The 12th Symposium on Accelerator Science and Technology, Wako, Japan 1999

Shielding Design of RIKEN RI Beam Factory
NobuhisaFUKUNISHI, Sachiko ITO, Yoshitomo UWAMINO and Yasushige YANORIKEN (The Institute of Physical and Chemical Research)
2-1, Hirosawa, Wako-shi, Saitama 351-01, JapanAbstract
The construction of the RIEKN RI Beam Factory has
started and will be finished by the end of March 2003. It
plans to accelerate all the ions from hydrogen to uranium
with the intensity of 1 pj.tA Its maximum beam energy is400 MeV/nucleon for light ions (A<40) and 150
Me VInucleon for uranium. Since the RI Beam Factory willproduce such high-intensity heavy-ion beams, radiation
shielding is a serious problem. We report here the shielding
design of the RI Beam Factory giving emphasis toprescription for dose estimation.

--Odeg.
------··· 7.5deg.
-------15deg.
-----30deg.
--60deg.
-----90deg.

1 RI Beam Factory

10 ~1~~~~~~1~0--~~~~1~0~0~~~~~

Neutron energy (MeV)The RIKEN RI Beam Factory (RIBF) aims to produce
the world's most intense RI beams at energies of several
hundreds of Me VI nucleon over the whole range of atomic
masses [1]. To this end, two cyclotrons will be constructed
as post-accelerators of the existing RIKEN Ring Cyclotron(RRC). One is the K930-MeV Intermediate-stage Ring
Cyclotron (IRC) and the other is the K2500-MeV
Superconducting Ring Cyclotron (SRC). This series ofcyclotrons is capable of accelerating light ions (A<40) up to400 MeV/nucleon and very heavy ions more than 100
Me V/nucleon with the beam intensity of 1 p~A. The
accelerated beams will be used to produce RI beams via
projectile-fragment reaction. The RI-beam production will
be done at a new projectile-fragment separator (Big-RIPS).
RI beams produced at the Big-RIPS will be guided toexperimental halls to perform various experiments.

Fig.l Double-differential neutron yields at a thick Cu target
bombarded by a 400-MeV/nucleon 2 ~e beam
2.2 Deep Penetration of High-energy Neutrons

The next step is to evaluate attenuation of the neutron
dose. To this end, we calculated deep penetration ofneutrons using the ANISN code [4]. The cross-section data
set used here is the DLC-119/HIR086R group constant [5].
Fig.2 illustrates attenuation of effective dose in shielding
materials that are made of normal concrete slab and ironslab. Note that the neutron fluence calculated by the ANISN
was converted to the effective dose using the ICRP-74
conversion factors.
'E 1 o" r-----------------;===========~~.o2 Shielding Calculation

Ql--Cone .

--------- 0.5m Fe + Cone.

1 014,if-,< 1012\~.~'\~····-.•·,"'- ·--...

5:

We will hereafter concentrate on the radiation shieldingof the SRC and the Big-RIPS because the maximum beamenergy is 127 MeV!nucleon for the IRC, which is nearlysame as the existing RRC. To make reliable estimation ofradiation dose, we used neutron production data as a source
term of shielding calculations. We calculated the dose
attenuation in shielding material and compared the resultswith shielding experiments.

- - - - • 1.0m Fe+ Cone.

'.':- •• ·-...

~ 1010_ .________:_.

~~-~:<·:·:-----", ........ ~...................... ···· .. .

,o-'=\-~ o'o•Q)- ·- • ·1.5m Fe+ Cone.
- - -2.0m Fe+Cone.
---2.5mFe+Cone.
-·---3.0mFe+Cone.

"- .... --- ·-•••··<:. ~~~:~:~:~:::::·:·:·-. . _1"' 1·........................... ·.......... ...

0"0'-.:--...' ~--­'·.:--...'' .

Q)>

t5 1 o'~~Q)

2.1 High-energy Neutron Production by Heavy Ions-'

1 o'0200

400600Thickness of shield L(cm)Recent vigorous measurements of neutron production inheavy-ion reactions [2-3] gave us a firm basis of shielding
calculation. Fig. 1 shows an example, the thick-target yieldof neutrons by a 400-MeV/nucleon 2 ~e beam. We used thedata shown in Fig.l as a source term of shielding
calculation. As we will discuss later, a 400-MeV/nucleon
2 ~e beam is not the most serious beam in radiation
shielding of the RIBF. We introduce a simple scaling law toapply the present data to other cases.

