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THE DIRECT 18O(p, γ)19F CAPTURE AND THE ANC METHOD

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Presentation on theme: "THE DIRECT 18O(p, γ)19F CAPTURE AND THE ANC METHOD"— Presentation transcript:

1 THE DIRECT 18O(p, γ)19F CAPTURE AND THE ANC METHOD
V. Burjan Nuclear Physics Institute, Řež near Prague, Czech Republic 333

2 CNO cycles (p,α) (p,γ) (p,γ) 13C 14N 17O 18F (e+,ν) (p,γ) (e+,ν) 13N
hot CNO cycle (e+,ν) (p,γ) (e+,ν) 13N 15O 17F (e+,ν) (p,γ) I (e+,ν) II III (p,γ) (p,α0,1) (p,α) 15N 12C 18O (p,γ) IV (p,γ) p capture 18O(p, γ)19F (p,α) (p,γ) 16O 19F 20Ne competing reaction: 18O(p, α)15N

3 Astrophysical significance of the 18O(p, γ)19F capture
- the 18O/16O is a unique parameter of isotopic matter in our solar system - some presolar grains incorporated in meteorites have a characteristic 18O/16O ratio ≤ 1.5 x 10-3 while the solar value is (2.09 ± 0.1) x 10-3 -the presolar grains retain the isotopic ratio of stelar layers originating during the alternating periods of hydrogen and helium burning within AGB stars in their final developing stages -the 18O(p,γ)19F capture causing the 18O depletion could play a certain role in such processes

4 DIRECT MEASUREMENT OF THE (p, γ) CAPTURE DIRECT CONTRIBUTION
Wiescher M. et al.:Nucl. Phys. A349(1980)165 E_p = 80 – 2200 keV S(E) = 15.7 – 0.34x10-3 E – 1.21x10-7 E2 (keV.b) Buckner et al. Phys. Rev. C86(2012)065804 E_p = 50 – 215 keV (LENA facility) S(E) = x10-3E – 2.6x10-7 E2 (keV.b) Astrophysical S-factor: S(E)=σ(E)Ee2πƞ, η Coulomb parameter

5 ANC METHOD A + p  B + γ 18O 19F 18O 19F(18O + p) γ 3He(d + p) p d
C2/b´2=1.19

6 -To apply ANC‘s from this reaction for determination the direct
The aim of our work was therefore to measure precisely the differential cross section of the reaction 18O( 3He, d) 19F (Q = MeV) especially at forward angles -To apply ANC‘s from this reaction for determination the direct capture cross section of 18O(p, γ)19F reaction The reaction 18O(3He,d)19F was measured by Green et al. [Nucl. Phys. A142(1970)137] E3He = 11 MeV, target tungsten oxide WO3 Schmidt and Duhm [Nucl. Phys. A155(1970)644] E3He = 16 MeV, target tungsten oxide WO3

7 The beam of the isochronous Cyclotron U120M in NPI, Řež
EXPERIMENTAL EQUIPMENT AND SETUP The beam of the isochronous Cyclotron U120M in NPI, Řež 3He-ion beam energy MeV ΔE/E ~ 5 *10-4

8 The target chamber and gas target
18O GAS CHAMBER Material: body from steel, front window foil: Ti, thickness: 2.0 μm rear window foil: HAVAR, thickness: 3.05 μm Dimensions: diameter: 124 mm height: 36 mm inner diameter: 104 mm inner height: 20 mm input slit diameters: 2mm and 2.5 mm volume: ~170 cm3 Gas: pure 18O (99 %) working pressure: 150 mbar effective thickness: ~ – particles/cm2 working temperature: ~ +23 ºC 0.2 bar 0.2 bar Angular range of gas chamber: - 45 º º

9 Beam spot r = 2 mm l = l1 + l2 l1 = 80 mm l2 = 105 mm
Slits s1 = 1 x 3 mm2 Slits s2 = 1 x 4 mm2

10 Detectors in ΔE - E telescopes
E : Si(Li) Ortec detectors 5mm ΔE: Si(Li) Ortec detectors 250 μm Resolution on the beam: ~105 keV GEOMETRY OF TELESCOPES distance from the center of the gas chamber: 185 mm (8 telescopes) detector slits: 1 x 3 mm2 on detectors and 1 x 4 mm2 at 80 mm distance from detectors Acquisition system Preamplifiers: ORTEC 142A Amplifiers: ORTEC 572 ADCs: VME system + gate generator (8 telescopes) PCs + proprietary software (list mode)

11 Data processing VME acquisition system Storage of 4k x 4k matrices ΔE‘
3He elastic peak VME acquisition system Storage of 4k x 4k matrices deuteron locus ΔE‘ Filter 4k x 4k for deuterons 1D 4k spectrum of deuterons ΔE + E

12 Spectrum of the 18O(3He, d)19F reaction
THE ANALYSIS OF MEASURED DATA FROM THE 18O(3He, d)19F REACTION Spectrum of the 18O(3He, d)19F reaction

13 Level scheme of 19F 18O(3He, d)19F, E = 24.6 MeV, Q = MeV

14 DWBA analysis of the reaction 18O(3He, d) 19F E3He = 24
DWBA analysis of the reaction 18O(3He, d) 19F E3He = 24.6 MeV Optical model potential for input channel: Fit of deuteron elastic scattering ECIS code, Raynal

