Thed(7Li,p)8Li cross section nearE cm=0.61 MeV

The absolute cross sectionσ of thed(⁷Li,p)⁸Li reaction near theE _cm=0.61 MeV resonance has been measured using a⁷Li ion beam and a windowless gas target system filled with D₂ gas. The proton yield of the reaction and theβ-delayedα-activity of the residual nuclides⁸Li were observed both concurrently with the elastic scattering yield, relatingσ to the Rutherford scattering cross sectionσ _R. The resulting values,σ (fromp)=143.6±8.9 mb andσ (from⁸Li)=151±20 mb, lead to a weighted mean value ofσ=153±6 mb (x ²=2.26) including all available values andσ=146±5 mb (x ²=0.05) removing some values from the data set. The consequences for the expected flux of high-energy solar neutrinos are discussed.     

Measurement of theΞ - p elastic cross section at 102 and 135 GeV/c

TheΞ ^- p differential elastic cross section has been measured in the SPS hyperon beam at 102 and 135 GeV/c. In the range 0.012, thet distributions are found to be compatible with the formA exp(Bt) whereB is 7.7±0.4(GeV/c)^?2 at 102 GeV/c and 8.2 ±0.5(GeV/c)^?2 at 135 GeV/c. The corresponding total elastic cross sections areσ _el=4.9±0.7 mb andσ _el=5.6±0.9 mb, respectively. These results are compared with the predictions of phenomenological models.     

Measurements of elastic scattering in alpha-alpha and alpha-proton collisions at the CERN intersecting storage rings

We measured the elastic scattering of $\text{αα}\text{at}\text{s}\text{= 126}\text{GeV}$ and of αp at $\text{s}\text{= 89}\text{GeV}$. For αα, the differential cross section dσ/dt has a diffractive pattern minima at |t| = 0.10 and 0.38 GeV². At small |t| = 0.05?0.07 GeV², this cross section behaves like exp[(100 ± 10) t]. Extrapolating a fit to the data to the optical point, we obtained for the total cross section α_tot(αα) = 250 ± 50 mb and an integrated elastic cross section σ_e1(αα) = 45 ± mb. Another method of estimating σ_tot(αα), based on measuring the interaction rate, yielded 295 ± 40 mb. For αp, dσ/dt has aminimum at |t| = 0.20 GeV², and for 0.05 < |t| < 0.18 GeV² behaves like exp[(41 ± 2) t]. Extrapolating this slope to |t| = 0, we found σ_tot(αp) = 130 ± 20 and σ_e1(αp) = 20 ± 4mb. Results on pp elastic scattering at $\text{s}\text{= 63}\text{GeV}$ agree with previous ISR experiments.     

The cross section of14N(n,p)14C at stellar energies and its role as a neutron poison forS-process nucleosynthesis

The absolute average cross section 〈σ〉 of the¹⁴N(n, p)¹⁴C reaction has been measured using neutron spectra that closely resemble Maxwell-Boltzmann distributions with thermal energies of kT=25.0 and 52.4 keV: 〈σ〉=0.81±0.05 and 0.52±0.06 mb, respectively. The resulting reaction rates are nearly the same at T₉=0.29 and 0.61, and their average, N_A〈συ〉=(1.3±0.1)×105 cm³ s^?1 mol^?1, is about a factor of three smaller than the previously adopted values obtained by extrapolation between thermal and higher-energy data. Thus, the¹⁴N(n, p)¹⁴C reaction plays a correspondingly smaller role as a neutron poison fors-process nucleosynthesis.     

The nonelastic projectile break-up cross section from particle-gamma coincidence measurements for the 6li + 40ca reaction at 156 mev

The cross sections for nonelastic break-up modes have been studied for the ⁶Li + ⁴⁰Ca reaction at E_Li = 156 MeV. Gamma-ray spectra from target-like residual nuclei were measured in coinci- dence with beam-velocity projectile fragments and a value for the nonelastic break-up cross section σ^b.u_non = 582 ± 110 mb has been found. Together with results of inclusive charged-particle measure- ments we infer for the total break-up cross section σ^b.u_tot = 930 ± 115 mb comprising about 50% of the total reaction cross section. The nonelastic contribution of the break-up reaction appears to be less than predicted by the DWBA break-up theory. This result is directly evident from the differential cross sections by comparing inclusive and exclusive results.     