8001000

Fig.2 Deep penetration of neutrons in shielding materials.
The 0-degree data in Fig. 1 are used as a source termof shielding calculation.
Beyond the neutron build-up region, effective dose (H)obeys the simple exponential law as follows,

Here, L is the distance from a source; t is the thickness of-349-

The 12th Symposium on Accelerator Science and Technology, Wako, Japan 1999

shield and A. is the dose attenuation length. The h0 parameter
depends on e, the angle between a beam axis and emitted
neutrons. The attenuation length A. also depends on thebut it ranged from 48.1 em to 49.1 em for all dataangle
shown in Fig. 1. 1bis fact enables us to use the constantvalue (49 em) for A.. In addition, dose attenuation in iron is
2.5 times faster than in normal concrete if there is at least
1.0-m thick normal concrete behind iron.

e,MeV/nucleon 12 C beam [3]. The result is that the effective
dose obtained from the scaling law always lies in the safety
side if we use 400-MeV/nucleon 2'Ne data as a source termof shielding calculation. From this investigation, wepredicted in Table 2 the amount of radiation for various
beams produced in the RIBF. A 300-MeV/nucleon 84Krbeam gives the largest amount of radiation. The scaling
factor of 2.36 is introduced for the 2 ~e data.
3 Dose Limit Criteria

2.3 Comparison with Shielding Experiments
In order to check the dose attenuation calculated by theANISN, we compared the present estimation with shielding
experiments [6-7]. We employed neutron production databy a 400-MeV/nucleon 12 C beam [3] in the present
comparison because the experiments were performed with
400-MeV/nucleon 12C beams. We summarize the results inTable 1. The present calculation reproduces well theexperiments except for the 0-degree direction. The
discrepancy for forward shielding should be resolved in thefuture. In the last column, we also calculated effective dosewith somewhat larger attenuation length (A.= 53 em). In thiscase, the calculated value is at least 2 times larger than theobserved value. We use the A value of 53 em for actual
shielding design taking into account experimental errors.
Comparison of shielding calculation withexperiments. Beam intensity is 3xl 08 pps except for
the first two data (lxl 08 pps). The unit of effective
dose is IJ.Sv/h. (* 380-cm thick normal concrete +50-cm thick iron)"A=53cm
Calc.
Obs.
S(deg.)
L(m) t(cm)
498
767
0.00
280
5.0
66
1.26
1.5
2.75
0.00
505*
10.0
24.9
16.8
38.7
13.38
286
13.86
29.8
21.48
268
19.7
12.98
13.9
20.1
30.56
13.6
256
6.5
12.38
5.66
3.15
8.32
40.29
250
12.12
1.52
54.94
1.02
256
12.40
0.75

TabletWe explain here the dose limit criteria of the RIBF. The
dose limit criteria was determined to meet the ICRP-60recommendation as shown in Table 3. The value for the siteboundary is an engagement with the local government.
Table 3 Criteria of effective dose for the RIBF
Dose limit
Item(boundary)Non-restricted area in radiation 25 1J.Sv/h (1 mSv/w)
controlled area
2.6 11Sv/h (1.3 mSv/3m)
Radiation controlled area
0.5 11Sv/h (250 mSv/3m)
Office in site
50 IJ.Sv/ySite boundary
4 Shielding of SRC
We applied the methods mentioned above for theradiation shielding of the SRC. The beam loss is assumed tobe point-like and its maximum value is 10 pnA for injectionand extraction, respectively. The beam loss will be kept lessthan 10 pnA by radiation and/or beam-loss monitoring. Fig.
3 shows the prediction of the effective dose on the roof of
the SRC room. In the present calculation, the roof is 3mthick normal concrete and the 3-m thick local shield ofnormal concrete is added to suppress the radiation produced
in extraction.
10 1 r---------------------------~~ )/~:~>-::-:··· . . . ;----;:·:/.~

2.4 Mass and Energy Dependence10°>Since the RIBF plans to accelerate all the elements up touranium, we should know which beam produces the largest
amount of radiation.

-1 ••I'0"'C<0::::Q)' 1 ,•

1 0"2:;~~');f ~~1 o-3 loC
0··,_, ·, 1/''r

- - - - - R=7m~:~rm:::::~~1~:::'100..

\•r'::I·,\ \·.
, \o250

•••

:: ~~

200:·\ '1 ~I,\ Ji150·-,

I~: 1 1150I,

, • 1 •

1·1:..:._-_·:- - 2.5microSv/hI'I', ,, ' , ''..._,:·•. •, ---·····- R=3m'!('' ------·R=5m~~-:'''j . , ,_ .:. ' \\\II.'' -R=1m.2:m,,.

'''·,,:·,'..
,·~ • 1 ~0Table 2 Relative value of effective dose in the RIBF
Intensity Relative dose
Beam energyion(MeV/nucleon)<e!!A)
l6o7+
0.80
1400
2~eJO+
1.00
1400
40Arl7+2.00
400
84Kf'IO+
2.36
1300
J29Xe38+1.61
1200
23su49+0.74
1100
23suss+0.33
0.2150.. ,••. , ••. \'''\'"'-'·.. :.r!:"-'il· ........ ' ., ........ (,-~'/.'-:'·, ~ :1::1.I ':'·.·. I I' ' ·' J I:.'N
r·1\'-·,.
ljl1 a·''•.,.
. ' " ---·--·

cg_·~

300

\••
350

rj>(degree)

Fig.3 Effective dose distribution on the SRC roof. The
position on the roof is given by the polar coordinates
R and <j>. The origin is just above the machine centerof the SRC. At the extraction point, the beam
direction is the 150-degrees direction.

