Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 47 (2014)

Radiation damage of plastic scintillation counter
D. S. Ahn,∗1 N. Fukuda,∗1 T. Kubo,∗1 K. Yoshida,∗1 N. Inabe,∗1 H. Takeda,∗1 D. Kameda,∗1 H. Suzuki,∗1Y. Shimizu,∗1 D. Murai,∗1,∗2 Y. Yanagisawa,∗1 K. Kusaka,∗1 M. Ohtake,∗1 H. Sato,∗1 and Y. Sato∗1The radiation damage was reported with respect tothe absorbed dose. The radiation absorbed dose wascalculated using Eq. 1. A dose of one Gray is equivalent
to a unit of energy [J] deposited in a kilogram of asubstance.
Dose[Gy] =Nbeam · ∆E · Rbeam,volume · density(1)

where Nbeam denotes beam intensity, ∆E is the energy loss of isotopes at the scintillation counter, andRbeam is the ratio of the number of events taking placein an exposed volume to the total number of events
taking place at the scintillation counter. The volumeis defined as 10×6×0.2 mm3 after checking the beam
spot size by the beam profile, and the density of theEJ-212 scintillator2) is 1.023 g/cc.
To define the exposed area, the concentrated irradiation region of the scintillation counter was determinedusing the beam profile shown in Fig. 2. Fig. 2(a) showsa scatter plot of beam profile and (b) and (c) show thex and y distributions of the beam, respectively. The∗1∗2Counts

1510210(b)

2500
2000
1500
1000

10-5-10Counts

0-200

6000-15-10-50-10-50

51015

20

5101520

X position@F3(mm)

(c)

5000
4000
3000

1-15-20-20

3000

500

5

2000
1000

-15-10-505101520

X position@F3(mm)0-20-15Y position@F3(mm)Fig. 2. Beam profile: (a) scatter plot of beam profile and(b), (c) shows x and y distribution of beam, respectively.

black square box in Fig. 2(a) indicates the defined exposed area, which is the concentrated irradiation region with 96.3% isotopes. The energy loss of isotopes
at the scintillation counter was calculated with the ratio of the cocktail beams as 108 Sn:107 In:106 Cd = 2.51%:
74.0%: 22.86%. It is noteworthy that the ratio of isotopes rarely influences the energy loss calculation because the difference of energy loss between isotopes isonly in the range of 2-3%.
Figure 3 shows the results of a relative light output
as a function of the accumulated dose. The relative
light output is defined as the relative peak positionof the light output before and after irradiation. It isclearly seen that the light output decreases with theincrease in the accumulated radiation dose at all thedifferent positions, and a similar decreasing tendency
is found at all the positions. The results indicate thatabout 50% radiation damage of the EJ-212 scintillation
counter occurs at an accumulated dose of 12×103 Gy.
Relative light output

Fig. 1. Experimental setup of the scintillation counter(a)20Y position@F3(mm)We studied radiation damage of a plastic scintillation counter in an isospin diffusion experiment (NP0709-RIBF42-01) using the BigRIPS separator1) of RIKEN RIBF. Heavy-ion cocktail beams(108 Sn,107 In,106 Cd) with high intensity (0.7∼1 MHz)
were produced by projectile fragmentation of a 124 Xebeam at an energy of 345MeV/nucleon.
Figure 1 shows the experimental setup of the scintillation counter at F3 of the BigRIPS separator1). Tochange the position of the scintillation counter after radiation damage, the movable ladder stage was designed
to be remotely operated during the experiment. The
EJ-212 scintillation counter2) was used in an isospin
diffusion experiment with a high-intensity beam, andthe position of the scintillation counter was changed
after 50% damage, which was identified by checking
the relative peak position of the light output.

1

position Aposition B
position C

0.8

0.6

0.4

0.2

00

2.5

5

7.5

10 12.5 15 17.5 20 22.5 25
3Accumulated Dose(x10 Gy)

Fig. 3. Relative light output as a function of the accumulated dose: The different colors indicate different positions on the scintillation counter.

References
1) T. Kubo et al.: Prog. Theor. Exp. Phys. 2012, 03C003
2) http://www.eljentechnology.com/

RIKEN Nishina Center
Department of Physics, Rikkyo University- 168 -