Four-body calculation of ΛH and ΛHe with realistic YN and NN interactions

We carried out four-body calculations of _Λ⁴H and _Λ⁴He taking both the 3N + Λ and 3N + Σ channels explicity with the use of realistic NN and YN interactions. The Σ-channel component plays an important role in binding energies of the A = 4 hypernuclei though the admixture is approximately 1%. The ΛN - ΣN coupling is found to be of central-force type in the Nijmegen model D and of tensor-force type in the model F.     

Mesonic and non-mesonic decay widths of ΛC

Results are reported on the precise measurement of the lifetime and the weak-decay branching ratios with charged particle(π⁻ and proton) emission from _Λ¹²C formed via ¹²C(π⁺,K⁺) reaction. The π⁻ mesonic decay width is consistent with the calculations including the pion wave function distortion effect. We observed large contribution of the neutron-stimulated decay widths, Γ(Λ + n → n + n), in the non-mesonic weak decay, which cannot be explained by the current theoretical calculations.     

Structure of a Λ-hypernucleus ΛY measured with the SKS spectrometer

We have measured an excitation energy spectrum of a Λ-hypernucleus _Λ⁸⁹Y via the (π⁺, K⁺) reaction by using the SKS spectrometer at KEK. The best quality data with the energy resolution of 1.63 MeV(FWHM) was obtained in the highest statistics so far. In the spectrum, we can find a splitting of the f-orbital of a Λ particle with the separation of 1.6±0.15 MeV(statistical error only), which may be attributed to the spin-orbit splitting.     

High-resolution gamma-ray spectroscopy

To obtain the highest possible resolution in a measurement has always been one of the major challenges for experimental physicists because increased resolution generally results in progress. At the Institut Laue-Langevin, gamma rays emitted after neutron capture can be recorded with parts-permillion resolution. This is achieved by diffracting the gamma rays on highly perfect Sior Ge crystals. Precise measurement of the Bragg angles and the crystal lattice spacings permits the determination of wavelengths or energies. This outstanding resolving power allows the measurement of extremely small Doppler effects caused by the emission of primary gamma rays. These so-called gamma-ray-induced Doppler broadening measurements have given rise to applications in both nuclear and condensed matter physics.     

Measurement of the proton spectra from non-mesonic weak decay of ΛHe, ΛLi and ΛC

The results of a measurement of the proton spectra following the non-mesonic weak decay of ⁵_ΛHe, ⁷_ΛLi and ¹²_ΛC are presented and discussed. The experiment was performed at the (e⁺ e⁻) collider DAΦNE at Laboratori Nazionale di Frascati of INFN. It is the first measurement for ⁷_ΛLi, and for all the spectra the lower limit on the energy of the protons is 15 MeV, never reached before. All the spectra show a similar shape, namely a peak at around 80 MeV as expected for the free Λp→np weak reaction, with a low energy rise that should be due to final state interactions and/or two-nucleon induced weak processes. The decay spectrum of ⁵_ΛHe is somehow similar to the ones reported by previous measurements and theoretical calculations, but the same does not happen for the ¹²_ΛC one.     

ΣΛ Conversion in ΛH and in other S-shell hypernuclei

The binding energy of the Λ-particle in the $\text{J =}\text{1}\text{2}\text{and}\text{3}\text{2}$ states of _Λ³H and the doublet and quartet Λ-d scattering lengths are calculated with a separable ΛN-ΣN potential matrix, fitted to experimental data in ΛN and ΣN channels. The dependence of the results on ΛΣ coupling is explained in terms of a perturbative treatment of ΛΣ coupling. This perturbative treatment is also applied in a qualitative discussion of the effects of ΛΣ conversion in the J = 0 and 1 states of _Λ⁴H-_Λ⁴He and in the $\text{J =}\text{1}\text{2}$ state of _Λ⁵He. The importance of three-body ΛNN forces caused by ΣΛ coupling is stressed.     

