ArticlePDF Available

Counting 241Am in the BfS Human Skull Phantom on Contact—Evaluation in the Human Monitoring Laboratory

Abstract and Figures

Skull counting can be used to assess the activity of radionuclides internally deposited in the bone. The Human Monitoring Laboratory (HML) at Health Canada conducted the measurement of Am in the BfS (Bundesamt für Strahlenschuts) skull phantom on contact with the skull for various positions. By placing the detector in contact, the HML can improve the counting efficiency by over 20% compared to placing the detector 1 cm above the surface of the skull. Among all the positions tested, the forehead position is the preferred counting geometry due to the design of HML's counting facility and the comfort it would provide to the individual being counted, although this counting position did not offer the highest counting efficiency for the gamma rays (either the 59.5 keV or the 26.3 keV) emitted by Am.
Content may be subject to copyright.
Note
COUNTING
241
AM IN THE BFS HUMAN SKULL PHANTOM ON
CONTACTEVALUATION IN THE HUMAN MONITORING LABORATORY
Chunsheng Li,* Barry Hauck,* Kevin Capello,* Pedro Nogueira,Maria A. Lopez,and Gary H. Kramer*
AbstractSkull counting can be used to assess the activity of ra-
dionuclides internally deposited in the bone. The Human Moni-
toring Laboratory (HML) at Health Canada conducted the
measurement of
241
Am in the BfS (Bundesamt für Strahlenschuts)
skull phantom on contact with the skull for various positions. By
placing the detector in contact, the HML can improve the counting
efficiency by over 20% compared to placing the detector 1 cm
above the surface of the skull. Among all the positions tested, the
forehead position is the preferred counting geometry due to the
design of HMLs counting facility and the comfort it would provide
to the individual being counted, although this counting position
did not offer the highest counting efficiency for the gamma rays
(either the 59.5 keV or the 26.3 keV) emitted by
241
Am.
Health Phys. 108(3):380382; 2015
Key words:
241
Am; bioassay; bones, human; phantom
INTRODUCTION
AMERICIUM-241 IS highly radiotoxic. Following an intake, a
fraction can deposit in the skeleton (ATSDR 2004). Bone
counting can be used to estimate the intake and its associ-
ated health risk (Kramer et al. 2011). Assuming a homoge-
nous distribution of
241
Am in the skeleton and with a known
percentage of the bone mass in the skull over that in the
skeleton (ICRP 1995), results from a skull count can be used
to infer the total activity of
241
Am in the skeleton.
The BfS (Bundesamt für Strahlenschutz) skull phan-
tom was manufactured around 1983 by Laurer
§
based on
real human bone from a small head. Americium-241was ar-
tificially labeled on both the inner and outer surfaces of the
phantom (Vrba 2011) with an overall activity of 5,239 Bq
on 1 January 2012.
The Human Monitoring Laboratory (HML) of Health
Canada, which operates the Canadian National Calibration
Reference Centre for Bioassay and in vivo Monitoring (Kramer
and Limson Zamora 1994; Daka and Kramer 2009), con-
ducted detailed measurements for the BfS phantom at va-
rious positions with the detector in contact or 1 cm above
the surface. This paper reports the results of the measured
counting efficiencies on contact for both the 26.3 keV and
the 59.5 keV gamma rays of
241
Am using HMLslung
counting facility (Kramer and Hauck 2005). This facility
has been used previously in the measurement of
241
Am in
two leg phantoms (Kramer et al. 2011).
MATERIALS AND METHODS
Fig. 1 depicts the specified counting positions for the
BfS skull phantom. In total, five positions were selected as
they either offered convenient counting geometries or pro-
vided large bone mass for a good counting efficiency. For
counting on contact, the detector was placed about 1 mm
above the surface of the skull to obtain a higher counting ef-
ficiency. Fig. 2 shows the placement of the detector when the
counting was conducted at one of the counting positions, the
forehead position (Position 1).
