Mass measurements on
neutron-rich nuclei with
the CPT mass
spectrometer @ CARIBU
Kumar S. Sharma
Department of Physics and Astronomy
Winnipeg MB
Outline
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Introduction
Past work with the CPT at ANL
CARIBU – opportunities for the CPT
Current status of the apparatus
Conclusion
Synthesis of the elements
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The r-process plays an important
role in the synthesis of the heavier
elements
from :
http://www.jinaweb.org/html/pprocess.html
Possible sites for the
r-process
Supernovae???
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Merging neutron stars???
Why these sources:
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high density of neutrons
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high temperature environments
r-process basics
(n,γ)
(γ,n)
β-
…
Z
N
Seed
Waiting-point
Nuclear reactions compete until a balance is reached
Abundance maxima along each chain occurs with the neutron separation
energy, Sn ~ 3 MeV
The Saha Equation
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The relative abundances of the elements synthesized in
the r-process are determined by the Saha Equation:
3
 2   A  1 
Y ( Z , A  1)
 nn 
 

Y ( Z , A)
kT
A




2
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2
3
2
G  Z , A  1
G  Z , A
 Sn  Z , A  1 
exp 

kT


determines the equilibrium between neutron capture and
photodisintegration in a very hot environment.
outcome is exponentially dependent on the neutron
separation energy.
Atomic masses of the nuclides along the reaction paths are
needed to determine the neutron separation energy: Sn
Neutron separation energies
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Single neutron separation energies:
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Sn values: [n – (M(Z,N) – M(Z, N-1))]c2
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Double neutron separation energies
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S2n values: [2n – (M(Z,N) – M(Z, N-2))]c2
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Converted to appropriate energy units
Fission Yields from a 252Cf source
1 Ci source
strength
Previous configuration of the CPT
CPT Fission Fragment Measurements
New CPT /
Previous CPT
measurements
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Ongoing program of measurements since March 2008, target 15 keV uncertainty
40 species, 5 have never been previously measured by any means, most others improved
by a typical factor of 5
Adds to 30 measurements taken at CPT in past years with small gas catcher
Comparisons with the AME03
JYFLTRAP
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1500
1300
1100
900
700
500
300
100
-100
-300
-500
AME2003
CPT
Ba
ME(Expt.)-AME2003) [keV]
ME(Expt.) - (AME2003) [keV]
CPT
1500
1300
1100
900
700
500
300
100
-100
-300
-500
AME2003
CPT
La
84 85 86 87 88 89 90 91 92 93 94
84 85 86 87 88 89 90 91 92 93 94
Neutron Number
Neutron Number
Deviations from 2003 atomic mass
evaluation increase with neutron number
Trends suggest r-process path is closer to
stability
U. Hager et al., Phys. Rev. Lett. 96, 042504 (2006).
S2n values: [2n – (M(Z,N) – M(Z, N-2))]c2
More recent work
Grander Plans
New CPT /
Previous CPT
measurements
What’s moving?
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CPT Tower
Associated electronics and vacuum control
Overview of CARIBU
CPT at CARIBU
CPT
CARIBU
Stable ion
source
Buncher
Elevator
Low energy beamline
Requirements at CARIBU
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Desired precision: ~ 10 – 100 keV
Required yield: 3000-30000 ions for a measurement
Considerations:
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‘Production’ yield (2-80 mCi)
Efficiency (~ 1%)
Half-life ~ 1 second
Plan for measurements
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Get online ASAP
 Gas catcher/RFQ
operational
 Buncher RFQ built and
being commisioned
 CPT assembled and
operational
 Low energy beam line
installed
Spend 6 to 18 months
measuring 100+ masses to <
10-7
Goals include r-process and
nuclear structure
Vastly
superior
to 238U
fission
Jon’s
Dan’s
Conclusion
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Previous results among neutron-rich nuclei
approaching the r-process path
Some interesting systematic effects observed
Higher yields of these nuclei at CARIBU will
allow us to push even further away from stability
The CPT Collaboration
A. Chaudhuri, G. Gwinner , K.S. Sharma
J.A. Clark, A.F. Levand, G. Savard, T. Sun,
F. Buchinger, J.E. Crawford, S. Gulick, G. Li
S. Caldwell, M. Sternberg, J. Van Schelt
D. Lascar, R. Segel
C.M. Deibel
Efficiencies at CARIBU
Efficiency:
• Yield (2-80 mCi 252Cf; 3% fission branch)
• Enter gas catcher (~ 50%)
• Stopped in gas catcher (~ 80%)
• Extracted from gas catcher (~ 33%)
• RFQ (~ 80%)
• Transfer through mass separator (~90%)
• Buncher (~ 60%)
• Transfer to Penning trap (~ 33%)
• Detection (~ 50%)
Total: ~ 1% efficiency
(excluding 3% fission branch)