An Introduction to Radiation Detection Instruments (1950)

[Music] la an atomic blast when matter is transformed into energy by a nuclear fishion something is created which is more than a pyrotechnic display and blast energy common to ordinary explosions Hiroshima is visible evidence of the tremendous physical energy released by an atomic explosion but other forms of energy such as the ionizing radiation given off by the radioactive particles in the atomic Cloud must also be considered these radioactive particles can be distributed over wide areas by the wind or precipitated by rain with possible harmful effects moreover with certain types of bursts many substances in the vicinity of the blast can be impregnated with fishing product which will emit ionizing radiation in harmful and even deadly amounts over long periods of time any atom burst is a breeder of dangerous radiations but test Baker at bikini prove that the shest spreaders of such contamination are submarine and possibly underground detonations but whether these radiations are absorbed into the body by contact by ingestion or by exposure ionizing radiation May disrupt the molecular structure of the various and complex substances which constitute a living organism but how do you identify and measure a menace that cannot be seen has no taste no odor and cannot be heard this is the question that must be answered if man is to intensify and broaden his use of atomic power today the ability to wage Atomic Warfare is shared with others next time we may be on the receiving end if that happens we can't arbitrarily condemn a center of population as a no man's land because of contamination it may be vital and strategic in a military sense or as a key in industrial center there'll be Salvage operations fires to fight relief and rescue work what can be done in a bombed area what procedures should be followed these are questions for the Command Decisions of authorities like all momentous decisions they must be based on facts there will be no guesswork because of radiac instruments radiac short radioactivity detection identification and computation these instruments are miracles of sensitivity designed to provide us with a sixth sense each has a special use and purpose but all of them share one thing in common they measure the ionization produced by radiation ionization the action that occurs in a radiac device is better Illustrated than defined think of it as a game of atomic pocket billiards the white balls represent the nucleus of an atom the black ones its electrons arranged in orbits like the planets of a solar system around its Sun the CU ball is radiation which strikes an electron knocking it away from its atom and thereby producing an ion pair another hit another score this is the game that goes on in a pocket dosimeter it has a dial that what the player is doing it keeps score and the pocket of the table represents the instruments collecting electrode a pocket decimeter is basically an electroscope like this which you'll probably remember from your high school physics the electroscope with the leaves of its electrodes together is dead uncharged by passing a comb through the hair a St itic electric charge is picked up and transferred to the electroscope the metal leaves carrying the same charge repel each other but the radiation given off by a radium button produces ions which neutralize the charge the motion of the leaves as they collapse is a measurement of radiation the movable Leaf of the pocket decimeter is a tiny quartz fiber about 110,000 of an inch thick to prepare a doemer for use a charge is placed on it with a charging box so that its graduated scale read zero the scale is marked in Renkin which is the unit employed in measuring a quantity of ionization when the indicator is set on zero the decimeter is properly charged and ready for use another radiac device used to safeguard Personnel is the pocket chamber unlike the dosimeter it has no scale and may not be read directly pocket decimeters and Chambers give readings of total amount of radiation exposure just as the mileage counter registers total distance but since a harmful amount of radiation can be absorbed very quickly in a heavily contaminated area it is necessary to have instruments which will give readings of radiation intensities at any particular time again like a speedometer which gives you the rate of travel for field survey work if measuring high intensity of gamma radiations an ionization chamber survey meter is used unlike the pocket devices this meter charges Itself by its own self-contained batteries here's another survey meter this chamber collects the ions produced by Gam radiation which is the most penetrating kind but this a thin window ion chamber may be used to detect Alpha and beta as well as gamma radiation gamma rays which are the most likely to affect Personnel because of their High penetrating ability pass through the case of the instrument with ease but beta particles cannot enter and neither can alpha particles the least penetrating of the three kinds of radiation but when a knob on the chamber is turned opening a slide on its Underside both beta and gamma are admitted but not Alpha that's solved by turning a second knob opening another slide now now it is possible to read Alpha as well as beta and gamma radiations the proportional counter which has a greater charging voltage than an ion chamber will count alpha particles in the presence of a strong beta gamma background to appreciate its selectivity think of an Orchestra conductor whose trained ears are attuned to pick out from a mass of Music the distinctive sound of a single