Yoshitomo Uwamino

Measurements of Secondary Neutrons Produced from Thick Targets Bombarded by High Energy Neon Ions

Following our preceding study on thick target neutron yields by He and C, we measured angular and energy distributions of neutrons produced by 100, 180 and 400 MeV/nucleon Ne ions stopping in thick carbon, aluminum, copper and lead targets using the heavy ion medical accelerator of the National Institute of Radiological Sciences. The neutron spectra in the forward direction have broad peaks which are located at about 60 to 70% of the incident particle energy per nucleon due to break-up process and spread up to almost twice as much as the projectile energy per nucleon. The neutron spectra at all angles consist of two components of cascade neutrons and evaporation neutrons. The phenomenological hybrid analysis of the moving source model for these two components and the Gaussian fitting of break-up process could well represent the measured thick target neutron spectra. The experimental results are also compared with the calculations using the HIC code, and the calculated results generally agree with the meas...

Absolute measurements of the response function of an NE213 organic liquid scintillator for the neutron energy range up to 206 MeV

Abstract The absolute values of the neutron response functions of a 12.7 cm diameter by 12.7 cm long NE213 organic liquid scintillator were measured using a quasi-monoenergetic neutron field in the energy range of 66– 206 MeV via the 7Li(p,n)7Be reaction in the ring cyclotron facility at RIKEN. The measured response functions were compared with calculations using a Monte Carlo code developed by Cecil et al. The measurements clarified that protons escaping through the scintillator wall induced by high-energy neutrons increase from 6% for 66 MeV neutrons to 35% for 206 MeV neutrons, and that this wall effect causes a difficult problem for n–γ discrimination. Measured response functions without the wall-effect events were also obtained by eliminating the escaping-proton events in the analysis, and compared with calculations using a modified Monte Carlo code. Comparisons between the measurements and calculations both with and without any wall-effect events gave a good agreement, but some discrepancy in the light output distribution could be found, mainly because the deuteron generation process was not taken into account in the calculation. The calculated efficiencies for 10 MeVee threshold, however, also gave good agreement within about 10% with the measurements.

Measurement of the Neutron Activation Cross Sections of 12 C, 30 Si, 47 Ti, 48 Ti, 52 Cr, 59 Co, and 58 Ni Between 15 and 40 MeV

Neutron activation cross sections between 15 and 40 Me V were measured by the activation method using a monoenergetic neutron field based on the 7 Li(p,n) 7 Be reaction. Natural samples of carbon and cobalt, and separated isotope samples of 30 Si, 47 Ti, 48 Ti, 52 Cr and 58 Ni were irradiated in the p-Li neutron fields generated by 20, 25, 30, 35, and 40 MeV protons. Neutron yields were determined from the amount of 7 Be induced in the lithium target. The amount of 7 Be was measured by observing the 0.478-MeV gamma rays of 7 Be(T 1/2 = 53.29 days) after the irradiation experiment. Cross sections of 12 C(n,2n) 11 C, 30 Si(n,np) 29 Al, 47 Ti(n,np) 46m+g Sc, 48 Ti(n,np) 47 Sc, 52 Cr(n,2n) 51 Cr, 59 Co(n,2n) 58m+g Co, 59 Co(n,3n) 57 Co, 59 Co(n,4n) 56 Co, and 58 Ni(n,2n) 57 Ni are reported.

Propagation of Errors from Response Functions to Unfolded Spectrum

AbstractAn analysis was made on the propagation of errors from the response functions to the unfolded spectrum in the unfolding process from a pulse height distribution to an energy spectrum. In the derivation of formulas, the terms of high variance were ignored. Assumed errors of the response functions were limited to statistical errors in Monte Carlo calculations for the response functions. The unfolding processes used were the SIMPLE method and the FERDO method. The test calculations were done assuming typical spectra having a sharp peak and the 252Cf fission spectrum. The response errors can have a serious influence on the flux error, especially in the case of a sharply peaked spectrum.

Development of a quasi-monoenergetic neutron field using the 7Li(p, n)7Be reaction in the 70—210 MeV energy range at RIKEN

A quasi-monoenergetic neutron field was developed using the 7Li(p, n)7Be reaction in the energy range from 70 to 210 MeV in the ring cyclotron facility at RIKEN. Neutrons were generated from a 10-mm-thick 7Li target injected by protons accelerated to 70, 80, 90, 100, 110, 120, 135, 150, 210 MeV. The neutron energy spectra were measured with an NE213 organic liquid scintillator using the TOF method. The absolute peak neutron yields were obtained by measurements of 478 keV c-rays from 7Be nuclei produced in a 7Li target through the 7Li(p, n)7Be (g.s.#0.429 MeV) reaction. Two relative neutron fluence monitors, which were calibrated to the absolute peak neutron fluences by the 7Be measurement, were equipped along the neutron beam line during an irradiation experiment. This high-energy neutron field is very useful for neutron cross-section measurements, response measurements of neutron detectors, and shielding experiments. ( 1999 Elsevier Science B.V. All rights reserved.

