The lith Symposium on Accelerator Science and Technology, Harima Science Garden City, 1997

Heavy Ion Microbeam Project in RIKEN Ring Cyclotron
Nobuhisa FUKUNISID, Misaki KOBAYASHI, Akira YONED A,
Masanori KIDERA, Masayuki KASE and Yasushige YANORIKEN, The Institute of Physical and Chemical Research, Hirosawa 2-1, Wako-shi, Saitama, 351-01 JAPAN.

Abstract
The RIKEN Accelerator Research Facility has
contributed to bio-science taking advantage of a variety ofheavy-ion beams. To make further contribution to bioscience, we are planning to construct the new beam course
which provides microbeams. As a first step, we design herea beam course for a 50-J..Lm microbeam. We employ thebeam collimation method in producing a microbeam. We
also introduce a position-sensitive detector and a
microscope to adjust a sight. The schedule of the first beamis the end of this fiscal year.

1 Introduction
The heavy-ion beam is high linear-energy-transfer(LET)
radiation and produces a great biological effect on anorganism. Hence, heavy-ion beams have played an
important role for studies of bio-science, for example
heavy-ion therapy and heavy-ion~induced mutations. Bioscience is one of the major research subjects in the RIKEN
accelerator research facility(RARF). Beam service time forbio-science was about 400 hours in 1996. In experiments
performed in the RARF, a target is irradiated uniformly by
heavy ions. Such a uniform irradiation experiment is very
useful when we investigate statistical aspects of aphenomenon, for example the survival rate of cells
irradiated by heavy ions.
Besides the uniform-irradiation experiment, biologists
suggest a new type of experiments in which we irradiate
specified cells or organs with heavy ions. To irradiate asmall part of an organism selectively, we need a heavy-ion
beam, the beam size of which is several micrometers on atarget. Such a fine beam is called a microbeam. The
microbeam is useful to elucidate complex communication
between cells or groups of cells(bio-crosstalk) and to makesurgical operations on a cell using heavy ions( cell-surgery).
In order to promote these programs, we are now planning toconstruct the new beam course which provides microbeams.
Heavy-ion microbeams are now available in several
facilities. For example, the Takasaki Radiation Chemistry
Research Establishment provides various types of
microbeams including sub-micrometer beams[ 1].
Compared with these facilities, the RIKEN Ring
Cyclotron(RRC) covers a wide energy range. Hence, wewill extend the energy frontier of the microbeam in thisproject. The final goal of this project is to produce heavyion beams with the beam size less than 10 J..Lm. As a firststep to this goal, we design here a 50-J..Lm microbeam course
because slight modification of the existing beam line issufficient to realize it.
In this report, we will introduce characteristic featuresof heavy ions accelerated by the RRC in Section 2. We will

illustrate the design of the new beam course in Section 3.
We will briefly summarize the present status of our projectin Section 4.
2 Heavy-ion Beams in RRC
One of the remarkable features of the RRC is that itprovides heavy-ion beams over the whole atomic mass
range and a wide energy range from 0.6 MeV/nucleon to
135 MeV/nucleon. In the case of the heavy-ion beam, theLET is proportional to the square of the charge of the ion
and is inverse proportion to the energy of the ion. We
summarize in Table 1 the energy and the LET of the heavy
ions which we use frequently to study bio-science in the
RARF. Note that the lower value of the LET corresponds tothe maximum energy for each ion. On the contrary, weobserved the higher value with a range shifter.
Table 1
Properties of the RRC beams
Ion
12C6+
zoNelO+
40Arl7+56Fe 24+

Energy(MeV/u)
135
135
95
90

LET
(keV/J..Lm)
23-29061-680280-1500
620-3500

Range inWater (mm)
40
23
8.2
4.3

Another important feature is· that the heavy ion
accelerated by the RRC has a long range because of its highenergy. We also tabulate the ranges in water in Table 1.
Because of this long range nature, irradiation experiments inthe air are easily performed. Moreover, this property makes
it possible to investigate the inner part of an organism
without undesired damages on a surface region.
Taking advantage of a wide variety of the LETs andlong range nature of heavy ions, many experimental studies
have been performed in the RARF. For example,
characteristics of heavy-ion-induced mutations,effectiveness of the DNA repair system in response to highLET radiation and an effective mutation method for plants
have been studied with the present irradiation system[2].
3 Design of Microbeam Course
In producing a microbeam, we may employ either (both)of the following two methods. The first one is to focus
heavy ions strongly at the target position with magnets. Thismethod is suitable for a small-emittance beam. The second
one is to use a collimator with extremely small aperture. In
this beam collimation method, a high-intensity beam isnecessary.

-270-

The 11th Symposium on Accelerator Science and Technology, Harima Science Garden City, 1997

QD17

QD16

QD15

QD14

QD13

QD12

QAll

QD18

QDlA

QD19

AOl

Fig. 1 Configuration of magnets in the ESC line. A box( semi-circle) shows a quadrupole( dipole) magnet.

