Physics ColloquiumⅡ 　 2003.12.18

Shibata Laboratory

99-0508-5 　 OKA, Hiroki

Nucleosyntheses studied with a Van de Graaff Accelerator

[Contents]1. Objective2. Method3. Germanium detector4. Test beam time5. Plans6. Summary

1. Objective

I study nucleosynthesis like the one in stars.

H, He, Li

C, N, O to Fe Created in stars.

To study nucleosynthesis with a Van de Graaff Accelerator and a germanium detector.

・ Nucleosyntheses

Beyond Fe Z (atomic number)

Ti V

The composition ratio of elements to hydrogen

Created in supernova explosion .

Created soon after big-bang.

2. Method

p ＋ 48Ti → 49V*

γ

Bombard Titanium target with proton beam. 　

The gamma rays are detected with the germanium detector.

Vanadium is in excited state and emits gamma ray.

γ

p

Van de Graaff Accelerator at Tokyo Tech

A semiconductor detector.

Energy resolution is much better than that of NaI scintillator.

～１ｍ3. Germanium detector

Gamma rays make electron-hole pairs.

The pairs converted to electric current.

・ Measurement of energy resolution

Na22 (511 keV, 1274 keV)

Red : GeBlack: NaI

E

FWHMR

Energy resolution: R

%154.0GeR %43.6NaIR、Energy resolution at 1274 keV;

4. Test beam time

・ Beam Time on November 6th, 2003

Proton Beam 1.5MeVTi Target 5μm thick

・ 48Ti (p,γ) 49V Cross Section at Ep=1.5MeV Y : Number of γ-rays emitted from VanadiumI : Beam Current n : Density of the Target Nucleix : Thickness of the Target

To count the number of γ-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.

Y σ ・ I ・ n ・ x

(This was a preparation for the 3rd year students’ experiment as well.)

The beam current was measured with Faraday cup.

Am241 (60 keV)Eu152 (122 keV etc.)

・ Measurement of Gamma ray absorption in the target chamber wall.

γ

chamber

50 100 500

absorption

radiation source

25.11

0 exp px

ppy

Target chamber is stainless steel.

Some γ-rays are absorbed in the chamber wall.

detector

90.6 152.9

1140.7

41037.1 barn

Obtained cross section

There is an uncertainty originating from background, efficiency, absorption in target chamber wall and the beam current.

I will evaluate these uncertainties.

0

90.6

152.9

748.3

1140.5

49V Level scheme

5. Plans

Jan. 20(Tue) ～ 23(Fri), 2004

・ Next Beam Time

・ Veto the Compton continuum

Anti-coincidence shielding

Compton scatteringγ

plastic scintillator

Germanium detector and plastic scintillator detect gamma ray in coincidence.

Compton Scattering

Compton continuum will be suppressed.

Veto

Ge detector

6. Summary ・ The objective is to study nucleosyntheses with a Van de Graaff Accelerator and a germanium detector.

・ The germanium detector’s energy resolution and its efficiency were measured.

・ I had test beam time and observed nucleosyntheses.

・ I will have a 4-day beam time in January, 2004.

Cross section was evaluated.

Need to evaluate uncertainty.

Try to suppress the Compton continuum.

・ Gamma ray absorption in target chamber was measured.

Beam current was measured with Faraday cup.