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Elastic resonance scattering of 13N+p and 17F+p
Nuclear Physics A 834 (2010) 100c–102c www.elsevier.com/locate/nuclphysa
Elastic resonance scattering of
13
N+p and
17
F+p
Y.B. Wanga∗ B.X. Wanga , S.J. Jina , X. Qina , X.X. Baia , W.P. Liua , Z.H. Lia , G. Liana , S. Zenga , B. Guoa , S.Q. Yana , J. Sua , Y.J. Lia , E.T. Lia , and X. Fanga a
China Institute of Atomic Energy, P.O. Box 275(46), Beijing 102413, P.R. China
The elastic resonance scattering of 13 N+p and 17 F+p has been studied in inverse kinematics via a thick-target method. The excitation function for the 13 N+p scattering was obtained in the energy interval of Ec.m. 0.5 − 3.2 MeV with a 13 N secondary beam of (47.8 ± 1.5) MeV. The resonance parameters for five low-lying levels in 14 O were deduced by R-matrix fitting calculations. In the case of 17 F+p scattering, preliminary result on the experimental excitation function is presented, in which the 4.52 MeV 3+ and 5.11 MeV 2+ states in 18 Ne are clearly discernable. 1. INTRODUCTION Nuclear Astrophysics deals with the energy generation, element synthesis during different stages of star evolution. As summarized by Smith and Rehm in 2001[1], different regions of nuclides in the chart of nuclides are connected to very different astrophysical scenarios. In general, the high temperature and high density at the very late evolution stage of massive stars will drive the reaction path from stability line to very proton or neutron-rich region. For example, in nova explosion and X-ray burst, started from the triple-α to 12 C reaction, followed by the hot CNO cycle, the thermonuclear runway will finally driven by αp- and rp- processes, the reaction flow can go up to A ∼ 100 in very short time scale. To elucidate these processes and integrate into a quantitative star model, nuclear data need a large number of (p, γ), (α, γ) and (α, p) reactions involving very proton-rich nuclei up to the proton drip line. This has been one of the main scientific motivations for the worldwide construction of next-generation RNB facilities. 13 N(p, γ)14 O and 17 F(p, γ)18 Ne are the key reactions involved in the very hot CNO cycle at T8 ∼ 3, intensive investigations have been carried out by applying various experimental methods[2–4]. Despite these efforts, ambiguities still remain even only the properties of very low-lying excited states in 14 O and 18 Ne are concerned. According to A=14 systematics, a low-lying 0− state in 14 O is missing. With 13 N+p entrance channel, the 1− (5.17 MeV) and the missing 0− state can be directly populated via a s-wave resonance. In the case of 18 Ne, there are about ten levels densely packed within 3 MeV region above the proton threshold, some of these are unclear concerning to the partial width in particular. As demonstrated in Refs. [4–6], the thick-target method is very useful for the measurement of the excitation function, the resonance parameters can be then deduced by R-matrix analysis. ∗
Corresponding author, Email: [email protected]
0375-9474/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.nuclphysa.2010.01.030
Y.B. Wang et al. / Nuclear Physics A 834 (2010) 100c–102c
101c
2. EXPERIMENT AND ANALYSIS The experiments were carried out at the radioactive secondary beam line of the HI-13 Tandem accelerator laboratory, Beijing. The 13 N and 17 F were produced via the reactions of 2 H(12 C,13 N)n and 2 H(16 O,17 F)n, respectively. The secondary beam was collimated by a φ9 to φ5 mm collimator complex to limit the beam spot size. The intensities of the 13 N and 17 F beams were about 10000 and 7500 particles/s, respectively, with a typical purity better than 75%. A schematic layout of the experimental setup is shown in Fig. 1. A 13.2 μm thin ORTEC silicon detector was used to monitor the secondary beam in front of the target. (CH2 )n foils with thickness enough to stop the 13 N and 17 F ions, respectively, were used as the reaction target, while carbon foils with equivalent thickness served for the background evaluation. The recoil protons were detected by a ΔE − E telescope, which was placed at 15◦ instead of 0◦ to avoid the direct bombardment of the DSSSD by leaked components.
Figure 1. Schematic layout of the experimental setup.
