Excitation and decay of the isovector giant monopole resonances via the 208Pb(3He,t p) reaction at 410 MeV

The excitation and subsequent proton decay of the isovector spin-flip giant monopole resonance (IVSGMR) is studied via the 208Pb(3He,t) reaction at 410 MeV. In the inclusive spectrum (60+/-5)% of the non-energy-weighted sum-rule strength for this 2 variant Planck's over 2h omega resonance was found in the region 29相似文献   

Giant resonances in the doubly magic nucleus 48Ca from the (e, e'n) reaction

The 48Ca(e,e(')n) reaction has been investigated for excitation energies 11-25 MeV and momentum transfers 0.22-0.43 fm(-1) at the superconducting Darmstadt electron linear accelerator S-DALINAC. Electric dipole and quadrupole plus monopole strength distributions are extracted from a multipole decomposition of the spectra. Their fragmented structure is described by microscopic calculations allowing for coupling of the basic particle-hole excitations to more complex configurations. Comparison of the excitation spectrum of the residual nucleus 47Ca with statistical model calculations reveals a 39(5)% contribution of direct decay to the damping of the giant dipole resonance.     

Out of plane measurements of the decay neutron from the giant resonance in the 12C(e,e(')n)11C reaction

Out of plane measurements of the angular correlations for the 12C(e, e(')n) reaction have been performed for the first time in the giant resonance region. The cross sections were directly separated into the longitudinal and transverse, longitudinal-transverse, and transverse-transverse components. The cross section at the peak of the giant resonance ( omega = 22.5 MeV) has been found to be almost all longitudinal. It was reproduced by the multipole expansion with E0 and E2 components besides E1. The longitudinal-transverse component might have a maximum around 24 MeV. The transverse-transverse component is very small over the giant resonance.     

Microscopic description of the E0, E2 and E1 giant resonances in 40Ca, 48Ca and 56Ni

The isovector E1 as well as the isoscalar, isovector and full electromagnetic E2 and E0 strength distributions for ⁴⁰Ca, ⁴⁸Ca and ⁵⁶Ni have been calculated in a large energy range up to 50 MeV of excitation. The microscopic model used includes the continuum RPA, 1p1h⊗phonon configurations and ground state correlations induced by these configurations. It is shown that the latter effect gives an increase of the energy weighted sum rules of 4–7%. In all these nuclei the isoscalar E0 and E2 resonances are spread out over the broad energy region. We obtained a reasonable good agreement with the available experimental data including the recent ones for the isoscalar E0 resonance in ⁴⁰Ca. The theoretical transition densities show a rather strong dependence on the excitation energy.     

Excitation of giant resonances in intermediate energy heavy-ion reactions

Quasielastic and deep inelastic processes in the reaction ¹⁶O + ²⁰⁸Pb have been studied at bombarding energies of 10–80 MeV per nucleon. The excitation probability of the giant modes becomes larger with increasing energies. At a given bombarding energy the multiple excitation of low-lying modes becomes predominant as the angle of observation moves away from the grazing angle. Near grazing, no appreciable background of this character is found for bombarding energies above 30 MeV per nucleon. At these energies the electromagnetic interaction becomes the most effective way to excite the giant modes in the excitation energy interval of 10–20 MeV. The importance of Coulomb excitation for the highest bombarding energies makes the excitation of isovector modes no longer negligible.     

Quenching of photon decay in hot giant dipole resonances

The quenching of photon decays in giant dipole resonances (GDR) at high excitation energy (E^*) is explained as due to the competition between γ-ray and particle emission. This effect is related to a large increase of the GDR width with the temperature of the nucleus in presence of a pre-equilibrium mechanism that also tends to reduce the collective dipole strength. A saturation of the GDR width at high excitation energy cannot account for the experimental data. Limiting temperatures for the observation of GDR γ-decays are deduced. The E^*-dependence of photon yields above the GDR region is also discussed.     

