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THE ACCELERATOR DRIVEN SPES-BNCT PROJECT AT INFN LEGNARO LABS
J. Esposito1, P. Colautti1, A. Pisent1, L. Tecchio1, S. Agosteo2, C. Ceballos Sànchez1, V. Conte1, L. De Nardo3, A. Gervash4,
R. Giniyatulin4, D. Moro1, A. Makhankov4, I. Mazul4, G. Rosi5, M. Rumyantsev4, R. Tinti6,
1 INFN-LNL, Via dell’Universita’ 2, Legnaro (PD), Italy, 35020, juan.esposito@lnl.infn.it
2 Nuclear Engineering Department, Milano Polytechnic, via Ponzio 34/3, Milano, Italy, 20133
3 Physics Department, Padova University, via F. Marzolo 8, Padova, Italy, 35131
4 NIIEFA, Efremov Institute, St. Petersburg, Russia, 196641
5 ENEA (FIS-ION), Via Anguillarese 301, S. Maria di Galeria (Roma), Italy, 00060
6 ENEA (FIS-NUC), Via Martiri di Monte Sole 4, Bologna, Italy, 40129
An attractive, accelerator-driven, high flux thermal
neutron beam facility is currently under construction at
the INFN Legnaro National Laboratory (LNL), in the
framework of the SPES research program. The
experimental treatment of extended skin melanoma tumor,
with a combined Boron Neutron Capture plus
Photodynamic therapy approach (BNCT+PDT), is being
investigated. The intense beam delivered by the 5 MeV, 30
mA (150 kW) cw RFQ which is the SPES proton driver,
will be employed. One of the main elements of the BNCT
facility is the construction of a reliable neutron producing
target, based on the 9Be(p,n)9B reaction. Two, original,
beryllium-based neutron converter concepts have been
developed and constructed for that purpose. Both full-
scale prototypes already passed a series of thermo
mechanical electron beam tests at operative and critical
power conditions. The additional radiation damage tests
are in progress. The Accelerator-Based Beam Shaping
Assembly (AB-BSA) modeling is currently underway. The
BNCT neutron irradiation facility, which main features
are here reported, based on the saddle-type beryllium
neutron converter, has reached an advanced design
status.
I. INTRODUCTION
The investigation of exotic, not stable nuclei has been
recognized in the last years as a new frontier in nuclear
physics research. The aim of SPES (Study and Production
of Exotic Species) project at LNL is the construction of an
advanced Radioactive Ion Beams (RIB’s) facility, having
an intermediate size between the existing, first generation,
GANIL-SPIRAL and CERN-ISOLDE ones and the next
generation, large scale, EURISOL. The Radioactive Ion
Beams (RIB’s) are generated via fission reactions induced
in 238U by an intense fast neutron source. The exotic
nuclei of interest will be then injected in the existing
superconducting linac PIAVE-ALPI complex as post
accelerator. A first feasibility study report on SPES
project, taking into account a proposal for a 100 MeV, 1
mA superconducting linac, was published in 1999 (Ref.
1). A first Technical Design Report (TDR) was instead
issued in 2002 (Ref. 2), where a general description of the
facility can be found. The first part of the original project,
named SPES-1, including the linac up to 20 MeV and the
R&D on fission fragments production in UCx targets, was
approved and funded by the INFN board in 2004. In the
last years, however, some significant modifications have
arisen with respect to the original project. A new detailed
TDR is therefore next to being issued3. The first major
difference is related to the exotic beam production
system. It has been modified into a Direct-Target,
working with a proton beam of 40 MeV energy and 0.2
mA average current, with respect to the original Two-Step
concept. In such a way the same nominal 1013 s-1 fission
rate is estimated. The second major difference introduced
deals with the high energy part of the accelerator system.
A 40 MeV Drift Tube Linac (DTL), operating at 352
MHz, pulsed at repetition rate of 50 Hz, is now being
taken into account. This last structure replaces the
superconducting linac which was originally foreseen in
the former TDR.