instrument [Music] another useful instrument is the guer counter its sensitivity is achieved by a further increase in charging voltage in these instruments ions are speeded up toward the collecting electrode producing secondary ionization One initial pair of ions can cause up to a billion events which Avalanche toward the electrode it's like a landslide touched off by a rolling stone Gathering momentum and mass and ending in a crashing climax radiation intensity is registered on the dial of a Geer counter and it can also be heard through earphones conceive of a hearing aid that would make a Tumo out of the movement of a fly on the wall and you'll get an idea of the amplifying powers of a Geer counter these then are some of the miraculous members of the radiac family but before they are used they all must be calibrated just as guns are properly cited prior to firing let's watch while this man prepares to calibrate these gamma survey meters he will have to work in a radioactive area and even as a doctor protects himself while working with infections he'll keep a check on himself by means of pocket decimeters or Chambers and as in this case with a film badge which he'll wear while doing the calibrating he checks the accuracy of the meter by taking readings at fixed distances from a radioactive source of known intensity which is a Cobalt 60 capsule the reading is recorded then the instrument is moved to the next Mark where the procedure is repeated other techniques are used for Alpha and beta instruments assume an atomic bomb explodes in the region of an important military establishment like a Marine green base at Air Force [Music] Base a Naval Shipyard an army camp disaster control plans are immediately put into action in Atomic Warfare and urgent problem confronting the commander is to determine whether or not there are any radiological hazards in the area of a bomb explosion so the monitors go into action their job is to get the facts through the prompt and effective use of radiac instruments except for high Air Bursts atomic bomb explosions particularly surface or subsurface explosions may leave some ground radioactivity or radiological Warfare agents may be disseminated the existence and seriousness of these hazards must be determined their pocket dosimeters give the monitors the radiation dosage to which they have been exposed in a suspected area monitors proceed with caution they wear protective clothing check themselves frequently each zone is covered thoroughly readings are taken and transmitted to a Communication Center this information is turned over to a control center which maintains a continuous estimate of the radiological situation hot spots are recorded these points of contamination are the dangerous rocks and shs of an area to which an a bomb has paid its violent visit the monitors leave nothing uncovered specimens are taken for laboratory analysis Earth being porous is susceptible to Serious contamination samples are carefully prepared for examination the prepared sample is put into a lead Shield containing a counter tube which transmits information to a scaler this furnishes data for determining the rate of radioactive decay the alpha activity of the sample is measured by a laboratory proportional counter there are other techniques for estimating the amount of alpha activity when you examine under a microscope a special photographic plate that has been exposed to such emissions you see this what roughly res resembles a culture of bacteria are really tracks made by alpha particles as these laboratory and field operations continue monitors themselves must be examined for contamination they tenet decontamination posts and turn in their film Badges and pocket meters if contaminated Beyond a usable condition the monitors consign their disposable outfits to the rag pile for Destruction the men undergo a thorough survey and the added precaution of a soap and water treatment film badges are recorded development and pocket Chambers are red everyone gets the full treatment but wait a moment those Clicks in the earph spell radiation intensity and when it's a steady cracker like that uh-oh where you been sitting m a monitor frequently makes direct contact with contamination especially when he sits down and when he does he loses his pants but the film badge he turned in isn't lost it's sent to a photo lab radiation takes its own picture producing blackening of the Badger's photographic film the lead cross ad it's only gamma radiation the exposed portion gamma plus beta the film is developed and read with a densitometer which measures the darkening of the film in comparison to a blank unexposed specimen of the same film stock the technician files the film away in a rogue's gallery of radioactivity as a permanent record following the initial emergencies brought by an atomic bombing comes reconstruction work the advanced Scouts and watchdogs for the repair parties are the monitors as soon as possible utilities are restored to operational efficiency the search for patches of strong radioactivity is exhausting when found steps are taken to cover them nothing escapes the monitor's attention normal living and daily routines are resumed in a bombed area as quickly as monitors can give Assurance of safety they inspect food and Provisions for possible contamination they collect water for laboratory study Atomic Warfare has widened the field of radiation detection bringing the instruments from the cloyed confines of scientific Laboratories into the open efforts continue to perfect them for field work to make them more compact mobile and rugged whether the Loft on land or at sea l