Broad Bump Research Articles

Dominance of the two-nucleon mechanism in 16O( pi +,pp) at 115 MeV.

Singles $^{16}\mathrm{O}$(${\mathrm{\ensuremath{\pi}}}^{+}$,p) and coincidence $^{16}\mathrm{O}$(${\mathrm{\ensuremath{\pi}}}^{+}$,2p${)}^{14}$N measurements have been made at ${\mathit{T}}_{\mathrm{\ensuremath{\pi}}}$=115 MeV over an extended range of the phase space of the two final-state protons. The coincidence measurements have a missing-mass resolution of 4 MeV. The direct two-nucleon absorption cross section extracted from the data is 58\ifmmode\pm\else\textpm\fi{}8 mb. After corrections for final-state interactions, it was found that the two-nucleon ${\mathrm{\ensuremath{\pi}}}^{+}$+np\ensuremath{\rightarrow}pp process accounts for about 76% of the total absorption cross section, and thus is the dominant absorption mechanism. Evidence for absorption on s-p pairs is seen as a broad bump near 32 MeV of excitation. At backward angles the inclusive $^{16}\mathrm{O}$(${\mathrm{\ensuremath{\pi}}}^{+}$,p) spectra show a distinct absorption peak, an important feature not previously observed. Comparisons of distorted wave impulse approximation calculations to both the coincidence data and inclusive data are presented.

Studies of coherent and diffuse x-ray scattering by porous silicon

The microstructure of porous silicon layers has been studied by means of x-ray diffraction. Using a double-crystal diffractometer, the observed diffraction patterns give directly the mismatch between the lattice parameters of the porous layers and of the substrate, and the curvature of various porous silicon samples obtained in different conditions. From measurements with the same experimental set-up, but with a larger scan range, broad diffuse bumps produced by the pore structure have been observed. This new feature allows us to obtain structural informations on the porous silicon in a nondestructive way. In particular, we have observed the anisotropic pattern showing a preferential elongation of the pores perpendicular to the (100) surface.

Duct‐model explanation of the broad component of plasma‐line spectra observed at Arecibo

The plasma‐line spectrum observed during on‐off cycling of the HF heater at Arecibo contains a broad component extending about 50 kHz from the first decay line. Shortly after HF turn‐on this spectrum can have a maximum intensity 10–20 kHz from the heater frequency (broad bump) or the intensity can decrease monotonically with frequency separation from the first decay line. One possibility is that Langmuir waves (L waves) generated by parametric‐decay of the heater wave are trapped in small‐scale field‐aligned ducts and are responsible for the first decay line. The heater electromagnetic wave can also become ducted near reflection in large‐scale field‐aligned ducts. If the heater wave is not ducted near reflection, its electric field is very nearly parallel to the earth's magnetic field B. The L waves then have wavenormals restricted to a range of angles about B. When these L waves decay parametrically into other L waves that can be detected by the radar, a broad‐bump spectrum results. If the heater wave becomes ducted near reflection (which is probable during spread‐F conditions), its electric field can make a considerable angle to B near reflection and the unstable L waves can propagate at all angles to B (including perpendicular). When these L waves decay parametrically into other L waves that can be detected by the radar, a monotonic spectrum results.

Study of a Broad Bump in Reaction Particle Spectrum Observed for the One-Neutron Pickup Reactions

Reaction particles from the ( d , t ) reactions on 110 Cd and 116 Cd at 33 MeV and the ( 3 He, α) reaction on 116 Sn at 65 MeV were measured to investigate the deeply-bound neutron hole states. Angular distributions of broad bumps in the reaction particle spectra with a width of 8 MeV on the scale of residual excitation are well reproduced with DWBA and coupled-channel analyses assuming that these structures are composed of the particles arising from the full-strength one-neutron pickup transitions to the 1 g 9/2 , 2 p 1/2 , 2 p 3/2 and 1 f 5/2 neutron hole states and those from the full-strength two-step transitions to the hole-vibration coupling states involving these neutron hole states and the first 2 + and 3 - states in the target or core nucleus. Existing data for the ( p , d ) reactions on 116 Cd and 124 Sn at 52 MeV and for the ( d , t ) reaction on 116 Sn at 50 MeV are also analyzed and the same conclusion as above is indicated.

