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MP-41 Teil 2: Physik exotischer Kerne, SS-2012 MP-41 Teil 2: Physik exotischer Kerne 13.4.Einführung, Beschleuniger 20.4.Schwerionenreaktionen, Synthese.

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Presentation on theme: "MP-41 Teil 2: Physik exotischer Kerne, SS-2012 MP-41 Teil 2: Physik exotischer Kerne 13.4.Einführung, Beschleuniger 20.4.Schwerionenreaktionen, Synthese."— Presentation transcript:

1 MP-41 Teil 2: Physik exotischer Kerne, SS-2012 MP-41 Teil 2: Physik exotischer Kerne 13.4.Einführung, Beschleuniger 20.4.Schwerionenreaktionen, Synthese superschwerer Kerne (SHE) 27.4.Kernspaltung und Produktion neutronenreicher Kerne 4.5.Fragmentation zur Erzeugung exotischer Kerne 11.5.Halo-Kerne, gebundener Betazerfall, 2-Protonenzerfall 18.5.Wechselwirkung mit Materie, Detektoren 25.5.Schalenmodell 1.6.Restwechselwirkung, Seniority 8.6.Tutorium Tutorium Vibrator, Rotator, nukleare Isomere, Symmetrien 29.6.Schalenstruktur fernab der Stabilität 6.7.Tutorium Klausur

2 MP-41 Teil 2: Physik exotischer Kerne, SS-2012 Production of Radioactive Ion Beams Fragmentation primary beam time-of-flight through the fragment separator FRS ~300 ns in ~20% of all cases the fragment is excited Isomeric states can be investigated!

3 MP-41 Teil 2: Physik exotischer Kerne, SS-2012 What is a nuclear isomer? Nuclear Isomer – a long-lived excited nuclear state (T 1/2 > 1 ns) decays by emission of p, fission, cluster 1/ ~ E | | The first one discovered by O. Hahn in Berlin in 1921 – decay of 234 Pa (70 s) von Weizsacker, A. Bohr & B. Mottelson K>0 j j j K=0 J=0 J max K max J K=0 J

4 MP-41 Teil 2: Physik exotischer Kerne, SS-2012 Gamma-rays and energy levels A Z N X JiJi JfJf Gamma ray: pure electromagnetic radiation change in charge distribution: electric moments change in current: magnetic moments Emission of a gamma-ray removes energy angular momentum, L one unit L = 1, dipole M1, E1 two units L = 2, quadrupole M2, E2 parity: electric (-1) L magnetic (-1) L+1 Selection rule: |J i - J f | L |J i + J f | and 0 0 transitions are forbidden only the lowest multipolarities are probable coincidence

5 MP-41 Teil 2: Physik exotischer Kerne, SS-2012 Gamma-ray decay electric multipole magnetic multipole E1:L=1,yesE2:L=2,noE3:L=3,yesE4:L=4,noE5:L=5,yes M1:L=1,noM2:L=2,yesM3:L=3,noM4:L=4,yesM5:L=5,no dipole quadrupole octupole hexadecapole

6 MP-41 Teil 2: Physik exotischer Kerne, SS-2012 Lifetime & internal conversion relation between,T 1/2 and Internal conversion: Energy difference between states carried away by atomic electron: Internal conversion coefficients: Important for heavy nuclei, where inner electron shells are closer to the nucleus Important for low-energy transitions

7 MP-41 Teil 2: Physik exotischer Kerne, SS-2012 Partial lifetime & transition probability reduced transition probability: contains the nuclear structure information γ-ray transition probability:

8 MP-41 Teil 2: Physik exotischer Kerne, SS-2012 Quadrupole deformation deformed nucleus Dy I (from spherical shell model)

9 MP-41 Teil 2: Physik exotischer Kerne, SS-2012 Hindrance factor in gamma-ray decay Hindrance Factor: Weisskopf (W): based on spherical shell model potential Nilsson (N): based on deformed Nilsson model potential ELML E1M1 E2M2 E3M3 E4M4 E5M5 … usually an upper limit, but …

10 MP-41 Teil 2: Physik exotischer Kerne, SS-2012 K-isomers in 178 Hf deformed axially symmetric nuclei K is approximately a good quantum number each state has not only J but also K K>0 j j j K=0 178 Hf

11 MP-41 Teil 2: Physik exotischer Kerne, SS-2012 K-Isomers – the building blocks E x ~2Δ n E x ~2Δ p high-K orbitals near the Fermi surface 178 Hf 31y K=0 J K max J E1 E3