The r.f. source and the RFQ driver were formerly
developed within the TRASCO (TRAsmutazione SCOrie)
research program, aimed at the construction of a high
intensity linac for ADS reactors dedicated to nuclear
waste transmutation. The source TRIPS4 (TRasco Intense
Proton Source) able to supply 30 mA beam at 80 keV,
was built and commissioned at LNS. It has then been
transferred to LNL in fall 2005 and began to produce the
first beam in mid 2006 (Ref. 5). The RFQ is a 7.13 m
long, continuous wave (c.w.), accelerating structure
composed by six modules fed by a single 352 MHz, 1.3
MW klystron. It has been designed to raise the proton
beam energy up to 5 MeV. The construction of this high
intensity accelerator has led to many technological
challenges. Two out of six modules of RFQ6 have already
been completed, while the remaining four modules are
currently under an advanced construction stage. A sketch
of the new SPES-1 accelerating layout, including the
RFQ, the DTL linac, and the first module of RFQ
completed ready for RF measurements after brazing
treatment, is shown in Figure 1.
II. THE SPES-BNCT PROJECT
The TRIPS ion source and the RFQ installed at LNL
will represent a unique facility, able to deliver 30 mA, 5
MeV beam, which may be also used as a standalone
system. The availability of an additional accelerator-
driven neutron source was recognized as a useful tool
since the beginnings of SPES project. Therefore a thermal
neutron beam facility, devoted to Boron Neutron Capture
Therapy (BNCT) experimental treatments on skin
melanoma tumors was, in fact, proposed in the framework
of SPES project. The neutron source spectrum, provided
through (p,xn) reactions by a suitable neutron converter,
is then slowed down to the thermal energy range (i.e.
En0.5 eV) by a proper spectrum shifter device. The in-
air thermal neutron flux level, at least of 1∙109cm-2s-1 at
beam port is in fact requested. A proof-of-principle layout
sketch of the final beam shaping assembly and the RFQ
driver is reported in Figure 2. Accelerator based neutron
sources having such a characteristics are not currently
available worldwide and the patient BNCT trails
performed are so far based on the use of nuclear reactors.
Even if other experimental applications using the
relatively intense neutron source may be concerned, the
BNCT application will be the main interdisciplinary user
of the SPES-1 facility. The SPES-BNCT project will
therefore represent a challenge to explore the treatment of
extended skin melanoma with such a therapeutic
modality. Furthermore it will be a fundamental test bench
for an operative, accelerator based BNCT facility concept,
which could provide in perspective a possible spin-off for
a hospital based system.
An overview on the items of the research program,
mainly focused on the neutron converter prototypes
developed and tested, as well as the status on irradiation
facility design, is here summarized. Additional
information on the BNCT project relying the in-vivo tests
with the new boron carriers which are being developed
and tested are reported in (Ref. 7). The new, mini Tissue
Equivalent Proportional Counter (mini-TEPC) developed
and constructed at LNL, for on-line biological dose
monitoring in both tumor and healthy tissues, are reported
elsewhere8.
Fig. 1. Schematic layout of SPES-1 facility with the beam line for the interdisciplinary application. TRIPS (TRasco
Intense Proton Source), RFQ (Radio Frequency Quadrupole) is the first accelerating stage, the MEBT (Medium Energy
Beam Transfer) is the connecting beam line to DTL (Drift Tube Linac), or to the dedicated line to the thermal neutron
facility for BNCT application.
III. THE NEUTRON CONVERTER DESIGN
A R&D effort has been carried out in order to select
the proper neutron converter type consistent with the
SPES design specifications. The main low energy, proton-
induced nuclear reactions considered for an accelerator
based BNCT facility to yield a neutron source:
7Li(p,n)7Be, 9Be(p,n)9B and 13C(p,n)13N, have been taken
into account at the design stage. A summary of neutron
yielding, as well as material main properties may be
found elsewhere9. A full set of detailed MCNPX
simulation trials, based on the LNL-CN demonstration
facility10 modeling, were preliminary performed to assess
the neutron beam performance11. Beryllium revealed at
last the best solution, due to both the neutron yielding at
the fixed RFQ output energy and the related design
requirements for a reliable solid target.
Different engineering solutions have been compared
to get a well balance between the primary need of a
compact neutron source design and the use of simple,
reliable solutions for target cooling. Preliminary thermal
investigations12 performed on simple, water-cooled
beryllium targets for feasibility study, revealed that
critical conditions for heat transfer to cooling system are
achieved at beam power densities of about 1 kWcm-2.
Such an extreme working condition has to be avoided, if
fairly large engineering safety margins have to be fulfilled
for a reliable neutron converter. A target beam spot area,
which should keep the surface heat load to a level ~0.7
kWcm-2 in order to make use of reliable and already
tested target cooling system, would instead be required.