Statistical giant resonance effects in heavy-ion radiative capture

Abstract Heavy-ion radiative capture has been observed in the two reactions 9 Be( 12 C, γ) 21 Ne and 16 O( 7 Li, γ) 23 Na for c.m. energies between 3 and 9 MeV. High-energy γ-rays populating levels up to 4.7 MeV in the final nuclei were detected with a large volume, anticoincidence-shielded NaI spectrometer. Peak cross sections for individual transitions in both reactions were found near 60 nb/sr. For 9 Be + 12 C all excitation functions were rather smooth with a broad bump around E c.m = 5–6 MeV. Statistical model calculations were in good agreement with the data suggesting that perhaps as much as half of the GDR strength in 21 Ne is statistical. More structure was found in 16 O + 7 Li superimposed on still sizeable statistical yield. Previous measurements of the same reaction were found to be partially in error.

Two lines of sight with exceedingly anomalous ultraviolet interstellar extinction

Low-resolution IUE data toward HD 62542 reveal an extinction curve with an extremely broad and weak UV extinction bump and the highest FUV extinction yet observed in the Milky Way. Parameters describing the central position and FWHM for weak bumps observed toward HD 62542 and HD 29647 are derived using analytical fitting techniques. In both cases, the bump central positions are shifted shortward of 2175 A with an initial wavelength of 2110 A for HD 62542 and an initial wavelength of 2128 A for HD 29647. The bump FWHM is found to be 1.29/micron and 1.62/micron for HD 62542 and HD 29647, respectively.

The neutron exit channel in 3He-induced break-up reactions

Inclusive neutron spectra of 3He-induced reactions with 27A1, 63Cu, 93Nb and 197Au were measured for 26.0, 34.4 and 43.1 MeV projectile energy at laboratory angles from 3° to 177° using time-of-flight techniques. The component remaining after incoherent subtraction of compound and precompound contributions from the inclusive spectra shows a broad continuous bump and is assigned to the direct projectile break-up. Due to Coulomb effects, the position of the bump is shifted from 1 3 E 3 He c.m. to lower and higher energies in neutron- and proton-spectra, respectively. Experimental and theoretical results characterize the projectile break-up as a peripheral process. Break-up neutron yields increase with incident energy and target mass. Experimental spectra are the more underestimated by DWBA model calculations the less the incident energy exceeds the Coulomb barrier of the target nucleus. These discrepancies are attributed to the neglect of reaction mechanisms, e.g. a sequential break-up involving a singlet deuteron as intermediate state or an excitation of the projectile into the continuum followed by an immediate decay.

Missing-energy dependence of the separated response functions for the 12C(e,e'p) reaction.

A longitudinal/transverse separation of the $^{12}\mathrm{C}$(e,e'p) reaction in the quasielastic region has been performed in parallel kinematics. Above the two-particle emission threshold a broad bump is seen which has been attributed to knockout from the deeply bound s shell. The s-shell region shows a large transverse enhancement compared to distorted-wave impulse-approximation calculations based on free-proton form factors. This enhancement increases with missing energy, indicating that a nonquasielastic reaction mechanism plays a significant role. The p shell is consistent with the free-proton behavior.

Photon scattering on 238U and the interpretation of near-threshold photofission resonances.

Cross sections for photon elastic scattering have been measured for $^{238}\mathrm{U}$ between 4.8 and 6.4 MeV with an energy resolution of about 50 keV. These data have been used along with existing photofission data to infer the total photoabsorption cross section ${\ensuremath{\sigma}}_{T}$ and the fission transmission coefficient ${T}_{f}$ below neutron threshold. We find that the inferred ${\ensuremath{\sigma}}_{T}$ varies smoothly with energy and generally follows the extrapolated tail of the giant dipole resonance, and that ${T}_{f}$ shows a broad bump between 5.6 and 5.9 MeV. These results strongly support the contention that resonances seen in near-threshold photofission cross sections are due to the fission and not the photon channel .