A new “parametrization” of the differential cross section for elastic scattering

A new parametrization of the differential cross section for elastic scattering is proposed. The parametrization incorporates correct analytic properties of the differential cross section and is based on optimized polynomial expansions of an analytic function. It is, in principle, valid for all energies and all angles. The parametrization has been tested for pp, $\text{p}\text{p}$, pd, π^± and K^±p elastic scattering at high energies and small angles. The results of the new fits are compared with those of the old ones. It has been found that with the same number of parameters one obtains practically the same values of χ². However, the new values of physical quantities, such as slope, α and (dσ/dt)₀, in most cases differ considerably from those obtained by the old parametrization. In particular, it has been found that the slope of the differential cross section for pp, $\text{p}\text{p}$, pd and K^±p elastic scattering increases continuously as the forward direction is approached.     

用低能弱γ源测量电子对的近阈产生截面

用2.7μCi的⁶⁰Co弱γ源和NaI(Tl)与Ge(Li)双探测器符合测量方法,测量了Al,Zn,Sn,Pb四种样品的电子对产生绝对截面。测量结果与前人用很强γ源得到的结果相符合,并验证了在近阈条件下,对产生截面满足Jaeger关系式:σ_pair=(Z²+aZ⁴)σ₀,求得对⁶⁰Co源γ光子,α=(1.51±0.23)×10^-4,σ_{0关键词：}     

Evidence of a rise in the antiproton-proton total cross section at the CERN intersecting storage rings

We measured the total cross section for $\text{p}$p scattering at $\text{s}\text{= 52.8}\text{GeV}$ at the CERN ISR, using the direct, total-rate method. The result obtained, $\text{σ}{}_{\mathrm{<mtext>tot</mtext>}}\text{(}\text{p}\text{p}\text{) = 44.70 ± 0.53}\text{mb}$, shows that, in common with σ_tot(pp), this cross section also starts to rise in the ISR energy range. We remeasured the total cross section for pp scattering at the same energy, obtaining σ_tot(pp) = 43.26 ± 0.33 mb, and found for the difference, $\text{Δσ}{}_{\mathrm{<mtext>tot</mtext>}}\text{= σ}{}_{\mathrm{<mtext>tot</mtext>}}\text{(}\text{p}\text{p}\text{) ? σ}{}_{\mathrm{<mtext>tot</mtext>}}\text{(}\text{pp}\text{)}$, a value of 1.44±0.45 mb.     

Cross section of the reaction 6Li(p, γ)7Be

The cross section of the reaction ⁶Li(p, γ)⁷Be has been measured using Ge(Li) γ-ray spectrometers for proton bombarding energies E_p from 200 keV to 1200 keV. At E_p = 800 keV, the total (p, γ) integrated cross section is found to be 3.1 ± 0.4 μb. The cross section adopted from consideration of this and previous measurements is in good agreement with that predicted from the known thermal neutron cross section for ⁶Li(n, γ)⁷Li on the assumption that properties of mirror direct capture reactions can be well described by optical potentials that use the same parmeter values for the two reactions.     

Inclusive single and double diffractive dissociations inK + p interactions at 32 GeV/c

We study single and double inclusive diffractive production in a 32 GeV/c K ⁺ p experiment in MIRABELLE at the Serpukhov accelerator. From reactionsK ⁺ p→K ⁺+X ⁺ andK ⁺ p→X ⁺+p we determine the total proton and kaon single diffractive dissociation cross sections \(\sigma (p\xrightarrow{{K^ + }}p_D ) = 0.90 \pm 0.12 mb\) and \(\sigma (K^ + \xrightarrow{p}K_D^ + ) = 0\) . 90±0.17 mb, respectively. In either case the only notable contributions come from dissociations into 1 and 3 charged particles. Kaon dissociation exhibits a pronounced slope-mass correlation. The search for double diffractive production in reactionsK ⁺ p→(K ⁺π^?π⁺)+X ⁺ andK ⁺ p→(pπ ⁺ π ^?)+X ⁺ leads in either case to an estimated total double diffractive cross section σ(K ⁺p→K _D ⁺ p_D) of ?220 μb. The double dissociation differential cross section exhibits a large slope of ?10GeV^?2 in the nearthreshold mass region, rapidly decreasing to ?4 GeV^?2 with increasing excitation mass. At our c.m. energy \((\sqrt s \simeq 8 GeV)\) the ratio σ_{inel dif}/σ_el is 0.85±0.10, the total diffractive cross section σ_dif≡σ_el+σ_{inel dif}=4.41±0.24 mb and the fraction σ_dif(K ⁺ p)/σ_tot(K ⁺ p) is 25±2%. TheK ⁺ andK ^? diffractive excitation mass spectra, differential cross sections and total diffractive cross sections are very similar for both single and double dissociations.     