The decay width of higher multipole giant resonances

The decay width of higher multipole giant resonances is described within the framework of the newly developed Fourier-Bessel random-phase approximation. We calculate the distribution of the isoscalar and isovector multipole strength for electric resonances up to $\text{J}{}^{\mathrm{\pi }}\text{= 7}{}^{\mathrm{?}}$. In our model we find no concentrated multipole strength beyond the hexadecapole.     

Search for isovector giant monopole resonances via the Pb(3He,tp) reaction

The (nat)Pb(3He,tp) reaction at E(3He) = 177 MeV was studied to identify 2Planck's over 2piomega isovector monopole strength in Bi isotopes. Monopole strength was found in the region -45相似文献   

The decay of isoscalar giant resonances in 24Mg and 40Ca

In this paper we present data on the charged-particle decay of the isoscalar 2⁺ strength between 10 and 20 MeV excitation energy (E_x) in ²⁴Mg and ⁴⁰Ca. The isoscalar strength was excited by inelastic scattering of 120MeV α-particles at 14° and 12.5° for ²⁴Mg and ⁴⁰Ca, respectively. The charged particles originating from the decay were detected in coincidence with the α′ particles at several angles in the scattering plane. J^π assignments of the decaying states were made on the basis of the angular correlation pattern of the α₀ decay to the ground state of ²⁰Ne and ³⁶Ar, respectively, using a DWBA calculation for the m-state population of the decaying state.For ⁴⁰Ca, about 40% of the E2 EWSR is found to be located in the interval E_x = 13.5 ± 1.5 MeV, which is similar to what has been found from previous inelastic scattering experiments at E_x = 18 ± 2 MeV, but much more than such experiments located in the region E_x = 12–15 MeV. The difference for the region E_x < 16 MeV is due to the fact that from our α₀ angular correlation pattern we conclude that virtually no continuum is excited in the (α, α′) process up to E_x = 16 MeV while all previous inelastic hadron scattering experiments assumed such a continuum to be present. The E2 strength distribution for ⁴⁰Ca thus obtained is very different from what previous theoretical calculations predict. For ²⁴Mg about 30% of the E2 EWSR is present in the interval 12.5 ? E_x ? experiments. 16.5 MeV which again is about twice as much as deduced from previous inelastic scattering The observed branching ratios are compared with calculated ones assuming statistical decay. Reasonable agreement was obtained for ⁴⁰Ca, but for ²⁴Mg especially the α₀-decay branch and to a lesser extent also the p₁ one are much stronger than the statistical calculations predict, indicating that especially the α₀ decay occurs mainly in a non-statistical way.A similar conclusion can be drawn from the behaviour of the forward-backward asymmetry in the angular correlations of the decay particles as a function of the excitation energy FBA(E_x). For ⁴⁰Ca, FBA(E_x) for all decay channels increases smoothly on the average once E_x is above a well-defined threshold, which is due to the onset of knock-out processes. For ²⁴Mg, however, the FBA(E_x) for the α₀ shows a large fluctuation as a function of E_x, indicating an interference process between semi-direct decay and knock-out processes.     

Isovector giant resonances in light nuclei observed by (7Li, 7Be) reaction

Isovector giant resonances were studied with the (⁷Li, ⁷Be) reaction on ¹²C, ²⁴Mg, ²⁷Al, ²⁸Si and ⁴⁸Ti at an incident energy of 150 MeV. Differential cross sections were measured at forward scattering angles including 0°. We observed the octupole resonance at E_x ∽ 16 MeV and the giant dipole resonance at E_x ∽ 20 MeV in all residual nuclei.     

On the gamma decay of analogue resonances in the58Fe(p, γ)59Co reaction

The spectrum of the delayed light radiation from a pulsed corona discharge in pure argon was investigated in cylindrical geometry. The band-like structure near 309 nm can be attributed to molecular transitions in the OH-radical of the typeA ² Σ ⁺ ?X ² Π(0?0). The weak bands at 337 nm and 357 nm originate from transitions in the N₂ molecule. The molecular states of OH and N₂ are excited by collisions of³P₂-metastable argon atoms (formed in the gas discharge) with H₂O and N₂ molecules present as small impurities. The pressure dependence of the time constant (some 100 μs) of the afterglow is discussed.     

