Use of Eichrom Resins for
Bioassay Pa-231
Bob Timm - GEL
Tim Chandler - GEL
Bill Burnett - FSU
Mike Schultz - PerkinElmer
Instuments, ORTEC
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Outline
What is Protactinium
 Pa-231 procedure development
 Conclusions
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Protactinium
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Originally called "protoactinium", Pa is
one of the rarest and most expensive
naturally-occurring elements
Pa-231 has a fast fission cross section
nearly the same as 239Pu
Pa(V) forms a very stable, water-soluble
complex with fluoride
Pa(IV) forms insoluble fluorides
Two naturally-occurring isotopes: 234Pa
and 231Pa
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Pa-231
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PARENT
U-235 half-life 7x10^8 yrs decays to Th-231
Th-231 half-life 25.52 hrs decays to Pa-231
Pa-231 half-life 3.3x10^4 yrs
DAUGHTER
Ac-227 Actinium 100.0 %
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History
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Method for Environmental developed by Burnett
and Yeh. (1995)
The earlier procedure was only concerned with
interferences from naturally occuring
radionuclides.
A method for Bioassay was required. Bioassay
samples could contain artificial radionuclides.
Made the decision to try developing method
using a single column method.
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Development Objectives
Try an analysis on TRU Resin and start
determining corrective steps.
 Begin making corrections to procedure
based on results of testing.
 Finalize procedure.
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Load Solution for Test 1
Perform a Ca(PO4) Precipitation on DI
water containing Nat Th, Nat U, Pu-239,
Am-241 and Pa-231.
 Followed procedure on next slide.
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Test-1
3 2 mL 9M HCl
4 10 mL 4M HCL
5 20 mL 0.1M HCl
6 Pa Elution 20 mL
0.1M HCL - 0.1M HF
10 mL 2M HNO3 2
20 mL 8M HNO3 -1
1M Al(NO3)3
.
TRU
Resin
6
Pa
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5
1-4 (discard)
Th (~90-95%)
Test 1 Results
Only about 50% Protactinium recoveries
with ~100% Plutonium and small
amounts of Thorium (Up to 10%) visible
in spectrum.
 Analyzed the fractions just before the
Protactinium Elution and determined the
remainder of the Protactinium was in
the Thorium elution.
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Test 2
Decision made to elute Thorium with 1M
HCL instead of 0.1M HCL to increase
Protactinium recovery.
 Decision to use a TiCl3 solution to elute
Plutonium when eluting Americium.
Added 0.5 mL of TiCl3 to 20 mL of 4M
HCL.
 Followed procedure on next slide.
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Test-2
3 2 mL 9M HCl
4 20 mL 4M HCL - 0.5 mL TiCl3
5 20 mL 1M HCl
6 Pa Elution 20 mL
0.1M HCL - 0.1M HF
10 mL 2M HNO3 2
20 mL 8M HNO3 -1
1M Al(NO3)3
.
TRU
Resin
6
Pa
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5
1-4 (discard)
Th (~90-95%)
Test - 2 Results
Plutonium was separated as expected
and Protactinium recoveries increased
to near 90%.
 We tested the procedure one additional
time adding the same actinides as
before but added Np-237 as well.
Unfortunately Np-237 followed Pa
through the procedure and gave a new
challenge.
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Test 3
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Added UTEVA column to remove Neptunium
and provide additional Uranium and Thorium
clean up.
Load solution changed to 2.5M HNO3 / 0.1M
Ferrous Sulfamate. Added 1 mL of 1.0 M
Ascorbic Acid to reduce Fe. This is optimal for
Neptunium (IV) retention on UTEVA while
Protactinium stays in the +5 oxidation state.
Followed procedure on next slide.
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Test-3
2 mL 9M HCl
3
4
20 mL 2.5M HNO3
10 mL 2.5
/ 0.1 M FeS / Asc
M HNO3
Acid
(2x)
1
2
5 20 mL 1M HCl
2
.
