R. Vondrasek

A Shorter 146Sm Half-Life Measured and Implications for 146Sm-142Nd Chronology in the Solar System

A New Lease on Half-Life Radiometric dating relies on measuring the abundance of long-lived radionuclides relative to the abundance of their radiogenic decay products—a process determined by the original radionuclides half-life. For primordial radionuclides that decay slowly, such as 146Sm decaying to 142Nd, this method provides the timing of some of the earliest processes in solar system history. Using accelerator mass spectrometry, Kinoshita et al. (p. 1614) provide a revised estimate for the 146Sm half-life of ∼68.7 million years, which is 30% shorter than the previously accepted value. This shorter half-life suggests that reductions need to be made in the estimated ages for differentiation of Earths mantle and the solidification of the Moons magma ocean and for other more recent processes. Mantle differentiation of Earth, the Moon, and Mars occurred earlier and over a shorter time scale than previously estimated. The extinct p-process nuclide 146Sm serves as an astrophysical and geochemical chronometer through measurements of isotopic anomalies of its α-decay daughter 142Nd. Based on analyses of 146Sm/147Sm α-activity and atom ratios, we determined the half-life of 146Sm to be 68 ± 7 (1σ) million years, which is shorter than the currently used value of 103 ± 5 million years. This half-life value implies a higher initial 146Sm abundance in the early solar system, (146Sm/144Sm)0 = 0.0094 ± 0.0005 (2σ), than previously estimated. Terrestrial, lunar, and martian planetary silicate mantle differentiation events dated with 146Sm-142Nd converge to a shorter time span and in general to earlier times, due to the combined effect of the new 146Sm half-life and (146Sm/144Sm)0 values.

Charge breeding results and future prospects with electron cyclotron resonance ion source and electron beam ion source (invited)a)

The Californium Rare Ion Breeder Upgrade (CARIBU) of the Argonne National Laboratory ATLAS facility will provide low-energy and reaccelerated neutron-rich radioactive beams for the nuclear physics program. A 70 mCi (252)Cf source produces fission fragments which are thermalized and collected by a helium gas catcher into a low-energy particle beam with a charge of 1+ or 2+. An electron cyclotron resonance (ECR) ion source functions as a charge breeder in order to raise the ion charge sufficiently for acceleration in the ATLAS linac. The final CARIBU configuration will utilize a 1 Ci (252)Cf source to produce radioactive beams with intensities up to 10(6) ions∕s for use in the ATLAS facility. The ECR charge breeder has been tested with stable beam injection and has achieved charge breeding efficiencies of 3.6% for (23)Na(8+), 15.6% for (84)Kr(17+), and 13.7% for (85)Rb(19+) with typical breeding times of 10 ms∕charge state. For the first radioactive beams, a charge breeding efficiency of 11.7% has been achieved for (143)Cs(27+) and 14.7% for (143)Ba(27+). The project has been commissioned with a radioactive beam of (143)Ba(27+) accelerated to 6.1 MeV∕u. In order to take advantage of its lower residual contamination, an EBIS charge breeder will replace the ECR charge breeder in the next two years. The advantages and disadvantages of the two techniques are compared taking into account the requirements of the next generation radioactive beam facilities.

ECRIS operation with multiple frequencies

The 10.5GHz electron cyclotron resonance ion source (ECRIS) at Argonne National Laboratory has been utilizing a 10.5GHz klystron and an 11–13GHz traveling wave tube amplifier (TWTA) for beam production in two-frequency heating mode. The beam intensities obtained from the source with two-frequency heating have shown a factor of 2 improvement over single-frequency heating for the higher charge states. Following a simple logic that an increased number of resonance zones leads to enhanced source performance, a 14GHz klystron was added to the source configuration enabling the plasma to be simultaneously excited with three discrete frequencies. In studies with three-frequency heating when compared to two-frequency heating, the beam intensity for O7+ increased from 70.4to84.2eμA, Kr23+ (mass 86, 99.9% enriched) increased from 3.5to7.2eμA, and Xe28+ (mass 136, 60% enriched) increased from 7.9to12.2eμA. A rf power combiner was added to the TWTA so that it could be driven simultaneously with two frequencies. With t...

Results with the electron cyclotron resonance charge breeder for the C252f fission source project (Californium Rare Ion Breeder Upgrade) at Argonne Tandem Linac Accelerator Systema)

The construction of the Californium Rare Ion Breeder Upgrade, a new radioactive beam facility for the Argonne Tandem Linac Accelerator System (ATLAS), is nearing completion. The facility will use fission fragments from a 1 Ci (252)Cf source; thermalized and collected into a low-energy particle beam by a helium gas catcher. In order to reaccelerate these beams, an existing ATLAS electron cyclotron resonance (ECR) ion source was redesigned to function as an ECR charge breeder. Thus far, the charge breeder has been tested with stable beams of rubidium and cesium achieving charge breeding efficiencies of 9.7% into (85)Rb(17+) and 2.9% into (133)Cs(20+).