The RPA nuclear continuum in16O(e,e′) reactions at low momentum transfer decay on (e,e′p) and (e,e′n) reaction channels

A theoretical investigation has been performed of¹⁶O(e, e′) and¹⁶O(e, e′x) reactions at low momentum transfer in the frame of a self-consistent HF and RPA theory with a SK3 interaction. Nuclear responses and their multipole components have been calculated in the whole energy-range for the two electron kinematicsi) ? _i =67 MeV and θ=40°,ii) ? _i =130 MeV and θ=50°. The microscopic structure of HF and RPA resonating states in the energy continuum has been inferred from the calculation. Decay properties in the reaction channels (e, e′p) and (e, e′n) have been discussed in the two cases of a semidirect and a knockout reaction process.     

Electromagnetic decay of the giant quadrupole resonances: (II). Nuclear structure aspects

We analyze experiments on the electromagnetic decay of the GQR from the point of view of the microscopic theory of the nuclear structure. The calculations are made systematically in the lowest contributing order of perturbation theory within the NFT formalism. Care is taken in order to prevent spurious mixing of the isoscalar and isovector parts of dipole operators. As in previous theoretical calculations, the results are consistent with the experimental limit of the ratio between the transition populating the 2.62 MeV 3⁻ state and the g.s. However they fail to reproduce the strong dipole transition to the 4.97 MeV 3⁻ state.     

Isovector giant dipole resonances in proton-rich Ar and Ca isotopes

The isovector giant dipole resonances(IVGDR)in proton-rich Ar and Ca isotopes have been systematic-ally investigated using the resonant continuum Hartree-F ock+BCS(HF+BCS)and quasiparticle random phase ap-proximation(QRPA)methods.The Skyrme SLy5 and density-dependent contact pairing interactions are employed in the calculations.In addition to the giant dipole resonances at energy around 18 MeV,pygmy dipole resonances(PDR)are found to be located in the energy region below 12 MeV.The calculated energy-weighted moments of PDR in nuclei close to the proton drip-line exhaust about 4%of the TRK sum rule.The strengths decrease with in-creasing mass number in each isotopic chain.The transition densities of the PDR states show that motions of pro-tons and neutrons are in phase in the interiors of nuclei,while the protons give the main contribution at the surface.By analyzing the QRPA amplitudes of proton and neutron 2-quasiparticle configurations for a given low-lying state,we find that only a few proton configurations give significant contributions.They contribute about 95%to the total QRPA amplitudes,which indicates that the collectivity of PDR states is not strong in proton-rich nuclei in the present study.     

离子极化势对钙原子共面对称(e,2e)反应影响的数值研究

本文使用扭曲波波恩近似方法(DWBA)研究了共面对称条件下钙原子的电子碰撞电离反应((e,2e)反应),在DWBA理论的基础上,考虑了原子极化势和离子极化势对三重微分散射截面的影响.采用发展的DWBA方法,我们研究了出射电子能量从6.75 e V到29.25 e V范围内电子与钙原子的碰撞电离过程,计算了电离三重微分截面.通过与已有理论和实验数据进行比较发现,离子极化势对钙原子的共面对称(e,2e)反应散射微分截面有较大的影响,很好的描述了碰撞电离微分截面的结构效应,特别是在散射角度较小时(≦60o),本文计算结果与实验测量非常一致.     

离子极化势对钙原子共面对称(e,2e)反应影响的数值研究

本文使用扭曲波波恩近似方法(DWBA)研究了共面对称条件下钙原子的电子碰撞电离反应( (e,2e)反应 ),在DWBA理论的基础上,考虑了原子极化势和离子极化势对三重微分散射截面的影响。采用发展的DWBA方法,我们研究了出射电子能量从6.75eV到29.25eV范围内电子与钙原子的碰撞电离过程,计算了电离三重微分截面。通过与已有理论和实验数据进行比较发现,离子极化势对钙原子的共面对称(e,2e)反应散射微分截面有较大的影响,很好的描述了碰撞电离微分截面的结构效应,特别是在散射角度较小时(≦60o),本文计算结果与实验测量非常一致。