Simulation and Radiochemical Analysesof Impurity Beam in Kr beam at RIBF
July 2018
NSREC

Background• When fast heavy-ion beam pass matter, part of the ion-beam nuclei
collide with nuclei in the matter and are converted to other nuclide
with nearly same velocities.
• These secondary ions contaminate the primary beam as impurity
beam, and may affect beam quality (LET distribution).
• Nuclear reaction may also occur in samples.

Radiochemical analyses• The production probabilities of impurity-beam nuclides wereevaluated with radiochemical analyses.
• Test samples were irradiated and the amount of radionuclides weremeasured through gamma-ray analyses.
• The beam condition:
Kr-84 beam at 70 MeV/u from accelerator
Al-degrader thickness=586.2μm
Energy of Kr-84 at Si =25 MeV/u, LET in Si =19MeV/(mg/cm2)• Two kinds of Test samples
Si-wafer（0.5mm-thick, 2 plates） to simulate client’s sample
Acrylic （1mm-thick, 2 plates） for comparison• Kr-beam is stopped in the 1st plate• 10-minutes irradiation each
• Gamma rays were measured from 7 min to 3 months after irradiation

4.5×1010 ions

5.5×1010 ions

Identification of nuclides• On the basis of gamma-ray energy, half life, and branching ratio• In acrylic, 49 nuclides from Na to Mo, in Si wafer 61 nuclides
from Na to Ag (isomers included)

Production probabilities of RI• Decay curve is fitted to measurements for each nuclide （cascadecorrections if necessary）• Decay curve is extrapolated to irradiation-end time,
radioactivity⇒number of RI nuclei• Correction for decay during irradiation ⇒ Number of produced RI
nuclei during 10 min of irradiation• Number of produced RI nuclei ÷ number of Kr ions
= RI production probability

Gamma-ray spectra

Examples ofDecay curves
Rb isotopes in Si

Probability of radionuclides production

Probability of radionuclides production

PHITS• Multi-Purpose Particle and Heavy Ion Transport code System• PHITS is a general purpose Monte Carlo particle transport simulation codedeveloped under collaboration between JAEA, RIST, KEK and several otherinstitutes. It can deal with the transport of all particles over wide energy
ranges, using several nuclear reaction models and nuclear data libraries.
• PHITS can support your researches in the fields of accelerator technology,
radiotherapy, space radiation, and in many other fields which are related toparticle and heavy ion transport phenomena.
https://phits.jaea.go.jp/index.html

Setup• Si-wafer（5cm or 10cm -diameter,10μm-thick）is placed• From left, a Kr-beam with 70mm or54mm-diameter comes.
• Nuclide, intensity, energy distribution,
LET of ions that impinge Si-wafer• Degrader thickness varied

Degrader thickness
（μm）

0586

837

LET in SI
MeV/(mg/cm2)

121938

Measurement and PHITS (Z=25-36)

Measurement and PHITS
Rb-isotopes (Z=37)

84Rb and 83Rb produced by inverse kinematics
84Kr(p,n), (p,2n) reactions with hydrogen in acrylic

Measurements and PHITS (Z=38-45)

Impurity beam nuclides

Impurity beam consists mainly of nuclides with Z ≤ 36.

Nuclides produced in the samples

Nuclides produced in Si are more broadly distributed than those in acrylic.
Rb isotopes are markedly produced in acrylic by the inverse (p,xn) reactions.

Total probabilities of nuclides in samples

Total probabilities by PHITS reproduce overall behavior of our experimental RI probabilities.
(There are some exceptions in Rb isotopes and low-Z nuclides.)PHITS can be used for simulation of our irradiations.
⇒ Degrader thickness dependence of the beam cleanness is studied.

Light impurities

Energy distribution• Energy distributions of light particles don’t depend on the degrader thickness.
• P and n below 100MeV , α below 300MeV• Energy distributions of heavy particles depend on the degrader thickness.

Heavy ions (1) without degrader (LET=12)

Ion energy distributes between 2000-4200 MeV.
Lighter nuclides have lower energy.
Impurity nuclides have LET lower than Kr-84.

Heavy impurities (2) 586-μm degrader (LET=19)

Impurity energy distributes from 0 to 2100MeV
Lighter nuclides have lower energy.
Most nuclides have higher LET than Kr-84.
LET distributes up to 43 MeV/mg/cm2

Heavy impurities (3) 837-μm degrader (LET=38)••

Very heavy nuclides (Nb) with LET up to 50
MeV/(mg/cm2) are found in the impurity
Most of lighter impurity nuclides are stopped
before the sample.

High-LET impurity• Ratio of heavy nuclides with higher LET than primary Kr
ions is calculated with PHITS• Maximum contamination ratio of 1.2 % is found at about
0.6-mm thick degrader [LET＝19MeV/(mg/cm2)]