Proton hole response function on 196Pt and 197Au transitional target nuclei up to high excitation energy

The proton-hole response functions have been studied on the transitional target nuclei 196Pt and 197Au via the (d, 3 He) reaction at E d = 108.4 MeV, up to 6 MeV and 18.5 MeV excitation energy respectively. 196Pt low-lying levels have been studied in addition at E d = 50 MeV. Spectroscopic information gained on the low-lying levels in the 195Ir and 196Pt residual nuclei allows the discussion of the 3 s 1 2 and 2 d 3 2 orbital filling. For both 195Ir and 196Pt, new 2d 5 2 and 1 h 11 2 levels or groups are observed. The 196Pt spectra exhibit a broad bump between 6 and 15 MeV excitation energy riding over a continuous background. The study of the excitation energy spectra up to 27 MeV leads to a consistent subtraction of the background. The contributions of the 1 g 9 2 , 2p and 1f inner-hole strengths are deduced by least square fits of DWBA angular distributions. About the whole 1 g 9 2 and 2p inner hole strengths and 50% of the 1f strengths are found below E x = 18.5 MeV. The background correction is also used to reanalyse previous data obtained via the same reaction on the spherical 208Pb target for comparison. Experimental results on centroid separation energies are compared with Hartree Fock predictions. The spreading widths and specific features of the strength distribution shapes in 195Ir and 196Pt and 207Tl are discussed in connection with the dominant quadrupole collective degrees of freedom of the two first nuclei contrasting with the strong vibrational modes in 207Tl. The valence hole fragmentation in 195Ir is described in the framework of the core quasiparticle coupling model.

Damping of high-spin single-particle strengths in 209Pb.

The stripping reaction (\ensuremath{\alpha},${\mathrm{}}^{3}$He) at 183 MeV incident energy has been used to study the neutron-particle response function on a $^{208}\mathrm{Pb}$ target nucleus up to 15 MeV excitation energy. Detailed spectroscopic information has been obtained on the low-lying neutron states (0--4 MeV) through angular distribution measurements and standard distorted wave Born approximation analysis. A large enhancement of cross section is observed between 5 and 15 MeV. It appears as a broad bump superimposed on a continuous background which has been analyzed within the framework of the plane wave breakup model. The excitation energies, angular distributions, and strengths of these high-lying transitions suggest that they arise from neutron stripping to high-spin outer subshells, i.e., 2${h}_{11/2}$, 1${k}_{17/2}$, and 1${j}_{13/2}$ in $^{209}\mathrm{Pb}$. The results are compared with predictions from the core-particle model and from the quasiparticle-phonon model.

Low-frequency noise and discrete charge trapping in small-area tunnel junction dc SQUID’s

We present measurements of the noise properties of very small-area, high current density tunnel junction dc superconducting quantum interference devices (SQUID’s). The low-frequency noise spectra display broad curves and bumps consistent with the presence of individual Lorentzian features superimposed on a background which is always much flatter than 1/f. When these features are most prominent, the voltage across the SQUID exhibits discrete switching behavior which we attribute to the trapping and untrapping of single electrons within the tunneling barrier. This observation, along with other evidence presented, suggests that critical current fluctuations displaying tunneling kinetics dominate the low-frequency noise of these ultrasmall devices.

An analysis on the shapes of ultraviolet extinction curves. I - The 2175 A bump

IUE data are used to investigate the properties of the 2175 A interstellar extinction bump toward 45 reddened Milky Way stars. Using analytic fitting functions, parameters are derived which describe the central position, FWHM, and strength of the bump. The bump position is very stable, with an extreme deviation which is still significantly larger than the measurement uncertainty, indicating true variability. The bump FWHM has a large range of intrinsic values, 0.77/micron to 1.25/micron. The normalized bump strength varies by more than a factor of three. There are no convincing correlations among the three bump parameters, but the width of the bump is strongly correlated with the dust grain environments. Dense quiescent regions yield broad bumps, while diffuse interstellar medium and regions of recent star formation yield narrower bumps. The absence of any correlation between bump width and central position argues strongly against graphite grains in the size range prescribed by the Mathis, Rumpl, and Nordsieck (1977) model as carriers of the bump.

