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Abstract.: A new technique has been developed at the TRIUMF’s TITAN facility to perform in-trap decay spectroscopy. The aim of this technique is to eventually measure weak electron capture branching ratios (ECBRs) and by this to consequently determine GT matrix elements of $ \beta$ $ \beta$ decaying nuclei. These branching ratios provide important input to the theoretical description of these decays. The feasibility and power of the technique is demonstrated by measuring the ECBR of 124Cs . [ABSTRACT FROM AUTHOR]

The shell structure of atomic nuclei is associated with 'magic numbers' and originates in the nearly independent motion of neutrons and protons in a mean potential generated by all nucleons. During ?+-decay, a proton transforms into a neutron in a previously not fully occupied orbital, emitting a positron-neutrino pair with either parallel or antiparallel spins, in a Gamow-Teller or Fermi transition, respectively. The transition probability, or strength, of a Gamow-Teller transition depends sensitively on the underlying shell structure and is usually distributed among many states in the neighbouring nucleus. Here we report measurements of the half-life and decay energy for the decay of 100Sn, the heaviest doubly magic nucleus with equal numbers of protons and neutrons. In the ?-decay of 100Sn, a large fraction of the strength is observable because of the large decay energy. We determine the largest Gamow-Teller strength so far measured in allowed nuclear ?-decay, establishing the 'superallowed' nature of this Gamow-Teller transition. The large strength and the low-energy states in the daughter nucleus, 100In, are well reproduced by modern, large-scale shell model calculations. [ABSTRACT FROM AUTHOR]

Knowledge of 2 νββ nuclear matrix elements is essential to probe the theoretical framework of 0 νββ decays. At TITAN, TRIUMF's Ion Trap for Atomic and Nuclear science, a novel technique has been developed to measure electron capture branches of virtual intermediate nuclei in ββ decays. During two experiments with radioactive Cs isotopes the feasibility of this new method was proven. [ABSTRACT FROM AUTHOR]

table-top setup for characterizing gaseous and liquid scintillating material is described. The key part of the instrumentation is a 300 nm thin ceramic membrane made from silicon nitride and silicon oxide. Low energy electrons with 12 keV particle energy are sent through this membrane into the material to be tested. Both fully continuous and pulsed beams can be used. Time resolved optical spectroscopy is used as the diagnostic method. The fluorescence of nitrogen and solutions of liquid scintillation material are described as examples for applying the technique. [ABSTRACT FROM AUTHOR]

We have studied the reaction ( ^7Li, p) on C targets at E = 44 MeV, populating states in the oxygen isotope O . The experiments were performed at the Tandem Laboratory (Maier-Leibniz Laboratorium) using the high-resolution Q3D magnetic spectrometer. States were populated up to an excitation energy of 21MeV, with an overall energy resolution of 45keV. We discuss shell model states and cluster bands related to the rotational bands in the O -isotope, using the weak-coupling approach. Similar to O , the broken intrinsic reflection symmetry in these states must give rise to rotational bands as parity doublets, so two K = 3/2 bands (parities, + and - are proposed with large moments of inertia. These are discussed in terms of an underlying cluster structure, ( ^14C ⊗ n ⊗ $ \alpha$) . An extended molecular binding diagram is proposed which includes the C -cluster. [ABSTRACT FROM AUTHOR]

Excited states in Ba were studied with the Ba ( $$ \vec d $$, tBa reaction at 24.0MeV, with polarized deuteron beam using the Munich magnetic spectrograph Q3D. Unambiguous spin-parity assignments were made for many levels up to an excitation energy of 2.2MeV. A detailed comparison is made between the experimental level scheme and interacting boson-fermion model calculations. [ABSTRACT FROM AUTHOR]

From Pb ( p, p') via isobaric analog resonances in Bi , at E = 6420 keV in the doubly magic nucleus Pb , a new state with spin 2 with half the s p strength and major g f , d f fractions is identified. Ten more 2 states up to E = 7.0 MeV are identified and their structure discussed, among them six states with new spin assignments. The known 6314 1 state is shown to contain almost the entire s p strength. [ABSTRACT FROM AUTHOR]

