Experiments at NSCLbrown/Uio-MSU-ORNL-UT-2011/Winter_AG... · A. Gade, 1/5/2011, Slide 1 Experiments at NSCL Who we are Nuclear science thrusts Production of rare isotopes at NSCL

A. Gade, 1/5/2011, Slide 1

Experiments at NSCL

Who we are

Nuclear science thrusts

Production of rare isotopes at NSCL

–Projectile fragmentation and separation

–Experimental consideration with fast beams

Selection of physics highlights

–Probing the limits of nuclear existence

–Ground-state half-lives and importance for nuclear astrophysics

–High-precision mass measurements

–In-beam spectroscopy – knockout, Coulomb excitation, excited-state lifetime measurements, tests of reaction dynamics, charged-particle spectroscopy

–Beyond the n-dripline: Spectroscopy of neutron-unbound states

–Charge-exchange reactions and EC rates

Very brief: NSCL’s future – reaccelerated beams and laser spectroscopy

A. Gade, 1/5/2011, Slide 2

NSCL – fast factsNational user facility for rare isotope research and education

– nuclear science, accelerator physics, nuclear astrophysics, societal applications

Selected to establish the facility for rare isotope beams FRIB433 employees, incl. 36 faculty, 70 graduate and 58 undergraduate students

as of January 2, 2011

August 2009

A. Gade, 1/5/2011, Slide 3

Where we are

Biochemistry

NSCL

Biomedical &

Physical Sciences

Plant Biology

Plant Science Greenhouses

Chemistry

Law

Engineering

Tennis, etc.

Performing Arts

A. Gade, 1/5/2011, Slide 4

Evolution of Nuclear Structure

–At and beyond the nucleon driplines

–Changes in shell structure, level schemes & collectivity

–Nuclear wave functions through direct reactions

–Spin-isospin response of nuclei through charge exchange reactions

Fundamental Interactions & Precision Measurements

–Mass measurements, IMME, CVC hypothesis

–Precise measurements of nuclear radii & moments (new)

–Search for new interactions & couplings (new)

Reaction Dynamics

–The nuclear equation of state

–Study of reaction mechanisms

Role of Nuclei in the Cosmos

–Origin of the elements, supernovae, X-ray bursts

–Neutron stars and nuclear equation of state

Accelerator physics

Research areas

A. Gade, 1/5/2011, Slide 5

Research all over the nuclear chart

A. Gade, 1/5/2011, Slide 6

Motivation and experimental reality

Motivation to study rare isotopes:

• Limits of nuclear existence

• Modifications to magic numbers

• Extreme charge and mass distributions

• Astrophysical reaction rates

• Experimental task: Quantify changes

encountered in rare isotopes and

measure observables that are

calculable and can serve to

discriminate between theories

• Experiments?! Largely done in inverse

kinematics with a beam of exotic nuclei

• New precision techniques have been

developed in past decade to enable

experimental study of these most

exotic nuclei

• Unfortunate fact of life: The nuclei with

the largest N/Z ratio accessible are

light nuclei and they have low beam

rates

A. Gade, 1/5/2011, Slide 7

Production of rare isotopes by projectile fragmentation

Adapted from A. Stolz

A. Gade, 1/5/2011, Slide 8

Nuclei produced by fragmentation


A. Gade, 1/5/2011, Slide 9

NSCL’s A1900 fragment separator


A. Gade, 1/5/2011, Slide 10Adapted from A. Stolz

A. Gade, 1/5/2011, Slide 11Adapted from A. Stolz

A. Gade, 1/5/2011, Slide 12

Selection of the beams of interest


A. Gade, 1/5/2011, Slide 13

Production and separation end-to-end


A. Gade, 1/5/2011, Slide 14

Selectivity is key!


