Erzeugung 21 neuer kurzlebiger Isomere durch Kernphotoreaktionen

Irradiation of 28 selected elements with 22.5 MeV bremsstrahlung led to the production of numerous short-lived isomeric states by photonuclear reactions. At least 21 of the observed isomeric transitions seem not to have been reported in the literature thus far. The energies and half-lives of the observed transitions were measured using a conventional scintillation spectrometer. The half-lives of the newly discovered isomeric states are in the region between 5·10^?6 and 6·10^?2 seconds. Isotopic assignments and multipolarities of the observed transitions have not yet been established.     

Isomeric E1 transitions with ΔK = 0 INLu

An experimental arrangement for ns lifetime measurements in nuclear reactions is briefly described. The half-life of the level at 208.1 keV in ¹⁷¹Lu has been determined in the reaction ¹⁶⁹Tm(, 2n) ¹⁷¹Lu as . Delayed and populating γ-ray spectra have been measured, applying the method of delayed γ-γ coincidences. In the radioactive decay of ¹⁷³Hf, the lifetime of the level at 425.1 keV in ¹⁷³Lu has been measured as . Comparisons with Weisskopf and Nilsson estimates have been performed taking into account pairing correlations. A modified Nilsson Hamiltonian has been used. The dependence of El transition probabilities between the states and on the difference of the initial- and final-state deformations is studied. Qualitative agreement with semi-microscopic calculations of equilibrium deformations is found. Lifetimes of the states are estimated.     

New isomeric states in Fr and At

Alpha spectroscopic data from the decay chain ²¹⁸Fr → ²¹⁴At → ²¹⁰Bi have been obtained. Previously unobserved isomeric states were found in both ²¹⁸Fr and ²¹⁴At. The half-life of the ground state of ²¹⁸Fr was measured to be 1.3^+0.5 _−0.4 ms. The half-life of the new isomeric state in ²¹⁸Fr was determined to be 22.0±0.5 ms and its decay was found to be very complex with no fewer than 20 -groups varying in energy between 6837 keV and 7952 keV. Two long-lived states in ²¹⁴At with half-lives of 558±10 ns and 760±15 ns, respectively, were found to be strongly populated in the decay of ^218mFr. These two states are proposed to be a 1⁻ ground state and a 9⁻ isomeric state arising from the coupling between the unpaired h_9/2 proton and g_9/2 neutron.     

Rotational bands in Ho

The excited states of the deformed odd-proton nucleus ¹⁶¹Ho have been studied in the reactions ¹⁵⁹Tb(, 2n), ¹⁶¹Dy(d, 2n) and ¹⁶¹Dy(p, n). Gamma-ray spectra in single and coincidence modes as well as angular distributions and excitation functions of the transitions were measured. The proposed level scheme of ¹⁶¹Ho contains besides of the ground state band ⁻[523] the bands ⁺[404], ⁺[411], ⁺[411] and ⁻ [541] (band heads at 252.7, 298.7, 211.2 and 423.9 keV, respectively). An attempt was made to estimate the influence of Coriolis coupling between the bands ⁺ [411] and ⁺ [411], which are very close in energy. The ⁺ [404] band was found to de-excite by very fast E1 transitions to the ground state band ⁻[523]. Nilsson retardation factors of about 0.03 for these transitions were deduced using the E2/E1 branching ratios. An investigation has also been made of the independent feeding of the levels from high-lying states.     

Isomerism in Ag and non-yrast levels in Pd and Rh, studied in β decay

The β decay of ⁹⁶Ag (Z=47,N=49) was investigated by measuring positrons, X rays as well as β-delayed protons and γ rays. The γ radiation was studied by means of germanium detectors and a NaI total-absorption spectrometer. Two β-decaying isomers in ⁹⁶Ag were established with half-lives of 4.40(6) and 6.9(6) s and tentative spin–parity assignments of (8⁺) and (2⁺), respectively. For both isomers, the intensities of β transitions to low-lying levels of ⁹⁶Pd (Z=46,N=50) and β-delayed proton decays to levels in ⁹⁵Rh (Z=45,N=50) were measured. Several new ⁹⁶Pd levels were firmly established. The level energies, their γ decays and the Gamow–Teller decay of ⁹⁶Ag are compared to shell-model predictions. A new low-lying level in ⁹⁵Rh was found at 680 keV excitation energy. Through a comparison with low-lying states of N=50 isotones, this level is interpreted as the first excited 7/2⁺ state built on the proton 9/2⁺ ground state. The assignments of further excited states in ⁹⁵Rh are discussed.     

Importance of the photo-beta process for the synthesis of “p” elements in stellar conditions

In this work, we compare positon capture and photo-beta disintegration probabilities in several stellar conditions.

