atlas users workshop august 8-9 2009 caribu: early science program guy savard argonne national...
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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
3G. Savard 2009 ATLAS Users Workshop August 8-9 2009
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
4G. Savard 2009 ATLAS Users Workshop August 8-9 2009
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
5G. Savard 2009 ATLAS Users Workshop August 8-9 2009
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.
6G. Savard 2009 ATLAS Users Workshop August 8-9 2009
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.
7G. Savard 2009 ATLAS Users Workshop August 8-9 2009
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
8G. Savard 2009 ATLAS Users Workshop August 8-9 2009
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:
9G. Savard 2009 ATLAS Users Workshop August 8-9 2009
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
10G. Savard 2009 ATLAS Users Workshop August 8-9 2009
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
11G. Savard 2009 ATLAS Users Workshop August 8-9 2009
CARIBU low-energy area experimental equipment
diagno
stics
tape s
tation
decay
tape
statio
n
CPTCPT
lase
r ta
ble
ion trap
12G. Savard 2009 ATLAS Users Workshop August 8-9 2009
GSFMA 155 (February 2005)Background subtracted, Doppler corrected spectrum
138Ce@480MeV
13G. Savard 2009 ATLAS Users Workshop August 8-9 2009
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
14G. Savard 2009 ATLAS Users Workshop August 8-9 2009
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)
15G. Savard 2009 ATLAS Users Workshop August 8-9 2009
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
16G. Savard 2009 ATLAS Users Workshop August 8-9 2009
Evolution of shell gaps in neutron-rich nuclei
CARIBU Reach
17G. Savard 2009 ATLAS Users Workshop August 8-9 2009
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.
18G. Savard 2009 ATLAS Users Workshop August 8-9 2009
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.
19G. Savard 2009 ATLAS Users Workshop August 8-9 2009
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
20G. Savard 2009 ATLAS Users Workshop August 8-9 2009
21G. Savard 2009 ATLAS Users Workshop August 8-9 2009
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
22G. Savard 2009 ATLAS Users Workshop August 8-9 2009
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
23G. Savard 2009 ATLAS Users Workshop August 8-9 2009
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