• 検索結果がありません。

RCNP C 3 1- γ M2 A A A A B B C D E, F G RCNP A, B, CYRIC C, D, E, F, G

N/A
N/A
Protected

Academic year: 2021

シェア "RCNP C 3 1- γ M2 A A A A B B C D E, F G RCNP A, B, CYRIC C, D, E, F, G"

Copied!
15
0
0

読み込み中.... (全文を見る)

全文

(1)RCNP研究会   「核子・ハイペロン多体系におけるクラスター現象」. 2013.07.27. 12C原子核における3 -状態の 1. 稀γ崩壊モード探索実験 京大理 M2 津村 美保. 足立智,天野宣昭,川畑貴裕,馬場辰雄,古野達也,小林史治,延與佳子,   民井淳A,橋本尚志A,畑中吉治A,松田洋平A,銭廣十三B,久保野茂B,   伊藤正俊C,前田幸重D,坂口聡志E,      秋宗秀俊F,藤村寿子G 阪大RCNPA,  理研B,  東北大CYRICC,  宮崎大工D,  九大理E,  甲南大理工F,  和歌山大医G  .

(2) Contents ² Physics Motivation. ² Previous experiment. ² Our test measurement. ² Plan to upgraded measurement. ² summary.

(3) Nucleosynthesis & Triple α reaction Stars are factory of nucleus. ・p-p chain : 4He production. ・A=5,8 wall are bottle neck. ・triple-alpha :12C production. Fred Hoyle proposed “3αlike” resonance excited state in 12C.. Hoyle state. 02+ (7.65 MeV) Triple a reaction is . important to synthesis . heavier nuclei..

(4) ma. helium burning proceeds -4 through the 02 state (Hoyle state) at Ex = 7.65 M 10 + The radiative decay width of the 0 state is March known -5 The Astrophysical Journal, 729:46 2(18pp), 2011 1 to be Γγ = 3.7 ± 0.5 10 At high temperature the 2 total width for this state is Γ = 8.5 ± 1.0 eV [1], thus, 4.4 × 10 The Astrophysical Journal, 729:46 (18pp), 2011 March 1. + 2 9.84 MeV + 032- states 1. relative to standard massfraction fraction mass. 9.64. −4 of th -6 10 0 9 K, the states . At T > 10 124 10 0 12 synthesize the C4 nuclei. 101 He(αα,γ) C *1 12 2 10 CF88 -1 21210 / above the Hoyle state. He(αα,γ) C * 1 2 10 4 10 MeV Angulo99 − -1 10 He(αα,γ) C * 1 2 10 CF88 Since the highly excited 3α resonances such as the 3 state at Ex = 9.64 M 10 CF88 become // 22 10 1 important. 10 -2 -2 + 10 8 + Angulo99 Angulo99 22 state at Ex = 9.8410MeV [2] locate about 2 MeV above the α-decay thres 0 1 -3 10-3 + 10. 8.87 MeV Be(2 )+α. 0 2 contribute little 10 to the triple α reaction under the normal sequence o 7.65 MeV states -4-4 10 Hoyle state revolution. However,10these highly excited resonances might play a part of t 8Be(g.s.)+α -1 -5-5 10 3α 10 MeV 7.37 4.44 MeV. + 2 1 by [3] given. relative solar relative to to standard relative to standard. reaction T9 > 1. γ at very high10temperature -6-6 9 7.27 MeV 10 12 8 10 The production rate of C in the second reaction (α+ Be) in the triple α Ni Ge Kr Zr Ru Cd Te Ba 4 12 γ 1 2Mo 10 Pd 8 Fe44He(αα,γ) Zn Se12CC*Sr He(αα,γ) 12 *1 2 10. 11 10 10 10 7 10. 10 He(αα,γ) C /*/1 22210 10 / 2 10. 6008π α8 Be 10 10 10 "σv# = 2 10µ5 α8 Be. !. µα8 Be 2πkB T. Sn. "3/2 #. Xe Ce CF88 CF88 Angulo99 CF88 Angulo99 Angulo99. ∞. σα8 Be (E) exp(−E/kB T )E dE. [Wanajo et.al., . γ The astrophys. j. . 4 -1-1 10 8 10 Co Ga of Br the Y α+ Ag Sb Cs 729,E46is(2011).]. where µα8 Be is the reduced and the energy w Mnmass Cu As Rb Nb Rh Be In system, I La 3 + 10 0 99 1 to its threshold. The reaction cross section σα8 Be is parametrized by 10 10 50 60 70 80 90 100110120130140 g.s. Ni Ge Kr Zr Ru Cd Te Ba Ba Ni Ge Kr Zr number Ru Cd Te mass 8 Fe Zn Se Sr Mo Pd Sn Xe Ce 8 Fe Zn Se Sr Mo Pd Sn Xe Ce 12C levels 12 10 $ 44He(αα,γ)12 10 C * 1 2 10 2 12 J 12 J He(αα,γ) C *1 2 10 CF88 CF88 0. eto tosolar solar. 210 10 variations π¯ h Angulo99 Γα (triple-α C , rate. E)Γγ ( C , // 2for Figure 12. Same77as Figure 2, but on the Angulo99 σα8 Be (E) 10 = (2J + 1) 10 J )2 + 1 Γ(12 CJ , (A color version of this figure is available in E the(E online journal.) 2µα8 Be −E r. 1066J=0, 2, 3. 4. E)Fig , E)2.