At the reaction point, the center-of-mass energy Ec.m. has a simple relation with the proton energy Ep as the following: Ec.m. = Ep ×
mp + mA , 4mA cos2 θlab
(1)
where mp and mA are the masses of proton and 13 N or 17 F, respectively. The focus of the data analysis is then to retrieve the energy loss in the target for each proton event according to laboratory scattering angle θlab . These have been done by using Monte-Carlo simulations combining energy loss and the reaction kinematics. After the Ep to Ec.m. conversion, the proton yields were added up over different θlab . Finally, the averaged differential cross section was deduced from the proton yields with the following formula,
dNp dNtarget dσ = Nbeam dE dE dΩ
dΩ,
(2)
lab
where dNp /dE refers to the net proton yield, dNtarget /dE the energy dependent hydrogen atom number.
102c
Y.B. Wang et al. / Nuclear Physics A 834 (2010) 100c–102c
3. RESULTS The performance of the detector setups was checked by a scattered 12 C beam on the (CH2 )n target, the three well-known low-lying resonances in 13 N are well reproduced with the resonance energies and widths[7]. The excitation function for the 13 N+p scattering was obtained in the energy interval of Ec.m. 0.5 − 3.2 MeV with a 13 N secondary beam of (47.8 ± 1.5) MeV. The resonance parameters for five low-lying levels in 14 O, including the new 0− state at 5.71 MeV, were deduced by R-matrix fitting calculations[8,9]. Our results show general agreement with those from a recent similar work[6]. In the case of 17 F+p scattering, preliminary result on the experimental excitation function is shown in Fig. 2, in which the 4.52 MeV 3+ and 5.11 MeV 2+ states in 18 Ne are clearly discernable. Further physics analysis is currently undertaken.
Figure 2. Preliminary excitation function of
17
F+p scattering.
4. ACKNOWLEDGEMENTS This work was supported by the Major State Basic Research Development Program under Grant No. 2007CB815003, the National Natural Science Foundation of China under Grant Nos. 10575136, 10875173, 10735100. REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9.
M. Smith and K.E. Rehm, Annu. Rev. Nucl. Part. Sci., 51(2001)91. P. Decrock et al., Phys. Rev. Lett., 67(1991)808. D.W. Bardayan et al., Phys. Rev. Lett., 83(1999)45. J. G´omez del Campo et al, Phys. Rev. Lett., 86(2001)43. T. Teranishi et al, Phys. Lett. B556(2003)27. T. Teranish et al, Phys. Lett. B650(2007)129. X. Qin et al, Chin. Phys. C32(2008)957. Y.B. Wang et al, Phys. Rev. C77(2008)044304. Y.B. Wang et al, Chin. Phys. C33(2009)181.
Elastic resonance scattering of
13
N+p and
17
F+p
Y.B. Wanga∗ B.X. Wanga , S.J. Jina , X. Qina , X.X. Baia , W.P. Liua , Z.H. Lia , G. Liana , S. Zenga , B. Guoa , S.Q. Yana , J. Sua , Y.J. Lia , E.T. Lia , and X. Fanga a
China Institute of Atomic Energy, P.O. Box 275(46), Beijing 102413, P.R. China
The elastic resonance scattering of 13 N+p and 17 F+p has been studied in inverse kinematics via a thick-target method. The excitation function for the 13 N+p scattering was obtained in the energy interval of Ec.m. 0.5 − 3.2 MeV with a 13 N secondary beam of (47.8 ± 1.5) MeV. The resonance parameters for five low-lying levels in 14 O were deduced by R-matrix fitting calculations. In the case of 17 F+p scattering, preliminary result on the experimental excitation function is presented, in which the 4.52 MeV 3+ and 5.11 MeV 2+ states in 18 Ne are clearly discernable. 1. INTRODUCTION Nuclear Astrophysics deals with the energy generation, element synthesis during different stages of star evolution. As summarized by Smith and Rehm in 2001[1], different regions of nuclides in the chart of nuclides are connected to very different astrophysical scenarios. In general, the high temperature and high density at the very late evolution stage of massive stars will drive the reaction path from stability line to very proton or neutron-rich region. For example, in nova explosion and X-ray burst, started from the triple-α to 12 C reaction, followed by the hot CNO cycle, the thermonuclear runway will finally driven by αp- and rp- processes, the reaction flow can go up to A ∼ 100 in very short time scale. To elucidate these processes and integrate into a quantitative star model, nuclear data need a large number of (p, γ), (α, γ) and (α, p) reactions involving very proton-rich nuclei up to the proton drip line. This has been one of the main scientific motivations for the worldwide construction of next-generation RNB facilities. 