FRIB Isotope Production for Rare Targets

Lawrence Livermore National Laboratory

Jennifer Jo Ressler

LLNL-PRES-453472

Lawrence Livermore National Laboratory, P. O. Box 808, Livermore, CA 94551

This work performed under the auspices of the U.S. Department of Energy by

Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344

FRIB Isotope Production for Rare

Targets

American Chemical Society, Aug. 22 – 24 2010

2LLNL-PRES-453472 ACS: Radiochemistry at FRIB 2010


FRIB isotope production

Hundreds of isotopes produced

Opportunity for materials: isotope “harvesting”

• Proposed for RIA

• Proposed for FRIB

Challenging prospect

• Collection: production rates, collection material

• Separation: elemental and isotopic

• Fabrication of secondary target

• Use of target: limited quantity, background rates



Isotope Applications - 1

Stockpile Stewardship

• Tracer reaction network

• Data for models of stockpile assessment

Forensics (origination of material)

• Data for reaction models

Homeland Security

• Data for models of interrogation systems

• Simulant threat sources



Isotope Applications - 2

Nuclear Safeguards

• Next generation reactors

• Transmutation schemes

Astrophysics

• Nucleosynthesis: r-process, s-process

• Stellar environments

Nuclear structure

• Evolution of excited states, reaction models



Target materials

Common theme:

• Fission products

• Actinides

General process:

• Collection

• Chemically separate

• Isotopically separate

• Irradiate with neutrons or light ions (surrogates)



Isotope collection sites

Beam dump

“soup” of isotopes

challenging separation

Mass slits

select isotopes

potentially easier separation



Target preparation

Three main steps

• Chemical separation

• Isotope separation

• Foil fabrication

Process will be highly element/isotope dependent

Need long half-lives

• Separation takes time

• Radiation safety

• Secondary experiments: background



Chemical Separation

Precipitation (solid/liquid)

Volatilization (distillation; gas/liquid)

Ion exchange column (complex/effluent)

Chromatography (migration through porous medium)

Solvent extraction (organic/aqueous)

Electrochemistry (anion/cation)

Lanthanides and actinides are challenging

• Numerous oxidation states

• Oxidation/reduction schemes

• Hot waste stream



Isotope Separation

Some lighter masses can be isotopically separated with

chemistry

Isotopic separation becomes increasingly challenging

with mass (ΔM/M becomes small)

Electromagnetic separator (Calutron!)

Laser excitation/separation

Plasma separator

Gas centrifuge (not likely)



Foil fabrication

Rolling

Vacuum evaporation

Electroplating

Ion sputtering

Powder or small sheets in an envelope

Dedicated facility to handle hot materials

Target procedure is not standard

• Thickness, abundance, backing, uniformity, surface

area…

Need close ties to current target community



Example #1: 134Cs

134Cs(n,γ)

• 134Cs/137Cs ratio used for reactor burn-up

• 135Cs proposed as a tracer

• Astrophysical s-process134Ba/136Ba ratio

determines physical

conditions

(neutron density, temp)

• EXFOR 1 measurement from 1969

133Cs 134Cs 135Cs 136Cs

133Xe 134Xe 135Xe

5.2 d

2.3E6 y2.1 y 13 d

29 b 140 b 9 b

2,700,000 b

136Xe

9.1 h

137Cs

30 y



Is Cs feasible?

2.1 y half-life: collection/separation can be slow

Separation chemistry is known

How much material is needed?

• 1 g = 1.3 kCi

• 1 μg = 1.3 mCi

12 mR/hr at 30 cm

1 x 108 γ/s: will need HEAVY shielding for prompt (n,γ)

Irradiate/count: 135Cs T1/2 too long



FRIB specific activity

Calculated activity [mCi] per μg



Example #2: 144Ce

144Ce(n,x)

• Fission basis in the analysis of nuclear test data

• Destruction important for fast reactor applications

• EXFOR: single (n,γ) measurement 1962

142Ce 143Ce 144Ce 145Ce

285 d1.4 d 3 m

29 b

n,2n n,γ

1.0(1) b at 0.025 eV

20 b at 10 MeV



Is Ce feasible?

long half-life: collection/separation can be slow

Separation chemistry is known

How much material is needed?

• 1 mg = 3.2 Ci

• 1 x 1010 γ/s, but < 400 keV

FRIB rate: 8x109 pps

• 1 mg is not possible; production/decay equilibrium of 67.5 μg

• 6 days for 1 μg

Harvesting from a reactor might be easier than FRIB



FRIB collection times

http://groups.nscl.msu.edu/frib/rates/fribrates.html

Days to collect 10 µg of material

• Assume 100% collection + chemistry efficiency



Neutron sources

Will have very small-mass targets

Will need high-flux neutron sources

Required neutron flux

• 1000 events at 1% detection efficiency

• 5-day neutron irradiation

• 10 μg sample: Φ≥106 – 107 per barn of cross section

Will need to design end experiment around information

sought and target properties

• Shielding

• Maximize neutron production



What will work…

Isotopes close to the primary beam species

• Longer half-lives

• High production rates

Preferably, isotopes with low radiation emission energies

FRIB rate is often the limiting factor – need >1010 pps

• 188W (T1/2 = 69 d)

198Pt, 1.7E8 pps => production/decay equilibrates at 0.47 μg

• 185W (T1/2 = 75 d)

186W, 7.1E10 pps => 10 μg takes 5.5 days



FRIB best bets

35S, 63Ni and 95Zr

39Ar, 85Kr, 56,57Co, and 26Al

300

250

200

150

100

50

0

30252015105

39Ar 35S 63Ni 85Kr 57Co 26Al 95Zr 56Co

Production [days]

Ma

ss [

μg]

95Zr(n,γ)

Stewardship science

Rxn network

Nuclear safeguards

Cladding rxns (Zircaloy, U)

Astrophysics

Branching point

Abundance in SiC grains

stable stable



95Zr collection

96Zr primary beam

Main experiment: delivery of 92Sr

95Zr

Zr collected on Fe or Ni foils

Zr separated from Y and metal backing

using thin layer chromatography (TLC)

Cannot measure (n,γ) using irradiation/count

scheme; use prompt system like DANCE

Gamma flux from decay will be challenging

10 day production yields ≤ 57 μg

T1/2 = 64 d; Ac = 1.2 Ci

Eγ = 724 (44%), 756 (54%)



Summary

Parasitic harvesting at FRIB is a challenging endeavor

Every target material is unique

• Plan for collection, separation, fabrication, end use

• End use will need to be designed around activity, mass of target

material

• Need equipment and expertise (radiochemists!)

Not every target is possible – most are not

Community Questions:

• What isotopes are the most important?

• How much effort are we willing to put into separation?

• Can we test this now?



Extra: Equations used

Activity

Days to produce mass m

Mass produced

10123

107.3/])[exp(11002.6

][][ xsA

xgmCiAc

360024

][1002.6][1ln

][

123

P

s

A

xgm

dT

)exp(11002.6

][23

TP

x

Agm

A: atomic mass in amu

P: FRIB production in pps

Documents

FRIB Isotope Production for Rare Targets