Download presentation

Presentation is loading. Please wait.

1
**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-1 15.6. Tutorium-2 22.6. Vibrator, Rotator, nukleare Isomere, Symmetrien 29.6. Schalenstruktur fernab der Stabilität 6.7. Tutorium-3 Klausur

2
**Production of Radioactive Ion Beams**

Fragmentation in ~20% of all cases the fragment is excited primary beam time-of-flight through the fragment separator FRS ~300 ns Isomeric states can be investigated!

3
**What is a nuclear isomer?**

Nuclear Isomer – a long-lived excited nuclear state (T1/2 > 1 ns) decays by emission of a, b, g, p, fission, cluster The first one discovered by O. Hahn in Berlin in 1921 – decay of 234Pa (70 s) von Weizsacker, A. Bohr & B. Mottelson 1/t ~ Eg 2l+1 |< yf | T | yi >| K=0 J w Jmax J=0 Kmax J j2 j1 j K>0 K=0

4
**Gamma-rays and energy levels**

Gamma ray: pure electromagnetic radiation change in charge distribution: electric moments change in current: magnetic moments Ji 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 coincidence Jf Selection rule: |Ji - Jf| L |Ji + Jf| and 0 0 transitions are forbidden only the lowest multipolarities are probable A Z N X

5
**Gamma-ray decay electric multipole magnetic multipole dipole**

quadrupole octupole hexadecapole E1:L=1,yes E2:L=2,no E3:L=3,yes E4:L=4,no E5:L=5,yes M1:L=1,no M2:L=2,yes M3:L=3,no M4:L=4,yes M5:L=5,no

6
**Lifetime & internal conversion**

relation between t,T1/2 and l 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
**Partial lifetime & transition probability**

γ-ray transition probability: reduced transition probability: contains the nuclear structure information

8
**Quadrupole deformation**

12+ deformed nucleus 10+ I 8+ 6+ 4+ 2+ 0+ 156Dy (from spherical shell model)

9
**Hindrance factor in gamma-ray decay**

Hindrance Factor: Weisskopf (W): based on spherical shell model potential Nilsson (N): based on deformed Nilsson model potential … usually an upper limit, but … EL ML E1 M1 E2 M2 E3 M3 E4 M4 E5 M5

10
**178Hf K-isomers in 178Hf w K>0 K=0**

j2 j1 j K>0 K=0 deformed axially symmetric nuclei K is approximately a good quantum number each state has not only Jp but also K 178Hf

11
**K-Isomers – the building blocks**

31y K=0 J Kmax J E1 Ex~2Δp Ex~2Δn 178Hf high-K orbitals near the Fermi surface

12
**Magnetic moments in 178Hf Ex~2Δp Ex~2Δn proton neutron**

g(h11/2) = g(g7/2) = g(f7/2) = g(i13/2)=-0.29 g(h11/2 x g7/2; 8-) = g(f7/2 x i13/2) = -0.36 g(8- x 8-; 16+) = → μ = g·I = 5.76 nm Ex~2Δp 7.26±0.16 nm Ex~2Δn Hyperfine Interaction 52 (1989) 79

13
**K-isomers: Where to find them?**

Deformed nuclei with axially-symmetric shape Mass 180 region : Yb (Z=70) - Ir (Z=77) w K j1 j2 j High-K orbitals near the Fermi surface : 7/2[404], 9/2[514], 5/2[402] n: 7/2[514], 9/2[624], 5/2[512], 7/2[633]

14
**K-selection rule and reduced hindrance**

K-isomer decay usually proceeds by minimizing ΔK Usually not this way! ν = ΔK-L – degree of K-forbiddenness – hindrance factor ΔK=16 K=16 ΔK=8 E3 K=8 ΔK=8 E1 K=0

15
**K-selection rule and reduced hindrance**

K-isomer decay usually proceeds by minimizing ΔK ν = ΔK-L – degree of K-forbiddenness – hindrance factor ΔK The solid line shows the dependence of FW on ΔK for some E1 transitions i.e. FW values increase approximately by a factor of 100 per degree of K forbiddenness fν=(Fw)1/ν – reduced hindrance per degree of K-forbiddenness – gives yardstick for “goodness” of K-quantum number E1 FW

16
K-isomer in 180Ta 75 keV >1015a !!! 8h The rarest natural isotope: abundance of 0.012%

17
**Spin isomers 98Cd E4 ~230 ns ~170 ns**

A. Blazhev et al., Phys.Rev.C69 (2004)

18
**Core excited states in 98Cd**

GDS: F.Nowacki, Nuc. Phys. A 704 (2002) 223c ESM: H. Grawe et al., NS98 AIP CP 481 (1999) 177 A. Blazhev et al., Phys.Rev.C69 (2004)

19
**possible decay through electron conversion**

Shape isomers Fission isomers discovered by S.M. Polikanov Sov. Phys. JETP 15 (1962) 106 axis ratio: prompt fission delayed fission For even-even nuclei bandheads Iπ = 0+ 0+ → 0+ isomers possible decay through electron conversion spontaneous fission

20
**Shape isomers 240Pu 238U(α, 2n)240fPu, Eα = 25 MeV deformation**

1. minimum minimum 5.8±0.3 MeV 5.5±0.3 MeV fission isomer t1/2=3.8 ns 238U(α, 2n)240fPu, Eα = 25 MeV conversion electrons in coincidence with delayed fission axis ratio: 2:1 H. Specht et al. Phys.Lett. B41 (1972) 43

21
**Excited states in the 2. minimum of 240Pu γ-ray and electron data**

D. Gassmann et al., Phys.Lett. B497 (2001) 181

22
**Manipulating isomeric lifetimes the role of electron conversion**

large α leads to shorter lifetimes of nuclear states 200mPt t1/2 = 14.3 ns Eγ = 51 keV (αtot ~ 100) for fully stripped ions !!! ? 300 ns M. Caamano et al. Eur. Phys. J. A23 (2005) 201

23
**Manipulating isomeric lifetimes the role of electron conversion**

γ-spectrum after 180 ns after prompt flash and 300 ns TOF through FRS M. Caamano et al. Eur. Phys. J. A23 (2005) 201

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 K1 to a state K2 change K by DK = K2 - K1 Electromagnetic transitions of multipolarity l are forbidden if DK > l

Similar presentations

OK

Monday, Oct. 2, 2006PHYS 3446, Fall 2006 Jae Yu 1 PHYS 3446 – Lecture #8 Monday, Oct. 2, 2006 Dr. Jae Yu 1.Nuclear Models Shell Model Collective Model.

Monday, Oct. 2, 2006PHYS 3446, Fall 2006 Jae Yu 1 PHYS 3446 – Lecture #8 Monday, Oct. 2, 2006 Dr. Jae Yu 1.Nuclear Models Shell Model Collective Model.

© 2018 SlidePlayer.com Inc.

All rights reserved.

To make this website work, we log user data and share it with processors. To use this website, you must agree to our Privacy Policy, including cookie policy.

Ads by Google