SECONDARY NEUTRON AND PHOTON YIELD FROM SEVERAL TENS MEV IONS
Masahiko Fujii, Kazuo Shin, Takashi Nakamura* andYoshitomo UwaminoM<Department of Nuclear Engineering, Kyoto University* Institute for Nuclear Study, University of Tokyo• National Institute of Radiological Science
Introduction
Accelerators of the energy of several
tens MeV are lately widely used for many
purposes. In these accelerators, secondary
neutrons and gamma rays generated from thebeam stoppers are the most important forIn thisthe accelerator shielding problem.
work, energy and angular distributions weresystematically measured of the secondary
neutrons and gamma rays from thick targetsof C, Fe, Cu and Pb bombarded by 30-MeV
protons, 35-MeV deuterons, 65-MeV 3 He particles and 65-MeV alpha particles.
Experiment
The particles accelerated by a SF
cyclotron of Institute for Nuclear Studyof University of Tokyo were injected tothe C, Fe, Cu and Pb targets whose thickness were thicker than the ranges of theincident particles. The generated neutrons and gamma rays from the targets
were measured simultaneously with a 3-in.
dia. by 3-in. thick NE-213 using
the pulse shape discriminationcircuit. The measurements weredone at the angles of 0°, 15°, 30°,45°, 75° and 135° with respect tothe incident beams. The obtained
pulse height distributions for bothneutrons and gamma rays were un-'folded to energy spectrum by theFERDO code with the aid of theresponse functions which were calculated by the Monte Carlo method.

Nt;utron

Ent>rgy

MeVFig. 1 Neutron spectra fromthick Cu target bombarded by
30-MeV protons.

Results for Secondary Neutrons
The spectra of secondary neutrons from Cu target bombarded by
30-MeV protons and 35-MeV deuterons
are shown in Figs. 1 and 2, as exIn the spectra of deuteronamples.
incidence, the broad peak aroundthe energy of 12 MeV rapidly beMeV
Neutron Energy
comes larger with decreasing ofthick Cu
fromspectraNeutron2Fig.
the angle. This can be explainedtarget bombarded by 35-MeV deuterons.
with the splitting reaction of-8 9-the incident deuterons. Contrary tothis, such broad peak can not be seenin the spectra of proton incidence.
Their spectral shape becomes hardermonotonically with decreasing theangle.
In Fig. 3 are shown angulardistributions of secondary neutrons
from Cu target which were obtainedby integrating the energy spectrawith the neutron energy. The angular dependence of neutron flux
shows a tendency to decrease withincreasing angle.
Results for Secondary Gamma Rays
The spectra of secondary gamma
rays from Cu target of 30-MeV proton
incidence are shown in fig. 4, asexample. Contrary to the neutrons,
the spectral shape does not changewith the angle. The angular distribution of secondary photon yield
which was obtained from the energy
spectra is shown in Fig. 5. In~thec.ase of proton_and 3 He incidence,the~distributions
seem neavl~ iso-tropic but haveslight peculiar
peaks at & = 30°
and 135°. Whilein the case of
deuteron andalpha particle
incidence, thedistributions
show forward
peaks.

EmissionFig. 3 Angular distribtuion ofneutron flux for Cu target.

hc~10- 3?:;;:t 10- 3~

w·•o!:-----+---..w...-1,
Photon Energy,

MeV

Fig. 4 Photon spectrafrom thick Cu target
bombarded by 30-MeV
protons.

-9 0-Fig. 5 Angular distribution ofphoton flux for Cu target.