In the doubly magic nucleus 208Pb , five states are observed at 5648, 5658, 5686, 5694, 5836keV by 208Pb ( p, p′) via isobaric analog resonances in 209Bi . The 5686, 5694, 5836 states with spins 6-, 7-, 8- are shown to contain almost the full strength of the particle-hole configuration g9/2 f7/2 . The 5658 5- state contains a major g9/2 f7/2 fragment with admixtures of d5/2 f5/2 , d5/2 f7/2 . The 5648, 5649keV states observed in a quintuplet at Ex = 5.63 - 5.65 MeV are preliminarily identified to have spins (4)- and 6+ to 9+. The 5648keV (4)- state contains almost half of the g9/2 f7/2 strength and half of the h9/2 d5/2 strength with admixtures of d5/2 f5/2 , d5/2 p3/2 , d5/2 f7/2 . [ABSTRACT FROM AUTHOR]

The temperature dependences of the quenching rate constants of the states N2 ( ${\rm C} \ {^{3}{ \rm \Pi }_{u}}$ v′=0,1) by N2 (X) and of the state N2 ( ${\rm C} \ {^{3}{ \rm \Pi }_{u}} \ v^{\prime}=0$) by O2 (X) are studied. Time-resolved light emission from the gas was analyzed in the temperature range from 300 K to 210 K keeping the gas at constant density. In case of quenching by N2 (X), the quenching rate constant for the vibrational level v′= 0 increases by (13 ±3)% with gas cooling whereas the quenching rate constant for v′= 1 decreases by (5.0 ±2.5)% in this temperature range. For quenching by O2 (X), the quenching rate constant decreases by (3 ±2)% with gas cooling. The temperature variation of the N2 (C 3Πu v′=0) emission intensity for pure nitrogen and dry air are calculated using the obtained quenching rate constants and is compared with the experimental data available in the literature. [ABSTRACT FROM AUTHOR]

Sharp resonant structures in the cross section of the atomic electron-ion collision process of dielectronic recombination are exploited to study isotope shifts and hyperfine interaction of heavy highly-charged ions. This novel approach provides a conceptual alternative to existing methods. In this contribution, we present a series of measurements, which we performed at the heavy ion storage ring ESR of the GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, Germany. In a first experiment the stable isotopes A = 142 and A = 150 of three-electron neodymium ANd57+ were studied. Isotope shifts of dielectronic resonances associated with 2s - 2pj ( j = 1/2, 3/2) transitions were extracted from the measured data. The evaluation of the energy shift was performed within a full QED framework and yielded a change in the mean-square charge radius of 142,150δ⟨r²⟩ = -1.36(1)(3) fm². At GSI, in addition to the investigation of stable isotopes unstable species can be artificially synthesized and studied. Radioisotopes produced in-flight from fragmentation of a 238U primary beam were injected into the ESR and were subsequently separated by their mass-to-charge ratio. This enabled us to perform first DR experiments with the exotic nuclei 237U89+ (Z = 92) and 234Pa88+ (Z = 91). [ABSTRACT FROM AUTHOR]

We have studied the multi-nucleon transfer reaction 12C ( 7Li ,p) at Elab = 44 MeV, populating states in the oxygen isotope 18O . The experiments were performed at the Tandem accelerator of the Maier-Leibniz Laboratory in Munich using the high-resolution Q3D magnetic spectrograph. States were populated up to an excitation energy of 21.2MeV with an overall energy resolution of 45keV, and 30 new states of 18O have been identified. The structure of the rotational bands observed is discussed in terms of cluster bands with the underlying cluster structures: 14C$ $\displaystyle \otimes$ $\displaystyle \alpha$$ and 12C ⊗ 2 n ⊗ $ \alpha$ . Because of the broken intrinsic reflection symmetry in these structures the corresponding rotational bands appear as parity doublets. [ABSTRACT FROM AUTHOR]

