IS414 collaboration CERN – PH/ISOLDEscoccola/iguazu/NS/02_NS02-fraile.pdf · L.M. Fraile...

L.M. Fraile for the ISOLDE L.M. Fraile for the ISOLDE IS414 collaborationIS414 collaborationCERN CERN –– PH/ISOLDEPH/ISOLDE

Advanced Time Delayed βγγ(t) measurements in the N~20 island of inversion

SLAFNAP6, Iguazú, October 2005

Advanced Time Delayed Advanced Time Delayed βγγ βγγ(t) measurements (t) measurements in the N~20 island of inversionin the N~20 island of inversion

SLAFNAP6, Iguazú, October 2005

L.M. Fraile SLAFNAP6, Iguazú 2005

The N~20 island of inversionThe N~20 island of inversion

Cl31

Cl32

Cl33

Cl34

Cl35

Cl36

Cl37

Cl38

Cl39

Cl40

Cl41

Cl42

Cl43

Cl44

Cl45

Cl46

Cl47

Cl48

Cl49

Cl51

16 S27

S28

S29

S30

S31

S32

S33

S34

S35

S36

S37

S38

S39

S40

S41

S42

S43

S44

S45

S46

S47

S48 34

P26

P27

P28

P29

P30

P31

P32

P33

P34

P35

P36

P37

P38

P39

P40

P41

P42

P43

P44

P45

P46 32

14 Si22

Si23

Si24

Si25

Si26

Si27

Si28

Si29

Si30

Si31

Si32

Si33

Si34

Si35

Si36

Si37

Si38

Si39

Si40

Si41

Si42 30

Al22

Al23

Al24

Al25

Al26

Al27

Al28

Al29

Al30

Al31

Al32

Al33

Al34

Al35

Al36

Al37

Al38

Al39 28

12 Mg20

Mg21

Mg22

Mg23

Mg24

Mg25

Mg26

Mg27

Mg28

Mg29

Mg30

Mg31

Mg32

Mg33

Mg34

Mg35

Mg36 26

Na19

Na20

Na21

Na22

Na23

Na24

Na25

Na26

Na27

Na28

Na29

Na30

Na31

Na32

Na33

Na34

Na35

10 Ne16

Ne17

Ne18

Ne19

Ne20

Ne21

Ne22

Ne23

Ne24

Ne25

Ne26

Ne27

Ne28

Ne29

Ne30

Ne32 24

F15

F16

F17

F18

F19

F20

F21

F22

F23

F24

F25

F26

F27

F29 22

8 O12

O13

O14

O15

O16

O17

O18

O19

O20

O21

O22

O23

O24 18

20N11

N12

N13

N14

N15

N16

N17

N18

N19

N20

N21

N22

N23

6 C8

C9

C10

C11

C12

C13

C14

C15

C16

C17

C18

C19

C20

C22

6 84 10 12 14 16

Island of inversionWarburton et al., PRC41 (1990) 1147

New region of deformation…WHY?

WHERE?

Ground state propertiesThibault et al., PRC12 (1975) 644Huber et al., PRC18 (1978) 1978

DeformationDetraz et al., PRC19 (1979) 164Motobayashi et al., PLB346 (1995) 9Keim et al., EPJA8 (2000) 31Pritychenko et al., PRC63 (2000) 011305(R)



Breakdown of N=20 shell → pf particle-hole excitations.

S2n of 30Na compared to the shell-model calculations. Corresponding dominant neutron configurations of the ground state and the ESPE’s obtained from each interaction.

E. Caurier et al., NPA 693 (2001) 374


T. Otsuka et al., EPJA 15 (2002) 151Y. Utsuno et al., PRC 70 (2004) 044307


Neutron Effective Single Particle energies for 30Si and 24O, relative to 1s1/2. The change is due to the strongly attractive interaction between a proton in 0d5/2 and a neutron in 0d3/2.

Sketch of the sources of the correlation energy of the intruder and the normal states of semi-magic and open-shell nuclei.


