Evidence for nontermination of rotational bands in 74Kr

Three rotational bands in 74Kr were studied up to (in one case one transition short of) the maximum spin I(max) of their respective single-particle configurations. Their lifetimes have been determined using the Doppler-shift attenuation method. The deduced transition quadrupole moments reveal a modest decrease, but far from a complete loss of collectivity at the maximum spin I(max). This feature, together with the results of mean field calculations, indicates that the observed bands do not terminate at I = I(max).     

Measurement of the sign of the spectroscopic quadrupole moment for the 2(1)+ state in 70Se: no evidence for oblate shape

Using a method whereby molecular and atomic ions are independently selected, an isobarically pure beam of 70Se ions was postaccelerated to an energy of 206 MeV using REX-ISOLDE. Coulomb-excitation yields for states in the beam and target nuclei were deduced by recording deexcitation gamma rays in the highly segmented MINIBALL gamma-ray spectrometer in coincidence with scattered particles in a silicon detector. At these energies, the Coulomb-excitation yield for the first 2+ state is expected to be strongly sensitive to the sign of the spectroscopic quadrupole moment through the nuclear reorientation effect. Experimental evidence is presented here for a prolate shape for the first 2+ state in 70Se, reopening the question over whether there are, as reported earlier, deformed oblate shapes near to the ground state in the light selenium isotopes.     

An improved,regioselective synthesis of the radiolabelling precursor for the translocator protein targeting positron emission tomography imaging radiotracer [F]GE-180

[¹⁸F]GE-180 has been demonstrated to be a promising new positron emission tomography radiotracer for targeting translocator protein. PET imaging of TSPO will enable measurement of neuroinflammation and microglia activity in vivo. The synthetic route used in the initial discovery of GE-180, whilst enabling the rapid evaluation of the structure–activity relationships (SAR) in this molecular class, was not high yielding and not suitable for scale-up. Here we present an optimised route towards GE-180 and the radiolabelling precursor of [¹⁸F]GE-180 with significantly improved yields due to a strategy which improves the regioselectivity of the key indole formation step of the synthesis.     

Ultrashort pulse compression and delivery in a hollow-core photonic crystal fiber at 540 nm wavelength

We have fabricated a bandgap-guiding hollow-core photonic crystal fiber (PCF) capable of transmitting and compressing ultrashort pulses in the green spectral region around 532 nm. When propagating subpicosecond pulses through 1 m of this fiber, we have observed soliton-effect temporal compression by up to a factor of 3 to around 100 fs. This reduces the wavelength at which soliton effects have been observed in hollow-core PCF by over 200 nm. We have used the pulses delivered at the output of the fiber to machine micrometer-scale features in copper.     

Quadrupole moment measurement of the highly deformed πg 9/2⊗νh 11/2 band in 130Pr

The quadrupole moment for the πg _9/2⊗νh _11/2 band in the ^130>Pr nucleus has been measured using the Doppler-shift attenuation method. A centroid shift analysis was carried out and a value of Q₀=6.1±0.4 eb, corresponding to an axial prolate deformation of β₂=0.35(3), has been determined. This is the first direct experimental confirmation of the deformation-driving character of the πg _9/2 orbital in an odd-odd nucleus in the A≃135 superdeformed region. Received: 23 April 1998     

High spin level structure of 63 143 Eu80

The level scheme of ¹⁴³ Eu has been extended to I=75/2 in an experiment with the NORDBALL Compton-suppressed Ge detector array and the ¹¹⁰ Pd(³⁷ Cl, 4n) reaction. Most of the scheme shows irregular structure of multiparticle excitations. A strongly populated straight cascade of more than 10 stretched E2 transitions suggests the onset of collectivity.     

Index reduction formulas for twisted flag varieties, I.

A general formula is proved for the change in the Schur index of a central simple algebra on passing from the ground field F to the function field F(X) of a twisted flag variety X, i.e., a projective variety such that there is an adjoint semisimple algebraic group G acting on X over F such that the action becomes transitive over the separable closure of F. The general formula encompasses special cases previously proved where X is a Brauer-Severi variety, or a generic partial splitting variety of a central simple algebra, or the transfer of such a variety, a quadric, or the involution variety of an algebra with orthogonal involution. For the classical simple groups G of inner type, all the corresponding varieties X are described, and the specific index reduction formula is given for each such X.The second author would like to express his thanks to J.-L. Colliot-Thélène for stimulating discussions on this subject.Supported in part by the NSF.     

Discriminants in characteristic two

The Kronecker-Weierstrass theory of pencils is extended to give a necessary and sufficient condition that two 2×m×n tensors are equivalent. The connection between equivalence class representatives and the triple transitivity of PGL(2,F) is discussed. One consequence of the discussion is that the number of inequivalent 2×3×n tensors is finite. An efficient algorithm is given for testing the condition which ultimately depends on a fast pattern matching algorithm.