senko-educational films presents one of a series of six films dealing with the subject of nuclear radiation [Music] thank you all out is of vitally important subject bombs are being tested which to some extent contaminate the atmosphere it is only natural that we ask ourselves what is the extent of such contamination and what are the possible results the release of atomic energy is always accompanied by certain invisible but powerful radiations nuclear radiations radiations which can be dangerous every time it rains it rains radioactive particles which are in the atmosphere because of the testing of nuclear weapons as a result all of us acquire radioactivity through the food we eat and drink there has always been some nuclear radiation in our environment such background radiation is usually quite small and it comes from two principal sources naturally radioactive substances such as uranium and radium which are found in rocks and soil and Cosmic radiations so named because they are thought to be produced beyond the Earth's atmosphere some cosmic rays are absorbed by the atmosphere but an appreciable amount does get through and consequently has an effect on living things cosmic rays change part of the atmospheric nitrogen 14 to Radioactive carbon 14. carbon 14 in the form of carbon dioxide enters all growing plants during photosynthesis we use many of these plants for food other plants are eaten by animals which are in turn eaten by man thus naturally occurring radioactive atoms are found within all living plants and animals every living thing is exposed to its own internal radiation as well as to radiation from the external background in the more industrially advanced countries such as ours most people have also been exposed to man-made radiations from medical and dental X-rays the average person in the United States receives roughly the same amount of radiation from X-ray and fluoroscopic examinations as he does from natural background radiations the danger from the amounts of radiations thus received is thought to be relatively slight however two important facts should be clearly understood number one radiation effects on living cells are cumulative they add up over a period of time number two most scientists would say that there is no minimum level of radiation below which no damage will be done [Music] in recent years the general public has become increasingly aware of the dangers from yet another source of radiation Fallout from Atomic explosions every nuclear or thermonuclear bomb throws into the air a large cloud of radioactive particles these man-made radioisotopes remain Aloft for varying periods of time but most of them eventually return to Earth it is this return which is known as Fallout to simplify study of its distribution patterns Fallout has been divided into three classes local intermediate and delayed local or close-in Fallout consists of the heaviest particles this type of Fallout is also known as atmospheric Fallout because the particles do not rise above the lower layers of the Earth's atmosphere their Fallout distribution is affected by the local wind patterns atmospheric Fallout is almost always restricted to the immediate area of the explosion it usually Falls within a period of one day and seldom farther than a few hundred miles from ground to zero intermediate Fallout is composed of much lighter particles most of these enter into the troposphere at altitudes between 35 000 and 55 000 feet tropospheric Fallout would descend very slowly if it were pulled down only by gravity actually it descends within a few weeks after the explosion because most of it is washed out of the air by rain and snow radioactive particles in the troposphere are carried around the world by prevailing winds and may spread over large areas of the Earth however it is possible for this type of Fallout to be concentrated in small areas if there is heavy rainfall while the radioactive cloud is overhead the third type delayed or stratospheric Fallout May remain in the air for months or even years meteorologists are attempting to learn more about the interchange of air between the stratosphere and the lower layers at the present time however they do not have sufficient information to predict exactly how long before the radioactive particles will fall or where they are likely to descend recent developments and the miniaturization of electronic components have made it possible to send many information gathering devices high above the Earth these include radiation detectors which measure the amount and kinds of radiation present at various altitudes then these findings are radioed back to Earth exploratory balloons are also used to chart air currents thus we have a clearer picture of probable Fallout distribution principal interest in radioactive fallout concerns the possible danger of biological damage will it hurt people and if so in what ways and how much for a moment let's review the main principal types of radiation alpha particles have a relatively high mass but their penetrating power is very slight alpha particles are easily stopped by a single sheet of paper they will not readily penetrate human skin however alpha particle emitters are dangerous if they enter the human body as in food beta particles are somewhat more penetrating their mass is much smaller but their velocity is greater their penetrating power is such that it takes several sheets of paper or a thin sheet of aluminum to stop them still as in the case of alpha particles betas from radioisotopes must actually be emitted inside the body before any great damage can be done gamma rays which are similar in character to x-rays are very penetrating gamma radiations can be stopped only by Massive shielding they are extremely dangerous from outside the body as well as from within radioactive fallout includes radioisotopes which emit all three alpha particles beta particles and gamma rays fortunately most of the Isotopes formed by the explosion of atomic devices have short half-lives the total level of radioactivity caused by Fallout Fades quite rapidly however some bomb debris remains active for many years it is the buildup of these products which is the cause for our concern the long-term Fallout problem particularly involves strontium-90 cesium-137 and carbon 14. strontium 90 because of a unique combination of properties probably represents the greatest Danger it is one of the more abundant fishing products strontium 90 has a half-life of 25 years and is a relatively strong source of radiation much of the strontium-90 is carried up into the stratosphere it spreads over the whole earth and is gradually deposited during a period of years at the present time strontium-90 is not considered a serious threat but the creation of additional radioactive fallout may cause it to become one we do know that strontium 90 has caused bone tumors in animals under experimental conditions the question of permissible radiation dosage in humans Remains the all-important consideration when we stop to consider that all living matter has always been exposed to some amount of background radiation it becomes evident that relatively small amounts do not cause significant damage most of our knowledge about radiation damage has been obtained from work done with animals in the laboratory but we have learned a great deal about the kinds of damage which may occur the data we have indicate that the effects of radiation in human beings are similar to those found in animals the importance of controlling the amount of radiation to which we are exposed is emphasized by the fact that people who work with atomic energy are required to wear radiation measuring devices careful records of the readings are kept these records help to keep the workers from receiving dangerous dosages when radiating waves or particles pass through a substance some of them bump into molecules and this is serious because of the delicate balance within a living cell each molecule must be just what it is any chemical change however slight May substantially change the normal life processes or even kill the cell every living cell contains a collection of tiny units called genes taken together the genes determine the characteristics with which an individual is born The Inheritance mechanism is particularly sensitive to radiation this has given rise to much concern about radiation-induced genetic mutations the reduplication of genetic patterns is not eternally static every so often a gene changes or mutates and a characteristic of the organism is altered we do not know the exact process by which mutations occur but we do know that they can be caused by radiation once changed the new form of the gene is passed on as Faithfully as the old one was the results of genetic mutation are almost invariably undesirable any radiation dose however small can produce mutations the number of them is in direct proportion to the amount of radiation presently existing evidence indicates that Fallout has caused only a small increase in background radiation and correspondingly only a minute increase in mutations we have discussed some of the major aspects of radioactive fallout The Fallout question is controversial perhaps The only positive statement we can make is that we have so far found no beneficial effect of penetrating radiation on healthy living matter on the other hand we have not observed any significant effect on the health and well-being of the human race as a whole so the studies of radioactive fallout remain inconclusive much has been and is being done in an attempt to solve the many problems involved but this we know mankind needs to proceed with caution knowing that only the future will produce scientifically acceptable answers