Anomalously hindered E2 strength B(E2;2+(1)-->0+) in 16C

The electric quadrupole transition from the first 2(+) state to the ground 0(+) state in 16C is studied through measurement of the lifetime by a recoil shadow method applied to inelastically scattered radioactive 16C nuclei. The measured mean lifetime is 77+/-14(stat)+/-19(syst) ps. The central value of mean lifetime corresponds to a B(E2;2+(1)-->0(+)) value of 0.63e(2) fm(4), or 0.26 Weisskopf units. The transition strength is found to be anomalously small compared to the empirically predicted value.     

Observation/confirmation of hindered E2 strength in 18C/16C

We have measured the lifetime of the first excited 2⁺ state in ¹⁸C using an upgraded recoil shadow method to determine the electric quadrupole transition. The measured mean lifetime is 18.9±0.9 (stat)±4.4 (syst) ps, corresponding to B(E2;2₁ ⁺ $ \rightarrow$ 0⁺ _gs) = 4.3±0.2±1.0e ² fm^4, or about 1.5 Weisskopf units. The mean lifetime of the first 2⁺ state in ¹⁶C was remeasured to be 18.3±1.4±4.8 ps, about four times shorter than the value reported previously. The discrepancy is explained by incorporating the $ \gamma$ -ray angular distribution obtained in this work into the previous measurement. The observed transition strengths in ^{16, 18}C are hindered compared to the empirical values, indicating that the anomalous E2 strength observed in ¹⁶C persists in ¹⁸C .     

Lifetime measurement of the first excited 2+ state in 16C

The lifetime of the 2_+(1) state in 16C has been measured with the recoil distance method using the 9Be(9Be,2p) fusion-evaporation reaction at a beam energy of 40 MeV. The mean lifetime was measured to be 11.7(20) ps corresponding to a B(E2;2_+(1)-->0+) value of 4.15(73)e_2 fm_4 [1.73(30) W.u.], consistent with other even-even closed shell nuclei. Our result does not support an interpretation for "decoupled" valence neutrons.     

高位K2(1Λg) 与基态原子的碰撞转移

在K原子密度约为0.5～5×1016cm-3的样品池中,脉冲激光710 nm线双光子激发K2基态到高位1Λg态,研究了K2(1Λg)+ K(4S)碰撞转移过程.K原子密度由测量KD2线蓝翼对白光的吸收得到.测量不同K密度下1Λg态发射的时间分辨荧光强度,它是一条指数衰减曲线,由此得到1Λg态的有效寿命,从描绘出的有效寿命倒数与K原子密度关系直线的斜率得到1Λg态总的碰撞猝灭截面为(2.1±0.2)×10-14cm2,从截距得到的辐射寿命为(22±2)ns.测量了K的6S →4P3/2和4D→4P3/2在不同K密度下的时间积分荧光强度,得到了K2(1Λg)+K→K2(11∑ +g)+K(6S,4D)碰撞转移截面为(1.5±0.3)×10-15cm2(对转移到6S)和(8.5±3.0)×10-15cm2(对转移到4D).     

Li(2P)+H_2→LiH+H反应截面的测量

在样品池条件下,用脉冲激光670.8 nm线激发Li原子基态至2P态,测量了的反应碰撞能量转移截面。池温保持在888 K,Li原子密度为10~(13)cm~(-3)量级,而H_2气压控制在60～300 Pa之间,测量时间分辨荧光光谱,它由两部分组成,在脉冲激光激发的瞬间(不超过10 ns),荧光迅速增强至最大值;激发结束后,荧光强度按指数衰减,由衰减曲线得到2P态原子在不同H_2气压下的有效寿命。根据Stern-Volmer方程,有效寿命与H_2气压成线性关系,由该直线的斜率给出了总的猝灭截面(25.1±4.0)×10~(-16)cm~2,而从直线的截距得到辐射寿命为(270±54)ns。总的猝灭截面是反应与非反应碰撞截面之和,由在不同H_2气压下记录的瞬态(10 ns)荧光快速增强信号得到反应截面为(0.2±0.1)×10~(-16)cm~2,虽只占总猝灭截面的1/125,但它在Li(2P)+H_2的碰撞传能中所起的作用是不能略去的。     

Lifetime measurement of the 2(1)+ state in 20C

Establishing how and when large N/Z values require modified or new theoretical tools is a major quest in nuclear physics. Here we report the first measurement of the lifetime of the 2(1)+ state in the near-dripline nucleus 20C. The deduced value of τ(2(1)+)=9.8±2.8(stat)(-1.1)(+0.5)(syst) ps gives a reduced transition probability of B(E2; 2(1)+→0(g.s.)+)=7.5(-1.7)(+3.0)(stat)(-0.4)(+1.0)(syst) e2 fm4 in good agreement with a shell model calculation using isospin-dependent effective charges.     

