Rb Isotopes Research Articles

Precision Measurements of Masses of Radioactive Atoms using ISOLDE and Ion Traps

A mass spectrometer has been set up at the on-line isotope separator ISOLDE at CERN/Geneva. Mass-separated radioactive ions are stored in a Penning trap. Their mass is determined by a measurement of the cyclotron frequency in the magnetic field of a superconducting magnet. A resolving power of up to 300 000 and a precision of some 10 keV were determined in case of mass measurements of neutron-deficient Rb and Cs isotopes.

Isotopic and Structural Responses of Granite to Successive Deformation and Metamorphism

Within the Sybella Granite west of Mount Isa in northern Australia, differential response of U-Pb and Rb-Sr isotopic systems to deformation/metamorphism enables ages of emplacement and three discrete deformation/metamorphic events to be determined. Based on zircon U-Pb systems, two of the plutons were emplaced at $1671 \pm 8 Ma$ and 1668 $\pm ^{26}_{21}$ Ma, and the third at $1610 \pm 10 Ma$. A separate microgranite body gives aberrantly old U-Pb ages of up to 1780 Ma, due to partial inheritance of older zircon. The three discrete deformation/metamorphic events ($D_{1}, D_{2} and D_{3}$) occurred at $1610 \pm 13 Ma, 1544 \pm 12 Ma, and 1510 \pm 13 Ma$ respectively, based on whole-rock Rb-Sr isotopic systems. The youngest body was emplaced syntectonically and has possible significance to the origin of the Mount Isa Ag-Pb-Zn orebodies. Homogenization of Rb and Sr isotopes via extensive syntectonic fluid migration, associated with deformation partitioning and resultant solution transfer, appears to have been...

Mass-spectrometric measurements of exotic Rb, Cs and Fr isotopes

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.

Laser spectroscopy and mass measurements on alkali isotopes

Isotope shifts, spins, hyperfine structures and masses have been measured for the series of the alkali isotopes including the nuclei far from stability. The method of laser spectroscopy and its combinations with rf excitation are described. Some results are discussed, namely the first observation of the red doublet D1-D2 of francium, and the study of shell effects and changes of shape with mass and δ〈r 2〉 measurements for Rb and Na isotopes.

β − Strength function phenomena of exotic nuclei: A critical examination of the significance of nuclear model predictions

Reliable predictions of β-decay properties of nuclei far from stability require knowledge of the β-strength distribution, S β ( E). By comparison of experimental strength functions of neutron-rich Rb isotopes in the transitional region around A = 100 with S β ( E) from different nuclear models, the sensitivity and physical significance of S β ( E) on various integral and spectral β-decay properties are examined. The reliability of extrapolations and the applicability to different fields in nuclear physics, astrophysics and reactor technology are discussed. It is shown that, although there has been considerable progress in the physical understanding of the decay properties of nuclei far from β-stability over the past few years, there are still open questions which make recent statements on the solution of long-standing problems related to the standard processes of β-decay premature.

Isotopic investigations of the Nordingrå rapakivi massif, north-central Sweden

Abstract Granite, gabbro and anorthosite together constitute the Nordingra massif. These igneous rocks have intruded a sequence of Svecokarelian metasediments and postdate the regional metamorphism and folding. Available field observations demonstrate that the granite intrudes the gabbro-anorthosite complex. Zircons separated from the granite and the anorthosite have an age of 1578 ± 19 Ma, which is considered to indicate the time of magmatic crystallization. The Rb-Sr whole rock age 1552 ± 18 Ma of the gabbro and anorthosite is slightly lower than the zircon age, whereas the Rb-Sr reference age of the granite, 1416 Ma, is considerably lower than the age of the zircons. Hypothetical models of genesis and history are discussed to explain this discordancy. It is suggested that post-crystallization hydrothermal fluids, circulating in the bedrock during the uplift and cooling of the orogenic belt and/or during subsequent epeirogenic movements, transported Rb and Sr isotopes in the whole rock system. This led ...

Age differences between RbSr whole rock and UPb zircon ages of syn- and postorogenic Svecokarelian granitoids in Sottunga, SW Finland

The UPb age on pooled data of zircnos from the postorogenic Svecokarelian Mosshaga granite is 1788 ± 11 Ma (2 σ). The corresponding RbSr whole rock age is 1742 ± 34 Ma (2 σ). The Mosshaga granite intrudes a synorogenic granodiorite, which has a UPb zircon age of 1889 ± 10 Ma and a RbSr whole rock age of 1850 ± 28 Ma. The age differences between the UPb zircon ages and RbSr whole rock ages are concluded to be geologically significant. It is shown that the Mosshaga pluton cooled rapidly and as a consequence the RbSr isotopic system closed at a time very close to the crystallization of the zircons. A commonly observed feldspar and biotite alteration in Svecokarelian granitoids indicates migration of Rb and Sr isotopes in the whole rock system which may lead to apparently younger RbSr ages.