Measurement of deep penetration of neutrons produced by 800-MeV proton beam through concrete and iron at ISIS

Abstract A deep penetration experiment through a thick bulk shield was performed at an intense spallation neutron source facility, ISIS, of the Rutherford Appleton Laboratory (RAL), UK. ISIS is an 800 MeV–200 μA proton accelerator facility. Neutrons are produced from a tantalum target, which is shielded with approximately 3-m thick iron and 1-m thick ordinary concrete in the upward direction. On the top of the shield, we measured the neutron flux attenuation through concrete and iron shields which were additionally placed up to 1.2-m and 0.6-m thicknesses, respectively, using the activation detectors of graphite, bismuth, aluminum and the multi-moderator spectrometer inserted indium. The attenuation lengths of concrete and iron for high-energy neutrons above 20 MeV produced at 90° to the proton beam were obtained from the 12 C ( n ,2 n ) 11 C reaction rates of graphite. The neutron spectra through concrete and iron were obtained by the unfolding analysis of the reaction rates of the 12 C ( n ,2 n ) 11 C , 27 Al ( n , α ) 24 Na , 209 Bi ( n ,x n ) 210−x Bi (x=4–10) and 115 In ( n , γ ) 116m In in the energy range of thermal to 400 MeV.

High-energy p-Li neutron field for activation experiment

Abstract A p- 7 Li quasi-monoenergetic neutron field for activation experiment has been developed at energies between 18 and 38 MeV. The absolute neutron intensity was accurately determined from the number of 7 Be nuclei produced in the 7 Li target which is equal to the number of the monoenergetic peak neutrons released in the 4π direction. The angular distribution function of the peak neutrons is necessary for the estimation of the monoenergetic neutrons emitted in the forward direction for the sample irradiation. The distribution function was measured for proton energies of 20, 30 and 40 MeV and was collected from papers for energies between 25 and 800 MeV to get the universal curve. Activation experiments of various natural and enriched samples were performed at this quasi-monoenergetic neutron field. Here we show the neutron activation cross sections of the 197 Au(n, 2n) 196 Au, 197 Au(n, 4n) 194 Au and 59 Co(n, 2nα) 54 Mn reactions as examples.

Measurements of Activation Cross Sections on Spallation Reactions for 59Co and natCu at Incident Neutron Energies of 40 to 120 MeV

In our previous work, we have measured the neutron spallation cross sections of 12C and 209Bi in the 20-to 150-MeV energy range. Here in this succeeding study, the neutron activation cross sections on spallation reactions for 59Co and natCu have been measured in the quasi-monoenergetic p-7Li neutron fields in the 40-to 120-MeV energy range which have been established at two cyclotron facilities of Takasaki Research Establishment of Japan Atomic Energy Research institute (TIARA) and the Institute of Physical and Chemical Research (RIKEN). The neutron spectrum has been measured with the TOF (Time of Flight) method using an organic liquid scintillator, and the absolute value of peak neutron fluence has been determined from the proton recoil counter telescope at TIARA and the activation method of lithium target at RIKEN. In this study, the following seventeen neutron activation cross section data are reported which produce 56Mn, 54Mn, 52Mn, 58Co, 57Co, 56Co, 55Co, 59Fe from 59Co reactions and 56Mn, 59Fe, 60Co...

Measurement and calculation of radioactivities of spallation products by high-energy heavy ions

Abstract Irradiation experiments were performed at the HIMAC (Heavy Ion Medical Accelerator in Chiba) facility, National Institute of Radiological Sciences, Japan. The radioactivity distributions of spallation products in a thick Cu target were obtained by irradiating 230 and 100MeV/nucleon Ne, C, He, p and 230MeV/nucleon Ar ions. The gamma-ray spectra from thin irradiated samples of C, Al and Cu inserted into a Cu target were measured with a HPGe detector. From the gamma-ray spectra, we obtained the spatial distribution of radioactive yields of spallation products of about 40 nuclides in Cu sample in the Cu target. Our results agree with other experimental data. We also calculated the spatial distribution of residual radioactivities in the Cu target by the PHITS (Particle and Heavy-Ion Transport code System) code and compared with measured results. The PHITS code provides good results on residual activity calculations.

Neutron skyshine from intense 14-MeV neutron source facility

The dose distribution and the spectrum variation of neutrons due to the skyshine effect have been measured with the high-efficiency rem counter, the multisphere spectrometer, and the NE-213 scintillator in the environment surrounding an intense 14-MeV neutron source facility. The dose distribution and the energy spectra of neutrons around the facility used as a skyshine source have also been measured to enable the absolute evaluation of the skyshine effect. The skyshine effect was analyzed by two multigroup Monte Carlo codes, NIMSAC and MMCR-2, by two discrete ordinates S /sub n/ codes, ANISN and DOT3.5, and by the shield structure design code for skyshine, SKYSHINE-II. The calculated results show good agreement with the measured results in absolute values. These experimental results should be useful as benchmark data for shyshine analysis and for shielding design of fusion facilities.