The 13th Symposium on Accelerator Science and Technology, Suita, Osaka, Japan, October 2001

Shielding Design for Radiation Safety for the Super SOR Project
Tak:eshi IIMOTO, Toshiso KOSAKO, and Nobuyuki SUGIURA
Research Center for Nuclear Science and Technology
The University of Tokyo
2-11-16 Yayoi Bunkyo-ku, Tokyo 113-0032, JapanAbstract
A concept for the construction of a shielding design for ahigh-energy accelerator is discussed, taking into
consideration of the dose estimation on the Super SOR
project at the University of Tokyo. The Super SOR supplies athird generation VUV and a soft X-ray synchrotron lightsource (1.6GeV). In order to calculate the annual effective
dose around the facility, the Swanson-Braeuer, Jenkins, andStevenson-Thomas formulas were used for simple
prospective estimations. Both the direct radiation from thestorage ring beam and the skyshine dose are considered. The
newest shielding design can accomplish the target dose of
0.05 msvy- 1for the public. In addition, because the dose issignificant, special care should be taken when constructing
tall buildings near the storage ring.

and (2) an annual effective dose due to direct radiation andskyshine around the facility boundary. This paper presents
the newest information based on the Super SOR design inFebruary 2000 for the following: LSR operation mode, beamparameters, calculation formula used for the dose estimation,safety margins, and a shielding design.
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rllit.•-1. INTRODUCTION

niiill'i
The "Super SOR" project, which supplies athird-generation VUV and soft X-ray synchrotron lightsource, is planned for construction on the Kashiwa Campusof the University of Tokyo in Japan. The main facilities of theproject are a 1.6 GeV Linear Accelerator (LINAC) and a 1.6GeV Light Source Ring (LSR). The layout of the facility isshown in Figures 1-1 and 1-2.

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Fig. 1-2 Super SOR Layout

LINAC: 1.6 GeV Linear Accelerator
LSR: 1.6 GeV Light Source Ring (storage ring)

A-C: Dose-estimated positions

0.-.

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e00&,.._._e e. e e • s e e e e e e e e e

8e e e e<11&e e e • e e.

c11.a=i-L-!

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Fig. 2 Super SOR Cross-section
2. OPERATION MODE AND
CALCULATION CONDITIONS

The length of the LINAC is about 1OOm, and this facility islocated underground. The circuit length of the LSR, which isin the shape of a racetrack, is about 230m and is located atground level. Estimates of the likely radiation andradioactivity levels are needed at the design stage of theaccelerator for radiation safety, machine layout, and cost.
This study presents (1) a concept for a shielding design

The plan for the annual operation pattern of the LSR isshown in Table 1.
Several beam parameters are necessary for dose
calculation formulas when providing for safe estimates. The
sources for the shape of the lines of the LSR are converted
into a 27 ~point representation. There are two points forstraight positions, 24 points for bending-magnet positions,and one point for a beam-incidence position from LINAC.

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The 13th Symposium on Accelerator Science and Technology, Suita, Osaka, Japan, October 2001

Beam-loss ratios at the point sources, which are extremely
difficult to calculate in advance, have been determined with alarge safety margin and are shown in Tables 2-1 and 2-2.
Table 1 Annual LSR operation mode
Operation mode
Multi Bunch (storage)
Multi Bunch (incidence)
Single Bunch (storage)
Single Bunch (incidence)
Setup
Burning
Machine Study
Incidence Machine Study
Incidence Machine Setup
StandbyOperationtime[hrs/y]4,000
32050080150
200400200
10050

Current
[rnA]
400
400
101010Incidence
frequency[times]3 /day3 /day5/day
5/day
20 /6hrs

For an annual dose of the side fraction in the beam-line
direction, the Jenkins formula [5] was selected:

Estimated ratio

Multi Bunch (storage)
Multi Bunch (incidence)
Single Bunch (storage)
Single Bunch (incidence)
Setup
Burning
Machine Study

100% beam loss
30% incidence ratio
100% beam loss
30% incidence ratio
10% incidence ratio
Two times the multi bunch mode
Two times the multi bunch modee

