Peltier-cooling-type High
Performance Cloud ChamberVer.2017.02.19

Produced byRadiation Research Center, Osaka Prefecture University,

Associate Professor Masafumi Akiyoshi（ akiyoshi@riast.osakafu-u.ac.jp ）Problems in Conventional Cloud Chambers

・Needs preparation and resupply dry-ice
・Hard to long time continuing presentation
・Requires several minutes to start observation
・Radiation tracks are not observed under bad weather condition
・Limited to just observation of alpha-rays track

Features of this products
・Dry-ice Free!
・Clear track observation and Stable long time・Oservation of not only alpha-rays tracks, but also beta-rays tracks,
and furthermore, delta-rays tracks arisen from gamma rays.
→ Intuitively radiological education of the difference in interaction
with materials from a kind of radiation-rays
・Cheap price from parts on the consumer market

Comparison of alpha- and beta-ray track

Main Unit

Cockcroft-Walton type HV Unit

Main unit and a connection cable

Van de Graaff type HV unit

A presentation related to this products won
the presentation prize at the JapaneseSociety of Radiation Safety Managem ent.

T his equipment consists of the main unit into which Peltier devices, an air cooling heat-sink, and LED lightings werepacked compactly, and the high-voltage unit. High-intensity LED lighting enable us to observe tracks in the brightroom. Although the power supply of 12V/5V is required, it can obtain using the AT X power supply taken out from oldPC. Cockcroft type HV unit that can be operated continuously is usually attached, while these high-voltage unit acan beused for a stusy of an accelerator, so it is also possible for you to choose a Van de Graaff type as short-time training.

40mmThe operation illustrate of theequipment（ Alpha-ray tracks）

Beta-ray tracks
Observation of radiations using conventional cloud chambers werelimited to only alpha-ray tracks and had many restrictions. While
this Peltier-cooling-type high performance cloud chamber enable us
to observe ve ry cle ar radiation tracks in a few tens of seconds
after a power supply even under a bad weather condition, of cause
without dry ices. T he technical features such as clearing assorted
ions in air using HV-unit, high-intensity LED illuminations and thefabric of the chamber enable us to obse rve be ta-ray tracks. Not
only simple observation of alpha-ray tracks, but also compare withbeta-rays track or a de lta-ray tracks arise n from gamma rays
enables us to perform far deep radiological education related tointeractions of radiations and materials.

Mechanism ofa Cloud Chamber

Liquid alcoholHigh vapor pressure athigh temperature
Ethanol Vapor

Liquid Ethanol Drops

A saturation vapor pressure
decrease at low temperature
Cooled via Peltier device ordry ice to less than -20℃

Supersaturated Vapor

At room temperature, vapor pressure of ethanol is relatively high. This ethanol
vapor getting cold at bottom of the chamber, and then a saturated vapor pressure
decrease and the vapor comes to supersaturated condition. At this condition, small
stimulation makes the supersaturated vapor to tiny liquid drops.

Why we can observe radiation tracks as white stripes?

When a charged particle runs in air, it knock-out manyelectrons from atoms in air, and many pair of plus-ion andminus-ions are generated (Ionizing). These ions in thesupersaturated ethanol vapor, it nucleate tiny liquid drops(Ethanol molecular have polarity and pulled to the ions).
Along the ionizing radiation path, a lot of tiny drops
nucleated in a row. This is why we can observe radiation
tracks as white stripes.
e-+e-

e-++Ionizing

Charged particle

e-+e-++e-

The radiated alpha-particles and electrons are too small to see, and furthermore, the speed ofthe particles does not catch up with a super-high-speed camera. However, the tracks remainin the air and we can observe it. This is the same as the jet stream in the sky. After anairplane flies, a jet stream can be seen remain for a while. A jet stream is created in the highaltitude cold sky where water vapor from the sea come to super saturation, and then theexhaust gas from the engine of the airplane stimulate it to nucleate tiny drop of liquid water,i.e., clouds.

α-rayMaximum range in water: about 50μm

Ionizing

The energy is emitted withina short range at a stretch
Especially, many energy is emmited just before stopping

β-ray

Maximum range in water: about 1cmThe energy is dropped on some places little by little
In fact, electrons does not run straight, but it is scattered and wind zigzag

γ-ray

Almost passthroughElectrons areknocked-out inseveral places

Radiation Weighting factor
Effective dose (Sv) = Σ Absorbed dose(Gy) × Radiation
Weighting Factor × Organization Weighting Factor→ α-Ray: 20, β、γ-Ray: 1

Refrects the different
interaction behavior*For Japanese weigh 60kg

Internal Radioactive Nuclide

Alpha-ray

Effective Doseper one year

Beta-rayK-40: 4,000Bq

170μSv/year

β・γ-Rays

Po-210: 20Bq

800μSv/year

α-R aysRadon and it's doughters radiate alpha-rays → 1.26mSv/year averaged in the world
In Japan: Many people live in wooden house → 0.48mSv/year