Experimental observation of the Σ hypernuclei, ΣH and ΣC

The hypernuclei _Σ⁶H and _Σ¹⁶C were observed by the (K⁻, π⁺) reaction on targets of ⁶Li and liquid O, respectively, at 713 MeV/c incident K⁻ momentum. Structure is seen in _Σ⁶H which may be interpreted in terms of particle-hole excitations similar to the previously observed states in _Λ⁶Li. The inablitity to resolve individual Σ hypernuclear levels in _Σ¹⁶C, due in part to the excitation of non-coherent states as a result of the large momentum transfer of about 130 MeV/c, precludes the extraction of the Σ-nucleus spin-orbit potential strength. The Σ-nucleus well depth appears to be 7 to 10 MeV less than that for the Λ.     

A measurement of the η radiative width Γη→γγ

The radiative width of the η meson has been measured at PETRA in photon-photon collisions. The resulting value is Γ_η→γγ = 0.53±0.04±0.04 keV.     

Relic neutrino asymmetry generation from να ↔ νs oscillations

Active-sterile neutrino oscillations provide a mechanism by which large differences in the neutrino and antineutrino number densities can be created in the early universe. The quantum kinetic equations are employed in the study of these neutrino asymmetries, which, when solved analytically in the adiabatic limit, generate physically transparent evolution equations that are very useful for the understanding of the nature of the asymmetry growth.     

High-resolution FTIR spectroscopy of the 3ν2 band of PH3

High-resolution Fourier transform spectrum of phosphine (PH₃) at room temperature has been recorded in the region of the 3ν₂ band (2730-3100 cm⁻¹) at an apodized resolution of 0.005 cm⁻¹. About 200 vibration-rotation transitions have been least squares fitted with an rms of 0.00039 cm⁻¹ after taking into account the ΔK = ±3 interaction.     

High-resolution vibration-rotation spectroscopy of fluoroform-d

The vibration-rotation spectrum of the ν₂ and ν₅ fundamentals of CDF₃ have been recorded using a Nicolet 7199 Fourier transform infrared spectrometer; in addition the Q branch and several subbands of each of these transitions have been investigated using a tunable semiconductor diode laser spectrometer. The Q branch and the K structure in several P(J) and R(J) subbands of ν₂, and in several Q branches of ν₅, are resolved and assigned for the first time. Constants derived for these bands are (in cm^?1) ν₂ = 1111.1823₆, B₂ = 0.32928₂, A₂ = 0.18872₂, α₂^B = 16.44₅ × 10^?4, α₂^B ? α₂^A = 12.43₅ × 10^?4, D₀^j = 3.7₃ × 10^?7, D₂^J = 4.8₃ × 10^?7; ν₅ = 975.39₁, B₅ = 0.33062, A₅ = 0.18887, α₅^B = 2.83₁ × 10^?4, α₅^A = 2.4₃ × 10^?4, ζ₅ = 0.736, D₅^J ? D₀^J = 1.2₂ × 10^?8. Some of these constants are nearly 100 times more precise than those reported in previous work.     

Li修饰的C$lt;sub$gt;6$lt;/sub$gt;分子对H$lt;sub$gt;2$lt;/sub$gt;O的吸附研究

采用密度泛函理论中的广义梯度近似研究C₆Li吸附H₂O分子并将之进行分解的催化过程. 几何优化发现：Li原子最稳定的吸附位置是位于C 原子顶位上方. 研究表明,第一个H₂O 分子吸附在C₆Li上需要克服1.77 eV的能量势垒,然后分解为H和OH且与Li原子成键. 当吸附第二个H₂O分子时,第二个H₂O分子需要克服1.2 eV的能量势垒分解为H和OH,其中H与Li原子上的H原子结合成H₂,OH则替代Li 原子上的H结合在Li原子上. 因此C₆Li 可以作为催化剂将H₂O分子进行分解得到H₂. 分析可知：C₆Li主要是通过Li原子与H₂O之间形成的偶极矩作用来吸附H₂O 分子,与C₆₀Li₁₂ 的储氢机制类似. 研究结果可为储氢材料的制备提供一个新的思路. 关键词： 6')" href="#">C₆ Li 2O')" href="#">H₂O 密度泛函理论     

High-resolution FTIR spectroscopy of HNSO—Analysis of the highly perturbed ν4, ν6 and 2ν5 bands

