基于放射性束的核结构、核天体物理研究

刘 忠

Outline• Brief introduction to RIB physics• 100Sn 区域奇异核衰变• 远离稳定线核素质量测量• ( 直接质子放射性核 )• Nuclear Detectors R&D for RIB physics• Outlook

Halo nuclei

208Pb

Hansen & Jonson, Europhys. Lett., 1987, 4:409.

Halo nuclei

Rm∝2/1

2 )2/( nS

100Sn:Gamow-Teller Strength in its Decay

rp process

Shell Model Orbitals

100SnGT-strength is unique tool to study wave fct.

pure spin-flip transition0+ => (pg9/2

-1 ng7/2)1+

large decay energy=> most of GT strength in b-decay window

measure:T1/2

b-endpoint energy(branching)=> GT-strength

Shell modelGrawe et al.

100Sn:Gamow-Teller Strength in its DecaySearch for its Isomer

rp process

100Sn:Gamow-Teller Strength in its DecaySearch for its IsomerParticle Stability of Neighbours: key to the rp-process

rp process

key to the astrophysical rp-process

100Sn history

year where production events quantity

1994 GSI fragm. 124Xe 7 T1/2 E() E() S139

1994 GANIL fragm. 112Sn 11 ident.1996 GANIL fusion 11 m

1998 GSI fragm. 112Sn 1 T1/2 E() E() S192

2007 MSU fragm. 112Sn 14 T1/2

2008 GSI fragm. 124Xe 259 T1/2 E() E() S330

1st Bρ separation 2nd Bρ separationΔE

identification F2-F4: DE => ZBr(x,x´,a´) = b g A/q m0c

q = ZTOF => b

F2F4

the FRagment Separator (FRS)

~109 s-1

the FRagment Separator (FRS)

~109 s-1

100Sn setting (full statistics, 15 days)

A/Q

Z

Te

Ag

Cd

In

Sn

Sb

N=Z+2N=Z+1N=ZN=Z-1

259 100Sn

s = 6pb 103Sb?

99Sn

97In

95Cd

93Ag

Silicon Implantation Detectorand Beta Absorber

SIMBA

100Sn

pixels in implantation zone: 3x60x40 = 7200

X SSSD 60x60x0.3 mm3

Y SSSD 60x60x0.3 mm3

10 SSSD 60x40x1 mm3

3 DSSD 60x40x0.7 mm3

Gassiplex+ MesytecR - chain

7 x-strips

7 x-strips10 SSSD 60x40x1 mm3

Implantation

RISING

SIMBA

DEG

RADER

and how it looks in reality

100Sn

RISING

+

15 x 7

Germanium detectors

ePhoto~ 11%@ 662 keV

Correlation of Implantation and Decay

require same position within ± 1mm in x,y,z

record all decay triggers within 15 s(b+ of 3 generations)

Maximum Likelihood analysisvarying the 100Sn half-lifewith known: daughter decays,efficiencies, dead times, background

T1/2 = 1.16 ± 0.20 s

Comparison: MSU 2007 0.55 s

GSI 1997 0.94 s

100Snonly 1st decays +0.70

-0.31

+0.54 -0.26

Gamma Spectrum after Beta Decay of 100Sn

all events within 4 s after implantation

511

141

436

96

1297 2048

141

436

96

Gamma Intensities

5 lines add up to 4018 keV ???

2003Stone, Walters 1985

(pg9/2)-1ng7/2

(pg9/2)-1nd5/2

what do we expect?

511

g intensitiescorrected for efficiencyand M1 conversion

70 100Sn b+ decays

111 total b+ decays

E*(1+) = (2.71 + x) MeV with x ≈ 0.05 MeVbecause:

• total sum energy = 2.76(0.43) MeV (Schneider et al.)

• DMc2 - QEC(1+)= 2.6(1.0) MeV (Chartier et al.)

• one b-delayed proton event:

Ep + Sp(100In) = 2.93(0.34) MeV (Audi et al.)

compare to shell model

Grawe et al. Nowacki, Sieja

Extraction of Beta Spectrum

100Snb spectrum

conv. line?

from maximum likelihood Emax = 3.29 ± 0.20 MeV

QEC = 4.31 ± 0.20 MeV

to excited state

=> I(b+) = 87%

=> log ft = 2.62

sum over total energy within 3 s after implantation

in implantation zone + calorimeter

tested (by eye) for uninterrupted tracks

range of analysis

result of ML analysis

-0.19+0.13

known log(ft) values

Nuclear Data Sheets 84 (1998) 487

log (ft)

100Sn

superallowed GT

Decay of the heaviest N=Z doubly magic nucleus 100Sn

Gamow Teller Strength

A. Bobyk, W. Kaminski, I. Borzov 2000

8.17

81

12

4 2/72/9

refGT

gg

refGT

B

NN

l

lB

ft26951

s86142

ftgg

Ft2B

22VA

GT

.

