Backward asymmetry measurements in the elastic pion-proton scattering at resonance energies

The asymmetry parameter P was measured for the elastic pion-proton scattering in the very backward angular region of 150 - 170^° at several pion beam energies in the invariant-mass range containing most of the pion-proton resonances. The general goal of the experimental program was to provide new data for partial wave analyses in order to resolve their uncertainties in the baryon resonance region to allow the unambiguous baryon spectrum reconstructions. Until recently the parameter P was not measured in the examined domain that might be explained by the extremely low cross-section. At the same time the predictions of various partial wave analyses are far from agreement in some kinematic areas and specifically those areas were chosen for the measurements where the disagreement is most pronouncing. The experiment was performed at the ITEP U-10 proton synchrotron, Moscow, by the ITEP-PNPI Collaboration in the latest 5 years.     

Calculation of forward proton-proton bremsstrahlung at 51.8 MeV

The double differential proton-proton bremsstrahlung cross section near 10^O−10^O is computed in the coplaner geometry using a simple one pion exchange off-shell extrapolation of the elastic phase shifts. This relatively simple calculation which has given excellent agreement with experiments at θ₁, θ₂ > 25^O does not agree with recent Japanese 8.5^O-8.5^O data at 51.8 MeV.     

Neutron-proton bremsstrahlung atE=76 MeV

We compare the electric and pure magnetic contributions to the differential cross sectiond(npnp)/ds' of neutron-proton bremsstrahlung. We conclude that the pure magnetic contribution cannot explain the discrepancy between the theoretical and experimental results as found by Dupont et al.This work was supported in part by CONACyT under contracts F246-E9207 and 1628-E9209     

A measurement of neutron-proton bremsstrahlung near 130 MeV

We have measured the double differential cross section for bremsstrahlung production in neutron-proton collisions near 130 MeV. Outgoing nucleons were detected at eight pairs of angles simultaneously. The cross sections agree with several theoretical predictions for those four angle pairs in which the proton emerged at 20° (θ = 20°), but are larger than expected in the four cases that θ_p = 32°. The method of data reduction, and the sources of uncertainty, are discussed in detail.     

Proton–proton bremsstrahlung towards the elastic limit at 190 MeV incident beam energy

A series of nucleon–nucleon bremsstrahlung (NNγ) experiments at 190 MeV incident beam energy have been performed at KVI in order to gain more insight into the dynamics governing the bremsstrahlung reaction. After initial measurements wherein the bremsstrahlung process was studied far away from the elastic limit, a new study was used to probe the process nearer to the elastic limit by measuring at lower photon energies. Measured cross sections and analyzing powers are compared with the predictions of a microscopic model and those of two soft-photon models. The theoretical calculations overestimate the data by up to ≈30%, for some kinematics.     

Production of long-lived isomers by 4 MeV endpoint energy bremsstrahlung

Long-lived isomers of ⁸⁷ Sr, ¹⁰³Rh, ¹¹¹Cd, ^{113, 115}In, ¹¹⁷Sn, ¹⁷⁶Lu, ¹⁸⁹Os, ¹⁹³Ir and ¹⁹⁵Pt were produced by means of bremsstrahlung from a 4 MeV end-point energy 25 A intensity electron beam. Isomeric ativities were measured by gamma-spectrometry. Photoex-citation exhibits a steep rise as compared to lower energy excitations of prior experiments by high activity ¹³⁷Cs, ⁶⁰Co, ¹⁴²Pr and ²⁴Na sources. The large variety in the magnitude of the excitation cross section may mostly arise from largely di?ering isomer ratios governed by spin differences between isomeric and ground levels, and likely by di?erences in the multipole character of the upward transitions, too. Isomer excitation seems to exhibit loose correlations with the product of photoabsorption cross section and isomer ratio derived from (n, n′) reactions on the one hand, and with the product of valence proton and neutron numbers and isomer ratio on the other hand.     

Production of long-lived isomers by 4 MeV endpoint energy bremsstrahlung

Long-lived isomers of⁸⁷Sr,¹⁰³Rh,¹¹¹Cd,^113,115In,¹¹⁷Sn,¹⁷⁶Lu,¹⁸⁹Os,¹⁹³Ir and¹⁹⁵Pt were produced by means of bremsstrahlung from a 4 MeV endpoint energy 25µA intensity electron beam. Isomeric activities were measured by gamma-spectrometry. Photoexcitation exhibits a steep rise as compared to lower energy excitations of prior experiments by high activity¹³⁷Cs,⁶⁰Co,¹⁴²Pr and²⁴Na sources. The large variety in the magnitude of the excitation cross section may mostly arise from largely differing isomer ratios governed by spin differences between isomeric and ground levels, and likely by differences in the multipole character of the upward transitions, too. Isomer excitation seems to exhibit loose correlations with the product of photoabsorption cross section and isomer ratio derived from (n,n′) reactions on the one hand, and with the product of valence proton and neutron numbers and isomer ratio on the other hand.     