H: annual dose [Svy- 1]
P: power equivalent to beam loss [W]r: distance [m]S: source [Svh- 1m 2kW- 1]
d: bulk shield thickness [em]A i: attenuation distance [em]E : duty factor [-]Xo: radiation length [em]J: beam-loss rate [electron s" 1]
Ee: electron energy [GeV]
X(Ee): maximum range of 11 particle at energy ofEe [em]e: angle toward beam-line direction [degree]1> : shield angle [degree]
f: source correction factor[-]Table 2-2 Beam-loss ratio at LSR for positions
ModeSetup
Incidence
Storagephoton; H = 3.6X 10- 14 J Eel? E
X [133exp(-d/ A sin cf> )1(1-0.98cos e)!. 2+f, 0.267exp(-d/ A I sin 1> )1(1-0.72cos 2]
neutron; H = 3.6 X 10" 14 J Eel? E
X [f1 exp(-d/ A ,sin cf> )l(l-0.72cos i+
f2 1Oexp(-d/ A 3 sin 1> )1(1-0. 75cos e)]+3.79 Z073 exp(-d/ A 2 sin cf> )] X2e)Table 2-1 Beam-loss ratio at LSR for operation mode
Operation modephoton; H = (Plr 2) X S exp(-d/ A i)
neutron; H = (Pir 2) X S exp(-d/ Ai) X 2.0 X E
11 particle; H = 251(25+X/Xo) X (X(Ee)-X)/X(Ee) X Ho(X(Ee)>X)
H = 0.0 (X(Ee)~X) H 0 = 8.0 X 10"15 J Eel?.

Estimated beam-loss ratio [%]90-degree Incidence Bending
Straight-magnet
bending
point
point
area
point
9x2
1x2
4040
24x2
1x20501x2098In the (b) calculation, the equation of Stevenson -Thomas[7-9] was applied:

3. FORMULAS
A large number of formulas that have been used tocalculate the dose rates that occur in the vicinity ofhigh-energy accelerators have been developed since the early
1960s. Deciding which formulas to use depends on the stageof the design and the purpose of the calculation. The designfor the current facility is still in a comparatively early stage
and is consequently not yet fixed. Therefore, the main
purpose of these calculations is to develop a rough estimateof the dosages with the newest designs. Therefore, thefollowing formulas were selected because of their reliability
for determining values and because they are based on easyarithmetical operations that require a small number ofparameters. Two kinds of doses, namely (a) direct and (b)skyshine, must be considered when calculating doses aroundthe boundaries of a facility. In the (a) calculation, there are
two categories: forward or side fraction in the beam-line
direction.
For an annual dose of the forward fraction in the beam-line
direction, the Swanson-Braeuer formula [1,2] was selected,
as follows:

H = 3.0 x 10·15 exp(-r/A) I ?x S x 3600
H: skysine dose (Svh- 1)
A: attenuation length in air of high-energy neutrons (m)r: distance from a source to a specific
S: total neutron source intensity on the surface ofthe building's ceiling (ns- 1)
The estimation procedure for the source neutron intensity
on the ceiling is as follows:

CD Bulk shielding estimation on the ceiling by the Jenkins
formula [5].
®Neutron flux estimation based on the obtained dose byassuming the liE spectrum.
@Total neutron intensity, S, estimation by multiplying thetotal ceiling surface.
@) Skyshine estimation by Stevenson-Thomas formula [7-9]to each point source.
@ Total skyshine estimation by summing up each dosecomponent from each source point.

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The 13th Symposium on Accelerator Science and Technology, Suita, Osaka, Japan, October 2001

1bis method provides a conservative estimate of the dose
because the assumption for 1/E allows for a wide safetymargin, and the Stevenson-Thomas formula overestimates
the distance by about 1OOm.
4. SAFETY MARGIN FOR THE DOSE LIMIT
For an annual estimate of the dose during the design stageof the facility, larger safety margins should be built into theplan. A new law in Japan that is based on a recommendationfrom ICRP Publication 60 prescribes that the public dose
limit in the vicinity of a facility boundary is 1 msvy- 1• We
established a target annual dose of 0.05 mSv, which wasbased on safety designs for radiation used for power plants inJapan. The limit we established is 1120 of the limit due to theJapanese regulation. The shielding design of the LSR for thisproject has been established to meet the target dose, which
includes both direct radiation and the skyshine.

