Facility Introduction

General

The  ion beam analysis system at LBNL is a User Facility of the Materials Sciences Division, jointly operated by the Materials Sciences and Accelerator Technology and Applied Physics Divisions, under the management of Dr. Andre Anders.   The system was installed at LBNL in 2009, primarily operated by Dr. Kin Man Yu, and maintained by Joe Wallig.  It is a complete instrument for rapid thin film analysis utilizing an energetic ion beam.  The facility is based on a model 5SDH Pelletron tandem accelerator manufactured by National Electrostatics Corporation (NEC).  Energetic alpha beam up to 5 MeV can be generated by the Pelletron with terminal voltage of up to 1.7 MV.

This instrument has the flexibility of variable beam energy from 0.6-5.1 MeV, depending on the terminal voltage setting and gas selection.  Variable beam energy allows optimization of the beam energy with respect to energy loss, the overall system resolution, and to the specific resonant reaction needed for the analysis.  Using the system as high energy also allows the investigation of low-Z elements (C, N, O) in higher-Z samples.


Accelerator (Pelletron)

The main part of the system is a NEC model 5SDH Pelletron tandem accelerator.  The accelerator produces a stable terminal voltage of up to 1.7 MV using a single metal pellet chain.  A negative ion beam from an injector at one end of the tandem is accelerated to the terminal where it is stripped in a gas canal to positive charge states which are then further accelerated to the other end of the tandem.  The high energy beam is analyzed by bending 15° in a switching magnet which insures high beam purity in the target chamber.

The negative ions are produced in an injector which uses an RF source to produce positive ions which then pass through an alkali vapor to produce negative ions.  The source parameters are controlled via manually operated control rods.  The negative ions are analyzed and focused into the tandem accelerator.

This accelerator includes electron suppression tube and x-ray shielding to insure that radiation levels are less than 2.0 mr/hr (0.02 mSv/hr) everywhere at the tank wall and to less than 0.25 mr/hr (0.0025 mSv/hr) at 1 meter from the tank wall for ion beams guaranteed.


The material analysis end station

Sample loading can be done through a target load lock in the lid of the chamber for rapid sample changing.  The target chamber is evacuated by a turbo-molecular pump after sample loading. The chamber is equipped with two particle detectors for Rutherford backscattering spectrometry (RBS) and a Si(Li) for particle induced x-ray emission measurement.  A gamma-ray detector (NaI(Tl)) is optional for gamma-ray detection for nuclear reaction analysis (NRA).  The control console provides computer-controlled data acquisition and sample manipulation.   The chamber is electrically isolated in order to be used as a Faraday cup to monitor beam current.


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