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Status of Simulations for the Cyclotron Laboratory at the Institute for
Nuclear Research and Nuclear Energy
To cite this article: G Asova et al 2018 J. Phys.: Conf. Ser. 1023 012008
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1234567890 ‘’“”
XXII International School on Nuclear Physics, Neutron Physics and Applications IOP Publishing
IOP Conf. Series: Journal of Physics: Conf. Series 1023 (2018) 012008 doi :10.1088/1742-6596/1023/1/012008
Status of Simulations for the Cyclotron Laboratory
at the Institute for Nuclear Research and Nuclear
Energy
G Asovaa, N Gouteva, D Toneva, A Artinyana
Institute for Nuclear Research and Nuclear Energy, BAS, BG-1784 Sofia, Bulgaria
E-mail: gasova@inrne.bas.bg
Abstract. The Institute for Nuclear Research and Nuclear Energy is preparing to operate
a high-power cyclotron for production of radioisotopes for nuclear medicine, research in
radiochemistry, radiobiology, nuclear physics, solid state physics. The cyclotron is a TR24
produced by ASCI, Canada, capable to deliver proton beams in the energy range of 15 to
24 MeV with current as high as 400 µA. Multiple extraction lines can be fed. The primary goal
of the project is the production of PET and SPECT isotopes as 18 F, 67,68Ga, 99m Tc, etc.
This contribution reports the status of the project. Design considerations for the cyclotron
vault will be discussed for some of the target radioisotopes.
1. Introduction
The Institute for Nuclear Research and Nuclear Energy (INRNE) at the Bulgarian Academy of
Sciences is building a facility dedicated to: production of well-established medical radioisotopes;
research and development on emerging radioisotopes for nuclear medicine; fundamental and
applied research with radiotracers in areas related to life sciences and industry [1]. The facility
is based on a TR24 cyclotron capable to deliver proton beams with current up to 400 µA and
energy as high as 24 MeV. The cyclotron has already been produced by ASCI and delivered at
the INRNE with its ancillary equipment like RF and water-cooling systems, a single Y-beamline
equipped with steering and focusing magnets, etc. The construction of the building housing the
cyclotron vault and the radiochemistry laboratories still has to be done. Meanwhile efforts are
dedicated to numerical studies on the possibilities to produce various isotopes for medicine and
radiological characterization of the setup.
The major objective for the start-up is the widely used 18F–FDG produced via 18O (p, n) 18 F
reaction in 18O-enriched target volume and, therefore, the radiological characterization has to
take into account production of neutrons and γ-rays. Part of the neutrons result from the nuclear
reaction within the target volume, whereas another part from primary particles (protons) or
secondaries (neutrons, γ-rays, etc.) interacting with cyclotron components, target, walls of the
facility. γ-rays can be generated by ongoing 18F–decay during irradiation or by neutron-induced
reaction with various components. This study shows numerical estimations of some internal
hazards coming along with the operation of the facility at maximal beam power. Radioactive
materials generated in the 18F–target and the vault will be discussed.
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1234567890 ‘’“”
XXII International School on Nuclear Physics, Neutron Physics and Applications IOP Publishing
IOP Conf. Series: Journal of Physics: Conf. Series 1023 (2018) 012008 doi :10.1088/1742-6596/1023/1/012008
2. Considerations for radiological characterization
2.1. Methodology for the simulations
For the simulations shown here FLUKA [2, 3] has been used due to its capabilities to numerically
estimate emission and transport of secondary particles and to evaluate the radioactive waste
generated as a result of reactions related to the secondary emission sources.
2.2. Radiation source
To adjust the simulation settings a real-size target for 18F was initially irradiated using various
sets of beam parameters [4]. Despite the fact that the highest beam current and energy are not
needed to be used for 18 F production, afterward such were chosen to irradiate the target due to
the stringent conditions they would impose on the radiation environment [5]. The target was
irradiated for six hours and the particles, emitted in a spherical volume as a result of the (p, x)
reactions with any of the target components, have been collected to be used later as sources
irradiating further components. Here x denotes neutrons and γ–rays as they are of practical
interest when dealing with proton accelerators [5]. As shown with red bars in Fig. 1, the energy
Figure 1. Spectrum of neutrons
emitted from the liquid water volume at
proton beam energies of 18 and 24 MeV
and current of 400 µA. Here the proton
beam meets a Havar foil separating
the enriched water from the vacuum
chamber at normal angle of incidence.
of the neutrons covers the full range of energy up to the energy of the primary particles corrected
with the Q-value of the 18O (p, n) 18F reaction (Q = −2.44 MeV) and the energy lost on a Havar
foil, separating the area of the liquid target from the vacuum chamber of the setup. Majority
of the neutrons are low energy to fast ones. The same trend is seen also for energy of 18 MeV.
