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10 pags.; 11 figs.; 2 tabs.; PACS number(s): 23.40.Hc, 29.30.Kv, 27.50.+e, 21.10.Pc; Open Access funded by Creative Commons Atribution Licence 3.0

Laser spectroscopy measurements have been performed on neutron-deficient and stable Ir isotopes using the COMPLIS experimental setup installed at ISOLDE-CERN. The radioactive Ir atoms were obtained from successive decays of a mass-separated Hg beam deposited onto a carbon substrate after deceleration to 1kV and subsequently laser desorbed. A three-color, two-step resonant scheme was used to selectively ionize the desorbed Ir atoms. The hyperfine structure (HFS) and isotope shift (IS) of the first transition of the ionization path $5d^{7}6s ^{2}^{4}F_{9/2} \to 5d^{7}6s6p ^{6}F_{11/2}$ at 351.5nm were measured for $^{182-189}$Ir, $^{186}Ir^{m}$ and the stable $^{191,193}$Ir. The nuclear magnetic moments μI and the spectroscopic quadrupole moments Qs were obtained from the HFS spectra and the change of the mean square charge radii from the IS measurements. The sign of μI was experimentally determined for the first time for the masses 182≤A≤189 and the isomeric state $^{186}Ir^ m$ . The spectroscopic quadrupole moments of $^{182}$Ir and $^{183}$Ir were measured also for the first time. A large mean square charge radius change between $^{187}$Ir and $^{186}Ir^g$ and between $^{186}Ir^m$ and $^{186}Ir ^g$ was observed corresponding to a sudden increase in deformation: from β2 ≃ + 0.16 for the heavier group A = 193, 191, 189, 187 and 186m to β2 ≥ + 0.2 for the lighter group A = 186g, 185, 184, 183 and 182. These results were analyzed in the framework of a microscopic treatment of an axial rotor plus one or two quasiparticle(s). This sudden deformation change is associated with a change in the proton state that describes the odd-nuclei ground state or that participates in the coupling with the neutron in the odd-odd nuclei. This state is identified with the π3/2+[402] orbital for the heavier group and with the π1/2-[541] orbital stemming from the 1h _9/2 spherical subshell for the lighter group. That last state seems to affect strongly the observed values of the nuclear moments.

Laser spectroscopy based on resonant ionization of laser-desorbed atoms has been used to study the neutron-rich tellurium isotopes with the COMPLIS facility at ISOLDE-CERN. Isotope shifts and hyperfine structures of several neutron-rich Te isotopes: $^{120−136}$Te and $^{123 m−133 m}$Te have been measured. From the hyperfine structure we have extracted magnetic and quadrupole moments. Changes in the mean square charge radii have been deduced and their comparison with the known data for the other elements near Z = 50 is presented. The experimental $\delta$ values are compared with those obtained from relativistic mean field calculations.

16 pages, 2 tables, 4 figures.-- PACS nrs.: 23.40.-s; 23.20.-g; 27.20.+n.-- Printed version published May 17, 2004., The γ-ray spectrum following β-decay of Li-11 has been remeasured at the ISOLDE facility at CERN. Two new transitions were observed through the use of large Ge-detectors. Most γ-decays will follow β-delayed neutron emission. Information on the energy of the neutron is derived from analysis of the γ line-shape and used to construct a partial decay scheme for Li-11. Lifetime values for the 1(-) and 2(-) levels in Be-10 are also derived. A new partial decay scheme is presented., This work has been partially supported by the Swedish Research Council VR.

4 pages, 3 figures.-- PACS nr.: 23.40.-s.-- Printed version published Apr 2004.-- et al., Beta-decay experiments are a primary source of information for nuclear-structure studies and at the same time complementary to in-beam investigations of nuclei far from stability. Although both types of experiment are mainly based on γ-ray spectroscopy, they face different experimental problems. The so-called Pandemonium effect is a critical problem in β-decay if we are to test theoretically calculated transition probabilities. In this contribution we will present a solution to this problem using total absorption spectroscopy methods. We will also present some examples of experiments carried out with the Total Absorption Spectrometer (TAS) at GSI an describe a new device LUCRECIA recently installed at CERN., This work was partially supported by C.I.C.Y.T. (Spain) under contract AEN96-1662, by MCYT (Spain)contract No. FPA2002-04181-C04-03, by C.S.R. (Poland) grant KBN-2Pp03B-039-13, by R.F.B.R. (Russia)-D.F.G. (Germany) contract 436 RUS 113/201/0(R). Support from the HPMF-CT-1999-00394 project as well as from the European Large Scale Facility program at CERN is also aknowledged.

