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Study of -Ray Multiplicities of Evaporation Residues in Heavy Fusion Systems Using the MINIBALL Spectrometer. Sebastian Reichert TU Munich , E12. Identification of Super Heavy Elements.

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slide1

Study of-Ray Multiplicitiesof Evaporation Residues in Heavy FusionSystems UsingtheMINIBALL Spectrometer

Sebastian Reichert

TU Munich, E12

identification of super heavy elements
IdentificationofSuper Heavy Elements

GSI: Research: Super Heavy Elements. http://www.gsi.de/start/forschung/forschungsgebiete_und_experimente/ nu%starenna/ she_physik/research/ super_heavy_elements.htm

  • Isle ofStability
  • Nuclearstructure
challenges
Challenges

GSI + RIKEN

Cold Fusion: Verylittlecrosssection (pbarn)Short lifetimes (μs – ms)

γ-energiesunknown

FLNR

Hot Fusion: Higher crosssection (pbarn)Long lifetimes (ms – d)

γ-energiesunknown

aims of our work
Aimsofourwork
  • Semi-empiricalmassdependentmultiplicity
    • Application: Radon
    • Derivation andfurtherresults  Ch. Berner
  • Reductionofthebackground
    • Offline: Searchingforcoincidenesbetweeen-raysand (unknown) γ-energies
    • Online: Appropriateshieldingofthefissionphotons
slide6

Setup

  • MLL in Garching
  • Alu-chamberwith 2mm wall thickness
  • 33% spacecovering
  • Implantation plate
slide7

Mass region

Average neutronnumber

Karwowski et al. (1982): -ray- -raycoincidencemethod;

slide8

Application: Element Radon

PtO,4nRn; Beam energy: 87 MeV

slide10

PtO,4nRn

Coincidence-spectrumofthedecayofthegroundstateat.9 keV

slide11

PtO,5nRn

PtO,4nRn

  • -raycoincidencemethod
  • Rn:
  • Rn:
  • Rn:
  • -ray-raycoincidencemethod
  • Rn:
  • Rn:
slide12

Comparisonwithfurther-raymultiplicities

H. J. Karwowski, S. E. Vigdor, W.W. Jacobs, S. Kailas, P. P. Singh, F. Soga, T. G. Throwe, T. E. Ward, D. L. Wark, and J. Wiggins: Phys. Rev. C Vol. 25, No. 3 (1982).

slide13

Reductionofthebackground

  • Heavy fusionelementsand high beam energies Fusion crosssectionsdecrease, fissionincreases
  • 1. Approach: Purifyingthespectra
  • 2. Approach: Suppression ofthefissionphotons

N. Shinohara, S. Usuda et al.: Phys. Rev. C 34, 909-913 (1986).

slide14

Purifyingthespectra

ThC,xn at 67 MeV

Coincidence-spectrum: No-rays

slide15

γ- coincidentevents

ThC,xn

Coincidence-spectrum: No-rays

Gate on 981 keV: Extractionof-rays?

slide16

Suppression ofthefissionphotons

  • Geometricalconsideration
    • Evaporation residuestowards Beam direction
    • Fission productsinto
slide18

Choice offusion- andfission-peaks

NoshieldingShieldingwithslit

Improvementoftheratio: 7.2(13)

slide19

Summary

  • Application: Radon
    • Different multiplicitiesfor different methods
    • Nuclearstructure
  • Reductionofthebackground
    • Offline: Searchingfortransitionenergies
    •  Resultunclear
    • Online: Shieldingwithleadpot
    • Improvementofthefusion- tofissionratio
solution ray multiplicity1
Solution: -raymultiplicity
  • Internal conversion: Interaction betweenelect.-magn. fieldsoftheexcitednucleiwithatomicelectrons (mostlyof K-shell).
  • Vacantshell will befilledfrom an electronof an highershell Charact. X-rayradiation
  • -rayenergycalculable via Moseley‘slaw
slide21

Purifyingthespectra

ThC,xn

981 keV 973 keV

Resultunclear

slide22

Processing todeterminethemultiplicity

  • -rayCoincidencemethod
    • Setting gate on decayline
    • Out oftheoriginatedspectrum:
    • No absolut effiziencynecessary
    • Considerationofcascadeswithoutinternalconversion
slide23

-ray-raycoincidencemethod

    • Unsufficientlevelschemeand large A high multiplicity:
    • Several-rays per decay Gate
    • Distribution ofcoincidentsignalsatfixedmultiplicity
    • e.g. measurementofexactlyone-ray
    • Numbers oftwosimultaneuousmeasured-rays
slide24

-ray-raycoincidencemethod

    • Absolut efficiency necessary
    • DirtySpectrumCascadeswithat least twiceinternalconversion
    • Iflowtransitionenergiesknown
  • -ray-raycoincidencemethod
      • Gate on γ-energypurifiesspectrum
      • Applyingthe-ray-raycoincidencemethod also countscascadeswithat least oneinternalconversion
slide25

PtO,4nRn

  • -raycoincidencemethod
  • -ray-raycoincidencemethod
slide26

Reasonsforthe different results

215 MeV 219 MeV

No

R.-D. Herzberg, S. Moon et al.: Eur. Phys. J. A 42, 333–337 (2009).

P. Reiter, T. L. Khoo, T. Lauritsen, C. J. Lister et al.: Phys. Rev. Letters Vol. 84, No. 16 (2000).

slide27

Suppression ofthefissionphotons

Improvementoftheratio: 7.2(13)

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