高位K_2分子与基态K原子及H_2分子间的激发转移

激光双光子激发K2至1Λg高位态,利用分子荧光光谱方法,研究了1Λg-3Λg间的碰撞转移截面。在纯K实验中,池温控制在553至603 K之间,K原子密度由光学吸收法测量得到。探测1Λg-11Σu+的直接时间分辨荧光的光强,它是一条纯指数衰减曲线,由此得到1Λg+态的有效寿命,有效寿命的倒数与K密度成线性关系,从直线的斜率得到1Λg态的猝灭截面为(2.5±0.3)×10-14cm2,从截距得到辐射寿命为(20±2)ns。由3Λg→13Σu+转移荧光的时间分辨谱,用类似的方法得到3Λg的猝灭截面为(2.5±0.6)×10-14cm2,辐射寿命为(16.0±3.2)ns。由1Λg→11Σu+与3Λg→13Σu+的时间积分强度比得到K2(1Λg)+K→K2(3Λg)+K的转移截面为(1.1±0.3)×10-14cm2。在K2-H2碰撞实验中,池温保持在553 K,K密度为5×1015cm-3,H2气压在40~400 Pa之间,其中K2-K碰撞效应是不能略去的,但可以用纯K结果扣除,得到K2(1Λg)+H2→K2(3Λg)+H2的碰撞转移截面为(2.7±1.1)×10-15cm2。K2(3Λg)+H2→K2(3Λg)以外态+H2的猝灭截面为(6.8±2.7)×10-15cm2。     

碰撞诱导振动能量转移：Cs2[B1∏u(v′=5)]+ N2→Cs2[B1∏u(v′=4，6)]+ N2

利用激光诱导荧光方法研究了Cs_2B~1Π_u[(v′=5)]与N2的碰撞能量转移.脉冲激光激发Cs_2基态至B~1Π_u[(v′=5)]态,池温保持在410 K,N_2气压在1.5×10~2 Pa～2.5×10~3 Pa之间变化.荧光中含有直接荧光和碰撞转移荧光成分,记录直接荧光B~1Πu(v′=5)→Χ~1∑~+_g(v″=0)的时间分辨强度.从荧光强度的对数值给出的直线斜率得到B~1Π_u(v′=5)→Χ~1∑~+_g(v″=0)的有效寿命,由Stern-Volmer方程,得到B~1Π_u(v′=5)→Χ~1∑~+_g(v″=0)的辐射寿命为(45±9)ns.B~1Π_u(v′=5)态与N_2碰撞的猝灭总截面为(9.8±1.5)×10~(-15)cm~2.用类似的方法得到B~1Π_u(v′=4,6)能级的辐射寿命.在不同的N_2气压下,测量B~1Π_u(v′=5,4,6)→Χ~1∑~+_g(v″=0)的时间积分荧光强度,首次得到v′=5→v′=4及v′=5→v′=6的碰撞转移截面分别为(3.9±0.8)×10~(-15) cm~2和(4.1±0.8)×10~(-15)cm~2.     

Tm掺杂的激光晶体生长、结构和光谱性能研究

采用顶部籽晶生长法从K2Mo3O10-B2O3助熔剂中生长出15 mm×15 mm×25 mm优质TmxGd1-x Al3(BO3)4(x=1,0.06)晶体.利用X射线单晶衍射仪测定了TmAl3(BO3)4晶体的结构.对Tm3+GAB晶体进行定向切割,测量得到了σ和π方向的偏振的吸收和发射光谱,并根据Judd-Ofelt理论计算了Tm3+在GdAl3(BO3)4中的J-O参数、各个能级的振子强度、自发辐射几率、荧光分支比等参数.     