A. Gade, 1/5/2011, Slide 15

Primary beams available at NSCL

A. Gade, 1/5/2011, Slide 16

Exotic beams produced at NSCL

More than 1000 RIBs have been made – more

than 680 RIBs have been used in experiments

A. Gade, 1/5/2011, Slide 17

Facility layout and experimental end-stationsComplementary approach: fast, stopped and reaccelerated rare isotope beams

ReAx

A. Gade, 1/5/2011, Slide 18

Nuclear existence

• What combinations of protons and neutrons can make up bound systems?

A. Gade, 1/5/2011, Slide 19

Establishing the limits of nuclear existence at NSCL

T. Baumann et al., Nature 449,1022 (2007)

O. B. Tarasov et al., PRC 75, 064613 (2007)

CCF + A1900 + S800 analysis lineTwo-stage separator

O. B. Tarasov et al., PRL 102, 142501 (2009)


48Ca fragmentation

76Ge fragmentation

A. Gade, 1/5/2011, Slide 20

Nuclear existence – highlights

Physics highlights at the limits

• Discovery of 40Mg,42,43Al, 44Si:

Bound 42Al implies dripline

extends further than believed

• Evidence for a new “island of

inversion” around 62Ti (?)

– From measured cross section systematics: Modifications to the underlying shell structure of these very neutron-rich may not be included in most mass models

Stable nucleus

Known nucleus

MSU 2007

MSU present result

Predicted to be bound

15 new isotopes

from 76Ge beam

4 new isotopes

from 48Ca beam

O. B. Tarasov et al., PRL 102, 142501 (2009)


T. Baumann et al., Nature 449,1022 (2007)


A. Gade, 1/5/2011, Slide 21

Beta-decay properties

• Nuclear structure

• Nuclear astrophysics

A. Gade, 1/5/2011, Slide 22

Beta-decay and information on the most exotic nuclei

Beta-decay spectroscopy

provides information at the

extremes of the nuclear chart

to be confronted with theory: • Half-lives• Q values (masses) • Absolute branching ratios • Excited states in daughter

nuclei• Microsecond isomers

New data

H. Crawford et al., PRC 79, 054320 (2009)

H. Crawford, PhD thesis (2010)

New data helped discriminate

between different shell model

configuration spaces

NSCL’s approach – fast-

fragment implantation and

event-by-event decay

correlation – is highly

sensitive and reaches the

most exotic nuclei, e.g.• Half-lives (few ions per day)• Excited states in daughter

nuclei (few ions/min)

Adapted from S. N. Liddick

61Cr-> 61Mn

A. Gade, 1/5/2011, Slide 23

Half-life of the doubly magic r-process nucleus

Particle identification

1.E-02

1.E-01

1.E+00

1.E+01

1.E+02

70 120 170 220

Mass (A)

Ab

un

da

nc

e (

A.U

.)

Observed Solar Abundances

Model Calculation: Half-Lives from

Moeller, et al. 97

Same but with present 78Ni Result

Model calculation for heavy element synthesis

(r-process in supernova explosion)

Measured half-life of 78Ni with 11 events

This is the most neutron rich of the 10

possible classical doubly-magic nuclei

in nature.

Heavy element synthesis in the r-process

proceeds faster than previously assumed

… one step towards a better understanding of the

origin of the elements in the cosmos

different types of

nuclei in the beam

78Ni

models produce excess of heavy elements

with new (shorter) 78Ni half-life

Result: 110 +100-60 ms

P.T. Hosmer et al.

PRL 94, 112501 (2005)

Adapted from H. Schatz

A. Gade, 1/5/2011, Slide 24

Mass measurements

• Fundamental symmetries



A. Gade, 1/5/2011, Slide 25

Masses – what are they good for?Nuclear structure

• Structure information

• Shell closures and deformation from separation energies ( m/m < 10-5)

• Astrophysics (Nucleosynthesis)• r process ( m/m < 10-5, m < 10 keV)

• rp process ( m/m ~ 10-7)

• Fundamental interactions and symmetries ( m/m<10-8)

