Doubly radiative thermal neutron capture in 2H and 16O: Experiment and theory

Measurements and calculations are presented for the cross sections for two-photon emission following thermal neutron capture in ²H and ¹⁶O. Upper limits for σ_2γ were measured in both cases. For ²H, σ_2λ = 8 ± 15 μb, for γ-rays in the energy region 700 < E_γ < 5550 keV. A detailed threeparticle calculation gives σ_2γ^tot = 26 nb. For ¹⁶O, the experimental result is σ_2γ = 3 ± 19 μb for 1200 < E_γ < 2943 keV. A single-particle, direct-capture calculation for ¹⁶O gives σ_2γ^tot = 41 nb. Contributions from excitation of the giant dipole state of the core change this result by ± 16 %. In a separate measurement the total cross section for ¹⁶O(n, γ)¹⁷O was measured to be 202 ± 28 μb. Branching ratios of (82 ± 3)% and (18 ± 3)% were determined for decays to the 3055 and 871 keV levels of ¹⁷O, respectively.     

Nuclear matter distributions for 16,17,18O from a microscopic analysis of elastic proton scattering

An analysis of 65 MeV elastic proton scattering by ^16,17,18O has been made in terms of a reformulated optical model. Matter distributions for ¹⁷O and ¹⁸O have been obtained relative to ¹⁶O. The results for the rms matter radii are R₁₇?R₁₆ = 0.04±0.03 fm and R₁₈?R₁₆ = 0.35± 0.07 fm.     

Vibrational analysis of the A′1Π state of barium oxide using two isotopes

Barium vapor is reacted with N₂¹⁶O and N₂¹⁸O at 0.7 Torr to produce clearly distinguishable isotopic bands of BaO A′¹Π-X¹Σ in the wavelength region of 320–415 nm. The unique vibrational numbering is determined by measuring the isotopic shift in the bandheads between Ba¹⁶O and Ba¹⁸O. Spectroscopic constants for the A′¹Π state are determined from the present analysis to be ν₀₀ = 17 588 ± 15 cm^?1, ω_e = 442.45 ± 0.3 cm^?1, and ω_ex_e = 1.652 ± 0.009 cm^?1. Uncertainties represent three standard deviations.     

Vibration-rotation spectrum of N2O in the region of the lowest fundamental ν2

The high resolution infrared spectrum of N₂O in the region of ν₂ has been studied with a Fourier transform spectrometer at a resolution of (about) 0.005 cm^?1 and an accuracy of about ±0.00005 cm^?1. In addition to ν₂, “hot” bands associated with this band and the bending fundamental ν₂ of ¹⁵N¹⁴N¹⁶O and ¹⁴N¹⁵N¹⁶O were analyzed.     

Torsional frequency,barrier to internal rotation,and dipole moment of N-sulphinylaniline from microwave rotational spectra

Microwave spectra of the ground and first three excited torsional states of N-sulphinylaniline have been assigned. The variation of the inertial defect with torsional number shows the molecule to be planar. The torsional frequency has been determined as ν = 41.1 cm^?1 and the barrier to internal rotation as V₂ = 2.3 kcal/mole. From the splittings of the Stark lobes of some lines the values μ_a = 2.20 ± 0.06, μ_b = 0.664 ± 0.005, and μ_tot = 2.30 ± 0.06 were obtained.     

Electron spin resonance study of oxygen-17 enriched N,N-dimethyl-4-nitroaniline radical anion

N,N-Dimethyl-d₆-4-nitroaniline enriched to approximately 11 atom. per cent in oxygen-17 has been prepared and the oxygen-17 isotropic hyperfine interaction in the corresponding radical anion has been examined. In dry dimethylformamide solution we find a _O = -8·85 ± 0·02 and a _N = 11·39 ± 0·10 gauss, while in moist acetonitrile solution a _O = -8·82 ± 0·07 and a _N = 12·23 ± 0·11 gauss. These results substantiate the recent suggestion that the isotropic oxygen-17 splittings in π-radicals may be described by a single parameter equation analogous to McConnell's relation for aromatic proton splittings, i.e. a _O = Q _OρO ^π, where Q _O = -41 ± 3 gauss.     

