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Studies of neutron-rich nuclei using the CPT massspectrometer at CARIBUTo cite this article A Chaudhuri et al 2011 J Phys Conf Ser 312 042009

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Studies of neutron-rich nuclei using the CPT mass

spectrometer at CARIBU

A Chaudhuri12 P F Bertone2 F Buchinger3 S Caldwell42 J A

Clark2 J E Crawford3 C M Deibel52 S Gulick3 D Lascar62 A F

Levand2 G Li32 G Savard24 R E Segel6 K S Sharma1 M G

Sternberg42 T Sun2 and J Van Schelt42

1 Department of Physics and Astronomy University of Manitoba Winnipeg MB R3T 2N2Canada2 Physics Division Argonne National Laboratory Argonne IL 60439 USA3 Department of Physics McGill University Montreal QC H3A 2T8 Canada4 Department of Physics University of Chicago Chicago IL 60637 USA5 Joint Institute for Nuclear Astrophysics Michigan State University East Lansing MI 48824USA6 Department of Physics and Astronomy Northwestern University Evanston IL 60208 USA

E-mail ankurphysicsumanitobaca

Abstract The nucleosynthetic path of the astrophysical r-process and the resulting elementalabundances depend on neutron-separation energies which can be determined from the masses ofthe nuclei along the r-process reaction path Due to the current lack of experimental data massmodels are often used The mass values provided by the mass models are often too impreciseor disagree with each other Therefore direct high-precision mass measurements of neutron-rich nuclei are necessary to provide input parameters to the calculations and help refine themass models The Californium Rare Isotope Breeder Upgrade (CARIBU) facility of ArgonneNational Laboratory will provide experiments with beams of short-lived neutron-rich nucleiThe Canadian Penning Trap (CPT) mass spectrometer has been relocated to the CARIBU low-energy beam line to extend measurements of the neutron-rich nuclei into the mostly unexploredregion along the r-process path This will allow precise mass measurements (sim 10 keVc2) ofmore than a hundred very neutron-rich isotopes that have not previously been measured

The basic framework for understanding the various nucleosynthesis processes occurring instars and supernovae which are crucial for the stellar energy generation and the creation ofheavy elements in the universe was summarized in [1] The rapid neutron-capture process (r-process) is responsible for the creation of about half of the elements heavier than iron in theuniverse [2 3 4] However the astrophysical site of the r-process is not known with certainty Ithas been believed that this process takes place in exploding supernovae because of the requiredhigh-neutron densities A number of possible theoretical models exist to explain the r-processwith different degrees of success Among other data nuclear masses probably have the mostdecisive influence on the reaction rates and r-process path [2] They determine the neutroncapture Q-value and the position of neutron drip line which are of particular importance inr-process modelsThe r-process is not well understood partly due to the lack of reliable nuclear data involving thevery neutron-rich isotopes participating in the r-process These isotopes are not easily produced

International Nuclear Physics Conference 2010 (INPC2010) IOP PublishingJournal of Physics Conference Series 312 (2011) 042009 doi1010881742-65963124042009

Published under licence by IOP Publishing Ltd 1

in the laboratory Due to the current lack of experimental data on atomic masses in this regionmass models are often used to provide the needed inputs to r-process calculations However themass values provided by the models particularly as one moves further away from nuclei whosemasses are known are often too imprecise or disagree with each other Therefore direct high-precision mass measurements of neutron-rich nuclei are necessary to provide input parametersto the calculations and help refine the mass modelsPenning traps have been widely used as a very accurate tool for high-precision mass spectrom-etry Recently high-precision mass measurements of short-lived neutron-rich nuclei have beenperformed with the Canadian Penning Trap (CPT) mass spectrometer at the ATLAS facilityof the Argonne National Laboratory [5 6] The nuclei measured were obtained from the spon-taneous fission of a 100 microCi 252Cf fission source inside a gas catcher [7] The fission productswere stopped and thermalized in the gas catcher system The ions were injected into the firstPenning trap where the sample is purified by a mass-selective buffer gas cooling [8] The selectedions were transferred into the precision Penning trap where the cyclotron frequency is measuredby a time-of-flight detection method [9] A high-precision mass determination is carried outby measuring the ion cyclotron frequency ωc = qBmion where qmion is the charge-to-massratio of the ion and B is the strength of the magnetic field The mass of the ion of interest isobtained from the comparison of its cyclotron frequency ωc with that of a well-known referenceion Details of the CPT mass measurement technique can be found in [10 11]

