Radioactivity at the limits of nuclear existence Zenon Janas Institute of Experimental Physics University of Warsaw
Chart of nuclei - stable - β + - β - - α - fission - p
p and 2p radioactivty proton radioactivity two-proton radioactivity - stable - β + - β - - α - fission - p
Proton radioactivity (Z, N) (Z - 1, N ) + p
History of studies of proton radioactivity 1960 prediction of possibility of p emission 2000 1p sep. energy (kev) 1500 1000 500 0-500 -1000-1500 Z=71 150 152 154 156 158 160 Mass number 175 Lu stable
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
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 2 2 2 = 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
Proton radioactivity (Z, N) (Z - 1, N ) + p V(r) neutrons protons Q p r
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
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) 20 0-10 V C V 151 p (l = 5) Lu 10 V p (l = 0) R in R out -20 10 20 30 40 50 r (fm)
WKB calculations for 151 Lu 100 (s) WK KB T 1/2 10 1 0.1 0.01 1E-3 1E-4 1E-5 151 71Lu l = 3 l = 4 l = 5 1.0 1.2 1.4 1.6 Q p (MeV)
WKB calculations for 151 Lu 100 1.24 MeV 10 1 151 71Lu WKB T (s) 1/2 0.1 0.01 1E-3 l = 3 l = 4 l = 5 T 1/2 = 0.12 s 1E-4 1E-5 1.0 1.2 1.4 1.6 Q p (MeV) WKB T1 / 2 for l p = 5 = 0. 6 exp T 1/ 2
Single-particle states MeV 0 d 3/2 82 151 Lu 71 80-5 h 11/2 s 1/2 d 5/2 g 7/2 64 50 h 9/2 Valent particles: 5 protons on h 11/2 p 5/2 2 neutrons on d 3/2 f 7/2-10 82-15 protons neutrons d 3/2 h 11/2 s 1/2
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 80 78 76 74 72 70 68 66 64 Z f P.J. Woods et al., Anu. Rev. Nucl. Part. Sci. 47 (1997) 541
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
decay spectroscopy detector Double-sided Silicon Strip Detector ions A/q = 131 / 31 + (X, E X, t) (Y, E Y, t) Typical parameters: 40 40 0.1 mm 40 40 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
Proton decay of 131 Eu 63 t = 100 ms 932 kev 131 Eu T 1/2 = 18 ms E p = 932 kev 0 + 130 Sm 0 120 hours of measurement A. Sonzogni et al., Phys. Rev. Lett. 83 (1999) 1116
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 -5-10 -15 s 1/2 d 5/2 g 7/2 64 50 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) 054315
Map of nuclear deformation 151 Lu β 2 = 0.1 131 Eu β 2 = 0.3 Z Eu
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 % 2 + 121 0 + 130 Sm 0 Systematics of E(2 + ) vs β 2 E(2 + ) = 121 kev β 2 0.35 A. Sonzogni et al., Phys. Rev. Lett. 83 (1999) 1116
WF structure of odd proton in 131 Eu 63 [ N, n ] c N, l, j π Ω,Λ z = l,j lj 100 80 70 clj 2 60 3/2 + [411] 40 Energia (M MeV) 20 0 100 80 17 10 2 d 3/2 d 5/2 g 7/2 g 9/2 2 84 clj 60 40 5/2 + [413] β 2 20 0 6 9 d 3/2 d 5/2 g 7/2 g 9/2 B.Barmore et al., Phys. Rev. C62 (2000) 054315
Calculations including deformation Lifetime 70 feeding of 2 + 40 60 T + 1/2 (0 ) (ms) 50 40 30 20 10 3/2 + [411] 5/2 + [413] I(2 + ) / I tot (%) 30 20 10 3/2 + [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
Known proton emitters 30 p-decays of ground states 15 p-decays of isomers 82 50 L. protonów 20 28 50 82 β - β + α stable decay decay decay p decay L. neutronów
p and 2p radioactivty proton radioactivity two-proton radioactivity - stable - β + - β - - α - fission - p
Two-proton radioactivity (3 isotopes) (Z, N) (Z - 2, N ) + p + p
2p emission process V(r) neutrons protons E 2p r r
Two-proton radioactivity prediction - V. Goldansky in 1960 10 Separation energy (MeV) 8 6 4 2 0-2 Z = 26 S 2p S p 45 46 47 48 49 50 51 Ene ergy 43 Cr 44 Mn 2p 45 Fe β Mass number single proton branch closed large Q β value
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
Experiment at NSCL / MSU Production: 58 Ni (161 MeV/u ) + nat Ni 45 Fe Identification in-flight: E + TOF OTPC
Ion identification 45 Fe: 2 / hour 43 Cr: 8 / min.
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
Optical Time Projection Chamber (1 3) 15 cm CCD 2/3 1000 1000 pix. 12-bits image ampl. ( 2000) 20 cm Frame Grabber Digitizer 100 MHz D A Q trigger 5 PMT
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 -1.94 MeV 13 N 12 C+ p 0 MeV PMT 200 ns K. Miernik. et al., NIM A 581(2007)194
Protons after beta decay of 13 O CCD p p 13 O 13 O PMT 4.1µs 3.7µs
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 )
2p decay of 45 Fe CCD 45 Fe 45 Fe zoom K. Miernik et al., PRL 99, 192501 (2007)
Decay scheme of 45 Fe 0-2 -4 44 Mn+p 45 Fe 43 Cr+2p β + 70% 30% 2p β + -6 Energy [MeV] -8-10 -12-14 -16-18 -20-22 β2p βp 41 Sc+2p 42 Ti+p 43 V 45 Mn β3p β2p βp 43 V+2p 42 Ti+3p 44 Cr+p
β + decay of 45 Fe 24 events βp 10 events β2p 4 events β3p K. Miernik et al., PRC 76 (2007) 041304(R)
Lifetime of 45 Fe Counts / 0.8 ms 25 20 15 10 5 T 1/2 = 2.6 ± 0.2 ms 0 0 2 4 6 8 10 12 14 16 18 Time (ms)
Partial 2p half-life of 45 Fe Γ 2p [MeV] 10 18 10 19 10 20 45 Fe 26 p 2 1.0 50.0 0.9 24.0 0.8 10.1 1.0 98.4 The fitting configuration p 2 /f 2 30/70 0.5 0.9 1.0 1.1 1.2 1.3 Q 2p [MeV] f 2 10 3 10 2 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) 054005 SMEC: J. Rotureau, J. Okołowicz, M. Płoszajczak, NPA 767 (2006) 13 R-matrix: B.A. Brown, F.C. Barker, PRC 67 (2003) 041304
p-p angular correlation 12 Uncertainties of θ included 10% p 2 24% p 2 43% p 2 Events 8 4 0 0 30 60 90 120 150 180 θ pp [deg] K. Miernik et al., PRL 99, 192501 (2007) L.V. Grigorenko and M.V. Zhukov, PRC 68 (2003) 054005
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