FN Tandem Accelerator Research Articles

Earthquake protection and other improvements to the Bucharest FN tandem accelerator

The HVEC-FN type tandem accelerator of the Institute of Atomic Physics in Bucharest was twice, in 1977 and 1986, severely damaged by strong earthquakes

Band structures in 126Xe

Excited states of 126Xe have been investigated with the (α, n) and the ( 13C, 3n) reactions by means of the OSIRIS-12 spectrometer at the Cologne FN-tandem accelerator. With the ( 13C, 3n) reaction 13 bands were established and the yrast band was extended up to a tentative (20 +) state. With both reactions in total 178 levels and 307 transitions were observed. The data are compared to the predictions of different models.

High spin states in66,68Ge

High spin states of66,68Ge have been investigated at the FN Tandem accelerator of the University of Koln via the reactions40Ca(32S,α2p,4p)66,68Ge at a beam energy of 100 MeV and58Ni(16O,α2p)68Ge at 65 MeV. The OSIRIS spectrometer with 12 escape suppressed Ge detectors was used to measure γγ coincidences and γ-ray angular distributions. In66Ge (68Ge) 33 (22) new levels were found and 63 (62) new γ-transitions were placed in the level scheme. Both nuclei show a rather complicated but similar excitation pattern, ruled by the interplay of quasiparticle and collective degrees of freedom. The results are compared to the recently published EXVAM calculations for68Ge.

Success with an automated computer control system

LLNL has successfully implemented a distributed computer control system for automated operation of an FN tandem accelerator. The control system software utilized is the Thaumaturgic Automated Control Logic (TACL) written by the Continuous Electron Beam Accelerator Facility and co-developed with LLNL. Using TACL, accelerator components are controlled through CAMAC using a two-tiered structure. Analog control and measurement are at 12 or 16 bit precision as appropriate. Automated operation has been implemented for several nuclear analytical techniques including hydrogen depth profiling and accelerator mass Spectrometry. An additional advantage of TACL lies in its expansion capabilities. Without disturbing existing control definitions and algorithms, additional control algorithms and display functions can be implemented quickly.

Distributed computer control at the LLNL tandem

Livermore is developing hardware and software tools to provide automated operation of an FN tandem accelerator. Automated operation is planned for several nuclear analytical techniques including hydrogen depth profiling and accelerator mass spectrometry. The control system utilizes a distributed computer system to provide 16 bit precision in control of accelerator power supplies.

14C AMS at the University of Washington: measurements in a shared facility at the 1% level on 0.4 mg samples

The FN tandem accelerator at the University of Washington has been used for AMS measurements for more than ten years. The current sample preparation methods, measurement procedures and system capacity are described. Preliminary results of an ongoing study of 14CH 4 in atmospheric methane and methane from wetlands environments are presented. The development of new preparation methods has reduced our sputter-source sample size requirements from 2–4 mg to 200–400 μg and allows essentially complete utilization of the sample during the sputtering process. At the ± 1% level, the current precision and accuracy of our measurements are limited by counting statistics uncertainties. Ongoing improvements to the measurement system are also discussed.

Evidence for variable γ deformation in 126Xe

Low spin states of 126Xe have been investigated by means of the OSIRIS-12 spectrometer at the Cologne FN-Tandem accelerator using the nonselective (α, n)-reaction. New “K=0” and “K=4” bands were established. The experimental “B(E2)” ratios are compared with the predictions of the interacting boson, asymmetric rotor-vibration model. The data rules out the asymmetric rotor model with rigid γ deformation as a description of this nucleus.

41Ca: Measurement by accelerator mass spectrometry and applications

We describe in detail methods and techniques we have developed to measure 41Ca 40Ca ratios to a sensitivity of 6 × 10 −16 us our FN tandem accelerator. The major steps involved were (1) adoption of 41CaH 3 − negative ions to reduce 41K ( 41K/ 40Ca ~ 5 10 −13); (2) production of typically 5 μA of 40CaH 3 −ions from calcium hydride in a high-intensity source; (3) refinement of a technique to efficiently convert CaO samples, as small as 15 mg, into CaH 2; (4) implementation of a high resolution velocity selector to remove interferring 40Ca and 42Ca ions and (5) use of a multi-anode gas ionization detector to provide excellent discrimination of 41Ca from the remaining background ions. The system performs admirably, enabling measurements with ± 5% reproducibility on extraterrestrial samples, such as meteorites and lunar rocks. In addition, we have also carried out the first measurements, without pre-enrichment, of 41Ca in terrestrial rocks and bones. From these measurements, we conclude that radiocalcium dating of bones will most likely not develop into a viable dating technique. The 41Ca concentrations in modern bones are not only disappointingly low and quite close to our sensitivity limit, but show a marked variability. On the other hand, the study of 41Ca in extraterrestrial samples offers much promise as a means of determining terrestrial ages and pre-atmospheric sizes of meteorites, and of investigating the average solar cosmic ray flux during the past 300 000 years.

