Neutron scattering lengths and cross sections of the barium isotopes

Coherent neutron scattering lengths and total cross sections have been measured for barium compounds and on isotopically enriched samples for neutron energies from 0.5 meV up to 132 eV using different techniques. From the experimental data the following quantities were obtained:

the coherent scattering lengths (in fm) of Ba (5.07±0.03) and of the isotopes with mass numbers 130 (?3.6±0.6); 132 (7.8±0.3); 134 (5.7±0.1); 135 (4.66±0.10); 136 (4.90 ±0.08); 137 (6.82±0.10); and 138 (4.83±0.08).

the absorption cross sections σ_γ (at 0.025 eV in barn): of Ba (1.1±0.1) and of the isotopes: 130 (30±5); 136 (0.68±0.17); 137 (3.6±0.2); and 138 (0.27±0.14).

zero-energy scattering cross sections for Ba and the isotopes 136, 137 and 138. On the basis of these data, the isotopic- and spin-incoherent cross sections and the (s)-resonance contributions to the coherent scattering lengths have been determined and discussed.

     

Interaction of slow neutrons with the isotopes of molybdenum

Coherent neutron scattering lengths and total cross sections were measured on samples of ordinary Mo and isotopically enriched samples. From the experiments with neutrons of 0.57 meV and 1.26 eV the following values have been obtained:

1. the coherent scattering lengths (in fm) of the bound atoms of Mo (6.715±0.020) and for the isotopes with the mass numbers 92 (6.93±0.08), 94 (6.82±0.07), 95 (6.93±0.06), 96 (6.22±0.06), 97 (7.26±0.08), 98 (6.60±0.07) and 100 (6.75±0.07);
2. the incoherent scattering cross section at zero-energy for ordinary Mo: σ_i=0.02 ± 0.02 barn;
3. the absorption cross sections (in barn) for Mo (2.48 ± 0.04) and for the isotopes with the mass numbers 95(13.4 ± 0.3), 97(2.5 ± 0.2) and 100(0.4 ± 0.2). The relation of the present results to the resonance parameters of the neutron — Mo interaction has been discussed.

     

Interaction of slow neutrons with nuclides of scandium,titanium, vanadium and manganese

Total cross section measurements at various neutron energies were performed on metallic and oxide samples of natural Sc, Ti, V, and Mn. By means of the Christiansen filter technique the coherent scattering lengths were determined on natural and isotopically enriched samples of Ti-, V-, and Mn-compounds. From the measured values we deduced the following data:

? the absorption cross sections (at 0.0253 eV in barn) of^natTi (6.43±0.06) and of^natV (5.06±0.04);

? the bound coherent scattering lengths (in fm) of^natTi (?3.370±0.013),⁴⁶Ti (4.72±0.05),⁴⁷Ti (3.53±0.07),⁴⁸Ti (?5.86±0.02),⁴⁹Ti (0.98±0.05),⁵⁰Ti (5.88±0.10),^natV (?0.443±0.014), and Mn (?3.750±0.018);

? the free potential radii (in fm) of Sc (3.60 ±0.10),⁴⁶Ti (3.50±0.10),⁴⁷Ti (3.60±0.10),⁴⁸Ti (3.90±0.10),⁴⁹Ti (4.10 ±0.15),⁵⁰Ti (4.50±0.15),⁵¹V (5.20±0.20), and Mn (6.50±20).

On the basis of the well known resonance parameters in combination with new fits of bound levels the spin state scattering lengths, the spin incoherence, and the obtained potential radii are discussed. Total cross section calculations were performed by multi-level formalism and are compared with the measurements.     

Interaction of neutrons with zinc and its isotopes

Coherent neutron scattering lengths and total cross sections have been measured for elemental Zn,Zn-compounds and on isotopicly enriched samples for neutron energies from 0.5 meV up to 143 keV using different techniques. From the experimental data the following quantities were obtained:

the coherent scattering lengths (b in fm) of Zn (5.689±0.014);⁶⁴Zn (5.23±0.04);⁶⁶Zn (5.98±0.05);⁶⁷Zn (7.58±0.08;b ₊=9.4±0.5/5.8±0.5;b _?=5.0±0.7/10.1±0.7);⁶⁸Zn (6.04 ±0.03);

the potential scattering radii (R′ in fm) of Zn (6.2±0.2),⁶⁴Zn (6.0±0.3) and⁶⁶Zn (6.2 ±0.3);

the absorption cross sections (σ _γ at 0.025 eV in barn) of Zn (1.11±0.02);⁶⁴Zn (1.1 ±0.1) and⁶⁶Zn (0.62±0.06).