12 MP-41 Teil 2: Physik exotischer Kerne, SS-2012 Magnetic moments in 178 Hf E x ~2Δ n E x ~2Δ p proton neutron g(h 11/2 ) = 1.42 g(g 7/2 ) = 0.49 g(f 7/2 ) = g(i 13/2 )=-0.29 g(h 11/2 x g 7/2 ; 8 - ) = 1.08 g(f 7/2 x i 13/2 ) = g(8 - x 8 - ; 16 + ) = 0.36 μ = g·I = 5.76 nm 7.26±0.16 nm Hyperfine Interaction 52 (1989) 79

13 MP-41 Teil 2: Physik exotischer Kerne, SS-2012 K-isomers: Where to find them? Deformed nuclei with axially-symmetric shape High-K orbitals near the Fermi surface : 7/2[404], 9/2[514], 5/2[402] 7/2[514], 9/2[624], 5/2[512], 7/2[633] Mass 180 region : Yb (Z=70) - Ir (Z=77) K j j j

14 MP-41 Teil 2: Physik exotischer Kerne, SS-2012 K-selection rule and reduced hindrance K-isomer decay usually proceeds by minimizing ΔK K=16 K=8 K=0 ΔK=8 E3 ΔK=8 E1 Usually not this way! ΔK=16 ν = ΔK-L – degree of K-forbiddenness – hindrance factor

15 MP-41 Teil 2: Physik exotischer Kerne, SS-2012 K-selection rule and reduced hindrance K-isomer decay usually proceeds by minimizing ΔK ν = ΔK-L – degree of K-forbiddenness – hindrance factor The solid line shows the dependence of F W on ΔK for some E1 transitions i.e. F W values increase approximately by a factor of 100 per degree of K forbiddenness f ν =(F w ) 1/ν – reduced hindrance per degree of K-forbiddenness – gives yardstick for goodness of K-quantum number ΔKΔK FWFW E1

16 MP-41 Teil 2: Physik exotischer Kerne, SS-2012 K-isomer in 180 Ta 8h >10 15 a !!! The rarest natural isotope: abundance of 0.012% 0 75 keV

17 MP-41 Teil 2: Physik exotischer Kerne, SS-2012 Spin isomers ~230 ns ~170 ns E4 98 Cd A. Blazhev et al., Phys.Rev.C69 (2004)

18 MP-41 Teil 2: Physik exotischer Kerne, SS-2012 Core excited states in 98 Cd A. Blazhev et al., Phys.Rev.C69 (2004) e π = 1.3(2) e π = 1.1 GDS: F.Nowacki, Nuc. Phys. A 704 (2002) 223c ESM: H. Grawe et al., NS98 AIP CP 481 (1999) 177

19 MP-41 Teil 2: Physik exotischer Kerne, SS-2012 Shape isomers delayed fission spontaneous fission prompt fission axis ratio: For even-even nuclei bandheads I π = isomers possible decay through electron conversion Fission isomers discovered by S.M. Polikanov Sov. Phys. JETP 15 (1962) 106

20 MP-41 Teil 2: Physik exotischer Kerne, SS-2012 Shape isomers H. Specht et al. Phys.Lett. B41 (1972) U(α, 2n) 240f Pu, E α = 25 MeV conversion electrons in coincidence with delayed fission 240 Pu deformation 1. minimum 2. minimum 5.8±0.3 MeV5.5±0.3 MeV fission isomer t 1/2 =3.8 ns axis ratio: 2:1

21 MP-41 Teil 2: Physik exotischer Kerne, SS-2012 Excited states in the 2. minimum of 240 Pu γ-ray and electron data D. Gassmann et al., Phys.Lett. B497 (2001) 181

22 MP-41 Teil 2: Physik exotischer Kerne, SS-2012 Manipulating isomeric lifetimes the role of electron conversion large α leads to shorter lifetimes of nuclear states 200m Pt M. Caamano et al. Eur. Phys. J. A23 (2005) 201 t 1/2 = 14.3 nsE γ = 51 keV (α tot ~ 100)for fully stripped ions !!! 300 ns ?

23 MP-41 Teil 2: Physik exotischer Kerne, SS-2012 Manipulating isomeric lifetimes the role of electron conversion M. Caamano et al. Eur. Phys. J. A23 (2005) 201 γ-spectrum after 180 ns after prompt flash and 300 ns TOF through FRS

24 MP-41 Teil 2: Physik exotischer Kerne, SS-2012

25 K quantum number K is the projection of total angular momentum of a nucleon state on the symmetry axis, and can be used to label nuclear states K is a conserved quantum number, if -nucleus is axially deformed -the system is non-rotating Electromagnetic transitions from a state K 1 to a state K 2 change K by K = K 2 - K 1 Electromagnetic transitions of multipolarity are forbidden if K >

26 MP-41 Teil 2: Physik exotischer Kerne, SS-2012


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