Spectroscopy of 17C via one-neutron knockout reaction

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dc.description학위논문(박사)--서울대학교 대학원 :자연과학대학 물리학부,2015. 8. 최선호.-
dc.description.abstractThe great interest in unique features of the neutron-rich nuclei which are anticipated to play a key role in the neutron capture processes has heightened the need for experimental investigation of the nuclear properties such as masses, lifetimes, and reaction rates. In the present work, we focus on the measurement of excited states in 17C and the assignment of their spin-parities (Jπ).

The low-lying excited states of 17C below the neutron separation energy have been well established with de?nite Jπ [1]. For unbound states of 17C, however, a few experiments have been carried out. Negative parity states were found at the excitation energies (Ex) of 2.71(2), 3.93(2), and 4.05(2) MeV with Jπ = 1/2?, 3/2?, and (5/2?), respectively, by β-delayed neutron measurement [2] while positive parity states were observed at Ex = 2.20(3), 3.05(3), and 6.13(9) MeV with Jπ = 7/2+, 9/2+, and 5/2+, respectively, by proton inelastic scattering [3].

In this measurement, the spectroscopy of 17C was conducted via one-neutron knockout reaction capable of removing an inner neutron with a large momentum transfer and large cross section. The nucleon knockout reaction allows us to derive the orbital angular momentum of the removal nucleon by comparison of the parallel or the transverse momentum distributions between the data and the model calculation. The experiment was performed during the first physics runs of SAMURAI spectrometer [4] at RIBF in RIKEN. By one-neutron knockout reaction of 18C on a carbon target, three unbound states at the excitation energies (Ex) of 2.66(2), 3.16(5), and 3.97(3) MeV and a bound state at Ex = 321.3(18) keV in 17C were measured. To determine the orbital angular momenta (L) of them, the parallel and transverse momentum distributions were illustrated and compared with calculated distributions. As the results, two unbound states at Ex = 2.66(2) and 3.97(3) MeV were confirmed as L = 1 while the bound state was well described by the calculated distribution of L = 2. For the unbound state at Ex = 3.16(5) MeV, Jπ was assigned as 9/2+ state by the calculation of the decay width.

[1]Y. Kondo et al.: Phys. Rev. C 79 (2009) 014602.
[2]H. Ueno et al.: Phys. Rev. C 87 (2013) 034316.
[3]Y. Satou et al.: Phys. Lett. B 660 (2008) 320.
[4]T. Kobayashi et al.: Nucl. Instrum. Methods Phys. Res., Sect. B 317 (2013) 294.
dc.description.tableofcontents1 Introduction
1.1 One-neutron knockout reaction
1.1.1 One-neutron knockout reaction
1.1.2 Eikonal reaction theory
1.1.3 One-neutron knockout cross section calculation
1.2 Invariant mass spectroscopy
1.3 Previous experiments
1.4 Theoretical research

2 Experimental apparatus
2.1 Superconducting dipole magnet
2.2 Detectors
2.2.1 Beam proportional chamber (BPC)
2.2.2 Ion chamber for beam (ICB)
2.2.3 Beam drift chamber 1 and 2 (BDC1, BDC2)
2.2.4 Forward drift chamber 1 (FDC1)
2.2.5 Forward drift chamber 2 (FDC2)
2.2.6 Hodoscope for fragments (HOD)
2.2.7 Neutron detector NEBULA
2.2.8 DALI2
2.3 Trigger and electronics

3 Data Analysis
3.1 Beam analysis
3.1.1 Beam production
3.1.2 Bρ by a beam proportional chamber (BPC)
3.1.3 TOF by plastic detectors at F7 and F13
3.1.4 ?E by an ion chamber for beams (ICB)
3.1.5 Calibration of atomic number Z and mass number A
3.1.6 Beam drift chambers (BDC1 and BDC2)
3.2 Fragment analysis
3.2.1 Forward drift chambers (FDC1 and FDC2)
3.2.2 Bρ by matrix elements in the magnet
3.2.3 ?E by hodoscope for fragments (HOD)
3.2.4 TOF by hodoscope for fragments(HOD)
3.2.5 Calibration of atomic number Z and mass number A.
3.3 Neutron analysis
3.3.1 Timing and position calibration
3.3.2 Pulse height calibration
3.3.3 Velocity comparison between fragments and neutrons
3.3.4 Acceptance correction
3.4 γ-ray analysis
3.4.1 Calibration
3.4.2 Efficiency of DALI2
3.4.3 Measured photo-peaks and response generation
3.5 Detection efficiency of NEBULA
3.6 Response function for resonances
3.7 Relative energy spectrum
3.8 Systematic error
3.8.1 Acceptance correction
3.8.2 Target thickness
3.8.3 Tracking efficiencies in FDC1 and FDC2
3.8.4 Detection efficiency of NEBULA
3.8.5 Fragment Bρ in B-field
3.8.6 Neutron TOF
3.8.7 Background shape

4 Results
4.1 Relative energy
4.2 Momentum distributions for the bound state at Ex = 321.3(18) keV
4.3 Momentum distributions for the unbound state at Erel = 1.920(1) MeV
4.4 Momentum distributions for the unbound state at Erel = 3.23(1) MeV
4.5 Momentum distributions for the unbound state at Erel = 0.66(2) MeV

5 Discussion
5.1 L assignments by momentum distributions
5.1.1 State at Ex = 2.66(2) MeV
5.1.2 State at Ex = 3.97(3) MeV
5.2 Comparison of the measurement with calculations and reported levels
5.2.1 Jπ assignment of the state at Ex = 3.16(5) MeV

6 Conclusion

A Background study by removal neutrons
A.1 Relative energy reconstruction with a fastest neutron
A.2 Reconstruction by 16C and a removal neutron
A.3 Miscellanea
A.4 Multiplicity
B Calculation in YSOX interaction
C Cross section of 2+ state in 16C
dc.format.extentxiv, 115-
dc.publisher서울대학교 대학원-
dc.subjectknockout reaction, 17C, unbound state, momentum distribution, invariant mass, SAMURAI-
dc.titleSpectroscopy of 17C via one-neutron knockout reaction-
dc.contributor.department자연과학대학 물리학부-
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College of Natural Sciences (자연과학대학)Dept. of Physics and Astronomy (물리·천문학부)Physics (물리학전공)Theses (Ph.D. / Sc.D._물리학전공)
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