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

Skyshine Dose Estimation from Large Storage Ring of Electrons
Toshiso KOSAKO, Takeshi IIMOTO, Nobuyuki SUGIURA and Toshio KAWANISlll
The University of Tokyo
Research Center for Nuclear Science and Technology
Yayoi 2-11-16, Bunkyo-ku, Tokyo 113-0032, JapanAbstract

For high energy and large-scale accelerator, doseestimation of skyshine at the facility boundary is very
important to achieve the dose limit to the public. Hereskyshine dose estimation was done by using calculation toobtain a design concept of the synchrotron facility which
had a linear accelerator and a large scale storage ring of 1-2
Ge V electrons. Through the detailed consideration a basic
ideas are obtained under several operation modes.

1 Introduction

We are promoting the project of Synchrotron Radiation
Facility in Kashiwa New Campus of the University ofTokyo. For the accelerator building construction, shielding
and their radiation dose estimations are requested.
des:Shielding calculations are categorised into two parts: bulk
shielding and skyshine. Here we would like to discuss
about the skyshine dose from this accelerator facility.
There are several accelerator designs. One is a 400 MeV
linear accelerator (LINAC) and a 2 GeV storage ring(SR),another is a 1 Ge V linear accelerator and a 1 GeV storage
ring. These situations may change depending on the final
decision of the plan. Here several discussions are done forthe base of design by performing a typical calculation ofskysine phenomena to these designs.
So we did a setting of typical case as: Phase I , having
400 MeV LINAC [on the ground] and 2 GeV SR [on theground] (see Fig.l), Phase II, having 1 GeV LINAC [in theunderground] and 1 GeV SR [on the ground] (see Fig.2).
0 .:....::

2 Method of Shielding Calculation

For the estimation of skyshine dose, the equation of
Stevenson-Thomas[2,3,4] was applied.
H = 3.0 x 10 15 exp(-r/ A) I r2 x S x 3600
Here,
H: skysine dose (Sv!h)
A :attenuation length in air of high energy neutrons (m)r : distance from a source to a considering point
S : total neutron source intensity on the surface ofbuilding ceiling (n/s)

converter and 3 slits), and 33 at Storage Ring (32 bendingmagnets and one beam injection point).
For Phase II: Source points were set only for the storage
ring because the linear accelerator was set under the groundand caused Jess dose contribution to the skyshine. The 24
point sources distributed on the race track storage ring.
The procedure of source term neutron intensity
estimation on the ceiling is as follows.
<D Bulk shielding estimation on the ceiling by the Jenkins
formula[!].
® Neutron flux estimation based on the obtained dose by
assuming 1/E spectrum.
@ Total neutron intensity, S, estimation by multiplying
total ceiling surface.
® Skyshine estimation by Stevenson-Thomas formula toeach point source.
@ Total skyshine estimation by summing up each dosecomponent from each source points.
This method gives conservative dose estimation because theassumption of 1/E is a safety side discussion and theStevenson-Thomas formula is overestimation within about
100 m distance.

3 Accelerator Operation Mode and Beam Loss

Operation modes are 5 pattern to LINAC and 10 pattern
to Synchrotron Storage Ring. LINAC has an energy of 0.31 GeV to electron or positron and its modes are <Delectron
short pulse ®electron semi-long pulse @electron longpulse @positron short pulse @positron semi-long pulse.
Storage ring has a maximum energy of 2 Ge V and its modes
are <Dmulti bunch operation (accumulation) ®multi bunch(injection) @ single bunch operation
operation(accumulation) ®single bunch operation (injection) @startup adjustment @operation under baking ([)machine study@machine study for injector ®start up adjustment forinjector @)stand by. The beam parameters like beam energy,
peak current, pulse width, duty cycle, duty factor, average
current, beam intensity, beam loss rate and beam loss, weregiven to each parameter and to each region.
Beam loss rate is a very important parameter and wasgiven by an empirically estimated value based onexperiments. The used values are listed in Table 1.1 and 1.2.
It is noted that these values are safe side values to keep theconservative shielding result.

Point neutron source was assumed in the skyshine dose
calculation.
For Phase 1: source points were 4 at LINAC (de+-337-The 12th Symposium on Accelerator Science and Technology, Wako, Japan 1999

4 Dose Estimated Result

4.1 Result of Phase I
The estimated annual dose to each facility were shownin Table 2.1 and 2.2 to LINAC and SR respectively. Byaddi.-.~ skyshine dose and direct dose, we could obtain thetotal dose to each points (see Table 3). The nearness of thesite boundary gives a little higher value. The marking pointis a value at the 5th floor of control building (in Table 3). At
that point a little high value was obtained for the reasons ofreaching a little more direct arrival of radiation (not somuch skyshine).
The targeting dose level is 50 JJ-Sv/y for skysine at thesite boundary. The dose limitation to the public given byICRP (International Commission on RadiologicalProtection) is 1 mSv/y. In this meaning the obtained value
is sufficient.
4.2 Result of Phase II
Next, the phase II situation was estimated. In this case 1Ge V, LINAC locate in the underground. That means noestimation was needed for the environment dose at heboundary.
1 GeV racetrack type storage ring wasconsidered for skyshine source.
The same procedure was used for the skyshine doseestimation as Phase I. Skyshine point sources in the storage
ring are 24.
These skyshine component and directcomponent of neutrons were summing up and the tabulated(see Table 4). These values are smaller than the phase I.
This is because the following reasons: CDenergy is smaller®small size of storage ring gives a large distance to aboundary ®change of the distribution of sources.