(5) γ transition of. 31. state. Total decay width 9.64 MeV. 3-1. Γ = Γα + Γγ = 34 keV. Γα � Γγ. Gamma decay width is still unknown. 7.65 MeV 0+2 (Hoyle state) α decay. threshold. 4.44 MeV. 2+1. known. g.s.. Γγ =Γ3− →g.s.+Γ3− →0+ →g.s. + Γ3− →2+ →g.s. 1. 2. 1. 1. ・Direct decay. E1  Measured by electron scattering.. = 0.31±0.04 meV lower limit ・Cascade decay via the Hoyle state . Contributes little to the total gamma width. ・Cascade decay via the 2+1 state might be . 100% a main decay branch.. 0+1 12C. 1. levels. Typical width of isospin forbidden . E1 transition ∼ 10 meV.

(6) Previous Experiment Measurement by 12C(α, α’ 12C) reaction. [D. Camberlin et.al., Phys.Rev.C 10, 2 (1974).]. Only to get the upper limit due to. contamination in 12C enriched target.. α. α. α beam. 12C. C target. (with 13C). γ decay 13C. α beam C target. decay 3α. Upper limit 68% CL : 4.1×10-7 (14 meV). 95% CL : 8.2×10-7 (28 meV). α decay. causes serious backgroundcontamination in 12C enriched target..

(7) Our test measurement To remove background events from 13C, . we measured the inverse kinematic CH2(12C, 12C*p) reaction.. Excited events γ decay events. α decay events. proton. proton. proton. Target. proton. Target 12C. 3a. 12C Beam. 12C Beam. Target : natCH2(Background run → natC) measured in March 2012 in RCNP. Recoiled proton : Si+CsI telescope. Scattered 12C : Grand Raiden spectrometer & Plastic Scintillator. branching ratio.

(8) Detector & Setup • natCH2(12C, 12C*p ). • Beam Energy: 250MeV. • Target: cold CH2 2mg/cm2. Si: 3mm×48mm. ×16strips×2. 325um thick. CsI: 30mm×30mm. ×4blocks×2. CsI & . ESR film. Si + CsI. (cover 31.3°∼ 42.7°). 37°. → select proton. 12C. 3°. 12C. Only a can. penetrate. α 1mm-Scintillator. → trigger 1mm 10mm. brass collimator. CH2. Target. Beam. 250MeV. Grand Raiden Spectrometer. (cover 2.5°∼3.8°) Plastic Scintillators. 1mm & 10mm. ↓. → select γ decay events.

(9) 9.64MeV. 4.44MeV. g.s.. Single(Si+CsI) ΔEx=680 keV. (FWHM). counts. results of test measurement. 12.7MeV. Coincidence (Si+CsI & GR) Our measurement(8 hours) Upper limit of branching ratio 1σ-CL. 2σ-CL Ex(MeV). branching ratio Γ =34keV. Ex(MeV). 3.87×10-6 (132meV). 1.27×10-5 (432meV). cf.) Previous experiment 1σ-CL. 2σ-CL. 4.12×10-7(14meV). 8.24×10-7(28meV). [D. Camberlin et.al., Phys.Rev.C 10, 2 (1974).].

(10) Upgraded experiment We need to accumulate more statistics and to improve the signal-to-noise ratio.. To accumulate more statistics. • Beam time 8 hours -> 10 days. • Large Si strip detector 1.7 times. Si+CsI for event tagging. To improve S/N. • Target: CH2 -> Solid Hydrogen Target. Si+CsI. … decrease background events from C. • Introduce Si+CsI detector for event tagging. … remove accidental coin events from H. • Track 12C with low-material MWDC. …select using scattering angle. detect. 12C or α. detect p. 12C. SHT. Beam. Grand Raiden spectrometer. MWDC(CH4&He) 1 mm & 10 mm. Plastic Scintilator. Target 12C. beam. True coincidence. 12C. beam. Accidental coincidence.

