The scattering of slow neutrons by phosphorus and nitrogen

The coherent scattering lengthsb and the free cross sections for the scattering of slow neutrons by P and N were measured on powdered samples. From the results we derived data for the incoherent cross sections and for the spin state scattering lengths. We found for phosphorus:b=5.13±0.01 fm, σ_free=3.134±0.010b and σ_inc=0.006±0.016b, and for nitrogen:b=9.36±0.02 fm, σ_free=10.03 ±0.08 b and σ_inc=0.4±0.1 b. Derived values for resonance parameters of N are given.     

Nuclear charge radii of Al and Si from elastic electron scattering between 25 and 60 MeV

Elastic electron scattering cross sections of²⁷Al and Si (natural isotopic mixture) have been measured relative to carbon. The rms charge radiiR _m , deduced with partial wave calculations, are (3.01±0.05) fm for²⁷Al and (3.06±0.05) fm for Si, in good agreement with results from muonic X-ray energies. The values given are those for a Fermi charge distribution with skin thickness 2.5 fm; harmonic oscillator shell model distributions yield radii smaller by 0.03 fm. The ratioR _m (²⁷Al)/R_m(Si) is 0.984±0.016.     

Isotopenanalyse an niederenergetischen Teilchen der Elemente Bor,Kohlenstoff, Stickstoff und Sauerstoff aus der kosmischen Strahlung in Plastik-Detektoren

In eight cellulose nitrate sheets of a plastic detector stack flown in 1968 from Ft. Churchill in 1.8 g/cm² floating altitude stopping heavy cosmic ray particles of about 100 MeV/Nuc were measured. In 0.2 m² of the 1.6 m² large stack 30 boron, 190 carbon, 83 nitrogen and 263 oxygen particles were analysed. A resolution of ΔZ=±0.1 charge units and ΔM=±0.7 mass units was obtained. Using oxygen particles for a calibration at¹⁶O the mean values of the mass distributions of the other elements are: 10.79±0.17 for boron, 12.22±0.08 for carbon, 14.61±0.12 for nitrogen.     

Measurement of the rms radius of12C by elastic electron scattering at 53 MeV

Elastic electron scattering cross sections for carbon were measured relative to hydrogen. An analysis of the data with phase shift calculations and a static charge distribution yields a model-independent rms radius of (2.42±0.04) fm for the natural isotopic mixture of carbon.     

New methods for interferometric neutron scattering lengths measurements

A skew symmetric neutron interferometer has been used for tests of a nondispersive and phase contrast variation measuring technique of scattering lengths and for the measurement of anomalous scattering lengths of strongly absorbing substances. The following bound coherent scattering lengths have been obtained: b_c(Pt)=9.60 ± 0.01 fm, b_c(Te) =5.6 ± 0.1 fm and as real parts of anomalous scattering lengths at λ=l.86Å: b_c(Sm) =0.7 ± 0.2 fm, b_c(Eu)=5.3 ± 0.3fm, b_c(Gd)=5.1 ±0.4 fm, b_c(Dy)=16.9 ± 0.3 fm.     

Neutron scattering lengths of molten metals determined by gravity refractometry

Very accurate values of the coherent neutron scattering lengths of the heavy elements Bi and Pb are important quantities for the investigation of the electric interactions of neutrons with atoms. We performed, therefore, a series of experiments to determine accurate scattering lengths by means of neutron gravity refractometry on liquid mirrors of molten metals. The possible perturbations of the necessary reflection measurements have been discussed in details. After taking into account the uncertainties and corrections associated with observable pertubations we obtained the following values for bound atoms:b(Bi)=8.532±0.002 fm,b(Pb)=9.405±0.003 fm,b(Tl)=8.776±0.005 fm,b(Sn)=6.225±0.002 fm andb(Ga)=7.288±0.002 fm. These data are corrected for the local field effect occuring in the reflection on liquids. The recently reported results for the neutron's electric polarizability and the neutron-electron scattering length are supported by the Bi- and Pb-scattering length of this work.     