4 MeV闪光X光机轫致辐射靶设计

对4 MeV闪光X光机的轫致辐射靶参数进行了设计和模拟计算。利用蒙特卡罗程序,计算得到当轫致辐射靶的有效钽靶材厚度约为0.6 mm时,靶正前方1 m处产生的单脉冲X光的照射量值最大,可以达到约2.86×10^－3 C/kg,满足4 MeV闪光X光机对其单脉冲X光的设计要求。对不同能量下的单脉冲电子束加载在轫致辐射靶上的能量沉积密度进行了计算和比较,分析研究了不同结构下的靶破坏,结果表明：轫致辐射靶采用叠靶结构的钽靶能够满足4 MeV闪光机的实验需求。     

Target asymmetry measurement of deuteron photodisintegration at a photon energy of 550 MeV

The target asymmetry of the deuteron photodisintegration was measured at a photon energy of 550±50 MeV and at proton center-off-mass angles between 25 and 155 degrees.D-butanol andND ₃ were used as target material yielding a maximum deuteron polarization of 41%. Proton and neutron were detected in coincidence. The data show a structure which cannot be described by the existing analyses.     

Z dependance of bremsstrahlung of electrons between 2.5 and 4.0 MeV

TheZ-dependance of the high frequency part of the bremsstrahlung spektrum in the forward direction is investigated with a 4.3 MeV electron linear accelerator for electron kinetic energies ranging from 2.5 to 4.0 MeV. We used thin beryllium, carbon, aluminium, titanium, copper, zirconium, silver and gold foils as targets. The relative photon yields are measured by counting the number of neutrons from the Be⁹ (γ, n) Be⁸ reaction, the neutrons being detected by a long counter. An adequate correction factor to the bremsstrahlung yield for multiple scattering of the electrons before radiating is presented and checked at 3.5 MeV with a number of Al foils ranging in thickness from 0.27×10^?3 to 1.61×10^?3 radiation lenghts. The results are compared with five different theoretical expressions for the bremsstrahlung cross section. The presence of electron-electron bremsstrahlung is very clear. For each used theoretical cross section the amount of photons due to this effect was determined supposing the theoretical nuclear cross section be exact for lowZ elements. It is found that theoretical yields obtained with the Elwert corrected Born approximation formulas agree with experiment for all used elements except for gold. The experimental results for gold as compared with the Born approximation formulas are in agreement with the curves given byKoch andMotz.     

Influence of acoustic waves on coherent bremsstrahlung from 20 MeV electrons

We investigate coherent bremsstrahlung from electrons with the energy 20 MeV incident at small angles to crystallographic planes of quartz crystal periodically deformed by acoustic waves. Depending on the parameters of the acoustic wave and on the incidence angle, the presence of deformation can either enhance or reduce the bremsstrahlung cross-section.     

Parity violation in pion-proton scattering

Parity-violating pion-proton scattering is strongly dominated by so-called penguin operators. These operators are due to the presence of the neutral current, and their strength is further enhanced by the QCD renormalization effects. Without such contributions the elastic asymmetry (A_l) would be an order of magnitude smaller (up to 150 MeV of the pion laboratory kinetic energy). Possible contributions from the resonance poles (?-meson, ($\text{1}\text{2}{}^{\mathrm{+}}\text{)}{}^1\text{-}\text{reson}$) have been also included. Thus pion scattering on the polarized proton can test the commonly-used effective QCD renormalized weak hamiltonian.     

Fission yields of 28 elements by bremsstrahlung photons of 1000 MeV maximum energy

The photofission cross section per equivalent quantum of 28 elements from Bi to Fe has been measured at 1000 MeV bremsstrahlung maximum energy. The fission fragments have been detected by means of the glass sandwich technique. Information is deduced on the dependence of the nuclear fissility on Z²/A.     

30 MeV电子束轰击旋转钽靶产生轫致辐射分析

提出了一种基于射频直线加速器的多脉冲X光照相系统,有望用于材料动态性能诊断等流体物理动力学研究。基于射频加速器的特点,该套照相系统能够产生时间跨度10 s以上、数个脉冲间隔可调、脉宽为几十至一百ns的脉冲电子束,产生电子束束斑半高宽尺寸小于1 mm。通过蒙特卡罗模拟程序Geant4,分析计算了特定的几何布局以及不同厚度及电子束束斑条件下,电子束打靶后在靶中的能量沉积,靶中的电子束散射对X光焦斑的影响,以及1 m处的照射量,探讨了这套X光照相系统的应用可行性。结果表明,在30 MeV,400 nC电子束轰击厚度为1 mm的靶条件下,1 m处照射量约为9.1 R,靶厚在1~2 mm范围内并未引起X光焦斑的明显增大。较小横向尺寸的电子束会引起靶体局部升温严重,将会制约脉冲数量;采用旋转靶能够提升脉冲数量,通过分析二维旋转靶的应力,分析了靶材升温以及钽/钽合金屈服强度对脉冲间隔的限制作用。