.

/exp

exp. FFS

QRPA

SM truncatedextreme SM

GT strength of even Sn isotopes

H. Grawe, 2010

6203GT 19B .

.exp .

why is BGT that large?

wave functions must be rather pure

I i > = {(pg9/2)10} 0+

< f I = {(pg9/2)9 (ng7/2)1} 1+

10 protons can transform into a neutron

the 100Sn shell gap

is robust

Conclusions

- doubly magic -

3 isomer decays after ToF=200nsdecaying within 25 ns ?

6+ isomer in 100Sn ?

1

5

4

3

2

Eg/MeV

0 2015105 T/ms

Eg/MeV

what‘s new?

93Ag

103Sb T1/2 < 50 ns !

99Sn

95Cd

T 1/2 > 0.2 m

s

97In

Conclusions

• first observation of 93Ag, 95Cd, 97In, and 99Sn

• reduced rate of 103Sb => T1/2 < 50 ns

• 102Sn: new isomeric state

• 100Sn: probably no isomer

• 1st g-spectrum after decay of 100Sn

• 100Sn decay: T1/2, Ebmax, E , g BGT

• superallowed GT transition

=> dominant configurations (pg9/2)10 =>(pg9/2)9 (ng7/2)1

The 100Sn Team

photo taken by Hans Geissel

Shell structure near doubly-magic 100Sn Abundance of isomeric states Exotic decay mode

Study of N ≥ Z proton drip-line nuclei 96,97,98Cd with astrophysical consequences

Spokespersons: A. Blazhev, P. Boutachkov Z. Liu, R. Wadsworth

T=0, S=1

T=1, S=0

Tz=0

Neutron-proton pairing

N=Z nuclei, unique systems to study np correlations

T=0 Pairing may become Important in A>80 N=Z nuclei

A. L. Goodman , PRC 60, 014311 (1999)

Experimental signals for T=0 np pairing

Binding energy diff erences

 Deutron transfer reactions

 Rotational properties: delayed alignments in N=Z nucl

Level structure: 9 2 Pd, B. Cederwall et a l . Nature 469, 68-71 (2011)

Spin-gap isomer:

9 6 Cd

Effect of T=0 np interaction in 96Cd

Shell model calculations by H. Grawe

T=0

No T=0

E6 Spin gap

96Cd

T=0

Primary beam124Xe @ 850 MeV/u

RISING S352 Experimental SetupStopped RISING

Z

A/Q

96Ag

Active stopper

0.27(14) s

1.58(3) s

78(8) s

B(E4; 19+ 15+) = 0.4(3) W.u.

B(E2; 19+ 17+) = 4(3) W.u.

B(E3; 13- 10+) = 0.187 (20) W.u.

E[keV]

Coun

ts

known: R. Grzywacz et al. PRC 55 (1997) 1126

new

96Ag

4264

4168

SE

Tf<1 s

96Cd

0.2 – 4.5 μs

96Cd

0-0.2 μs

T1/2 (421) = 0.67 0.15 s (96Cd g.s.)

0.2 – 4.5 μs

T1/2 (470, 1506, 667) = 0.29-0.10 + 0.11 s

E6 Spin gap

Effect of iso-scalar np interaction in 96Cd, 16+ isomer

Beta decay GT strengths in GF space 100% g

9/2 → g

9/2, similar to the case of g

9/2 → g

7/2 seen in 100Sn

16+ 15+

BGF = 0.14 with quenching factor of 0.6 (Herndl and Brown NPA627, 35 (1997))

Bexp = [3860(18) * ] / (f T1/2) = 0.19 + 0.08-0.07 with T1/2 = 0.29 secs

96Cd Results

B. S. Nara Singh, Z. Liu et al. , Phys. Rev. Lett. 107, 172502 (2011)

• Evidence for the existence of the 16+ E6 “spin-gap” isomer in 96Cd

• Evidence for the strong influence of the iso-scalar neutron-proton interaction

• Our work allows to deduce T1/2 = 0.67 ± 0.15 s for the g.s. in 96Cd

Results in other nuclei

-decaying high-spin isomers were observed in 94Pd

96Ag 98Cd

Core-excited states aross the N=Z=50 shell closure

identified in 96Ag

more in 98Cd

Phys. Rev. C 82, 061309(R) (2010) Phys.Rev. C 84, 044311 (2011)

J.Phys.:Conf.Ser. 205, 012035 (2010)

SMS and IMS

In jection

Septum

E lectronC ooler

(m /q)

