Experimental Approach to Explosive Hydrogen Burning with Low-Energy RI Beams

Transcription

1 Hirschegg 06-1 Experimental Approach to Explosive Hydrogen Burning with Low-Energy RI Beams S. Kubono Center for Nuclear Study (CNS) University of Tokyo 1. Low Energy RI Beam Production 2. Proton Resonance Search for rp-process Nuclei 3. Direct Measurement of the αp-process Reaction 4. Other Possibilities at CNS/RIKEN

2 Nucleosynthesis Scenarios Proton X-burst H-burning αpprocess s-process 90 Th, 92 U r-process Hot pp-chain pp-chain M CNO Cycle M α- process Explosive Phenomena Neutron Number Unstable Nuclei

3 Low Energy RI Beam Production

4 How to Produce RI Beams? Low Energy High Energy ISOL LLN none -based TRIUMF Method ORNL TRIAC, In-flight Notre Dame GSI, MSU Method ANL RIKEN, GANIL CRIB/CNS Lanzhou, Not much developed!

5 Direct Method with RI Beams RIB intensities reaction type 10 4 pps Resonant scattering w/thick target method eg. 11 C+p 10 6 pps Rearrangement reactions eg. (α,p), (α,n), (d,p), pps (p,γ), (α,γ),... Total system development; 1. Ion source 2. Accelerator 3. Beam transport 3. Production target 5. Separator Kubono/ Hirschegg06

6 CNS Facilities at RIKEN (Under CNS-RIKEN joint venture) RIBF PA CRIB AVF-BT Parallel processor system (Theory/Otsuka) CNS-BT Ge AVF /HyperECR CSM AVF Upgrade Project Another Facility in RIKEN Campus Kubono/ Hirschegg06

7 AVF Upgrade Project HyperECR AVF PA CRIB BT Kubono/ Hirschegg06

8 F1: Momentum Dispersive Focal Plane -MomentumSlit - Degrader (thin foil) Degrader Low-Energy in-flight RI Beam F1 RIB ~ pps at F3 ΔE/E ~ % Purity ~ % Q RI Beam 0 5 m Separator CRIB F0 Production target F0: Production Target Gas target with window foils Primary Beam (Low-Energy HI) F2 From RIKEN AVF Cyclotron F2:Achromatic Focal Plane Experimental setup Q Q Q Q B E Wien Filter System (under construction) Wien Filter F3 F3 From AVF

9 Beam Size of 14 O at F3 Wien Filter -> 100 % 14 O of > 10 6 aps Y (mm) ~ 7 x 6 mm 2 Without a degrader Small spot size Higher order correction X (mm) Smaller RI beam spot size!

10 7 Be Beam Production at CRIB 4-MeV 7 Be beam of 6x10 6 aps available! (w/ 0.5 pμa) More beam available! ( > 50 pμa) (Limited by the production target) 7 Be(p,γ) 8 B Reaction: ; Solar model, first generation stars

11 RIB Intensity to Be Reached at CRIB Production target Primary beam intensity Upgrade the cyclotron 10 8 pps direct measurement of (p,γ) reactions Z available N 105

12 Proton Resonance Search for rp-process Nuclei

13 Elastic Resonant Scattering of p + A(RIB) (Thick target method) Y( E) = I( E) σ( E E+ Δ E/ 2 i E ΔE/ 2 ε( Ei ) ) de i I(E) : Number of beam particles ε(e) : Stopping cross sections

14 Early Stage of rp-process Breakout process from NeNa Cycle Production of 22 Na

15 PPAC1 Setup for Elastic Scattering (x1,y1) cm 22 Mg: 21 Na: 72.2 cm 6.6 cm cm Mg/ Na 2 TOF After PPAC2 4.4 AMeV 6.6 kaps (3%) 4.0 AMeV (x2,y2) cm 24.3 kaps (12%) 20 Main Background: Ne PPAC2 2 Target (CH ) φ3 cm, 90 μm (C target) 2 n p Rej cm --ΔE(75 μm, PSD) --E(1.5 cm, SSD) --E (1.5 cm, SSD)

16 Spectrum of 22 Mg+p Scattering C ounts / 35 k ev b in θlab 0 Ex: (inelastic) E (MeV) cm (elastic) 3.00 (inelastic) Expt. Calc. (inelastic) Calc. (elastic) E= x 3.13,3.29,3.00, E cm (MeV)

17 R-Matrix Fits for 3.95-MeV State dσ/ dω(b/sr) 1: 2: 3: 4: 5: 6: 7: π + J =7/2 π J =7/2 π + J =5/2 π J =5/2 π + J =3/2 π J =3/2 π J =1/2 θ cm 172 θcm 147 E (MeV) cm