The Advanced Time Delayed The Advanced Time Delayed βγγ βγγ(t) method(t) method

Ge-1BetaBaF

2 -1

BaF 2-

2

ISOLDE beam

Detectors• 1 Beta and 2 BaF2: timing• 2 Ge: E resolution, selection of decay branches

Triple coincidence events:

• β–BaF2–Ge: lifetime measurements

• β–Ge–Ge: coincidences, level scheme

Method:

• De-convolution: ns range

• Centroid shift: 10’s of ps H. Mach et al., NPA 523 (1991) 197

βγγ(t) setup @ ISOLDE


Experimental investigation of 30,31,32Mg• 30,31Mg: coexistence of spherical and intruder configurations

• Excited states not clearly characterized• Candidate for 0+ in 30Mg?

• 32Mg: half-life of the first excited 2+ state (885 keV)• Other nuclei observed in β-decay: 33,34Mg

Experiments performed at ISOLDE at CERN• October 2003 (30,31,32Na decays)

• August 2004 (30,32Na decay)

• August 2005 (30,32,33Na decay)

The IS414 experimentThe IS414 experiment


The intruder structure in The intruder structure in 3030MgMg

→ Timing: 306-1482 cascade


3030Na decayNa decay


Beta-Ge-Ge

Beta-Ge-BaF2(t)

Fast timing: 1482 – 306 keV

A long lifetime of the 1789 keV state makes it a natural candidate for the intruder 0+ state. But there is a 1789 keV gamma to the g.s.

Beta-BaF2(t)

3030Mg: fast timingMg: fast timing


3030Mg: Evidence for 0Mg: Evidence for 0++ candidatecandidate

Gate on 3178 keV

1482

Gate on 1789 keV

1482

1820

Gate on 1820 keV

1482

1789

Coincidences:The 3178 gamma feeding the 1789 keV

level from above shows no coincidences with the 1789 keV line.

There is clear evidence for a 1482-1820-1789 keV cascade defining a new level at 3302.3 keV.


3030Mg: proposed level schemeMg: proposed level scheme

There is now an intensity imbalance for the 1789 keV state: with 6.6(4) feeding and 4.8(3) de-exciting the state = 1.8(5).

Below 3.3 MeV there are now only 3 known excited states in 30Mg: 2+ 1482, (0+) 1789, and (2+) 2467 keV.


B(E2; 21+ → 01+) = 40(9) e2fm4 (Scheit et al.)

B(E2; 21+ → 02+) = 10.8(11) e2fm4

B(E2; 22+ → 21+) > 123 e2fm4 (if pure E2; likely M1)

Strenght of E0 02+ → 01+ ?

3030Mg: the intruder structureMg: the intruder structure

There are close-lying 22+ and

23+ states in 28Mg: 22+ decays

only by an M1 transition to the

21+ state, while 23+ decays by a

strongly mixed M1+E2 transition

to 21+ and by an E2 to 01+. The

2467 state could be equivalent

to the 22+ case.

R. Rodriguez-Guzman et al., NPA 709 (2002) 201


Study of Study of 3131MgMg

The 461 and 1154 keV levels are populated in the beta-delayed neutron emission of 32Na, while the other states are populated in the decay of 31Na.

New 1/2+ 2p2h configuration of the ground state [Neyens et al. PRL 94 (2005) 22501].

New possible location of the 1p1h 11/2− state included coming from our coincidence data.

Lifetimes: expected long lifetime for the 461 keV level (7/2−).


These and other experimental results confirm the model interpretation of the observed states in 31Mg, they do not provide a unique identification.

The measured lifetimes provide strong constraints on any alternative interpretation of these states

The 461 keV state is the 1p1h intruder:

The 240 keV ray is the collective E2 7/2− → 3/2− transition.

B(E2) = 67(6) e2fm4

B(E2; 2+ → 0+) = 67(14) e2fm4 for the 2p2h configuration in 32Mg [B.V. Pritychenko et al., PLB 461(1999) 322]

Study of Study of 3131MgMg


Lifetime of the 2Lifetime of the 2++ state in state in 3232MgMg

Centroid shift technique using a

two gamma ray cascade involving

beta and 2151-885 keV gammas.

Important is to select beta sources

providing time response calibrations

of the BaF2 detectors for the full

energy peaks matching as close as

possible the energies of 2151 and

885 keV, and cascading via levels of

precisely known lifetimes.

Calibration sources: 88Rb (energies 898-1836 keV), 30Al (1263-2235 keV), 24Na (1369-2754 keV), and other.