(11) Monte Carlo Simulation Monte Carlo Simulation was carried out considering experimental condition as below. Beam. Energy: 250 MeV(20.8 MeV/u) . Intensity: 0.1pnA. Energy spread: 0.2 MeV (sigma) . Angular spread: 2 mr (sigma, in-plane) . Spot size: 0.5 mm (sigma). Target : Solid Hydrogen Target 0.5 mm. (0.0763 g/cm2) Si+CsI detector. Angle: 35.5°. Distance from target: 125 mm. Energy resolution: 0.3 MeV (sigma). Grand Raiden spectrometer. Angle: 2.8°. Acceptance: ±14 mr (Horizontal). ±35 mr (Vertical) . ∆p/p = ±2%. Focal plane detector. Intrinsic angular resolution: 2 mr (sigma, Horizontal). 4 mr (sigma, Vertical). Detector thickness: 60 mg/cm2.

(12) Accidental coin events  from H(12C,12C*) Accidental coincidence events from 1H(12C, 12C*) , especially from . 1H(12C, 12C(4.44 MeV)), is serious. detect p. detect. 12C or α. 1st segment. (trigger,. 2 mmごと). Target 12C. beam. True coincidence. 12C. beam Accidental coincidence. 24 mm 24 mm. 2nd segment . for event tag. (6 mmごと). 128 mm. (4 mmごと). Accidental coincidence rate for each states are estimated as below: Jπ. use only 1st segment. 1st and 2nd segment. 01+(g.s.). 1.0 × 10-3 cps. 1.0 × 10-4 cps. 21+(4.44 MeV). 5.6 × 10-1 cps. 2.7 × 10-3 cps. 02+(7.65 MeV). 4.4 × 10-5 cps. 8.8 × 10-7 cps. Accidental coin events from H(12C, 12C*) can be reduced by a factor of 190 ..

(13) Background elimination gate true. φ gate using scattering azimuthal angle. φ12C ∼ φp θp θ12C. φ. γ gate Ex ∼ Eγ . = Ebeam – Ep –E12C. The φ and γ gates suppress. the accidental coincidence . events by a factor of 35.. accidental.

(14) Yield estimation Numbers of the coincidence events between proton and 12C was estimated as below. for 10 days beam time. Jπ. Γ. Γγ. Γγ/Γ. 0+1. εcoin. Number of events. 0.0. 2+1. 10.8 (6) meV. 10.8 (6) meV. 1. 0.021. 6.0 × 107. 0+2. 8.3 (10) eV. 3.7 (5) meV. 4.4 (5) × 10−4. 0.535. 8.2 × 104. 3-1. 34 (5) keV. < 14 meV. < 4.1 × 10−7. 0.753. < 2.4 × 103. >0.31±0.04meV. >9.1×10−9. Number of accidental coin events:. >54. Using Si+CsI for event tag, SHT, φ and γ gates test setup. upgraded setup. Background from H(12C,12C*). 450 k. 67. Background from X(12C, 12C*). 150 k. 104. Even if the γ decay width of 31- state is 0.31 meV (Γγ/Γ∼10-8,. lower limit) , γ decay width can be determined. .

(15) Summary • Purpose: . measure the rare γ decay width for 12C(31- → g.s.). • Our test measurement indicated the effectiveness of . using inverse kinematic reaction 1H(12C, 12C*p) .. • Detail simulation for upgraded experiment was done.. – Our upgraded experiment has sensitivity of 10-8 about Γγ/Γ . . • 2nd test measurement is scheduled in this October.. Thank you for your attention!!.

(16)

参照

関連したドキュメント

ペルフルオロオクタンスルホン酸、ペルフルオロ

Let G be a cyclic group of order n, and let (C, D, D') be a partial difference triple over G associated with a nontrivial strongly regular semi-Cayley graph F with parameters 2n, k,

One can show that if C e is a small deformation of a coassociative 4–fold C of type (a) or (b) then C e is also of type (a) or (b) and thus, Theorem 1.1 implies analogous results on

また適切な音量で音が聞 こえる音響設備を常設設 備として備えている なお、常設設備の効果が適 切に得られない場合、クラ

[r]

* 施工手順 カッター目地 10mm

Proof: The observations at the beginning of this section show for n ≥ 5 that a Moishezon twistor space, not fulfilling the conditions of Theorem 3.7, contains a real fundamental

のようにすべきだと考えていますか。 やっと開通します。長野、太田地区方面