MeV Level Research Articles

Calculation of the Matrix Elements of 12C for the 15.1 MeV Level

We present here the result of the calculation on the ratio of |⟨1+||T1mag||0+⟩|2/|1/q⟨1+||T1mag||0+⟩|q=02 for the 15.1 MeV level in 12C. We use the wave function corresponding to the nucleons moving in a common harmonic potential plus a hard core.

Determination of the 13N(p, γ) 14O reaction rate through the Coulomb break-up of a 14O radioactive beam

In stellar-evolution models, the 13N(p, γ) 14O reaction plays an important role in the hot CNO cycle. Its reaction rate depends directly on the magnitude of the radiative width of the 5.17 MeV level in 14O. That width has been measured using the Coulomb break-up technique. A 70 MeV u 14O beam was excited in the Coulomb field of a 208Pb target, the 13N and proton fragments being recorded using a magnetic spectrometer and CsI scintillators, respectively. The experimental value Γ γ = 2.4 ± 0.9 eV is in overall agreement with other recent measurements.

Theory of Rare-Earth Impurities in Semiconductors

The theory of rare-earth impurities in semiconductors is reviewed. Results of Green's function calculations are presented. The particular case of Ytterbium (Yb) in InP is analyzed in detail. We show that the optical transitions of Yb in InP and their Zeeman splitting can be interpreted by a small coupling between quasi degenerate 5d and 4f states. It also explains the observed lifetimes. This model is coherent with the attribution of the Ec-30 meV level to the Yb3+/Yb2+ acceptor level as proposed recently. We detail the mechanism which allows the energy transfer between a free exciton and the rare-earth impurity. The conditions required for an efficient luminescence are analyzed.

RII spectroscopy of trap levels in bulk and LPE Hg1-xCdxTe

Resonant impact ionization (RII) spectroscopy, a new technique for studying low concentrations of trap levels in narrow-gap Hg1-xCdxTe has been used to investigate impurity and defect levels in both bulk and liquid phase epitaxy (LPE) crystals of this ternary material. Mercury interstitials, deliberately introduced into bulk samples with x approximately=0.22 and x approximately=0.24, provide direct evidence for the formation of trap levels near 45 and 61 meV above the valence band edge for these x-value samples. The 61 meV level in the x approximately=0.24 (Eg=121 meV at 5 K) sample is seen to enhance the transition strength of resonant two-photon magneto-absorption (TPMA) observed at high fields by acting as a near-resonant intermediate state for the two-photon process. In the LPE material, samples which have received just a post-anneal in an Hg-saturated atmosphere show strong RII structure due to defect levels at approximately=60 meV above the valence band, whereas samples which are both doped with indium and post-annealed show only intrinsic one-photon magneto-absorption structure.

18O(3He,p)20F reaction.

The {sup 18}O({sup 3}He,{ital p}){sup 20}F reaction has been studied at 18 MeV. Energy levels are measured up to {ital E}{sub {ital x}}{similar to}8.5 MeV and several new levels are observed. Angular distributions are measured for many of the levels and distorted wave Born approximation analyses are carried out. The {ital L} assignments are made and {ital J}{sup {pi}} limits are obtained.

Resonant absorption by the lowest two [formula omitted] levels of 9Be

The ground-state radiative widths of the E x = 14.393 and 16.975 MeV, T = 3 2 levels of 9Be were measured with a new γ-ray resonant absorption technique. Thin boron targets and broad resonances in the 11B(p, γ 0γ 1) 12C reaction were used to produce the required monochromatic γ-rays of variable energy. The total width of the 16.98 MeV level was obtained from measurements in a separate high-resolution 7Li(d, γ) 9Be experiment. The result leads to a revision of partial widths of the 16.98 MeV level that were reported earlier. The present results are compared to results of (e, e') scattering and, along with the revised particle widths of the 16.98 MeV level, to shell-model calculations. The isospin mixing and giant M1 character of the levels are also discussed.

Deep level transient spectroscopy measurement on tin-doped n-indium selenide

Deep level transient spectroscopy measurements in indium selenide samples doped with different amounts of tin are reported. Three tin-related electron traps have been detected with activation energies for emission of 56, 74, and 110 meV. The capture cross-section has also been measured and it is very low and weakly dependent on temperature for the 74 and 110 meV deep levels that are attributed to electron trap states related to ionized acceptor centers. For the 56 meV level the apparent capture cross-section shows an activated temperature dependence with an activation energy of 35 meV, which yields an ionization energy of 21 meV for the related level, which corresponds to the tin-related shallow donor. That behaviour is interpreted through the presence in InSe of stacking-fault-related barriers. When one of these barriers is swept by the depletion zone edge during the emptying or filling pulses, electrons must overcome that barrier in order to be emitted or captured, which results in a reduction of the effective capture and emission rates of shallow donors which thus become observable through capacitance transients.

Formation of Au Colloid Particles in Silica Glass by Ion Implantation.