We assumed that effective dose originated from aheavy-ion beam was proportional to the ion mass and thesquare of the ion energy per nucleon. To verify this simple
scaling law, we made dose calculations with neutron
production data by 400-MeV/nucleon 12C, 56pe ,and a 180-

5 Shielding of Big-RIPS
The Big-RIPS needs very thick shield because a 1-p~J.A
primary beam stops at the target and the analysing magnet.
It is necessary to contain the Big-RIPS in tunnel-like local~350~

The 12th Symposium on Accelerator Science and Technology, Wako, Japan 1999

shield. Local shield is usually placed close to a radiation
source. This implies that fast neutrons emitted from thesource inject into shielding material with a large injection
angle, especially in the forward direction. Note that theinjection angle (a) defined here is an angle from the normalof a shielding wall. Assuming that a path of neutrons acrossthe shield is straight, the shielding thickness increases
effectively by a factor of 1/cosa. It holds for neutrons with asmall injection angle. On the contrary, the effective
thickness of shield cannot be determined by the simple
geometric consideration for neutrons with a large injection
angle, because injected neutrons scatter many times in theshield and diffuse in direction. Hence, we calculated thedose attenuation of slantwise-injected neutrons using theHETC-3step code [8]. The dose attenuation is slower than
the 1/cosa correction for a> 30 degrees as shown in Fig. 4.

loss in the Big-RIPS. We show results- in Fig. 6, in which
the dose limit is 25 11Sv/h at the outer surface of the room.
In the present design, the thick iron shield near the second
dipole magnet and two sets of triplet Q-magnets (TQl,
TQ2) work as a neutron collimator of 400 mm-<j>. In thiscase, thin iron shield is sufficient below the second dipole
magnet.
10°~--------------------~

90 d grees- 0 deg. injection........ 15deg. injection-+- .. 30deg. injection-.o.·-- 45deg. injection- ·.,.-- 60deg. injection-o- · 75deg. injection

1 o" . - - - - - - - - - - - - - - - - - - ,0 deg. A.=23.9cm
15deg. A.=23.1cm
30deg. A.=21.3cm' 'i'•.
45deg. A.=18.5cm"-. ·,,..· .. ::_:..
60deg. A.=16.7cm' 'c.'·,.··~--..
75deg. A.= 15.9cm,o1 o·3 l.J__,__.__._-L:-......._..___.-f:::::::::::==::::i:;==:::=~
80
°40
040
80
angle( degree)
0~- ----~~~f~:'l·<":::·· ..
't ; '· .·. .:.:·
L

Referenceneutron.-------.
- 0 deg. injection····•··· 15 deg. injection
30 deg. injec1ion-.o.· .. 45 deg. injection- . .,. · · 60 deg. injection-o- · 75 deg. in;ection
00 0 . . oOFig.5 Angular differential effective-dose albedo function.

'...

,

• '.

.

''-...

1 o'' Ll=======t......L. .... . . . . .L..... . . . . .L..... . . . . .L.....::....J
020
40
60
80
100120140160thickness of iron L(cm)Fig.4 Dose attenuation of slantwise-injected neutrons.
We also calculated effects of back-scattered neutrons
from a shielding wall. The back-scattered neutrons are mainradiation in the downstream of the second bending magnetof the Big-RIPS, because the direct neutrons from thesource are missing in this region. Results are summarised inFig. 5 where the angular differential albedo function isgiven as a function of the injection angle of neutrons.
Using these results, we made shielding design of theBig-RIPS. The assumed beam loss is 20 % at the target,
100 % at the first bending magnet and 1.6 % at the first
focusing point (Fl) where selection of RI beams areperformed. The present assumption is a simplified model ofthe actual complicated situation. Further investigations arenecessary which include realistic simulation of the beam

[1] Y. Yano et al., "RIKEN RI Beam Factory Project",
Proc. of 1997 Part!. Accel. Conf., in press.
[2] T. Kurosawa et al., "Measurements of Secondary
Neutrons Produced from Thick Targets bombarded by
High-energy Ne Ions", J. Nucl. Sci. Techno!., 36,
1(1999).
[3] T. Kurosawa et al., "Measurements of Secondary
Neutrons Produced from Thick Targets bombarded by
High-energy He and C Ions", Nucl. Sci. Eng., 132,
30(1999). Fe data are also from T. Kurosawa, privatecommunication.
[4] W. W. Engle, Jr., "A User's Manual for ANISN, A One
Dimensional Discrete Ordinates Transport Code with
Anisotropic Scattering", K-1963, Oak Ridge GaseousDiffusion Plant, Oak Ridge (1967).
[5] H. Kotegawa eta!., JAERI-M 93-020 (1993).
[6] Two 0-degree data are from Y. l(uwamoto, privatecommunication.
[7] Other data are from S. Ito eta!., private communication.
[8] P. Cloth et al.,"HERMES, A Monte Carlo Program
System for Beam-Materials Interaction Studies", JOI2203, Kernforshungsanlage, JOiich (I 988).
Fig.6 Plane figure of theradiation shield for theBig-RIPS. We assume
that albedo neutrons areproduced at the "albedopoint". The "albedosurface" determines theinjection and scattering
angles of neutrons.

-351-