Status of the electron cyclotron resonance charge breeder for the {sup 252}Cf fission source project at ATLAS

The construction of the Californium Rare Ion Breeder Upgrade, a new radioactive beam facility for the Argonne tandem linac accelerator system (ATLAS), is in progress. The facility will use fission fragments from a 1 Ci (252)Cf source, thermalized and collected into a low-energy particle beam by a helium gas catcher. In order to reaccelerate these beams, the existing ATLAS ECR1 ion source has been redesigned to function as a charge breeder source. The design features, initial results, and status of this charge breeder configuration are presented.

Performance of the Argonne National Laboratory electron cyclotron resonance charge breeder

An electron cyclotron resonance charge breeder for the Californium rare ion breeder upgrade (CARIBU), a new radioactive beam facility for the Argonne Tandem Linac Accelerator System (ATLAS), has been constructed and commissioned. Charge breeding efficiencies up to 15.6% have been realized for stable beams with a typical breeding time of 10 ms∕charge state. The CARIBU system has been undergoing commissioning tests utilizing a 100 mCi (252)Cf fission source. A charge breeding efficiency of 14.8 ± 5% has been achieved for the first radioactive beam of (143)Cs(27+).

Ultra-sensitive detection of p-process nuclide 146Sm produced by (γ, n), (p, 2nε) and (n, 2n) reactions

We are developing a technique of ultra-sensitive detection of the p-process 146Sm nuclide by accelerator mass spectrometry. 146Sm was produced via the reactions (γ,n), (p,2ne) and (n,2n) on 147Sm. Preliminary results demonstrate for the first time the capability of identifying unambiguously 146Sm through separation and discrimination of its stable 146Nd isobar and other background ions. We consider applying the detection method to an independent determination of 146Sm half-life and to the measurements of cross sections of low-energy nuclear reactions producing long-lived nuclides in the vicinity of 146Sm.

Completion of the ATLAS ECR-I ion source upgrade project

A new 10 GHz electron cyclotron resonance ion source (ECRIS) has been constructed and commissioned for the ATLAS accelerator. This new source replaces the original ATLAS ECRIS that has been in operations since 1987. The goal of this upgrade project was to significantly improve the source performance while maintaining maximum operational flexibility for solid material feeds. The new source design includes a large magnetic-field gradient, aluminum plasma chamber, and bias disk following modern ECRIS design concepts. Eight solenoid coils from the original source along with a new iron yoke form the magnetic mirror. Hall Probe measurements showed the axial B field to be within 1% of the POISSON design model calculated at 400 A per coil. The injection and extraction mirror ratios are approximately 4.4 and 2.9, respectively, with a minimum field of 3.0 kG. A new aluminum plasma chamber houses the NdFeB hexapole magnets, which are encased in austenitic stainless steel to allow for direct water cooling. An open he...

ATLAS 10 GHz electron cyclotron resonance ion source upgrade project

A major upgrade of the first ATLAS 10 GHz electron cyclotron resonance (ECR) ion source, which began operations in 1987, is in the planning and procurement phase. The new design will convert the old two-stage source into a single-stage source with an electron donor disk and high gradient magnetic field that preserves radial access for solid material feeds and pumping of the plasma chamber. The new magnetic-field profile allows for the possibility of a second ECR zone at a frequency of 14 GHz. An open hexapole configuration, using a high-energy-product Nd–Fe–B magnet material, having an inner diameter of 8.8 cm and pole gaps of 2.4 cm, has been adopted. Models indicate that the field strengths at the chamber wall, 4 cm in radius, will be 9.3 kG along the magnet poles and 5.6 kG along the pole gaps. The individual magnet bars will be housed in austenitic stainless steel, allowing the magnet housing within the aluminum plasma chamber to be used as a water channel for direct cooling of the magnets. Eight sole...

A one-dimensional axial electron cyclotron resonance source model

A conventional zero-dimensional (uniform plasma parameters with no spatial variations) fluid model will provide a good match with an experimental electron cyclotron resonance ion source (ECRIS) charge-state distribution (CSD) if provided with a judicious set of user inputs. However, this arbitrarily chosen set of inputs is not necessarily unique. To be truly predictive, an ECRIS model should rely on experimental parameters as inputs. A multi-species model for an ECRIS plasma using experimental parameters as inputs is under development. The model eliminates electron temperature as a user input by employing a 2 V(v,θ) Fokker–Planck code with an ECR heating term to calculate the non-Maxwellian anisotropic electron distribution function. Further arbitrary user inputs are eliminated in favor of controlled parameters by bounce averaging the Fokker–Planck coefficients for a one-dimensional (1D)/2 V axial model. The neutral gas modeling has been extended to 1D using axially coupled particle balance equations. The...