We show that the second process can be neglected with regard to the first one in strongly endothermic nuclear transitions, whereas photo-beta disintegration can be competitive with positon capture and even can have a greater likelihood than the latter process in weakly endothermic and exothermic transitions.

In the range of temperature we consider here (T ≈ 10⁹ °K), it appears that the lifetime ratio τ(ph)/τ(e_c⁺) against photo-beta disintegration and positon capture is the smallest for densities in the neighbourhood of 10⁶ g/cm³.

Thus, we arrive at the conclusion that the photo-beta process can play a role in the synthesis of two “p” elements at least, ₆₂¹⁴⁴Sm and ₈₀¹⁹⁶Hg, for which the ratios τ(ph)/τ(e_c⁺) are close to 10 and 20, respectively, in the most favourable stellar conditions.     

Predictions for all processes ee → fermions + γ

The complete matrix elements for e⁺e⁻ → 4 and e⁺e⁻ → 4fγy are calculated in the Electroweak Standard Model for polarized massless fermions. The matrix elements for all final states are reduced to a few compact generic functions. Monte Carlo generators for e⁺e⁻ → 4f and e⁺e⁻ → 4fγ are constructed. We compare different treatments of the finite widths of the electroweak gauge bosons; in particular, we include a scheme with a complex gauge-boson mass that obeys all Ward identities. The detailed discussion of numerical results comprises integrated cross sections as well as photon-energy distributions for all different final states.     

The (p, t) and (p, τ) reactions on O at 39.8 MeV

Differential cross sections have been measured at forward angles for (p, t) and (p, τ) transitions from ¹⁷O to the ⁻ ground states and lowest-energy ⁻ states in the ¹⁵O and ¹⁵N mirror nuclei. The data are compared with DWBA calculations using simple single-particle and single-hole wave functions. When the (p, t) and (p, τ) transitions are considered separately, the calculated and experimental ratios of the ⁻ integrated cross sections to the ⁻ integrated cross sections agree to within 30 %; however, the ratios of (p, τ) cross sections to the mirror state (p, t) cross sections are calculated to be about twice as large as actually measured. This experimentally observed reduction of the (p, τ) cross section relative to the (p, t) cross section can possibly be attributed to interference between the S = 0 and S = 1 components of the (p, τ) transitions.     

Identification of Hg and shape coexistence in odd-A Hg isotopes

In-beam γ-ray transitions in ¹⁸¹Hg, the lightest odd-A Hg isotope known thus far, have been identified from fragment mass-γ and γ-γ coincidence measurements. Five prolate deformed rotational bands were placed in the level scheme. A decoupled band built on the strongly prolate deformed 1/2⁻[521] ground state was observed up to 29/2⁻. A 5/2⁻[512] configuration is suggested for a pair of strongly coupled bands displaying no signature splitting. The other two bands are also signature partner bands. They are populated with the largest intensity and exhibit splitting. They have been associated with the mixed neutron i_13/2 orbitals and are proposed to decay to an i_13/2 isomeric state associated with an oblate state.     

Electroproduction of π from C leading to low-lying residual states in B

Energy distributions of π⁺ produced from ¹²C by electrons of total energy 195 MeV were measured at various angles. The results show large contributions from transitions leaving the residual nucleus in the ground (1⁺), first (2⁺) excited state and states at around 4.5 MeV. The angular distributions of ¹²C(γ, π⁺)¹²B leading to these residual states are deduced from the energy distributions by the unfolding method with the virtual photon theory. Theoretical results with the Helm model and the shell model are compared with the experimental results. Their relative shapes are in good agreement. A better agreement in the absolute value is found for the theoretical results which include the final-state interaction estimated with a pion optical potential. The surface production model shows better agreement with the experimental (γ, π⁺) cross sections than the volume production model.     

Scattering and resonance properties of the interaction of slow neutrons with the isotopes of silicon and sulfur

In¹¹⁷Te,¹¹⁹Te and¹²¹Te isomeric states withJ ^π=5/2⁺, 5/2⁺ and 7/2⁺ and half-lives of 19.1(9)ns, 2.2(2) ns and 86(6) ns, respectively, have been identified at low excitation energies using (α, 2n) reactions on enriched^115–119Sn targets. Positive parityΔJ=1 bands built on these isomeric states have been observed up to 17/2⁺. The states are interpreted as members of rotational bands built on deformation driving 5/2⁺ [402] and 7/2⁺ [404] Nilsson orbitals which overcome theN=64 subshell gap. The irregular level spacings and electromagnetic properties of the bands are well explained in Coriolis calculations. The moment of inertia parameter as function of collective angular momentum has been derived from the doubly even Te cores. The hindrance of the band head deexcitation may be caused by shape fluctuations of these transitional nuclei.     

