grupo de física nuclear experimental iemiem csic curso de doctorado estructura nuclear m.j.g....

Curso de DoctoradoEstructura Nuclear M.J.G. Borge, IEM, CSIC 8 Junio 2007

Grupo de Física Nuclear Experimental

IEM

CSIC

Estudio experimental de la Estructura Nuclear:

Modos Exóticos

de DesintegraciónMª José García Borge



IEM

CSIC

The Nuclear landscape

Decay +-EC Decay -

Decay Fission

256 stable nuclei

Terra

Incógnita

4 o-o 157 e-e

104e-o

Near de Drip-line

Halo structure

Re-ordering of shells gaps

Beta asymmetry

Exotic decays

Order to Chaos



IEM

CSIC

Beta decay Studies

Transport system

target

Ion source Mass

Separator

recoil.

βγ

+ ZAN

Z-1AN+1

γ

γ

Accelerator



IEM

CSIC

Producción de Núcleos Exóticos

p 1GeV

p n

2 3 8

U

2 0 1

F r

+ espalación

1 1

L i X

+ + fragmentación

1 4 3

C s Y

+ + fisión



IEM

CSIC

I SOLDE 23-Enero-2004 M.J .G. Borge 1

G rupo de F ísica N uclear E xperim ental

IEM

C S IC

I mán separador

Blanco + Fuente de I ones

Titulo

Energy: 1 GeV (1.4 GeV)

Pulse frequency: 1.2 s

Intensity: 3.2x1013 protons per pulse

I (average): 2 A

Firenze, 6 March 2006

Target + Ion Source

Separator

Isotope Separator on Line @ CERN



IEM

CSIC

Nuclear Stability

BE(A,Z) = ZMpc2 + NMnc2 – M’(AZXN)c2

Using the Bethe-Weizsäcker ec. for BE(A,Z)

M’(AZXN)c2 = ZMpc2 + NMnc2 - avA + asA

2/3 + acZ(Z-1)A-1/3+ aA(A-2Z)2/A - apA-1/2

Odd-A-impar 1 Stable nucleus

The rest

Even-A 2 parabolas

3/20

'

007.01

2/

0

A

AZ

Z

M

For each A Parabolic behaviour with Z

x = Mnc2 -av + aA + asA1/3

M’(AZXN)c2 = xA + yZ + zZ2 + 0() y = (Mp-Mn)c2 - 4aA- acA

1/3

z = acA1/3 + 4aA/A



IEM

CSIC

Decay properties of exotic nuclei

• Selection rules:• Fermi: T= J=0 ; f = i

• Gamow-Teller: T=0±1; J=0±1 ; f = i

Very Selective probe

B(GT)B(F)

CK

..*

22222/1

AV GGRBT

ftf

• Reduced transition probability:

Global properties• Short half-lives (10ms)

• High Q values

• Low Sp/n values

-delayed particle emission

1916 Rutherford & Wood [Philos. Mag. 31

(1916) 379]

1963 Barton & Bell identified 25Si as p

Particle energy spectrum determined by 2 factors 1-intensity of -decay branches from precursor to the emitter 2-probability of emission by proton rather gamma



IEM

CSIC Beta Delayed Proton Emission (TODAY)Today more than 134 precursor known

Yb15170

Tm15069

Kr7336

Ar3318

Properties well understood This spectroscopic tool is often the only way

to identify exotic nuclei Data provide large spectroscopic information

Level densitySpin, isospinWidth & density-decay properties

In 33Ar low level density, spectrum marked for proton peaks Cut off at low energy at the Coulomb barrier IAS (only in precursors with TZ -3/2)

In the rest bellshape spectrum with superimpose peak structure no individual transition rather cluster of them atributed to Porter-Thomas fluctuations

81150

69Tm

Yb15170

Emitter even-even QEC and Bp large populate high excited states rather smooth spectrum

Emitter even-odd Bp low proton emitted from low states fluctuations more pronunced

Notice differences

IAS



IEM

CSIC

Electron-Neutrino Correlations (p emitters)

03 42 Ep (MeV)

33Arp-spectrum free of -summing

32Ar

02.5 3.