Derived quantities are the “zero energy” scattering cross sections (σ ₀ in barn) for Zn (4.128±0.010) and⁶⁷Zn (7.8±0.3) and the incoherent bound cross sections of Zn (0.061 ±0.023) and⁶⁷Zn (0.6±0.4). In the epithermal region the Zn-cross section can be described by introduction of two strong bound levels of⁶⁷Zn+n for which estimated parameters are given.     

Interactions of neutrons with gallium and its isotopes

Coherent neutron scattering lengths and total cross sections were measured on elemental Ga, Ga-compounds and on isotopically enriched samples at neutron energies from 0.5 meV up to 143 keV using different techniques. From the experimental data the following quantities could be obtained:

the coherent scattering length of Ga and the spin state scattering lengths of the isotopes.

the potential scattering radii (R′)

the absorption cross sections of Ga,⁶⁹Ga,⁷¹Ga and⁷⁵As.

As derived quantities are given the coherent and incoherent cross sections and the resonance spin scattering lengths for theJ=1 andJ=2 states of⁷⁰Ga and⁷²Ga. The physical meaning of these data and ofR′ and the comparison with the resonance parameters are considered.     

Interaction of slow neutrons with natural terbium,holmium and erbium and its isotopes

Coherent neutron scattering lengths and total cross sections have been measured on samples of ordinary Tb, Ho and Er and on isotopically enriched Er-compounds. From the experiment the following data were obtained:

• - the coherent scattering lengths (in fm) of the bound atoms ¹⁵⁹Tb(7.34 ± 0.02), ¹⁶⁵Ho(8.44 ± 0.03), ^ordEr(7.79 ± 0.02), ¹⁶²Er(9.01 ± 0.11), ¹⁶⁴Er(7.95 ± 0.14), ¹⁶⁶Er(10.51 ± 0.19), ¹⁶⁷Er(3.06 ± 0.05), ¹⁶⁸Er(7.43 ± 0.08), and ¹⁷⁰Er(9.61 ± 0.06)
• - the thermal absorption cross sections (in b) ¹⁴¹Pr(12.7 ± 0.6), ^ordNd(58 ± 1), ¹⁵⁹Tb(30 ± 2), ¹⁶⁵Ho (65 ± 2), ^ordEr (145 ± 2), ¹⁶⁶Er (18 ± 2), ¹⁶⁷Er(568 ± 9), ¹⁶⁸Er(2.3 ± 0.3), and ¹⁷⁰Er(15 ± 1). In combination with the resonance parameters, the measured coherent scattering lengths allowed the determination of potential scattering radii R′ which are of particular interest for the optical model theory.

     

Testing general relativity: Progress,problems, and prospects

Recent results from radar and radio gravity experiments are:

1. Retardation of radar signals: 1.02 +?0.05 (planetary radar), 1.00 +? 0.04 (spacecraft);
2. Deflection of radio waves: 0.99 +? 0.12 (short baseline interferometry), +0.15 1.04 (short baseline interferometry), ?0.10. 0.90 +? 0.05 (short baseline interferometry);
3. Relativistic perihelion advance of Mercury: 0.99 +? 0.03 (planetary radar), 1.00 +? 0.01 (radar plus optical);
4. Time variation of the gravitational constant: (G/G) < 4 ×10^?10/yr (planetary radar). The first three results are expressed as fractions of the corresponding effects predicted by general relativity. In terms of the Eddington-Robertson parameters, the first two are approximately equal to (1+γ)/2 and the third to (2 + 2γ-β)/3. The third result depends on the assumption that the solar gravitational quadrupole moment vanishes; its effects cannot be separated usefully from those of general relativity with the present data set. The uncertainties are as given by the individual experimenters; in some cases they represent formal standard errors, in others an allowance for possible systematic errors is included.