Low-energy transition depopulating the isomeric 8+ level in 208Po

Conversion electron measurements of the low-energy transition depopulating the isomeric 8⁺ level in ²⁰⁸Po yielded E_γ = 4025 ± 20 eV and the conversion intensity ratios N₁/N₂ ? 0.2, N₂/N₃ = 0.75 ± 0.10, N_4.5/N₃ ? 0.2, O/N₃ = 0.35 ± 0.10, P/N₃ ? 0.1 and N₃/M₃ = 0.4 ± 0.2. These ratios are in accord with our calculations for the E2 multipolarity and exclude all other multipolarities with L ≦ 4. The total conversion coefficient was calculated to be 1.31 × 10⁷.     

Pressure-Broadened Linewidth Measurements in the ν2Band of the CH3Radical

Pressure broadening coefficients for an infrared transition of the methyl radical have been measured for the first time. CH₃radicals, generated by pyrolyzing di-tert-butyl peroxide in a flow of either N₂or Ar, were probed using a tunable diode laser and a multipass absorption cell. The Lorentz half-width of theQ(6,6) line of the ν₂band of CH₃at 607.024 cm⁻¹was measured as a function of pressure at 295 K. The broadening coefficients (HWHM) areb(Ar) = 0.0310 ± 0.0012 cm⁻¹atm⁻¹andb(N₂) = 0.0390 ± 0.0020 cm⁻¹atm⁻¹. These coefficients are lower than those for CH₄–Ar, N₂broadening. This may be due to a lower polarizability or smaller effective hard collision diameter for CH₃relative to CH₄.     

Electric moments of the first excited state of 18O

The static quadrupole moment Q_2⁺ and the B(E2; 0⁺ → 2⁺) value of the first excited state of ¹⁸O at e_x = 1.982 MeV have been determined using the reorientation effect in Coulomb excitation. Surface-barrier detectors at laboratory angles of 90° and 174° were used to detect ¹⁸O ions elastically and inelastically scattered from ²⁰⁸Pb. At both angles, we determined experimentally the maximum bombarding energies at which nuclear interference effects were negligible. It is found that Q_⁺ = ?0.023 ± 0.021 e · b (?0.052 ± 0.021 e · b) for destructive (constructive) interference from higher states. This result is in good agreement with theoretical expectation. For the transition moment we find B(E2; 0⁺ → 2⁺) = 0.00390 ± 0.00018 e² · b² (0.00371 ± 0.00018 e² · b²) for destructive (constructive) interference.     

Determination of theE2/M1 mixing ratio of the 122-keV transition in the57Co-decay by nuclear orientation

TheE2/M1 mixing ratio of the 122 keV γ-ray in the decay of⁵⁷Co has been measured by a nuclear orientation experiment. In order to obtain a very accurate value, special care was taken to reduce all possible systematic errors. The final value is δ=?0.116±0.001, from which we deduced the transition probabilitiesB(M1)=0.0021±0.0001 μ _N ² andB(E2)=0.00267±0.00011e ² b ².     

Pressure dependence of the Néel temperature of f.c.c. stainless steel

The Néel temperature T_N of f.c.c. stainless steel has been measured as a function of pressure using the Mössbauer effect. A sample with approximately 74 wt.% Fe, doped with ^57Co, and having T_N = 58.4 ± 0.1 K at zero pressure, shows T_N rising with pressure with increasing slope. Our results indicate that T_N is raised to room temperature by a pressure of 175 ± 5 kbar.     

Rotation-inversion spectrum of methylaminoethane

Microwave spectral assignments have been made for the ground and several excited vibrational states of the normal and amino d₁ species of methylaminoethane. The inversion-rotation spectrum is consistent with a trans rotameric form with an amino inversion barrier of ～5.2 kcal mole^?1. The dipole moment of 8.88 ± 0.02 Debye has components |μ_a| = 0.00 ± 0.03, |μ_b| = 0.25 ± 0.03, and $\text{|〈 ± μ}{}_{\mathrm{c}}\text{? 〉| = 0.84 ± 0.01}$ Debye. The normal species N¹⁴ nuclear quadrupole coupling constants are (in MHz) 2.82 ± 0.09, 0.88 ± 0.13, and ?3.70 ± 0.09 for χ_aa, χ_bb, and χ_cc, respectively.     