The measurements were performed in the HMLslung
counting facility, which has four high purity germanium de-
tectors mounted individually on a track that allows each de-
tector to be moved independently. These detectors are used
typically for in vivo monitoring of radionuclides such as
238
Uand
241
Am in the energy range of 10500 keV. For
the measurements of
241
Am in the BfS skull phantom,
only one of the four detectors was used.
The detector was a GEM Series coaxial detector manu-
factured by Ortec®. It is a p-type germanium crystal with the
nominal dimensions of 85 mm diameter and 30 mm length.
The crystal is mounted within an aluminium end cap with a
0.76mm-thick carbon fiber window. The counting chamber
is made of low background steel walls, with the inner surface
*Radiation Protection Bureau, Health Canada, 775 Brookfield Rd,
Ottawa, Canada K1A 1C1; Helmholtz Zentrum München, Institute of
Radiation Protection, Ingolstädter Landstraße 1, 85764 Neuherberg,
Germany; Centro de Investigaciones Energéticas, Medioambientales y
Tecnológicas, Avda. Complutense 40, Madrid 28040, Spain.
The authors declare no conflicts of interest.
For correspondence contact: Chunsheng Li, Radiation Protection
Bureau, Health Canada, 775 Brookfield Rd, Ottawa, Canada K1A 1C1,
or email at li.chunsheng@hc-sc.gc.ca.
(Manuscript accepted 16 July 2014)
0017-9078/15/0
Copyright © 2015 Health Physics Society
DOI: 10.1097/HP.0000000000000180
§
Laurer G. Letter to W. Burkhart from 8th April 1993. New York Uni-
versity Medical Center, Laboratory for Radiation Studies; 1993.
380 www.health-physics.com
Copyright © 2015 Health Physics Society. Unauthorized reproduction of this article is prohibited.
covered by 6.3 mm of lead as well as a graded Z liner con-
sisting of tin (0.8 mm thick) and copper (1.8 mm thick). The
inside dimensions of the counting chamber are 1.52 m
2.13 m 2.13 m (W DH). The access to the chamber
is made through a set of double doors made of the same ma-
terial as the chamber. The doors are operated by electric
motors outside the chamber. The thickness of the cham-
ber wall, doors, floor, and ceiling is 0.2 m. The chamber
has a large water-filled window of dimensions 0.3 m
0.46 m 0.6 m.
Measurements were made either for a 60,000scount
(long counting) or a 3,600s count (short counting), and both
the 59.5 keV (branching ratio, 35.9%) and the 26.3 keV
(branching ratio, 2.4%) gamma rays were counted. The
acquisition and analysis of spectral data were performed
using the Ortec® Renaissance Version 4.01 software.
At the HML, the forehead counting position (position
1, Fig. 1) is the preferred position, as the detector place-
ment is constrained by the design of the counting facility.
This position also provides the best comfort to an individual
being measured.
RESULTS AND DISCUSSION
Table 1 shows the counting efficiencies (cps Bq
1
)for
241
Am in the BfS skull phantom for the on-contact geome-
try obtained for various positions as shown in Fig. 1. Each
of the five counting positions was counted for 60,000 s.
Both the 59.5 keVand the 26.3 keV gamma rays were mea-
sured and evaluated. The uncertainty associated with each
of the reported eff iciencies (Table 1) was calculated from
counting statistics only. The counting efficiency was derived
from dividing the count rate (total counts/counting time in
seconds) by the activity (Bq) of
241
Am in the phantom at
the time of counting and the respective branching ratio of the
gamma ray, 35.9% for the 59.5 keV gamma and 2.4% for
the 26.3 keV gamma, respectively.
For the 59.5 keV gamma ray, position 3(Fig. 1) of-
fered the highest counting efficiency, possibly due to the
higher bone mass being counted, while position 12(Fig. 1)
offered the lowest counting efficiency. It was lower by over
24% compared to that of position 1.The HMLspreferred
position, the forehead position (1, Fig. 1), offered an effi-
ciency lower by about 20% compared to that of position 3.