     

Interactions of slow neutrons with nuclides of antimony,tellurium and iodine

Coherent neutron scattering lengths and total cross sections have been measured on samples of ordinary Sb, Te, I and on isotopically enriched compounds. From the experimental data for neutron energies of 0.57 meV, 1.26 eV and 5.2 eV the following data were obtained: the coherent scattering lengths (in fm) of the bound atoms Sb (5.57±0.03);¹²¹Sb(5.71±0.06),¹²³Sb(5.38±0.07); Te(5.80±0.03) and for its isotopes of the mass number 122(3.8±0.2); 123(?0.05±0.25?i·0.100); 124(7.95±0.10); 125(5.01±0.08); 126(5.55±0.07); 128 (5.88±0.07); 130(6.01±0.07). the thermal absorption cross sections (in barn) for Sb(4.91±0.05);¹²¹Sb(5.77±0.12);¹²³Sb(3.8±0.2); Te(4.05±0.05) and I(6.15±0.06). The combination of the measured values of scattering lengths and -cross sections resulted in data for coherent and incoherent cross sections. Taking account of resonance data a complete set of spin state- and reconance scattering lengths has been obtained and discussed.     

Untersuchung der vier ersten angeregten Zustände des6Li-Kernes durch Elektronenstreuung

Inelastic electron scattering cross sections were measured for energies below 60 MeV and momentum transfersq between 0.2 and 0.6 fm^?1. Ground state radiative widths Γ _γ ⁰ and transition radiiR _tr were deduced. 2.18 MeV: Γ _γ ⁰ (E2)=(4.40±0.34) · 10^?4 eV,R _tr=(4.28±0.39)fm; 3.56MeV: Γ _γ ⁰ (M1)=(8.31±0.36)eV,R _tr=(2.90±0.10)fm; 4.27 MeV: Γ _γ ⁰ (E2)=(5.4±2.8) · 10^?3 eV,R _tr=(3.4±1.2) fm. The excitation of the 5.37 MeV level shows a transverse angular dependence.     

Polarization effects of picosecond CARS in liquids

Coherent Raman scattering of delayed probing pulses after ultrafast excitation is investigated under generalized polarization conditions. Three factors are shown to contribute to the scattering signal:

1. scattering off the isotropic part of the resonant material excitation via the isotropic component of the Raman polarizability
2. scattering via the anisotropic part of the Raman polarizability from a second, oriented component of the resonant material excitation
3. four-wave mixing via the non-resonant part χ_NR of the third-order susceptibility. We demonstrate theoretically and experimentally that different polarization conditions lead to drastic changes of the signal transients in liquids. For the ring breathing mode of C₆H₅Br the ratio of non-resonant to resonant contributions is measured to be χ_NR/χ_res=0.037±0.015.

     

Optically-pumped stimulated recombination radiation inp-type InSb in high magnetic fields

In this paper measurements of the frequency, linewidth and polarization of stimulated recombination radiation (SRR) fromp-type InSb are reported. The samples had low excess-carrier concentrations between 10¹⁴ and 10¹⁵ per cm³ and different lengths between 0.4 and 9 mm. They were held in magnetic fields up to 6T at temperatures of pumped liquid helium. The excitation was done optically by the radiation of a Q-switched CO-laser. We could observe a number of different stimulated processes:

1. band-to-band recombination (tuning between 1875 and 1980 cm^?1),
2. band-to-acceptor recombination (tuning between 1840 and 1930 cm^?1),
3. stimulated spin-flip Raman scattering (SFR) of the SRR by excited electrons,
4. SFR of the laser by excited electrons and its interaction with the SRR.

From the observed shift of the band gap by exchange and correlation energy the number of created electron-hole pairs can be calculated to be up to 10¹⁶ per cm³. The observed acceptor binding energy varies from 66 cm^?1 atB=0 to 71 cm^?1 at 4.5T.     

Neutron scattering lengths of the isotopes of thulium,ytterbium and lutetium

Coherent neutron scattering lengths and total cross sections have been measured on samples of ordinary Tm, Yb and Lu and on isotopically enriched compounds. From the experimental data for 0.57 meV neutron energy the following data were obtained: the coherent scattering lengths (in fm) of the bound atoms¹⁶⁹Tm (7.07+0.03);¹⁷⁰Yb (6.8±0.1);¹⁷¹Yb (9.7±0.1);¹⁷²Yb (9.5±0.1);¹⁷³Yb (9.56±0.10);¹⁷⁴Yb (19.2±0.1);¹⁷⁶Yb (8.7± 0.1); Yb (12.41±0.03);¹⁷⁵Lu (7.28±0.09);¹⁷⁶Lu (6.3±0.2) and Lu (7.21±0.03); the thermal absorption cross sections (in barn) for¹⁶⁹Tm (100±2); Yb (34.8±0.8) and Lu (74±2). In combination with the resonance parameters the measured coherent scattering lengths allowed the determination of potential scattering radii R′ which are of particular interest for the permanently deformed and deformable nuclei in the rare-earth region.     