5. RESULTS AND DISCUSSION
Table 3 shows the determined shielding design.
Table 3 LSR or Super SOR Shielding Design
Positionon the beam direction of the storage ring. At the forward
position of the beam direction, the dose would be higher than
it would at the side position based on the formulas in section

3.
The south boundary is far from the storage ring. Therefore,
if the northeast (A) and northwest (B) boundaries canaccomplish the target dose for public, the south could do sotoo. However, there is a plan to construct a five-floor
building around position C, as shown in Figure 1. In this case,people working and studying on the higher floors, forexample four and five, would be exposed to a higher dose ofradiation directly from the storage ring because they would
be directly over the ring beam separated by a comparatively
thin concrete ceiling. Position C is absolutely inside theboundary. Therefore, there is no need for it to be below thetarget dose for the public. According to Japanese regulations,the dose limit at position C is considered to be 1.3 mSv per
3M for the boundary limit of the controlled area. However, it
is important to roughly estimate the annual dose around such
positions because they will become special points withcomparatively high doses. As a result, the estimated annual
dose at position C around the ring-side glass window at thefifth floor is 0.127 msvy- 1• The direct radiation dose is 0.101
msvy· 1, and the skyshine dose is 0.026 mSvy" 1•

Material and Thickness

6. CONCLUSION

Sidewall of storage ring
50 cmofOC
Forward wall to beam line
70 em of OC + 20 em ofleadCeiling of storage ring
50cmofOC
Building wall ofLSR
50cmofOC
OC: Ordinary Concrete
In the presented calculation, the values shown in Table 3
are used. However, additional shielding material might beneeded in the area of the ceiling that is over the beam's
incidence position from the LINAC. In addition, thethickness of the sidewall of the storage ring depends on how
the experimental hall beside the LSR beam is used. If the area
immediately adjacent to the LSR wall will be frequently used
for experiments, additional shielding material will benecessary. Table 4 shows the annual dose at the boundaries ofthe facility. The estimated positions are indicated asinFigure 1-2.

The concept for the construction of a shielding design for ahigh-energy accelerator was discussed using estimates. ofdose rates on the Super SOR project at the University ofTokyo. In order to calculate dose rates around the facility,several formulas, including the Swanson-Braeuer, Jenkins,
and Stevenson-Thomas, were used for simple prospective
estimations. In order to calculate the annual dose around thefacility boundary, direct radiation from the storage ring beamand skyshine were considered. The newest shielding design
can meet the target dose for the public, which is 1/20 of thatindicated by Japanese regulations. In addition, because thedose is significant, special care should be taken whenconstructing tall buildings near the storage ring.

*Table 4 Annual dose values at boundaries
Position name of Position Annual dose
Target doseboundaryID[mSvy- 1]
msvy- 1]
NortheastA
0.026
0.050
Northwest
B
0.012
0.050
SouthC
0.127
For the estimated point of A, the direct radiation dose is0.009 msvy· 1, and the skysine dose is 0.017 msvy- 1• For theestimated point ofB, the direct radiation dose is 0.000 msvy- 1,
and the skysine dose is 0.012 msvy- 1• These positions
represent the public dose at the boundaries of the facility.
They are the nearest to the facility and would make thehighest annual dose. The direct radiation dose of position A
is much higher than that of position B. This depends strongly

7. REFERENCES[1] W. P. Swanson, Technical Report Series No.188, IAEA
(1979).
[2] E. Braeuer, ESRF/SHIELD/88-04 Oct.(1988).
[3] M. Sakano et al., Radiat. Protec. Dosim., 25, 107(1988).
[4] B. J. Moyer, in Proc. 1st Int. Conf. Shielding around HighEnergy Accelerators, Presses Universitaires de France,Paris (1962).
[5] T. M. Jenkins, Nucl. lnstrum. Meth., 159, 265(1979).
[6] H. Dinter et al., Nucl. Instrum. Meth., A276, 1(1989).
[7] R. H. Thomas et al., NIRL/M/30, Rutherford Laboratory,Cambridge University (1962).
[8] R. H. Thomas, in Engineering Compendium on Radiation
Shielding, 1, 56, Splinger-Verlag, Berlin (1968).
[9] G. R. Stevenson et al., Health Physics, 46, 1158(1985).

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