Operational experience of the atlas accelerator

The ATLAS accelerator consists of a HVEC model FN tandem accelerator injecting into a linac of independently-phased niobium superconducting resonators. The accelerator provides beams with masses 6⩽ A⩽127 and with energies ranging up to 20 MeV/ A for the lightest ions and 4 MeV/ A for the heaviest ions. Portions of the linac have been in operation since 1978 and, over the last decade, more than 35000 h of operating experience have been accumulated. The long-term stability of niobium resonators, and their feasibility for use in heavy-ion accelerators is now well established.

Development of a knowledge-based control system for a model FN Van de Graaff accelerator: An operator's perspective

In light of the manpower- and monetary restraint situation at the FN Tandem Accelerator facility of McMaster University and the difficulty in acquiring experienced personnel to operate and maintain the machine, an approach to solving this problem has been to firstly construct and operate a computer based knowledge system. This passive expert system directs an experienced person in the operation of the accelerator and helps diagnose many simple problems incurring in day-to-day operation. The system leads the person on a step by step diagnostic journey to the solution of the problem or at least to a reasonable response that will protect personnel and equipment until qualified experts can be contacted. The expert system contains all the required formulae, log readings, safety procedures and operating procedures in either database or knowledge base forms that are used to set the sequential steps in the consultation mode of the diagnostician. As the completion of this system nears, phase two will be initiated with the development of an active expert system where the interfacing of all machine variables will allow direct parameter assignments. At this time, the interface between expert system and operator of the machine will no longer require a human, except in a supervisory capacity.

Improvements at the Cologne FN tandem accelerator

In order to increase the maximum terminal voltage of the Cologne FN tandem accelerator the inhomogeneous voltage divider at tube #1 was replaced by a homogeneous one. After this alternation it was possible to operate the accelerator at 10.6 MV and in test experiments up to 11 MV. Because of the stronger focusing strength at the entrance of the first accelerator tube the beam optics at the injector was modified.

Integrating knowledge-based systems into operations at the McMaster University FN Tandem Accelerator Laboratory

The development of an accelerator operators' companion, which incorporates a knowledge-based front-end that is tuned to user operational expertise is described. The front-end also provides connections to traditional software packages such as database and spreadsheet programs. Two prototype implementations are presented. The importance of modifying expert procedures when a multitasking environment is involved, as discovered during work on the back-end (that is, during real-time expert system control development), is discussed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

An accelerator operator's companion for the McMaster University Model FN tandem accelerator

A prototype accelerator operator's companion was developed to investigate the feasibility of automating the operation of the McMaster University Model FN Van De Graaff accelerator. Its purpose is to provide the accelerator staff with a working model with which they can experiment and which would motivate discussions to further pinpoint their needs. Initial needs and goals were established at the outset of this project and, on the whole, were met with this first version of the software system. As presently constituted, the operator's companion functionally provides an electronic log book system that stores all the operating parameters, a procedures system that presents the operating procedures with the appropriate operating parameters embedded in them at display time, and a diagnostic system that is able to diagnose problems associated with the accelerator when utilizing information from the log book and input from the user. Through discussions with the accelerator staff at various stages throughout the development and at the final evaluation, important feedback was generated, which helped to define operational needs further. >

A nanosecond pulsing system for the cologne FN tandem accelerator

A nanosecond pulsed heavy ion beam facility comprising a multiplate-deflector chopper and a two-gap buncher has been installed at the upgraded 9 MV Cologne Van de Graaff tandem accelerator. The paper reports on the properties of the new injection line and the time performance of pulsed beams of ions with 1 ≤ Z ≤ 16 produced in a duoplasmatron or Penning ion source.

Radiocarbon Dating with the University of Washington Accelerator Mass Spectrometry System

The University of Washington FN tandem accelerator mass spectrometry (AMS) system has been used in a series of 14C studies. 1) The 14C concentrations in annual growth rings for 1962, 1963, and 1964 of a Sitka spruce, each divided into ten sequential segments, were measured; a full and rapid response of tree-ring cellulose to atmospheric changes in 14CO2 is indicated, with a delay, if any, of not more than three weeks. 2) The C concentrations in two chemical fractions of dissolved organic carbon and in two fractions (by size) of particulate organic carbon were measured for Amazon River samples from several locations. All contain bomb carbon, but the amounts differ significantly. 3) Algae samples from lakes in the dry valleys of Antarctica were dated in order to assist in the reconstruction of the climatic history of Antarctica. 4) Background studies indicate that the contribution of the AMS system itself to the observed 14C concentrations is equivalent to an age of ca 60,000 14C yr BP; for a prepared sample of 5mg of carbon the background corresponds to ca 50,000 years.

