Ⅳ. OPERATION RECORDS

RIKEN Accel. Prog. Rep. 47 (2014)

Radiation monitoring in the RIBF using ionization chambers
M. Nakamura,*1 K. Yamada,*1 A. Uchiyama,*1 H. Okuno,*1 and M. Kase*1
In recent years, we attempted to monitor radiation due tobeam loss at several important components in the RIBF byusing
self-madeionizationchambers(ICs)1)-5).
Furthermore, we input an alarm signal from the IC to theRIBF beam interlock system (BIS)5). The next focus of
this study is the detection of the most suitable alarm level
for acceleration operations. Firstly, we attempted tocalibrate the alarm level by using an IC near theelectrostatic deflection channel (EDC) of SRC3)-5). In SRC
operations, many ions, such as N, O, Ar, Ca, Zn, Xe, and U,
were used. In the present study, we investigated beam-loss
calibration for the N, O, Ca, and U beams. In this report,
we summarize the results and consider the suitable alarmlevels for the BIS.
The experimental conditions of IC measurements havebeen described in the previous papers2),-4). When weattempted the calibrations, 18O8+, 48Ca20+, and 238U86+ wereaccelerated at 345 MeV/nucleon, and only 14N7+ wasaccelerated at 245 MeV/nucleon. The beam currents ofthese ions were less than about 300 enA. In the calibration
tests, firstly, each ion beam current was attenuated to about
1/40 to 1/2 times the current under usual experimental
conditions by using an attenuator. Subsequently, the EDC
was irradiated by these attenuated ion beams for a fairly
short time such that the EDC was never damaged. We
measured the IC signal at this time. As a result, we couldestimate the signal intensity when the beam loss was about
2.5% to 50%, and we could calibrate the IC signal for
determining alarm levels.
㻝㻠㻻㼡㼠㼜㼡㼠㻌㼛㼒㻌㻵㻯㻌㻔㼂㻕㻝㻞㻝㻜㻤㻢㻠㻞㻜㻜㻡㻜㻝㻜㻜㻝㻡㻜㻞㻜㻜㻮㼑㼍㼙㻌㼘㼛㼟㼟㻌㼍㼠㻌㻱㻰㻯㻌㻔㼃㻕

Fig. 1. The correlation between beam power loss and ICintensity.
blue rhombus: 14N7+
pink square: 18O8+
red triangle: 48Ca20+
black circle: 238U86+*1

RIKEN Nishina Center- 310 -The results are shown in Fig. 1. The horizontal axis
shows the beam power lost at the EDC. The vertical axis
shows the output voltage of the IC. The calibration curvesof 14N7+, 18O8+, 48Ca20+, and 238U86+ beams are drawn andcompared with each other in the same figure.
The data of 18O8+ and 48Ca20+ beams showed littledispersion, and most of the data existed near the calibration
curves. In the case of the 238U86+ beam, we could collect
only three data. However, the dispersion of the data waslow, and a favorable calibration curve could be drawn. In
the case of the 14N7+ beam, we collected only four data at
this stage, and the dispersion of the data was significant.
Hence, the 14N7+ beam should be studied further in the nearfuture. Furthermore, among the calibration curves of 14N7+,
18 8+ 48
O , Ca20+, and 238U86+ beams, the sharpest slope wasobserved for the calibration curve of the 18O8+ beam. This
result showed that the intensity of radiation caused by the18 7+
O beam loss is the largest, at least in the presentcalibrations. Conversely, the calibration curve of the238 86+
U beam showed the lowest slope, indicating that theintensity of radiation caused by the 238U86+ beam loss is thesmallest among these ion beams.
We investigated the alarm signal for the BIS using thesedata. In a previous paper4), we reported that problems with48
Ca20+ ion beam in the EDC of SRC frequently occurred
when the IC output had risen to about 4 V. On comparing
the values in the previous paper with the values in Fig. 1,problems occurred in the EDC when the 48Ca20+ beam loss
at the EDC increased beyond about 130 W. The exact
value of this threshold is still under investigation.
Furthermore, the thresholds of the beam loss at whichproblems begin to occur in the EDC have to be studied foreach ion. However, from these estimations, suitable alarmlevels can be determined and input to the BIS.
At present, in addition to the elements estimated in thispaper, Zn, Ar, and Xe ion beams were accelerated in theexperiments using SRC. We plan to investigate the beamloss and alarm levels for these elements in the near future.
References
1) M. Nakamura et al.: RIKEN Accel. Prog. Rep. 42, 141(2009)
2) M. Nakamura et al.: RIKEN Accel. Prog. Rep. 43, 138(2010)
3) M. Nakamura et al.: Proc 7th Annual Meeting ofParticle Accelerator Society of Japan, WEPS135,Himeji, Japan.
4) M. Nakamura et al.: RIKEN Accel. Prog. Rep. 44, 293(2011)
5) M. Nakamura et al.: RIKEN Accel. Prog. Rep. 45, 228(2012)