Dynamical enhanced electron emission and discharges at contaminated surfaces

Broad-area electrodes show electron emission already at electric field strengthsF≈10⁷ V/m. This enhanced field emission (EFE) occurs only for contaminated surfaces. EFE is accompanied by photon emission and gas desorption yielding finally discharges. EFE is caused by dust and contaminants initiating the following effects:

an electron is stochastically emitted in a trigger zone

the electron gains energyΔE?eΔxF ^*

which excites electronic states

which relax by the emission of electrons, photons, and atoms

where the positive charges left behind enhanceF ^*=βF (β?1) initiating so an electron avalanche, i.e., a high conductivity channel. Because of charge migration and neutralization, this avalanche has a life time. This pulsating EFE is accompanied by light emission and gas desorption yielding finally a gas cloud and a discharge.

The pulsating, self-sustained EFE has the same root as:

the enhanced secondary emission found first by Malter

the conductivity switching exhibited by thin (≈ 1 μm) layers of semiconductors or insulators

the normal cathode fall and

the firing-wave instability in neurodynamics.

     

Anisotropy of the electron-phonon scattering rate in metals

A method of measuring the temperature dependent part of the electron scattering ratev(T) for separate groups of electrons has been developed on the basis of the radio-frequency size effect. The temperature dependence of the amplitude of a radio-frequency size effect line yields information on the probability of electron scattering averaged over the vicinity of the corresponding extremal cross section of the Fermi surface (FS). This method was applied to two problems:

1. the determination of the electron-phonon scattering rate on the FS point-by-point in noble metals; and
2. the extraction of the contribution of electron-phonon scattering collisions with electron transfering from one sheet of the FS to another to the total electron-phonon scattering rate.

     

Inclusive ϱ0,K *±(892) andf production in\bar p p Interactions at 12 GeV/c

Inclusive production of ?⁰,K ^*±(892), andf is studied in \(\bar p\) p interactions at 12 GeV/c. The inclusive cross sections for ?⁰,K ^*±(892), andf are found to be 6.7±0.3 mb, 1.0±0.2 mb, and 1.4±0.3 mb, respectively. The differential cross sections are presented as a function of c.m. rapidity, Feynmanx and square of the transverse momentump _T ² . Comparison with the correspondingpp data shows some interesting differences which can be attributed to the \(\bar p\) p annihilation. The results are compared with the predictions of the quark fusion model.     

SIMS and flash desorption studies of nickel oxygen interaction

O₂ exposure of polycrystalline nickel at 300 K results in characteristics changes of secondary ion emission. These can be described by a model which is in good agreement with corresponding LEED, AES, XPS, and ΔΦ results of other authors. According to this model, oxygen can be bonded on Ni in at least five different phases:

1. chemisorption, indicated by a rapid increase of Ni⁺, Ni ₂ ⁺ , and Ni₂O⁺ (≦5 L);
2. a rearranged chemisorption layer, characterized by a drastic decrease of Ni⁺, Ni ₂ ⁺ , and Ni₂O⁺ (5–15 L);
3. nickel oxide (NiO) responsible for a strong NiO^?- and NiO ₂ ^? -emission (≦40 L);
4. oxygen on top of this NiO layer, producing a final increase of Ni⁺ and NiO⁺ and a O₂-flash signal at 400 K (>40 L);
5. bulk dissolved oxygen in thermal equilibrium with a chemisorption layer (after several exposure/heating cycles).

During ion bombardment of a 100 L O₂ exposed Ni surface these different binding states occur in a reversed order of succession. O₂-flash signals at 400 and 1100 K, related to drastic changes in secondary ion emission at 400, 700, and 1100 K, reflect the disappearance of various oxygen binding states. The exchange between different oxygen phases was studied by¹⁶O₂/¹⁸O₂ isotope experiments.     