Comparison between solid graphite and graphite cloth as a target backing material for an Isol system

A high temperature target-ion source system developed for the TRISTAN on-line isotope separator at Brookhaven National Laboratory is described. The system consists of a surface ionization chamber with a Re surface and 235U in a graphite target matrix. Both solid graphite and graphite cloth targets were tested. The overall separation efficiencies for isotopes of Rb, Cs, Sr, Ba, In, Ce,Pr, Nd and Pm which were extracted directly from the ion source were measured. Production rates were measured as a function of temperature up to 2000°C and the ion source performance was monitored over long periods of time. The performance of solid graphite targets was found to give superior stable operation with no deterioration in production rates for operation times of up to 2000 h. In contrast, graphite cloth targets exhibited deterioration in efficiency with time for most elements with differing rates. The production rates of Ce and Pr isotopes increases significantly during the first 400 h of operation, followed by a slow decrease.

Mass spectrometric determination of Rb fission yields from 3He and 4He induced fission of 238U and 232Th

Cumulative and independent fission yields of Rb isotopes have been measured for 3He and 4He induced fission of 232Th and 238U at bombarding energies slightly above the Coulomb barriers. The on-line mass spectrometric technique provided yields for masses 89–97. Mean masses and widths of the Rb independent yield distributions were obtained and were compared to other fissioning systems with excitation energies up to 160 MeV.

Beta-decay energies and nuclear masses of very neutron-rich Rb and Cs isotopes

Theβ-endpoint energies of very neutron-rich Rb and Cs isotopes with mass numbers 94≦A≦98 and 142≦A≦146, respectively, have been measured with a plastic scintillatorβ-telescope at the on-line mass separator OSTIS. From these,Qβ-values and mass excesses are calculated and compared with the results obtained in direct mass determinations.

Masses of Rb, Cs and Fr isotopes

The results of the direct mass measurements of the unstable isotopes of Rb, Cs and Fr are rewritten in a form-linear combination of masses-which allows a direct analysis with other experimental data. An up-to-date least-square adjustment which takes into account new reference masses is subsequently performed. A systematic study of isomers is carried out for evaluating isomeric corrections to apply to the measured masses in order to obtain the ground-state masses.

Performance of the on-line isotope separation facility HELIOS at the Mainz reactor

Abstract The helium-jet on-line isotope eparation facility HELIOS is in operation at the Mainz reactor for spectroscopic studies on mass separated neutron-rich nuclides far from the line of beta-stability. The basic features and achievements of the facility are reported. A total of 45 isotopes of the elements Rb, Sr, Y, Sn, Sb, Te, Cs, Ba, La, Ce, Pr and Nd have been separated and identified so far. Overall efficiencies up to 2% have been obtained using the integrated skimmer ion source arrangement either in a hollow cathode or in a high temperature surface ionization mode. The delay time for the HELIOS system was determined to be about 1 s.

Fast isobaric separation at the collector of ISOL-facilities

Abstract The release of radioactive isotopes of Rb, Sr, Y, Zr, Ba, several rare earth elements, Ra, Ac and Th after implantation at 45 keV into collector foils using the isotope separator of the JASNAPP-facility have been investigated. The heating of the collector foils inside a vacuum chamber up to defined temperatures caused a separation of the implanted elements. The separation-coefficients α for a 180 s heating period in an off-line mode are the following (Ta-backing was used in all cases except for α Zr/Y in which case Zr-backing was used): α Sr/Rb = 14 T=1390 K α Tm/Yb = 8 T=1600 K α Y/Sr = 28 T=1680 K α Lu/Yb = 38 T=1700 K α La/Ba = 8 T=1590 K α Ac/Ra = 30 T=1650 K α Eu/Sm = 3 T=1470 K α Th/Ra = 30 T=1650 K α Gd/Eu = 22 T=1620 K α Zr/Y = 1000 T=1800 K . The influence of diffusion and desorption on the release process is discussed. A corresponding method is proposed to be used for on-line separation of several elements at the collector of ISOL-facilities.

Fission yield measurements of Rb, Sr, Cs and Ba isotopes far from the center of the isotopic yield distributions in 235U( nth, f)

Independent fission yields of 92–99Rb, 94–100Sr, 142–148Cs and 143–149Ba in the thermal neutron fission of 235U were determined at the SOLIS on-line mass separator. The independent fission yields of 99Rb, 147, 148Cs and 145–149Ba were measured for the first time. For all the elements a “wing effect” is apparent, i.e. the experimental independent fission yields in the wings of the isotopic (isobaric) yield distributions are considerably higher and their decline with mass (charge) less steep than predicted by fission yield systematics. To account for this effect a corrected semi-empirical distribution function for fission yields is proposed. Comparison of the experimental fission yields with the predictions of theoretical fission models also shows the existence of the “wing effect”. Since the theory predicts primary fission yields a correction due to prompt neutron emission was calculated. It is shown that the effect of prompt neutron emission is to broaden the isotopic distributions in the wing of heavy isotopes only slightly, and in the wing of light isotopes more significantly, but it does not explain the “wing effect” which seems to originate in the fission process.