Beta-delayed neutron decay of 33 Na has been studied using the on-line mass separator ISOLDE. The delayed neutron spectra were measured by time-of-flight technique using fast scintillators. Two main neutron groups at 800(60) and 1020(80) keV were assigned to the 33 Na decay, showing evidence for strong feeding of states at about 4 MeV in 33 Mg. By simultaneous β–γ–n counting the delayed neutron emission probabilities P 1n =47(6)% and P 2n =13(3)% were determined. The half-life value for 33 Na, T 1/2 =8.0(3) ms , was measured by three different techniques, one employing identifying gamma transitions and two employing beta and neutron counting.

The magnitude of the Coulomb mixing parameter δ 1 has been experimentally deduced, for the first time, for the β decay of 74 Rb. The estimated magnitude is derived from the feeding of the non-analog first excited 0 + state in 74 Kr. The inferred upper limit of 0.07% is small compared to theoretical predictions. The half-life was measured to be 64.90(9) ms.  2001 Published by Elsevier Science B.V.

Laser spectroscopy measurements have been carried out on very neutron-deficient isotopes of Au, Pt and Ir, produced as daughter elements from a Hg ISOLDE beam. For these transitional region nuclides, the hyperfine structure (HFS) and isotope shift (IS) were measured by Resonance Ionization Spectroscopy (RIS). Magnetic moments μ, spectroscopic quadrupole moments Qs and changes of the nuclear mean square charge radius δ〈rc 2〉along isotopic series have been extracted. For some results, a detailed comparison with theoretical predictions is presented.

The \ensuremath{\beta} decay of the neutron-rich nuclei $^{51\ensuremath{-}53}\mathrm{K}$ has been used to populate bound and unbound states in $^{50\ensuremath{-}53}\mathrm{Ca}$. Measurements of \ensuremath{\gamma} rays as well as \ensuremath{\beta}-delayed neutrons enabled detailed decay schemes to be established and levels identified in ${}^{50\ensuremath{-}53}$Ca. A delayed one-neutron emission probability ${P}_{1n}$ of $63\ifmmode\pm\else\textpm\fi{}8$% was determined for the decay of $^{51}\mathrm{K}$. A total of seven new \ensuremath{\gamma} transitions were observed following the decay of $^{51}\mathrm{K}$, and 25 neutron branches were found that enrich the level scheme of $^{51}\mathrm{Ca}$. Delayed neutron emission probabilities of ${P}_{1n}=74.4\ifmmode\pm\else\textpm\fi{}9.3$% and ${P}_{2n}=2.3\ifmmode\pm\else\textpm\fi{}0.3$% were determined for the decay of $^{52}\mathrm{K}$, and 12 new \ensuremath{\gamma} transitions were observed in $^{50,51,52}\mathrm{Ca}$. Three new \ensuremath{\gamma} transitions were observed in $^{52,53}\mathrm{Ca}$ following the \ensuremath{\beta} decay of $^{53}\mathrm{K}$. New limits on the ${P}_{1n}$ and ${P}_{2n}$ values were determined for the \ensuremath{\beta} decay of $^{53}\mathrm{K}$, and a decay scheme was established for $^{53}\mathrm{Ca}$ for the first time. The data obtained here should help clarify the structure of neutron-rich $\mathit{fp}$-shell nuclei around the $N=32\text{\ensuremath{-}}34$ subshell closures.

Laser spectroscopy measurements have been carried out on the neutron-rich tin isotopes with the COMPLIS experimental setup. Using the $5{s}^{2}5{p}^{2\phantom{\rule{0.3em}{0ex}}3}{P}_{0}\ensuremath{\rightarrow}5{s}^{2}5p6s\phantom{\rule{0.3em}{0ex}}{}^{3}{P}_{1}$ optical transition, hyperfine spectra of $^{126\ensuremath{-}132}\mathrm{Sn}$ and $^{125,127,129\ensuremath{-}131}\mathrm{Sn}{}^{m}$ were recorded for the first time. The nuclear moments and the mean square charge radius variation ($\ensuremath{\delta}\ensuremath{\langle}{r}_{c}^{2}\ensuremath{\rangle}$) were extracted. From the quadrupole moment values, these nuclei appear to be spherical. The magnetic moments measured are thus compared with those predicted by spherical basis approaches. From the measured $\ensuremath{\delta}\ensuremath{\langle}{r}_{c}^{2}\ensuremath{\rangle}$, the absolute charge radii of these isotopes were deduced in particular that of the doubly magic $^{132}\mathrm{Sn}$ nucleus. The comparison of the results with several mean-field-type calculations have shown that dynamical effects play an important role in the tin isotopes.

