Identification of a new isotope of121La by means of element-selective mass separation

A new isotope of¹²¹La was produced in the reaction³²S +⁹²Mo and mass-separated as¹²¹La¹⁶O⁺, being well separated from¹²¹Cs and¹²¹Ba. From γ-ray measurement, the half-life of this isotope was determined to be 5.3±0.2 s. Its partial decay scheme is proposed.     

Laser fluorescence on radio-active isotopes produced in very low yield

East particle-photon coincidence techniques, developed at Daresbury with strontium isotopes, allow ultrasensitive laser fluorescence spectroscopy of beams of radio-active isotopes which can only be produced in very low yields. The technique has now been applied to neutron-deficient barium isotopes down to¹²⁰Ba. From measured hyperfine splittings and isotope shifts, nuclear moments and changes in mean square radii have been determined. The work has revealed an abrupt increase in the mean square radius for¹²¹Ba large enough to disrupt the systematic staggering of nuclear size seen for the series. In a recent experiment an isomeric state of¹²⁷Ba with a half-life of about 2 seconds has been produced in a very low yield; nevertheless we have succeeded in obtaining a fluorescence spectrum.     

Pressure effects of argon and helium on the first diffuse series doublet of singly ionized barium

The shift and broadening of the first diffuse series doublet of Ba II in emission was observed under various relative densities of Ar (20–107) and He (35–121) at 2500°K. By comparing the present data with those of the shift of the principal series doublet from a previous paper, it is suggested that argon pressure causes a downward displacement for 6p²P and 6d²D levels and an upward one for 5d²D and 7s²S levels, with respect to the ground state of Ba II.     

Investigation of neutron-deficient isotopes in the barium-region

Bombarding targets of 106Cd,¹⁰⁸Cd and¹¹⁰Cd with¹⁶O ions of 52.5–66.0 MeV neutron deficient barium, cesium and xenon isotopes were produced and have been studied using excitation functions and neutron-gamma, proton-gamma, alpha-gamma and gammagamma coincidence measurements. Partial level schemes for¹²³Ba and¹²¹Ba were proposed. A number of gamma transitions was assigned to the different product nuclei. The measured particle emission probabilities from the compound nuclei are compared with different evaporation models. The models mostly underestimate neutron emission and often overestimate the emission of alpha particles.     

Investigation of neutron-deficient isotopes in the barium-region

Bombarding targets of 106Cd,¹⁰⁸Cd and¹¹⁰Cd with¹⁶O ions of 52.5–66.0 MeV neutron deficient barium, cesium and xenon isotopes were produced and have been studied using excitation functions and neutron-gamma, proton-gamma, alpha-gamma and gammagamma coincidence measurements. Partial level schemes for¹²³Ba and¹²¹Ba were proposed. A number of gamma transitions was assigned to the different product nuclei. The measured particle emission probabilities from the compound nuclei are compared with different evaporation models. The models mostly underestimate neutron emission and often overestimate the emission of alpha particles.     

Exotic decay in Ba isotopes via 12C emission

Considering Coulomb and proximity potentials as barriers, we have calculated the half lives for ¹²C emission from various Ba isotopes using different mass tables. The half life for ¹¹²Ba isotope calculated by us is 6.020×10³ s which is comparable with the experimental value 5.620×10³ s. From our study it is found that ¹¹⁴Ba is the good parent for ¹²C emission whose emission rate is favorable for measurement. The half lives predicted by us lie very close to those reported by Shanmugam et al using their cubic plus Yukawa plus exponential model. It is observed that inclusion of proximity potential does not produce significant deviation from the linear nature of the Geiger-Nuttall plots. Also it is found that the neutron excess in the parent nuclei slows down the exotic decay process.     

Observation of multiple superconducting gaps in the infrared reflectivity spectra of Ba(Fe<Subscript>0.9</Subscript>Co<Subscript>0.1</Subscript>)<Subscript>2</Subscript>As<Subscript>2</Subscript>

The results of infrared reflectivity measurements for the iron-based high-temperature superconductor Ba(Fe_0.9Co_0.1)₂As₂ are reported. The reflectivity is found to be close to unity at frequencies ω lower than 2Δ/h (2Δ is the superconducting gap and h is Planck’s constant). This is evidence for the s ^+/− or s ^+/+ symmetry of the superconducting order parameter in the studied compound. The infrared reflectivity spectra of Ba(Fe_0.9Co_0.1)₂As₂ manifest opening of several superconducting gaps at temperatures lower than critical T _c .     

The decay of121g+m In to levels in121Sn

The decay of¹²¹ g+m In to the excited states of¹²¹Sn was investigated.¹²¹In was produced by the¹²²Sn(γ,p)¹²¹In reaction on an enriched SnO₂ target. Strong indications of the isomeric transition of 321 keV to the¹²¹In ground state were found. In the beta decay of^121m In excited states at 60.1, 908.9, 1101.9, 1120.4, 1403.0, 2864.1, 3119.8 and 3228 keV in¹²¹Sn withJ ^π values 1/2⁺, 3/2(5/2)⁺, 3/2⁺, 5/2⁺, 5/2⁺ and 1/2⁺ or 3/2⁺ for the three levels around 3 MeV, are fed. In the decay of the¹²¹In ground state only the 7/2⁺ level in¹²¹Sn at 925.3 keV is fed.     

