Ⅳ. OPERATION RECORDS

RIKEN Accel. Prog. Rep. 52 (2019)

Radiation safety management at RIBF
K. Tanaka,∗1 Y. Uwamino,∗1 H. Sakamoto,∗1 R. Hirunuma-Higurashi,∗1 H. Mukai,∗2 A. Akashio,∗1T. Okayasu,∗1 R. Suzuki,∗3 M. Takekoshi,∗3 Y. Yamauchi,∗3 K. Igarashi,∗1 S. Iizuka,∗1 N. Usudate,∗1 andY. Shioda∗1
In this paper, the results of radiation monitoringat RIBF, conducted at the border of the facility andthe radiation-controlled area are reported. In addition, the residual doses along the accelerator setups
are presented. In 2018, a 238 U beam of approximately
345 MeV/nucleon was provided at an intensity of 70
particle nA during October to December. A 18 O beamof approximately 230 MeV/nucleon of 700 particle nA
was used in May and June.
The dose rates at the boundary of the radiationcontrolled area were monitored. Neutron and γ-ray
monitors were used at three locations: the roofs of theRRC, IRC, and BigRIPS. Figure 1 shows the annual
neutron dose at these positions. In 2018, even the highest annual dose of 51 µSv/y at the IRC roof was lower
than the legal limit of 5.2 mSv/y.
The dose rates at the site boundary, where the legal
limit is 1 mSv/y, were monitored. Neutron and γ-raymonitors were used, and the annual dose in 2018 was
found to be lower than the detection limit after background correction. The detection limit of the neutron
monitor is 2 µSv/y and that of the γ-ray monitor is
8 µSv/y. Therefore, it was inferred that the annual
dose at the boundary was less than 10 µSv/y, which isconsiderably lower than the legal limit.
The residual radioactivity at the deflectors of thecyclotrons was measured just before the maintenancework. The residual dose depends on factors such as

1000

µSv/y

100

101
2000

2005

2010

2015

year

Fig. 1. Radiation dose at the boundary of radiationcontrolled area.
∗1

∗2
∗3

RIKEN Nishina Center
Japan Environment Research Corporation
Daiwa Atomic Engineering Corporation- 235 -Fig. 2. Dose rates of residual radioactivity at the deflectorsof five cyclotrons.

beam intensity, accelerator operation time, and coolingtime. The dose rates from 1986 are shown in Fig. 2.
The dose rates for FRC, IRC, and SRC are shown foryears after 2006, when the RIBF started its operation.
For AVF, the dose rate increased in 2006 because theradioisotope production was started in that year andthus, the beam intensity increased.
The residual radioactivity along the beam lines wasmeasured after every experiment. Figure 3 shows thelocations of measurement points where high residual
doses were observed. Table 1 lists the dose rates,
beam conditions, and cooling time at the measurement
points. The maximum dose was 17.8 mSv/h at point
19, which is in the vicinity of beam dump of BigRIPS.
The radioactivity in the closed cooling system at BigRIPS was measured. The water for the F0 target,
exit beam dump, and side-wall dump were sampled inJune. The water in the closed cooling systems for theF0 target and exit beam dump was replaced in May
2018. Therefore, the detected radioisotopes in the F0target and exit beam dump were generated during one
month of operation in RIBF. For the side-wall beamdump, part of the water was replaced in January 2018,
but all the water was replaced in March 2015; the results are presented in Table 2. A liquid scintillation
counter (LSC-7400, Hitachi Co. Ltd.) was used forthe low energy β ray of 18 keV from H-3 nuclide. AGe detector (GC2019, Canbbera Co. Ltd.) was also
used for the γ rays emitted from other radionuclides.
The radionuclides, except H-3, were already filteredby an ion exchange resin in the closed cooling systems.

Ⅳ. OPERATION RECORDS

RIKEN Accel. Prog. Rep. 52 (2019)

Although the overall value of contamination was lessthan the legal limit for drain water, as presented inTable 2, the water from the closed cooling system will
be dumped into the drain tank before the next operation to prevent contamination in the room in case of awater leakage.
The e-learning module, which can be accessed anytime from anywhere (even from outside RIKEN), hasbeen used to the re-train the radiation workers atRIBF. Approximately 630 radiation workers have completed the training in 2018.

Table 1. Dose rates measured at beam lines in 2017.
Points 1–24 indicate the locations where measurements
were taken as shown in Fig. 3.

Point

Dose Date
Energy Intensity Coolingrate (M/D) Particle (MeV/u)(pnA) time
(μSv/h)
(h)

12200
400

8/24
8/24Ar-40
Ar-40

5.2
5.2

40
40

573
573

3170

8/24

Ar-40

5.2

40573

4

1000

10/10

N-14

135

357

120

5250

8/24

Ar-40

95

1571

6150

8/24

Ar-40

95

1571

75500

12/17

U-238

50

342

159

81800

12/17

U-238

50

342

159

9700

12/17

U-238

50

342

159

10100

12/20

U-238

345

72

231

119600

12/20

U-238

345

72

231

12140

12/20

U-238

345

72

231

13350

12/20

U-238

345

72

231

14

1600

7/25

Ar-40

160

1983

15400

7/25

Ar-40

160

1983
1133

16200

7/25

O-18

230

600

171430

12/20

U-238

345

72231

183450

12/20

U-238

345

72

231

1917800

12/20

U-238

345

72

231

20

241

12/20

U-238

345

72589

Table 2. Concentrations of radionuclide in the cooling water at BigRIPS, the allowable legal limits for drain water, and the ratios of concentration to the allowablelimit.

Fig. 3. Layout of the beam lines at RIBF. The measurement locations listed in Table 1 are indicated.

- 236 -Cooling Nuclide Concentration[a] Limit[b] Ratio towater(Bq/cm3) limit [a/b](Bq/cm3)
3.4
60
5.8e-2BigRIPS H-3
F0 targetsummation 5.8e-2
BigRIPS H-3
3.860
6.4e-2
exitMn-54
1.3e-31)1
1.3e-3beamsummation 6.4e-2
dump
53.
60
0.89
BigRIPS H-3
8.6e-230
2.9e-3side-wall Be-7
Mn-54
1.2e-31
1.2e-3beam
dump
summation 0.891) read as 1.3× 10-3