After both neutronic as well as technological
feasibility studies lasted two years in collaboration with
the STC Sintez of Efremov Institute in S. Petersburg, the
design of an original, beryllium-based target, shown in
Figure 3 and Figure 4, has thus been produced13. The
target main structural components are based on a
zirconium alloy (Zr + 2.5% Nb), while the neutron
converter exploits the tile concept, i.e. beryllium tiles
which are brazed on a 10 mm outer diameter, 1 mm
thickness, cooling pipes. These latter are produced by
casting of bronze (CuCrZr) alloy onto 0.3 mm thickness
SS pipe with the following quenching and ageing
manufacturing process. Such a composite pipe structure
allows for the application of the well-developed Be-Cu
joint technology, thus avoiding the corrosion of copper
alloy by the coolant.
Moreover a peculiar V-shaped like profile has been
chosen for the target geometry. The advantage of such an
approach is to meet the design criteria of a neutron
yielding volume as close as possible to the ideal point-like
source. Another important advantage is that the parabolic
power profile of RFQ beam (Figure 4) is changed in a
uniform distribution on the beryllium target surface, along
the beam axis direction. The maximum surface power
density lies in the target center, while reducing at the
extremities, as shown in Figure 5. The surface area is
limited at 130x170 mm2 on each target half which fulfills
the main requirement of a peak-power density as low as
~0.7 kWcm-2. Some concern relating the cooling fluid
capability, the cooling system simplicity as well as the
economic has led light water to be chosen as coolant, for
both the target and the related collimator. Due to the
given geometry of the cooling system full turbulent flow
conditions are achieved (Re ~40000) with a water
velocity of 4 m/s. In such a way the required high heat
transfer coefficient of about 6∙104 Wm-2K-1 is gained, with
a flow rate of about 180 L/min, able to remove the total
heat load impinging (150 kW). The main hydraulic
parameters are a coolant inlet pressure being fixed at 0.3
MPa, while, the pressure drop in the whole circuit being
of 0.02 MPa.
A detailed thermal-mechanical coupled analysis has
also been performed to assess the maximum working
temperatures, the related target mechanical stresses and
deformations, under static and cycling loading operating
Fig. 2. The accelerator-driven SPES-BNCT irradiation facility layout proposed
conditions. The steady state thermal analysis main results
are also reported in Figure 5. The maximum temperature
calculated in the different components: beryllium hitting
surface (673 °C), Cu-alloy pipes (362 °C), SS pipe liners,
(344 °C ) and Zirconium alloy cooling feed system (21
°C) are well below the correspondingly melting points.
Moreover the stress intensities calculated at loading
(beam on) and unloading (beam off) stages in all
structural parts have turned out to be within the allowable
design limits. The target also fulfills the other critical
design requirement to pass the limit of 2000 hrs lifetime,
under 200 thermal cycles (the beam is on and off per each
run).
Several mock-ups have been manufactured and tested
at the High Heat Flux (HHF) Tsefey electron beam
facility at the Efremov Institute, under different power
density levels, up to 1.1 kWcm-2. All destructive analyses
performed on inspected samples revealed good brazing
quality, with a uniform brazing layer. The joint between
tiles and cooling pipes was not damaged during the tests
and no any visible cracks and erosions have finally been
observed through Be thickness. The first, full-scale half-
target prototype, shown in Figure 6, was finally
constructed by the end of 2004. It successfully passed the
preliminary series of both operative and critical e-beam
power test conditions up to 0.75 kWcm-2 in March-July
2005.
The technology to braze a beryllium layer on a
CuCrZr support and heat sink material, although well
proven in the framework of ITER project, has however
the drawback of a relatively high prompt capture gamma
source level at the facility beam port. In order to reduce
such unwanted gamma component, a new technological
research has started, aiming at constructing a reliable
neutron converter made of bulk beryllium only. All the
target system: manifolds, cooling pipes, and the neutron
converter layer have, therefore, to be manufactured
starting from a full Be block. The main advantage with
respect to the former target version is less assembling
parts and a considerably less brazing joint. Moreover, the
same neutron yielding of Be-tile converter would be
provided, with an improvement in the neutron moderating
Fig. 3. Final design of Be neutron converter for SPES-BNCT facility: the target assembly with the first
moderator stage arranged in cylindrical form (left), the target plug system (right).
