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 Kubota Nagoya 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. 12 C (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 Track Latent image specks 0.2  m Gelatin Silver bromide crystal （ AgBr ） 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

Normalphotographic development Ag filaments are made from Ag + ions in a AgBr crystal fixation development １μm１μm K. Kuge et al. Radiation Measurements 42 (2007) Silver grain Silver bromide crystal Latent image speck Silver bromide crystal (AgBr)‏ Ag + Ag filament

New technique = Gold deposition development development fixation Au clusters are made from Au + ions in the developer １μm１μm K. Kuge et al. Radiation Measurements 42 (2007) Gold cluster Silver bromide crystal Au + Latent image speck Silver bromide crystal (AgBr)‏ Au cluster

Comparison Before development Normal photographic development Gold deposition development Deposit energy Low High Gold cluster Silver grain latent image speck

New estimation method Normal photographic developmentGold 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 : 10 7 ions/cm 2 Development –Normal photographic development Developer : XAA (made by Fujifilm)‏ Temp. : 20 ℃ Period : 25 minutes –Gold deposition development Developer : → Temp. : 23 ℃ Period : 2, 5 days Formula for the gold deposition solutions Beam property

Sample making for electron microscopes Incidence direction of the ions Thickness : 0.5, 3.0  m  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 1m1m Group of latent image specks are in around 0.2  m. The size of the silver bromide crystals is 0.2  m. Plural latent image specks are formed in a silver bromide crystal. More number of latent image specks = more deposit energy Silver grain Gold cluster Dev. period : 5 days Thickness : 0.5  m

Various ion tracks on electron micrograph H C C C Ar Fe 146 [MeV/n ] [keV/  m] m1m Dev. period : 2 days Thickness : 3.0  m

Raw data of the latent image specks number measurement He 146MeV/n Ar 463MeV/n C 51MeV/n C 113MeV/nFe 419MeV/n C 276MeV/n

Correlation of the number of latent image specks and deposit energy 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 100  m 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 0.2  m 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 formed on one silver bromide crystal, 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 developmentAfter 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 : 0.5  m → 3  m (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