Observation of latent image specks in nuclear emulsion for the purpose of precise estimation of local deposit energy

Kimio Niwa*

Toshiyuki Toshito**

Ken'ichi Kuge***

Nakahiro Yasuda****

Mitsunori Natsume*

Noriyuki Saito*

Hirotaka KubotaNagoya University F-lab.

*Nagoya University

**High Energy Accelerator Research Organization (KEK)

***Chiba University

****National Institute of Radiological Sciences (NIRS)

Study of fragmentation using nuclear emulsion

• We study nuclear fragmentation reactions of carbon ions for the heavy-ion radiotherapy.

• Precise measurement of the deposit energy.

12C (nucleus)180MeV/n

A point of nuclear fragmentation reaction

150 m

Micrograph of a fragmentation reaction recorded on a nuclear emulsion

Nuclear emulsion : Three-dimensional track detector

Exposure to a charged particle

Charged particle

TrackLatent image

specks

0.2 mGelatin

Silver bromide crystal （ AgB

r ）

A charged particle passes through silver bromide crystals

Formation of Latent image specks

Deposition of energy to the silver bromide crystals

Figure of nuclear emulsion

Normal photographic development

Ag filaments are made from Ag+ ions in a AgBr crystal

fixationdevelopment

１ μm

K. Kuge et al. Radiation Measurements 42 (2007) 1335-1341

Silver grain

Silver bromide crystal

Latent image speck

Silver bromide crystal (AgBr)

Ag+

Ag filament

New technique = Gold deposition development

development fixation

Au grains are made from Au+ ions in the developer

１ μm

K. Kuge et al. Radiation Measurements 42 (2007) 1335-1341

Gold cluster

Silver bromide crystal

Au+Au+

Au+Latent image speck

Silver bromide crystal (AgBr)

Au cluster

ComparisonBefore development

Normal photographic development

Gold deposition development

Deposit energy

Low

High

1

3

5

1

1

1

1

3

5

Gold cluster

Silver grain

latent image speck

New estimation method

Normal photographic development Gold deposition development

Range of developed　 silver bromide

Range of latent image specks

We can count latent image specks (gold grains) one by one

We can estimate deposit energy by line density of the number of latent image specks

Experiment• Exposure

– Accelerator : HIMAC synchrotron at NIRS

– Emulsion : OPERA film (made by Fujifilm)

– Beam : →– Density : 107 ions/cm2

• Development– Normal photographic development

• Developer : XAA (made by Fujifilm)

• Temp. : 20℃• Period : 25 minutes

– Gold deposition development• Developer : →• Temp. : 23℃• Period : 2, 5 days

Chemicals Concentration[mol/l]

KSCN 5×10-3

NaAuCl4 1×10-3

KBr 8×10-3

Na2SO4 0.2

Formula for the gold deposition solutions

Ion Kineticenergy

Deposit energyin AgBr

[MeV/n] [keV/m]C 388 45

He 146 9C 276 52C 113 93C 51 166Ar 463 389Fe 419 804

Beam property

• Used for the OPERA film

• Developing agent is ascorbic acid

Sample making for electron microscopes

Incidence direction of the ions

Thickness : 0.5, 3.0m

JEM-2010 (acceleration voltage is 200kV)

H-1250ST : High Voltage Electron Microscope (1,000kV)

Emulsion (After exposure and development)

Slice with microtome

Plastic base

Emulsion layer

Used transmission electron microscope

Electron micrograph of carbon ion tracks(388MeV/n)

Gold deposition development

Gold cluster

Normal photographic development

Silver grain

1m

• Group of latent image specks are in around 0.2m.

• The size of the silver bromide crystals is 0.2m.

• Plural latent image specks are formed in a silver bromide crystal.

More number of latent image specks = more deposit energy

Silvergrain

Goldcluster

Period : 5 days

Various ion tracks on electron micrograph

H C C C Ar Fe 146 [MeV/n ] 276 113 51 463 　 　 419 9 [keV/m] 52 93 166 389 　 　 804

1m

Raw data of the latent image specks number measurement

He 146MeV/n

Ar 463MeV/n

C 51MeV/n

C 113MeV/n

Fe 419MeV/n

C 276MeV/n

0

100

200

300

400

500

600

700

800

900

0 200 400 600 800 1000Deposit energy [keV/m]

Lin

e de

nsit

y of

late

nt im

age

spec

ks[c

lust

er /1

00μ

m]

He 146MeV/n

C 276MeV/n

C 113MeV/n

C 51MeV/n

Ar 463MeV/n Fe 419MeV/n

Correlation of the number of latent image specks and deposit energy

Ion

(Energy in MeV/n)

mean rms rms/√ NHe (146) 56 14 4C (276) 343 49 13C (113) 479 67 19C (51) 620 53 16

Ar (463) 810 60 18Fe (419) 817 65 19

Line density of latent image specks[cluster/100m]

• Linear relationship in low deposit energy region.

• Saturation in the region higher then 400keV/m.

• Average number of latent image specks formed in one AgBr crystal is 3.6 in the region of saturation. (The number of AgBr crystals per 100m is 230.)

Conclusion• We succeeded in making latent image specks visible

with having kept the shape of the track.– Like a case of the light, A study of the latent image specks

formation is enabled in the case of the charged particles.

– The estimation of the deposit energy of the charged particles is enabled with one silver bromide crystal which is 0.2m size.

• We developed the new measurement technique of the deposit energy by the line density of the number of latent image specks.– We showed that the deposit energy measurement was possible

with latent image specks.

– Because a plurality of latent image specks are generated on one silver bromide, the dynamic range of this measurement technique is wider than the conventional one.

Estimation of deposit energy by grain density

measurement

Deposit energy

Low

High

Before development After development

Grain density (GD) = Line density of the number of developed silver grains

GD

Low

High

saturate

The selection of the tracks

track

Slice surface

Thickness of the slice : 0.5m → 3m (Thicker)

High Voltage Electron Microscope (H-1250ST) acceleration voltage : 1,000kV

Stereoscopic observation

Latent image specks on one silver bromide crystal are divided

A slice

To avoid picking up tracks on surface . . .

1 m

Observation by stereo electron micrographs

Side view

: The track which is chosen

: The track which is not chosen

C 276MeV/n

The tracks inside of the layer are picked up

Three-dimensional observation is possible with a stereo glass.

Plastic base

Emulsion layer

Plastic base

Emulsion layer

Gelatin layer

21 m(Before dev.)

Plastic base

Emulsion layer

Gelatine layer

Broken by an electron beam