A one dimensional model für quantum Chaos

Spectral rigidityΔ ₃ (L) is calculated for the energy spectra of¹³¹Te,¹³⁵Ba and¹³⁷Ce, obtained in the IBFM calculation. Results reveal an intermediate situation between regularity and chaos, but remarkably closer to the chaotic limit. Influence of the model parameters on the fluctuation pattern is discussed.     

Octupole vibrational states in the even-mass barium isotopes

A low-lying state of ^{132, 134, 136, 138}Ba, strongly excited in the scattering of 20 MeV α-particles at 175°, is identified as the first 3^? octupole vibrational state in each case. Angular distribution measurements for α-particle scattering to this state and the well-known first 2⁺ state in ^{132, 134, 136, 138}Ba are in agreement with harmonic-vibration coupled-channel predictions. Deformation parameters are obtained, and the deduced isoscalar transition rates are compared with measured electromagnetic transition rates. The first 3^? states of ^{132, 134, 136, 138}Ba are found to be at excitation energies of 2.070, 2.251, 2.529 and 2.879 MeV, respectively. A state in ¹³⁰Ba at an excitation energy of 1.948 MeV is tentatively identified as the first octupole-vibrational state in this nucleus.     

Study of even-mass Ba nuclei by the (p,t) reaction

The (p, t) reaction on the nuclei ^{134, 136, 138}Ba has been studied at a bombarding energy of 52 MeV. Angular distributions of emitted tritons were obtained between 6° and 60°. The following six negative-parity states were strongly excited by the (p, t) reaction: 5^?(2.121 MeV) and 7^?(2.482 MeV) in ¹³²Ba, 5^?(1.998 MeV) and 7^?(2.274 MeV) in ¹³⁴Ba, and 5^?(2.139 MeV) and 7^?(2.031 MeV) in ¹³⁶Ba. DWBA calculations using the code DWUCK successfully reproduce these angular distributions. The 0⁺ assignment to the 1.761 MeV level in ¹³⁴Ba is confirmed. Intensities of the (p, t) reaction for low-lying states are discussed.     

A study of the 138Ba(d,p)139Ba reaction at 19 MeV

The ¹³⁸Ba(d,p) reaction has been studied at an incident deuteron energy of 19 MeV, using the injector-tandem accelerator and the multichannel magnetic spectrograph of the University of Oxford. Deuteron and proton optical model parameters have been obtained from the analysis of elastic scattering experiments on a ¹³⁸Ba target. The parameters have been used to calculate theoretical (d, p) angular distributions on the basis of the DWBA. From the comparison of experimental and theoretical distributions, orbital angular momentum transfers have been deduced and spectroscopic factors determined for all the levels observed up to an excitation energy of 2.5 MeV in ¹³⁹Ba. The spectroscopic information thus obtained is more complete than that from previous studies, and is in satisfactory agreement with expected sum rule limits. A notable item of new information is the assignment of an l_n = 6 transition to the level at 1.54 MeV in ¹³⁹Ba.     

Barium isotope fractionation during experimental formation of the double carbonate BaMn[CO3]2 at ambient temperature

In this study, we present the first experimental results for stable barium (Ba) isotope (¹³⁷Ba/¹³⁴Ba) fractionation during low-temperature formation of the anhydrous double carbonate BaMn[CO₃]₂. This investigation is part of an ongoing work on Ba fractionation in the natural barium cycle. Precipitation at a temperature of 21±1°C leads to an enrichment of the lighter Ba isotope described by an enrichment factor of?0.11±0.06‰ in the double carbonate than in an aqueous barium-manganese(II) chloride/sodium bicarbonate solution, which is within the range of previous reports for synthetic pure BaCO ₃ (witherite) formation.     

Structure of129Ba from the decay of129La

The structure of¹²⁹Ba is investigated through the beta decay of¹²⁹La, whose half-life is measured to be 11.6±0.2 m. The decay properties are studied by means of beta, gamma and conversion electron spectroscopy techniques. Many transitions are observed and a level scheme of¹²⁹Ba with deduced¹²⁹Ba values is proposed. The total decay energy of¹²⁹Ba is measured to be 3.72±0.05 MeV, which is compared with predictions of mass formulae. Low-lying structure of¹²⁹Ba is discussed in terms of collective models.     