The simulated spectrum for 18 MeV and 100 µA results in fluence rate of about 2.5e11 n/cm2s
which can be compared to the measurement results shown in [6] where 2.4e10 n/cm2s are given
for 15 µA and 17 MeV. The difference of an order of magnitude might be due to the lower beam
current used in the measured data.
Figure 2 shows the fluence of secondary neutrons overlaid on the target geometry.
2.3. Fields of secondary particles within the cyclotron vault
The vault is designed to house the cyclotron and four irradiation areas as only one of them will
be used for 18 F production. There are two possible locations for the 18 F–target in the vault -
close to the cyclotron but still externally to it and in a separated irradiation room. Figure 3
shows the distribution of neutrons when using both positions - the highest density shown in
black is the exact center of mass of the source from Section 2.2. The source obtained in the step
described above is positioned in either location of the target and the particles are transported
further depending on their spatial coordinates and momentum vector components in the source
3
1234567890 ‘’“”
XXII International School on Nuclear Physics, Neutron Physics and Applications IOP Publishing
IOP Conf. Series: Journal of Physics: Conf. Series 1023 (2018) 012008 doi :10.1088/1742-6596/1023/1/012008
Figure 2. Fluence (particles per
cm2per primary particle) of neutrons
crossing the target body in the three
planes. Proton beam with energy
of 24MeV and current of 400 µA
impinges into the (x, y) plane.
(a) Neutrons in the vaults when positioning the target
within the vault inner area.
(b) Neutrons in the vaults when positioning the target
outside the vault inner area in a dedicated irradiation
room.
Figure 3. Top view of the neutron fields in the cyclotron vault for two different positions of the
liquid target. The cyclotron is shown with a black circle in the center of the bunker. Thinner
concrete walls separate the cyclotron area from the four irradiation areas.
phase space. The vault space is surrounded by 2.5 m thick walls made of high-density concrete
as shown in Fig. 3. The target area is not shielded additionally. The neutron distribution
homogeneity around the target is disturbed by cyclotron metal parts mostly in Fig. 3(a), inner
and outer shield walls (Fig. 3(b)). As it might be assumed that the areas outside the vault
will be used for chemical synthesis, target preparation, etc., it is desirable to minimize any
leakages, thus, making the position of the target shown with Fig. 3(b) preferable if no further
shielding is used. Additionally, the shielding can be improved as it is shown with Fig. 4 where
a few centimeters thick marble-enriched concrete is used locally around the target. Further
optimization of the thickness of this shielding and its chemical composition still has to be done.
3. Activation of the vault walls
The distribution shown in Fig. 2 can be used to study the activation of components of the target
itself. It has already been shown [4, 7] that the nuclides generated in the Havar foil contain a
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XXII International School on Nuclear Physics, Neutron Physics and Applications IOP Publishing
IOP Conf. Series: Journal of Physics: Conf. Series 1023 (2018) 012008 doi :10.1088/1742-6596/1023/1/012008
Figure 4. Top view of the neutron
fields in the vault if the target is
positioned as in Fig. 3(b) and shielded
locally with marble-enriched concrete.
number of long-living ones (3H, 58Co). This study focuses on the activation of the vault using
the distributions from Fig. 2 and Fig. 3. It is assumed that a sacrificial layer takes 20 cm from
the wall thickness including also the walls, separating the cyclotron from the irradiation areas.
The last ones have thickness of 60 cm. Table 1 shows some of the nuclides generated in the
sacrificial layer after a month of operation with daily irradiation conditions as above - 6 hours
at 24 MeV and 400 µA, immediately after End of Beam (EOB) and after 3 weeks of cooling
time.
Table 1. Some of the nuclides generated in the outmost 20 cm of the walls of the cyclotron
vault. The irradiating target is positioned as in Fig. 3(b).