Fig. 1. The BfS Phantom with specified counting positions.
Fig. 2. Counting the BfS phantom at the forehead contact position
(Position 1) using the HML lung counter.
Tab le 1 . Counting efficiencies (cps Bq
1
)for
241
Am in BfS skull
phantom at HML contact geometry with uncertainty (counting time:
60,000 s; from counting statistics only).
26.3 keV 59.5 keV
Position Efficiency Uncertainty Efficiency Uncertainty
18.2110
3
0.03 10
3
2.190 10
2
0.01 10
3
31.04710
2
0.04 10
3
2.729 10
2
0.02 10
3
49.2810
3
0.04 10
3
2.463 10
2
0.01 10
3
78.5710
3
0.03 10
3
2.365 10
2
0.01 10
3
12 7.49 10
3
0.03 10
3
2.066 10
2
0.01 10
3
Tab le 2 . Counting efficiencies (cps Bq
1
)for
241
Am(59.5keV)inBfS
skull phantom at HML contact geometry: short counting (3,600 s)
versus long (60,000 s) counting, with uncertainty (from counting sta-
tistics only).
Short counting Long counting
Position Efficiency Uncertainty Efficiency Uncertainty
12.19310
2
0.06 10
3
2.190 10
2
0.01 10
3
32.69710
2
0.06 10
3
2.729 10
2
0.02 10
3
42.48610
2
0.06 10
3
2.463 10
2
0.01 10
3
72.33510
2
0.06 10
3
2.365 10
2
0.01 10
3
12 2.073 10
2
0.06 10
3
2.066 10
2
0.01 10
3
381Counting
241
Am in a human skull phantom cC. LIETAL.
www.health-physics.com
Copyright © 2015 Health Physics Society. Unauthorized reproduction of this article is prohibited.
For the 26.3 keV gamma ray, the advantage of position 3
in counting efficiency was even more significant over other
counting positions, probably due to lower attenuation at this
position for this lower energy gamma. As expected, the
59.5 keV gamma had a higher counting efficiency than
the 26.3 keV gamma by a factor of over 2.6 throughout
the five counting positions. As a result, the 59.5 keV
gamma would be the preferred energy for the measurement
of
241
Am in the skull, as expected.
For real-life skull counting, it is more practical to count
the individual for a shorter time than 60,000 seconds. A
3,600s counting was performed for each counting position.
Table 2 presents the obtained counting efficiencies and as-
sociated uncertainties for the shorter counting time and com-
pares with those obtained from the longer counting time.
Again, the uncertainties were from counting statistics only.
As discussed above, the 59.5 keV gamma provides a higher
counting efficiency. Therefore, Table 2 reports data for this
gamma emission only. For each counting position, the counting
efficiency for the 59.5 keV gamma rays obtained from the
short counting does not differ significantly from that ob-
tained from the long counting, as expected. However, the
associated uncertainty becomes larger, by a factor of 5, in-
creasing from 0.05% to 0.25% on average, for all of the
counting positions. Nevertheless, the uncertainty is still small
compared to the potential overall uncertainty in internal radi-
ation assessment where skull counting is involved. There-
fore, the 3,600s short counting provides conf irmation of the
counting efficiency results obtained from the longer count time.
As discussed above, the HMLs preferred counting ge-
ometry is the forehead position (position 1), although the
counting efficiency for the 59.5 keV gamma of
241
Am in
the BfS skull phantom is lower by 20% compared to the
highest efficiency obtained. Table 3 compares the counting
efficiencies obtained at on-contact geometry and at the 1 cm
geometry for both the 26.3 keV and the 59.5 keV gamma
rays. For the 1cm geometry, the detector was placed 1 cm
above the surface of the skull phantom. Table 3 shows that
compared to counting at the 1 cm geometry, counting on
contact improved the counting efficiency by more than
20% and 25% for the 26.3 keV and the 59.5 keV gamma
rays, respectively. This gain in counting efficiency was ob-
tained by simply placing the detector closer to the surface
of the skull phantom. In an actual skull measurement, this
would help improve the quality of the measurement results
when the counting time is fixed.