78Kr高自旋态的形状共存

用熔合蒸发反应 58Ni(2 3Na,3p) (Ein=70 Me V)和 58Ni(2 8Si,α4p) (Ein=1 30 Me V)研究了78Kr的高自旋态 ,用美国劳伦斯伯克利国家实验室的γ球测量了实验中产生的瞬时符合事件,对新发现的一个负宇称带用多普勒位移衰减法对 1 0 0 4 ke V(1 0 -→ 8-)和 873ke V(8-→ 6-)作了多普勒展宽谱线形状测量 .得到了负宇称带 1 0 -态能级的寿命τ=(2 .2± 0 .3) ps,8-态能级的寿命τ=(1 .6± 0 .2 ) ps.故可知此负宇称带呈现长椭形变 ,与正宇称带的扁椭形变形状共存. Doppler shift attenuation lifetime measurements were performed in the 58 Ni( 23 Na,3p) reaction at 70 MeV and 58 Ni( 28 Si, α4p) reaction at 130 MeV. By analyzing the Doppler broadened line shapes of the 1 004 keV(10 -→8 -) negative parity transition in coincidence with depopulating transitions, the lifetime of the 10 - state has been deduced as τ =(2.2±0.3) ps. A similar analysis of 873 keV(8 -→6 -)transition gave values of τ =(1.6±0.2)...     

Study of Proton Resonances in ~(22)Mg by Resonant Elastic Scattering of ~(21)Na+p and Its Astrophysical Implication in ~(18)Ne(α,p)~(21)Na Reaction Rate

Proton resonant states in ~(22)Mg have been investigated by the resonant elastic scattering of ~(21)Na+p.The ~(21)Na beam with a mean energy of 4.00 MeV/u was separated by the CNS radioactive ion beam separator(CRIB) and bombarded a thick(CH_2)_n target.The energy spectra of recoiled protons were measured at scattering angles of θ_(cm)～172° and 146°,respectively.A new state at 7.06 MeV has been observed clearly and another new one at 7.28 MeV is tentatively identified due to its low statistics.The proton resonant parameters were deduced from an R-matrix analysis of the differential cross section data.The astrophysical resonant reaction rate for the ~(18)Ne(α,p) ~(21)Na reaction has been estimated,and it is about five times larger than that assumed before.     

掺铥钨酸钡单晶生长和光谱研究

采用Czochralski 法生长出光学质量的BaWO₄:Tm³⁺单晶,利用X粉末衍射实验确定了不同掺杂浓度晶体的晶胞参数.测定了晶体的室温吸收光谱,应用Juud-Ofelt理论,拟合了光谱的3个强度参数,其值分别为Ω₂=404×10^-20cm²,Ω₄=0509×10^-20cm²,Ω关键词： 4：Tm³⁺单晶')" href="#">BaWO₄：Tm³⁺单晶 吸收谱 光谱参数 上转换发光     

Probing configuration mixing in 12Be with Gamow-Teller transition strengths

We present a novel technique for studying the quenching of shell gaps in exotic isotopes. The method is based on extracting Gamow-Teller (ΔL=0, ΔS=1) transition strengths [B(GT)] to low-lying states from charge-exchange reactions at intermediate beam energies. These Gamow-Teller strengths are very sensitive to configuration mixing between cross-shell orbitals, and this technique thus provides an important complement to other tools currently used to study cross-shell mixing. This work focuses on the N=8 shell gap. We populated the ground and 2.24 MeV 0+ states in 12Be using the 12B(1+) (7Li, 7Be) reaction at 80 MeV/u in inverse kinematics. Using the ground-state B(GT) value from β-decay measurements (0.184±0.007) as a calibration, the B(GT) for the transition to the second 0+ state was determined to be 0.214±0.051. Comparing the extracted Gamow-Teller strengths with shell-model calculations, it was determined that the wave functions of the first and second 0+ states in 12Be are composed of 25±5% and 60±5% (0s)4(0p)8 configurations, respectively.     

Coexistence of Prolate and Oblate Shapes in ~(98)Sr Nuclei Using IBM2

The properties of the low-lying states and the shape coexistence in Sr are investigated within the framework of the proton-neutron interacting boson model(IBM2).By considering the relative energy of the d proton boson to be different from that of the neutron boson,it is found that the calculated energy levels and the B(E2)transition strengths agree with the experimental data perfectly.Particularly,the second 0~+ state,which is associated with the shape coexistence phenomenon and has the lowest energy E(0_2~+) among all known even-even nuclei,is reproduced very well.The behavior of the calculated quadrupole shape invariants is consistent with the experimental results.     

