Radioactivity at the limits of nuclear existence

Transcription

1 Radioactivity at the limits of nuclear existence Zenon Janas Institute of Experimental Physics University of Warsaw

2 Chart of nuclei - stable - β + - β - - α - fission - p

3 p and 2p radioactivty proton radioactivity two-proton radioactivity - stable - β + - β - - α - fission - p

4 Proton radioactivity (Z, N) (Z - 1, N ) + p

5 History of studies of proton radioactivity 1960 prediction of possibility of p emission p sep. energy (kev) Z= Mass number 175 Lu stable

6 History of studies of proton radioactivity 1981 observation of 151 Lu 150 Yb + p decay E p = 1233 kev T 1/2 = 85 ms b p = 70% S. Hofmann et al., Z. Phys. A305 (1982) 111

7 Proton radioactivity I (N, Z) Energy conservation π i i p j p = l p ± 1 2 I π f f (N, Z - 1) Q p = Mi c Mf c mh c = Sp > 0 Angular momentum and parity conservation r I r r = I f + p + r 1 2 π i = 1 i l ( ) p f π l

8 Proton radioactivity (Z, N) (Z - 1, N ) + p V(r) neutrons protons Q p r

9 Probability of proton emission λ p = S ν P lj S spectroscopic factor ν frequency of proton movement in nucleus ν v 2R 21 1 = 6 10 s P lj probability of barrier penetration P lj = e 2G G lj Gamow s factor lj

10 Gamow s factor R out ( V ( r) Q ) = Gl j 2 R in 2µ h p 30 ~ p dr V p (r) interaction potential V (r) = V (r) + V (r) + V(r) p N R in, R out turning points C l V p (MeV) V C V 151 p (l = 5) Lu 10 V p (l = 0) R in R out r (fm)

11 WKB calculations for 151 Lu 100 (s) WK KB T 1/ E-3 1E-4 1E Lu l = 3 l = 4 l = Q p (MeV)

12 WKB calculations for 151 Lu MeV Lu WKB T (s) 1/ E-3 l = 3 l = 4 l = 5 T 1/2 = 0.12 s 1E-4 1E Q p (MeV) WKB T1 / 2 for l p = 5 = 0. 6 exp T 1/ 2

13 Single-particle states MeV 0 d 3/ Lu h 11/2 s 1/2 d 5/2 g 7/ h 9/2 Valent particles: 5 protons on h 11/2 p 5/2 2 neutrons on d 3/2 f 7/ protons neutrons d 3/2 h 11/2 s 1/2

14 S factors for p emitters with 64 < Z < 82 filled proton orbitals : s 1/2, d 3/2 i h 11/2 S = u f 2 S ex xp 151 Lu Z f P.J. Woods et al., Anu. Rev. Nucl. Part. Sci. 47 (1997) 541

15 Proton decay of 131 Eu 63 production in fusion-evaporation reaction 78 Kr + 58 Ni 136 Gd * 131 Eu + p4n σ = 90 nb recoil mass separation (FMA Argonne) beam E r B r E r A/q target decay spectroscopy

16 decay spectroscopy detector Double-sided Silicon Strip Detector ions A/q = 131 / 31 + (X, E X, t) (Y, E Y, t) Typical parameters: mm strips Rgistration of (X, E x, t) and (Y, E Y, t) enables: determination of X and Y position energy measurement determination of implantation decay time

17 Proton decay of 131 Eu 63 t = 100 ms 932 kev 131 Eu T 1/2 = 18 ms E p = 932 kev Sm hours of measurement A. Sonzogni et al., Phys. Rev. Lett. 83 (1999) 1116

18 Single-particle states for 131 Eu 63 MeV 0 d 3/2 h 11/2 82 for transition 131 Eu(d 5/2 ) 130 Sm(0 + ) + p s 1/2 d 5/2 g 7/ protons 82 neutrons h 9/2 p 5/2 f 7/2 d 3/2 h 11/2 s 1/2 WKB l p = 2 T 1/2 = 0.5 ms S exp = 0.5 ms 18 ms = 0.02 S 2 th = u j = 0.52!!! B.Barmore et al., Phys. Rev. C62 (2000)

19 Map of nuclear deformation 151 Lu β 2 = Eu β 2 = 0.3 Z Eu

20 Fine structure in the p-decay of 131 Eu 63 t = 100 ms 932 kev 131 Eu 121 T 1/2 = 18 ms 24 % 811 kev 76 % Sm 0 Systematics of E(2 + ) vs β 2 E(2 + ) = 121 kev β A. Sonzogni et al., Phys. Rev. Lett. 83 (1999) 1116