Figure 1 Schematic layout of the CARIBU high-voltage platform and the low-energy beamline The location of the (A) ion sourcegas catcher (B) isobar separator (C) RFQ buncher(D) elevator (E) parallel plate and spherical deflector assembly and the (F) CPT are shownalong the beam-line

Recent technological advances in radio-active ion beam production [12] opened a new erain nuclear physics An interesting scheme for radio-active ion beam production for studies ofr-process nuclei is the Californium Rare Isotope Breeder Upgrade (CARIBU) project [13 14] atthe ATLAS facility of Argonne National Laboratory The fission fragments from a 252Cf fissionsource (with an eventual strength of 1 Ci) will be thermalized and extracted from a gas catchersystem as a low-energy beam These beams of short-lived neutron-rich nuclei will be available

International Nuclear Physics Conference 2010 (INPC2010) IOP PublishingJournal of Physics Conference Series 312 (2011) 042009 doi1010881742-65963124042009

2

for a variety of experiments The CPT spectrometer has been relocated to the CARIBU low-energy beam line to allow us to continue our mass measurements on neutron-rich nuclei in anunexplored regionThe low-energy beam line to transfer the low-emittance ion beam from CARIBU to the CPTis under construction (figure 1) Beam-line optics calculations were done using SIMION Rcopy

software package An RFQ buncher is installed for the manipulation of the 50 keV continuousion beam from CARIBU Bunched ions will enter a 300 mm long pulsed cavity (elevator) whichwill bring the 50 keV ion beam to 15 keV or 10 keV ion beam depending on the requirement ofthe low-energy experiments The CPT is positioned approximately 58 m downstream from theelevator Einzel lenses and steerers are appropriately positioned to allow the efficient transferof the low-emittance (sim 20 π mm mrad at 15 keV) pulsed ion beam to CPT In addition asurface-ionization ion source (HeatWave Labs model 101139) to test the CPT system at thenew location is recently installedThe low-energy ion beam from CARIBU will also be delivered to other low-energy experiments

Figure 2 Ion trajectory through the combination of parallel-plate and spherical deflectorassembly as simulated using the SIMION Rcopy software package

by deflecting the beam by 45o into the alternate beam-line A combination of parallel-plate andspherical deflector located approximately 25 m downstream from the elevator will be used Theparallel-plate deflector will either allow the ion beam to reach the CPT or deflect the beam by 5o

to allow entry into the 40o spherical electrode deflector which in turn will direct the beam intothe alternate beam-line (figure 2) The spherical deflector consists of two concentric sphericalelectrode sections with radii of 267 mm and 285 mm respectively and will provide focusing inboth the plane of deflection and the orthogonal planeThe installation of the CPT at the new location will allow the precise mass measurements ofmore than a hundred very neutron-rich isotopes that have not been previously measured witha precision of sim 10 keVc2 These measurements will greatly improve our ability to predict theoutcomes of the r-process

Acknowledgments

This work is supported by NSERC Canada application number 216974 and the USDepartment of Energy Office of Nuclear Physics under Contract No DE-AC02-06CH11357

International Nuclear Physics Conference 2010 (INPC2010) IOP PublishingJournal of Physics Conference Series 312 (2011) 042009 doi1010881742-65963124042009

3

References[1] Burbidge E M Burbidge G R Fowler W A and Hoyle F 1957 Rev Mod Phys 29 547[2] Cowan J J Thielemann F-K and Truran J 1991 Phys Rep 208 267[3] Qian Y-Z 2003 Prog Part Nucl Phys 50 153[4] Sneden C and Cowan J J 2003 Science 299 70[5] Savard G et al 2006 Int J Mass Spectrom 251 252[6] Van Schelt J et al 2008 Proc 10th Symp Nuclei in the Cosmos Mackinac Island Michigan 2008 PoS NIC