The 1.73 μm XeI laser has been operated in a fully continuous mode using a table-top electron beam pumped laser setup. A 12 keV electron beam sent through a 300 nm thick silicon nitride membrane into a laser gas mixture of typically 600 mbar gas pressure was used for pumping. A low loss cavity was installed, resulting in a very low pumping power of 37 mW to reach laser threshold. The geometrical conditions for the laser setup such as the shape of the beam pumped volume and its overlap with the optical mode volume are discussed. The laser scheme has been clearly identified as a recombination laser scheme by operating the laser in pulsed mode and observing the time structure of the laser pulse. [ABSTRACT FROM AUTHOR]

At ISOL (Isotope Separator On-Line) facilities, which utilize thick primary production targets, beams of neutron-rich iron isotopes are difficult to obtain due to the long extraction time of these isotopes out of the target matrix. At REX-ISOLDE, an exploratory experiment was carried out to investigate the possibility of producing a post-accelerated beam of neutron-rich iron isotopes by the in-trap decay of neutron-rich manganese isotopes, which are available at ISOLDE using the Resonance Ionization Laser Ion Source (RILIS). This production mechanism was tested for the first time at REX-ISOLDE with an intense and short-lived beam of 61Mn isotopes. In this work, the proof of principle of this method is demonstrated, although the technical details of the trapping process are currently not well understood and are still under investigation. The first physics results on the Coulomb excitation of 61Mn and 61Fe are presented and compared to shell model calculations. [ABSTRACT FROM AUTHOR]

By comparing the Q -values for the 46Ti ( 3He , t46V and 47Ti ( 3He , t47V reactions to the isobaric analogue states the Q -value for the superallowed Fermi decay of 46V has been determined as QEC( ^46V ) = (7052.11±0.27) keV. The result is compatible with the values from two recent direct mass measurements but is at variance with the previously most precise reaction Q -value. As additional input quantity we have determined the neutron separation energy Sn( ^47Ti ) = (8880.51±0.25) keV. [ABSTRACT FROM AUTHOR]

Excited states in 133Ba were studied with the 132Ba ( $$ \vec d $$, p) 133Ba reaction at 24.0MeV, with a polarized deuteron beam using the Munich magnetic spectrograph Q3D. Many unambiguous spin-parity assignments were made up to an excitation energy of 2.2MeV, which allow a detailed comparison with different theoretical calculations, such as the interacting boson-fermion model and the shell model. [ABSTRACT FROM AUTHOR]

The reaction 54Fe( $$ \vec d $$, p)55Fe was studied at the Munich Q3D spectrograph with a 14MeV polarized deuteron beam. Excitation energies, angular distributions and analyzing powers were measured for 39 states up to 4.5MeV excitation energy. Spin and parity assignments were made and spectroscopic factors deduced by comparison to DWBA calculations. The results were compared to predictions by large-scale shell model calculations in the full pf -shell and it was found that reasonable agreement for energies and spectroscopic factors below 2.5MeV could only be obtained if up to 6 particles were allowed to be excited from the f7/2 orbital into p3/2 , f5/2 , and p1/2 orbitals across the N = 28 gap. For levels above 2.5MeV the experimental strength distribution was found to be significantly more fragmented than predicted by the shell model calculations. [ABSTRACT FROM AUTHOR]

The lifetime of the 17/2+ yrast state in 195Po has been measured using the recoil distance Doppler-shift technique to be $ \tau$ = 43(11) ps. The lifetime was extracted from the singles $ \gamma$ -ray spectra obtained by using the recoil-decay tagging method. The present work provides more information of the coupling schemes, shapes and configuration mixing in neutron-deficient odd-mass Po nuclei. [ABSTRACT FROM AUTHOR]