5Ep (MeV)

Study of the proton line shape

Physics beyond the SM

Isospin mixing in Fermi decays

Configuration mixing

Level interferences

Spin assignment

Excitation energies

Schardt & Riisager, Z. Phys. A 345 (1993) 265

Adelberger & Garcia, Hyp. Int 129 (2000) 237

Instead of detecting the neutrino

32Ar

32Cl

31S+p

The proton has infoabout the 32Cl recoil(Doppler)



IEM

CSIC

Production of nProduction of neutron deficient nuclei @ eutron deficient nuclei @ GGANILANIL

In-flight production allowed to extract very short species.

Beams of 160, 36Ar, 40Ca, 58Ni,70Ge & 78Kr on secondary targets

p, 2p in the sd-, pf-shell has been produced by fragmentation reaction at GANIL using the LISE-spectrometer

2p Radioactivity



IEM

CSIC

Analysis of -protons data

Cou

nts

Energy (keV)

Strong beta summing

Experiment Theory21Mg



IEM

CSIC

= 4.8 (4) %

Mirror Asymmetry & Systematics

Average asymmetry :

11 (1) % in the 1p shell (A<17)

0 (1) % in the (2s,1d) shell (17<A<40)

Allowed Gamow-Teller transitions (log(ft)<6)

17 couples of nuclei

46 mirror transitions

Thomas et al., AIP Conf. Proc 681, p. 235

- : n → p + e- +

n p

ft-

+ : p → n + e+ +

E.C. : p + e- → n +

n p

ft+

1

ft

ft

= nuc + SCC



IEM

CSIC

Spectroscopy studies wuth -p--

23 isotopes Studied

Macroscopy Properties : T1/2, Pp

Spectroscopy:

• Partial Decay scheme

•IAS Identification

• IMME

T1/2 = (20.8 ± 0.3) ms

Pp = (79.0 ± 2.7) %

43Cr

Spectroscopy of Neutron Deficient nuclei 22 < Z < 28

43Cr

M(A,T,Tz) = a() +b()Tz + c()Tz2 +



IEM

CSIC

Exotic Radioactivities

2p-radioactivity

(Z,N) 2p + (Z-2,N)

1p-radioactivity

(Z,N) p + (Z-1,N)



IEM

CSIC

1 Proton Radioactivity

Proton-radioactivity from gs determine the limit for neutron deficient nuclei

Qp = ( MZ+1 – MZ – mp – me ) c2 > 0 Qp = BEZ – BEZ+1 > 0 (Qp (151Lu) = 1241 keV)

Emission of protons only from odd-Z [50-83] The sensitivity of T1/2 to angular momentum permit to assign the orbital from which the proton is emitted. As protons are detected with high efficiency, proton emitters are used to identify nuclei in Recoil Decay Tagging (RDT).

The observation of protons from 151Lu & 147Tm fixed the proton drip-line of this region

(GSI, 1981)



IEM

CSIC

Proton emitters known today

Known proton emitters

Proton emitting from isomers and g.s.Fine structure in proton emitters

In the 90´s explosion of information on proton radioactivity

50

82

Theoretical models are able to reproduce the systematic of p-decay spectroscopic factors for a wide range of spherical nuclei sensitive test of Shell Model at the edge of stability

p-emission from highly deformed nuclei has been observed and decay rates explained assuming Nilsson states



IEM

CSIC

Direct two proton radioactivity

Predicted in 1960 [Vitali & Gol’danskii, Nucl. Phys. 19 (60)482;27(61)648]

General property of light nuclei with even number of protons (Z=10 to Z=50) close to the proton instability limit

Origin pairing forceEasier to eject a pair of protons from a nucleus than to break the pair apart

