Dipole Strength Distributions from HIGS Experiments

A series of photon scattering experiments has been performed on the double-beta decay partners 76Ge and 76Se, in order to investigate their dipole response up to the neutron separation threshold. Gamma-ray beams from bremsstrahlung at the S-DALINAC and from Compton-backscattering at HIGS have been used to measure absolute cross sections and parities of dipole excited states, respectively. The HIGS data allows for indirect measurement of averaged branching ratios, which leads to significant corrections in the observed excitation cross sections. Results are compared to statistical calculations, to test photon strength functions and the Axel-Brink hypothesi

Energy separation of the 1⁺/1⁻ parity doublet in ²⁰Ne

The parity doublet of 1⁺/1⁻ states of Ne⁻²⁰ at 11.26 MeV excitation energy is one of the best known test cases to study the weak part of the nuclear Hamiltonian. The feasibility of parity violation experiments depend on the effective nuclear enhancement factor (RN/|E(1⁺) − E(l⁻)|) which amplifies the impact of the matrix element of the weak interaction on observables indicating parity mixing. An extreme large value of Rn/|E(1⁺) − E(l⁻)| = (670 ± 7000) MeV⁻¹ was reported for the doublet in ²⁰Ne. The large uncertainty depends amongst others on the large uncertainty of |E(1⁺) − E(l⁻)| = 7.7±5.5 keV of the parity doublet. Nuclear resonance fluorescence (NRF) experiments with linearly and circularly polarized photon beams were performed at the High Intensity Gamma-Ray Source at Duke University, Durham, NC, USA, to determine the energy difference of the parity doublet with higher precision. The different angular distributions for 0⁺ → 1⁻ → 0⁺ and 0⁺ → 1⁺ → 0⁺ NRF cascades in polarized γ-ray beams were used to determine the energy difference of the parity doublet to 2.9(13) keV

Structure of high-lying levels populated in the Y-96 -> Zr-96 beta decay

The nature of $J^{\pi}=1^-$ levels of $^{96}$Zr below the $\beta$-decay $Q_{\beta}$ value of $^{96}$Y has been investigated in high-resolution $\gamma$-ray spectroscopy following the $\beta$ decay as well as in a campaign of inelastic photon scattering experiments. Branching ratios extracted from $\beta$ decay allow the absolute $E1$ excitation strength to be determined for levels populated in both reactions. The combined data represents a comprehensive approach to the wavefunction of $1^-$ levels below the $Q_{\beta}$ value, which are investigated in the theoretical approach of the Quasiparticle Phonon Model. This study clarifies the nuclear structure properties associated with the enhanced population of high-lying levels in the $^{96}$Y$_{gs}$ $\beta$ decay, one of the three most important contributors to the high-energy reactor antineutrino spectrum

Structure of high-lying levels populated in the 96Y →96Zr β decay

WOS:000713124400027The nature of the high-lying final levels of the 96Ygs β decay, one of the three most important contributors to the high-energy reactor antineutrino spectrum, has been investigated in high-resolution γ-ray spectroscopy following the β decay as well as in a campaign of inelastic photon scattering experiments. The comprehensive approach establishes 1− levels associated with the Pygmy Dipole Resonance as high-lying final levels in the β decay. Branching ratios extracted from β decay complement photon scattering and allow the absolute E1 excitation strength to be determined for levels populated in both reactions. The combined data represents a comprehensive approach to the wavefunction of the 1− levels below the Qβ value, which are investigated in the Quasiparticle Phonon Model. The calculations reveal that the components populated in β decay contribute only with small amplitudes to the complex wavefunction of these 1− levels. A comparison of the β decay results to data from total absorption γ-ray spectroscopy demonstrates a good agreement between both measurements

Real-world Automotive Emissions—Summary of Studies in the Fort McHenry and Tuscarora Mountain Tunnels