Independent yields of Rb and Cs isotopes from thermal-neutron induced fission ofU235

The relative yields of Rb and Cs isotopes from thermal-neutron fission of $^{235}\mathrm{U}$ have been redetermined using the mass separator OSTIS, on-line at a neutron guide of the High-Flux Beam Reactor at the Institut Laue-Langevin, Grenoble, France. The separator ion source was a hot oven containing $^{235}\mathrm{U}$ in a graphite matrix. The neutron beam was pulsed. Alkali fission products diffused out of the graphite and were ionized, thus producing a stepwise increase in the analyzed ion beam proportional to the independent fission yield. The ion beam and the fissions in the source were monitored simultaneously. The diffusion of Rb and Cs from the source was exponential in time with half-lives ranging from 2.8 to 18 sec, depending upon the element and source temperature. The independent fission yields of Rb and Cs are normalized by equating their element yields to each other and to a value computed from the charge distributions observed with the recoil separator LOHENGRIN and well established mass yields. Fractional independent yields are deduced from the independent fission yields, and these compare very well with the EOZ model described by Wahl.NUCLEAR REACTIONS $^{235}\mathrm{U}$($n$,$f$), $E=\mathrm{thermal}$; measured relative abundances; deduced independent fission yields, fractional chain yields, charge displacement and dispersion, odd-even $Z$ effect. Mass separator, fast neutron detector.

Nuclear moments and charge radii of neutron-rich Rb isotopes by fast-beam laser spectroscopy

A systematic study of nuclear moments and rms charge radii in Rb was made possible by extending high-resolution cw laser spectroscopy into the deep blue. Measurements of optical isotope shifts and hyperfine structure of fission-produced 89−93Rb are reported.

High-temperature carbide targets for fast on-line mass separation of alkali and noble gas elements

Targets of vanadium, lanthanum and uranium carbides kept at temperatures around 2000 °C have been used at the ISOLDE on-line isotope separator at the CERN 600 MeV Synchro-cyclotron for production of Ar, Xe, Rb, Cs and Fr isotopes. The target materials are prepared either by sintering finely divided powders or by impregnation of graphite cloth with the respective target elements. Isotopic production yields peak at 10 8 –10 9 atoms/s, and the distribution of time delays between production and measurement extend well below 1 s. The measured delay is treated in the framework of simple diffusion theory and a relation between observed and decay-loss-corrected yields has been derived. Approximate formation cross-sections have been deduced and compared with empirical systematics. In the course of the development work the following new nuclides were identified: 32 Ar( T ½ ∼ 75 ms), 46 Ar(9 ± 1 s), 201 Fr(48 ± 15 ms), 202 Fr(0.35 ± 0.02 s) and 230 Fr(19 ± 1 s).

Determination of nuclear spins of short-lived Rb and Cs isotopes by β radiation detected optical pumping

Determination of nuclear spins of short-lived Rb and Cs isotopes by β radiation detected optical pumping

Independent yields of fast-neutron fission ofTh232: Observation of proton odd-even effect and neutron shell effect on the yields

Elemental yields in the fission of $^{232}\mathrm{Th}$ induced by reactor neutrons were measured and found to disclose a pronounced odd-even effect. Independent and cumulative yields of isotopes of Kr, Xe, Sn, and Sb were measured and the independent yields of isotopes of Rb, Cs, and Sb were subsequently derived. A comparison of the yield values obtained with the calculated "normal" yields reveals a constant enhancement of products with an even number of protons, relative to those with an odd number. An average amplitude of 30(\ifmmode\pm\else\textpm\fi{}12)% in the fluctuation of proton pairing was established for all isotopes measured, except for the doubly magic $^{132}\mathrm{Sn}$, which shows an extreme effect, apparently due to its closed neutron shell. The odd-even effect is discussed in connection with the mass distribution, excitation, and total kinetic energies. The neutron shell effect on the yields is discussed with regard to the primary mass split and the neutron emission probabilities.[NUCLEAR REACTIONS, FISSION Fission yields $^{232}\mathrm{Th}(n,f)$, calculated proton odd-even effect, calculated neutron closed shell effect.]

Delayed-neutron emission probabilities of separated isotopes of Br, Rb, I, and Cs

Delayed-neutron emission probabilities (P/sub n/) were measured for 16 isotopes of Br, Rb, I, and Cs. Sources of chemically and mass separated nuclides were obtained from an on-line mass spectrometer facility. Neutrons were counted in a multitube polyethylene-moderated detector. The total number of precursor atoms was determined by direct counting of ions deposited on the first dynode of an electron multiplier. The P/sub n/ values from this work generally agree with earlier measurements for the longer-lived precursors but are consistently higher for the shorter-lived precursors. A log-log plot of P versus the reduced energy window (Q/sub ..beta../ - B/sub n/)/(Q/sub ..beta../ - C) gives a straight line with a slope of 6.0 +- 1.4, in agreement with simplified theoretical predictions. Half-lives of Rb and Cs nuclides measured by neutron decay curves are given.