If Bp,odd<0Bp,even=Epair+Bp,odd=Epair-|Bp,odd|Bp,even>0 2p-radioactivity

2p-radioactivity is a 3 body problemPenetration through Coulomb barrierlead to strong energy and angular correlations

Interesting because the correlation between emitted protons can give yield information on the nature of their transition within and outside the nucleus

Z=2m+2 Z=2m+1 Z=2m

Epp

=|B

p,od

d|-B

p,ev

en

Bp,

oddB

p,ev

en

Pai

ring

2p

Sp

S2pKnown: 6Be 2p +

p + 5Li (= 1.5 MeV) p + How does it decay?



IEM

CSIC

Direct Two-Proton Emission Candidates

The discovery of direct g.s. 2p-decay has been hampered by1-the stringent energetic requirement (Sp>0, S2p<0)2-need to detect low energy protons (in light nuclei, coulomb barrier low)

Use of the Garvey and Kelson mass formula for mirror nuclei [Phys. Rev. Lett 16 (1966) 197]

Assumption: charge symmetry of nuclear forces Independent particle picture

Accuracy in M200 keV

12T

12Tj 2

1j,AM

2

1j,AMTA,MA,-TM

Correction by Thomas Ehrmann Shift effect S (negative separation energy for the unbound individual particle state). S = (0.28(9))xS (where S is Sp>0 or S2p < 0)Comay, Kelson &Zidon [ADNDT 39(1988)251]

4.34.17.4

Candidates for 2p radioactivity

Sp S2p S2p+S T1/2(ms)

22Si +1.10 +0.01 +0.01(?) 6(3) 31Ar +0.48 -0.23 -0.17 14.1(7) 39Ti +0.43 -0.79 -0.57 31.6(7) 42Cr +1.19 -0.69 -0.40 13.4-2.4

+3.6

45Fe +0.07 -1.14 -0.82 48Ni +0.46 -1.35 -0.97 54Zn +0.40 -1.51



IEM

CSIC

Giovinazzo et al., PRL 89 (2002) 102501



IEM

CSIC

Giovinazzo et.al. Phys Rev Lett. 89(2002)102501



IEM

CSIC

Status of 2p-radiaoctivity

Agreement with 3-body

model for p-wave emission

45Fe

Blank et al., PRL 94 (2005) 232501

Giovinazzo et al., PRL 89 (2002) 102501

57(6) % 2p

E2p = 1.154(16) MeV

msT 5.03.02/1 6.1

87(13) % 2p

E2p = 1.48(2) MeV

msT 8.18.02/1 2.3

54ZnNext Steps:

Search for new two-proton emitters

48Ni , 59Ge …..

Detailed study of the decay process

Measurement of proton-proton correlation:

p-p angle

Individual proton energies

Modelling of the 2p resonance

GANIL

Fragmentation reactions 58Ni-beam

45Fe

54Zn

Dossat, PRC, submitted



IEM

CSIC

An Exotic Nucleus:

Z=18, N=13

Q = 18.5 MeV



IEM

CSIC

Emisión retardada de 2-protones

Predicho en 1980 [Goldanskii, JETP Lett. 32 (1980) 554]

3 modos de desintegración:

Emision secuencial.

E1, E2 ind. Picos, E2 ensanchado por retroceso

Emisión casi isótropica

Emision di-protonica

E1E2, anchos

Gran correlacion angular

Emision democratica

E1E2, anchos

Cierta correlacion angular



IEM

CSIC

Experimento 1995



IEM

CSIC

Experimento 1997

Yield 2 atom/s

Solid angle 14 + 11 %

1p 23.7 %

2p 5.2 %

3p 1.3 %

N

ijii

N

Iip

1

2

2

12 2



IEM

CSIC

IAS

2p/1p (IAS) 9

31Ar @ the dripline: 18p + 13n

Unique Spectroscopic Information

Q2p EIAS = 12322(2)(50) keV

QEC = EIAS + Ec - np

Ec =7045 keV

QEC = 18490(110) keV

f(EIAS)tIAS = 6145(4) s / [B(F) +

B(GT)]

