Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 47 (2014)

Identification of every target mounted on a rotating wheel
and its application
D. Kaji,∗1 K. Morimoto,∗1 and K. Tanaka∗1,∗2
Several pieces of sector-shaped targets mounted ona rotating wheel have been employed for superheavy
element (SHE) production experiments with highintensity beams. Thus far, it had not been possible todetermine the thickness diﬀerence between each target
without which, we adopted the average thickness of all
the peaces. To distinguish it, we have developed a newwheel frame with an extra ID-tag placed between thespoke-position-indicator tags on the circumference of
the wheel (Fig. 1).
(A)

ID-tag (B)hole

eration of the signal [A] with [D], which is an inverted
signal of [B]. This pulse is delivered to the accelerator
in order to chop the beam.
As a typical example, a two-dimensional plot (Fig.
3) of the event rate is monitored over a long irradiation
period (abscissa) for a rapid rotation timing (ordinate).
Event rates for targets #11, 12, and 14 become relatively higher than those for other targets caused bypin-holes on the target foils as shown in Fig 1(B,C,D).
Thus, this plot is useful in identifying the condition ofevery target foil. Moreover, it enables additional beam
chopping for masking the broken target, as shown inFig. 3. The masking signal can be easily obtained witha logical ’OR’ operation of the inverted signal [E] witha certain delayed signal of [C].

Loss ~ 50% ?
(C)

hole

Loss ~ 30%(D)holehole

Loss ~ 30%Fig. 1. (A) New wheel frame with an ID-tag. (B,C,D) Observed pin-holes on irradiated targets #11, 12, and 14,
respectively.

∗1∗2RIKEN Nishina Center
Faculty of Science and Technology, Science of Tokyo University- 215 -Fig. 2. Block diagram for ID of every target-frames.

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Target sector number

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Rotation time [s] A circuit block diagram for identifying each target
frame is shown in Fig. 2. To avoid unnecessary beamirradiation of the spokes, timing signals of each tag detected by a photo-diode sensor are used. In the caseof a rotational speed of 2000 rpm, the timing signals
from the spoke tags are periodically generated for every 1.875 ms, whereas an additional signal from theID-tag is generated for every 30 ms in one rotation.
A signal timing chart [A], shown in Fig. 2, indicatesthat an original signal is generated from the photo sensor. The chart [B] is modiﬁed from the signal [A] bychanging its delay and width. The chart [C] is obtained by a logical ’AND’ operation of the signal [A]with [B], resulting in a useful timing for one rotation of
the wheel. This pulse is delivered to a reset scalar andthe scaler measure the timing in every rotation. This
angle-timing information is recorded together with thereaction-event data measured at the focal-plane detector for each separate event. The chart [E] indicates thetiming of the spokes with elimination of the timing ofthe ID-tag. The [E] is obtained by a logical ’AND’ op-Irradiation time [hour] Fig. 3. A target-condition monitoring chart using event
timing. Sudden changes in event density at A, B, C,and D indicate the broken parts of the target sector#12, 14,11, and 14, respectively.