Ⅱ-9. Instrumentation
RIKEN
Accel. Prog. Rep. 56 (2023)

RIKEN Accel. Prog. Rep. 56 (2023)

Activation measurement of copper by 238 U irradiation
A. Akashio,∗1 K. Tanaka,∗1 N. Shigyo,∗1,∗2 and K. Sugihara∗1,∗2,∗3
γ-ray residual radiation dose around the copper
beam dump of BigRIPS, where the highest radiationdose rate is expected at RIBF, is occasionally estimated by Monte-Carlo radiation transport code suchas PHITS.1) However, there are no measured data forthe activation caused by uranium beam and the accuracy of the calculation remains unknown. Therefore,
345 MeV/nucleon uranium beams were irradiated ona stack of copper sheets, which is the material of thebeam dump, to measure the produced radioisotopes
and compare them with the PHITS calculation.1)
Ten 1 mm thick copper sheets were stacked. A
10 mm thick copper plate was applied as the radiation sample. After the irradiation of the uranium
beam, γ rays were measured with a germanium detector to identify the nuclide and quantity of the produced radioisotopes. To consider long-lived radiationfrom the beam dump, the γ rays were measured ninemonths after the irradiation. Figure 1 shows the depth
dependence of the observed radioactive nuclei. The
depth was reduced from the copper sheet number. The
amount of the radioisotopes was evaluated from theindividual measurements of the copper sheets. The
range of 345 MeV/nucleon uranium-238 beam in copper was approximately 3.3 mm. Manganese-54, cobalt56, -57, -58, and cobalt-60 were observed at all the copper sheets. Therefore, the isotopes of manganese andcobalt in the range 1–3 mm were produced through areaction between the uranium and copper nuclei. The
isotopes deeper than 4 mm were produced by a nuclear reaction of secondary neutrons with copper nuclei. Further, the secondary neutron was produced

from the reaction with uranium beam and copper.
Consequently, osmium-185, hafnium-175, zirconium97, and ruthenium-103 were observed in the depth
range of 4–6 mm. As nuclei of mass number of approximately 180 are heavier than typical ﬁssion fragments of uranium which mass are approximately 140,
osmium and hafnium are supposed to be produced byprojectile fragmentation of uranium beam. Zirconium
and ruthenium, with approximate mass number of 100,
are typical nuclides from in-ﬂight ﬁssion of uranium
beam. The range of produced nuclei in copper waslonger than the 3.3 mm range of uranium beam because their atomic number are smaller than that of uranium. Moreover, the nuclei produced by ﬁssion were
not observed at 7 mm depth and beyond.
The measured activity of nuclei was compared withthe calculation by PHITS. Figure 2 shows the activity
ratio of the calculated to measured value.

Fig. 2. Ratio of nuclei calculated evaluation by PHITS tomeasured values.

Fig. 1. Depth dependence of the observed radioactive nuclei in the copper sheets. The depth was converted fromthe number of the sheets.
∗1
∗2
∗3

RIKEN Nishina Center
Department of Applied Quantum Physics and Nuclear Engineering, Kyushu University
High Energy Accelerator Research Organization (KEK)- 119 -The calculated activation rate of copper by the secondary neutron was approximately 50% of measuredvalue. The calculated production rate of projectilefragmentation nuclides of osmium-185 and hafnium175 were several times higher than measured values.
However, the ratios of the ﬁssion nuclei zirconium-97,
and rutheniu-103 were approximately identical to themeasured values.
Consequently, the benchmark of activation for
345 MeV/nucleon uranium-beam irradiation on copper material was obtained. The PHITS evaluation wasconsistent the measured values within a factor of several.
Reference1) T. Sato et al., J. Nucl. Sci. Tech. 55, 684 (2018).