X 150[7] Savard G et al 2003 Nucl Instrum Meth B 204 582[8] Savard G et al 1991 Phys Lett A 158 247[9] Graff G Kalinowsky H and Traut J 1980 Z Phys A 297 35[10] Fallis J et al 2008 Phys Rev C 78 022801(R)[11] Clark J A et al 2007 Phys Rev C 75 032801(R)[12] Tanihata I 2008 Nucl Instrum Meth B 266 4067[13] Pardo R C et al 2007 Nucl Instrum Meth B 261 965[14] Savard G et al 2008 Nucl Instrum Meth B 266 4086

International Nuclear Physics Conference 2010 (INPC2010) IOP PublishingJournal of Physics Conference Series 312 (2011) 042009 doi1010881742-65963124042009

4

in the laboratory Due to the current lack of experimental data on atomic masses in this regionmass models are often used to provide the needed inputs to r-process calculations However themass values provided by the models particularly as one moves further away from nuclei whosemasses are known are often too imprecise or disagree with each other Therefore direct high-precision mass measurements of neutron-rich nuclei are necessary to provide input parametersto the calculations and help refine the mass modelsPenning traps have been widely used as a very accurate tool for high-precision mass spectrom-etry Recently high-precision mass measurements of short-lived neutron-rich nuclei have beenperformed with the Canadian Penning Trap (CPT) mass spectrometer at the ATLAS facilityof the Argonne National Laboratory [5 6] The nuclei measured were obtained from the spon-taneous fission of a 100 microCi 252Cf fission source inside a gas catcher [7] The fission productswere stopped and thermalized in the gas catcher system The ions were injected into the firstPenning trap where the sample is purified by a mass-selective buffer gas cooling [8] The selectedions were transferred into the precision Penning trap where the cyclotron frequency is measuredby a time-of-flight detection method [9] A high-precision mass determination is carried outby measuring the ion cyclotron frequency ωc = qBmion where qmion is the charge-to-massratio of the ion and B is the strength of the magnetic field The mass of the ion of interest isobtained from the comparison of its cyclotron frequency ωc with that of a well-known referenceion Details of the CPT mass measurement technique can be found in [10 11]

Figure 1 Schematic layout of the CARIBU high-voltage platform and the low-energy beamline The location of the (A) ion sourcegas catcher (B) isobar separator (C) RFQ buncher(D) elevator (E) parallel plate and spherical deflector assembly and the (F) CPT are shownalong the beam-line

Recent technological advances in radio-active ion beam production [12] opened a new erain nuclear physics An interesting scheme for radio-active ion beam production for studies ofr-process nuclei is the Californium Rare Isotope Breeder Upgrade (CARIBU) project [13 14] atthe ATLAS facility of Argonne National Laboratory The fission fragments from a 252Cf fissionsource (with an eventual strength of 1 Ci) will be thermalized and extracted from a gas catchersystem as a low-energy beam These beams of short-lived neutron-rich nuclei will be available

International Nuclear Physics Conference 2010 (INPC2010) IOP PublishingJournal of Physics Conference Series 312 (2011) 042009 doi1010881742-65963124042009

2

for a variety of experiments The CPT spectrometer has been relocated to the CARIBU low-energy beam line to allow us to continue our mass measurements on neutron-rich nuclei in anunexplored regionThe low-energy beam line to transfer the low-emittance ion beam from CARIBU to the CPTis under construction (figure 1) Beam-line optics calculations were done using SIMION Rcopy

software package An RFQ buncher is installed for the manipulation of the 50 keV continuousion beam from CARIBU Bunched ions will enter a 300 mm long pulsed cavity (elevator) whichwill bring the 50 keV ion beam to 15 keV or 10 keV ion beam depending on the requirement ofthe low-energy experiments The CPT is positioned approximately 58 m downstream from theelevator Einzel lenses and steerers are appropriately positioned to allow the efficient transferof the low-emittance (sim 20 π mm mrad at 15 keV) pulsed ion beam to CPT In addition asurface-ionization ion source (HeatWave Labs model 101139) to test the CPT system at thenew location is recently installedThe low-energy ion beam from CARIBU will also be delivered to other low-energy experiments