The γ-decay of the [formula omitted] and 2p inner-hole states in 111Sn via the 112Sn( 3He, αγ) reaction at 32 MeV

The γ-decay of the deeply-bound hole states in 111Sn has been investigated at 32 MeV incident energy by means of the 112Sn( 3He, αγ) reaction. The α-particles emitted near 0° were detected in a Si counter located at the image plan of the superconducting solenoidal spectrometer SOLENO. The γ-rays in coincidence with the α-particles were detected by two Ge(Li) detectors located at 90° and 142° with respect to the beam direction, respectively. Energies, spins and decay schemes have been established for the low-lying states up to 2.5 MeV excitation energy in 111Sn. The γ-decay of the broad bump, located around 4.2 MeV and previously attributed to neutron pick-up from the inner 1 g 9 2 , 2 p 1 2 , and 2 p 3 2 neutron. Subshells, reveals the importance of quasiparticle-phonon m the spreading mechanism of the inner-hole strengths. The 1 g 9 2 and 2p strength functions have been deduced from the α-decay of the enhanced structures (3 ≦ E x≦ 8 MeV). They are compared to the ones measured in previous inclusive neutron pick-up experiments and to those calculated in the framework of the quasiparticle-phonon nuclear model.

γ-decay of the deeply-bound hole states in 101Pd, 105Pd, 107Pd, 111Sn, 117Sn observed in the ( 3He, αγ) reaction at 70 MeV

The γ-decay of deep-hole states in 101, 105, 107Pd was studied via the ( 3He, αγ) reaction at E 3 he = 70 MeV and supplemented by data from 112, 118Sn targets to investigate the deep-hole spreading mechanism. The γ-decay pattern for the g 9 2 deep-hole state shows a strong dependence on the spreading width: if the deep-hole state is observed as a sharp peak, it mainly decays to the low-lying 7 2 + state by a spin-flip M1 transition with a large M1-E2 mixing ratio; if the deep-hole state is observed as a broad bump, it decays statistically indicating the complete spreading of the hole strength over the underlying states; if the deep-hole state is observed with a structure intermediate between a sharp peak and broad bump, its γ-decay shows both decay patterns. A sharp peak at E x = 2.396 MeV in 101Pd which carries a large fraction of the g 9 2 hole strength ( C 2 S = 2.0) was found to be a single state having a width of less than 2.5 keV. For the spin-flip M1 transition the destructive interference between the g 9 2 component and the coupled components of the deep-hole state was found in heavily spread states. A quasiparticle-plus-rotor (QPR) model was applied to calculate the fragmentation in the doorway stage for the g 9 2 neutron deep-hole state in the Pd isotopes. A reasonable agreement between the calculation and the experimental results was obtained for the strength fragmentation, for the nucleus 101Pd. However, the large M1-E2 mixing ratio experimentally observed was not reproduced.

Proton stripping to outer subshells and the damping of single-particle states: 116Sn, 144Sm, and 208Pb( alpha,t) reactions at 80 MeV.