In summary, the HML has decided that the preferred
counting position is a subjects forehead due to positioning
constraints in the design of its counting facility. This counting
position also provides the best comfort to the individual being
counted in a real-life count, although this counting position
doesnt provide the highest counting efficiency for the gamma
rays emitted by
241
Am. By placing the detector just above the
surface (on contact), the HML can improve the counting ef-
ficiency by over 20% compared to placing the detector 1 cm
above the surface of the skull. Other laboratories that have
no positioning constraints in the design of their counting fa-
cility would be advised to consider the more efficient counting
positions for detector placement when performing skull counts.
REFERENCES
Agency for Toxic Substance and Disease Registry. Toxicological
profile for americium. Washington, DC: U.S. Department of
Health and Human Services; 2004.
Daka JN, Kramer GH. The Canadian National Calibration Refer-
ence Centre for Bioassay and In Vivo Monitoring: an update.
Health Phys 97:590594; 2009.
International Commission on Radiological Protection. Basic anatom-
ical and physiological data for use in radiological protection
the skeleton. Oxford: ICRP; Publication 70, Annual ICRP
25(2); 1995.
Kramer GH, Limson Zamora M. The Canadian National Calibra-
tion Reference Centre for Bioassay and In Vivo Monitoring: a
program summary. Health Phys 67:192196; 1994.
Kramer GH, Hauck BM. The Human Monitoring Laboratorys
new lung counter: calibration and comparison with the previ-
ous system and the CAMECO Corporationslungcounter.
Health Phys 89:383392; 2005.
Kramer GH, Hauck BM, Capello K, Rühm W, El-Raramawy N,
Broggio D, Franck D, Lopez MA, Navarro T, Navarro JF,
Perez B, Tolmachev S. Comparison of two leg phantoms con-
taining
241
Am in bone. Health Phys 101:248258; 2011
Laurer G. Letter to W. Burkhart from 8th April 1993. New York
University Medical Center, Laboratory for Radiation Stud-
ies; 1993.
Vrba T. Head calibration phantoms for actinides: measurements
and simulations. Radiat Protect Dosim 144:357360; 2011.
■■
Table 3. Comparison of counting efficiencies (cps Bq
1
)for
241
Am
in BfS skull phantom position 1at the contact geometry and at
1 cm above the surface using the HML lung counter (60,000 s
counting; uncertainty from counting statistics only).
26.3 keV 59.5 keV
Position Efficiency Uncertainty Efficiency Uncertainty
Contact 8.21 10
3
0.03 10
3
2.190 10
2
0.01 10
3
1cm 6.8010
3
0.03 10
3
1.747 10
2
0.01 10
3
Gain (%) 20.7 25.4
382 Health Physics March 2015, Volume 108, Number 3
www.health-physics.com
Copyright © 2015 Health Physics Society. Unauthorized reproduction of this article is prohibited.
ResearchGate has not been able to resolve any citations for this publication.
Article
Full-text available
Three facilities (CIEMAT, HMGU and HML) have used their in vivo counters to compare two leg phantoms. One was commercially produced with (241)Am activity artificially added to the bone inserts. The other, the United States Transuranium and Uranium Registries' (USTUR) leg phantom, was manufactured from (241)Am-contaminated bones resulting from an intake. The comparison of the two types of leg phantoms showed that the two phantoms are not similar in their activity distributions. An error in a bone activity estimate could be quite large if the commercial leg phantom is used to estimate what is contained in the USTUR leg phantom and, consequently, a real person. As the latter phantom was created as a result of a real contamination, it is deemed to be the more representative of what would actually happen if a person were internally contaminated with (241)Am.