Figure 2 Ion trajectory through the combination of parallel-plate and spherical deflectorassembly as simulated using the SIMION Rcopy software package

by deflecting the beam by 45o into the alternate beam-line A combination of parallel-plate andspherical deflector located approximately 25 m downstream from the elevator will be used Theparallel-plate deflector will either allow the ion beam to reach the CPT or deflect the beam by 5o

to allow entry into the 40o spherical electrode deflector which in turn will direct the beam intothe alternate beam-line (figure 2) The spherical deflector consists of two concentric sphericalelectrode sections with radii of 267 mm and 285 mm respectively and will provide focusing inboth the plane of deflection and the orthogonal planeThe installation of the CPT at the new location will allow the precise mass measurements ofmore than a hundred very neutron-rich isotopes that have not been previously measured witha precision of sim 10 keVc2 These measurements will greatly improve our ability to predict theoutcomes of the r-process

Acknowledgments

This work is supported by NSERC Canada application number 216974 and the USDepartment of Energy Office of Nuclear Physics under Contract No DE-AC02-06CH11357

International Nuclear Physics Conference 2010 (INPC2010) IOP PublishingJournal of Physics Conference Series 312 (2011) 042009 doi1010881742-65963124042009

3

References[1] Burbidge E M Burbidge G R Fowler W A and Hoyle F 1957 Rev Mod Phys 29 547[2] Cowan J J Thielemann F-K and Truran J 1991 Phys Rep 208 267[3] Qian Y-Z 2003 Prog Part Nucl Phys 50 153[4] Sneden C and Cowan J J 2003 Science 299 70[5] Savard G et al 2006 Int J Mass Spectrom 251 252[6] Van Schelt J et al 2008 Proc 10th Symp Nuclei in the Cosmos Mackinac Island Michigan 2008 PoS NIC

X 150[7] Savard G et al 2003 Nucl Instrum Meth B 204 582[8] Savard G et al 1991 Phys Lett A 158 247[9] Graff G Kalinowsky H and Traut J 1980 Z Phys A 297 35[10] Fallis J et al 2008 Phys Rev C 78 022801(R)[11] Clark J A et al 2007 Phys Rev C 75 032801(R)[12] Tanihata I 2008 Nucl Instrum Meth B 266 4067[13] Pardo R C et al 2007 Nucl Instrum Meth B 261 965[14] Savard G et al 2008 Nucl Instrum Meth B 266 4086

International Nuclear Physics Conference 2010 (INPC2010) IOP PublishingJournal of Physics Conference Series 312 (2011) 042009 doi1010881742-65963124042009

4

for a variety of experiments The CPT spectrometer has been relocated to the CARIBU low-energy beam line to allow us to continue our mass measurements on neutron-rich nuclei in anunexplored regionThe low-energy beam line to transfer the low-emittance ion beam from CARIBU to the CPTis under construction (figure 1) Beam-line optics calculations were done using SIMION Rcopy

software package An RFQ buncher is installed for the manipulation of the 50 keV continuousion beam from CARIBU Bunched ions will enter a 300 mm long pulsed cavity (elevator) whichwill bring the 50 keV ion beam to 15 keV or 10 keV ion beam depending on the requirement ofthe low-energy experiments The CPT is positioned approximately 58 m downstream from theelevator Einzel lenses and steerers are appropriately positioned to allow the efficient transferof the low-emittance (sim 20 π mm mrad at 15 keV) pulsed ion beam to CPT In addition asurface-ionization ion source (HeatWave Labs model 101139) to test the CPT system at thenew location is recently installedThe low-energy ion beam from CARIBU will also be delivered to other low-energy experiments