The stripping reaction (\ensuremath{\alpha},t) at 80 MeV incident energy has been used to study the proton-particle response function on $^{116}\mathrm{Sn}$, $^{144}\mathrm{Sm}$, and $^{208}\mathrm{Pb}$ target nuclei up to 22 MeV excitation energy. Rather complete spectroscopic information has been obtained on the low-lying proton states (0--3 MeV) through angular distribution measurements and standard distorted wave Born approximation analysis. Strong transitions to high-lying proton states located between 5 and 12 MeV excitation energy in $^{145}\mathrm{Eu}$ and $^{209}\mathrm{Bi}$ are observed whereas the spectrum from the $^{116}(\mathit{\ensuremath{\alpha}}$,t) reaction displays only broad, weak enhancement of cross sections at high excitation. These transitions appear as broad bumps superimposed on a continuous background for which a qualitative analysis within the framework of the breakup model has been attempted. The excitation energies, angular distributions, and strengths of these high-lying transitions suggest that they arise from proton stripping to high-spin outer subshells, e.g., 1h(9/2) and 1i(13/2) in $^{145}\mathrm{Eu}$, and 1i(11/2) and 1j(15/2) in $^{209}\mathrm{Bi}$. A distorted-wave Born approximation analysis using resonant form factors for the states located above the proton threshold has been carried out. The deduced proton strength distributions are compared with the predictions from the quasiparticle-phonon and single-particle vibration coupling nuclear models. Around 12--14 MeV excitation energy, narrow peaks corresponding to the population of the isobaric analog states in $^{117}\mathrm{Sb}$ and $^{145}\mathrm{Eu}$ are also observed. Our results are compared to the known spectroscopic properties of the corresponding parent states in $^{117}\mathrm{Sn}$ and $^{145}\mathrm{Sm}$.

Reaction mechanisms in 3He projectile breakup at 52MeV on 12C, 28Si and 58Ni

Inclusive proton and deuteron spectra from 3He-induced reactions on 12C, 28Si and 58Ni have been studied. Each spectrum contains a continuum part that may be separated into a broad bump, centred around beam velocity energies at forward angles, and an exponential tail. The properties of each of these components have been investigated as function of outgoing particle, detection angle and target mass. The centroid position of the bump and the bump width are found to be almost independent of target mass and detection angle. The total (energy- and angle-integrated) cross sections for the bump show a mass dependence almost proportional to A 2 3 for both protons and deuterons. The total cross section for the exponential tail has a different mass dependence for protons and deuterons: proportional to A and A 1 3 , respectively. The results for the proton tail are qualitatively reproduced by calculations assuming absorption of the projectile. Charged particle-proton coincidences have been measured and analysed in order to identify the major contributors to the inclusive proton and deuteron spectra at θ = 10°. The following processes have been identified: (i) elastic and inelastic breakup in which the projectile breaks up into two constituents leaving the target in its ground state or an excited state, (ii) absorptive breakup in which one part of the projectile continues virtually undisturbed while the other part is captured, and (iii) a process resulting in the preequilibrium emission of deuterons or tritons followed by the statistical emission from the residual compound system. These three processes account for 75–100% of the inclusive cross section. A semi-empirical model is presented that allows the calculation of the relative coincidence yields from the total inclusive cross sections. The total projectile breakup cross section amounts to about 20% of the total reaction cross section independent of target. A quasi-free breakup model is proposed for the description of the breakup spectra. The model reproduces the data qualitatively very well. The absolute cross sections are not reproduced since the absorption of the spectator is not included. The normalization constant for proton spectator processes are consistently a factor 4 larger than for the corresponding deuteron processes. It is suggested that this is related to the difference in transmission of the peripheral region of the nucleus.

Neutron and photon production from thick targets bombarded by 30-MeV p, 33-MeV d, 65-MeVHe3, and 65-MeVαions: Phenomenological analysis of experimental neutron energy spectra

The measured energy spectra, reported in the preceding paper, of neutrons produced from thick carbon, copper, and lead targets exposed to 30-MeV protons, 33-MeV deuterons, 65-MeV /sup 3/He, and 65-MeV alpha particles were analyzed with the phenomenological hybrid model of equilibrium and preequilibrium emissions, together with the Serber model for deuteron stripping. Both spectral components of equilibrium and preequilibrium were well fitted to two Maxwellian-type functions having different nuclear temperatures. The former temperature values were only a function of the excited energy of the compound nucleus per nucleon, independently of the neutron emission angle, while on the other hand, the latter temperature values were dependent on the emission angle and the total energy delivered into the compound nucleus by the projectile. For deuteron, /sup 3/He, and alpha projectiles, a broad bump was seen in the forward spectrum which corresponds to the direct knockout and the deuteron and /sup 3/He breakup processes. The deuteron breakup process calculated by the Serber model showed rather good agreement with the measured spectrum.