Fig.l Disposition ofLINAC and SR (Phase I).. ~--··-~· ----- ... -· ·--------·- ........ ·-· "'•,

! !I '·· . . . . . _ ...
i-- --- .. '1j' !:ti .. -- -- .... - - - :j ::i:i____-----·" l.,,;L. .... - -1,Ir - - :- - -- -,! 1 ·il:\ \\'- ....- .,-.,.......
-:~---.:.·::) IL.

_________

i!

llII

1 , 'I,..,./

6 Conclusion

By using the calculation we could estimate skyshine
neutron dose estimation around high-energy electron
storage ring used for synchrotron orbit radiation. The
detailed discussion of source term was done by introducing
several operation modes and segmentation of radiation
generation points. The obtained typical results of Phase I
and Phase II will be effectively used for the efficientdesigning of this facility.

Fig.2 Disposition of LINAC and SR (Phase II)
Table 1.1 Beam Loss Ratio of Lineae

References[1] T.M. Jenkins, Nucl. Instrum. Meth., 159, 265 (1979).
[2] R.H.Thomas et al., NIRL/M/30, Rutherford Laboratory,Cambridge University (1962).
[3] P Tf. Thomas, in Engineering Compendium on
Radiation Shielding, 1, 56, Splinger-Verlag, Berlin(1968).
[4] G.R.Stevenson et al., Health Physics 46, 115 81985).

input30%

first slit

10%

second & third slits

2%

beam dump

100%

e- I e+ converter

100%line accelerator

1%

Table 1 2 Beam Loss Ratio of Storage Ring
adjustment period

beam input period

storage period-338-

r-.:======-~\1 'incidence area95%

others5%

incidence area95%

others5%

incidence area

80%

others20%

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

Tabe2.1 Annual Dose around LINAC (Phase I)
klystron room (side)madline room (U[l side)siteareabulk shieldthicknessemID
1lineae2slit

3lineae

4

slit

6

lineae6converter

7lineae

8slit

9lineaeoc 250oc 250oc 250oc 250oc 250oc 250oc 250oc 260oc 250point
annual doseshielding
ern
mSv/y

wall side
mSv/y

mSv/y

3m
apatt
mSv/y

oc 200oc 200oc 200oc 200oc 200oc 200oc 200oc 200oc 200

116.5

70.5

33.8

27.2

16.5

7.9

48.8

29.5

14.2

96.6

58.4

28.0

3.6
0.8
2.7
5.3
2.6
Fe 25

6.6

Fe 5

19.7

Fe 20

18.3

Fe 5

19.2

lm

bulk shieldthicknessem

ll[lHI't47.3

28.6

13.7

42.6

25.7

12.3

223.8

135.4

64.9

443.6

268.3

128.6

217.5

13L6

63.1

Tabe2.2 Annual Dose around SR (Phase I)· cidence area
Bearn mannual oparation
periodforwardsidesource
forward shieldingocside shielding

ocPb

Pb

forward distance to sourceside distanse to source
annual dose
multi-banti-mode(input)
multi-banti-mode(store)
single-banti-mode(input)
single-banti-mode (store)
preparation I
preparation 2
machine stugy

4000h
320h
500h
80h
!SOh
200h
400h

estimated site ID and Sv
B-2
B-1
A-2
unit
S3,SO SO S4 S5
S2,S3
S4soso
em
65
65
65
65
em
1540
2015em60
60
6060()
em
0150Ill
10.3, 3.0 16.5, 8.2 13.5, 6.5 7.5,10.3,3.0Ill
3.0
4.8
5.8
9.3 mSv/y
11.1
9.6
17.3
0.771 JLSv/h
0.480
0.386
0.703
10.253 JJ.Svlh
14.17613.18023.8380.034 JJ.Svn1
0.021
0.017
0.031
0.229 JJ.Svlh
0.338
0.294
0.532
2.160 /L Svlh
3.206
2.784
5.036
6.479 fL Svlh
9.618
8.353
15.1073.239 fL Svlh
4.809
4.176
7.553
A-1S2,S3side hulk shieltling_§(Jcm (OC)forwarrl hulk shielding 80cm (OC65+Ph15)
Other than beam incidence area
annual oparalion
estimated site ID and Sv
period
C-3
C-4
unit
C-2
C-1
C-0
m
14.5
10.3
9.8
15.0
forward distance to source
1.5
m
3.0
1.5
3.0
1.5
side distanse to source
mSv/y
0.20 1.75
0.20
1.75
1.74
annual dose
0.024 0.207
0.206
0.024
0.205
1L Svlh
4000h
multi-banti-mode(input)
0.175 1.507
JJ.Svlh
320h
1.508
0.175
1.500
multi-banti-mode(store)
0.001 0.009
0.009
JJ.Sv/h
500h
0.009
0.001
single-banli-mode(input)
0.004 0.034
0.034
0.033/LSv/h
80h
0.004
single-banti-mode (store)/LSv/h
0.037 0.319
0.318
0.037
0.317
!SOh
preparation I
0.111 0.956
0.955
0.111
0.950
JLSvn1200h
preparation 2
0.055 0.478/1 Svlh
0.478
0.055
0.475
400h
machine stugy

Tabe3 Total Dose at the Boundary (Phase I)site 1D12
3

Border direction

NENW
5th floor of control building*Distance(m)635750Annual dose(Jt Sv/y)33.4
38.3
72.5

*directly an·lval dose, not skyshine

Tabe4 Total Dose at the Boundary (PhaseSite ID

Border directio n

Point ANE

Point BNWm

Annual dose ( .U Sv /y)3.8(Dire ct) + 10.2(sky shine)= 14.00.03(Dir ect) + 5 .1(skysh ine) = 5.1-339-