18 23 Al Level Scheme in 23 Al + (7/2 ) + + (7/2,5/2 ) + + (7/2,5/2 ) (3/2 + ) Present 22 Mg+p 3.95(30) 3.26(30) 3.14(30) Shell-model + 7/2 3 3/2-1 5/2+ 3 3/2+ 3 7/2+ 2 1/2+ 2 3/2+ 2-1/ / / Mg( Li, He) 3.699(24) 3.204(21) 2.575(34) 1.773(35) 23 Al( γ, p) ; / ; Mg+p 0 + 5/ (20) (1/2 + ) 0 (5/2 + ) Al

19 R-Matrix Fitting Results E x (MeV) J π Γ p (kev) Γ p (kev) 3.00 (0.02) (5/2 +, 3/2 + ) 17 (3), 32 (5) 3.14 (0.03) (7/2, 5/2) 2 Γ p 5 30 (20) 3.26 (0.03) (7/2, 5/2) 2 Γ p 5 30 (20) 3.95 (0.03) (7/2 +, 5/2 - ) 20 (10) 30 (20)

20 Comparisons E x J π expt J π calc l Γ exp p,(p ) Γ cal p,(p ) 0.55 (1/2 + ) 1/ (3/2 + ) 3/ Good tool to study weak-coupled 32(5), 17(3) Structure! 3.00 (3/2 +, 5/2 + ) 3/ * (7/2 +, 5/2 + ) 7/ (20) * (7/2 +, 5/2 + ) 5/ (20) * (7/2 + ) 7/ (20) 18 * Their widths are for the decay branches to the 1 st states in 22 Mg. (Energy in MeV and width in kev) 44

21 Direct Measurement of the αp-process Reaction

22 High T rp-process (e.g. X-ray burst, SN) 14 O(α,p) 17 F

23 14 O(α,p) Stellar Reaction T Studied previously; Transfer reactions 20 Ne(p,t) 18 Ne 17 F(p,α) 14 O

24 Kubono/ Hirschegg06 Experimental Setup of CRIB Thick Target Method

25 Ecm( 14 O+α)[MeV] Kubono/ Hirschegg06 14 O( O(α,p) 17 F Reaction Ecm( 17 F+p) 10 6 pps

26 Astrophysical Reaction Rate 14 O+α 18 Ne * (7.05,(4+)) 17 F * +p New transitions enhance the reaction rate through the MeV level This implies the temperature at cross point of and 7.05-MeV curves reduced. B. Harss et al., PRC65 p (2002) Kubono/ Hirschegg06

27 14 O(α,p) Stellar Reaction Both 6.15 and 6.29 important Transition to 17 F*(0.495) important Branching ~ 1/2

28 Problems of the Study Need reliable total cross sections, especially those go through the states at around 6.2 MeV in 18 Ne. Need cross sections for the fist excited state in 17 F - Need clear decay-channel ID. Better experimental setup Better beams

29 Other Possibilities at CNS/RIKEN

30 RIBF Project at RIKEN 2 Linac 3 Ring Cyclotron 1 Ion Source Present facility 0 50 m 4 frc Highest-energy cyclotron Highest intensity RI beam factory r-process rp-process 5 IRC p-process... CNS-SHARAQ Under construction (2006 first beam!) 6 SuperCond.RC (8000 tons)

31 Available RI Beams at RIBF RI Beam Intensity at the RI Beams Factory 100 Primary beam of 1 pµa is assumed. Calculated by Intensity II By Nakamura 82 Proton numbers Z 50 St able Unst able limit of Tachibana Production rate ~ 10-5 /s N Neutron numbers No. of particles per second 100 Nuclear Chart 1993 by Chiharu Tanihata (from Tanihata)

32 CNS-Project: SHARAQ Spectrograph Δp/p < 1/15000 ΔΩ~10msr Bρ~6.8Tm momentum acceptance +/- 3% (Shimoura + CNS members) Length 19 m Weight > 400t

33 Subjects Understanding of the r-process: - Evolution of the Early Universe Cosmo-chronology, Mechanism of Supernovae Pathway Second, third peaks Details around the waiting points The time dependence - Mass (separation energy), Magicity, Half-life, resonances, fission process,..

34 Scope 1. Small machine facility can produce low-energy RIB of 10 8 pps. 2. Direct approach with low-energy RIB for - primordial NS, rp-process, hot pp-chain, early stage of SN will be possible in near future. 3. Very short-lived nuclei will be available at RIBF.

35 End