Recent Progress on Developing High Quality Beams for High Resolution Measurements

Results from a development held on April 2004

• A very small energy spread of 37 keV has been achieved by the achromatic beam transport. Figure. 1 shows the spectrum of the ¹⁹⁷Au(p,p) elastic scattering which was accumulated for three hours.

Figure 1.  197Au(p,p) scattering events for measuring the beam energy spread at the laboratory angle of 8.0 deg. The target thickness is 1.7 mg/cm².

An energy resolution of 37 keV has been  achieved by the achromatic beam transport. A tail can been seen at the higher excitation-energy (low-enegy) side of the ground state peak. The tail has been fitted by a gaussian with the same width as the one of the ground state. The obtaind peak position of the tail was 55 keV which was a little bit shifted from the first excited state of 197Au at 77 keV. Thus a part of the tail was possibly coming from the beam itself. The continuous background events up to 0.6 MeV were caused by carbon and oxygen contaminants in 197Au target.
   
The width of the peaks at 0.28 and 0.56 MeV was 38 and 35 keV, respectively.
   

• Test of high-resolution measurments of proton inelastic scattering at 0 deg has been carried out by using lateral and angular dispersion matching technique.

The targets, 12C, 28Si, and 58Ni were used. Both standard focus mode and over-focus mode of the GR spectrometer were tested.

Figure 2 (3) shows the (enlarged) spectrum of the 58Ni(p,p') reaction at 0 degrees with a very small cut (+-0.05deg) of the scattering angles in the horizontal direction. In this analysis the energy resolution was as small as 20 keV.

Figure 2.  Spectrum of the 58Ni(p,p') reaction at 0 degrees.

     
     

     

     

Figure 3.  Enlarged spectrum of the 58Ni(p,p') reaction at 0 degrees. A resolution of 20 keV has been achieved. Note that the states located at excitation energies higher than the proton separation energy (Sp=8.17 MeV) may have a larger natural decay width as the excitation energy increases. The neutron separation energy is Sn=12.22 MeV.

  
Figure 4 (5) shows the (enlarged) spectrum of the 58Ni(p,p') reaction at 0 degrees with a wider cut (+-0.5deg) of the scattering angles in the horizontal direction. Background subtraction was applied by using the Y position at the focal plane.
From the figures it can be seen at least in the region of low-lying discrete states that the background events were properly subtracted. The energy resolution was around 32 keV, which is a little bit worse comparing with the figures 2 and 3. The resolution will be possibly improved by a more sophisticated analysis.

Figure 4.  Spectrum of the 58Ni(p,p') reaction at 0 degrees after background subtraction.

Figure 5. Enlarged spectrum of the 58Ni(p,p') reaction at 0 degrees after background subtraction.

Results from a development held on October 2003

 
• The highest relative energy resolution (dE/E) by the    achromatic beam transport has been obtained (Fig. 1).
       The small energy spread and emittance largely is indespensible for reliable    measurements by the dispersion matching.
          
          
                                                 
  
  

          
  

           Figure 1 : The energy resolution of 67 keV has been  obtained by the achromatic beam transport using a 420 MeV 3He beam.
  

       
  
                        
• The highest energy resolution (22 keV) of the ( ³He,t) reaction has been obtained by the dispersion   matching method (Fig. 2-5).

(Analyzed by T. Adachi)

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        Figure 2 : The energy resolution of the   ²⁷ Al(³He,t) reaction obtained by the dispersion matching method.
  
          
  
        Figure 3 : The spectorum of the ²⁷ Al(³He,t) reaction obtained by the dispersion matching method.
  
           
  
          
  
           
  
        Figure 4 : The energy resolution of the   ²⁷ Fe(³He, t) reaction obtained by the dispersion matching method.
  
          
  
        Figure 5 : The spectorum of the ²⁷ Fe(³He, t) reaction obtained by the dispersion matching method.