ABSTRACTFormation of Au colloid particles and their optical property have been investigated in silica glasses implanted with Au+ ions at an acceleration energy of 1.5MeV and fluence levels of 1016-1017 ions/cm2. The Au colloid particles are formed in the as-implanted glasses. It is inferred that the average radius of Au colloid particles depends on the fluence level, although the fluence level does not affect the distribution of Au atomic concentration. The heat-treatment little affects the Au atomic distribution. The Au colloid particles grow to 4.3nm in average radius during heat treatment. It is revealed that the large nonlinear optical property of the Au+ -ion-implanted silica glass is attributed to the high concentration of the Au colloid particles in the narrow region.

The 12C(a,g)16O Cross Section at Low Energies

An R-matrix formula for the cross section for radiative capture reactions is developed and applied to fit recently measured 12C(oc,y)160 data, for both ground-state transitions and cascade transitions through the 6�92 and 7 �12 MeV levels. The correct treatment of the channel contributions is significant for the E2 cascade transitions. Consistent fits of the cascade and ground-state data suggest a value of the channel radius larger than those previously used, and consequently a value of the low-energy astrophysical S-factor appreciably larger than that adopted recently.

Radiative decay of the 15.235 MeV level in28Si

In27Al(p, γ)28Si reaction, a narrow resonance was located for the incident proton energyEp=3.785 MeV. It is tentatively identified as the analogue of the 5.91 MeV level in28Al. It is found to populate only levels of high spin (J≥3) and the angular distributions are consistent with spin-parity assignment ofJπ=3+ for the resonance. Gamma-decay strengths and branching ratios are deduced. The transition strengths from the otherJπ=3+,T=1 are compiled and compared against the strength expected from the positron decay of the ground state of28P (Jπ=3+). It is apparent that there is considerable configuration mixing among theJπ=3+,T=1 levels in28Si.

Spectroscopic information on 24Mg and 28Si from proton capture

Abstract Gamma-ray spectra with good statistics have been measured at three 23Na(p, γ)24Mg and five 27Al(p, γ)28Si resonances. The Ex = 9.30 MeV level of 24Mg is proved to be a triplet, and those at 9.53 and 10.66 MeV of 24Mg and at 10.67 MeV of 28Si are found to be doublets. Substantial improvements over previous work are obtained in the γ-ray branchings of the resonances and bound states, in excitation energies, and in lifetimes of 28Si levels (from observed Doppler shifts). The new information has led to new Jπ; T assignments (or restrictions) for 16 levels of 24Mg and 16 of 28Si. A shell-model calculation has helped to clarify the level schemes of both nuclei, in particular with regard to the T = 1 states. New information has also been obtained on levels close above the α-particle binding energy, which are important in nucleosynthesis.

Nucleon alignment in 191Hg. A competing mechanism at moderate spins

Detailed spectroscopic studies of the discrete γ-rays feeding and deexciting a 41 2 − , 4.6 MeV level in 191Hg are reported. The resulting decay scheme indicates single-particle nature for the states above the 41 2 − level. At moderate spin, the corresponding particle alignment mode competes favorably with collective oblate rotation. It is suggested that this sequence is associated with a non-collective prolate shape ( ϵ=0.1–0.15, γ≅−120°).

The total width of the 9.17 MeV level in 14N

A simple method for the determination of the total width of the 9.17 MeV level in 14N is described. The method is based on the use of a resonant detector which contains nitrogen in its active volume. With the help of the resonant detector the ratio of Γ γ0/Γ T was found to be 0.052 ± 0.004. This result together with the data from a conventional resonant absorption experiment yields for the total width of the level a value of 122±8 eV.

Alpha-particle decay widths of levels in 19F

Levels of 19F in the excitation region 4< E x<11 MeV were studied with the 12C( 11B, α) reaction, using a recoil-coincidence technique to measure values of γ γ/γ. The information obtained has been combined with known values of ωγ to determine alpha-particle widths in the range ~1−100 eV for various levels. The highest lying level observed to have a significant gamma-decay probability was a new level at E x = 10.927 ±0.008 MeV with γ γ / γ = 0.051±0.004. The 11 2 4 − , 9.873 MeV level was observed to have a surprisingly large value for γ / γ of 0.43 ±0.04, which gives γ α = 1.4±0.3 eV, γ p = 0.10 ± 0.03 eV, and a total width γ = 2.6±0.4 eV. The present measurement of γinα for the 11 2 1 − and 11 2 4 − levels, together with previous information for the 11 2 2 among these 11 2 − levels and clarify a long outstanding problem concerning the 11 2 − member of the K π = 1 2 − alpha-cluster band. We conclude that the 11 2 2 − , 8.953 MeV level is the best candidate for this alpha-cluster state, and there is very little configuration mixing among the 11 2 − levels.

