DEPTH DOSE MEASUREMENT OF NEGATIVE PIONS IN WATER
M. Kawai 9 K. Owaki, A. Iwata and M. Yoshiwa
Kawasaki Heavy Industries,Ltd.
1-1, Kawasaki-cho, Akashi, 673 Japan
T. ToaiMasu, T. Mikado, H. Ohgaki, K. Chiwaki, R. Suzuki
Electrotechnical Laboratory
1-1-4, Umezono, Tsukuba, Ibaraki, 305 JapanS. Okabe
Okabe Keisoku Kogyosho
1 , Nozawa, Setagaya, Tokyo, JapanABSTRACT
A pion spectrometer(Qi-Q 2 -D-Q 3 type) has been constructed astheETLpionchannel to study depth dose distributions of negative pious in tissue equivalentmaterials (water). The depth dose peak were observed, and the peakwater can be controlled by changing

thethickness

position

inof

thealuminumabsorber

pion

beams

have

allowedtoradio-therapy due to the production of highly localized ionizationinducedbyplaced in the entrance of the water bath.
I- INTRODUCTION
Recentinterests”star” formation.

intheapplicationsofA pion spectrometer (Q 1 -Q 2 -D-Q 3 type) has been constructed as

the ETL pion channel (1,2,3) to study depth dose distributions of negative pionsin tissue equivalent materials.
II. ETL PION CHANNELA schematic layout of this channel is shown in F i g . l . A lead shieldplatewith an elliptical hole is set between a copper target and the inlet of the pionchannel.

The function of the first and second quadrupole magnets, Qi and Q 2 , isto achieve large solid angle of 0.12 sr..

A lead absorber having an

cross section with respect to axis of Qi Q 2 is set between Qi and Q 2
photoneutrons and X-rays, while the effective solid angle

isellipticaltoreducedreduce
to0.09sr.. The focal plane of charged pions is designed so as to cross the centerofthe small quadrupole magnets Q 3 . The vertical focusing is provided by theedge

focusing of the bending magnet D andQ3 .

Theelectronbeam

fromalinear

accelerator (TELL) is directly transported to the pion laboratory and is focusedto the center of a w-target (copper) shown in Fig.l.
the target is about 1.5cm > 2 cm > 2 cm.

Theeffective

volumeofThe target is set in front of the beam

PION SPECTROMETERPbABSORBER ( P b )BEAM DUMPQ2yI<L

0oVNn S1Js<3m7C TARGET.......

^^

ABSORBER ( /SUTW ATER BATH

IRON OREFig.l Layout of the ETL pion channel.
dump consisting of a tank filled with water, it is combining a Faraday

cup

for

measurement of the electron beam current. The target and theFaradaycup

arecooled with circulating water 。 The size and position of the electron

beam

arecontrolled bytransition

afocusingsystemandarewatchedradiations from a thin aluniinum plate attackedonbytheobserving

surfac efrontofthetarget with a TV set.
The beam was always controlled to become a sise of the order of 5 mm 4 . The
irradiatedelectrons

generate

highenergy

X-rays produce pions, neutrons, electrons andX-rays

inpositrons

thein

About 70 % of the irradiated electron beam passed throughcaptured by the Faraday cup.

targetthethesam etargetandthetarget.
andwasOf the ionizing radiations produced in the target,some of radiations scattered in near 90° direction with respect to theelectron

beam direction can pass through the elliptical hole of the lead shield plate set
particlessuchascharged pious(?r and 刃+ ) ， electrons and positrons are focused by Qi Q 2andcanSomeof

between the target and the pion channel. Somepass through the Qi Q 2channel, keeping

awayofthecharged
lead

absorber,non-charged particles such as X-rays, neutrons and t?° are absorbed orscatteredby the absorber set between Qi and Q 2 .

fromtcand 7?+ (135 MeV/c±5%)

thecopper target can be focused to a beam size of 3 cm > 3 cm on the foca 1 plane bychanging* the direction of magnetic field of D.

III. DEPTH DOSE DISTRIBUTIONS OF PIONSIn the depth dose Dieasurement, depth

dosedistributions

ofnegativeandpositive pions in water have been measured using

therraolurainescence

dosimeters(TLDs , M g 2 Si 0 4 ：Tb) as small size dose detectors.

Figuredepth

distributions ofin water.

2showsdose

In the depth dose distributions of t t ，remarkable

dose peaks have been seen near the range of t t in water• These dosepeaks

aredue to star formations» which is induced by heavy ions and protons scatteredat3 〇i:---- — i----- ----1---------- 1-----ー1(E )2soa Q I
cc2LL

1QS VCQCCCQ

050

1020

15DEPTH(cm)F i g . 2 Depth dose distribution ofposition of depth dose by changing

n~in water and control of the peak
the thickness of the aluminum absorber.

the disintegration of 刃-. The position of depth dose peak in the water bath canbe controlled by changing the thickness of the aluminum absorber placed intheentrance of thewater bath.

bythe total rangeof tt inSince the position of dose peakbothwater

functions as a scatter for electrons

andthewith theabsorber.
same

through the pion channel, since the electrons can be

isThe absorber

momentumeasilydetermined
as?r

dose

distributionof方+inwater.

Detailspassing*

scattered byabsorber, compared with charged pions. No significant dose peak has
in the depth

also

on

thebeen

pions

seen
yield

efficiencies and their electron energy dependence are discussed in else where.
References
1 ) T • Toittiniasii, Proc•

2nd China-Japanjoint

Their Applications( IMP, Lanzhou, China, Oct.

SyittposiumonAcceleiatois

1983) p.135.

2) T.

Tomimasu et al., Bull electrotechnical L ab• 42,19(1978)•3) T.

Tomimasu et al., TELL-TERAS ACTIVITY REPORT 1987-1990. 75(1990)

and