Lifetime Setup

The  lifetime  setup  for standard beam-foil  and  beam-two-foil  spectroscopy  was installed in GDA beam-line with only 10mm flight length using the plunger  used for nuclear lifetime measurement . The setup was used for lifetime measurements of  Helium and Lithium  like vanadium and nickel. Latter to increase the flight length we have made a new facility  at GPAC. This   includes three major components  which have been discussed in detail in this section.  The setup gives 80 mm of flight length  giving  access to lifetime study of metastable states up 400 ps lifetime with  ~ 3 MeV/A  energy.  The setup was commissioned a couple of years ago in  GPAC .  Recent experiments carried out  include the lifetime study of  metastable states of highly charged Titanium and Iron at various beam energies ranging from 90-170 MeV.

Rail Track Setup

Horizontal Rail Track  (HRT) is  a  solid aluminum block (240 mm *60mm *30mm) having a tapering slot at certain angle  and  rectangular at the bottom  to guide the foil  movement  along the beam  direction.  HRT  is placed  horizontally at  the  required height by  means of  three stands  fixed at the base plate of   the chamber.  The  base of the  moveable foil  stand fits  properly in the groove and moves freely. The horizontal rail arrangement is fixed to the bottom of the chamber such that  moveable foil  in the stand is horizontal and parallel to the beam axis.

Target Foil Holders

Foil Holder for single foil spectroscopy:

To carry standard beam foil  spectroscopy  the movable  foil is loaded on the  target holder. The  aluminum base  of the moveable target holder  is  coupled to the externally  controlled motorized linear motion feed through.   The aluminum base is connected  to a  rectangular  teflon holder   having a 10 mm hole at  appropriate  height  through   which  the beam passes.  The foil is actually mounted on a aluminum   holder  connected  at  the  top of  Teflon  piece.   A  viton O-ring  fixed  between the Teflon piece and   aluminum  holder  is used to align the moveable  foil at  right angle to the  beam direction.  The  only  purpose  of  using the  teflon is to  ensure the electrical insulation of the aluminum foil  holder,   which   is  an essential  requirement   for  minimum  distance  measurement in  case  of two-foil  experiments  using capacitance measurement technique.   The foil  of thickness   typically between  60-90 microgram  is floated on a  circular aluminum disc having  3 mm  hole  at  the  center,   which is stuck   on the  aluminum  holder   by using   double   sticking  tape  or  some  adhesive.  For dissipation of the   charge  collected  on  the foil  the  foil disc  is connected to  the  aluminum  holder   by  applying  silver paste  at proper positions.

Stationary Foil Holder For Two foil Spectroscopy:

The upper Lid of the chamber is fitted with a motor for the vertical movement of the lid.  Another motor  have been  installed on the lid  to control up and down moment of the target ladder connected to its shaft inside the chamber.  Arrangements were made so that  the target ladder coupled to the shaft exactly coincides  with the central axis of the chamber and to see that the shaft  is capable  of rotating about its own axis which helps in making  the foil parallel to the movable foil .  A multiple foil holder made up of  aluminum  (170mm* 20m *10mm)  is fixed to the shaft by means of a teflon piece so as to provide electrical isolation.   A slot of  of 8 mm width and 1 mm depth was made  along the breadth of this aluminum piece at each foil position. When foil holder  is fixed  in front  of this slot,  it behaves as a slit for  emerging X-rays. Multiple foil holder gives also option to study excitation mechanism  of excited states colliding with  thin carbon-foil.

Linear Motion Feed Through

To achieve fine horizontal movement, a motorized linear motion  feed through (Model MFL-275-4) and a programmable motor logic controller (Model MLC-1, programmable indexer / driver) were procured from Huntington  Laboratories Inc., Mountain View, CA 94043. The linear motion feed through has the following features : Linear travel  4  inch, Ext 6.58 inch, Ret 2.58 inch, L 14.06 inch, backlash 0.002 inch,  shaft pitch 0.125 inch and motorized accuracy 25,000 microsteps / revolution. The linear motion feed through was rigidly connected to the base of the first carbon foil holder. The distance traveled in a microstep was 0.127  micron. A Computer program (written at IUAC)  is used to control and read out its movement through a PC.