Electron beams with particle energy of ~10 keV were sent through 300 nm thick ceramic (Si3N4 + SiO2) foils and the resulting electron energy distribution functions were recorded using a retarding grid technique. The results are compared with Monte Carlo simulations performed with two publicly available packages, Geant4 and Casino v2.42. It is demonstrated that Geant4, unlike Casino, provides electron energy distribution functions very similar to the experimental distributions. Both simulation packages provide a quite precise average energy of transmitted electrons: we demonstrate that the maximum uncertainty of the calculated values of the average energy is 6% for Geant4 and 8% for Casino, taking into account all systematic uncertainties and the discrepancies in the experimental and simulated data. [ABSTRACT FROM AUTHOR]

Excited states in 130Ba have been studied with the 25MeV 132Ba(p, t)130Ba reaction with 8keV energy resolution, at the Munich Q3D spectrograph. 27 excited states were observed up to 2.6MeV excitation energy, for 21 of them spin and parity being confirmed or assigned. These results complement earlier measurements concerning the systematics of 0+ states in 132Ba and 134Ba , and allow a more detailed comparison with predictions of different nuclear-structure models. The comparison with interacting boson model calculations brings additional evidence in favor of a description of this nucleus by parameters close to the O(6) symmetry. [ABSTRACT FROM AUTHOR]

Continuous and pulsed 12 keV electron beams were used to excite nitrogen within a gas cell at pressures ranging from 10 to 1400 hPa. The pressure dependence of the ratio of photon fluxes for emission from vibrational levels v'=0 and 1 of the C 3Π u state has been studied. The results confirm the presence of a collisional excitation mechanism populating v'=0, 1 in addition to electron impact excitation. Rate constants of (1.27 ±0.04)×10-11 cm3s-1 [ v'=0] and (2.68 ±0.08)×10-11 cm3s-1 [ v'=1] were measured for C 3Π u quenching by ground state nitrogen. For electron beam conditions relative excitation efficiencies of 1:0.59:0.22 for vibrational levels 0, 1 and 2 were calculated. The recorded flux ratios are compared with the predictions given by a vibrational relaxation model. [ABSTRACT FROM AUTHOR]

Excited states in the deformed nucleus 168Er have been studied with high energy resolution in the ( p, t) reaction, with the Munich Q3D spectrograph. A large number of excited 0+ states (25) and 2+ states (64) have been assigned up to 4.0-MeV excitation energy. This allows detailed investigations along two directions of current interest: first, an extension of microscopic model interpretations into the region of medium level density above the pairing gap; second, a first analysis of the statistical fluctuation (order/chaos) properties of pure sequences of levels, in one deformed nucleus. Predictions of two models (the quasiparticle-phonon model and the projected shell model) are compared to the data, and it is concluded that, in both cases, mixing of more configurations is required in the wave functions. [ABSTRACT FROM AUTHOR]

The evolution of the structure of the gamma-vibrational band head 2+ γ in well-deformed rare-earth nuclei is studied within the framework of RPA calculations using a quasiboson approximation based on the Nilsson model. The obtained evolution of the quasiparticle structure of the gamma-vibrational band head is shown to correlate well with the evolution of the same nuclei within the IBA symmetry triangle when described in the extended consistent- Q formalism. An empirical relation is presented that links the IBA parameter χ with the quasiparticle structure of the gamma-vibrational band head. [ABSTRACT FROM AUTHOR]

A detailed account on the distribution of radioactive nuclei in the vacuum system of the planned Munich Accelerator for Fission Fragments (MAFF) located at the FRM-II research reactor is presented. Tools used for the simulation of spacial and temporal distribution of radionuclides are explained. The latter allows for a detailed activity budget as well as estimates for the mass-separated ion yields at MAFF. Additionally, a concept to reduce the activity release from the MAFF slit system due to surface sputtering is presented. It is shown, that the use of low-density carbon foam, as a surface coating, reduces sputtering by orders of magnitude. [ABSTRACT FROM AUTHOR]