Renormalization group invariant matrix elements of ΔS=2 and ΔI=3/2 four-fermion operators without quark masses

We introduce a new parameterization of four-fermion operator matrix elements which does not involve quark masses and thus allows a reduction of systematic uncertainties. In order to simplify the matching between lattice and continuum renormalization schemes, we express our results in terms of renormalization group invariant B-parameters which are renormalization-scheme and scale independent. As an application of our proposal, matrix elements of ΔI=3/2 and SUSY ΔS=2 operators have been computed. The calculations have been performed using the tree-level improved Clover lattice action at two different values of the strong coupling constant (β=6/g²=6.0 and 6.2), in the quenched approximation. Renormalization constants and mixing coefficients of lattice operators have been obtained non-perturbatively. Using lowest order χPT, we also obtain ππ|O₇|K^NDR_I=2=(0.11±0.02) GeV⁴ and ππ|O₈|K^NDR_I=2=(0.51±0.05) GeV⁴ at μ=2 GeV.     

A study of the Ti(He, t) and Ni(He, t) reactions to isobaric analogue states

The (³He, t) reaction populating 0⁺ and 2⁺ states in ^{58, 60}Cu and ^{46, 48}V which are isobaric analogue states (IAS) of the 0⁺ ground states and 2⁺ first excited states in ^{58, 60}Ni and ^{46, 48}Ti have been studied at an incident ³He energy of 24.6 MeV. Triton spectra were measured for the targets ^46,48Ti, ^natNi and ⁵⁸Ni and angular distributions for the 0⁺ and 2⁺ IAS of ^{46, 48}Ti and ^{58, 60}Ni determined. The data were obtained using a magnetic spectrometer and position-sensitive detectors. The results have been analysed using DWBA theory. The 0⁺ → 0⁺ transitions to analogue states are described quite well using a microscopic form factor derived from a nucleon-nucleon interaction. However, with a Gaussian form, the m.s. radius of this interaction is only limited to the region 0–9 fm². Comparisons with data at other incident energies indicate that the strength of the effective interaction is strongly energy dependent. The Coulomb energies and (³He, t) angular distributions of the states assigned as the 2⁺ analogues in ⁴⁸V and ^58,60Cu are not described well by the models investigated. The ⁴⁶V 2⁺ IAS angular distribution is reproduced by a microscopic calculation, however. The ratios of the 0⁺ → 2⁺ IAS to the 0⁺ → 0⁺ IAS transitions are used to deduce a quadrupole deformation for the valence neutrons. The difference in the quadrupole deformations of the matter and proton distributions, as determined by other means, is found to be correlated with those of the valence neutrons. Several transitions to non-analogue states are also investigated.     

Frequency measurement of RuO4 transitions in the υ3 vibrational band

The frequencies of the most intense RuO₄ transitions in coincidence with the emission lines of CO₂ and N₂O lasers have been measured with respect to the CO₂ lines with an uncertainty of less than 3× 10^-9. Difference and absolute frequency values are here reported.     

Calculations of the dynamic dipole polarizabilities for the Li~+ ion

The B-spline configuration-interaction method is applied to the investigations of dynamic dipole polarizabilities for the four lowest triplet states(2~3S,3~3S,2~3P,and 3~3P) of the Li~+ ion.The accurate energies for the triplet states of n~3S,n~3P,and n~3D,the dipole oscillator strengths for 2~3S(3~3S)→n~3P,2~3P(3~3P)→n~3S,and 2~3P(3~3P)→n~3D transitions,with the main quantum number n up to 10 are tabulated for references.The dynamic dipole polarizabilities for the four triplet states under a wide range of photon energy are also listed,which provide input data for analyzing the Stark shift of the Li~+ ion.Furthermore,the tune-out wavelengths in the range from 100 nm to 1.2 μm for the four triplet states,and the magic wavelengths in the range from 100 nm to 600 nm for the 2~3S→3~3S,2~3S→2~3P,and 2~3S→3~3P transitions are determined accurately for the experimental design of the Li~+ ion.     

Half-life measurements and gamma spectroscopy in the decay184Re m →184W

The half-lives of the intrinsic states at 1,285.8 and 1,502.2 keV in¹⁸⁴W have been measured in the decay of¹⁸⁴Re ^m to be 8.33±0.18Μs and 2.35±0.10 ns, respectively. These half-lives determine absolute gamma-ray transition probabilities of eight transitions and yield upper limits for three transitions. The decay scheme of¹⁸⁴Re ^m →¹⁸⁴W is improved through measurements of delayed gamma-ray spectra with a Ge(Li) detector. Spin and Nilsson model interpretations are discussed.     