Data Set 1

Ge-1 energy projection Gates in gamma detectors are selected only on the full-energy gamma peaks

Beta energy

Triple coincidences:Beta-Ge-GeBeta-Ge-BaF2(t)

3232Mg: the 885Mg: the 885--2151 keV cascade 2151 keV cascade


BaF2 and Ge-2 gated spectra by the 885 and 2151 keV gamma peaks




Beta-BaF2(t) Time-delayed spectra with a Ge gate


Time response curveTime response curve

Two-point calibrations for

the energy pairs 898-1836,

1263-2235, and 1369-2754

keV.

Time response calibration

curve for the region 898-2754

keV.

Other data confirm good

linearity over the region 898-

2235 keV and a small

bending down above (due to

limits on the CFD input

range).

The

precision of

the error bars

is as low as

0.6-0.7 ps.

The line is set

to cross zero at

885 keV.


HalfHalf--life of the 885life of the 885--keV level in keV level in 3232MgMg

Centroid Shift for 32Mg from 1 data set

Cascade 2151-885Shift due to the lifetime of the 2+

state at 885 keV

T1/2(2+) = 16.0(4.2) ps B(E2; 01+ → 21+) = 327(87) e2fm4


3232Mg lifetime from two data setsMg lifetime from two data sets

T1/2(1) = 16.0(4.2) ps

T1/2(2) = 13.6(6.1) ps

B(E2) = 342(78) e2fm4

T1/2average = 15.3(3.5) ps

Expected final uncertainty of ~2.5 ps

Data Set 2


[from O. Niedermaier]

Low E CoulEx, Timing

Intermediate E CoulEx

B(E2)B(E2)’’s for Mg isotopess for Mg isotopes

ATD


Status IS414Status IS414

• New states identified in 30MgEvidence for the 0+ intruder state in 30Mg

• Direct lifetime measurement of the 885 keV 2+ state in 32Mg

Currently T1/2 = 15.3(3.5) ps.

The analysis is in progress; further improvement is expected. The final aim is ~2 ps error.

• New fast timing measurements run on 33Mg and 32Mg in 2005

• Search for the E0 transitions in 30Mg also performed in 2005


New Fast Timing Crystals and New Fast Timing Crystals and PhototubesPhototubes

New crystals are being produced with much improved energy resolution, yet not as good timing resolution as BaF2.

The energy resolution of LaBr3:Ce is about 2.7% at 661 keV in comparison to 6% for NaI:Tl and 9-10% for BaF2.

Strong time decay variation is observed for LaBr3 for 0.5% doping with Ce (A) and 4% (B), compare to NaI:Tl (C).

[P.Derenbos et al., IEEE Trans.Nucl.Scien. 51 (2004) 1289]

Many other references!


The IS414 CollaborationThe IS414 Collaboration

H. Mach, M.J.G. Borge, R. Boutami, P.A. Butler, J. Cederkäll, P. Dessagne, B. Fogelberg, H. Fynbo, R. Gernhauser, P. Hoff. A. Jokinen, C. Jollet, A. Korgul, U. Köster, T. Kröll, W. Kurcewicz, F. Marechal, T. Motobayashi, J. Mrazek, G. Neyens, T. Nilsson, W. Płóciennik, S. Pedersen, A. Poves, B. Rubio, E. Ruchowska, M. Stanoiu, W. Schwerdfeger, O. Tengblad, P. Thirolf, D.T. Yordanov and the ISOLDE collaboration

Uppsala University, Studsvik, SwedenISOLDE-CERN, Geneva, SwitzerlandUniversidad Complutense, Madrid, SpainIEM-CSIC, Madrid, SpainIReS, Strasbourg, FranceASINS, Świerk, PolandK.U. Leuven, IKS, Leuven, BelgiumIPNO, Orsay, FranceUniversity of Liverpool, Liverpool, UKLund University, Lund, Sweden

Århus University, Århus, DenmarkOslo University, Oslo, NorwayJYFL, Jyväskylä, FinlandWarsaw University, Warsaw, PolandRIKEN, Wako, JapanRez, Czech RepublicUniversidad Autónoma, Madrid, SpainUniversity of Valencia, Valencia, Spain.Technical University, Munich, Germany

IS414 collaboration CERN – PH/ISOLDEscoccola/iguazu/NS/02_NS02-fraile.pdf · L.M. Fraile...

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