[Triumf-seminars] TRIUMF Seminar today at 14:00

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Date/Time: Thu 2007-03-22 at 14:00

Location:  Auditorium          

Speaker:   Kenshi Sagara (Kyushu University)

Title:     Direct measurement of 4He(12C,16O)gamma cross section

Abstract: As is well known, 4He+12C->16O+gamma reaction is very important in helium burning in stars, however, the reaction rate at the stellar energy of Ecm = 0.3 MeV has been measured yet in spite of many attempts in the world for about 40 years.  Due to resonances in 16O the cross section (S-factor) varies sharply around 0.3 MeV.  Hence we have to measure the cross section at energy as low as possible, e.g., down to 0.7 MeV where the cross section is about 1 pbarn.  

In Kyushu University tandem accelerator laboratory (KUTL), direct measurement of 4He+12C -> 16O+gamma reaction cross section is in progress.  A 12C beam is injected onto a 4He windowless target, and all the 16O recoils in a charge state are separated from the 12C beam by a recoil mass separator and are detected by a Si detector. 
   To measure the 4He+12C->16O+gamma cross section down to 0.7MeV, we need 
1) to increase the beam intensity, target thickness and detection efficiency, because 16O counts at 0.7 MeV are estimated as about 5 counts/day at most, and
2) to thoroughly reduce backgrounds, because the number of 16O recoils at 0.7MeV is 10-18 smaller than the number of 12C beam particles. 
  
   I will talk on several methods and instruments at KUTL, such as 
a) a blow-in type windowless gas target and its cooling, 
b) a new accel-decel strong-focus operation of the tandem accelerator, 
c) a recoil mass separator, and 
d) a long-time chopper to reduce backgrounds by 10-3.  
Also our recent data on 4He(12C,16O)? cross section at Ecm = 2.4 MeV will be  shown.


Stimulants available 15 minutes before the talk.

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