ATLAS Users Workshop August 8-9 2009 CARIBU: early science program Guy Savard Argonne National...

ATLAS Users WorkshopAugust 8-9 2009

CARIBU: early science program

Guy Savard

Argonne National Laboratory

and

University of Chicago

2G. Savard 2009 ATLAS Users Workshop August 8-9 2009

Outline

CARIBU yield curve versus time

– It is all about the sources CARIBU early physics program

– Low-energy • Mass measurements• Decay studies

– Reaccelerated beams• Coulomb excitation• Single nucleon transfer reactions

Scheduling


ATLAS physics program evolution

The ATLAS research program is aligned to the current low-energy nuclear physics priorities

– nuclear structure of exotic nuclei• gamma-ray spectroscopy (mostly n-deficient but some light n-rich)• the structure of the heaviest elements• detailed structure of the lightest nuclei by transfer reactions

– Astrophysics• nuclear reactions with light radioactive beams (mostly CNO breakout)• masses of exotic nuclei (rp-, p- and r- processes)

– Fundamental interactions• CKM unitarity, search for non-standard currents in weak interaction

An emerging interest for both nuclear structure and nuclear astrophysics is moving towards the neutron-rich region (shell-structure modification, r-process)

– CARIBU provides ATLAS with new isotopes that can address these evolving priorities of the field


Yields for Representative n-rich species versus time

Expected 252Cf fission source strength:

• 2.5 mCi end of summer 2009

• 80 mCi fall 2009

• 1 Ci source early 2010

Isotope Half-life (s)

Low-Energy BeamYield (s-1)

Accelerated BeamYield (s-1)

104Zr 1.2 1.5x103 / 4.8x104 / 6.0x105 5.3x101 / 1.7x103 / 2.1x104

143Ba 14.3 3.0x104 / 9.6x105 / 1.2x107 1.1x103 / 3.4x104 / 4.3x105

145Ba 4.0 1.4x104 / 4.4x105 / 5.5x106 5.0x102 / 1.6x104 / 2.0x105

130Sn 222. 2.5x103 / 7.8x104 / 9.8x105 9.0x101 / 2.9x103 / 3.6x104

132Sn 40. 9.3x102 / 3.0x104 / 3.7x105 3.5x101 / 1.1x103 / 1.4x104

138Xe 846. 2.5x104 / 7.8x105 / 9.8x106 1.8x103 / 5.8x104 / 7.2x105

110Mo 2.8 1.6x102 / 5.0x103 / 6.2x104 5.8x100 / 1.8x102 / 2.3x103

111Mo 0.5 8.3x100 / 2.6x102 / 3.3x103 0.3x100 / 9.6x100 / 1.2x102


Early physics program

Once in full production mode, the experimental program will be determined by the PAC … we are here just putting down informed guesses as to what would make the most sense early on with reduced intensities.

Even at reduced intensities in the first half year, CARIBU will provide unique physics possibilities

– Low-energy • Mass measurements• Decay studies

– Reaccelerated beams• Coulomb excitation• Single nucleon transfer reactions

This early physics program will also be a learning period on the machine and experimental sides.


Astrophysics: the r-process path

r-process:- Process known to

exist- Exact site unknown- Path critically depends

on nuclear properties of neutron-rich nuclei:- mass- lifetime -delayed neutrons- fissionability

Fission recycling

Efficient techniques exist to obtain this information but the required beams are missing in most of this region of the chart of nuclides.