Cross sections and partial kerma factors for elastic and inelastic neutron scattering from carbon in the energy range 16.5-22.0 MeV

The Studsvik high resolution, low background time-of-flight facility has been used to obtain a comprehensive set of differential neutron scattering cross sections for carbon at the neutron energies 16.5, 17.6, 18.7 19.8, 20.9, 21.6 and 22.0 MeV. Angular distributions in the range 10-160 degrees have been measured for elastic scattering, and also for inelastic scattering from the levels at 4.44, 7.65 and 9.64 MeV. Angle integrated cross sections have been determined by fitting Legendre polynomial expansions to the differential data. partial kerma factors for elastic and inelastic (4.44 MeV level) scattering have been deduced from these fits. Analyses in terms of a spherical optical model as well as in terms of the coupled-channels formalism with a deformed potential have provided information for cross section and partial kerma factor calculations also outside the measured energy range.

Parity-violating effects in the 6Li(α, γ) 10B capture reaction via the 5.1 MeV doublet resonance

Strengths and mixing ratios of γ-transitions from the parity-mixed 5.112 and 5.166 MeV levels in 10B following α-capture resonances at E α = 1.085 and 1.175 MeV have been measured using a Ge(Li) detector. The E2/M2 admixture to M1/E1 has been found to be small for most of the strong transitions. Estimations of the magnitude of longitudinal vector analyzing power A γ 2 and circular polarization P γ for some strong radiative transitions have been made using the Kurath and Teeters' value of the parity-mixing matrix element for the 6Li(α, γ) 10B capture resonance, predicted on the basis of the Weinberg-Salam model. A strong effect on P γ ( θ) arising from the interference of partial waves of opposite parity in the capture channel has been located for some strong transitions.

Linear induction accelerators for industrial applications

There are many industrial radiation processes that require electron beam sources capable of operating at 1–10 MeV and power levels of 50–500 kW. These processes include medical product sterilization, food sterilization and decontamination of waste products. Linear induction accelerators (LIAs) driven by magnetic pulse compression (MC) systems are particularly attractive for these applications. Pulse Sciences, Inc. has developed a prototype LIA/MC system to demonstrate the capabilities of this technology to meet industrial requirements where low cost, high efficiency and high reliability are essential. The prototype is designed to operate at a beam energy of 1.6 MeV and a beam current of 1–2 kA in 65 ns pulses at average powers exceeding 20 kW. Higher energies and average power levels can be achieved by adding more acceleration modules and by increasing the pulse repetition rate. This paper discusses the prototype system design and its performance characteristics.

Response of a thin avalanche detector to simultanous minimum ionizing particles

A thin multiwire avalanche detector, operating in the saturated mode, has been constructed and tested for its response to 1 and 2 (simultaneous) minimum-ionizing particles. These measurements employed the 19F(p,α)16O reaction to form the Jπ = 0+, Eex = 6.05 MeV level of 16O, which deexcites 100% by nuclear pair emission yielding energetic β+-β− pairs. The result peak detector pulse amplitude is directly proportional to n, the number of particles, for n ≤ 2, whereas the fractional resolution (FWHM/PEAK) is approximately proportional to 1√n.

Mixed-symmetry states and the structure of 200Hg

Mixed-symmetry assignments are made to the 1.570 (11+), 1.573 (23+) and 1.659 (31+) MeV levels in 200Hg. The characteristics of the 23+ level are shared with nearby 2+ levels at 1.254 and 1.593 MeV. An interacting boson approximation (IBA-2) analysis examines the sensitivity of the mixed-symmetry states to the xi i parameters of the Majorana term and finds that both the magnitude and sign of the delta (E2/M1) mixing ratio of 2+-21+ transitions are well reproduced at the values of the xi i parameters used to obtain a level energy fit. The IBA-2 calculations also give a satisfactory fit to the energy levels and in general provide X(E0/E2) values close to the experimental data. These calculations agree with the known oblate deformation of the ground state which is found to be predicted by Kumar's (1984) dynamic deformation model. Experimental data from n, gamma gamma ( theta ) experiments together with internal conversion coefficient (ICC) results allow 1+ levels to be unambiguously established at 1.570, 1.631, 1.718, 2.061, 2.370, 2.640 and 2.979 MeV. The measurements also provide precise delta values of many transitions while event-by-event coincidence information permits the decay scheme to be developed with previous unlocated transitions now firmly assigned.

Electronic stopping power for 7Li, 11B, 12C, 14N and 16O at energies 0.4 to 2.1 MeV/nucleon in Ta and Au, and for 12C at energies 0.4, 0.8 and 1.4 MeV/nucleon in 18 elemental solids

Stopping powers have been measured for 0.4 to 2.1 MeV/nucleon beams of 7Li, 11B, 12C, 14N and 16O in Au and of 7Li, 12C and 14N in Ta. The results are compared with the predictions of an empirical model. By application of the Doppler-shift attenuation method, the measured electronic stopping powers for 12C in Ta and Au are used to deduce the mean lifetime 58 ± 5 fs for the 4.439 MeV level in 12C. Deviations of the electronic stopping power from the predictions of the empirical model have been studied for 12C at energies 0.4, 0.8 and 1.4 MeV/nucleon in 18 Z = 14–82 elemental solids by application of the Doppler-shift attenuation method and the lifetime value of the 4.439 MeV level.