mass measurements on neutron-rich nuclei with the cpt mass spectrometer @ caribu kumar s. sharma...
TRANSCRIPT
Mass Mass measurements on measurements on
neutron-rich nuclei neutron-rich nuclei with the CPT mass with the CPT mass
spectrometer @ spectrometer @ CARIBUCARIBUKumar S. SharmaKumar S. Sharma
Department of Physics and Department of Physics and AstronomyAstronomy
Winnipeg MBWinnipeg MB
OutlineOutline
IntroductionIntroduction Past work with the CPT at ANLPast work with the CPT at ANL CARIBU – opportunities for the CPTCARIBU – opportunities for the CPT Current status of the apparatusCurrent status of the apparatus ConclusionConclusion
Synthesis of the Synthesis of the elementselements
from : http://www.jinaweb.org/html/pprocess.html
The r-process plays an The r-process plays an important role in the important role in the synthesis of the heavier synthesis of the heavier elementselements
Possible sites for the Possible sites for the r-processr-process
Why these sources:Why these sources: high density of neutronshigh density of neutrons high temperature high temperature
environmentsenvironments
Supernovae??? Merging neutron stars???
r-process basicsr-process basics
Nuclear reactions compete until a balance is reached
Abundance maxima along each chain occurs with the neutron separation energy, Sn ~ 3 MeV
N
Z
(n,γ)
(γ,n)
β-
Seed Waiting-point
…
The Saha EquationThe Saha Equation
The relative abundances of the elements The relative abundances of the elements synthesized in the r-process are determined by synthesized in the r-process are determined by the Saha Equation:the Saha Equation:
determines the equilibrium between neutron capture determines the equilibrium between neutron capture and photodisintegration in a very hot environment.and photodisintegration in a very hot environment.
outcome is outcome is exponentiallyexponentially dependent on the neutron dependent on the neutron separation energy.separation energy.
Atomic masses of the nuclides along the reaction Atomic masses of the nuclides along the reaction paths are needed to determine the neutron separation paths are needed to determine the neutron separation energy: Senergy: Snn
3 32 2 2 , 1 , 1( , 1) 2 1
exp( , ) ,
nn
G Z A S Z AY Z A An
Y Z A kT A G Z A kT
Neutron separation Neutron separation energiesenergies
Single neutron separation energies:Single neutron separation energies:
SSnn values: [n – (M(Z,N) – M(Z, N-1))]c values: [n – (M(Z,N) – M(Z, N-1))]c22
Double neutron separation energiesDouble neutron separation energies
SS2n2n values: [2n – (M(Z,N) – M(Z, N-2))]c values: [2n – (M(Z,N) – M(Z, N-2))]c22
Converted to appropriate energy units
New CPT /
Previous CPT measurements
CPT Fission Fragment CPT Fission Fragment MeasurementsMeasurements
Ongoing program of measurements since March 2008, target 15 keV Ongoing program of measurements since March 2008, target 15 keV uncertaintyuncertainty
40 species, 5 have never been previously measured by any means, most 40 species, 5 have never been previously measured by any means, most others improved by a typical factor of 5others improved by a typical factor of 5
Adds to 30 measurements taken at CPT in past years with small gas catcherAdds to 30 measurements taken at CPT in past years with small gas catcher
Comparisons with the Comparisons with the AME03AME03
CPT
U. Hager et al., Phys. Rev. Lett. 96, 042504 (2006).
JYFLTRAP
-500-300-100100300500700900
110013001500
84 85 86 87 88 89 90 91 92 93 94Neutron Number
ME
(Exp
t.)-
AM
E20
03)
[keV
] AME2003
CPT La
-500-300-100100300500700900
110013001500
84 85 86 87 88 89 90 91 92 93 94Neutron Number
ME
(Ex
pt.
) -
(AM
E2
00
3)
[ke
V]
AME2003
CPT Ba
Deviations from 2003 atomic Deviations from 2003 atomic mass evaluation increase with mass evaluation increase with neutron numberneutron number
Trends suggest r-process path is Trends suggest r-process path is closer to stabilitycloser to stability
What’s moving?What’s moving? CPT TowerCPT Tower Associated electronics and vacuum controlAssociated electronics and vacuum control
Requirements at CARIBURequirements at CARIBU Desired precision: ~ 10 – 100 keVDesired precision: ~ 10 – 100 keV Required yield: 3000-30000 ions for a Required yield: 3000-30000 ions for a
measurementmeasurement Considerations:Considerations:
‘ ‘Production’ yield (2-80 mCi)Production’ yield (2-80 mCi) Efficiency (~ 1%)Efficiency (~ 1%) Half-life ~ 1 secondHalf-life ~ 1 second
Plan for measurementsPlan for measurements
Jon’sDan’s
Vastly superior to 238U fission
Get online ASAPGet online ASAP Gas catcher/RFQ Gas catcher/RFQ
operationaloperational Buncher RFQ built Buncher RFQ built
and being and being commisionedcommisioned
CPT assembled and CPT assembled and operationaloperational
Low energy beam Low energy beam line installedline installed
Spend 6 to 18 months Spend 6 to 18 months measuring 100+ measuring 100+ masses to < 10masses to < 10-7-7
Goals include r-Goals include r-process and nuclear process and nuclear structure structure
ConclusionConclusion
Previous results among neutron-rich Previous results among neutron-rich nuclei approaching the r-process nuclei approaching the r-process pathpath
Some interesting systematic effects Some interesting systematic effects observedobserved
Higher yields of these nuclei at Higher yields of these nuclei at CARIBU will allow us to push even CARIBU will allow us to push even further away from stabilityfurther away from stability
The CPT CollaborationThe 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
D. Lascar, R. Segel
S. Caldwell, M. Sternberg, J. Van Schelt
C.M. Deibel
Efficiencies at CARIBUEfficiencies at CARIBUEfficiency:
• 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)