Mass measurements on neutron-rich isotopes

Continuation of CPT program

Greatly benefits from even the weakest CARIBU source

– Requires > 0.1 ion/s

All marked nuclei accessible with 80 mCi source

All but about half of the grey nuclei are accessible with 2.5 mCi source

CPT moved to CARIBU for about 1.5 years to take advantage of these opportunities

N ew CPT/O ld CPTM easurem ents

N ew CPT/O ld CPTM easurem ents

CARIBU (1 Ci source) Extracted Fission Product Yield


CARIBU

Moving the CPT to CARIBU

CPT tower moved into CARIBU

experimental area at the end of July:

CPT tower, electronics and superconducting magnet in final

position at CARIBU:


Initial focus of measurements with the CPT at CARIBU

First measurements:

• 132Sn and neighbors

• 130Cd and neighbors

Future measurements:

• go as neutron-rich as possible … on r-process path


Tape station for decay spectroscopy, beam diagnostics, …

Tape station for beam diagnostics

– beta counter

– simple gamma detection system

Tape station for decay spectroscopy

– detector systems• X-array• Total absorption spectrometer• Neutron detectors• 4 beta counter

– research topics• nuclear spectroscopy• r-process• decay heat and other

applications

existing tape station

new tape stations under construction and X-array


CARIBU low-energy area experimental equipment

diagno

stics

tape s

tation

decay

tape

statio

n

CPTCPT

lase

r ta

ble

ion trap


GSFMA 155 (February 2005)Background subtracted, Doppler corrected spectrum

138Ce@480MeV


How much beam do we need with Gammasphere?

105

104

103

102

103

102

10

104

10

103

102

14h at 6.109 pps!1/25

1/250

1/2500

107 pps for 2 weeks

106 pps for 2 weeks

105 pps for 2 weeks

• To get B(E2) of first 2+ state, we need ≥ 102 pps

• To identify excited 2+ state (beyond the 2+1) in

vibrational nucleus (B(E2)~1Wu) with Gammasphere for 2 weeks beam time we need ~105 pps.

•For complete spectroscopy, 106-107 pps is needed


How Octupole collective are neutron rich barium nuclei?This has been an open question for 20 years.

Fission fragment spectroscopy and -decay have found parity-doublet bands of states.

But almost NO data on real matrix elements, either quadrupole or octupole.

Octupole correlations only from E1/E2 ratios

Key Study: Coulomb excitation of 144,146Ba

On Lead target at ~750MeV for multi-step.

On Carbon target at ~630MeV for non-yrast.

Measure

B(E1), B(E2), B(E3)

GS Photopeak yield with 104pps ~ 70 cts/hr

Leander at al PL 152B (1985)


Requirements of n-rich physics: Nucleon transfer reaction … single particle state

Single particle/hole states around magic nuclei• 132Sn, 104Zr, 78Ni

(d,p) reactions

– best done well above Coulomb barrier in both entrance and exit channels … i.e. about 7.5 MeV/u around 132Sn

– requires 104 per second to get information on angular distribution

(3He, ), (,t) reactions

– Well matched to higher angular momentum transfer

– Energy requirements again set by Coulomb barrier … want ~ 11 MeV/u

– Required beams are not available anywhere at present

The Helios spectrometer, together with the beam energies available with the ATLAS upgrade, provides ideal conditions for these experiments.

132Sn(d,p) 7.5 MeV/u

0

10

20

30

40

50

0 90 180angle (degree)

cros

s-se

ctio

n (m

b/sr

)

L=0

L=1

L=2

L=3

L=4

L=5

L=6

132Sn( ,3He) 11 MeV/u

0.001

0.01

0.1

1

10

0 10 20 30 40 50

angle (degree)

cros

s-se

ctio

n (m

b/sr

) L=1

L=3

L=5

L=6

A No Strip Strip No Strip Strip16 13.0 15.7 18.5 21.540 12.4 13.4 17.5 19.958 9.9 11.8 13.5 17.978 9.5 11.2 12.8 16.7132 8.0 9.3 10.4 13.4197 6.6 7.9 8.4 10.9238 6.4 7.4 7.9 10.0

Current ATLAS ATLAS Upgrade


Evolution of shell gaps in neutron-rich nuclei

CARIBU Reach


Single-neutron transfer on N=82: CARIBU ATLAS HELIOS➝ ➝

• d(134Te,p)135Te @ 8 MeV/u

• Q value = 1.115 MeV, B = 2T

• Clearly identify low-ℓ transfer (1,3) from angular distributions

• Isobaric contaminants low (factor 10 lower), recoil detector not crucial

• Expect ~1×104 134Te per second on 200 μgcm–2 CD2 target with (d,p) cross sections of ~1-15 mb/sr

• Current array ~50% ‘dead’ area, however, ~6 days beam should yield >1000 cts per state.