Fig. 4. Cross sectional view of TRASCO RFQ proton beam power density distribution (kW/cm2) at the target
collimator on a plane normal to the beam line (left). The neutron converter profile with main sizes given in mm
(center). Target main structural components (right).
power because of beryllium better neutron slowing down
properties. In such a way a higher neutron flux per unit
accelerator current at the patient position may be
provided.
After a feasibility study by STC Sintez of Efremov
Institute (S. Petersburg) lasted four years, a first full-scale
prototype, shown in Figure 7, has been assembled on mid
2005. The new target positively passed the preliminary
He leakage tests on late summer 2005, thus proving the
proper manufacturing process adopted. The Be-bulk
neutron converter works with a slightly larger beam spot
area (120x210 mm2) on each target half, in order to lower
the peak power density down to 0.5 kWcm-2.
The half target prototype has then undergone a series
of both operative and critical power test conditions on fall
2006 at the (HHF) Tsefey electron beam testing facility.
The main goal was to assess both the target design criteria
and the prototype reliability under heat loading condition
as close as possible to the real ones. The electron
scanning beam was tuned to heat the target surface with a
power deposition parabolic profile, quite close to that one
provided by the RFQ proton accelerator. The half target
has undergone a series of test ranging from the designed
0.5 kWcm-2 up to 0.7 kWcm-2 peak power density. As a
result the half target positively passed the test: no any
visible damage (cracks) has been observed at the visual
inspection on the heated surface. Therefore this second
target version may be taken into account as a possible,
alternative solution for the BNCT facility. The additional
investigation concerning radiation damage tests the target
undergoes after 5MeV 30mA irradiation are scheduled on
2007. The radiation damage study will be done by using
both proton and high neutron flux beams in condition as
close as possible to the real ones.
IV. PRESENT STATUS OF THE IRRADIATION
FACILITY MODELING
As a general rule the neutron beam shaping and
filtering assembly design is closely linked with the target
Fig. 5. Target surface heat power load distribution from SPES RFQ parabolic beam shape (left). Corresponding
surface temperature distribution in steady state operation (center). Target deformation (displacements along
beam normal direction) under thermal stress condition (right). ANSYS® code.
Fig. 6. Target prototype final assembly (left) and surface visual inspection after the first electron beam power test
performed at the HHF facility (right).
design, which must take into account the real-scale
geometry of the neutron converter and the support
structure effects on the neutron and gamma transport.
The experience gained in the last years at LNL labs
with the 5 MeV, 1 A demonstration facility14, driven by
the CN Van de Graaff accelerator, revealed quite useful
for the next Monte Carlo facility design stage. Different,
real-like, Be neutron converter concepts were, in fact,
tested during the preliminary feasibility study15. Extensive
MCNPX simulation trials were performed, taking into
account the CN demonstration facility as geometry
reference. Basic beam parameters, calculated at the
irradiation port, lying on the side surface, have then been
compared, in order to get the basic knowledge on the
beam shaping assembly layout useful to the final facility
design. The treatment of shallow tumors with BNCT
technique requires an eminently thermal neutron beam,
with a limited non-thermal and gamma doses
contaminations. A set of in-air Figure Of Merit (in-air
FOM) beam reference parameters, given at the irradiation
port, having a fixed standard area of 10x10 cm2, have at
this purpose been developed in the BNCT community, as
a quick and useful method to compare the calculated
parameters. The more stringent and widely accepted
recommended goals, here used to make a useful
comparison among beam port neutron spectra, supplied
by the different facility configurations investigated, as
well as related energy group ranges, are listed in Table I
(Ref. 16). On the other hand, a detailed depth-dose
distribution calculation only, inside tissues of a simulated
phantom, would be a further, more reliable step, to
characterize the neutron beam quality. However, due to
the lack of a full set of experimental double-differential
neutron yielding spectra at 5 MeV proton energy, the
experimental data set at 4 MeV17 have been used instead
in the preliminary BSA design. Starting from the original
demonstration facility configuration, new simulation trials
were performed, all housing the final, full-scale, saddle-
Fig. 7. The Be-bulk type neutron converter developed: final target layout (left). First, real scale, half target
prototype constructed (right)
Fig. 8. 3D view of real-like geometry modelling for the irradiation facility (left). The current configuration proposed
with the final Be neutron converter: MCNPX geometry
type, Be neutron converter modeling. After having
assessed different moderator models, the best results have
been obtained with the irradiation facility shown in Figure
8, which beam port parameters calculated are enlisted in
Table II.
