Download presentation

Presentation is loading. Please wait.

Published byJemimah Barton Modified about 1 year ago

1
Experimental techniques to deduce J Joint ICTP-IAEA Workshop on Nuclear Structure and Decay Data Theory and Evaluation 28 April - 9 May 2008 Tibor Kibédi

2
Outline: Tibor Kibèdi, Dep. of Nuclear Physics, Australian National University ICTP-IAEA Workshop 7-May-2008 Lecture I: Experimental techniques to deduce J from Internal Conversion Coefficients Angular distributions and correlations Directional Correlations from Oriented nuclei (DCO) Lecture II: New developments in characterizing nuclei far from stability

3
Electromagnetic Decay and Nuclear Structure Tibor Kibèdi, Dep. of Nuclear Physics, Australian National University ICTP-IAEA Workshop 7-May-2008 E i J i E f J f E , L, Angular momentum and parity selection rules; multipolarities |J i - J f | ≤ L ≤ J i + J f ; L ≠ 0 J i = J f = no;E2, E4, E6 M1, M3, M5E0 = yes; E1, E3, E5 M2, M4, M6 Energetics of -decay: E i = E f + E + T r 0 = p r + p where T r = (p r ) 2 /2M; usually T r /E ~10 -5 Mixed multipolarity ( `L`) = I ( `L`) / I ( L) Multipolarity known J may not be unique unique

4
Electromagnetic decay modes Tibor Kibèdi, Dep. of Nuclear Physics, Australian National University ICTP-IAEA Workshop 7-May-2008 Angular distribution with spins oriented Angular correlations Polarization effects -ray

5
Electromagnetic decay modes Tibor Kibèdi, Dep. of Nuclear Physics, Australian National University ICTP-IAEA Workshop 7-May-2008 Electron conversion coefficients E0 transitions: L=0 electron conversion Angular distribution with spins oriented Angular correlations Polarization effects -ray K L M

6
Pair conversion coefficients E0 transitions: L=0 Electromagnetic decay modes Tibor Kibèdi, Dep. of Nuclear Physics, Australian National University ICTP-IAEA Workshop 7-May-2008 Electron conversion coefficients E0 transitions: L=0 electron conversion Angular distribution with spins oriented Angular correlations Polarization effects -ray K L M e - - e + pair Higher order effects: for example 2 photon emission is very weak

7
Angular distributions of Gamma-rays Tibor Kibèdi, Dep. of Nuclear Physics, Australian National University ICTP-IAEA Workshop 7-May-2008 Mixing ratio ( L/ `L`) = I ( `L`) / I ( L) 2 → 2 transition Mixed, L=1, L`=2

8
Angular distributions of Gamma-rays Tibor Kibèdi, Dep. of Nuclear Physics, Australian National University ICTP-IAEA Workshop 7-May-2008 Mixing ratio ( `L`) = I ( `L`) / I ( L) Mixing ratio ( L/ `L`) = I ( `L`) / I ( L) 2 → 1 transition Mixed, L=1, L`=2

9
Angular distributions of Gamma-rays Tibor Kibèdi, Dep. of Nuclear Physics, Australian National University Nuclear orientation can be achieved by interaction of external fields (E,B) with the static moments of the nuclei at low temperatures by nuclear reaction ICTP-IAEA Workshop 7-May-2008 Attenuation due to relaxation of nuclear orientation For F k (LL`J f J i ) see E. Der Mateosian and A.W. Sunyar, ADNDT 13 (1974) 391

10
Angular distributions of Gamma-rays (n,n ) reaction on 92 Zr Tibor Kibèdi, Dep. of Nuclear Physics, Australian National University ICTP-IAEA Workshop 7-May-2008 ‘ Gas Cell 3 H(p,n) @ E p = 4.9 MeV E n = 3.9 MeV Sample (41 gr) Pulsed Proton beam Tungsten Copper Lead Ring Polyethylene Annular BGO HPGe Detector n` θ = 40° - 150 ° C. Fransen, et al., PRC C71, 054304 (2005) at Univ. of Kentucky Figure courtesy of S.W. Yates

