Presentation is loading. Please wait.

Presentation is loading. Please wait.

Collective properties of even- even nuclei Vibrators and rotors With three Appendices.

Similar presentations


Presentation on theme: "Collective properties of even- even nuclei Vibrators and rotors With three Appendices."— Presentation transcript:

1 Collective properties of even- even nuclei Vibrators and rotors With three Appendices

2 What happens with both valence neutrons and protons? Case of few valence nucleons: Lowering of energies, development of multiplets. R 4/2  ~2 Vibrational modes, 1- and multi-phonon 2-particle spectra Intermediate

3 Lots of valence nucleons of both types R 4/2  ~3.33

4 B(E2; 2 +  0 + )

5 Broad perspective on structural evolution: R 4/2 Note the characteristic, repeated patterns

6 Development of collective behavior in nuclei Results primarily from correlations among valence nucleons. Instead of pure “shell model” configurations, the wave functions are mixed – linear combinations of many components. Leads to a lowering of the collective states and to enhanced transition rates as characteristic signatures. How does this happen? Consider mixing of states.

7 A illustrative special case of fundamental importance T Lowering of one state. Note that the components of its wave function are all equal and in phase Consequences of this: Lower energies for collective states, and enhanced transition rates. Lets look at the latter in a simple model.

8 W

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24 Even-even Deformed Nuclei Rotations and vibrations

25

26 Rotational states Vibrational excitations Rotational states built on(superposed on) vibrational modes Ground or equilibirum state

27 Systematics and collectivity of the lowest vibrational modes in deformed nuclei

28 E2 transitions in deformed nuclei Intraband --- STRONG, typ. ~ 200 W.u. in heavy nuclei Interband --- Collective but much weaker, typ W.u. Which bands are connected? Alaga Rules for Branching ratios

29

30 0

31 Experimental B(E2) values in deformed nuclei

32

33

34

35

36

37

38

39

40

41 How to fix the model? Note: the Alaga rules assume that each band is pure – ground or gamma, in character. What about if they MIX ?? Bandmixing formalism

42 Mixing of gamma and ground state bands

43

44

45

46 Axially Asymmetric Nuclei Two types: “gamma” soft (or “unstable”), and rigid

47 First: Gamma soft E ~  (  + 3 ) ~ J max ( J max + 6 ) Note staggering in gamma band energies

48 E ~ J ( J + 6 ) E ~ J ~ J ( J + )  E ~ J ( J + 1 ) Overview of yrast energies

49 “Gamma” rigid or Davydov model Note opposite staggering in gamma band energies

50 Use staggering in gamma band energies as signature for the kind of axial asymmetry

51

52 Appendix A on Intruder States Another form of collective mode that sometimes appears in the low lying spectrum or can even become the ground state equilibrium cofiguration

53

54 The basic idea behind Intruder States: a 2- particle - 2-hole excitation that costs energy but gains it back by added collectivity which increases with increasing valence nucleon number.

55

56 Burcu Cakirli et al. Beta decay exp. + IBA calcs.

57

58

59 Appendix B on development of collectivity and lowering of collective energies by configuration mixing

60

61 Appendix C on energies and transition rates of 3- phonon states in terms of 2- phonon state anharmonicities

62

63

64

65

66


Download ppt "Collective properties of even- even nuclei Vibrators and rotors With three Appendices."

Similar presentations


Ads by Google