• CVC

• CKM

A. Gade, 1/5/2011, Slide 26

Penning trap mass measurements

Mass measurement via deter-

mination of cyclotron frequency

from characteristic motion of stored

ions

B

q/m

B

q/m

z0

r0

ring

electrode

end cap

Ion source

PENNING trap

• Strong homogeneous

magnetic field of known

strength B provides radial

confinement

• Weak electric 3D

quadrupole field provides

axial confinement

Bm

qfc

2

1

Mass excess=-22058.53(28) keV

m = 280 eV, m/m=8·10-9

A. Gade, 1/5/2011, Slide 27

70mBr+, T1/2=2.2 s

-20 -10 0 10 2040.0

40.5

41.0

41.5

42.0

42.5

me

an

tim

e o

f flig

ht /

s

RF -2060450 / Hz

-10 -5 0 5 10

18

20

22

24

RF [Hz] - 7595522

mean t

ime o

f flig

ht

/s

38Ca++, T1/2=440 ms

m = 280 eV m/m = 8·10-9

Precise masses for 36 isotopes of 12 elements25Al, 26,32,33Si, 29P, 34P, 37Ca, 38Ca, 40-44S, 63-65Fe, 65mFe, 66Fe,64-67Co,

63,64Ga, 64-66Ge, 66,68As, 80As, 68-70Se, 81Se, 81mSe, 70mBr, 71Br

Neutron shell closure at N=28

Mass measurements at the dripline

CVC tests

rp-process waiting point and isospin symmetry along the N=Z line

-30 -20 -10 0 10 20 30

33.0

33.5

34.0

34.5

35.0

35.5

36.0

36.5

37.0

37.5

38.0

me

an

tim

e o

f flig

ht /

s

RF [Hz] -2528609.5

44SCH+, T1/2=123 ms

-6 -4 -2 0 2 4 6

36

37

38

39

40

41

42

TO

F [

s]

RF[Hz] -2121268

R = m/ m ~ 1.1·106

68Se+, T1/2=35.5 s

Discovery of new Isomer in 65Fe

LEBIT Results

Savory et al., PRL102 (2009) 132501

Block et al., PRL100, (2008) 132501

Bollen et al., PRL96 (2006) 152501

Kwiatkowski et al., PRC81 (2010),058501

Ferrer et al., PRC81 (2010) 044381

Ringle et al., PRC80 (2009) 064321

Kwiatkowski et al., PRC80 (2009) 051302

Ringle et al., PRC75 (2007) 055503

Schury et al., PRC75 (2007) 055801

Adapted from G. Bollen

A. Gade, 1/5/2011, Slide 28

Probing nuclear physics via reactions• Experimental considerations

• Experimental equipment

A. Gade, 1/5/2011, Slide 29

Studying nuclei and their reactions –typical parameters

• NR × NT × NB

Cross section

– NT Atoms in target

– NB Beam rate

– NR Reaction rate

• Example

= 100 mbarn

– NT = 1021

– NB = 3 Hz

– NR =26/day = 3×10-4 Hz

• Fast exotic beams allow for

– thick secondary targets

– event-by-event identification

– Clean triggerbeam target

reacted

beam

v/c=0.3-0.4

A. Gade, 1/5/2011, Slide 30

Equipment for coincidence spectroscopy

Sweeper

S800

CAESAR

MoNA - LISA

LENDA

SeGA

GRETINA (2012)

A. Gade, 1/5/2011, Slide 31

In-beam spectroscopy



• Reaction dynamics

A. Gade, 1/5/2011, Slide 32

Experimental reality – fast beams

• High-Z target as electromagnetic probe

reduced matrix elements

• Intermediate-energy Coulomb excitation

T. Glasmacher, Annu. Rev. Nucl. Part. Sci. 48, 1

(1998)

beam targetreacted

beam

• Light target for wave-function

spectroscopy

location of single-particle orbits,

identifies orbital angular momentum

l, occupation number)

• Nucleon knockout reactions

P.G. Hansen and J. A. Tostevin, Annu. Rev. Nucl. Sci.