High-resolution (e,e') study of isovector M1 and M2 transitions in the oxygen isotopes: (I). 16O

The M1 and M2 transition strength distribution for ¹⁶O in the excitation energy range from 16 to 20 MeV has been measured in a high-resolution electron scattering experiment. The M1 strength is concentrated in three sharp states at E_x = 16.22, 17.14 and 18.79 MeV (± 0.01 MeV) with B(M1, k)↑ = 0.20 ± 0.02, 0.32 ± 0.03 and 0.13 ± 0.03 μ_N², respectively. An additional strength of 0.35 ± 0.09 μ_N², distributed over eight weakly excited states with excitation energies E_x = 17.4 to 18.0 MeV, brings the total measured M1 strength to B(M1, k)↑ = 1.0 ± 0.1 μ_N². The experimental M2 strength is distributed over states at E_x = 16.82, 17.78, 18.50 and 19.0 MeV (± 0.01 MeV) with B(M2, k)↑ = 19 ± 2, 13 ± 2, 59 ± 7 and 341 ± 51 μ_N² · fm², respectively. Electric transitions were also measured to states at E_x = 16.45 MeV (2⁺, E2), 17.30 MeV (1⁺, E1) and 18.20 MeV (2⁺, E2). Calculations were performed using the modified surface delta interaction in a 2p-2h shell model for the M1 transitions and the random phase approximation for the M2 transitions. The results show the sensitivity of the M1 strength as a measure of ground-state correlations and compare well with results from the ¹⁵N($\text{p}$, γ) reaction.     

Studies in molecular structure,symmetry and conformation—Part XIV. Crystal and molecular structure of L-isoleucine hydrochloride monohydrate form II

The crystal structure of a new form of L-isoleucine hydrochloride monohydrate C₆H₁₃O₂NHClH₂O (termed form II) has been determined using three-dimensional photographic data. This differs conformationally from the hydrochloride derivative (termed form I, Trommel and Bijvoet 1954) reported earlier. The crystal belongs to the orthorhombic space group P2₁2₁2₁ with cell dimensions,a=5.87±0.01,b=24.77±0.02 andc=6.85±0.01 ? and four molecules per cell,ρ _obs=1.240 g/cm³,ρ _cal=1.238 g/cm³,μ for CuKa=32.6 cm⁻¹. Contribution No. 420 from the Department of Crystallography and Biophysics, University of Madras, Madras 600025.     

The decay of115 mIn

The decay of^115m In has been investigated using accurate counting methods. The emission rate of conversion electrons plusβ ^?-particles was determined with a 4π proportional flow counter. The total andK-shell internal conversion coefficients of the 336 keVγ-ray in¹¹⁵In were measured by the electron X-ray coincidence method using combinations of a Si surface barrier with a NaI(Tl) detector and of a magneticβ-spectrometer with a high energy resolution Si(Li) detector, respectively. The conversion ratioR=K/(L+M+...) was deduced from electron spectra recorded with the magneticβ-spectrometer. The 336 keVγ-ray emission rate of all used sources was determined with a calibrated NaI(Tl)γ-ray spectrometer. A Ge(Li) detector has been used to determine the relative intensity of the 497 keVγ-ray in¹¹⁵Sn. As results have been deduced the 336 keVγ-ray emission per decay (N _γ1/N ₀=(45.9 ± 0.1)%), the total internal conversion coefficient (α=1.073 ± 0.014), theK-shell internal conversion coefficient (α _K=0.843±0.012), the conversion ratioR=3.63±0.07, theβ ^?-transition per decay going to the ground state (N _β1/N ₀=(5.0 ± 0.7)%) and to the first excited level in¹¹⁵Sn¹¹⁵Sn(N _β2/N ₀=(0.047 ± 0.002)%), and the 497 keVγ-ray emission (N _γ2/N _γ1=(0.103 ± 0.004)%). From the obtained internal conversion data it follows that the 336 keVγ-ray transition is ofM4 character with anE5 admixture of less than (3.5±1.5)%. The half-life of the isomeric state¹¹⁵ mIn has been determined with four different methods. The result isT _1/2=(4.486±0.004) h.     

The reaction 36(α, γ)40Ar: γ-transition properties of resonance and bound states in 40Ar

The El character of the de-excitation of the 9 to 10 MeV states in ⁴⁰Ar has been studied through the reaction ³⁶S(α, γ)⁴⁰Ar. Angular distributions and γ-yield asymmetries of primary transitions from the E_α = 2.35 to 3.50 MeV resonances have been measured. The Doppler-shift attenuation method was used to obtain the following lifetime values: 720 ± 120fs (E_x= 2.52 MeV), 89 ±17 (3.21), 90±17(3.511), 22 ±9 (4.33), and 105 ± 17 (4.60).     

