Takashi Mikumo

A 160 cm Synchro- and Variable Energy Ordinary Cyclotron

A 160 cm cyclotron have been constructed as the first accelerator of the Institute for Nuclear Study, University of Tokyo. This cyclotron can be used as a variable energy ordinary cyclotron as well as a synchro-cyclotron by changing the dee-system and the oscillator system. As an ordinary cyclotron it can produce protons of any desired energy between 7.5 and 15 MeV, deuterons between 15 and 21 MeV, and α particles between 30 and 42 Mev. These beams are now being used for various experiments on nuclear reactions and for production of radioisotopes. As a synchro-cyclotron, it can produce protons of 57 MeV in energy and the beam is extracted with high efficiency at a radius near n =1 with an electrostatic deflector.

Angular Distributions of Protons from the Reaction 12C(α, p)15N

Angular distributions of protons corresponding to the ground state transition from the reaction 12 C(α, p ) 15 N have been measured at twelve energies of alpha particles between 25 and 39 MeV. Each angular distribution shows pronounced diffraction-like patterns, but there exists apparently a systematic shift in the shape and magnitude of angular distributions as the energy changes. At lower energies a sharp rise in the backward angles is observed, while at higher energies it is not observed. Angular distributions of protons corresponding to some excited state transitions have also been measured at 34.6 MeV.

Anomalies in the Scattering of Alpha Particles by Carbon

Angular distributions of elastic and inelastic scattering ( Q =-4.43 MeV) of alpha particles by the carbon nucleus have been measured at eight different alpha particle energies between 27.0 and 35.5 MeV. These data are discussed together with those reported previously in this journal and with those of other authors. Angular distributions for both elastic and inelastic alphas show remarkable variation with bombarding energy and cannot be explained with simple direct interaction theories. There appear anomalies in the angular distributions for E α in the neighbourhood of 30 MeV. Also in the excitation energy near 30 MeV in the compound system, some resonances were found in the elastic excitation function and in the integrated cross section for the inelastic scattering ( Q =-4.43 MeV). Even at such high excitation energies the effect of the compound system seems to be important.

Reactions of Iron-54 with Alpha-Particles

Excitation functions for the (α, p ), (α, n ), (α, p n ), (α, 2 n ), (α, p 2 n +α, 3 n ), (α, α n ), (α, α p n ) and (α, α2 n ) reactions on Fe 54 were measured by the activation method using a “stacked-foil” technique, the alpha-particle energies ranging from 10 MeV to 40 MeV. The predominance of proton emission over neutron emission has been observed. The ratios of σ(α, p )/σ(α, n ) and σ(α, p n )/σ(α, 2 n ) in the region of maximum yield were found to be 3.4 and 60, respectively. The ratio of σ(α, α p n )/σ(α, α2 n ) at 40 MeV was about 180. A small “knee” was observed at the incident alpha-particle energy of about 20 MeV in the excitation function for the (α, 2 n ) reaction. The total reaction cross section was found to agree with the value calculated from continuum theory for a nuclear radius constant r 0 of 1.7×10 -13 cm assuming a nuclear square well potential.

Excitation Functions for Alpha-Induced Reactions on Manganese-55

Excitation functions for the reactions Mn/ sup55/( alpha ,n)Co/sup 58/, 5/( alpha ,n)Mn/sup 55/ and hod using a stacked-foil technique, the alpha- particle energies rangnng from 10 to 40 Mev. Bombardments were made with the alpha-particle beam of 32 and 40 Mev from the 160 cm INSJ cyclotron. The beam was collected in a Faraday cup and measured by a current integrator. After bombardments, manganese, cobalt, and iron were chemically separated. The disintegration rates of product nuclei Co/sup 58/, Co/sup 57/, Co/sup 56/, and Mn/ sup 54/ were obtained by the gamma-ray scintillation spectrometry, while that of Mn/sup 56/ by a calibrated end-window type Geiger counter. The reaction cross section was found to agree with calculated value for a nuclear radius constant r/ sub 0/ of 1.7 x 10/sup -13/ cm. Competition between different reactions was analyzed in terms of the statistical model of nuclear reaction by use of a level density expression of mu = c expSTA2(aE)/sup 1/2!, and agreed with the calculated values for a = 2 Mev/sup -1/. (auth)