Motor vehicle emission rates of CO, NO, NOx, and gas-phase speciated nonmethane hydrocarbons (NMHC) and carbonyl compounds were measured in 1992 in the Fort McHenry Tunnel under Baltimore Harbor and in the Tuscarora Mountain Tunnel of the Pennsylvania Turnpike, for comparison with emission-model predictions and for calculation of the reactivity of vehicle emissions with respect to O3 formation. Both tunnels represent a high-speed setting at relatively steady speed. The cars at both sites tended to be newer than elsewhere (median age was \u3c 4 yr), and much better maintained as judged by low CO/CO2 ratios and other emissions characteristics. The Tuscarora Mountain Tunnel is flat, making it advantageous for testing automotive emission models, while in the underwater Fort McHenry Tunnel the impact of roadway grade can be evaluated. MOBILE4.1 and MOBILES gave predictions within ± 50% of observation most of the time. There was a tendency to overpredict, especially with MOBILES and especially at Tuscarora. However, light-duty-vehicle CO, NMHC, and NOx, all were underpredicted by MOBILE4.1 at Fort McHenry. Light-duty-vehicle CO/NOx ratios and NMHC/NOx, ratios were generally a little higher than predicted. The comparability of the predictions to the observations contrasts with a 1987 experiment in an urban tunnel (Van Nuys) where CO and HC, as well as CO/NOx, and NMHC/NOx, ratios, were grossly underpredicted. The effect of roadway grade on gram per mile (g mi−1) emissions was substantial. Fuel-specific emissions (g gal−1), however, were almost independent of roadway grade, which suggests a potential virtue in emissions models based on fuel-specific emissions rather than g mi−1) emissions. Some 200 NMHC and carbonyl emissions species were quantified as to their light- and heavy-duty-vehicle emission rates. The heavy-duty-vehicle NMHC emissions were calculated to possess more reactivity, per vehicle-mile, with respect to O3 formation (g O3 per vehicle-mile) than did the light-duty-vehicle NMHC emissions. Per gallon of fuel consumed, the light-duty vehicles had the greater reactivity. Much of the NMHC, and much of their reactivity with respect to O3 formation, resided in compounds heavier than C10, mostly from heavy-duty diesel, implying that atmospheric NMHC sampling with canisters alone is inadequate in at least some situations since canisters were found not to be quantitative beyond ∼ C10 The contrasting lack of compounds heavier than C10 from light-duty vehicles suggests a way to separate light- and heavy-duty-vehicle contributions in receptor modeling source apportionment. The division between light-duty-vehicle tailpipe and nontailpipe NMHC emissions was ∼ 85% tailpipe and ∼ 15% nontailpipe (evaporative running losses, etc.). Measured CO/CO2 ratios agreed well with concurrent roadside infrared remote sensing measurements on light-duty vehicles, although remote sensing HC/CO2 ratio measurements were not successful at the low HC levels prevailing. Remote sensing measurements on heavy-duty diesels were obtained for the first time, and were roughly in agreement with the regular (bag sampling) tunnel measurements in both CO/CO2 and HC/CO2 ratios. A number of recommendations for further experiments, measurement methodology development, and emissions model development and evaluation are offered

Real-World Automotive Emissions-Summary of Studies in the Fort McHenry and Tuscarora Mountain Tunnels

Motor vehicle emission rates of CO, NO, NOx, and gas-phase speciated nonmethane hydrocarbons (NMHC) and carbonyl compounds were measured in 1992 in the Fort McHenry Tunnel under Baltimore Harbor and in the Tuscarora Mountain Tunnel of the Pennsylvania Turnpike, for comparison with emission-model predictions and for calculation of the reactivity of vehicle emissions with respect to O3 formation. Both tunnels represent a high-speed setting at relatively steady speed. The cars at both sites tended to be newer than elsewhere (median age was \u3c 4 yr), and much better maintained as judged by low CO/CO2 ratios and other emissions characteristics. The Tuscarora Mountain Tunnel is flat, making it advantageous for testing automotive emission models, while in the underwater Fort McHenry Tunnel the impact of roadway grade can be evaluated. MOBILE4.1 and MOBILES gave predictions within ± 50% of observation most of the time. There was a tendency to overpredict, especially with MOBILES and especially at Tuscarora. However, light-duty-vehicle CO, NMHC, and NOx, all were underpredicted by MOBILE4.1 at Fort McHenry. Light-duty-vehicle CO/NOx ratios and NMHC/NOx, ratios were generally a little higher than predicted. The comparability of the predictions to the observations contrasts with a 1987 experiment in an urban tunnel (Van Nuys) where CO and HC, as well as CO/NOx, and NMHC/NOx, ratios, were grossly underpredicted. The effect of roadway grade on gram per mile (g mi−1) emissions was substantial. Fuel-specific emissions (g gal−1), however, were almost independent of roadway grade, which suggests a potential virtue in emissions models based on fuel-specific emissions rather than g mi−1) emissions. Some 200 NMHC and carbonyl emissions species were quantified as to their light- and heavy-duty-vehicle emission rates. The heavy-duty-vehicle NMHC emissions were calculated to possess more reactivity, per vehicle-mile, with respect to O3 formation (g O3 per vehicle-mile) than did the light-duty-vehicle NMHC emissions. Per gallon of fuel consumed, the light-duty vehicles had the greater reactivity. Much of the NMHC, and much of their reactivity with respect to O3 formation, resided in compounds heavier than C10, mostly from heavy-duty diesel, implying that atmospheric NMHC sampling with canisters alone is inadequate in at least some situations since canisters were found not to be quantitative beyond ∼ C10 The contrasting lack of compounds heavier than C10 from light-duty vehicles suggests a way to separate light- and heavy-duty-vehicle contributions in receptor modeling source apportionment. The division between light-duty-vehicle tailpipe and nontailpipe NMHC emissions was ∼ 85% tailpipe and ∼ 15% nontailpipe (evaporative running losses, etc.). Measured CO/CO2 ratios agreed well with concurrent roadside infrared remote sensing measurements on light-duty vehicles, although remote sensing HC/CO2 ratio measurements were not successful at the low HC levels prevailing. Remote sensing measurements on heavy-duty diesels were obtained for the first time, and were roughly in agreement with the regular (bag sampling) tunnel measurements in both CO/CO2 and HC/CO2 ratios. A number of recommendations for further experiments, measurement methodology development, and emissions model development and evaluation are offered