TRU
.
UTEVA
Resin
6
Pa Elution 20 mL
0.1M HCL - 0.1M
HF
Resin
1
6
Pa
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20 mL 4M HCL 0.5 mL TiCl3
1-5
(discard)
Test - 3 Results
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80 to 90% of the Neptunium was removed by the
UTEVA.
We have not identified exactly why the Neptunium
is not fully separated by the UTEVA resin. We
have ruled out column overloading of any sort by
adding a TEVA column to the sequence and still
seeing Neptunium interferance.
One possibility is phosphate interferance with
Neptunium’s retention on UTEVA. (see next slide)
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Sensitivity to PO4
UTEVA.Resin
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TRU.Resin
Test - 3 Results cont’d
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Another thought was to separate
Neptunium using spectral separation.
~84% of the energy lines can be used
which do not have Neptunium interferance
with them.
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0.5
0.4
0.3
0.2
0.1
0
Np-237
Pa-231
4.
63
1
4.
66
4
4.
70
8
4.
73
6
4.
77
1
4.
80
3
4.
85
1
4.
93
3
4.
98
4
5.
02
8
5.
05
7
Abundance
Spectral Separation of Np-237
from Pa-231
Energy (MeV)
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Oxalic Acid rinse
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Began testing to see if the separation of
Neptunium and Protactinium on TRUResin
was possible using oxalic acid.
We loaded Neptunium and Protactinium
onto a TRU Column and performed a rinse
with 1M HCL/0.015 M Oxalic acid.
Neptunium did not show up in the
Protactinium rinse. We proceeded with
Test-4.
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Test-4
3 2 mL 9M HCl
4 20 mL 4M HCL - 0.5 mL TiCl3
5 15 mL 1M HCl / 0.015 M Oxalic Acid
6 10 mL 1M HCl
10 mL 2M HNO3 2
20 mL 8M HNO3 -1
1M Al(NO3)3
.
TRU
7
Pa Elution 20 mL
0.1M HCL - 0.1M HF
Resin
(Pa) 7
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1-6 (discard)
Test - 4 Results
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Tracer yields were ~50% and spectrums
were free of interfering actinides.
Approximately 15% of the Pa tracer came
off with the 10 mL rinse of 1M HCL. No
other actinides were detected. This rinse
can be combined with the Pa elution to
obtain tracer yields of ~65%.
The remaining Protactinium tracer came
off with the oxalic acid rinse containing
Neptunium.
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Test 5
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Increased the molarity of HCL with the
Oxalic acid rinse to 2M HCL. Our thought
was that maybe the total volume of 1M
HCL rinses was causing the Protactinium
to elute early. The Thorium will still elute
with the 2M HCL rinse.
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Test-5
3 2 mL 9M HCl
4 20 mL 4M HCL - 0.5 mL TiCl3
5 15 mL 2M HCl / 0.015 M Oxalic Acid
6 10 mL 1M HCl
10 mL 2M HNO3 2
20 mL 8M HNO3 -1
1M Al(NO3)3
.
TRU
7
Pa Elution 20 mL
0.1M HCL - 0.1M HF
Resin
(Pa) 7
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1-6 (discard)
Test - 5 Results
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Tracer yields were ~95%. Spectrums had
1% of the Np-237 added. No other
actinides were present.
Two tests are currently in progress.
a.) Increase the Oxalic rinse to 0.03M
Oxalic acid.
b.) Perform the oxalic acid rinse under
HNO3 conditions.
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Conclusions
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Eichrom Resins can be effectively utilized to
separate Protactinium from other actinides for
alpha measurements.
Np-237 if present may interfere. We can
resolve this interference with spectral
separation or by using an oxalic acid rinse.
A Ce(OH) method of co-precipitation is
necessary for alpha counting. Flouride coprecipitations will not work with Pa(V).
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