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RIKEN Accel. Próg. Rep. 24 (1990)

IM-5-23. A Test for SMART Neutron Detectors

H. Orihara, K. Hatanaka, T. Ichihara, M. Ishihara, S. Kato, H. Ohnuma, M. Ohura,

H. Okamura, H. Sakai, 'H. Shimizu, Y. Tajima, H. Toyokawa,

Y. Yano, Y. Yashiro, H.Y. Yoshida, and M. Yosoi

The SMART system,” with its beam swinger magnets, alJows neutron angular distribution mea-surements at the maximum flight path of 22 m. A test neutron time-of-flight (TOF) measurement was carried out during a SMART diagnostic run in July-August, 1990, using a 140 MeV deuteron beam and a 1 mm thick Al target. A cylindrical NE213 liquid scintillator detector, 20 cm in diameter and 5 cm in thickness, was placed at 8.6 m from the target. Stop signals were taken from the RF of the injector AVF cyclotron.

Figures l(a) and (b) show a raw TOF spectrum

RUN1013 d —» 27A1    140.00MeV 20.0deq. 20-AUG-90 16:16:08

Fig. 1. Time-of-flight spectra (a) without and (b) with the neutron gate. The fuli rangę corresponds to 80 ns. A sharp peak is due to gamma flash. The energy of the center of the broad peak is about 70 MeV, indicating this peak is due to breakup neutrons.

and a TOF spectrum gated by neutron events, respectively. Neutron-gamma discrimination was madę with a pulse-shape discriminator. The raw spectrum shows a sharp peak due to gamma flash, and a broad neutron peak due to deuteron breakup.

Pulse-height spectra corresponding to various slices of flight times ard shown in Fig. 2. One can identify a plateau extending to the heighest puse-height region due to the H(n,p) events, a bump due to the ¹²C(n,p) events, and a steep rise toward the Iow pulse-height region due to the ¹²C(n,a) and ^I2C(n,n')3a events.

The threshold for the neutron detection was set at about 35 MeV during the test run. The dynamie rangę was limited by the natural burst of the beam, which was 12.5 MHz. A beam chopper is necessary to obtain a wider dynamie rangę and a higher efficiency with the maximum flight path of 22 m.