15 Optical model parameters – input channel 3He + 18O
Pot V(r) (MeV) r (fm) a W rw aw Wd rd Seed A Vernotte et al. 173.7 1.15 0.67 13.8 1.849 0.772 - Our fit A 186.44 0.6335 20.84 1.4099 1.0292 Seed B Trost et al. 0.765 9.00 1.293 0.800 Our fit 1.4854 0.746 M. Vernotre et al.: Nucl. Phys. A390(1982)285 H. J. Trost et al.: Nucl. Phys. A462(1987)333 rcoul = 1.40 fm in both cases Fit by Raynal’s code ECIS Optical model parameters – outgoing channel d + 19F Watson: parameters used in paper of Crozier, PRC11(1975)393 for the reaction 17O(t, p)19O, Q= MeV, Et=12 MeV thus corresponding to our energy for departing protons. Pot V(r) (MeV) r (fm) a Wd rd ad Wso rso aso Perey & Perey 81.8 1.15 0.81 20.9 1.3400 0.68 - C. M. Perey & F. G. Perey: Atomic Data & Nucl. Data Tables 17(1976)1 rcoul = 1.15 fm

16 DWBA calculations dσ/dΩ(mb/sr) dσ/dΩ(mb/sr) Θcom(deg) Θcom(deg)

17 DWBA calculations dσ/dΩ(mb/sr) dσ/dΩ(mb/sr) Θcom(deg) Θcom(deg)

18 DWBA calculations dσ/dΩ(mb/sr) dσ/dΩ(mb/sr) Θcom(deg) Θcom(deg)

19 Some conditions for application of the ANC method:
Peripheral reaction: a) Weak dependence of dσ/dΩ on cutoff radius b) Weak R(b) dependence on the shape of the nuclear potential Single step reaction mechanism Compound nucleus contribution negligible Suitable and accurate parameters of the optical model

20 Rcutoff influence 1d5/2 transfer Δσmax(0 – 3 fm) ~ 3 % 2s1/2 transfer Δσmax(0 – 3 fm) ~ 5 % The absolute value of the main maximum of dσ/dΩ is almost constant when changing the cutoff radius of interaction in the 0 – 3 fm range for ground and MeV states

21 ro radius of the potential well
R(b) dependence ro radius of the potential well of the bound state OM parameters: 3He - fit , d - Perey

22 Table of ANCs 19F state jtr blj(fm-1/2) ANC(Clj2) (fm-1) Slj(our work)
Slj(Schmidt) g.s. (1/2+) 2s1/2 16.364 78.3 0.292 0.32 0.197 (5/2+) 1d5/2 5.1638 16.2 0.609 0.61 1.554 (3/2+) 1d3/2 3.5842 4.14 0.322 0.38 (5/2+) 1.9767 0.347 0.089 - 5.535 (5/2+) 1.7195 7.55E-2 0.026 6.088 (3/2-) 2p1/2 5.0714 8.96E-1 0.035 6.497 (3/2+) 1.1438 2.42E-2 0.019 0.05 6.787 (3/2-) 2p3/2 4.48 0.422 0.021 0.032 6.927 (7/2-) 1f7/2 0.2625 0.82E-3 0.099 0.072 7.113 (5/2+) 1.066 3.45E-2 0.030 0.022 7.54 (5/2+) 1.0907 0.464 0.39 0.332 8.014 (5/2+) 7.3883 4.23 0.077 0.065 Uncertainties

23 SPECROSCOPIC FACTORS

24 Calculations of the 18O(p, γ)19F direct radiation capture (potential model)
18O(p, γ)19F, Q = MeV, R = 3.3 fm, E1 operator Without scaling Scaled by C_lj^2/b_lj^2

25 Calculations of the 18O(p, γ)19F direct radiation capture (potential model)
18O(p, γ)19F, Q = MeV, R = 3.3 fm, E1 interaction, FRESC O code by Thompson

26 RESULTS AND CONCLUSIONS
Determination of ANCs for 12 direct captures in 18O (peripheral character of the process) Dominance of DC contributions from transitions (p –wave) to ground, 0.197, and 7.54 MeV states of 19F Similar tendency of DC contribution calculated with pure Coulomb potential S(E) = x10-3E – 8.64x10-8 E2 (keV.b) as data of Buckner et al. [Phys. Rev. C86(2012)065804] S(E) = x10-3E – 2.6x10-7 E2 (keV.b)

27 COLLABORATORS Z. Hons, V. Kroha, J. Mrázek, Š. Piskoř
Nuclear Physics Institute, Czech Academy of Sciences, Řež near Prague, Czech Republic Cyclotron Institute, Texas A & M University, College Station, TX 77843 M. La Cognata, R. G. Pizzone, S. Romano, C. Spitaleri Università di Catania and INFN Laboratori Nazionali del Sud, Catania, Italy Z. Hons, V. Kroha, J. Mrázek, Š. Piskoř A. M. Mukhamedzhanov, L. Trache, R. E. Tribble M. La Cognata, M. Gulino, L. Lamia, R. G. Pizzone, S. M. R. Puglia, G. G. Rapisarda, S. Romano, M. L. Sergi, R. Spartà, C. Spitaleri, A. Tumino

28 Thank you for attention

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