Interactions of slow neutrons with the chromium isotopes

Neutron transmission experiments and determinations of coherent scattering lengths were performed on natural chromium and enriched samples of⁵⁰Cr,⁵²Cr,⁵³Cr and⁵⁴Cr. By means of the Christiansen-filter-technique we obtained new values for the scattering lengths of the bound atoms:b(^natCr)=3.635±0.007 fm,b(⁵⁰Cr)=?4.50±0.05 fm,b(⁵²Cr)=4.914±0.015 fm,b(53Cr)=?4.20±0.03 fm, andb(⁵⁴Cr)=4.55±0.10 fm. The transmission experiments with neutrons of 510 ΜeV, 1.26 eV and 5.19 eV energy resulted in data for the absorption cross sectionσ _a (^natCr) =3.05±0.08 b and for the scattering cross section at “zero energy”:σ ₀ (^natCr)=3.381±0.010 b. Data for incoherent and spin-state scattering and for the potential-scattering radius of the nuclei could be deduced from these results.     

Measurement of the coherent neutron scattering length of 3He by neutron interferometry

A precise determination of the coherent scattering length of ³He with a neutron interferometer yields a value a_c = 4.29 ± 0.04 fm. A comparison with varoous theoretical perdictions is made and its relation to the few-body problem is discussed. A combination with other experimental results yield as most probable values for the free singlet- and triplet scattering length a_s = 8.0 ± fm and a_t = 3.05 ± 0.07 fm, respectively.     

Elastic electron deuteron scattering

Measurements of the ratio of the deuteron to proton electric form factors were made for low q. The rms radius of the deuteron structure factor was found to be 1.9635 ± 0.0045 fm, yielding an rms charge radius of 2.095 ± 0.006 fm.     

Slow neutron scattering lengths of the isotopes of silver and indium

By means of the Cristiansen filter method we measured on filters containing powder, filings or wires of silver or powder of indium oxide the coherent scattering lengths for the bound atoms of the following isotopes:b(¹⁰⁷Ag)=7.64±0.04 fm,b(¹⁰⁹Ag)=4.19±0.03 fmb(nat.Ag)=5.97±0.01 fm,b(¹¹³In)=5.39±0.06 fmb(¹¹⁵In)=4.00±0.03 fm andb(nat.In)=4.065±0.020 fm. From these values and taking account of incoherent and resonance data we deduced values for the fundamental spin state scattering lengths and incoherent cross sections. These zero energy scattering parameters and the resonance parameters for silver are consistent if bound levels of¹⁰⁸Ag and¹¹⁰Ag are assumed. No indications were found for bound levels of the In isotopes.     

Antiproton-proton interactions at 5·7 GeV/c II. Two-pion correlations in annihilations

We have investigated the two-pion interference effect. The space-time parameters of the production region have been estimated:R=2·2±0·2 fm,cτ=2·9±0·6 fm. The azimuthal correlations of pions are also presented.     

Bose-Einstein correlations in e+e− annihilation in the γ(1S) and continuum

Bose-Einstein correlations in direct γ(1S) decays and continuum in the energy region √s=7.2?10.3 GeV have been studied using data taken with the MD-1 detector at VEPP-4 storage ring. Assuming gaussian density of the pion source the data indicate the radius of the sourceπ=0.73±0.10±0.04 fm for direct γ (1S) decays andπ=0.83±0.22±0.05 fm for the continuum. The correlation strengthsλ for both data samples also are similar. Thus Bose-Einstein correlations do not reveal a noticeable difference between quark and gluon fragmentation.     

The neutron zero-energy total cross section and scattering lengths for tritium

New results for the neutron total cross section for tritium extrapolate to 1.70 ± 0.03 b at zero energy. With a theoretical constraint A₁/A₀=0.92 ± 0.04, the scattering lengths A₁=3.60 ± 0.10, A₀ = 3.91 ± 0.12, and A_c=3.68 ± 0.05 fm can be inferred independently of, but consistently with, the previous experimental value for the coherent length A_c=3.82 ± 0.24 fm.     

Neutron-neutron scattering length from the 2H(n,np)n reaction at bombarding energies up to 27 MeV

The n-n interaction has been investigated in a kinematically complete experiment with high statistical accuracy via the ²H(n, np)n reaction at bombarding energies up to 27 MeV, extending previous measurements to higher energies and to a different geometry. The analysis with exact three-body calculations yields ann = ?16.9 ± 0.6 fm.     