In situ observation of dynamics of plasma self-channeling and bulk modification in silica glasses induced by a high-intensity femtosecond laser

The time-resolved dynamics of plasma self-channeling and refractive index bulk modification in silica glasses were first observed in situ using a high-intensity femtosecond (110 fs) Ti:sapphire laser (λ_p=790 nm). Plasma channeling is induced in silica glass at an irradiation higher than an input intensity of 1.5×10¹² W/cm² and photoinduces either the refractive-index modification or optical crack modification. In the domain of refractive-index modification, the lifetime of induced plasma self-channeling was 20 ps and the structural transition time for forming the refractive-index change was 10 ps. In the domain of optical cracks, however, the lifetime of induced plasma formation was 30 ps and the structural transition time for forming the optical cracks was 40 ps. According to electron spin resonance spectroscopic (ESP) measurement, it was found that the defect concentration of the SiE^′ center increased significantly in the refractive index modification region. A maximum value of the refractive-index change Δn was measured to be 1.6×10^-2. The intensity profile of the output beam transmitted through the refractive-index modification showed that the bulk modification produced a permanent optical waveguide. Received: 8 April 2002 / Accepted: 12 April 2002 / Published online: 22 November 2002 RID="*" ID="*"Corresponding author. Fax: +81-48/462-4682, E-mail: shcho@riken.go.jp     

Lifetime of the 2755 keV 15/2− state in43Ca

Using the recoil distance Doppler shift method, we measured the lifetime of the 2755 keV 15/2^? state in⁴³Ca populated in the reaction²⁸Si(¹⁸0,2p n) to beΤ=39 ±5 ps. We also remeasured the lifetime of the 2751 keV 4⁺ state in⁴²Ca excited in the reaction²⁸Si(¹⁶O,2p) to beΤ=3.8±0.4ps. Effective charges derived fromE2 transition between (f _7/2)^v high-spin states are discussed.     

Microstructural evolution of ZnS during sintering monitored by optical and positron annihilation techniques

Positron lifetime and optical absorption techniques were employed to track the microstructural evolution of polycrystalline ZnS grown by Chemical Vapor Deposition (CVD). As grown material and material treated with Hot Isostatic Pressure (HIP) was sintered at temperatures ranging from 400 to 1000°C for 2–18 h. A 290 ps defect lifetime could be resolved in all samples, while an additional longer lifetime (=430 ps) was found only in samples annealed at low temperatures. This component gradually disappeared during annealing at 800°C. Associated with the disappearance of the long-lived component, the apparent bulk lifetime of the material changed from 235 to 215 ps. A 215±2 ps bulk parameter was also found for HIP-treated material annealed at temperatures greater than 400°C and hence is taken to represent the delocalized state of the positrons in ZnS. Optical absorption measurements showed that annealing at 800°C also caused the absorption profiles of the CVD and HIP samples to converge. The rate of the bulk lifetime transition correlates with the absorption changes. The observed sharpening of the absorption profile is attributed to a decrease in scattering from grain boundaries and voids, and a decrease in absorption from point defects. The 430 ps lifetime is believed to be due to trapping at voids and grain boundaries, while the 290 ps lifetime likely is due to a monovacancy stabilized as a small complex.Paper presented at the 132nd WE-Heraeus-Seminr on Positron Studies of Semiconductor Defects, Halle, Germany, 29 August to 2 September 1994     

双原子分子离子XY+部分电子态完全振动能谱的精确研究

关于双原子分子离子XY 的完全振动能谱,目前还没有实验和理论的数据报道。本文首次应用代数方法AM(Algebraic Method),获得了BeH -X1Σ 态,CO -X2Σ 态,F2 -X2Πg态,O2 -A2Πu态和Li2 -X2Σg 态的精确振动光谱常数和完全振动能谱,解决了实验方法和精确量子力学理论方法难以获得双原子分子离子XY 的包含最高振动能级在内的所有高阶振动能级的精确数值这一问题。所有研究结果表明:由部分较低的实验精确振动能级,可用AM产生双原子分子离子XY 的精确振动光谱常数和包含全部激发态的完全振动能谱;所得的AM振动能谱比其他理论方法得到的结果更好。     

Observation of two-proton radioactivity of 19Mg by tracking the decay products

We have observed the two-proton radioactivity of the previously unknown (19)Mg ground state by tracking the decay products in-flight. For the first time, the trajectories of the 2p-decay products, (17)Ne+p+p, have been measured by using tracking microstrip detectors which allowed us to reconstruct the 2p-decay vertices and fragment correlations. The half-life of (19)Mg deduced from the measured vertex distribution is 4.0(15) ps in the system of (19)Mg. The Q value of the 2p decay of the (19)Mg ground state inferred from the measured p-p-(17)Ne correlations is 0.75(5) MeV.     

The l-forbidden 1i112 → 2g92 M1 transition in 209Pb

The mean lifetime of the 0.78 MeV first excited state in ²⁰⁹Pb was measured by the recoil distance method to be τ_m = 11.1±1.3 ps. The B(M1) for the l-forbidden transition is in good agreement with one of several recent theoretical predictions.