Formation of 24Mg* in the spallation of 28Si nuclei by 1-GeV protons

The ²⁸Si(p, p′γ₀ X)²⁴Mg reaction has been studied at the ITEP accelerator by the hadron-gamma coincidence method for a proton energy of 1 GeV. Two reaction products are detected: a 1368.6-keV γ-ray photon accompanying the transition of the ²⁴Mg* nucleus from the first excited state to the ground state and a proton p′ whose momentum is measured in a magnetic spectrometer. The measured distribution in the energy lost by the proton in interaction is attributed to five processes: the direct knockout of a nuclear α cluster, the knockout of four nucleons with a total charge number of 2, the formation of the _ΔSi isobaric nucleus, the formation of the Δ isobar in the interaction of the incident proton with a nuclear nucleon, and the production of a π meson, which is at rest in the nuclear reference frame. The last process likely corresponds to the reaction of the formation of a deeply bound pion state in the ²⁸P nucleus. Such states were previously observed only on heavy nuclei. The cross sections for the listed processes have been estimated.     

Deformation effects in the 28Si+12C and 28Si+28Si reactions

The possible occurrence of highly deformed configurations is investigated in the ⁴⁰Ca and ⁵⁶Ni di-nuclear systems as formed in the ²⁸Si + ¹²C, ²⁸Si reactions by using the properties of emitted light charged particles. Inclusive as well as exclusive data of the heavy fragments and their associated light charged particles have been collected by using the ICARE charged particle multidetector array. The data are analysed by Monte Carlo CASCADE statistical-model calculations using a consistent set of parameters with spin-dependent level densities. Significant deformation effects at high spin are observed as well as an unexpected large ⁸Be cluster emission of a binary nature.     

The (3He,t) reaction on 24Mg and 28Si

The (³He, t) charge exchange reaction on ²⁴Mg and ²⁸Si has been studied at 38.5 MeV. The angular distributions provide a number of new spin assignments in ²⁴Al and ²⁸P. A two-step excitation through intermediate α-particle channels was used to predict the ²⁴Al cross sections. The fits are fair in shape, but about a factor of three too large when a perfect overlap of initial and final shapes is assumed. The data to three 1⁺ states of ²⁸P are compared to the known electromagnetic reduced transition rate B(M1) to the analog states in ²⁸Si.     

Alpha decay of isobaric analogue states in24Mg and28Si

Theα-decay of isobaric analogue states (which are forbidden by isospin selection rules) excited in²⁴Mg and²⁸Si through preton capture by²³Na atE _p=677 and 739 keV and by²⁷Al atE _p=295, 327 and 405 keV, respectively, have been studied using solid state track detectors. The ratio ofα-decay widths of the two resonance states in²⁴Mg to the state at 1.632 MeV (2⁺) in²⁰Ne yields the value 0.065 for the mixing parameterε and the value 4.01 keV for the Coulomb matrix element responsible for the isospin mixing in²⁴Mg. In²⁸Si the measurement of theα-decay widths of the three resonance states resulted in the determination of the proton, gamma and alpha partial widths which comprise the total width of the resonance states. Limits have been set for the value of the two mixing parameters involved in this case. Upper limits of 16 and 39 keV have been obtained for the Coulomb matrix elements responsible for the isospin mixing in²⁸Si.     

Coupled-channel description of the photodisintegration of 24Mg, 28Si, and 32S nuclei within the intermediate-coupling scheme

The coupled-channel method is used to calculate photonuclear reactions on ²⁴Mg, ²⁸Si, and ³²S nuclei within the intermediate-coupling scheme. The origin of relatively narrow peaks corresponding to photoabsorption on these nuclei is studied. Partial channels of giant-dipole-resonance decay are considered. It is shown that the splitting of the giant dipole resonance in the ²⁴Mg nucleus into two broad maxima is due to the deformation of its surface.     

Resonant structures in24Mg+28Si elastic and inelastic scattering

The data on the excitation functions of²⁴Mg+²⁸Si elastic and inelastic (2⁺ ?0⁺, 2⁺ ?2⁺, 4⁺ ?0⁺ and 4⁺ ?2⁺) scattering fromE _c.m.=48.97 to 57.21 MeV have been subjected to a statistical analysis consisting of the calculations of deviation function, cross-correlation function, summed excitation function, cross-channel correlation coefficients, coherence widths, and the distribution of cross sections. Based on the outcome of the analysis resonant structures atE _c.m.=49.23, 50.02, 50.51, 52.10, 52.53, 53.27 and 54.14 MeV have been confirmed and three new structures of the same nature have been identified atE _c.m.=51.42, 54.88 and 55.60 MeV.     

