Physics Colloquium? 2003.12.18

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Physics Colloquium? 2003.12.18
Nucleosyntheses studied with a Van de Graaff
Accelerator
Contents 1. Objective 2. Method 3. Germanium
detector 4. Test beam time 5. Plans 6. Summary
99-0508-5 OKA, Hiroki
Shibata Laboratory
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1. Objective
To study nucleosynthesis with a Van de Graaff
Accelerator and a germanium detector.
Nucleosyntheses
The composition ratio of elements to hydrogen
H, He, Li
Created soon after big-bang.
C, N, O to Fe
Created in stars.
Beyond Fe
Z (atomic number)
Created in supernova explosion .
V
Ti
I study nucleosynthesis like the one in stars.
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2. Method
Bombard Titanium target with proton beam.
Van de Graaff Accelerator at Tokyo Tech
Vanadium is in excited state and emits gamma ray.
The gamma rays are detected with the germanium
detector.
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1m
3. Germanium detector
A semiconductor detector.
Gamma rays make electron-hole pairs.
The pairs converted to electric current.
Measurement of energy resolution
Energy resolution is much better than that of NaI
scintillator.
Energy resolution R
Energy resolution at 1274 keV
?
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4. Test beam time
(This was a preparation for the 3rd year
students experiment as well.)
Beam Time on November 6th, 2003
Proton Beam 1.5MeV Ti Target 5µm thick
48Ti (p,?) 49V Cross Section at Ep1.5MeV
Y Number of ?-rays emitted from Vanadium I
Beam Current n Density of the Target
Nuclei x Thickness of the Target
The beam current was measured with Faraday cup.
To count the number of ?-rays emitted from
Vanadium, energy calibration, detection
efficiency, and the solid angle acceptance is
needed.
Gamma ray absorption in the target chamber wall
is needed.
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Measurement of Gamma ray absorption in the
target chamber wall.
Am241 (60 keV) Eu152 (122 keV etc.)
radiation source
detector
chamber
Target chamber is stainless steel.
Some ?-rays are absorbed in the chamber wall.
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49V Level scheme
Obtained cross section
1140.5
barn
748.3
152.9
90.6
0
There is an uncertainty originating from
background, efficiency, absorption in target
chamber wall and the beam current.
I will evaluate these uncertainties.
1140.7
90.6
152.9
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5. Plans
Veto the Compton continuum
Germanium detector and plastic scintillator
detect gamma ray in coincidence.
Anti-coincidence shielding
Ge detector
Compton scattering
?
Compton Scattering
Veto
plastic scintillator
Compton continuum will be suppressed.
Next Beam Time
Jan. 20(Tue)23(Fri), 2004
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6. Summary
The objective is to study nucleosyntheses with
a Van de Graaff Accelerator and a germanium
detector.
The germanium detectors energy resolution and
its efficiency were measured.
Gamma ray absorption in target chamber was
measured.
I had test beam time and observed
nucleosyntheses.
Beam current was measured with Faraday cup.
Cross section was evaluated.
Need to evaluate uncertainty.
I will have a 4-day beam time in January, 2004.
Try to suppress the Compton continuum.