We report a rovibrational analysis of the ν₄ and ν₆ fundamentals and the 2ν₅ overtone of HNSO from high-resolution Fourier transform infrared spectra. The ν₆ band (out-of-plane bend) centred at 757.5 cm⁻¹ is c-type. The ν₄ band (HNS bend) centred at 905.9 cm⁻¹ is predominantly a-type with a very weak b-type component (). Numerous global perturbations and localized avoided crossings affecting the v₄ = 1 rotational levels were successfully treated by inclusion of Fermi and c-axis Coriolis resonance terms between v₄ = 1 and v₅ = 2, and a b-axis Coriolis resonance term between v₄ = 1 and v₆ = 1. The latter term gives rise to an avoided crossing with an extraordinary ΔK_a = 5 selection rule. The Fermi resonance between v₄ = 1 and v₅ = 2 gives rise to strong mixing of their rotational wavefunctions in the vicinity of K_a = 18. The resultant borrowing of intensity made it possible for 2ν₅ transitions in the range K_a = 16–19 to be assigned and included in a global rovibrational treatment of all three band systems.     

High-resolution spectroscopy of SO2 using a frequency-doubled,continuous-wave dye laser

The SO₂ molecule is of considerable interest in the context of atmospheric pollution, and in many laser monitoring techniques the ultraviolet absorption band at 300 nm is used to determine SO₂ concentrations in the atmosphere. Recent laboratory experiments with a resolution of 2 × 10^-3 nm showed that variations could occur in absorption cross-section measurements made with different laser bandwidths due to unresolved fine structure. We have investigated absorption spectra with a line width of 3 × 10^-6 nm, using a frequency-doubled continuous-wave dye laser, and have confirmed the existence of fine structure in the absorption even when collisionally broadened with an atmosphere of nitrogen. These measurements provide a data base from which valid absorption cross sections may be calculated for all monitoring laser bandwidths. We estimate the pressure broadening coefficient for nitrogen in this wavelength region as 83 ± 38 kHz Pa^-1 (11 ± 5 MHz torr^-1). The temperature dependence of the absorption cross-section was also investigated.     

High-resolution tunable spectroscopy of rotational transitions of NO near 30 cm−1

The rotational spectrum of ¹⁴N¹⁶O is studied in the far infrared. The monochromatic tunable far-infrared radiation is generated by mixing the radiatin of an HCN laser with that of a tunable klystron. Five rotational transitions in both the ${}^2\text{Π}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ and ${}^2\text{Π}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}$ states are observed in the frequency region between 852 and 1053 GHz. The results are compared with the known RF, microwave, and IR data.     

High-resolution laser Stark and Fourier transform spectroscopy of the ν2 fundamental band of HFCO

The ν₂ (CO stretch) fundamental band of formyl fluoride (HFCO) was studied in the region 1800 to 1910 cm^?1 using the two techniques of intracavity CO laser Stark spectroscopy at sub-Doppler resolution and Fourier transform spectroscopy at Doppler-limited resolution. Accurate values of the molecular parameters of the ground and excited (v₂ = 1) vibrational states were obtained from a combined fit of the ν₂ band data and available microwave data. The results include precise determinations of the electric dipole moment components (μ_a and μ_b) of HFCO in the ground and excited states.     

α-and γ-irradiation of aqueous DNA solutions

A simple exposure system has been developed for α-irradiation of aqueous DNA solutions, utilizing α-particles from an ²⁴¹Am surface source emitting in vacuo. Care is taken for uniform irradiation of the liquid samples at a variety of dose-rates and reliable dosimetry. For α-dosimetry simple but accurate analytical LET-energy and range-energy relations for liquid water are proposed. For γ dosimetry energy transfer by electrons is considered.     

Update on the search for μ→ e oscillations by the 2 experiment

The neutrino experiment sets the most stringent exclusion limits for _μ→ _e oscillations. Analyzing the data set recorded from Feb.1997 up to March 2000 with the upgraded experimental configuration, the search of _e appearance via the p( _e, e⁺)n reaction yields no hints for neutrino oscillations. Applying a likelihood method to the measured event sample of 11 events (background expectation 12.3 events), we deduce an upper limit of sin² (2Θ) < 1.3 · 10⁻³ for large Δm² > 100 eV² and Δm² < 0.049 eV² for sin² (2Θ)=1.