High temperature coadsorption study of zirconium and oxygen on the W(100) crystal face

The coadsorption of zirconium and oxygen on W(100) has been studied by Auger electron spectroscopy, low energy electron diffraction, mass spectroscopy, ion sputtering, and work function measurement techniques. Adsorption of zirconium onto W(100) followed by heating in an oxygen partial pressure produces rapid diffusion of a ZrO complex into the bulk and the formation of a tungsten oxide layer. Heating in vacuum causes desorption of the tungsten oxide and segregation of the ZrO complex to the surface. The activation energy for the ZrO bulk-to-surface diffusion is 30 ± 2 kcal/mole. Upon heating in vacuum at 2000 K the composite surface exhibits predominantly a (1 × 1) LEED structure with a room temperature field emission retarding potential work function of 2.67 ± 0.05 eV. The Richardson work function for this unusually thermally stable surface is 2.56 ± 0.05 eV with a pre-exponential of 6 ± 2. The effects of carbon and nitrogen contamination on this low work function ZrOW composite surface are discussed and a structural model for the surface is presented.     

碳在钼(100)和钼(111)表面上的超结构

用一定能量的氩离子束轰击含碳、氧的钼(100)和(111)表面,不能除去表面上的碳。而用能量为1千电子伏,束流为6微安的氮离子轰击10—15分钟,氮在表面的吸附达到饱和值。加热到400—600℃之间碳、氧从表面上基本消失,600—650℃之间吸附在表面上的氮大量脱附,即氮峰陡降到较低值,碳又偏析到表面上。加热到730℃和775℃氮从表面消失,分别得到碳在钼(100)表面上的p(2×2)和c(6×2)结构。而若将大量脱附氮的钼(111)表面,冷却到室温,氧又偏析到表面上。重新加热到650℃以上碳先从表面消失 关键词：     

n-n Effective range from the photon spectrum of the reaction π−d→γnn

Notable improvements in the treatment of the reaction π^?d→γnn, extending the validity of the calculation to lower photon energies, permit a new analysis of a high statistics photon spectrum. A precise value of the effective range parameter γ_nn = 2.83 ± 0.11 fm has been obtained. The theoretical uncertainty is 0.11 fm. The value of the scattering length previously extracted from the same spectrum is confirmed, with a_nn = ? 18.6 ± 0.5 fm.     

The scattering of slow neutrons by cobalt

Different techniques have been used to determine with slow neutrons the coherent scattering amplitude b_c and the total scattering cross-section σ_sc of Co. We found values for the bound atom b_c=2.78+0.04 fm and for the free nucleus σ_sc=5.95+0.05 barns.From these quantities, the spin state scattering amplitudes b₊ and b_? corresponding to the compound nucleus states of spin I+1/2 or I?1/2 have been determined as b₊=?2.78±0.04 fm and b_?=+9.91±0.06 fm. These results are not in agreement with previous data, but they are found to be consistent with data obtained from resonance parameters.     

Nuclear radii of 17,19B and 14Be

The interaction cross sections (σ_I) of light radioactive nuclei close to the neutron drip line (^17,19B, ¹⁴Be) have been measured at around 800A MeV. The effective root-mean-square (r.m.s.) matter radii of these nuclei have been deduced from σ_I by two different methods, a Glauber-type calculation based on the optical limit approximation and a few-body reaction model. The deduced radii from both approaches agree with each other within experimental uncertainty. The r.m.s. radii of ¹⁷B (2.99±0.09 fm) and of ¹⁴Be (3.10±0.15 fm) in this work are consistent with the previously determined values, and have a higher accuracy. The r.m.s. radius of ¹⁹B (3.11±0.13 fm) was newly determined. Assuming a “core plus 2n” structure in ¹⁷B and ¹⁴Be, the mixing of ν(2s_1/2) and ν(1d_5/2) was studied and the s-wave spectroscopic factor is found to be 36±19% and 47±25%, respectively. A valence radius analysis suggests a “core plus 4n” structure in ¹⁹B.     

On the rms radius of the deuteron

We use the world data on electron-deuteron elastic scattering to determine the deuteron structure functions and the charge rms radius. Coulomb distortion is included using second-Born approximation. We find a radius of 2.130 ± 0.003 ± 0.009 fm (±stat., ±syst.), which agrees with the information obtained from nucleon-nucleon scattering and from optical isotope shifts.