IAEA Regional Training Course
on
ASSESSMENT
OF
OCCUPATIONAL EXPOSURE
DUE TO
INTAKES OF RADIONUCLIDES
Laboratory Practices Module VI.2/2
Determination of uranium in urine by alpha
spectroscopy
Introduction
The alpha-spectroscopy is a very sensitive, nuclide specific method for the determination
and identification of alpha emitting isotopes in low level activity (MDA= 0,5 mBq). In spite in
the fact that it is a time consuming procedure, the alpha emitting radionuclides can be measured
directly. The quantification of possible internal exposure by inhalation and ingestion is an
important requirement in radiation protection, knowing that the alpha particles have a high health
hazards if they were incorporated to the human body. The measurements therefore should yield
not only the quantity (activity) of the radionuclide(s) but the identification of them as well.
Objective
The objective of this exercise is to demonstrate the steps involved in use of alpha
spectroscopy to determine the content of alpha emitting radionuclides in excreta samples. This
includes counter calibration, sample preparation, spectrometric measurement, determination of
sample activity, and use of the uptake information to determine the intake quantity and the
committed effective dose that results from that intake..
This information will be useful for those concerned with the planning, management and
operation of occupational monitoring programmes including application of individual dosimetry
due to intakes of radionuclides based on indirect measurements of internal contamination.
Scope
The exercise is intended to familiarize the students with the elements of alphaspectrometric low-level activity measurements such as energy and efficiency calibration,
background measurement, radiochemical preparation of the urine sample, alpha-spectrometric
evaluation of measurements. Due to the fact that only a very limited time is available for this
practical work, the exercise will focus on the presentation of the instruments and chemical
reagents required for the radiochemical preparation of urine samples for the determination of
uranium isotopes, energy and efficiency calibration and evaluation previously recorded alphaspectra by identification of radionuclides involved, determination of their activities and the
origin possibility of the internal contamination.
Sample preparation
The steps involved in radiochemical determination of uranium in urine samples by ionexchange and alpha spectroscopy are illustrated in the following figure. Details of the suggested
procedure are attached. In this procedure, 232U is added to the sample (spike) at the beginning of
the process. It will serve as a tracer to determine chemical yield. The specific analytical method
employed for the exercise may be modified based on procedures used by the host facility.
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Spike sample (U-232)
500 ml of Urine
Boil to dry
Iron hydroxide ppt.
9M HCL solution
Anion exchange column
(chloride form)
Elute
URANIUM
Load
THORIUM
Micro Co-precipitation
La(U)F3
Count by alpha
spectrometry
Figure 1 – Outline of the radiochemical process used to prepare uranium bioassay sample for
alpha spectroscopy
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Alpha-spectrometry
The alpha spectrum is measured with Passivated Implanted Planar Silicon (PIPS) detectors.
They typically have effective areas of the order of 300 mm2 and alpha particle resolutions of
about 20 keV (FWHM). For the identification of the alpha emitting isotopes the system energy
calibration should be carried out.
Radionuclides for energy calibration
Nuclide
Pu-239
Am-241
Cm-244
Alpha Energy
[MeV]
5.16
5.49
5.81
Determination of the radiochemical recovery
Detection Efficiency

N
A  tc
where;  is the counting efficiency
N is the counts in the alpha peak
A is the activity of the radionuclide
tc is the counting time
Total Efficiency
t 
N ( tracer )
A( tracer )  t c
where;  is the total efficiency
N is the counts in the tracer peak
A is the activity of the tracer
tc is the counting time
Chemical Yield
Ych 
t

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Activity Calculation
The activity per unit volume (or mass), CA, on the sample date (decay corrected) for each
energy in the alpha spectrum is calculated as
CA 
N
  t c  Ych  K s  V
where; N is the counts of the alpha peak,
V is the sample volume (or mass),
 is the detection efficiency,
tc is the live time of the collect in seconds
Ych is the chemical recovery
KS is the correction factor for the nuclide decay from the time the sample was
obtained to the start of the collect, namely
KS e

ln 2tS
T1 / 2
where;
T1/2 is the half-life of the nuclide in question,
tS is the elapsed clock time from the sample was taken to the
beginning of the measurement (in the same unit as T1/2)
Outline of the Practice
1. Facility familiarization – The facility staff will provide an over view of the conduct of the
practical including facility operations, rules and guidelines, specific analytical procedures