53, 219 (2003)

• Experimental tasks

Use photons to tag the final state

- -ray spectroscopy

Identify the final state

Tag the inelastic process

-Particle spectroscopy

Identification of the reaction

residues

Momentum distributions

Scattering angle

v/c>0.3

A. Gade, 1/5/2011, Slide 33

Nuclear Spectroscopy with Knockout Reactions

Different P -distributions for individual states, tagged by -rays: cross section is

sensitive to wavefunction; shape identifies l of knocked-out nucleon

Breakdown of N=8 shell closure in 12Be: only 32% (0p)8 and 68% (0p)6-(1s,0d)2

A. Gade, 1/5/2011, Slide 34

Collectivity from intermediate-energy Coulomb excitation

68Se + 197Au using SeGA-S800

Motivation: N=Z nuclei are a

challenge for theory – subtle

interplay of deformation-driving

proton and neutron orbits leads to

rapid shape changes and shape

coexistence

Experimental input is needed to

constrain different theories

First measurement of the B(E2) strength in 68Se - good agreement was found with a novel

parameter-free beyond-mean-field approach

using the D1S Gogny interaction.

68Se was found to be transitional between -

soft (64Ge) and oblate deformation (72Kr)

A. Obertelli et al., PRC 80, 031304(R) (2009).

A. Gade, 1/5/2011, Slide 35

Precision excited-state lifetime measurements

Plunger device (used with

SeGA@S800)

Inelastic scattering

Direct reactions,

e.g., knockout,

nucleon exchange

reactions

• Model-independent method

to determine electromagnetic

transition strengths between

nuclear states using the

Doppler shift

• A variety of reactions can be

employed to populate states

of interest

66Fe

v1

v1 v2

E

Example: Lifetime of

the 2+ states

measured in 62,64,66Fe

→ B(E2) values

deduced as measure

of quadrupole

collectivity. The results

show and increase in

collectivity due to

occupancy of dg orbits

W.Rother et al., PRL in press

34 36 38 40 42

400

300

200

100Ni isotope (Z=28)

Fe isotope (Z=26)

B(E

2)

[e2fm

4]

N

Adapted from H. Iwasaki

A. Gade, 1/5/2011, Slide 36

Constraining rp-process powering of X-ray bursts

Most rp-process nuclei can be studied at NSCL

p-capture on 32Cl producing 33Ar is an important step in the rp-process powering

thermonuclear explosions on surfaces of accreting neutron stars (X-ray bursts)

rea

ctio

n r

ate

(cm

3/s

/mo

le)

New experimental data

strongly reduce

uncertainty

Typical X-ray burst temperatures

R.R.C. Clement et al. PRL 92, 172502 (2004)

Previous reaction rate

uncertain by up to x 10,000

temperature (GK)

-rays from predicted 3.97 MeV state establish level energy of 3.819(4) MeV

2 orders of magnitude improvement in uncertainty

of level energy reduced uncertainty of calculated 32Cl(p, )33Ar stellar reaction rate by 3 orders of

magnitude

Gate on E = 2460 keV

Adapted from H. Schatz

A. Gade, 1/5/2011, Slide 37

Testing reaction dynamics

E.C. Simpson et al., PRL 102, 132502 (2009)

Sensitivity of the shape of the longitudinal momentum

distribution in two-nucleon knockout to the spin of the

final state Spin determination in exotic nuclei

D. Bazin et al., PRL 102, 232501 (2009)

Data from: A. Gade et al., PRL 99, 072502 (2007)

Data from: A. Gade et al., PRC 76, 024317 (2007)

One-proton knockout

reactions with detection

of the proton:

9Be(9C,8B+X)Y9Be(8B,7Be+X)Y

Accurate measurement

of the diffractive breakup

channel where the

removed proton is at

most elastically

scattered.