Comparison of Enhancement Effect of DNA-Mediated Energy Transfer by Divalent Cations:Mg~(2+),Ca~(2+),Mn~(2+),Co~(2+),and Ni~(2+)

The effect of various metal ions on the DNA mediated energy transfer between simultaneously bound drugs was investigated using spectroscopic methods. It was found that addition of divalent metal ions (Mg2+, Ca2+, Mn2+, Co2+ and Ni2+) resulted in further decrease of the ethidium fluorescence intensity, while a small increase was observed in the TMPyP emission band, implying that the energy of excited ethidium was transferred to TMPyP. This DNA-mediated quenching efficiency between ethidium and TMPyP was significantly enhanced by the presence of all metal ions. Among the divalent metal ions, alkali earth metal ions and Mn2+ displayed higher quenching efficiencies than other transition metal ions. The distances required to permit the energy transfer between the two drugs in DNA were calculated as 68, 66, 62, 48 and 38  in the presence of 100 μmol·L-1 of Mg2+, Ca2+, Mn2+, Co2+ and Ni2+ ion, respectively. The disturbed binding conformation of TMPyP in DNA by metal ions presumably accounts for the difference.     

Tensor polarization of 12C[2+ 1] in the 16O(13C,12C)17O reaction at 50 MeV

The ¹⁶O(¹³C,¹²C)¹⁷O reaction at 50 MeV has been investigated using the kinematical coincidence method. Polarization tensors t ₂₀ and t ₄₀ of ¹²C[2⁺ ₁] for the quantization axis taken along the direction of propagation have been measured by analyzing the energy spectrum of ¹²C[2⁺ ₁], modulated by the effect of γ ray emission. The deduced t ₄₀ values significantly deviate from zero, contrary to the prediction of the distorted-wave Born approximation theory based on one-step p shell neutron stripping without spin-dependent interactions. The phenomenological spin–orbit interaction necessary to reproduce the magnitude of measured t ₄₀ is found to be much larger than the folding model prediction. It is shown that the experimental polarization tensors as well as the cross sections can be reproduced by introducing multi-step processes involving excitations in ¹²C and ¹³C without introducing spin-dependent interactions. Received: 2 August 1999 / Revised version: 3 February 2000     

Optical potential for 12C + 28Si scattering

¹²C + ²⁸Si elastic scattering angular distributions are smooth functions, relatively easily fit by optical potential predictions, at laboratory bombarding energies, E_1ab, within ≈ 10 MeV of the Coulomb barrier (i.e. up to E_1ab ≈ 27 MeV). Between E_1ab = 27 and 36 MeV the angular distributions show pronounced oscillatory structure which is not easily fit with an optical potential. No optical potential has been found to give a very good account of all the angular distributions simultaneously; the best simultaneous fit to all the data was achieved with a surface-transparent potential whose real and imaginary well depths are energy dependent.     

Enhanced green fluorescence and afterglow in (Zn,Mg)_2GeO_4: Mn~(2+), Cd~(2+)

<正>Long-lasting phosphorescent(LLP)materials have attracted considerable attention since green and blue emitting persistent Eu~(2+) doped alkaline earth phosphors were reported in the mid-1990s[1-3].Over the past few decades,a considerable effort has been made to design novel LLP materials for a wide range of applications such as emergency lighting,interior decoration,road signs,and in vivo bioimaging[4-6].For these applications,long persistence times are often desirable.Two types of active center involved are:emitters and     

Y3Al5O12:Ce3+,Cr3+和Y3Al5O12:Ce3+,pr3+,Cr3+荧光粉体系中的能量传递

通过在YAG:Ce3+和YAG:Ce3+,pr3+荧光粉体系中分别掺入Cr3+离子来提高蓝光管芯白光LED的显色指数.Cr3+离子的加入,增加了红光发射,这归因于Cr3+的2E-4 A2跃迁的零声子线和声子边带发光.Ce3+→Cr3+的能量传递是增强红光发射的重要方式,在YAG:Ce3+,Cr3+体系中,由发射光谱得到...     

Ca8Mg(SiO4)4Cl2:Eu2+,Nd3+的近红外发光

用高温固相法制备了Ca<,8>Mg(SiO<,4>)<,4>Cl<,2>:Eu<'2+>,Nd<'3+>近红外发光材料,通过X射线衍射仪,近红外,可见发射光谱和激发光谱,荧光寿命等对样品进行了测试.研究了Eu<'2+>、Nd<'3+>的掺杂浓度对近红外发光性能的影响及相对强度变化的规律,结果表明,Ca<,8>Mg(Si...     