b.r.(IAS) = T1/2 / tIAS

B(F) = [T(T+1)-TziTzf ]if= 5

Expected b.r. (IAS) = 4.35(31)%

Experimentally: b.r. (IAS) =

4.25(30) %



IEM

CSIC

-delayed 2p emission from 31Ar

pr

r

PP

Qm

P

m

P

m

P2

22

2

2

1

222

022

2

2

1 rPPP

pr

pp EEEE

m

mEEQ 22121212 cos2

1



IEM

CSIC

31Ar -2p emitter

Decay of IAS through 2p emission

Diagonal from decays via singleintermediate state from manyinitial states fed in beta-decay

1p-spectrum.

2p-spectrum



IEM

CSIC

Gamow-Teller 2p-transition

• Kinematics of sequential emission• 2He branch present at some level ?

1st emitted

2nd emitted

30S* 29P

Isospin allowed transitions increasing # of intermediate states possible



IEM

CSIC

Surprise at the neutron drip line

1985, First experiments with radioactive nuclear beams, Berkeley (USA)

Tanihata

R(11Li) = 3.30(24) fm

2)]()([),( tRpRtp III

11Li 1/22masaI rσ

Be, C and Al

6Li 7Li 8Li 9Li11Li

¿Why is the mass radius so large?

Deuterio

Tanihata, 1985



IEM

CSIC Experimental Studies at the drip line

SpinsMomentsSpins

Moments

Elastic ScatteringElastic

Scattering

MomentumDistributions

MomentumDistributions

ReactionCross Sections

ReactionCross Sections

BetaDecay

BetaDecay

UnboundNuclei

UnboundNuclei

MassesMasses



IEM

CSIC

Beta decay of an exotic nuclei

10Be+n0.504

1974

9Be+2n7.315

1979

0.320

10.59

8.82

11Be

20.6

Energías (MeV)

3/2-

8Li+t15.721

1983

Even a neutron rich - nuclei emit charged particles!

Even a neutron rich - nuclei emit charged particles!

2+3n8.982

1980

1966

T1/2 = 8 ms

-

8

113Li

17.916

1996

9Li+d

pd

9Li

11Be½+

0.320 ½-



IEM

CSIC

Beta-delayed deuterons

00 500 1000Ed (keV)

Inte

nsi

ty (

deca

y-1 M

eV-1) 10-4

10-5

10-6

M.J.G. Borge et al., Nucl. Phys. A560 (1993) 664

F.C. Baker, Phys. Lett. B 322 (1994) 17

D. Baye et al., Prog. Th. Phys. 91 (1994) 271

M.V. Zhukov et al., PRC47 (1993) 2937

Qd = 3.007 – S2n MeV

6He

6Li

+d

Anthony et al.,

PRC 65 (2002) 034310

Exploring w.f. 10 fm



IEM

CSIC

11Li, gamma rays

11Be

320 keV

M.J.G. Borge et al., PRC55 (97) R8

N. Aoi et al., NPA616 (97) 181c

D. Morrisey et al., NPA627 (97) 222

Q = 20.62 MeV, T 1/2= 8.2 msb(320) = 6.3(6) %

log ft = 5.73

(1s1/2)2/(0p1/2)2 ~1(1s1/2)2/(0p1/2)2 ~1

½-

½+



IEM

CSIC

11Li (284 MeV/u) + C 9Li + n @ GSI

10Li10Li

9Lin2

(1s 1/2)2 = 45(10) %

in the 11Li g.s Single-particle momentum distributions, Hankel functions

H. Simon et al., PRL 83 (1999) 496

n1

grupo de física nuclear experimental iemiem csic curso de doctorado estructura nuclear m.j.g....

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