Sr和Ba替代对Eu掺杂Ca2.955Si2O7的结构和发光特性的影响研究

利用固相反应法制备了Sr和Ba替代的Ca_2.955-xM_xSi₂O₇: 0.045Eu²⁺ (M= Sr, Ba, x= 0.1-0.5)系列荧光粉, 利用较大离子半径的Sr和Ba元素替代Eu掺杂Ca_2.955-xM_xSi₂O₇ 中的Ca元素,研究Sr和Ba替代对样品结构和发光特性的影响. X射线衍射测试结果表明,少量Sr和Ba替代不会改变基质的晶体结构, 样品仍然为单斜晶系.未替代前, Ca_2.955Si₂O₇: 0.045Eu²⁺ 样品的发射峰在574 nm左右,随着Sr含量的增加,样品的发射峰发生蓝移; 而Ba含量在x= 0.1-0.4时不会引起发射峰位置的移动, 但x= 0.5样品的发射峰发生蓝移.同等含量的Sr和Ba部分替代样品中的Ca元素, Ba替代样品的光谱强度较强.     

Measurement of the lifetime of the first 2+ state in 124Ba

The lifetime of the first 2⁺ state in the nucleus ¹²⁴Ba has been measured by γ-γ coincidence recoil-distance Doppler shift method. The ¹⁰⁹Ag(¹⁹F, 4n)¹²⁴Ba reaction at a beam energy of 75 MeV was employed to populate excited states in ¹²⁴Ba. The mean lifetime was determined to be 275(12) ps using the differential decay curve method. The value of B(E2;0₁ ⁺→ 2₁ ⁺) for ¹²⁴Ba deduced from the lifetime is in reasonable agreement with the prediction of the proton-neutron interacting boson model(IBM-2) without Pauli blocking effect. Received: 23 February 1998     

Barium isotope fractionation during the experimental transformation of aragonite to witherite and of gypsum to barite,and the effect of ion (de)solvation

In this study, we present the experimental results for stable barium (Ba) isotope fractionation (¹³⁷Ba/¹³⁴Ba) during the transformation of aragonite (CaCO₃) and gypsum (CaSO₄·2H₂O) in Ba-bearing aqueous solution to witherite (BaCO₃) and barite (BaSO₄), respectively. The process was studied at three temperatures between 4 and 60?°C. In all cases, the transformation leads to a relative enrichment of the lighter ¹³⁴Ba isotope in the solid compared to the aqueous solution, with ^137/134Ba enrichment factors between –0.11 and ?0.17?‰ for BaCO₃, and –0.21 and –0.26?‰ for BaSO₄. The corresponding mass-dependent ^138/134Ba enrichment factors are ?0.15 to –0.23?‰ for BaCO₃, and –0.28 to –0.35?‰ for BaSO₄. The magnitude of isotope fractionation is within the range of recent reports for witherite and barite formation, as well as trace Ba incorporation into orthorhombic aragonite, and no substantial impact of temperature can be found between 4 and 80?°C. In previous studies, ion (de)solvation has been suggested to impact both the crystallization process of Ba-bearing solids and associated Ba isotope fractionation. Precipitation experiments of BaSO₄ and BaCO₃ using an methanol-containing aqueous solution indicate only a minor effect of ion and crystal surface (de)solvation on the overall Ba isotope fractionation process.     

Non-yrast level structure of121Xe via beta decay of121m+g Cs

The results of measurements of the gamma-ray and conversion-electron singles and coincidence spectra from the decay of the 122 s^121m Cs and the 155 s^121g Cs to levels of¹²¹Xe are reported. TheM 3 multipolarity of the 68.5 keV isomeric transition in¹²¹Cs has been deduced. Numerous low-lying levels below 1.6 MeV excitation energy are found. A negative-parity level at 355.9 keV is observed for the first time. The results supplement the low lying energy level systematics in odd-A xenons. A comparison is made with theN=67 barium isotone.     

BaxOy小团簇修饰Ru(0001)表面的结构稳定性和氮分子吸附性质

为了说明钡助剂的存在形式, 本文采用第一性原理方法研究了Ba_xO_y小团簇修饰Ru(0001)表面的结构稳定性和氮分子吸附性质. 基于总能的热力学分析发现, 在实验条件下(500 K, P_H2O/P_H2<10^-3), Ba₂O团簇比BaO₂, BaO, Ba和O等团簇(原子)更加稳定. 这证实含有金属性钡原子的团簇也是氧化钡助剂可能的工作状态. 表面电荷差分密度说明Ba₂O团簇的氧和钡原子与衬底的作用不同. 不过Ba₂O团簇氧和钡原子附近的氮分子吸附行为相似, Ba₂O团簇增强了氮分子和衬底的相互作用. Ba₂O团簇氧和钡原子附近的氮分子吸附能分别为0.78 和0.88 eV, 均大于清洁表面的0.67 eV. 氮分子间距和氮分子的拉伸振动频率都表明Ba₂O团簇在一定程度上活化了吸附氮分子. Ba₂O团簇氧和钡原子附近的N–N键长分别为0.117和0.116 nm, 大于清洁表面的0.114 nm. 氧和钡原子附近氮分子的拉伸振动频率分别为 1888 和1985 cm^-1, 小于清洁表面的2193 cm^-1. 电荷差分密度的计算结果说明, 削弱作用主要来自于Ba₂O团簇中钡离子和氮分子间的静电作用. 两者间的静电作用增加了氮分子π 反键轨道的占据数, 促进了氮分子极化, 从而削弱氮分子键.