Untersuchung einiger Kernniveaus des B10 und B11 durch unelastische Elektronenstreuung

Cross sections as a function of momentum transfer and angle have been measured for inelastic electron scattering from B¹⁰ and B¹¹. Primary energies between 32 and 57 MeV, and scattering angles from 92° to 165° were used. For the levels at 8.93 and 8.56 MeV in B¹¹, and 7.477 and 6.01 MeV in B¹⁰ the following multipolarities and radiation widths to the ground state (in eV) have been deduced: 4.0±0.6 (M1); 0.72±0.30 (M1) +0.40±0.10 (E2); 12.0±2.2(M1) and 0.122±0.020 (E2), respectively. Transition radii were evaluated for the levels mentioned, and for the 2.12 MeV state in B¹¹.     

Detection of highly ionizing particles: Nonlinear near-surface phenomena in silicon radiation detectors

As far as the detection system is concerned, experimens on synthesis and study of the properties of superheavy nuclei is one of the most difficult tasks. In fact, these experiments can be considered extreme in many senses:

• —extremely low (fractions of a picobarn-picobarns) formation cross sections of the products under investigation
• —extremely high heavy ion beam intensities for example, ～1.1–1.5 pμA^{1 48}Ca
• —high radioactivity of actinide targets, which are used in the experiments aimed at the synthesis of super-heavy nuclei
• —very long duration of the experiment (as long as a year)
• —extremely low yield of the products under investigation (sometimes less than 1 per month)
• —very high sensitivity of the detection system
• —radical suppression of the background products (method of “active correlations”).

The two last points are the subject of the present paper, as well as the subject of two of my reviews published before. It is evident that without knowledge of the nature of the internal processes in semiconductor detectors it is virtually impossible to provide clear detection of ultra rare signals. In the present paper, the author reports on the investigation of near-surface phenomena in silicon radiation detectors, first of all bearing in mind the theoretical-methodological aspect of these phenomena. Non-equilibrium electron-hole recombination, pulse height defect formation, charge multiplication, and formation of “hot” electron system, are considered. With just these phenomena one can observe nonlinearity of energy-charge-amplitude conversion for heavy ion (recoil nucleus) registered by a silicon detector. Practical applications are also considered. One of them is a deeply modified method of “active correlations”. Projection of applying the method in the experiments with the modernized cyclotron (DC-280 FLNR project) is projected as well as possible applications in the heavy-ion-induced complete fusion nuclear reactions.     

Ambiguities in theη-nucleon scattering length determination

The positive sign of theη-nucleon scattering lengthb _ηN was predicted in [1] assuming the resonance mechanism for theπ ^?p → ηn reaction. We demonstrate that

1. the assumption about thet-channel mechanism of the reaction leads tob _ηN < 0 and
2. the experimental data on theη production cross section are equally compatible with both resonance andt-channel mechanisms.

     

Charged particle and π0 multiplicity distributions and the annihilation properties of\bar p p interactions at 70 GeV/c

The elastic and inelastic \(\bar p\) p cross sections at 70 GeV/c have been determined in an experiment performed at CERN using BEBC equipped with a TST. The topological cross sections were measured and the moments of the inelastic multiplicity distribution are 〈n _c 〉=6.16±0.09, 〈n _c 〉/D=2.04±0.05 andf ₂ ^cc =2.97±0.03. The average number of Dalitz pairs per inelastic event is (3.12±0.09)×10^?2. Assuming that these all arise from π⁰ decay the average π⁰ multiplicity is \(\langle n_{\pi ^0 } \rangle = 2.71 \pm 0.14\) . The \(\bar p\) p?pp cross section differences lead to an annihilation cross section σ _A = 4.42±0.41 mb and the moments of the annihilation multiplicty distribution are 〈n _A 〉=8.0±0.3, 〈n _A 〉/D=2.5±0.2 andf ₂ ^A?? =?1.4±0.3. An independent check of σ _A was made by investigating fast forward charged and neutral secondary interactions in the TST and in the surrounding neon-hydrogen mixture, and gives a value σ _A = 5.0±1.6 mb. The ratio of fast \(\bar n\) to \(\bar p\) production in non-annihilation interactions at 70 GeV/c is found to be 0.45±0.11.