The irradiation facility is basically made of a large
(70x70x50 cm3), Teflon (CF2)-made, heavy water tank,
which surrounds the neutron converter mainly towards the
irradiation port. The tank is then inside a beryllium oxide
(BeO) structure instead of the former RG-Graphite. This
latter choice is due to exploit its remarkable albedo
property for better confining and moderating the neutrons
inside the BSA volume. Another important improvement
is a 2.5 cm thickness of, hydrogen-free, lithium fluoride
(LiF) panels around five out of six walls of the BSA (1
cm covering the beam port wall), for absorbing the
thermal neutrons that escape throughout walls. A grid of
2x2 cm2 pixel size was put in front of the wall for
mapping the neutrons and gamma dose rate distribution
over the beam port facility wall. Figure 9 show the results
for the thermal neutron component of the beam.
Additional data are published elsewhere18. The square on
the 2D images represent the 10x10 cm2 irradiation port
position. Table III reports the average dose rate on the
beam port and over the rest of the wall for each
component of the beam, along with the fraction of the
total dose rate that corresponds to the beam port area.
As can be seen from both the table data and the
related figure, the neutron beam is very well collimated
on the irradiation port for the proposed configuration. The
less collimated component of the beam is due to the
prompt gamma radiation, because those gammas are
mainly produced by radiative capture of thermal neutrons
inside the BSA volume and thermal neutrons diffuse
stochastically inside the BSA. Nevertheless 92 % of the
gammas come out through the irradiation port.
V. CONCLUSION
An accelerator-based source of thermal neutrons, for
treating skin melanoma with BNCT technique, is foreseen
in the framework of the SPES project, proposing a facility
for exotic nuclei production at LNL in Italy. An extensive
technological development has been performed on two
different Be-based neutron converters. The prototypes
constructed successfully passed the electron beam test at
heat loading condition quite close to that provided by the
RFQ, which is the SPES proton driver. The present
computational MCNPX design study of the proposed
irradiation facility, based on a 4 MeV proton-driven Be
neutron source, would already be able to provide a high
collimated thermal neutron beam (99.7 %), fulfilling all
the established design requirements for a BNCT
irradiation facility. Further improvements are in progress
for better shielding the gamma radiation. An experimental
project is planned by LNL to measure neutron yield
spectra from the 9Be(p,xn)9B reaction, using a thick target
and 5 MeV proton beam. When the whole set of Be
neutron data will be available, the actual model will be
implemented and minor facility modifications are
expected to be made. Because the total neutron yield at 5
MeV is expected to be at least a factor of three higher
than those ones at 4 MeV9,17, the final thermal neutron
irradiation facility performance is expected to be better
than results here presented.
Fig. 9. Thermal neutron dose rate (Gy/hr) 3D profile
over the beam port wall surface (top). The same plot in
2D view: the square represents the irradiation beam port
position (bottom). The pixel size in the plot scales is
2x2 cm2. MCNPX calculation
TABLE.I: BNCT in-air neutron beam port recommended
limits. (Ref. 16)
BNCT beam port parameters
Required limits
th [cm-2s-1]
1.109
th / total
0.9
K
n epi-fast / th [Gycm2]
~2.10-13
K
/ th [Gycm2]
~2.10-13
Fast energy group E > 10 keV
Epithermal energy group 10 keV E 0.5 eV
Thermal energy group E< ~ 0.5 eV
REFERENCES
1. The SPES Collaboration, SPES Project Study of an
advanced facility for Exotic Beams at LNL, LNL-
INFN (REP) 145/99 (1999).
2. SPES Technical Design Report, LNL-INFN (REP)
181/2002 and http://www.lnl.infn.it/~spes/, A.
BRACCO and A. PISENT Ed., (2002).
3. SPES Technical Design for an Advanced Exotic Ion
Beam Facility at LNL, INFN report (2007) (to be
issued)
4. G. CIAVOLA, L. CELONA, S. GAMMINO, “First
Beam from the TRASCO Intense Proton Source
(TRIPS) at INFN-LNS”, Proc. of the 2001 Particle
Accelerator Conference (PAC2001), Chicago-USA
June 18-22, 2001, p.2406, edited by P.Lucas and
S.Webber, IEEE, Piscataway, N.J. ,2001
5. E. FAGOTTI et al., “First Beam of SPES source at
LNL”, LNL Annual Report, 2006, p. 189, INFN-
LNL-210(2006), ISSN 1828-8545.
