RIKEN Accel. Prog. Rep. 50 (2017)

Ⅱ-9. Instrumentation

Radiation evaluation for RILAC irradiation room
K. Tanaka,䠆1 A. Akasiho,䠆1 H. Sakamoto,䠆1 H. Mukai,䠆1 R. Suzuki,䠆1 H. Haba,䠆1 K. Morimoto,䠆1 S. Yanou,䠆1 D. Kaji,䠆1and Y. Uwamino䠆1The radiation doses at and around the irradiation room at
RILAC facility were measured and evaluated. The
permitted maximum intensity is 10 particle PA at 7.0
MeV/nucleon. The maximum energy in the room is 7.5
MeV/nucleon at which the permitted intensity reduced to 5
particle PA. Monte-Carlo simulations, such as PHITS1), areoften applied for radiation evaluations. However, theiraccuracy would not be good at these energies in general.
Therefore, we measured the neutron dose rates using an 18O
beam at 6.8 MeV/nucleon. The 18O beam can provide ahigher neutron dose than other beam nuclides in this room.
Three types of measurements were performed. Firstly,
neutron dose rates near the radiation sources were measured
using several target materials. Secondly, the neutron dose
rates inside and outside the radiation shield wall of theirradiation room were measured. Thirdly, the high-energy
neutron flux was measured using bismuth samples.
The neutron dose from thick targets of aluminum, carbon,copper, and tantalum were measured using a neutron survey
meter at GARIS-II. Table 1 lists the preliminary result ofmeasured and calculated dose at a 90 degree direction ofbeam axis and a beam intensity of 5 particle PA. A
TPC-451C neutron survey meter (HITACHI Co Ltd.) waslocated on the top of the target chamber. Its distance fromthe beam axis was 31 cm. The width and height of thetargets were 25 mm and 25 mm commonly, and thethicknesses are listed in Table 1. Another neutron survey
meter is located in the beam direction immediately after theGARIS-II D1 magnet. The beam stopped in the thick targets
and then only the neutrons from the targets irradiated thesurvey meter. Because the neutron scattering at the magnet
affects the dose measurement, the analysis of beam
direction is ongoing.

beam irradiated the tantalum beam dump of GARIS andGARIS-II individually. Figure 1 and 2 show measured dose
results on the top view of the experimental room. Themaximum doses on the roof and basement are also shown.
The neutron dose outside the shield wall was less than about
1/1000 of inside dose.
The evaluation for bismuth samples is ongoing.

Fig. 1. Measured result for neutron dose rate from theGARIS beam dump. The red values show the dose rates atthe beam level of GARIS which was at the first floor. The
blue value indicates the maximum measured dose on theroof and the black value indicates that on the first basementlevel.

Table 1. Measured neutron dose rates and comparison withvalues calculated using by PHITS code
PHITS
measuredTarget andratio
resultdosethickness
PHITS/measurement(mSv/h)(mSv/h)C 150Pm

3300

6100

1.8

Al 200Pm

3100

5500

1.8

Cu 50Pm

2500

4400

1.8

Ta 100 Pm

1600

1900

1.2Fig. 2. Measured results for neutron dose rate from theGARISII beam dump.The legendisthe same as for Fig. 1.

The distribution of neutron dose rates in and around theshield wall of the irradiation room were measured. The 18O
䠆1Reference1) T. Sato et al., J. Nucl. Sci. Technol. 50, 913 (2013).

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