HiRA

Experimental results agree with eikonal reaction theory

A. Gade, 1/5/2011, Slide 38

Spectroscopy of neutron-unbound states

A. Gade, 1/5/2011, Slide 39

Neutron-fragment coincidence spectroscopy

26Ne n

23O

24O

In the proximity of the neutron dripline or beyond, excited states or

even the ground state are not n-bound anymore -> decay neutron

spectroscopy to characterize the unbound states!

MoNA

A. Gade, 1/5/2011, Slide 40

Spectroscopy of neutron-unbound systemsExample: 24O, Unexpected doubly magic nucleus

C.R. Hoffman* et al., PLB 672, 17 (2009)

24O

23O+n

• In nuclei far from stability the first 2+ state can

be unbound with respect to neutron emission

• Excitation energy can be reconstructed

by kinematic coincidence experiments of

fragments with neutrons.

• Observed high excitation of first excited 2+

state is strong evidence for double magic

nucleus.

R.V.F. Janssens, News and Views, Nature 459,

1069 (2009).

Adapted from M. Thoennessen

A. Gade, 1/5/2011, Slide 41

Spin-isospin response of nuclei

Nuclear structure and astrophysics information from charge-exchange reactions

A. Gade, 1/5/2011, Slide 42

Spin-isospin response of nuclei

• Charge-exchange reactions are an

ideal tool to study the spin-isospin ( T=1, S=0,1) response of nuclei

• Extraction of Gamow-Teller transitions

strengths beyond the Q-value window for -decay in a model independent

way.

Cou

nts

Adapted from R. Zegers

A. Gade, 1/5/2011, Slide 43

Testing shell model with respect to weak interaction strength

Measure of Gamow-Teller

strengths via charge exchange

reactions

NSCL: (t,3He) at E/A = 120 MeV:

0.4-1 107/s 3H via fragmentation

of 16O

– Better resolution than (n,p)

Accompanying (3He,t) program at

RCNP, Osaka, Japan

Proof of principle: measured GT

strength constrain theoretical

uncertainties of e-capture rates in pre-

supernovae

Adapted from R. Zegers

A. Gade, 1/5/2011, Slide 44

In the future: Reaccelerated rare-isotope beams at NSCL (0.3-3 MeV/u for Uranium)

• Low-energy

reactions important

for nuclear

astrophysics

• Transfer reactions,

Coulomb excitation,

fusion evaporation

reactions, … for

nuclear structure

studies

A. Gade, 1/5/2011, Slide 45

In the future: Reaccelerated rare-isotope beams at NSCL and laser spectroscopy

At ReA3 (0.3-3MeVu for

Uranium):

• Low-energy reactions

important for nuclear

astrophysics

• Transfer reactions,

Coulomb excitation, fusion

evaporation reactions, …

for nuclear structure

studies

BECOLA

• Charge radii and

magnetic moments

• Provide polarized beams

for

• Tests of Maximal Parity

Violation

• Tests of Second Class

Currents

• Test of Time Reversal

Symmetry

A. Gade, 1/5/2011, Slide 46

Related literature

• The NSCL Laboratory and the FRIB Facility, A. Gade and C.K. Gelbke,

Scholarpedia 5 (2010) 9651.

[http://www.scholarpedia.org/article/The_NSCL_laboratory_and_the_FRI

B_facility]

• Impact and Perspectives of Radioactive Beam Experiments for the rp-

Process, M. Wiescher and H. Schatz, Nucl. Phys. A 693 (2001) 269.

• NSCL- Ongoing activities and future perspectives, C.K. Gelbke, Prog. in

Part. and Nucl. Phys 62 (2009) 307 and references within.

• Radioactive nuclear beam facilitiesbased on projectile fragmentation, D.J.

Morrissey and B. M. Sherrill, Phil. Trans. R. Soc. Lon. A 356 (1998) 1985.

Experiments at NSCLbrown/Uio-MSU-ORNL-UT-2011/Winter_AG... · A. Gade, 1/5/2011, Slide 1 Experiments at NSCL Who we are Nuclear science thrusts Production of rare isotopes at NSCL

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