Study of fluorescence for cryogenic fine-grain emulsion*H. Ichiki, T. Naka, T. shiraishi* Nagoya University, Japan
Contact e-mail: ichiki@flab.phys.nagoya-u.ac.jp

Nuclear emulsion and destination of excited electrons
Nuclear emulsion is a solid detector which contains gelatins and AgBr(I) crystals
and records charged particles as tracks.
Charged particle

Ag grain

Ag coree-electrone- eCharged particle

AgBr(I)
crystalNuclear emulsions

General usage

Charged particle

e-e e-ee- e

AgBr(I) crystal

e-e e-Gelatin

Photodevelopment
ee-e-100 um
Image of track formatione- ee-AgBr(I) crystal

track image of 200nm crystal-Eelectron

When a charged particle penetrates crystals, it deposits
energy and electrons are excited.

Ag coreformation

SEM image of NIT crystal

Excitedelectrons

We have emulsion production machines and can control crystal size. In thisstudy, we use emulsion with about 40nm crystals , called Nano Imaging
Tracker(NIT), developed for directional dark matter search, because it shows
stronger light emission than emulsion with other crystal size (20nm or 200nm)
from the result of easy test.

phonon≫Photonemission

Test
Roomexperiment temperature

Enhanced

90Y

Thermal luminescence
HV

6mm
PMTH1161

Integralcircuit

Thermocouple

Al90ZrActivity:~594kBq(D.C.1990→D.C.2016)28.79y64.00hrate of β(@sample)：1160[/s]From isotope notebook

NIT

NIT

PreAMP

RI source: Sr90(βsource)
β:100%
β:100%
2.28MeV
0.546MeV

Lq. N2241Am

phononMeasurement system

Valence bandaPhotonemission

Photographic scientists prove this tendency at 77K or 4K, but they use light source or rubbing to excite electrons.

90Srhole

Relaxation processes of excited electrons

Ag coreformation

Cryogenictemperature

Hole trap(I-)2※Photon rate[/s]Ag coreformation

excitation

Photonemission

suppressedRoomtemperature

recombination

phononTemperature dependence of relaxation processes

Conduction band

Sample only

RI source

MCA

5.5cm
3.5cm

baseline

3.5cm

Time[s]simulation

Al

Procedure of measurement•Pour Lq. N2 until the baseline•Supply HV to PMT•
To count photons by MCA for 20s every 2min.

Lq.N2※Photon rate[/s]1cm

samplesamplesfilm : NIT(crystal + gelatin) 150um
Gel.: gelatin 80um (60% of film is gel.)

RI only

Gel. and RI※Photon rate[/s]※Photon rate[/s]Photon rate[/s]※PhotonKinetic E[MeV]

film and RI

Excess!

Time[s]results

keep onLq. N2 temperature
Time[s]Time[s]Time[s]※Attention
Raw signals from PMT are integrated, so rate 1 doesn’t always consistent with 1 photon.

Acknowledgements•We would like to thank Nagoya University program for LGS for
the MCA, japan.
•We would like to thank Technical Center of Nagoya University for
digital multimeter, Japan

Under some assumptions, 1000 photons are generated by 1 β-ray, and 7of them are detected incurrent setup.

-Next planWe want to use nuclear emulsion as a scintillation detector (e.g. event position trigger for large
scale experiment, possibility of particle identification). As a next step, we will measure the time
constant of this fluorescence. At that time, main back ground should be thermal noise of thephoto detector. Assuming that thermal noise rate is 1kHz, we hope that the time constant ＜100μconservatively.