3.1Beam transport system

divergence of the beam below the last quadrupole magnet.
Due to this property, we can choose freely the position of
the collimator and the end-point of the beam line where we
extract heavy ions into the air.
Here, we will explain more detailedly properties of thissolution. Following the first-order beam optics theory, th~position(x) and the angle(9) of heavy ions are given using atransfer matrix as

We use a branch of the beam distribution system of theRRC, which we call the ESC course, as a microbeam line.
We do not change the configuration of magnets illustrated
in Figure 1 because other beam lines use same magnets
except for the last triplet of quadrupole magnets. In spite ofthis, we have sufficient number of adjustable parameters,i.e., field gradients of quadrupole magnets.
Making use of these degrees of freedom, we design the
beam transport system which satisfies the following
requirement. The requirement is to reduce a beam loss at thecollimator because a great beam loss may cause a serious
problem for the radiation protection. To this end, we insert
two sets of slits in the upper stream of the beam line. One
set of slits works for both horizontal and vertical directions.
We determine positions of slits as these slits also work to
define the emittance of the beam.
It is easy to find solutions to satisfy the requirement. We
illustrate here the beam envelope of a typical solution in
Figure 2. In this solution, we suppress strongly theHere, x0 and 90 mean the position and the angle at the
AOI point, respectively. The AOl point is the object point.
We adopt the point-to-parallel transport to suppress thebeam divergence, and consequently m 22 is zero. The
maximum~angle of heavy ions depends on the values ofm 21
and x0 • In this solution, heavy ions which fulfill thecondition as -0.08 (mm) < x0 < 0.08 (mm) can pass throughthe first set of slits. We choose m 21 as -O.OS mradlmm forboth horizontal and vertical directions at the exit of the lastquadrupole magnet. Consequently, the maximum angle ofheavy ions is 4 )lrad. The transmission efficiency is
1.3S* 1o- 9 , and the resulting current of the microbeam is 840
ions/second for a 100 pnA heavy-ion beam. Finally, the·achromaticity is fulfilled in this case.

We adopt here the second one because the beam currentof the RRC is sufficiently high and insertion of few devices
into the present beam line realizes a SO-)lm microbeam. To
avoid the divergence of the beam on the target, it isimportant that we make a parallel beam at the collimatorand set a target just behind the collimator.

5
0

0.0

~ ~~

---

.... - -~~ -20 ~

Cll

0

10

,.• c:,~ slit•

20,, .......

~

r.,...- ~~~>(

slit

~, -

I

I

30

40

.
50

~ 1-

..

1--

60

." ,

70

Distance from A01 (m)Fig. 2

Beam envelope in the ESC course. A solid(dashes) line is the horizontal(vertical)
component. The AO 1 point is the object point of the beam optics. Vertical lines
show positions of magnets, slits and the collimator.

-271-

I--

·~ n~ . !\: ._ .
....
'•' DMD5 SWSI ......
II ,.

... -r:"~......

II

QD5C Collimator

QD17 QD18 QD19 QD!A

·

DAAI&
DMAI
I II

-30

QD16

QD14 QD15~

ffi -10 K~v

CD

QD12 QD13

20 ~

~ 10
~

QAII

QA02

'E 30

80

The 11th Symposium on Accelerator Science and Technology, Harima Science Garden City, 1997

3.2 Collimator and Irradiation System
Figure 3 shows .the conceptual design of the irradiation
system. First, we need a collimator with aperture of 50 Jlm
to produce a microbe am. The thickness required is 10 mm
when we use a heavy metal, because the energy of heavy
ions is quite high. It is difficult but technically possible to
make such a narrow and thick collimator[3] and a test benchof the collimator is in course of production. In Figure 3, weplan to use another collimator placed in the upperstream(left one in Figure 3). The aim of this collimator is toselect an essential part of a beam beforehand.
In addition, we use a position-,sensitive detector(PSD) to
resolve the beam axis. We employ a microscope todetermine the target position. We fix the target to a movablestand. We drive the stand using a stepping motor and choose
the minimum step as 50 Jlill. Utilizing these apparatuses, we
set the target precisely on the beam axis. The scintillation
counter placed above the target numerates heavy ions. We
also prepare a range shifter in order to vary the LET. We set
all devices on the same table which defend them fromvibration. A beam profile monitor and a Faraday cup arefor beam tuning and we set them off the beam axis duringexperiments.

line. A small fraction of the beam, 0.02 % in the example
mentioned in Section 3, can pass through these slits. Hence,
the maximum current is 0.2 pnA. To measure the beamprofile for such a low-density beam, members of our groupdeveloped a new profile monitor. The profile monitor isdesigned to work effectively for a small current[4]. In
addition, we should refine the design of the irradiation
system. We plan to finish the detailed design till the next
spring. The first irradiation experiment is scheduled in
1998.
References[l]T. Kamiya, N. Utsunomiya, E. Minehara, R. Tanaka and
I. Ohdomari, Nucl. lnstr. and Meth. B64 (1992) 362.
R. Tanaka and T. Kamiya, Nucl. Instr. and Meth. B79(1993) 423.
T. Karniya, T. Suda and R. Tanaka, Nucl. Instr. andMeth. B104 (1995) 43.
[2]Studies of bio-science in the RARF are reported briefly
in RIKEN Accelerator Progress Report. Examples listed
in the text are included in vol.30(1996) and references
are therein.
[3]M. Anzai, private communication.
[4]A. Yoneda et al, in proceeding of this conference~

Fig. 3 Conceptual design of the irradiation system.
4 Present Status of ProjectIn the preceding section, we outlined the design of our
new beam course. We mention here the present status of the
project. As stated previously, it is in progress to make thecollimator, which is the key ingredient of our project. It
will be completed in this fall. We will test it and produce thefirst microbeam in this fiscal year. At the same time, we will
study the beam transport and examine the position-sensitive
detector. In producing a microbeam, a new beam profile
monitor is necessary because the beam intensity is very low.
Recall that we plan to insert two sets of slits in the beam-272-