The accelerator mass spectrometry facility at the University of Washington: Current status and an application to the 14C profile of a tree ring

The University of Washington accelerator mass spectrometry system, based upon a Model FN tandem accelerator, is described. Preliminary data on 14C in thin sequential sections of a single Sitka spruce annual ring (1963) are presented; the 14C profile reflects the dramatic nuclear-weapons-induced changes in atmospheric 14C observed for 1963.

The University of Washington superconducting booster project

The University of Washington Nuclear Physics Laboratory has designed a superconducting linac booster with an equivalent dc accelerating voltage of 24.35 MV, which will be injected by the existing FN tandem Van de Graaff accelerator. The design is based on the lead-plated copper quarter-wave resonator units developed by the Stony Brook/Weizmann group. The UW booster, unlike previous designs, will accelerate p, d, t, 3He, and 4He as well as light heavy ions ( A < 56). Design studies of system performance give proton energies of almost 38 MeV and energies for light-heavy ions of over 15 MeV/amu, diminishing with A to about 7 MeV/amu for 56Fe (assuming most probable charge). Beam dynamics studies show that debunching gives ΔE/E ⋍ 10 −4 or about 5 keV for protons, and bunching gives a time resolution on target of about 40–60 ps. The UW Booster Project has been recommended by NSAC and is to be funded in the FY'84 and FY'85 budgets of the US Department of Energy at a cost of about $8 million. Final planning and development are now in progress; construction is to begin in late 1983.

A search for doubly-charged negative ions via accelerator mass spectrometry

The Argonne FN tandem accelerator in conjunction with an Enge split-pole magnetic spectrograph has been used as a highly sensitive mass spectrometer to search for doubly-charged negative ions of 11B, 12C and 16O. No evidence for the formation of these ions in an inverted sputter source and the subsequent acceleration in the tandem has been found. The following limits for the ratio of doubly-charged singly-charged ions were measured: 11B 2−/ 11B − < 1 × 10 −15, 12C 2−/ 12C − < 2 × 10 −15, 16O 2−/ 16O − < 2 × 10 −14. A relatively abundant formation of the short lived, metastable He − ion in the sputter source has been observed.

Accelerator mass spectrometry with 26Al

The cosmogenic radioisotopes 10Be, 14C and 36Cl are routinely being measured in several laboratories but the potentially important 26 Al (τ 1 2 =7.2×10 5 y) has received scant attention - largely because it is difficult to produce negative-ion beams of aluminum (particularly from the oxide) and the high abundance of 27Al results in small 26Al: 27Al ratios (typically ≲10 −14 terrestrial and 10 −10 extraterrestrial). A new ion source is described which typically generates 1 to 2 μA of 27Al − ions from small samples (≈4mg) of Al 2O 3 with an ionization efficiency of about 0.25%. Modifications have been made to the University of Pennsylvania's FN-tandem accelerator for quantitative measurement of 26Al: 27Al ratios as low as 5×10 −15 and some of the problems encountered are contrasted with those met during 10Be measurements. Although measurement of 26Al: 27Al ratios in terresrial samples are often close to the limit of our sensitivity, we have made measurements on a variety of terrestrial samples including stratospheric air filters, manganese nodules, tektites, and various impact glasses and on extraterrestrial samples including cosmic spherules, a meteoric and several lunar samples.

Half-life ofTi44

The half-life of $^{44}\mathrm{Ti}$ has been measured to be ${T}_{\frac{1}{2}}=54.2\ifmmode\pm\else\textpm\fi{}2.1$ yr, somewhat higher than previously published values of 46.4\ifmmode\pm\else\textpm\fi{}1.7 and 48.2\ifmmode\pm\else\textpm\fi{}0.9 yr. The present value was obtained from the specific activity and the radioisotope concentration of several Ti${\mathrm{O}}_{2}$ samples, each spiked with a $^{44}\mathrm{Ti}$ activity of about 1.2 \ensuremath{\mu}Ci. The specific activity was measured via the 1157 keV $\ensuremath{\gamma}$ line from the decay of the $^{44}\mathrm{Sc}$ daughter. $^{44}\mathrm{Ti}$/Ti concentrations were measured with the Argonne FN tandem accelerator in conjunction with an Enge split-pole magnetic spectrograph using the technique of accelerator mass spectrometry. An overall sensitivity of ${10}^{\ensuremath{-}10}$ was achieved which proves accelerator mass spectroscopy to be a powerful tool for radioisotope detection also in a region of rather heavy ion masses. A detailed description of the subtleties of accelerator mass spectroscopy when applied to measure absolute radioisotope concentrations in this heavy mass region is presented.RADIOACTIVITY Measured half-life of $^{44}\mathrm{Ti}$ via accelerator mass spectroscopy.