and counting equipment be used for this exercise
2. Radiochemical preparation of the urine sample This will consist of a) Mineralisation.
Separation of water and organic compounds; b) Chemical separation. Separation of
inorganic salts and other radionuclides (Th isotopes); and c) Source preparation for alpha
spectroscopy. Co-precipitation of uranium isotopes.
3. Equipment familiarization – The facility staff will demonstrate the use of the main parts
of the instrumentation and their functions
4. Manual calibration of the detector –The facility staff will assist the students in a)
collection of the alpha spectra; b) Energy calibration; and c) Efficiency calibration.
5. Uranium spectra analysis – This will consist of a) Identification of nuclides; b)
Calculation of the radiochemical recovery; and c) Calculation of the uranium activity and
activity ratios.
6. Determination of intake – Following identification and quantification of the
radionuclide(s), the facility staff will provide the students with simulated data on intake,
i.e. mode of intake, pattern of intake (acute or chronic) and date. Additional relevant
information that may be needed. Using retention data from ICRP 78 or a similar
reference, the students will determine the estimated intake value (Bq).
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7. Determination of Committed Effective Dose (C.E.D.) – The students will use the intake
value determined in step 6, together with dose coefficients from ICRP 78 or similar
reference to determine the committed effective dose value that would be assigned to the
measurement results.
8. Discussion – Following completion of the practical steps 1-7, the facility staff and
lecturers will conduct a discussion to review the experience of the practical, including
problems encountered, questions that the students may have and key points that the
practical has illustrated.
Notes to the Facility Staff and Lecturers
This practical is intended to provide an illustration of the steps involved in sample
preparation and counting by alpha spectrometry. Emphasis should be given in this practical on
the principles involved in routine alpha bioassay for occupational protection. Other issues
related to operation of a radiochemical laboratory should also be highlighted during the
demonstration, including housekeeping, quality control, etc.
The scenario developed as a basis for intake and committed effective dose determination
from the counting results should be realistic, but not excessively complicated. It should illustrate
the principles involved in making this determination. A scenario based on a case history would
be useful.
References
INTERNATIONAL ATOMIC ENERGY AGENCY, Assessment of Radioactive Contamination
in Man, IAEA-SM-276, Vienna (1985)
INTERNATIONAL ATOMIC ENERGY AGENCY, INTERNATIONAL LABOUR OFFICE,
Occupational Radiation Protection, Safety Standards Series No. RS-G-1.1, IAEA, Vienna (1999)
INTERNATIONAL ATOMIC ENERGY AGENCY, INTERNATIONAL LABOUR OFFICE,
Assessment of Occupational Exposure due to Intakes of Radionuclides, Safety Standards Series
No. RS-G-1.2, IAEA, Vienna (1999)
INTERNATIONAL ATOMIC ENERGY AGENCY, Indirect Methods for Assessing Intakes of
Radionuclides Causing Occupational Exposure, Safety Reports Series No. 18, IAEA, Vienna
(2000)
INTERNATIONAL ATOMIC ENERGY AGENCY, Calibration of Radiation Protection
Monitoring Instruments, Safety Report Series No. 16, IAEA, Vienna (2000)
INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION, Individual
Monitoring for Intakes of Radionuclides by Workers: Design and Interpretation, Publication 54,
Ann. ICRP 19 1-3, Pergamon Press (1988)
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INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION, Individual
Monitoring for Internal Exposure of Workers (Replacement of ICRP Publication 54), Publication
78, Ann. ICRP 27 3-4, Pergamon (1997)
NATIONAL COUNCIL ON RADIATION PROTECTION AND MEASUREMENTS, Use of
Bioassay Procedures for Assessment of Internal Radionuclide Deposition, Rep. 87, NCRP,
Bethesda, MD (1987)
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Attachment I
Suggested Analytical Procedure for Uranium Bioassay
Initial Sample Preparation
1. Measure out 500 ml of urine.
2. Add spikes as require (U-232)
3. Add 50 ml concentrated nitric acid and carefully 10ml H2O2 drop wise. Evaporate to
dryness.