13 N(p, γ)14 O and 17 F(p, γ)18 Ne are the key reactions involved in the very hot CNO cycle at T8 ∼ 3, intensive investigations have been carried out by applying various experimental methods[2–4]. Despite these efforts, ambiguities still remain even only the properties of very low-lying excited states in 14 O and 18 Ne are concerned. According to A=14 systematics, a low-lying 0− state in 14 O is missing. With 13 N+p entrance channel, the 1− (5.17 MeV) and the missing 0− state can be directly populated via a s-wave resonance. In the case of 18 Ne, there are about ten levels densely packed within 3 MeV region above the proton threshold, some of these are unclear concerning to the partial width in particular. As demonstrated in Refs. [4–6], the thick-target method is very useful for the measurement of the excitation function, the resonance parameters can be then deduced by R-matrix analysis. ∗
Corresponding author, Email: [email protected]
0375-9474/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.nuclphysa.2010.01.030
Y.B. Wang et al. / Nuclear Physics A 834 (2010) 100c–102c
101c
2. EXPERIMENT AND ANALYSIS The experiments were carried out at the radioactive secondary beam line of the HI-13 Tandem accelerator laboratory, Beijing. The 13 N and 17 F were produced via the reactions of 2 H(12 C,13 N)n and 2 H(16 O,17 F)n, respectively. The secondary beam was collimated by a φ9 to φ5 mm collimator complex to limit the beam spot size. The intensities of the 13 N and 17 F beams were about 10000 and 7500 particles/s, respectively, with a typical purity better than 75%. A schematic layout of the experimental setup is shown in Fig. 1. A 13.2 μm thin ORTEC silicon detector was used to monitor the secondary beam in front of the target. (CH2 )n foils with thickness enough to stop the 13 N and 17 F ions, respectively, were used as the reaction target, while carbon foils with equivalent thickness served for the background evaluation. The recoil protons were detected by a ΔE − E telescope, which was placed at 15◦ instead of 0◦ to avoid the direct bombardment of the DSSSD by leaked components.
Figure 1. Schematic layout of the experimental setup.
At the reaction point, the center-of-mass energy Ec.m. has a simple relation with the proton energy Ep as the following: Ec.m. = Ep ×
mp + mA , 4mA cos2 θlab
(1)
where mp and mA are the masses of proton and 13 N or 17 F, respectively. The focus of the data analysis is then to retrieve the energy loss in the target for each proton event according to laboratory scattering angle θlab . These have been done by using Monte-Carlo simulations combining energy loss and the reaction kinematics. After the Ep to Ec.m. conversion, the proton yields were added up over different θlab . Finally, the averaged differential cross section was deduced from the proton yields with the following formula,
dNp dNtarget dσ = Nbeam dE dE dΩ
dΩ,
(2)
lab
where dNp /dE refers to the net proton yield, dNtarget /dE the energy dependent hydrogen atom number.
102c
Y.B. Wang et al. / Nuclear Physics A 834 (2010) 100c–102c
3. RESULTS The performance of the detector setups was checked by a scattered 12 C beam on the (CH2 )n target, the three well-known low-lying resonances in 13 N are well reproduced with the resonance energies and widths[7]. The excitation function for the 13 N+p scattering was obtained in the energy interval of Ec.m. 0.5 − 3.2 MeV with a 13 N secondary beam of (47.8 ± 1.5) MeV. The resonance parameters for five low-lying levels in 14 O, including the new 0− state at 5.71 MeV, were deduced by R-matrix fitting calculations[8,9]. Our results show general agreement with those from a recent similar work[6]. In the case of 17 F+p scattering, preliminary result on the experimental excitation function is shown in Fig. 2, in which the 4.52 MeV 3+ and 5.11 MeV 2+ states in 18 Ne are clearly discernable. Further physics analysis is currently undertaken.
Figure 2. Preliminary excitation function of
17
F+p scattering.
4. ACKNOWLEDGEMENTS This work was supported by the Major State Basic Research Development Program under Grant No. 2007CB815003, the National Natural Science Foundation of China under Grant Nos. 10575136, 10875173, 10735100. REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9.
M. Smith and K.E. Rehm, Annu. Rev. Nucl. Part. Sci., 51(2001)91. P. Decrock et al., Phys. Rev. Lett., 67(1991)808. D.W. Bardayan et al., Phys. Rev. Lett., 83(1999)45. J. G´omez del Campo et al, Phys. Rev. Lett., 86(2001)43. T. Teranishi et al, Phys. Lett. B556(2003)27. T. Teranish et al, Phys. Lett. B650(2007)129. X. Qin et al, Chin. Phys. C32(2008)957. Y.B. Wang et al, Phys. Rev. C77(2008)044304. Y.B. Wang et al, Chin. Phys. C33(2009)181.