Reactions of Argon-40 with Alpha-Particles

Excitation functions for the (α, p ), (α, n ), (α, p n ), (α, 2 n ), (α, p 2 n +α, 3 n ), (α, α n ), (α, α p n ) and (α, α2 n ) reactions on Fe 54 were measured by the activation method using a “stacked-foil” technique, the alpha-particle energies ranging from 10 MeV to 40 MeV. The predominance of proton emission over neutron emission has been observed. The ratios of σ(α, p )/σ(α, n ) and σ(α, p n )/σ(α, 2 n ) in the region of maximum yield were found to be 3.4 and 60, respectively. The ratio of σ(α, α p n )/σ(α, α2 n ) at 40 MeV was about 180. A small “knee” was observed at the incident alpha-particle energy of about 20 MeV in the excitation function for the (α, 2 n ) reaction. The total reaction cross section was found to agree with the value calculated from continuum theory for a nuclear radius constant r 0 of 1.7×10 -13 cm assuming a nuclear square well potential.

An Experimental Survey of Nuclear Reactions Induced by 57 MeV Protons Part II (p, d) Reactions

With 57 MeV incident protons, energy spectra of deuterons from the ( p , d ) reactions on C 12 , Al 27 , Ni 58 , Ag, Sn, Au 197 and Bi 209 have been measured by a scintillation counter telescope. Several prominent peaks were observed on C 12 , Al 27 and Ni 58 while very few on Ag, Sn, Au 197 and Bi 209 . The energy resolution was about 2.5% at half maximum. Angular distributions were obtained for the prominent peaks and were analyzed in terms of j l ( q r ) 2 and of Butler curves. The peaks are considered to correspond to removal of neutron leaving a hole in a single particle state occupied in the target nucleus. In some cases, however, residual interactions may be taken into account. No clear peak was observed in the region of Q value less than about -25 MeV.

Single- and Multi-Nucleon Transfer Reactions Induced by 14N and 12C on fp-Shell Nuclei

Transfer reactions on 52 Cr, 53 Cr, 50 Ti and 54 Fe nuclei induced by 14 N and 12 C projectiles were studied at energies of 60, 70 and 90 MeV, about two to three times higher than the Coulomb barrier. It is seen from this experiment that energy spectra of emitted particles consist of two parts: the one corrresponding to selectivepeaks at low excitation energies and the other a broad bump at higher excitationregion. In sigle nucleon transfer, several peaks were observed in the energy spectrum and the yield of the bump was small, whereas the cross sections of selectivepeaks were very small and the broad bumps were prominently observed in multi-nucleon transfer. In the case of selective peaks on single proton stripping the differential cross sections could be analyzed by DWBA method including recoilcorrection.

An Experimeotal Survey of Nuclear Reactions Induced by 57 MeV Proton, Part I

Several targets, covering a wide range of mass number, were bombarded with the 57 MeV proton beam from the INS (Tokyo) synchro-cycrotron. Energy spectra of emitted charged particles and their angular dependence were measured. In this article (Part I), the experimental method and the results concerning emitted protons are presented. The observed proton spectra were structureless compared with those for deuterons which will be reported in Part II. However, the continuum proton spectra do have a pronounced angular dependence, which may be explained by the mechanism of direct collision of neucleons inside the nucleus and/or at the diffused rim of the nucleus. Excitation energies were determined for the few spectral peaks which were strongly excited at forward scattering angles. These peaks may be concerned with some collective excitations.

The Reaction 15N(p, α)12C in the Energy Range of Protons from 6.70 to 15.16 MeV

Studies on excitation functions and angular distributions of alpha-particles emitted by the reaction 15 N( p , α) 12 C have been performed in the energy range of protons from 6.70 to 15.16 MeV. Excitation functions at 60°, 90°, 120° and 150° were measured in steps of 100 keV. Angular distributions of alpha-particles associated with the ground and the first excited states of 12 C were also measured in steps of 400 keV (200 keV when necessary). Many sharp or broad peaks were found in the excitation curves. The shapes of the angular distributions depend sensitively on the incident proton energy. Analysis of these results according to the cross section fluctuation theory by Fricson shows that the proportion of direct reaction is large for this reaction.