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Outline

Title
Abstract
Introduction
Experimental Considerations
Overview
-E -B Separation Method
Bρ-∆e-Bρ Separation Method
Atomic Background Radiation
Data Acquisition and Trigger
Data Summary
Analysis and Results
Analysis Procedure
Gamma Ray Analysis Detector Calibrations
Gamma Analysis Conditions
Experimental Results
Chapter 6 Discussion
The Background Measurement
References
All Topics
Computer Science
Computer Graphics

Sn108studied with intermediate-energy Coulomb excitation

Profile image of Samit MandalSamit Mandal

2005, Physical Review C

Abstract

In this doctoral thesis the unstable neutron-deficient 108 Sn isotope has been studied in inverse kinematics by intermediate-energy Coulomb excitation. Previously the method has been applied to measure the energy of the first excited 2 + state and its E2 decay rate in nuclei with Z < 30 only, 108 Sn being the highest-Z nucleus studied with this method. The purpose of the in-beam gamma-spectroscopy measurement described in the thesis was to measure the unknown reduced transition probability B(E2; 0 + g.s. → 2 + 1 ) in 108 Sn. The extracted B(E2) value of 0.230 (57) e 2 b 2 has been determined relative to the known value in the stable 112 Sn isotope. The experiment has been carried out at GSI with the newly RISING/FRS experimental set-up, developed within the framework of the RISING project. Secondary beams of interest ( 108 Sn, 112 Sn) at energies of around 150 MeV/nucleon impinged on a 197 Au target of 386 mg/cm 2 thickness. The projectile fragments were selected and identified using the fragment separator (FRS) and its associated particle detectors. The calorimeter telescope (CATE) was used behind the target for the channel selection as well as for measuring the scattering angle of the outgoing fragments. Gamma rays in coincidence with projectile residues were detected by the RISING Germanium-Cluster detectors. At intermediate energies, Coulomb excitation is an experimental challenge because of intense atomic background radiation and relativistic Doppler effects that have to be accounted for. With respect to these challenges, the Sn isotopes having large transition energies and short lifetimes provide a new methodological benchmark. The experimental B(E2; 0 + g.s. → 2 + 1 ) value in 108 Sn, measured for the first time, is in agreement with recent large scale shell model calculations performed with realistic effective interactions, and can be understood phenomenologically within a generalized seniority scheme model. This thesis work can be considered as bringing more insight into the investigation of E2 correlation related to core polarization studied in the vicinity of 100 Sn.

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References (148)

  1. 1 Paring and seniority in Sn isotopes . . . . . . . . . . . . . . . . . . .
  2. 2 Isomeric systematics in Sn isotopes . . . . . . . . . . . . . . . . . . .
  3. 3 Systematics of the excitation energy of the first excited 2 + state and the E2 strength B(E2; 2 + 1 → 0 + g.s. ) for the even Sn isotopes . . . . . .
  4. 1 Projectile orbit in the Coulomb field of the target nucleus . . . . . . .
  5. 2 Excitation cross sections as a function of the beam energy . . . . . .
  6. 1 Schematic layout of the RISING set-up . . . . . . . . . . . . . . . . .
  7. 2 Projectile fragmentation at relativistic energies . . . . . . . . . . . . .
  8. 3 Low energy fission process . . . . . . . . . . . . . . . . . . . . . . . .
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  16. 11 The electronic read-out scheme of the time-of-light detectors . . . . .
  17. 12 Schematic layout of a two-stage MWPC . . . . . . . . . . . . . . . .
  18. 13 Secondary beam profile at the reaction target . . . . . . . . . . . . .
  19. 14 Secondary beam velocity distribution by comparison with the primary beam velocity distribution . . . . . . . . . . . . . . . . . . . . . . . .
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  23. 18 Schematic drawing of a typical two-dimensional position sensitive CATE(Si) detector module . . . . . . . . . . . . . . . . . . . . . . . .
  24. 19 Distorted position pattern . . . . . . . . . . . . . . . . . . . . . . . .
  25. 20 Corrected position pattern . . . . . . . . . . . . . . . . . . . . . . . .
  26. 21 Theoretical position patterns . . . . . . . . . . . . . . . . . . . . . . .
  27. 22 CATE(Si) electronics . . . . . . . . . . . . . . . . . . . . . . . . . . .
  28. The CATE(CsI) detector array . . . . . . . . . . . . . . . . . . . . .
  29. 24 ∆E-E res correlation plot . . . . . . . . . . . . . . . . . . . . . . . . .
  30. 25 Doppler shift variation with the γ-ray emission angle in the laboratory frame . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
  31. 26 Uncertainty in the γ-energy measurement due to Doppler broadening 4.27 Gamma angular distribution in laboratory reference . . . . . . . . . .
  32. 28 A photograph of the RISING Ge cluster detectors . . . . . . . . . . .
  33. 29 Configuration of the 15 Ge-Cluster detectors for experiments with relativistic beams of 100 A•MeV . . . . . . . . . . . . . . . . . . . . .
  34. 30 VXI readout hardware configuration . . . . . . . . . . . . . . . . . .
  35. 31 Block diagram of the RISING DAQ system . . . . . . . . . . . . . . .
  36. 32 Time calibrator trigger (electronic scheme) . . . . . . . . . . . . . . .
  37. 33 Event synchronization online checking histograms . . . . . . . . . . .
  38. 34 Conceptual RISING trigger scheme . . . . . . . . . . . . . . . . . . .
  39. 1 108,112 Sn identification before the reaction target . . . . . . . . . . . .
  40. 2 Typical identification plot behind the reaction target using CATE . .
  41. 3 Fragment velocity distribution after the FRS . . . . . . . . . . . . . .
  42. 4 Fit of the fragment velocity dependencies . . . . . . . . . . . . . . . .
  43. 5 Velocity distributions before and after the target . . . . . . . . . . . .
  44. 6 Ge-Cluster sum time spectrum . . . . . . . . . . . . . . . . . . . . . .
  45. 7 Optimization of the prompt gamma radiation time condition . . . . .
  46. 8 Peak-to-background ratio dependence on the prompt gamma radia- tion time condition . . . . . . . . . . . . . . . . . . . . . . . . . . . .
  47. 9 Scattering angle conditions . . . . . . . . . . . . . . . . . . . . . . . .
  48. 10 "Crate-wise" data analysis results . . . . . . . . . . . . . . . . . . . .
  49. 11 Coulomb excitations γ-ray lines observed in 112,108 Sn . . . . . . . . . .
  50. 12 Four cases of background selection to determine the Coulomb excita- tion photon yield in 108 Sn and 112 Sn . . . . . . . . . . . . . . . . . . .
  51. 13 Scattering angle spectra recorded with the scaled down particles . . .
  52. predictions . . . . . . . . . . . . . . . . . . . . . . . . . .
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  54. B.1 Saturated Ge preamplifier signal by π + -induced particle background. . . .
  55. B.2 Schematic layout of the experimental set-up. . . . . . . . . . . . . . . . .
  56. B.3 Time-of-flight separation for beam particles measured at 1.12 GeV/c mo- mentum. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
  57. B.4 Background particle identification by using BaF 2 pulse shape analysis. . .
  58. 1 Performance of an array of Ge detectors in RISING . . . . . . . . . .
  59. 2 Experimental parameters for the Coulomb excitation measurements on 108,112 Sn . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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