Laser spectroscopy based on resonant ionization of laser-desorbed atoms has been used to study the neutron-rich tellurium isotopes with the COMPLIS facility at ISOLDE-CERN. The isotope shift and the hyperfine structure of several neutron-rich Te isotopes: $^{120–136}$Te and $^{123m–133m}$Te have been measured. From the hyperfine structure and the isotope shift we can extract the magnetic and quadrupole moments and the change in the mean square charge radius respectively. The mean square charge radii of the even-even isotopes have been deduced and their comparison with the known data for the other elements near Z=50 is presented. The experimental $\delta$ is compared with that obtained from the relativistic mean field calculations.

p decays of the neutron-rich nuclei 51,52,53K have been used to populate bound and unbound levels in 50,51,52,53Ca. y r a y spectroscopy as well as P-delayed neutron spectroscopy by time of flight were carried out to obtain a detailed decay scheme to levels in 53Ca, 52Ca, 51Ca and 50Ca. A half-life of 1 1 6 f 6 ms was deduced and new PI, and Pzn delayed neutron emission probabilities have also been determined for 52K. A total of 11 and 3 new y transitions have been observed in the decay of 52K and 53K, respectively. The low-lying level structure of 52Ca is compared to shell-model calculations. Implications of these results on the determination of the Y-Y interaction in the fp shell are discussed.

4 pages, 1 figure.-- Published in: Proceedings of the 22nd International Nuclear Physics Conference (Part 2), Göteborg, Sweden, Jun 27-Jul 2, 2004., Printed version published on Apr 18, 2005., This article explains the importance of β decay studies far from stability with the Total Absorption technique using as an example the decay of Sr-76. In this case the proper measurement of the BGT strength distribution over the full Qβ window, confirmed the ideas proposed long ago by Hamamoto of obtaining information about the nuclear deformation from beta decay.

A novel method of deducing the deformation of the N=Z nucleus Sr-76 is presented. It is based on the comparison of the experimental Gamow-Teller strength distribution B(GT) from its beta decay with the results of quasi-random-phase approximation calculations. This method confirms previous indications of the strong prolate deformation of this nucleus in a totally independent way. The measurement has been carried out with a large total absorption gamma spectrometer, "Lucrecia," newly installed at CERN-ISOLDE.

4 pages, 2 figures.-- Issue title: "Proceedings of the Eighth International Conference on Nucleus-Nucleus Collisions (NN2003, Moscow, Jun 17-21, 2003)"., A new Total Absorption Spectrometer (TAS) called "Lucrecia" has been installed at ISOLDE (CERN) to investigate the β-decay of some nuclei with A≈70-80 in the vicinity of the N=Z line. In this work we report on the decay of the N=Z nucleus 76Sr, measured with a TAS for the first time. The Gamow-Teller strength distribution B(GT) for this decay is presented and compared with theoretical calculations.

A novel method of deducing the deformation of the N=Z nucleus 76Sr is presented. It is based on the comparison of the experimental Gamow-Teller strength distribution B(GT) from its beta decay with the results of quasi-random-phase approximation calculations. This method confirms previous indications of the strong prolate deformation of this nucleus in a totally independent way. The measurement has been carried out with a large total absorption gamma spectrometer, "Lucrecia," newly installed at CERN-ISOLDE.

A total absorption spectrometer, dedicated to the study of very short-lived atomic species, has been built and installed at the CERN/ISOLDE mass separator. The beta decay of the neutron-deficient Kr-74 nucleus has been studied using this new device. The Gamow-Teller strength distribution has been observed over most of the Q(EC) window, and a total strength of 0.69(3) g(A)(2)/4pi has been measured for states with excitation energy below 3 MeV. Shape mixing in the Kr-74 ground state is inferred from a comparison of the experimental strength distribution with self-consistent, deformed, quasiparticle-random-phase-approximation calculations.