Spektroskopische Untersuchungen an DyAsO4

DyAsO₄ undergoes a crystallographic phase transition atT _D=11.2K which is induced by a cooperative Jahn-Teller-effect. As deduced from the optical absorption spectra the distance between the two lowest lying Kramers doublets of the Dy³⁺ ion is increased from (6.1±0.5) cm^?1 aboveT _D to (25.0±0.5) cm^?1 at 4.2 K. BelowT _D the splitting factor of the lowest doublet becomes nearly uniaxial with a maximum value ofg _b =17.5±1.0 along the crystallographicb-axis. AtT _N=2.44 K the crystals order antiferromagnetically. The absorption lines of Er³⁺ ions in DyAsO₄ show already a splitting immediately belowT _D which is explained by magnetic short range ordering of the Dy³⁺ ions in the temperature rangeT _{N D} .     

Electron paramagnetic resonance of Gd3 in YCl3·6H2O

The electron paramagnetic resonance spectrum of Gd³⁺ in YCl₃·6H₂0 with $\text{1}\text{100}$ dilution of Gd/Y ions, has been studied with an X-band spectrometer at 295, 77 and 1.77°K and with a K-band spectrometer at 295 and 77°K. The individual values of all the parameters are evaluated from the data at the three temperatures. In particular, the following values for the g-tensor and the zero-field splitting parameters b₂⁰ and b₂² are obtained from X-band data: at 295°K, g_zz = 1.994±0.005, g_xx = 1.992±0.005, g_yy = 1.997±0.005, b₂⁰ = 1.898 ±0.015 GHz, b₂² = ?2.247 ± 0.015GHz; at 77°K, g_zz = 1.999±0.008, g_xx = 2.000±0.008, b₂⁰= 1.978 ±0.022 GHz, b₂² = ?1.574±0.022GHz; at 1.77°K, g_zz = 2.002±0.010, g_xx = 1.990 ±0.010, b₂⁰ = 2.011 ± 0.025 GHz, b₂² = ?1.650 ±0.025 GHz. (The K-band values are found to be consistent with the X-band values). From the angular dependence of the data in the ZX plane (i) the angle X₀ which the Z axis makes with the a vector of the unit cell, is determined to be 58.00 ±0.25° and (ii) the existence of pseudo-symmetry axes at ±5° from the Z axis in the ZX plane as found by heat capacity and specific heat data has been confirmed. An estimate is also made of the extent of admixture of the excited ${}^6\text{P}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ state with the ground state ${}^8\text{S}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$.     

Mößbauereffekt in Eisenstilben und FeCl2·H2O

Using Mößbauer effect measurements in the temperature range between 3 °K and 310 °K the magnetic fields at the nucleus in iron-stilbene, FeCl₂·H₂O and FeCl₃ are determined to beH _T=0=(250±10) kOe, (252±18) kOe and (468±10) kOe; a Néel-temperature ofT _N=(23±1) °K is measured for iron-stilbene. The electric quadrupole splittings atT=0 °K for iron-stilbene and FeCl₂ ·H ₂ O, ΔE=(+2.52±0.02) mm/sec and (+2.50±0.05) mm/sec, yield electric field gradients at the iron nucleus ofq _z=+9.7·10¹⁷ V/cm² and +9.6·10¹⁷ V/cm², whereq _z⊥H; Debyetemperatures of θ=162 °K and 188 °K are obtained. The energy of the excited 3d-electron levels in iron-stilbene is estimated to Δ₁=309 cm^?1 and Δ₂=618cm^?1 as deduced from the temperature dependence ofΔE. In contrast to the suggestion ofEuler andWillstaedt bivalence of the iron in ironstilbene is found; its composition is shown to be 4(FeCl₂ ·H ₂O)·stilbene.     

Magnetic moment measurements in64Zn and66Zn

The ratios of the ∥g∥-factors of the 7^?, 4.635 MeV level in⁶⁴Zn and 6^?, 4.074 MeV and 7^?, 4.250 MeV levels in⁶⁶Zn has been found to be (1±0.18)∶(0.64±0.14)∶(0.60±0.12) by means of the recoil-into-gas (helium) integral perturbed angular correlation technique. The studied states were populated by the reactions⁵¹V(¹⁶O,p2n)⁶⁴Zn atE ₀=51 MeV and⁵⁵Mn(¹⁴ N,2pn)⁶⁶Zn atE _N =54 MeV.