Current work explores the impact of γ-softness on partner bands built on the πh11/2νh11/2 particle-hole configurations in triaxial odd-odd nuclei. The results of calculations conducted using a core-particle-hole coupling are presented. The model Hamiltonian includes the collective core, the single-particle valence nucleons, and separable quadrupole-quadrupole interactions. The Kerman-Klein method was applied to find eigenstates, which provided a convenient way for exploring core effects. Calculations were made for triaxial cores with various γ-softness using the General Collective Model keeping the expectation value for the triaxiality parameter fixed at (γ)=30°. The degeneracy in the πh11/2νh11/2 bands results from the calculations for the γ-rigid core but is lifted for the γ-unstable core. [ABSTRACT FROM AUTHOR]

Experimental transition probabilities between states of the ground-state alternating-parity bands of 144Ba and their theoretical analysis are presented. Lifetimes of states in 144Ba have been measured using the recoil distance method following spontaneous fission of 252Cf. The experiment was performed at the Lawrence Berkeley National Laboratory employing the Gammasphere array and the New Yale Plunger Device. The experimental data show a significantly larger value of the E2 transition probability between the negative-parity states compared to the positive-parity ones. It is shown that this effect can be explained by a higher weight of the deformed component in the wave functions of the odd- I states. In the framework of the cluster approach it is explained by a higher weight of the alpha-cluster component in the wave function of the negative-parity states compared to the positive-parity ones. In the framework of the traditional collective model with the quadrupole and octupole degrees of freedom the same effect is explained by a higher value of the quadrupole deformation at the minima of the potential energy as a function of β20 and β30 compared to its value at the top of the barrier separating two physically equivalent minima, having opposite signs of the octupole deformation. Additionally, the dependence on parity of the E2 transition probability is analyzed qualitatively in nuclei with a minimum at β30 = 0 in the collective potential energy and compared to experimental data for 148Nd. [ABSTRACT FROM AUTHOR]

A table-top set-up for studying gas kinetic processes in dense gases via time resolved optical spectroscopy is presented. The set-up uses low energy electron beams for gas excitation. A thin silicon nitride membrane separating the electron source and the gas cell allows to use electron energies as low as 10–15 keV. The electron source is operated in a fast pulsing mode with a pulse width of 5 ns and repetition rates up to 30 kHz. Light emission from the target gas sample is studied and time resolved photon counting is used to measure decay times and collisional rate constants for specific excited states. The experimental concept is applied to measure the rate constants for quenching of molecular nitrogen in the C 3Πu state (vibrational levels 0 and 1) by water vapour. Quenching rate constants of (7.1 ±0.7) × 10-10 s-1 cm3 and (6.7 ±0.7) × 10-10 s-1 cm3 were obtained for the C 3Πu (v = 0) and C 3Πu (v = 1) vibrational levels, respectively. [ABSTRACT FROM AUTHOR]

Reliable and precise lifetimes of excited states in 154Gd and 156Dy were measured using the recoil distance Doppler shift (RDDS) technique. Excited states of 154Gd were populated via Coulomb excitation with a 32S beam at 110 MeV delivered by the FN tandem accelerator at the University of Cologne. For 156Dy a coincidence plunger experiment was performed at the Laboratori Nazionali di Legnaro with the GASP spectrometer and the Cologne coincidence plunger apparatus using the reaction 124Sn(36S,4n)156Dy at a beam energy of 155 MeV. Shape changes previously suggested to appear in the ground-state band (gsb) of 156Dy and in the s-band above the first band crossing were not supported by the transition probabilities determined in this work. The measured transition probabilities of 156Dy and 154Gd as well as the corresponding energy spectra are compared with the predictions of the recently proposed X(5) model and in the case of 156Dy also with an IBA fit. [ABSTRACT FROM AUTHOR]