4. Add 20 ml conc. HNO3 and evaporate to dryness. Repeat this step twice.
5. Leach three times with 20 ml of concentrated HCl.
6. Add 50 ml of 1M HCl and boil.
7. Leave the solution stand until it is completely cold.
8. Centrifuge the solution.
9. Retain the supernatant for analysis.
Main Analytical Procedure
1. Add 200 mg of iron carrier to the supernatant.
2. Add conc. ammonia with heating and stirring to precipitate the iron
3. Centrifuge and retain precipitate.
4. Dissolve precipitate with 50 ml of 9M HCl.
5. Filter the solution if it is necessary.
6. Wash the anion exchange column with 60 ml of 9M HCl.
7. Anion exchange column: 10 mm ID with DOWEX 1 resin soaked in distilled waterto a
depth of 12 cm
8. Transfer the sample to the column, immediately washing in with 60 ml of HCl.
9. Collect the elute and keep for thorium.
10. Elute the uranium and iron off with 100 ml of 1M HCl.
11. Add 1ml of 5% (w/w) NaHSO4 solution.
12. Evaporate the solution to dryness.
13. Add 2 ml conc. HNO3 and evaporate to dryness. Repeat this step twice.
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14. Add 20 ml of 0.5M HNO3 and boil.
15. Cool the solution to room temperature
MICROPRECIPITATION SOURCE PREPARATION FOR ALPHA SPECTROMETRY
Special Precautions - Due to the use of HF in the preparation of the reagents and in the
precipitation procedure, rubber gloves must be worn and plastic ware must be used
SPECIAL REAGENTS
1. 1N HNO3 - add 69 ml of concentrated HNO3 to 931 ml of distilled water and store in a
plastic bottle.
2. Lanthanum carrier solution, 1000 g ml-1 , or equivalent.
3. Lanthanum carrier solution, 0.5 mg ml-1 . Dilute 10 ml of the 1000 g ml-1 La carrier
solution to 20 ml with distilled water.
4. 48% HF.
5. Lanthanum fluoride substrate solution - 10 g ml-1 - pipette 5 ml of La carrier (1000 g
ml-1 ) into a 500-ml plastic bottle. Add 460 ml of 1N HNO3 to the plastic bottle. Cap the
bottle and shake to mix. Measure 40 ml of 48% HF in a plastic graduated cylinder. Uncap
the bottle and add the HF. Recap the bottle and shake to mix thoroughly.
6. Ammonium Iron(II) Sulphate 6-hydrate.
Procedure
1. Transfer the solution to plastic vial.
2. Add 200 mg of Ammonium Iron(II) Sulphate 6-hydrate to plenty reduce Uranium
3. Add 50 g of lanthanum carrier.
4. Add 5 ml of conc. HF and wait for at least 30 minutes.
5. Filter 15 ml of Lanthanum fluoride substrate solution through 25 mm diameter membrane
filter, 0.25 m pore size.
6. After 30 minutes filter the La(U)F3 ppt through the substrate mentioned above
7. Reduce or turn off the vacuum to remove the filter. Discard the filtrate. (Caution – If the
filtrate is to be retained, it should be placed in a plastic container to avoid dissolution of
the glass vessel by dilute HF.)
8. Dry the source under I/R lamp at low temperature.
9. Mount the membrane filter with fast-drying glue onto a 25 mm stainless steel disk.
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Attachment II
Determination of Minimal Detectable Activity (MDA)
The Minimum Detectable Activity (MDA) for a given nuclide, at the 95% confidence level, may
be determined as follows:
MDA 
where;
2.71  4.65  B1/ 2
  t c  V  Ych
B is the background counts at the energy of interest
V is the sample volume (or mass),
 is the detection efficiency,
tc is the live time of the collect in seconds
Ych is the chemical recovery
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