The 3000 A bump in quasars

view Abstract Citations (65) References (33) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The 3000 A bump in quasars. Oke, J. B. ; Shields, G. A. ; Korycansky, D. G. Abstract Absolute spectrophotometry of 30 quasars with redshifts 0.53 ≤ z ≤ 0.70 has been obtained with the multichannel spectrometer on the 5 m Hale telescope. The rest wavelength coverage of 2000 Å < λ0 ≤ 5500 Å contains the entire λ3000 emission "bump". The continuum observations are well represented by a single power law plus a smooth, broad bump and superposed Fe II multiplets. The shape of the bump is quite uniform from object to object, but the ratio of bump intensity to power-law intensity varies considerably. The observed continuum energy distributions are compared with models consisting of a power law plus emission in the Balmer and higher continua of hydrogen. Motivated by recent observations of abundant γ-rays from active galactic nuclei, a simple analytic treatment of the physical conditions and continuum emission from a dense slab of hydrogen heated by γ-rays. Publication: The Astrophysical Journal Pub Date: February 1984 DOI: 10.1086/161671 Bibcode: 1984ApJ...277...64O Keywords: Astronomical Spectroscopy; H Lines; Quasars; Red Shift; Spectral Energy Distribution; Spectrophotometry; Emission Spectra; Gamma Rays; H Beta Line; Hydrogen; Iron; Magnesium; Thermal Emission; Astrophysics full text sources ADS | data products SIMBAD (30) NED (28)

Breakup fusion ofLi7

A breakup process of $^{7}\mathrm{Li}$ has been studied by performing the following measurements with a 77 MeV $^{7}\mathrm{Li}$ beam; (i) energy and angular distributions of $z=1 \mathrm{and} 2$ particles in the $^{159}\mathrm{Tb}$+$^{7}\mathrm{Li}$ reaction measured in singles and in coincidence with $\ensuremath{\gamma}$ rays from some heavy residual nuclei, (ii) out-of-plane angular distributions of $\ensuremath{\gamma}$ rays taken in coincidence with $\ensuremath{\alpha}$ particles in the $^{159}\mathrm{Tb}(^{7}\mathrm{Li}, \ensuremath{\alpha}x\mathrm{n})^{162\ensuremath{-}x}\mathrm{Dy}$ reaction to deduce the spin alignment involved, and (iii) in-plane and out-of-plane angular distributions of fission fragments measured in coincidence with $z=1 \mathrm{and} 2$ particles emitted in the reaction of $^{232}\mathrm{Th}(^{7}\mathrm{Li}, xf)$ to extract the magnitude and alignment of the transferred angular momenta. The observed energy spectrum of tritons and $\ensuremath{\alpha}$ particles measured at forward angles exhibits a broad bump centered at a kinetic energy corresponding to the beam velocity, which is characteristic of the breakup mechanism. Roughly a half of the yield at this bump has been shown to originate from a breakup-fusion process, in which one of the breakup fragments is captured by a target nucleus. It is also shown that angular momenta transferred to residual nuclei by breakup fusion are well aligned along the normal to the reaction plane and have the magnitude, on the average, consistent with a direct reaction process occurring at the surface region of projectile and target nuclei.NUCLEAR REACTIONS $^{159}\mathrm{Tb}(^{7}\mathrm{Li}, x)$, ($^{7}\mathrm{Li}$, $\ensuremath{\alpha}x\mathrm{n}$), $E=77$ MeV; measured $\ensuremath{\sigma}({E}_{x}, {\ensuremath{\theta}}_{x})$, $\ensuremath{\alpha}\ensuremath{-}\ensuremath{\gamma}$ coin, angular correlations $W({\ensuremath{\theta}}_{\ensuremath{\gamma}})$ of discrete $\ensuremath{\gamma}$ rays; deduced $\ensuremath{\sigma}({E}_{\ensuremath{\alpha}})$ in coin with final nuclei; $^{232}\mathrm{Th}(^{7}\mathrm{Li}, xf)$, $E=77$ MeV; measured $x\ensuremath{-}f$ angular correlations; deduced magnitude and alignment of average $J$. Average $l$ for particle emission.