(محفظه ابر) اطاق ابر برای رویت ذرات الفا بتا و اشعه کیهانی

محفظه ابر ساخته شده است از یک جعبه اکواریوم شیشه ای با جدار سیاه رنگ که داخل ان مقداری الکل ریخته می شود و می توان با نزدیک کردن فلزاتی که دارای خاصیت رادیو اکتیو هستند و دارای ذرات و الفا و بتا هستند مسر حرکت و خود ذرات را به صورت یک نقطه نورانی و یا ابر ناشی از برخورد بخار الکل رویت کرد در زیر جعبه ابر مقداری یخ ریخته می شود با استفاده از این جعبه حتی می توان ذرات نوری در حد اموج گاما (اشعه کیهانی ) را هم مشاهده کرد

اتاقک ابر یا اتاقک ویلسون (به انگلیسی: Cloud chamber یا Wilson chamber) نوعی محفظه برای آشکارسازی ذرات پرتوهای یونیزان است.

این اختراع را به سال ۱۹۱۱ و به چارلز تامسون ریس ویلسون نسبت می‌دهند.

Cloud chamber محفظه ابر

From Wikipedia, the free encyclopedia

A Cloud Chamber, also known as a Wilson Cloud Chamber, is a particle detector used for visualizing the passage of ionizing radiation.

A cloud chamber consists of a sealed environment containing a supersaturated vapor of water or alcohol. An energetic charged particle (for example, an alpha or beta particle) interacts with the gaseous mixture by knocking electrons off gas molecules via electrostatic forces during collisions, resulting in a trail of ionized gas particles. The resulting ions act as condensation centers around which a mist-like trail of small droplets form if the gas mixture is at the point of condensation. These droplets are visible as a "cloud" track that persist for several seconds while the droplets fall through the vapor. These tracks have characteristic shapes. For example, an alpha particle track is thick and straight, while an electron track is wispy and shows more evidence of deflections by collisions.

Fig. 1: Cloud chamber photograph of the first positron ever observed by C. Anderson.

Cloud chambers played a prominent role in the experimental particle physics from the 1920s to the 1950s, until the advent of the bubble chamber. In particular, the discoveries of the positron in 1932 (see Fig. 1) and the muonin 1936, both by Carl Anderson (awarded a Nobel Prize in Physics in 1936), used cloud chambers. Discovery of the kaon by George Rochester and Clifford Charles Butler in 1947, also was made using a cloud chamber as the detector.[1]. In each case, cosmic rays were the source of ionizing radiation.

Invention اختراع

Charles Thomson Rees Wilson (1869–1959), a Scottishphysicist, is credited with inventing the cloud chamber. Inspired by sightings of the Brocken spectrewhile working on the summit of Ben Nevis in 1894, he began to develop expansion chambers for studying cloud formation and optical phenomena in moist air. Very rapidly he discovered that ions could act as centers for water droplet formation in such chambers. He pursued the application of this discovery and perfected the first cloud chamber in 1911. In Wilson's original chamber the air inside the sealed device was saturated with water vapor, then a diaphragm was used to expand the air inside the chamber (adiabatic expansion), cooling the air and starting to condense water vapor. Hence the name expansion cloud chamber is used. When an ionizing particle passes through the chamber, water vapor condenses on the resulting ions and the trail of the particle is visible in the vapor cloud. Wilson, along with Arthur Compton, received the Nobel Prize in Physics in 1927 for his work on the cloud chamber.[2] This kind of chamber is also called a Pulsed Chamber because the conditions for operation are not continuously maintained. Further developments were made by Patrick Blackettwho utilised a stiff spring to expand and compress the chamber very rapidly, making the chamber sensitive to particles several times a second. A cine film was used to record the images.

The diffusion cloud chamber was developed in 1936 by Alexander Langsdorf.[3] This chamber differs from the expansion cloud chamber in that it is continuously sensitized to radiation, and in that the bottom must be cooled to a rather low temperature, generally colder than −26 °C (−15 °F). Instead of water vapor, alcohol is used because of its lower freezing point. Cloud chambers cooled by dry ice or Peltier effect thermoelectric cooling are a common demonstration and hobbyist devices; the alcohol used in them is commonly isopropyl alcohol or methylated spirit.

Structure and operation ساختار و طرز کار

Diffusion-type cloud chambers will be discussed here. A simple cloud chamber consists of the sealed environment, a warm top plate and a cold bottom plate. It requires a source of liquid alcohol at the warm side of the chamber where the liquid evaporates, forming a vapor that cools as it falls through the gas and condenses on the cold bottom plate. Some sort of ionizing radiation is needed.

Fig. 2: In a diffusion cloud chamber, a 5.3 MeV alpha-particle track from a Pb-210 pin source near Point (1) undergoes Rutherford scattering near Point (2), deflecting by angle theta of about 30 degrees. It scatters once again near Point (3), and finally comes to rest in the gas. The target nucleus in the chamber gas could have been a nitrogen, oxygen, carbon, or hydrogen nucleus. It received enough kinetic energy in the elastic collision to cause a short visible recoiling track near Point (2). (The scale is in centimeters.) From video in Ref.[4].

Methanol, isopropanol, or other alcohol vapor saturates the chamber. The alcohol falls as it cools down and the cold condenser provides a steep temperature gradient. The result is a supersaturated environment. As energetic charged particles pass through the gas they leave ionization trails. The alcohol vapor condenses around gaseous ion trails left behind by the ionizing particles. This occurs because alcohol and water molecules are polar, resulting in a net attractive force toward a nearby free charge. The result is cloud formation, seen in the cloud chamber by the presence of droplets falling down to the condenser. Since the tracks are emitted radially out from the source, their point of origin can easily be determined.[5] (See Fig. 2. for example.)

A Home Made Cloud Chamber

Image taken in the Pic du Midi at 2877 m in a Phywe PJ45 cloud chamber (size of surface is 45 x 45 cm). This rare picture shows in a single shot the 4 particles that are detectable in a cloud chamber : proton, electron, muon (probably) and alpha