Lifetime measurements for the 2+1 levels of162Er and162Yb were obtained in β+/ɛ decay at the Yale Moving Tape Collector by fast electronic scintillation timing of β+γ coincidences. [ABSTRACT FROM AUTHOR]

Lifetimes for low-lying members of the irregular Δ I = 1 band in 196Pb have been measured by means of the EUROBALL spectrometer using the coincidence recoil distance technique. The 164Dy(36S,4n)196Pb reaction at a beam energy of 168 MeV was used. The data were analyzed with the differential decay-curve method (DDCM). A characteristic drop in the reduced transition probabilities with increasing angular momentum was observed in agreement with predictions by the semiclassical model for the shears mechanism. [ABSTRACT FROM AUTHOR]

High-spin states in 112Pd were studied using prompt γ-ray spectroscopy with Gammasphere following heavy-ion-induced fission in the reaction 18O + 208Pb at 91 MeV. A new 8+ level at 2638 keV was discovered with transitions connecting it to the yrast band and the quasi-gamma band. The three, now established, closely spaced 8+ states indicate a mixing between the ground-state band, s-band, and quasi-gamma band. Several high-spin structures with likely negative parity have been extended to higher spin and it is proposed that they are based on the ν h11/2( g7/2 d5/2) and ν h11/2( s1/2 d3/2) configurations. [ABSTRACT FROM AUTHOR]

Lifetimes of states in the two strongest superdeformed (SD) bands in 193Tl were measured using the Doppler-shift attenuation method. The reaction 176Yb(23Na,6n)193Tl at a beam energy of 129 MeV was used and γ-rays were detected by the Gammasphere array. Quadrupole moments of 18.3(10) eb and 17.4(10) eb were extracted for SD bands 1 and 2, respectively, using the fractional Doppler-shifts of the SD transitions. The previously reported linking transitions of these SD bands to normal deformed near yrast levels could not be confirmed. No other candidates for linking transitions could be established. [ABSTRACT FROM AUTHOR]

The mean lifetimes of the lower spin states of the superdeformed band inNd have been measured with the coincidence recoil distance method. The reaction used to populate the band wasPd (S, 2p2n)Nd at a beam energy of 152 MeV, and the gamma-rays were detected with the POLYTESSA array. The differential decay curve method was used to analyse the data and transition quadrupole moments, Q, were extracted from the measured lifetimes. The results obtained from the three lowest transitions in the superdeformed band are: Q=6.3±0.9 eb (21+/2→17+/2), Q=6.7±1.1 eb (25+/2→21+/2) and Q>5.0 eb (29+/2→25+/2). These results are consistent with previous results for the high spin members of the band, and are compared to theoretical calculations of total routhian surfaces. The calculation of reduced transition probabilities for the transitions that feed out of the band, allows the effect of hindrance due to K-forbiddenness to be investigated. [ABSTRACT FROM AUTHOR]

Lifetimes in 188Pb were measured using the Köln plunger in combination with the RITU separator and JUROGAM. Four lifetimes were measured, from which the deformation of the prolate band was experimentally determined for the first time. The squared prolate mixing amplitude of the 21+ state was deduced from the measured B( E2) values. [ABSTRACT FROM AUTHOR]

A strong rise of E0 transition strengths between the first excited 0+ state and the ground state is predicted in shape transitional regions within the Interacting Boson Model (IBM). This rise matches well existing data and is not connected to a large mixing amplitude between both states. Moreover, a coherence of amplitudes in the wave functions causes the strong transition, without a requirement of explicit mixing of normal and intruder configurations. [ABSTRACT FROM AUTHOR]

The properties of the M1 bands in the Pb region are reviewed. They can be explained by 'magnetic rotation' which is a new concept in nuclear excitations. Spin and excitation energy along the bands are increased by the shears effect, a step-by-step alignment of large proton-particle and large neutron-hole spins into the direction of the total angular momentum. First evidence is presented for band termination connected with the closing of the shears. [ABSTRACT FROM AUTHOR]