Indian J. Phys. 75B(2), 105-108 (2001) I J P B — an iniemalional journal Beam-foil studies on aluminum Apama Shastri, Saraswathy Padmanabhan, B N Rajasekhar, P Meenakshi Raja Rao*, C A Desai^ and M B Kurup^ Spectroscopy Division, Bhabha Atomic Research Centre, Trombay, Mumbai-400 085, India ^Taia Institute of Fundamental Research. Homi Bhabha Road. Mumbai-400 005, India E-mail pmrr^r^apsara bare emel in Received 7 September 2000, accepted 22 January 2001 Abstract The beam-foil spectrum of aluminum was recorded m the wavelength region of 3400-4700 A, using Ar beam of energy 296 KeV Several lines belonging to Al II, Al III and A1IV were observed Lifetime measurements and excitation function studies were carried out on some of the intense lines observed Mean lifetime of the lines at 4663 A (Al II) and 3492 A (Al IV) arc being reported for the llrM lime Keywords Beam-foil spectroscopy, lifetime, excitation function FACS Nos. 32 70 Cs, 34 50 Fa 1. Introduction Beam-foil spectioscopy is a very sensitive technique for studying the lifetimes of excited states of atoms and ions. Due to the non-selective nature of the beam-foil excitation, a large number of charge states and excited levels which are not easily accessible by conventional excitation processes are populated copiously. Excitation function studies give valuable information about the charge state of the emitting species as well as the nature of interactions within the foil. The beam foil spectrum of aluminum has been studied previously by several authors. In the low energy region of 400 KeV, spectra as well as lifetimes have been studied for Al I to Al III [1-4]. A more extensive study was carried out by Weckstrdm and Nyst^n [5] at 720 KeV. They were able to observe lines belonging to Al 1 -Al VI in the wavelength region of 1800 A to 7000 A. Several excitation function studies and lifetime determinations were also carried out by them However, for many of the lines, only a single lifetime determination exists, often with large experimental errors, for some of the spectral lines, there were discrepancies in the assignment of the emitting species eg. 4654 A, which 'vas listed as belonging to Al IV by WeekstrOm e( a l [5] and as belonging to Al 11 by Kaufman et al [ 6 j. Keeping in view the important contribution of accurate data to a better understanding of the spectra, it was found worthwhile to reinvestigate the excitation functions and lifetimes of some of the spectral lines in the region 3400 A to 4700 A. 2. Experimental setup The experiments were carried out using singly ionized aluminum beams from the 400 KeV accelerator at the Tata Institute of Fundamental Research. The ions arc produced in a Nielson-type hot cathode ion source using AICI3 as the charge material and CCI4 as the carrier gas. The positive ions produced in the ion source are extracted using an extraction voltage and then focussed axially by an Einzel lens and mass analyzed by an analyzing magnet. A mass analyzed AF beam is accelerated and then focussed by a quadrupole lens before entering the target chamber. The target chamber is basically a stainless steel cross of 100 mm diameter containing the target holder assembly. It is evacuated to a pressure of 1 x 10 ^ mbar using a cryo pump to give hydrocarbon free vacuum. The target holder is a stainless steel rod with a target ladder capable of holding up to 10 carbon foils at a time. In case of foil rupture during the experiment, one can change the foil under vacuum without disturbing the other experimental conditions. The target holder can be moved vertically in order to select the foil as well as traversed horizontally by a maximum distance of 75 mm. The isotopically pure AF beam of energy 296 KeV is then made • c, ‘ ^'"csponding Author C 2001 lACS