Scheduling constraints

CARIBU will use 3 different degrader foil thicknesses to cover the full range of fission fragments

• one degrader to cover the light fission peak, two degraders to cover the heavy fission peak

• System is designed so that the degraders can be changed locally without going back to the hot cells

Initial commissioning of CARIBU will be performed with a 143Ba beam … hence a degrader tuned for this mass range

These beams will be used to “debug” CARIBU, this might take some time, and hence the first series of CARIBU experiments must concentrate on this mass range

Next degrader will be tuned for the light masses and experiments will concentrate around the Mo and Zr region which are particularly interesting for nuclear structure physics.


CARIBU beamtime scheduling

The PAC will accept proposals for CARIBU beams once we have gained sufficient understanding of what beams will be available, at what intensity, with what properties, and how well they can be used in the different experimental setups

Until then, CARIBU beamtime will be used to determine the real capabilities of the new facility, emphasizing:

– determining the yields at low energy and with reaccelerated beams … with some measurements on both the heavy and light fission peaks

– commissioning beam diagnostics and accelerator tuning

– learning how to use the various experimental setups with these beams

This development period is expected to last until the end of the year and during this period the physics that can be performed simultaneously with the development runs will be opened to all collaboration members


Single-neutron transfer on N=82: CARIBU ATLAS HELIOS➝ ➝144Smstable

143Pm

142Ndstable

141Prstable

140Cestable

139Lastable

138Bastable

137Cs>106

136Xestable

135I>106

134Te>106

133Sb>106

132Sn105-106

N=82

Z=50

(A-Z

) in

crea

ses

• Key nuclear structure: energies (and character) of single-particle states in these nuclei are essential information for nuclear structure models.

• The N=82 isotones allow us to track the evolution of single-particle energies over a large range of neutron excess.

• Data limited to only the stable N=82 isotones.

• CARIBU provides intense beams for the 50≤Z≤54 – so far no definitive data for these.

• HELIOS, with prototype detectors, capable of these measurements

• Low-lying states thoroughly studied

• (d,p) low-ℓ transfer • (α,3He) high-ℓ transfer• Recent interest in the

evolution of h9/2 and i13/2 orbitals

• Gas-cell target (d,p), poor resolution

• GSI, 1991, did reaction in inverse kinematics

• ORNL, 2005, 13C(136Xe,12C) γ, γ correlations

(Near) future CARIBU beam

• 13C(134Te,12C) correlations• ORNL, 2007, d(134Te,p)• Do (d,p) at optimum beam

energy now


Preparation for mass measurements at CARIBU

Site preparation ongoing

Need to turn CW 50 keV beam into 3 keV bunched beam for highest efficiency

• RFQ buncher under construction within CPT collaboration

• Beamline optics calculations completed

• CPT was turned off at ATLAS in July and main components have been moved to CARIBU

CPT reassembly at CARIBU should be completed in September

Deceleration optics

RFQ buncher

“Elevator”

to CARIBU low-energy

area


Do neutron rich barium nuclei show X(5) symmetry?

Analytic model for nuclei at critical point of transition from spherical to deformed shapes

Provides good description of N = 90 isotones of Nd, Sm, and Gd

Key signatures involve low-spin, non-yrast states

Lighter Z, N=90 nuclei seem to have similar structure BUT essential states are not known

Key Study:

Beta decay into 146,148Ce

Measure:

Non-yrast state energies and branching ratios

ATLAS Users Workshop August 8-9 2009 CARIBU: early science program Guy Savard Argonne National...

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Transcript of ATLAS Users Workshop August 8-9 2009 CARIBU: early science program Guy Savard Argonne National...