A new Total Absorption Spectrometer (TAS) called “Lucrecia” has been installed at ISOLDE (CERN) to investigate the β‐decay of some nuclei with A≈70–80 in the vicinity of the N=Z line. In this work we report on the decay of the N=Z nucleus 76Sr, measured with a TAS for the first time. The Gamow‐Teller strength distribution B(GT) for this decay is presented and compared with theoretical calculations.

The low-energy βγ-decay from 11Li has recently been shown to be a sensitive tool for extracting information about halo wave functions [1]. Here we present a method for using the shape of Doppler-broadened γ-lines to extract information about excited states fed in β-decay [2]. The procedure has been used to extract new information about the β-decay of 11Li through the de-excitation of excited states in 10Be.

Experimental indications have been found in the seventies for the deformation of neutron-rich A ≃ 32 nuclei [1]. This could be explained by Hartree-Fock calculations, predicting deformed configurations in the ground state of nuclei in the A = 33−35, N ≃ 21 mass region. This exotic region, called the island of inversion [2], knows a renewed interest since it can be now experimentally accessible for detailed studies.

Laser spectroscopy measurements have been carried out on the very neutron-rich tin isotopes with the COMPLIS experimental setup. Using the 5s 2 5p 2 3 P 0 → 5s 2 5p6s 3 P 1 optical transition, hyperfine spectra of 126–132 Sn and 125 m ,127 m ,129 m –131 m Sn where recorded for the first time. The variation of the mean square charge radius ( δ 〈 r 2 〉 ) between these nuclei and the nuclear moments of the isomers and the odd isotopes were thus measured. From the quadrupole moments values, all these nuclei appear to be spherical. The experimental magnetic moments are thus compared with the Schmidt values calculations. Moreover, the measured δ 〈 r 2 〉 are compared with several mean field calculations.

A PARRNe 1 experiment (Production d'Atomes Radioactifs Riches en Neutrons) aimed at the production of neutron-rich radioactive noble gases produced by photofission has been performed at CERN. The LEP Pre-Injector (LPI) has been used to deliver a 50 MeV electron beam. The results obtained show clearly that the use of an electron beam to produce neutron-rich fission fragments for futur RNB facilities is an option that should not be neglected.

The Na-33 beta decay was studied online using mass separation techniques and a first description of the level structure of the neutron-rich isotope Mg-33, with N=21, has been obtained. The experiment involved the measurement of beta-gamma, beta-gamma-gamma, and beta -n-gamma coincidences as well as neutron spectra by time-of-flight technique. The first low energy level scheme for the daughter nucleus Mg-33 is given with five bound states. Spin and parity assignments are proposed according to beta feedings and gamma -ray multipolarities, beta -strength distribution is evaluated, taking into account 1n- and 2n-emission channels and it is compared with the calculated GT strength distribution. In particular, the 1p-1h and 2p-2h excitations are shown to result in substantial contribution to the low energy configurations. Allowed beta branch to the (33)Ma g.s. [log ft = 5.27(26)] gives direct evidence for the inversion of nu (f(7/2)) and nu (d(3/2)) states. (Less)

Laser spectroscopy measurements have been carried out on the very neutron-rich tin isotopes with the COMPLIS experimental setup. Using the 5s 25p 23P 0 → 5s 25p6s 3P 1 optical transition, hyperfine spectra of 126-132Sn and 125m, 127m, 129m-131mSn where recorded for the first time. The variation of the mean-square charge radius ( δ〈r 2〉) between these nuclei and nuclear moments of the isomers and the odd isotopes were thus measured. An odd-even staggering which inverts at A = 130 is clearly observed. This indicates a small appearance of a plateau on the δ〈r 2〉 which has to be confirmed by measuring the isotope shift beyond A = 132.

The PARRNe (Production d’Atomes Radioactifs Riches Neutrons) R&D program is dedicated to the determination of the best conditions for the production of neutron-rich beam in prospect of the SPIRAL2 project. A complete description of this program, its subdivisions (PARRNe 0, 1 and 2 sub-programs) and the different experimental setup involved can be found in [1,2]. An experiment using the “PARRNE 1” procedure aimed at measuring on-line production of rare gases was performed at CERN.

The MISTRAL* experiment has measured its first masses at ISOLDE. Installed in May 1997, this radiofrequency transmission spectrometer is to concentrate on nuclides with particularly short half-lives. MISTRAL received its first stable beam in October and first radioactive beam in November 1997. These first tests, with a plasma ion source, resulted in excellent isobaric separation and reasonable transmission. Further testing and development enabled first data taking in July 1998 on neutron-rich Na isotopes having half-lives as short as 31 ms.

