Lund Pelletron Research Articles

The charge state distribution of Be, C, Cl and Al ions at the Lund Pelletron accelerator with the recently modified terminal pumping in use

Some years ago terminal pumping for the gas stripper system at the 3 MV Lund Tandem Pelletron accelerator was installed and charge state distribution measurements using the new installation were reported. Since then, new modifications of the mechanical design of the stripper system have been made. The results of pressure profile measurements as well as the results of charge state distribution measurements in a N 2 and Ar gas stripper at different, new geometrical modifications of the stripper system using C, Be, Al and Cl ion beams are reported. A comparison between pressure profiles obtained for different geometries shows a clear improvement of the vacuum conditions outside the stripper housing for the smallest conductance pipes between the stripper system and the accelerator tubes. These improvements are also well reflected in the charge state distribution measurements, as a higher mean charge state is obtained under the same vacuum conditions in the accelerator tubes for the improved stripper system in comparison with the former mechanical design.

The pressure profile in the Lund Pelletron accelerator with the newly installed terminal pumping in use

Terminal pumping has recently been installed in the Lund tandem Pelletron electrostatic accelerator. The equipment allows a higher gas density in the stripper and an improved vacuum in the accelerator tubes compared to the former system. This improvement has led to an increased beam transmission and to superior measurements for our accelerator mass spectrometry programme. The pressure profile of the stripper system as well as of the accelerator tubes has been calculated using kinetic gas theory. The result will be used to identify possible technical improvements in the future.

Mechanical design of the recirculating, terminal pumping in the lund pelletron, and experimental experience

A recirculating terminal pumping system has been installed in the 3 MV Pelletron tandem accelerator in Lund. An extremly limited space in the high voltage terminal and the absence of electrical power in the terminal, forced us to provide a unique design for the installation and powering of the new pumps. Details of the technical design, as well as experience of the use of the new system for accelerator mass spectrometry, will be given.

The charge state distribution of a carbon beam measured at the lund pelletron accelerator with the newly installed terminal pumping system in use

Charge state distributions for 12C and 13C ions have been measured at the Lund Pelletron tandem accelerator for the N 2 gas stripper with a newly installed terminal pumping system in use. A comparison of the results obtained for the ion energies between 1.5 and 2.8 MeV with the foil stripper and the gas stripper without terminal pumping demonstrates the great improvement of the stripping process achieved with the new terminal pumping.

Some examples of the application of an analitical technique to ion-optical calculations for a new injector of the Lund Pelletron accelerator

The 3UDH Pelletron tandem accelerator in Lund is being developed to be more suitable for accelerator mass spectrometry of heavy ions. This development includes the installation of an electrostatic and a magnetic analyzer in a new injector aimed to obtain better mass and energy separation. In the present paper some applications of the first-order analytical calculation technique, used at the design stage of the new injector, are discussed. The estimation of the maximum possible opening of the analyzer slits was carried out, followed by the calculation of the analyzer acceptances. The values of the acceptances for the two transversal planes, as well as their contours are given. Some results of more detailed numerical calculation of the ion beam transport through the analyzers are reported.

Development of Accelerator Mass Spectrometry at the Lund Pelletron

Accelerator mass spectrometry (AMS) is a highly sensitive method for counting atoms. It is used for detecting very low concentrations of both radionuclides and stable nuclides. The main advantages of AMS compared to conventional radiometric methods are the use of smaller samples (mg size) and shorter measuring times (less than one hour). In AMS, rare isotopes from a sample material placed in the ion source of an electrostatic tandem accelerator are measured by counting individual atoms with nuclear detection techniques after acceleration to energies in the MeV range. A dramatic improvement in background rejection for AMS systems has, in the best cases, led to a 108 increase in sensitivity for isotope ratio measurements compared to the older technique of mass spectrometry. In this report some current applications of the AMS technique at the Lund Pelletron accelerator, as well as the recent improvements of the Lund system, are presented.

New design of an ion source for accelerator mass spectrometry at the Lund Pelletron

The requirements for negative ion sources designed for accelerator mass spectrometry (AMS) are, e.g., a high and stable beam current, a high efficiency, a low memory effect, and a quick system for switching between different samples. For the AMS program at the Lund 3 MV Pelletron tandem accelerator a new caesium sputtering source was constructed and installed a few years ago. Some new mechanical features of the source, as well as tests of how well the requirements are fulfilled are reported.

The transmission of a carbon beam through a tandem accelerator

The charge state distribution and the transmission of a carbon beam through the Lund Pelletron accelerator have been measured, both under foil-stripping and gas-stripping conditions. The transmission and charge state distribution have also been calculated. The calculations seem to describe the charge exchange processes in the accelerator system quite well. The results will be used to optimize the present AMS setup and also give guidelines for future improvements.

The pressure profile in the Lund Pelletron accelerator

The pressure profile in the Lund Pelletron tandem accelerator has been calculated based on the gas kinetic theory. The results show the limitation of the present gas-stripper setup. A new stripper design that allows higher gas density in the stripper and improved vacuum in the accelerator tubes in presented. This will lead to improved transmission through the accelerator system when the gas stripper is used.

Accelerator mass spectrometry analysis of aroma compound absorption in plastic packaging materials

Absorption of aroma compounds in plastic packaging materials may affect the taste of the packaged food and it may also change the quality of the packaging material. A method to determine the aroma compound absorption in polymers by accelerator mass spectrometry (AMS) is being developed at the Lund Pelletron AMS facility. The high sensitivity of the AMS method makes it possible to study these phenomena under realistic conditions. As a first test low density polyethylene exposed to 14C-doped ethyl acetate is examined. After converting the polymer samples with the absorbed aroma compounds to graphite, the 14C 13C ratio of the samples is measured by the AMS system and the degree of aroma compound absorption is established. The results are compared with those obtained by supercritical fluid extraction coupled to gas chromatography (SFE-GC).

The charge state distributions of carbon beams measured at the Lund Pelletron accelerator

The equilibrium charge state distributions for 1.7–2.8 MeV 12C and 13C ions stripped in the high voltage terminal of a tandem accelerator have been measured just in front of the analysing magnet. The results are compared with earlier reported measurements using external stripper mediums and with calculated charge state distributions.

Calculations of the beam transport through the low energy side of the Lund Pelletron accelerator

A new recursive technique has been used to solve the equations of motion of charged particles in electric and magnetic fields taking into account the effect of space charge. Based on this technique a computer code has been written and calculations have been carried out for the beam optics, from the ion-source to the terminal stripper of the Lund Pelletron tandem accelerator. The code has been found capable of describing the beam-optics of the existing setup and will in future be used together with a library of typical field descriptions to design new beam lines.

The effect of space charge on beam transport through the injection system of the Lund Pelletron accelerator

A new recursive technique is used for the solution of the equations of motion for charged particles, taking into account the effect of space charge. The paraxial equations are solved for an infinitely long beam with an elliptical cross-section in a static electric field. An effective computer code, based on the method of a continuous generalized analogue of the Gauss brackets and on the method of the envelope matrix, has been written. The code has been used to study the beam dynamics in the injection system of the Pelletron electrostatic accelerator in Lund.

A new design for the low-energy optics of the Lund Pelletron accelerator

Several improvements have been implemented on the low-energy side of the Lund 3UDH Pelletron tandem accelerator. We report on the use of an ANIS sputtering source, the installation of a new injector with two legs and the rebuilding of the low-energy optics between sources and accelerator. New lenses have been placed at optimuum positions which, together with a higher pump capacity. increased the beamtransmission. Angular misalignment of the beam has been minimized by repositioning steerers and profile monitors.