Low-energy γp scattering and determination of proton polarizabilities

For the first time, an analysis of all experimental data on the differential cross section for elastic γp scattering at photon energies below 150 MeV is performed in order to determine the electric (α _p) and magnetic (β _p) polarizabilities of the proton. A fit to these data with two free parameters α p and β _p embedded into the theoretical cross section obtained on the basis of finite-energy s-channel dispersion relations gives the following world-average values of the proton polarizabilities: α _p=11.7±0.8 (stat.+syst.)±0.7 (model), β _p=2.3±0.9 (stat.+syst.)±0.7 (model) in units of 10^?4 fm³. The first error is combined—it takes into account the statistical and systematic errors in the experimental cross sections—while the second error comes from the theoretical uncertainties in the dispersion-theory cross sections.     

K +-meson production inpBe interactions atT p=2.9 GeV

The production ofK ⁺ andπ ⁺ mesons and protons inpBe collisions atT _p=2.9 GeV has been studied at the ITEP proton synchrotron. Ejectiles with a momentum ofp=545 MeV/c were observed under an emission angle ?=17°. The detectors which have been developed for the identification of kaons out of a six orders of magnitude more intense background of pions and protons are described. A cross-section ratio d²σ _K ⁺/dΩdp: d² σ _p /dΩdp: d²σ _p /dΩdp of (1±0.34):(85±1):(31±1) has been measured. Normalization with existing pion data yields an invariant differential cross sectionE·d³σ _K ⁺/d³ p=(3.1±1.2) mbGeV^?2c³sr^?1 and a total cross section of σ_tot(pBe)=(3.7±1.5) mb. These cross sections are compared with existing data and theoretical predictions. TheA dependence ofK ⁺ production in the few-GeV range is analyzed.     

Fusion and nonfusion phenomena in the 6Li + 40Ca reaction at 156 MeV

Reaction products from ⁶Li-induced reactions on ⁴⁰Ca at 156 MeV have been studied using the dE × E identification as well as the inclusive γ-ray method. The complete fusion cross section has been found to be σ_F = 67 ± 20 mb. The Z-distribution of fusion evaporation residues is compared with statistical model predictions. The Z-spectrum of reaction products shows a maximum at 15 ? Z ? 20, probably due to transfer and to incomplete fusion. It is suggested that the small value of the fusion cross section is due to the strong competition of ⁶Li break-up processes.     

Antiproton-proton cross sections at 200 and 900 GeV c.m. energy

Data on antiproton-proton cross sections at the c.m. energies 200 and 900 GeV are presented. The data were obtained at the CERN antiproton-proton Collider operated in a new pulsed mode in which the same beams were accelerated and decelerated between beam energies of 450 and 100 GeV. The properties of the machine determine the ratio of the luminosities at the two energies to about 1% and thus an accurate measurement of the ratioR of the inelastic cross sections could be made. We findR (=σ ⁹⁰⁰/σ ²⁰⁰)=1.20±0.01±0.02, where the first error is statistical and the second systematic. Interpolating existing data to estimateσ _ine1(200 GeV) this measurement ofR leads toσ _ine1(900 GeV)=50.3+0.4+1.0 mb. Using an extrapolated value ofσ _e1/σ _tot we estimate the total cross section at 900 GeV to be 65.3±0.7±1.5 mb. Both the inelastic and total cross sections are compatible with a ln² s dependence. Comparisons are made with different fits to the total cross section energy dependence.     