Isotope Activity at EOB [Bq] Activity in 4 weeks [Bq] Parent nucleus
59Fe 2.1×1010 1.4×1010 58Fe
56Mn 1.8×109-56 Fe
55Fe 1.8×1010 1.7×1010 55Mn
54Mn 4.3×1094.1×109 54 Cr, 54Fe
51Cr 1.1×1095.7×108 52 Cr
47Ca 1.1×1091.6×107 46 Ca
47Sc 1.0×1095.0×107 47 Ti
45Ca 2.3×1010 2.0×1010 44 Ca
41Ca 2.5×1062.5×106 40 Ca
42K 2.2×1011 -41 K
41Ar 5.9×106-40 Ar
39Ar 8.1×1078.1×107 39 K
37Ar 5.2×1011 2.9×1011 40 Ca
36Cl 2.8×1042.8×104 39 K
24Na 1.7×1012 -27 Al
14C 2.2×1032.2×103 13 C
3H 3.1×1063.1×106(p,3H)
41Ar resulting from neutron capture on 40 Ar is also seen in the air of the vault in activities
in the range of 1×107Bq - above the limit of 200 Bq/m3with respect to the volume of the
vault increasing the cooling time before maintenance access. In 18 hours the activity decreases
to 3×104Bq with which the specific activity within the inner cyclotron room decreases below
5
1234567890 ‘’“”
XXII International School on Nuclear Physics, Neutron Physics and Applications IOP Publishing
IOP Conf. Series: Journal of Physics: Conf. Series 1023 (2018) 012008 doi :10.1088/1742-6596/1023/1/012008
the exemption limit. Further estimations are needed considering that the usable lifetime of a
cyclotron can be about 20 years. At the moment such estimations with the software package
used can be done for operation time of one month.
4. Conclusion
The distribution of neutrons emitted as a result of primary reaction on 18 F target from a mid-
energy high-intensity cyclotron was evaluated using Monte-Carlo simulations. Two different
locations of the target were considered as the one positioned in a separate irradiation room
showed to be preferable with respect to possible leakages of low-energy neutrons through the
walls of the vault. It was also shown that local target shielding with marble-enriched concrete
would lead to further improvements.
A number of toxic and long-living isotopes were seen in the sacrificial layer of the inner walls
(55Fe, 45Ca, 41Ca, 39 Ar). 41 Ar is also seen in the air limiting the time needed for maintenance
access.
5. Future steps
Characterization of the vault depends on the targets being irradiated and therefore more isotopes
will be studied. At the moment efforts are spent on the production routes of 67,68Ge and 99m Tc
and they will also be used to assess the activation in the vault. Additionally the local target
shielding needs to be optimized with respect to ease of usage (weight), composition, leackage
and neutrons and γ-rays.
Acknowledgments
The research has been supported by the Bulgarian Science Fund under Contracts No. DN 08/6,
13.12.2016 and DM 18/2, 12.12.2017 and DFNP-17-165/03.08.2017.
References
[1] Tonev D, Goutev N, Georgiev L S 2015, Cyclotron laboratory of the Institute for Nuclear Research and
Nuclear Energy J. Phys.: Conf. Series 724 012049
[2] B¨ohlen T T, Cerutti F, Chin M P W, Fass`o A, Ferrari A, Ortega P G, Mairani A, Sala P R, Smirnov
G, Vlachoudis V 2014, The FLUKA code: Developments and challenges for high energy and medical
applications Nuclear Data Sheets 120 211 214
[3] Ferrari A, Sala P R, Fass`o A, Ranft J 2005, FLUKA: A multi-particle transport code (program version 2005),
CERN-2005-010, INFN-TC-05-11, SLAC-R-773
[4] Yavahchova M, Asova G, Goutev N, Tonev D 2016, FLUKA simulations on the thick target yield of 18F
production by proton-induced reaction, Science and Technologies VI 3
[5] IAEA Technical Report Series No 283 1988, Radiological Safety Aspects of the Operation of Proton Accelerators
(Vienna)
[6] Sadat-Eshkevar S et al. 2012 Assessment of the staff absorbed dose related to cyclotron operation and service
in the production of 18F radiopharmaceuticals Nukleonika 57-3 407-410
[7] Asova G, Artinyan A, Goutev N, Mineva M, Tonev D, Ivanova S, Zheleva N 2017 Monte-Carlo simulations
on the radiological characteristics of a smal l medical cyclotron C. R. Acad. Bulg. Sci 70 10