11
Angular distributions of Gamma-rays (n,n ) reaction on 92 Zr Tibor Kibèdi, Dep. of Nuclear Physics, Australian National University ICTP-IAEA Workshop 7-May-2008 ‘ C. Fransen, et al., PRC C 71, 054304 (2005), at Univ. of Kentucky Fit to data 92 Zr(n,n`) reaction 12 angles and 12 hours / angle -spectrometer at 1.4 m Deduced A 2 =A 22 /A 0 A 4 = A 44 /A 0 Typical valuesA2A4 J=2 (stretched quadrupole) +0.3-0.1 J=1 (stretched dipole) -0.20 J=1, D+Q +0.5 to -0.8>0 E = 2123.0 keV

12
Angular distributions – mixing ratio Tibor Kibèdi, Dep. of Nuclear Physics, Australian National University ICTP-IAEA Workshop 7-May-2008 ‘ Mixing ratio, deduced from 2 of as a function of But no information on Electric or Magnetic character: E1+M2 or M1+E2 = 0.69(16) (D+Q) Beam defines a symmetry axis where B k (J) is the statistical tensor Approximation with Gaussian distribution E = 2123.0 keV

13
Directional Correlations from Oriented nuclei (DCO) Tibor Kibèdi, Dep. of Nuclear Physics, Australian National University ICTP-IAEA Workshop 7-May-2008 ‘ L 2 L 2 2 J1J1 J2J2 J3J3 L 1 L 1 1 ` ` For a J 1 → J 2 → J 3 cascade (see A.E. Stuchbery, Nucl. Phys. A723 (2003) 69) 1 (k 1 ) 2 (k 2 ) xkxk ykyk zkzk

14
Directional Correlations from Oriented nuclei (DCO) example Tibor Kibèdi, Dep. of Nuclear Physics, Australian National University ICTP-IAEA Workshop 7-May-2008 ‘ 184 Pt from nat Gd + 29 Si @ 145 MeV CAESAR array (ANU) M.P. Robinson et al., Phys. Lett B530 (2002) 74 10 + 8+8+ 6+6+ 4+4+ 2+2+ 0+0+ 11 2 ( □) 2 ( ●) 2 ( ○)

15
Directional Correlations from Oriented nuclei DCO ratio Tibor Kibèdi, Dep. of Nuclear Physics, Australian National University ICTP-IAEA Workshop 7-May-2008 L 2 L 2 2 J1J1 J2J2 J3J3 L 1 L 1 1 ` ` By ignoring dependence we get 1 (k 1 ) 2 (k 2 ) xkxk ykyk zkzk DCO L 1 = L 2 1 L 1 =1 & L 2 =2~2 For stretched transitions

16
Conversion electrons (CE) Tibor Kibèdi, Dep. of Nuclear Physics, Australian National University ICTP-IAEA Workshop 7-May-2008 -ray K L M r Radial distribution of EWF free particle electron bound state electron Electron conversion Energetics of CE-decay (i=K, L, M,….) E i = E f + E ce,i + E BE,i + T r - and CE-decays are independent; transition probability T = + CE = + K + L + M …… Conversion coefficient i = CE,i /

17
The physics of conversion coefficients Tibor Kibèdi, Dep. of Nuclear Physics, Australian National University ICTP-IAEA Workshop 7-May-2008 Nuclear Electron Multipolar source Same for and CE Fermi’s golden rule bound state electron free particle electron Density of the final electron state (continuum)

18
Sensitivity to transition multipolarity Tibor Kibèdi, Dep. of Nuclear Physics, Australian National University ICTP-IAEA Workshop 7-May-2008 K NOT SELECTIVE i depends on 1)Transition energy ( E 2)Atomic number ( 3)Multipol order (L; the angular momentum carried away) 4)Electric (E ) or magnetic (M ) character 5)The shell or subshell the electron is ejected 6)Atomic screening 7)Nuclear structure effects (penetration) NOTE (3) and (4) often referred as multipolarity L)