Complete fusion studies of the 20Ne+235U system

The probability for complete fusion has been measured for the ²⁰Ne+²³⁵U system at bombarding energies of 175 and 252 MeV. The fission fragment angular correlation technique was used to obtain both the absolute cross section for complete fusion and relative cross sections for the ratio of complete fusion to incomplete fusion processes. Total reaction cross sections were also determined from elastic scattering measurements. Values of σ_R = 1900±40 and 2810 ± 140 mb were obtained at 175 and 252 MeV, respectively. These measurements yield if$\text{σ}{}_{\mathrm{<mtext>CF</mtext>}}\text{σ}{}_{\mathrm{<mtext>R</mtext>}}\text{= 0.74±0.05}\text{at}\text{175}\text{MeV and}\text{0.48 ±0.06}\text{at}\text{252}\text{MeV}$. The corresponding values of the critical angular momentum are compared with the predictions of several heavy-ion interaction models. It is observed that the l_c values obtained from these data agree well with the current models, although the energy dependence is not as strong as predicted. In addition, it is observed that these values of l_c exceed the limiting value for a charged rotating drop.     

Absolute cross section of p(<Superscript>7</Superscript>Be,γ)<Superscript>8</Superscript>B using a novel approach

The absolute cross section σ (E) of the radiative capture reaction p(⁷Be,γ)⁸B at the center-of-mass energy E = 992 keV has been measured using a radioactive ⁷Be ion beam and a windowless gas target system filled with H₂ gas. The ⁸B residual nuclides were detected with a recoil separator consisting of momentum and velocity filters and a ΔE-E detector telescope. The ⁸B yield was observed concurrently with the ⁷Be + p elastic scattering yield, relating σ(E) to the Rutherford scattering cross section. The resulting value, σ(E) = 0.41 ± 0.11 μb, leads to an S(E) factor at zero energy of S(0) = 16 ± 4 eV b, in fair agreement with recommended values. Received: 8 February 2000     

Relaxationserscheinungen im 63 P 2-Zustand des Quecksilber-Isotops199Hg bei Stößen mit Quecksilberatomen im Grundzustand

The decay ofrf resonance signals (Δm _F =± 1, ΔF=0) in the hfs-states (F=3/2, 5/2) of the 6³ P ₂-state of¹⁹⁹Hg has been observed by means of a sampling method. By comparing the relaxation times to those of the even isotopes, the cross section σ₂(F) for the destruction of an alignment in the hfs-states by collisions with ground state Hg-atoms could be measured. The following ratios were obtained: σ₂(F=3/2)/σ₂=1.04±0.06 and σ₂(F=5/2)/σ₂=0.90± 0.03. The cross section σ₂ for the even isotopes was found to be (2.620±0.265) 10^?14cm². Assuming total decoupling of nuclear spinI and electronic angular momentumJ during the collision, the cross sections for the destruction of an orientation (σ₁) and an “octupolarisation” (σ₃) could be calculated. For the even isotopes the following ratios were derived: σ₁/σ₂=0.76 ± 0.07 and σ₃/σ₂=1.08 ± 0.09.     

Quadrupole interaction of8Li and9Li in LiNbO3 and the quadrupole moment of9Li

The quadrupole interaction of nuclear spin polarized⁸Li (I=2) and⁹Li (I=3/2) in LiNbO₃ has been studied at room temperature. The polarization was achieved by optical pumping of a fast atomic beam with circularly polarized laser light. The atoms were implanted into a hexagonal LiNbO₃ single crystal and the quadrupole splitting ofβ-NMR spectra was measured. A ratio of ¦Q(⁹Li)/Q(⁸Li)¦=0.88(4) for the nuclear quadrupole moments was deduced, yielding a new value of ¦Q(⁹Li)¦=25.3 (9) mb for the quadrupole moment of⁹Li.     

The cross section of the7Be(n,p)7Li reaction at 24.5 keV neutron energy

The 24.5 keV neutrons induced reaction with the⁷Be radioactive nucleus was studied. The value of σ_np=(18±4)b was obtained for the⁷Be(n, p)⁷Li reaction cross section.     

Charged particle multiplicities in 100 GeV/cpp interactions

Results are presented on the topological cross sections obtained for antiproton-proton interactions from an exposure of the Fermilab 30-inch bubble chamber to a 100 GeV/c negative beam enriched in $\text{p}$'s. The $\text{p}$p inelastic cross section is found to be σ_inel = 34.6 ± 0.4 mb, and the average inelastic charged particle multiplicity to be 〈n〉 = 6.74 ± 0.05.