Figure 2 Ion trajectory through the combination of parallel-plate and spherical deflectorassembly as simulated using the SIMION Rcopy software package

by deflecting the beam by 45o into the alternate beam-line A combination of parallel-plate andspherical deflector located approximately 25 m downstream from the elevator will be used Theparallel-plate deflector will either allow the ion beam to reach the CPT or deflect the beam by 5o

to allow entry into the 40o spherical electrode deflector which in turn will direct the beam intothe alternate beam-line (figure 2) The spherical deflector consists of two concentric sphericalelectrode sections with radii of 267 mm and 285 mm respectively and will provide focusing inboth the plane of deflection and the orthogonal planeThe installation of the CPT at the new location will allow the precise mass measurements ofmore than a hundred very neutron-rich isotopes that have not been previously measured witha precision of sim 10 keVc2 These measurements will greatly improve our ability to predict theoutcomes of the r-process

Acknowledgments

This work is supported by NSERC Canada application number 216974 and the USDepartment of Energy Office of Nuclear Physics under Contract No DE-AC02-06CH11357

International Nuclear Physics Conference 2010 (INPC2010) IOP PublishingJournal of Physics Conference Series 312 (2011) 042009 doi1010881742-65963124042009

3

References[1] Burbidge E M Burbidge G R Fowler W A and Hoyle F 1957 Rev Mod Phys 29 547[2] Cowan J J Thielemann F-K and Truran J 1991 Phys Rep 208 267[3] Qian Y-Z 2003 Prog Part Nucl Phys 50 153[4] Sneden C and Cowan J J 2003 Science 299 70[5] Savard G et al 2006 Int J Mass Spectrom 251 252[6] Van Schelt J et al 2008 Proc 10th Symp Nuclei in the Cosmos Mackinac Island Michigan 2008 PoS NIC

X 150[7] Savard G et al 2003 Nucl Instrum Meth B 204 582[8] Savard G et al 1991 Phys Lett A 158 247[9] Graff G Kalinowsky H and Traut J 1980 Z Phys A 297 35[10] Fallis J et al 2008 Phys Rev C 78 022801(R)[11] Clark J A et al 2007 Phys Rev C 75 032801(R)[12] Tanihata I 2008 Nucl Instrum Meth B 266 4067[13] Pardo R C et al 2007 Nucl Instrum Meth B 261 965[14] Savard G et al 2008 Nucl Instrum Meth B 266 4086

International Nuclear Physics Conference 2010 (INPC2010) IOP PublishingJournal of Physics Conference Series 312 (2011) 042009 doi1010881742-65963124042009

4

References[1] Burbidge E M Burbidge G R Fowler W A and Hoyle F 1957 Rev Mod Phys 29 547[2] Cowan J J Thielemann F-K and Truran J 1991 Phys Rep 208 267[3] Qian Y-Z 2003 Prog Part Nucl Phys 50 153[4] Sneden C and Cowan J J 2003 Science 299 70[5] Savard G et al 2006 Int J Mass Spectrom 251 252[6] Van Schelt J et al 2008 Proc 10th Symp Nuclei in the Cosmos Mackinac Island Michigan 2008 PoS NIC

X 150[7] Savard G et al 2003 Nucl Instrum Meth B 204 582[8] Savard G et al 1991 Phys Lett A 158 247[9] Graff G Kalinowsky H and Traut J 1980 Z Phys A 297 35[10] Fallis J et al 2008 Phys Rev C 78 022801(R)[11] Clark J A et al 2007 Phys Rev C 75 032801(R)[12] Tanihata I 2008 Nucl Instrum Meth B 266 4067[13] Pardo R C et al 2007 Nucl Instrum Meth B 261 965[14] Savard G et al 2008 Nucl Instrum Meth B 266 4086

International Nuclear Physics Conference 2010 (INPC2010) IOP PublishingJournal of Physics Conference Series 312 (2011) 042009 doi1010881742-65963124042009

4