MISTRAL is an experimental program to measure masses of very short-lived nuclides (T1/2 down to a few ms), with a very high accuracy (a few 10−7). There were three data taking periods with radioactive beams and 22 masses of isotopes of Ne, Na, Mg, Al, K, Ca, and Ti were measured. The systematic errors are now under control at the level of 8×10−7, allowing to come close to the expected accuracy. Even for the very weakly produced 30Na (1 ion at the detector per proton burst), the final accuracy is 7×10−7.

Laser spectroscopy measurements have been performed on neutron-deficient iridium isotopes. The hyperfine structure and isotope shift of the optical Ir I transition 5d76s2 4F9/2→5d76s6p 6F11/2 have been studied for the 182–189Ir, 180Irm and 191,193Ir isotopes. The nuclear magnetic and quadrupole moments were obtained from the hyperfine splitting measurements and the changes of the mean square charge radii from the isotope shift measurements. A large deformation change between 187Ir and 186Ir and between 186Irm and 186Irg has been observed.

The MISTRAL experiment for measuring masses of very short-lived nuclides at ISOLDE has been installed during the summer of 1997 and has had its first radioactive beam in November 1997. Tests are presently been carried out to study all possible systematic effects. This paper recalls the basic principles of the Smith-type radio-frequency spectrometer, gives its present characteristics and limitations, and describes the methods used to improve its performances.

The MISTRAL* experiment is now on-line at ISOLDE. Installed in May 1997, MISTRAL received its first stable beam in October and first radioactive beam in November 1997. These first tests, with a plasma ion source, resulted in excellent isobaric separation and reasonable transmission. Further testing and development enabled first data taking in July 1998 on neutron-rich Na isotopes having half-lives as short as 31 ms.

The MISTRAL project (Mass measurements at ISolde using a Transmission RAdiofrequency spectrometer on-Line) is scheduled to begin experiments towards the end of 1996. With high resolution (105), potentially high accuracy (5×10–7) and excellent sensitivity (10 s–1), the MISTRAL spectrometer promises to provide needed mass measurements in regions of very-short lived nuclei. The spectrometer operation principles are described and a discussion concerning the interest in using highly charged ions is presented.

An RF mass spectrometer of the L. G. Smith type was built with 2 aims: to provide an experimental test of the CPT invariance (proton-antiproton mass comparison) and to measure the atomic masses of nuclei far from stability produced in the ISOLDE-PS Booster facility. As a priority was given to the first application, the features of the spectrometer are presented in this framework. Then, a discussion is made about the adaptation, currently under way, to the second application.

Direct mass measurements of exotic nuclei have been performed with a double-focussing mass spectrometer on line with an isotope separator. We report here on mass measurements with improved accuracy of exotic isotopes of Rb and Cs and on the first measurement of the masses of 116Cs and 148Cs.

The first information on the level structure of the N =21 nuclei, 35 Si and 33 Mg, has been obtained by the beta decay study of 35 Al and 33 Na, produced by fragmentation of an UC target with 1.4 GeV protons at CERN/ISOLDE. The experimental technique involved β – γ , β – γ – γ , and β –n– γ coincidences, neutron spectra being obtained by time of flight measurements. Gamma detection was made either using large Ge counters or small BaF 2 scintillators (for lifetime measurements). In the case of the 35 Al decay, ( T 1/2 =41.6(2.2) ms), a simple structure has been found for the level scheme of 35 Si ( Z =14, N =21) which has been interpreted with the level sequence : 7/2 − , 3/2 − and 3/2 + corresponding respectively to the ground state and the states at 910 and 974 keV. The life-time of the 974 keV [ T 1/2 =5.9(6) ns] is found consistent with the proposed level scheme and multipolarities. The investigation of the N =21, very neutron rich isotones, has been carried on with the study of 33 Mg resulting from the 33 Na decay, ( T 1/2 =8.0(6) ms). In this case also, a level scheme could be obtained for the first time, with 5 bound states in 32 Mg and 31 Mg levels, populated in the 1n and 2n channels. These results are compared with sd–fp shell model calculations which give a fair account of the Gamow–Teller distribution and a reasonable explanation of the lowest levels with predominant contribution of 1p–1h and 2p–2h excitations.