21 WF structure of odd proton in 131 Eu 63 [ N, n ] c N, l, j π Ω,Λ z = l,j lj clj /2 + [411] 40 Energia (M MeV) d 3/2 d 5/2 g 7/2 g 9/ clj /2 + [413] β d 3/2 d 5/2 g 7/2 g 9/2 B.Barmore et al., Phys. Rev. C62 (2000)

22 Calculations including deformation Lifetime 70 feeding of T + 1/2 (0 ) (ms) /2 + [411] 5/2 + [413] I(2 + ) / I tot (%) /2 + [411] 5/2 + [413] 0 0,24 0,28 0,32 0,36 0 0,24 0,28 0,32 0,36 β 2 β 2 Conclusion: proton emission from deformed 3/2 + [411] state observed C. Davids et al., Phys. Rev. Lett. 80 (1998) 1849

23 Known proton emitters 30 p-decays of ground states 15 p-decays of isomers L. protonów β - β + α stable decay decay decay p decay L. neutronów

24 p and 2p radioactivty proton radioactivity two-proton radioactivity - stable - β + - β - - α - fission - p

25 Two-proton radioactivity (3 isotopes) (Z, N) (Z - 2, N ) + p + p

26 2p emission process V(r) neutrons protons E 2p r r

27 Two-proton radioactivity prediction - V. Goldansky in Separation energy (MeV) Z = 26 S 2p S p Ene ergy 43 Cr 44 Mn 2p 45 Fe β Mass number single proton branch closed large Q β value

28 Experimental challenges detection of individual protons energy measurement determination of angular correlation Predicted p-p opening angle for 45 Fe L. Grigorenko : simulation for 200 events

29 Experiment at NSCL / MSU Production: 58 Ni (161 MeV/u ) + nat Ni 45 Fe Identification in-flight: E + TOF OTPC

30 Ion identification 45 Fe: 2 / hour 43 Cr: 8 / min.

31 Optical Time Projection Chamber 150 V/cm v drift = 1 cm/µs 9 kv/cm 0.5 kv/cm 14 kv/cm active volume 66%He + 32%Ar gating electrode amplification CCD PMT light detection M. Ćwiok et al., IEEE TNS, 52 (2005) 2895 K. Miernik et al., NIM A581 (2007) 194

32 Optical Time Projection Chamber (1 3) 15 cm CCD 2/ pix. 12-bits image ampl. ( 2000) 20 cm Frame Grabber Digitizer 100 MHz D A Q trigger 5 PMT

33 Protons after beta decay of 13 O 13 O 3/2 - T 1/2 = 8 ms p CCD 1.59 MeV 3/2 - p 1.44 MeV 13 O MeV 13 N 12 C+ p 0 MeV PMT 200 ns K. Miernik. et al., NIM A 581(2007)194

34 Protons after beta decay of 13 O CCD p p 13 O 13 O PMT 4.1µs 3.7µs

35 Events reconstruction Z t θ Y L Z = v d t X φ PMT XY CCD L XY Track coordinates (r, Θ, φ ) L XY = r sinθ L Z = r cosθ r 2 = L XY2 + L Z 2 Θ = arctan( L XY /L Z )

36 2p decay of 45 Fe CCD 45 Fe 45 Fe zoom K. Miernik et al., PRL 99, (2007)

37 Decay scheme of 45 Fe Mn+p 45 Fe 43 Cr+2p β + 70% 30% 2p β + -6 Energy [MeV] β2p βp 41 Sc+2p 42 Ti+p 43 V 45 Mn β3p β2p βp 43 V+2p 42 Ti+3p 44 Cr+p

38 β + decay of 45 Fe 24 events βp 10 events β2p 4 events β3p K. Miernik et al., PRC 76 (2007) (R)

39 Lifetime of 45 Fe Counts / 0.8 ms T 1/2 = 2.6 ± 0.2 ms Time (ms)

40 Partial 2p half-life of 45 Fe Γ 2p [MeV] Fe 26 p The fitting configuration p 2 /f 2 30/ Q 2p [MeV] f old exp. this work SMEC R-matrix T 2p [s] 1/2 3-body model: L.V. Grigorenko and M.V. Zhukov, PRC 68 (2003) SMEC: J. Rotureau, J. Okołowicz, M. Płoszajczak, NPA 767 (2006) 13 R-matrix: B.A. Brown, F.C. Barker, PRC 67 (2003)

41 p-p angular correlation 12 Uncertainties of θ included 10% p 2 24% p 2 43% p 2 Events θ pp [deg] K. Miernik et al., PRL 99, (2007) L.V. Grigorenko and M.V. Zhukov, PRC 68 (2003)

42 Summary studies of p and 2p decays provide information on: - limits of nuclear existence - masses of exotic nuclei - sequence of single-particle states - structure of WF of nuclear states