19
Mixed multipolarity and E0 transitions Tibor Kibèdi, Dep. of Nuclear Physics, Australian National University ICTP-IAEA Workshop 7-May-2008 In some cases the mixing ratio can be deduced E0 transitions – pure penetration effect; no -rays (I =0) Pure E0 transition: 0 + → 0 + or 0 - → 0 - J → J (J≠0) transitions can be mixed E0+E2+M1

20
Tibor Kibèdi, Dep. of Nuclear Physics, Australian National University ICTP-IAEA Workshop 7-May-2008 134.363(18) keV M1+E2 transition in 172 Yb 2 (MR) hyper surface MR=1.3(3) (ENSDF) MR=1.52(24) (BrIccMixing from Chi-squared fit) MR=1.5(+12-4) (BrIccMixing from Χ 2 (MR) hyper surface) CE data 1968Ka01 K 0.63(16) 1968Ka01 L1/L2 0.62(19) 1968Ka01 L2/L3 1.3(3)

21
More on conversion coefficients Tibor Kibèdi, Dep. of Nuclear Physics, Australian National University ICTP-IAEA Workshop 7-May-2008 Conversion coefficient i = CE,i / Total conversion coefficient T K L M + ….+ K-shell L1-shell M1-shell Electron- positron pair production Z=30 (Zn) E2 Fewer electrons than -rays

22
Measuring conversion coefficients - methods Tibor Kibèdi, Dep. of Nuclear Physics, Australian National University ICTP-IAEA Workshop 7-May-2008 NPG: normalization of relative CE (I CE,i ) and (I ) intensities via intensities of one (or more) transition with known CEL: Coulomb excitation and lifetime measurement XPG: intensity ratio of K X-rays to -rays with K-fluorescent yield, K And many more, see Hamilton`s book

23
Internal Conversion Process – the Pioneers Tibor Kibèdi, Dep. of Nuclear Physics, Australian National University ICTP-IAEA Workshop 7-May-2008 May 1965, Vanderbilt University, Nashville, Tennessee T.R. Gerholm M.E. Rose J.H. Hamilton E.F. Zganjar M. Sakai E. Seltzer & R. Hager

24
Conversion electron spectroscopy with PACES Tibor Kibèdi, Dep. of Nuclear Physics, Australian National University ICTP-IAEA Workshop 7-May-2008 Based on new data, favoured interpretation is that isomer is not a high-K, but K =0 + Electrons are vital! Built by E. Zganjar, LSU channel number (0.6 keV/ch) Figure courtesy of P.M. Walker (Surrey) and P. Garrett (Guelph) K/L(E3) ~ 0.3

25
Magnetic spectrometers Tibor Kibèdi, Dep. of Nuclear Physics, Australian National University ICTP-IAEA Workshop 7-May-2008 Mini-orange (looks like a peeled orange) transmission > 20% small size and portability, but poorer quality Superconducting solenoid Broad-range mode – 100 keV up to a few MeV Lens mode – finite transmitted momentum bandwidth ( p/p~15-25%) – high peak-to-background ratio ATOMKI, Debrecen

26
Super-e Lens (ANU) Tibor Kibèdi, Dep. of Nuclear Physics, Australian National University ICTP-IAEA Workshop 7-May-2008

27
Tibor Kibèdi, Dep. of Nuclear Physics, Australian National University ICTP-IAEA Workshop 7-May-2008 Super-e Lens (ANU) 194 Pt( 12 C,4n) 202 Po @ 76 MeV Pulsed beams (~1 ns) with 1.7 s separation

28
The SACRED Electron Spectrometer (Liverpool-JYFL) Tibor Kibèdi, Dep. of Nuclear Physics, Australian National University ICTP-IAEA Workshop 7-May-2008 H. Kankaanpää et al., NIM A534 (2004) 503 see also P.A. Butler et al., NIM A381 (1996) 433

