Design of Radiation Shielding for the RIKEN SSC
T.Shikata, S.Fujita, S.Yamaji, H.Kamitsubo
The Institute of Physical and Chemical Research, Wako-shi, SaitamaandT. Kosak.o*
University of Tokyo, Institute for Nuclear Study, Midori-cho, Tanashi,Tokyo
Abstract.-- A diagram usefUl in shield design was shown. Rough estimation ofthe skyshine of neutrons passing through the roof above the sse facility wasalso carried out.
1. Introduction.- The RIKEN SSC will operate protons in the 200 MeV energy range,from deuterons to neon ions up to 135 MeV/A,and heavier ions in lower energy
region. The maximum beam curre£y 2~~tl be lJLA. Spectra of neutrons which will
• Allowed radiation levels for the human
be emitted are given elsewhere
health are also decided in Ref.3.
2. Design of the neutron shielding.
2-1. Ordinary con~rete shielding.- On tg' basis of the calculated results ofAlsmiller et al. and of Roussin et al. , a diagram which gives the neutron
dose as a function of depth in the shield was obtained. It is shown in Fig. 1.
To see if there are any differences between the attenuation characteristic s ofparallel neutron beams incident on a slab and those of neutrons incident on acovering enclosing a point source or not, calculations with the ANISN code werecarried out for the case of a spherical shell at which center a monoenergetic
source was located. The spherical shell has 6 meter radius and 3 meter thickness.
Results are shown in Fig.2. It seems that there is no pronounced difference
between these two cases.
2-2. Iron-concrete shilding.- After Smithl), w3)made a rough dose-geometry
contours for dg,igning iron-concrete beam dump . These contours and calculatedshow that the concrete shielding of 2 meter thickness attenuates
results of Ban
the dose to the same level as the iron shielding of 0.8 meter thickness does
for the given neutron source. Dose attenuation for monoenergetic neutrons in aconcrete beam dump with 3 meter radius, in a double layer beam dump whichconsistsof iron sphere with 0.8 meter radius inside and spherical concrete shell of 1
meter thickness outside, and in a large spherical concrete shell mentioned inparagraph 2-1 were calculated with the ANISN code. Results are shown in Fig.3.
This shows that the concrete beam dump of 3 meter radius and the large sphericalconcrete shell attenuate the neutron dose to nearly the same level at 9 meter.
3. Skyshine.- Figure 4 plots the dose equivalent of skyshine as a ~ction ofdistance. This was obtained by using the method of Alsmiller et al. • In thiscase, some corrections concerning to the effect of the location of a point
source on the dose at a close §~nge were made with the aid of the calculated
results of Nakamura and Kosako .
4. Concluding remarks.- Using Figs.l and 4, the radiation levels at any places
can be estimated easily. Shielding by the concrete wall of 3 meter thickness
around the target area with the typical iron-concrete beam dump (combination of
an iron .sphere of 0.8 meter radius and a concrete spherical shell of thickness
from 1 to 2 meter) proved to be adequate to reduce radiation beneath theallowable level. Assuming the operating time of SSC with fUll power to be 3000
hours per year, the radiation dose at the boundary of the campus can besuppressed to less than 5 mrem/year.

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Fig.l. Dose rate multipliedlo·"

2by r vs depth in concrete
shield.

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Fig.3. Dose equivalentvs depth in several
shields.

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__Fig.4. Neutron dose
rate for skyshine .

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Distance from the source (m)References

1) H.A.Smith, IUCF Internal Rep., No. 74-6 (Radiation Shielding Note 1).
2) J.Drouet and A.Leleux, D. CEN-S/SPR/SRI/78-342 GRA-066JD/AI 5 mai (1978).
3) S.Fujita, S.Yamaji, and T.Shikata, Riken-Hohkoku, 57, 239 (1981) (in Japanese)4) R.G. Alsmiller,Jr., F.R. Mynatt, J.Barish, and W.W~Engle,Jr., Nucl. Instr.
Meth. 72, 213 (1969).
5) R.W.Roussin, R.G.Alsmiller,Jr., and J.Barish, Nucl.Eng.Design 24, 250 (1973).
6) S. Ban, Private communication.
7) R.G. Alsmiller, Jr., J. Barish, and R.L: Childs, ORNL/TM-7512
8) T. Nakamura and T.Kosako, Nucl. Sci. Eng., ll, 168 (1981).

*Present Adress: Reseach Center for Nuclear Sience and Technology,University of Tokyo-64-