(m /q)

(m /q)

(m /q)

>

>

>

SchottkyN oise-P ickups

v 1

(m /q)0

(m /q)0

(m /q)1

v 1

(m /q)1

v 0

In jection

Septumv 0

TO F-D etector

ff

vv

(m /q)m /q2

t= + 2

t

21 (1 )

vv

0 t

SCHOTTKY M A SS SPECTROM ETRY ISOCHRONOUS M A SS SPECTROM ETRY

Cooled Fragments Hot Fragments

SMS: Broad Band Frequency Spectra

M.W.Reed et al., PRL 105 172501, (2010)

FAIR (Facility for Antiproton and Ion Research) (Darmstadt, Germany)

~1GeV/u 350m

ring branch

GSI 现有和将来的实验装置

RISING

NEUTRON DETECTOR

DSSD IMPLANTATIONDETECTOR

GE γ-ARRAY

RADIOACTIVEBEAM

DEcay SPECtroscopy (DESPEC)

Total Absorption Spectrometer (TAS)Fast timing measurementsCompact, flexible and modular geometryg-factors and quadrupole moments

8 x 8 cm128 x 128 strips1 mm (Micron)3 dssd

24 c

m

8 cm

E

Veto

AIDA: Advanced Implantation Detector Array

ww

w.p

h.ed

.ac.

uk/~

td/A

IDA

Implantation energy measurementDecay energy measurement (several layers)Low threshold: ~40 keV (conversion electron!)Fast recovery (~µs); ASIC

beam

ASIC Design Requirements

Selectable gain 20 1000 20000 MeV FSRLow noise 12 600 50000 keV FWHM

energy measurement of implantation and decay events

Selectable threshold < 0.25 – 10% FSRobserve and measure low energy , b b detection efficiency

Integral non-linearity < 0.1% and differential non-linearity < 2% for > 95% FSRspectrum analysis, calibration, threshold determination

Autonomous overload detection & recovery ~ msobserve and measure fast implantation – decay correlations

Nominal signal processing time < 10msobserve and measure fast decay – decay correlations

Receive (transmit) timestamp datacorrelate events with data from other detector systems

Timing trigger for coincidences with other detector systemsDAQ rate management, neutron ToF

Schematic of Prototype ASIC Functionality

Note – ASIC will also evaluate use of digital signal processing

Potential advantages• decay – decay correlations to ~ 200ns• pulse shape analysis• ballistic deficit correction

AIDA: ASIC schematic

High-speed bufferx10

DC fdbk

shaper

9R

R

Slowcomparator

Clamp comparator(for x10)

PeakHoldpositivePolarity

PeakHoldnegativePolarity

RC filter(with reset)

Fastcomparator

RC filter(with reset)

CM

OS

sw

itches

I thresholdR threshold

I thresholdR threshold

DC fdbk

shaperPeakHold

positivePolarity

PeakHoldnegativePolarity

Fastcomparator

RC filter(with reset)

I thresholdR threshold

4:1 MUX

1

2

2

3 4

4

5

6

6

7

8

9

9

10

10

10

10

1010

11

11

11

11

1111

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1919

1919

19

19

19

19

19

19

AIDA: status• Systems integrated prototypes available

- prototype tests in progress• Production planned Q3/2010

Mezzanine: 4x 16 channel ASICs Cu cover EMI/RFI/light screen cooling

FEE: 4x 16-bit ADC MUX readout (not visible) 8x octal 50MSPS 14-bit ADCs Xilinx Virtex 5 FPGA PowerPC 40x CPU core – Linux OS

Gbit ethernet, clock, JTAG portsPower

FEE width: 8cmPrototype – air coolingProduction – recirculating coolant

FEE Assembly Sequence

Prototype AIDA Enclosure

• Prototype mechanical design• Based on 8cm x 8cm DSSSD

evaluate prior to design for 24cm x 8cm DSSSD• Compatible with RISING, TAS, 4p neutron detector

• 12x 8cm x 8cm DSSSDs 24x AIDA FEE cards

• 3072 channels (x 3)

• Design complete

• Mechanical assembly in progress

(3He,p)

np

Even-even

?s

T=0 J=0

Odd-odd

T=1 J=0

T=0 J=1

L=0 transfer – forward peaked

/1|| 2 iTf

Measure the np transfer cross section to T=1 and T=0 states

Both absolute s(T=0) and s(T=1) and relative s(T=0) / s(T=1) tell us about the character and strength of the correlations

(3He,p) Transfer Reactions

Proton Radioactivity

Many thanks to my collaborators:

A. Blazhev, P. Boutachkov, , Tom Davinson, L. Livinov, B. T.Faestermann, B. S. Nara Singh et al.