6. A. PISENT, et al. “The TRSACO-SPES RFQ”, Proc.
of the XXII Int. Linac Acc. Conference (LINAC2004),
Lubeck-Germany, August 16-20, 2004, p. 69 JaCoW
website. (2004)
7. E. FRISO et al, “A novel 10B-enriched carbora-
containing phthalocyanine as a radio- and
photosensitizing agent for boron neutron capture
therapy and photodynamic therapy of tumours: in
vitro and in vivo studies”, Photochemical &
Photobiological Sciences, 5 (1), 39, (2006)
8. L. DE NARDO, et al, “Mini-TEPCs for radiation
therapy”, Radiation Protection Dosimetry., 108, 345,
(2004)
9. T. BLUE and J. YANCH, “Accelerator-based
epithermal neutron sources for boron neutron capture
therapy of brain tumor” Journal of Neuro-Oncology,
62, 19, (2003)
10. S. AGOSTEO et al., “An Accelerator-Based Source
of Thermal Neutrons for BNCT of Skin Melanoma:
Status of the Project”, Proc. of 7th Int. Conf. on
Applications of Nuclear Techniques, Crete, Greece,
17-23 June, 2001 (CD-ROM). Ed., G. Spichiger,
(2001)
11. J. ESPOSITO, “The SPES-BNCT project: An
experimental neutron beam facility aimed at the
treatment of skin melanoma” LNL Annual Report
2001, p. 236, LNL-INFN (REP) -182/2002,
12. B. W. BLACKBURN, J.C. YANCH, R.E.
KLINKOWSTEIN, “Development of a high-power
water cooled beryllium target for use in accelerator-
based boron neutron capture therapy”, Medical
Physics 25, 1967 (1998)
13. A. MAKHANKOV et al. “An accelerator based
thermal neutron source for BNCT application” Proc.
of EPAC 2004, Lucerne, Switzerland, July 5-9, 2004,
p. 2745, Published by European Physical Society
Accelerator Group (EPS-AG), (2004) ISBN 92-9083-
231-2 (Web version)
14. S. AGOSTEO et al., “An accelerator-based thermal
neutron source for BNCT”, Advances in Neutron
Capture Therapy, Vol. 1, pp. 483-489, B. LARSSON
et al., Ed., Elsevier Science, Zurich, Switzerland
(1997)
15 J. ESPOSITO, “The SPES-BNCT project: Advances
towards the experimental accelerator-based neutron
beam facility” LNL Annual Report 2003, p. 65, LNL-
INFN (REP) -202/2004, ISBN 88-7337-004-7
16. Current Status of Neutron Capture Therapy, IAEA-
TECDOC-1223, International Atomic Energy
Agency, IAEA, Vienna, Austria, (2001)
17. W.B. HOWARD et al., “Measurements of thick
target 9Be(p,n) neutron energy spectra”. Nuclear.
Science. Engineering, 138, 145, 2001
18. C. CEBALLOS, J. ESPOSITO, “The SPES-BNCT
project: Current Status of the accelerator-driven
thermal neutron facility Monte Carlo modelling”,
INFN-LNL-219(2007)
TABLE.II: Summary of data calculated at beam port for
the proposed irradiation facility for 4 MeV 30 mA
proton beam. MCNPX calculations.
Beam Port data
th (E 0.5 eV) (cm-2s-1)
(1.17 ± 0.003) 109
th / total
0.99
K
n epi-fast (Gy·h-1)
(3.00 ± 0.70) 10-3
K
n epi-fast /
K
n tot
4.27 10-3
K
(Gy·h-1)
0.58 ± 0.01
K
/
K
n tot
8.2 10-1
K
epi-fast / th (Gy·cm2)
7.93 10-16
K
/ th (Gy·cm2)
1.38 10-13
TABLE.III: Summary of data calculated at beam port
and at rest of wall for the current BSA proposed.
Beam
component
Beam
Port
(Gy/h)
Rest of Wall
(Gy/h)
Beam port
fraction vs.
total
(%)
Thermal
neutrons
7.0∙10-1
1.9∙10-3
99.7
Epithermal
neutrons
6.8∙10-4
1.4∙10-5
98
Fast
neutrons
2.6∙10-3
8.3∙10-5
97
Gamma
5.8∙10-1
5.3∙10-2
92