29
The SACRED array example Tibor Kibèdi, Dep. of Nuclear Physics, Australian National University ICTP-IAEA Workshop 7-May-2008 Sacred + RITU recoil tagged CE 208 Pb( 48 Ca,2n) 254 No S. Eeckhaudt, et al., Eur. Phys. J. A 25, 605 (2005) P.A. Butler, et al., Phys. Rev. Lett. 89, 202501 (2002)

30
Super-e & Honey (ANU) Tibor Kibèdi, Dep. of Nuclear Physics, Australian National University ICTP-IAEA Workshop 7-May-2008 Electrons from atomic collisions are the major difficulty in low energy CE spectroscopy using ion induced reactions HPGe

31
Super-e Honey (ANU) ee coincidences Tibor Kibèdi, Dep. of Nuclear Physics, Australian National University ICTP-IAEA Workshop 7-May-2008 63.1 LM 63.1 Gate on ALL gammas Gate on ALL CE E =63.1 keV transition not visible in the gamma spectrum T (M1) = 7.3! K-shell conversion not allowed BE K =90.5 keV 208 Pb(p,n) 208 Bi @ 9 MeV K.H. Maier et al, Phys. Rev. C 76, 064304 (2007)

32
Tibor Kibèdi, Dep. of Nuclear Physics, Australian National University ICTP-IAEA Workshop 7-May-2008 Super-e Honey (ANU) ee coincidences 538.2 63.1 LM 63.1 Gate on 538.2 keV gammas Gate on 63 LM CE Gate on 538.2 keV gammas Gate on 63 LM CE 63.1 63.1 LM

33
ICC from total intensity balances –example 1 Tibor Kibèdi, Dep. of Nuclear Physics, Australian National University ICTP-IAEA Workshop 7-May-2008 Out-of-beam (or decay) coincidence data OUT IN 228/463 1085/463

34
ICC from total intensity balances – when to use Tibor Kibèdi, Dep. of Nuclear Physics, Australian National University ICTP-IAEA Workshop 7-May-2008 K L M N Be careful near energies close to shell binding Accuracy of gamma-ray measurements controls the range of its use E1 M1 E2 M2 E3 M3 I /I ~ 10%

35
ICC from total intensity balances –example 2 Tibor Kibèdi, Dep. of Nuclear Physics, Australian National University ICTP-IAEA Workshop 7-May-2008 In-beam: only when gating from “above” 577/611 207/311 Side feeding

36
ICC from X- and -ray intensities Tibor Kibèdi, Dep. of Nuclear Physics, Australian National University ICTP-IAEA Workshop 7-May-2008 Vacancies in the atomic shell give rise to rearrangements in the shells which are accompanied by the emission of X-rays Auger electrons B Schönfeld and h. Jansen, Nucl. Instr. and Merh. in Phys. Res. A 369 (1993) 527. K x-rays: K (K-L shells) Kb (K-M, K-MN, etc. shells)

37
ICC from X- and -ray intensities Tibor Kibèdi, Dep. of Nuclear Physics, Australian National University ICTP-IAEA Workshop 7-May-2008 661.657 Ba-KX Singles gamma measurement No other photon and/or contaminates Well calibrated spectrometer Correct treatment of the photon attenuation, scattering, etc. Knowledge of the fluorescence yield N. Nica, et al. Phys. Rev. C75 (2007) 024308

38
Acknowledgements Tibor Kibèdi, Dep. of Nuclear Physics, Australian National University ICTP-IAEA Workshop 7-May-2008 G.D. Dracoulis, G.J. Lane, P. Nieminen, H. Maier (ANU) F.G. Kondev (ANL) P.E. Garrett (University of Guelph and TRIUMF) S.W. Yates (Univ. of Kentucky)

Similar presentations

© 2017 SlidePlayer.com Inc.

All rights reserved.

Ads by Google