Fluctuations in12C+24Mg elastic and inelastic scattering

The data on the ϑ_c.m.=180° excitation functions of¹²C+²⁴Mg,¹²C* (4.43 MeV)+²⁴Mg and¹²C+²⁴Mg*(1.36 MeV) from 12.27 to 22.80 MeV, 16.53 to 27.47 MeV, and 11.33 to 26.40 MeV(c.m.) respectively have been subjected to statistical analysis. The effect of averaging interval, employed for data reduction, on the coherence widths as obtained from the autocorrelation function has been studied. The fluctuating features of the cross-sections turn out to be consistent with the statistical model expectations.     

First study of the (14C, 12C) reaction: Selectivity of the reaction and the energy levels of 28Mg and 30Si

The first measurements are reported for (¹⁴C, ¹²C) two-neutron stripping reactions. Energy spectra up to an excitation energy of 12 MeV have been measured at 69 MeV for the ²⁶Mg(¹⁴C, ¹²C) and ²⁸Si(¹⁴C, ¹²C) reactions. A strong selectivity of this reaction is observed. Using this selectivity, the comparison of the spectra suggests J^π assignments for several ³⁰Si and ²⁸Mg states. The results from the other two-neutron stripping reactions, (t, p) and (¹⁸O, ¹⁶O) are compared with those of the (¹⁴C, ¹²C) reaction.     

28Si+12C中的两体反应与全熔合反应

利用ΔE-E望远镜系统测量了156.3MeV ²⁸Si+¹²C反应(近对称系统)中出射的Z=4—14的产物元素的能谱和角分布,并由此给出了这些产物的胁变截面图.从理论上计算了Z=4—11产物的实验室系最可几动能分布E₁(θ)和各元素的质心系的总动能分布Et(Z),指出了这些产物主要来自系统的两体反应过程.还给出了该反应系统的全熔合截面值为(980±68)mb,并指出从低能数据外推到此能量下的全熔合截面值与实验值之差主要归因于两体过程.     

90° excitation functions for elastic scattering of 28Si+16O and 28Si+12C

The gross structures in the excitation functions for elastic scattering of ²⁸Si+¹⁶O and ²⁸Si+ ¹²C, measured at 90°, where only even partial waves contribute, are found to be anti-correlated with those at 180°. Excitation functions at both angles, including the enhanced gross structure at 180°, can be reproduced by calculations using a potential which attracts odd partial waves more than even partial waves.     

Optical properties of Mg~(2+),Yb~(3+),and Ho~(3+) tri-doped LiNbO_3 crystals

A series of LiNbO_3 crystals tri-doped with Mg~(2+),Yb~(3+),and Ho~(3+) are grown by the conventional Czochraski technique.The concentrations of Mg~(2+),Yb~(3+),and Ho~(3+) ions in Mg:Yb:Ho:LiNbO_3 crystals are measured by using an inductively coupled plasma atomic emission spectrometry.The x-ray diffraction is proposed to determine the lattice constant and analyze the internal structure of the crystal.The light-induced scattering of Mg:Yb:Ho:LiNbO_3 crystal is quantitatively described via the threshold effect of incident exposure energy flux.The exposure energy(E_r) is calculated to discuss the optical damage resistance ability.The exposure energy of Mg(7 mol):Yb:Ho:LiNbO3 crystal is 709.17 J/cm~2,approximately 425 times higher than that of the Mg(l mol):Yb:Ho:LiNbO_3 crystal in magnitude.The blue,red,and very intense green bands of Mg:Yb:Ho:LiNbO_3 crystal are observed under the 980-nm laser excitation to evaluate the up-conversion emission properties.The dependence of the emission intensity on pumping power indicates that the up-conversion emission is a two-photon process.The up-conversion emission mechanism is discussed in detail.This study indicates that Mg:Yb:Ho:LiNbO_3 crystal can be applied to the fabrication of new multifunctional photoluminescence devices.     

NMR of 29Si and 25Mg In Mg2SiO4 with dynamic polarization technique

Nuclear magnetic resonance of ²⁹Si and ²⁵Mg in natural abundance has been observed in Cr³⁺ doped Mg₂SiO₄ after cooling the nuclear spin system by dynamic nuclear polarization. The quadrupole coupling tensors of ²⁵Mg at the 4a and 4c positions have been determined.