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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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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


Solution ray multiplicity
Solution: -raymultiplicity


Aims of our work
Aimsofourwork

  • Semi-empiricalmassdependentmultiplicity

    • Application: Radon

    • Derivation andfurtherresults  Ch. Berner

  • Reductionofthebackground

    • Offline: Searchingforcoincidenesbetweeen-raysand (unknown) γ-energies

    • Online: Appropriateshieldingofthefissionphotons


Setup

  • MLL in Garching

  • Alu-chamberwith 2mm wall thickness

  • 33% spacecovering

  • Implantation plate


Mass region

Average neutronnumber

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


Application: Element Radon

PtO,4nRn; Beam energy: 87 MeV


PtO,4nRn


PtO,4nRn

Coincidence-spectrumofthedecayofthegroundstateat.9 keV


PtO,5nRn

PtO,4nRn

  • -raycoincidencemethod

  • Rn:

  • Rn:

  • Rn:

  • -ray-raycoincidencemethod

  • Rn:

  • Rn:


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).


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).


Purifyingthespectra

ThC,xn at 67 MeV

Coincidence-spectrum: No-rays


γ- coincidentevents

ThC,xn

Coincidence-spectrum: No-rays

Gate on 981 keV: Extractionof-rays?


Suppression ofthefissionphotons

  • Geometricalconsideration

    • Evaporation residuestowards Beam direction

    • Fission productsinto


Suppression ofthefissionphotons


Choice offusion- andfission-peaks

NoshieldingShieldingwithslit

Improvementoftheratio: 7.2(13)


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


Purifyingthespectra

ThC,xn

981 keV 973 keV

Resultunclear


Processing todeterminethemultiplicity

  • -rayCoincidencemethod

    • Setting gate on decayline

    • Out oftheoriginatedspectrum:

    • No absolut effiziencynecessary

    • Considerationofcascadeswithoutinternalconversion


  • -ray-raycoincidencemethod

    • Unsufficientlevelschemeand large A high multiplicity:

    • Several-rays per decay Gate

    • Distribution ofcoincidentsignalsatfixedmultiplicity

    • e.g. measurementofexactlyone-ray

    • Numbers oftwosimultaneuousmeasured-rays


  • -ray-raycoincidencemethod

    • Absolut efficiency necessary

    • DirtySpectrumCascadeswithat least twiceinternalconversion

    • Iflowtransitionenergiesknown

  • -ray-raycoincidencemethod

    • Gate on γ-energypurifiesspectrum

    • Applyingthe-ray-raycoincidencemethod also countscascadeswithat least oneinternalconversion


PtO,4nRn

  • -raycoincidencemethod

  • -ray-raycoincidencemethod


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).


Suppression ofthefissionphotons

Improvementoftheratio: 7.2(13)


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