Article
Full-text available
The paper deals with the physical skull phantoms Bundesinstitut fuer Strahlenschutz and BPAM-001, which are used in order to calibrate in vivo detection systems for estimation of 241Am activity in the skeleton. Their voxel models were made and used in the Monte Carlo simulations. The results of the simulation were compared with measurements and reasonable agreement was observed. Several aspects such as materials and source distributions used in the models were discussed.
Article
The Canadian National Calibration Reference Center (NCRC) for Bioassay and In Vivo Monitoring is part of the Radiation Protection Bureau, Health Canada. The NCRC operates three performance testing programs that are designed to confirm that workplace monitoring results are accurate and provide the necessary external verification that is part of a comprehensive quality assurance program. The NCRC performance testing programs cover the in vitro, in vivo, and internal dosimetry parts of Canadian facilities' radiation protection programs. The internal dosimetry performance testing is a new addition to the performance testing suite. This summary also describes the recent reorganization of the NCRC.
Article
The Canadian National Calibration Reference Center for Bioassay and in-vivo Monitoring is part of the Radiation Protection Bureau, Department of Health. The Reference Center operates a variety of different intercomparison programs that are designed to confirm that workplace monitoring results are accurate and provide the necessary external verification required by the Canadian regulators. The programs administered by the Reference Center currently include urinalysis intercomparisons for tritium, natural uranium, and 14C, and in-vivo programs for whole-body, thorax, and thyroid monitoring. The benefits of the intercomparison programs to the participants are discussed by example. Future programs that are planned include dual spiked urine sample which contain both tritium and 14C and the in-vivo measurement of 99mTc.
Article
The Human Monitoring Laboratory has replaced its lung counting system with four large area (85 mm x 30 mm) HPGe detectors, electronics, and software. The system has been calibrated with the same lung set and phantom that was used to calibrate the Human Monitoring Laboratory's previous lung counting system and the Cameco Corporation's mobile lung counter. The performance characteristics (efficiency and sensitivity) of all three systems are compared, with the Human Monitoring Laboratory's new system being more sensitive than the other systems by factor of 1.3. The large area detectors highlight the design deficiency of the Lawrence Livermore National Laboratory's torso phantom, namely short lungs, as the lower two detectors are over inactive tissue (approximately 40%). As a result, both a two-detector and a three-detector array are actually more sensitive than a four-detector array in certain circumstances. This is, however, an unrealistic finding as human lungs are much longer (approximately 10 cm) than the Lawrence Livermore National Laboratory's phantom's lungs. The dosimetric implications of the new system's minimum detectable activities are put into perspective using (57)Co, (235)U, (238)U, (239)Pu, (241)Am, and natural uranium as example radionuclides.
Toxicological profile for americium Department of Health and Human Services
  • Toxic Agency
  • Disease Substance
  • Registry
Agency for Toxic Substance and Disease Registry. Toxicological profile for americium. Washington, DC: U.S. Department of Health and Human Services; 2004.
International Commission on Radiological Protection. Basic anatomical and physiological data for use in radiological protectionthe skeleton
  • J N Daka
  • G H Kramer
Daka JN, Kramer GH. The Canadian National Calibration Reference Centre for Bioassay and In Vivo Monitoring: an update. Health Phys 97:590-594; 2009. International Commission on Radiological Protection. Basic anatomical and physiological data for use in radiological protectionthe skeleton. Oxford: ICRP; Publication 70, Annual ICRP 25(2); 1995.
Letter to W. Burkhart from 8th
  • G Laurer
Laurer G. Letter to W. Burkhart from 8th April 1993. New York University Medical Center, Laboratory for Radiation Studies; 1993.
The Canadian National Calibration Reference Centre for Bioassay and In Vivo Monitoring: a program summary.
  • Kramer