorption, is achieved by shielding the ion collector from the electron impact surface. JHP calibration has been made by the adjustable conductance method used with a monitor gauge acting as an additional control. Sensitivity for argon is ≃3.3/Torr with an experimental accuracy Eexp of ±2% and a reference pressure error (MDI) of ±1.5%. Absolute calibration for various gases leads to determination of the sensitivity ratios taking argon as reference: 0.82 for N2, 0.36 for H2 and 0.16 for He. These values are compared to the yields deduced from the classical values of total ionization cross-sections. Using the same calibration system for BA gauges, the JHP allows one to determine sensitivity with an Eexp of 2% and also to check their linearity, the upper limit of which is accurately measured.

Properties of the B-meson observed in 11 GeV/c π±p interactions

Production and decay properties of the B-meson are studied in the reactions π±p→B±p at 11 GeV/c. Values for mass, width, total and differential cross-sections and spin density matrix elements are given. The spin and parity, and the helicity states in the B→πω decay, are analysed.

Vacuum ultraviolet measurements of the electron impact excitation of helium

Total cross sections for the excitation of helium from its ground state to the 21P, 31P and 41P levels by electron impact have been measured in a polarization free manner using a crossed beam apparatus. The apparent excitation functions have been cascade corrected and made absolute using the optical oscillator strengths. The excitation functions exhibit shapes which differ from some other recent measurements particularly around the peak of the cross section curves. Agreement at high energies between the measured total cross section values and the Bethe approximation is verified within experimental error.

Cross Section for Pair Production in Al, Cu, Cd, and Pb at 2.615-MeVγ-Ray Energy

Cross sections for pair production by 2.615-MeV $\ensuremath{\gamma}$ rays incident on Al, Cu, Cd, and Pb have been found by subtracting tabulated values of the photoelectric cross section from measured values of total cross sections. The latter were determined to be 129.8, 137.0, 147.6, and 181.9 mb per electron, respectively, for the above elements. The statistical uncertainty is \ifmmode\pm\else\textpm\fi{}0.2%. Subtraction of photoelectric cross sections gives 0.0642 (\ifmmode\pm\else\textpm\fi{}5%), 0.343 (\ifmmode\pm\else\textpm\fi{}2.3%), 0.991 (\ifmmode\pm\else\textpm\fi{}1.4%), and 3.55 (\ifmmode\pm\else\textpm\fi{}0.8%) b per atom for pair production. The present result in Pb is 38.9% higher than the Bethe-Heitler Born approximation result and is about 14% higher than Jaeger-Hulme non-Born theoretical results but only 6% higher than the recent, exact non-Born calculation (neglecting screening) by \O{}verb\o{}, Mork, and Olsen. Differences between our values for Al, Cu, and Cd and the calculated values of these authors are even smaller, namely, 0.5% for Al and Cd, and 3% for Cu. It is pointed out that pair-production cross sections can be found from Born-approximation values by multiplication by $a+bZ$ for $0<Z<50$, with $a=0.97\ifmmode\pm\else\textpm\fi{}0.01$ and $b=4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$, and by a factor $1+\ensuremath{\alpha}{Z}^{2}$ for $Z\ensuremath{\ge}50$ with $\ensuremath{\alpha}=(5.8\ifmmode\pm\else\textpm\fi{}0.1)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$.

Use of 50 psec linac beam for high-resolution neutron time-of-flight measurement

The 50-psec high-intensity (14 A, 20.5 MeV) beam from the EG&G/AEC electron linear accelerator was used with subnano-second timing techniques to make high-resolution (80 psec/m) neutron time-of-flight measurements over a short (25.35 m) flight path. The fast-neutron transmission through a carbon absorber was measured by an NE-102 organic fluor scintillation detector, and the results were used to determine the total neutron cross section for carbon over the energy range of 2.05 to 3.4 MeV Total cross-section values obtained show good agreement with those determined by others using longer flight paths. Apparatus and techniques used in this experiment are described in detail.