icMRCI+Q理论研究CF离子12个-S态和23个?态的光谱性质

采用考虑Davidson修正的内收缩多参考组态相互作用(icMRCI+Q)方法结合相关一致基组aug-ccpV5Z和aug-cc-pV6Z计算了CF~+离子第一离解极限C~+(~2p_u)+F(~2P_u)对应的12个∧-S态(X~l∑~+,a~3∏,1~3∑~+,1~3Δ,1~1∑~-,1~1∑~-,1~3∑~-,2~1∑~+,1~1∏,2~3∏,2~1∏和2~3∑~+)所产生的23个Ω态的势能曲线.计算中考虑了旋轨耦合效应、核价相关和标量相对论修正以及将参考能和相关能分别外推至完全基组极限.基于得到的势能曲线,获得了束缚和准束缚的9个∧-S态和16个Ω态的光谱常数,并且X~1∑~+,a~3∏~(势阱一)∧-S态的光谱常数与已有的实验结果非常符合.此外,计算了CF自由基X~2∏态到CF~+离子束缚和准束缚的9个∧-S态的垂直电离势和绝热电离势,并且CF~+(X~1∑~+)←CF(X~2∏)和CF~+(a~3∏(势阱一))←CF(X~2∏)的垂直电离势和绝热电离势与相应的实验结果也非常符合.由a~3∏,1~1∏态和其他激发∧-S态势能曲线的交叉现象,借助于计算的旋轨耦合矩阵元,分析了a~3∏~(势阱一),1~1∏~(势阱一)和2~1∑~+态的预解离机理.计算的23个Ω态离解极限处的相对能量与实验结果十分吻合.最后计算了(2)0+~(势阱一)(v'=0-5),(1)1~(势阱一)(v'=0-5)和(2)1~(势阱一)(v'=0)到X0~+态跃迁的Franck-Condon因子和辐射寿命.     

Experimental observation of the Σ hypernuclei, ΣH and ΣC

The hypernuclei _Σ⁶H and _Σ¹⁶C were observed by the (K⁻, π⁺) reaction on targets of ⁶Li and liquid O, respectively, at 713 MeV/c incident K⁻ momentum. Structure is seen in _Σ⁶H which may be interpreted in terms of particle-hole excitations similar to the previously observed states in _Λ⁶Li. The inablitity to resolve individual Σ hypernuclear levels in _Σ¹⁶C, due in part to the excitation of non-coherent states as a result of the large momentum transfer of about 130 MeV/c, precludes the extraction of the Σ-nucleus spin-orbit potential strength. The Σ-nucleus well depth appears to be 7 to 10 MeV less than that for the Λ.     

Magnetic dipole moments near Sn: Measurement on isomeric 11/2 states in odd-A Te and Te by NMR/ON

On-line low temperature nuclear orientation (OLNO) experiments have been performed on the odd-A Te isotopes ¹³¹Te and ¹³³Te using the technique of nuclear magnetic resonance on oriented nuclei (NMR/ON). The magnetic moments of the isomeric 11/2⁻ states have been measured extending the known data on these states in the Te isotopes up to the neutron shell closure at N = 82. The contribution to the 11/2⁻ magnetic moment in ¹³³Te due to core polarisation is calculated using an RPA shell model as well as corrections to the magnetic dipole operator caused by mesonic exchange currents. The neutron number dependence of the magnetic moments of the 11/2⁻ isomers in heavy Te isotopes is discussed in terms of particle-core coupling model (PCM) calculations.     

GeO分子激发态的电子结构和跃迁性质的组态相互作用方法研究

应用多参考组态相互作用方法计算了GeO分子的第一解离极限(Ge(³P_g)+O(³P_g))对应的18个Λ-S电子态的电子结构. 计算中纳入了Ge原子的3d轨道电子的内壳层-价壳层电子关联效应、标量相对论效应和Davidson修正. 基于计算的电子态的电子结构, 通过求解径向Schrödinger方程获得了束缚电子态的光谱常数R_e, T_e, ω_e, ω_eχ_e, B_e, 理论计算给出的这些电子态的光谱常数与之前的实验结果符合得很好. 计算了电子态的电偶极矩随核间距的变化, 分析了电子态的组态成分的变化对电偶极矩的影响. 计算的势能曲线表明, 激发态A¹Π, 1¹Σ^-, D¹Δ, a³Π, a’³Σ⁺, d³Δ 和 e³Σ^-的绝热激发能密集地分布于26000-37000 cm^-1范围内, 这些密集分布的电子态之间的相互作用对振动波函数有明显扰动作用. 借助于激发态之间的自旋-轨道耦合矩阵元, 阐明了邻近的激发态对A¹Π和a³Π的扰动作用. 基于计算的A¹Π-X¹Σ⁺和A’¹Σ⁺-X¹Σ⁺跃迁的电偶极跃迁矩和Franck-Condon 因子, 给出了A¹Π 和A’¹Σ⁺态的最低的六个振动能级的辐射寿命.