hello everyone in this video we're going to look into radioactivity so in the last video we talked about the structure of an atom and specifically we investigate the Solar System model of an atom we know that there is a nucleus in the center of every atom and today we're going to look into what happens when this nucleus undergo a Decay process and what are the particles that it releases following the decay so we'll start off with introduction for radioactive substance is a substance that decays by emitting radiation from its Atomic nuclei and there are two ways in which radioactive element can affect us versus contamination if you eat something that involve um that it that has radioactive element on it we say that we have been contaminated and the other way is that this radioactive substance can hit our bodies and that's when we receive a dose of radiation and we have been irradiated so here are some of the sources of radiation first one is from the air that we are breeding now and the air is radioactive it contains the radioactive gas called Radian which sits out from the Earth surface from radioactive uranium rocks underground the other thing is that because we stay in a home like that we also um taking radioactive substance from the ground and because we use materials from the ground to build our houses so radiant shape can also reach us via cosmic ray from from the space so that's um they are all natural radiation source and for artificial radiation Source it could be x-ray gamma ray and also medical and radiography and stuff in a nuclear power station they also work with radiation so in order to detect radiation we can use this device called geiger counter they um the unit to calculate how much radiation there are is called the concrete that kind of concrete the more radioactive particles there are so let's look into the process of radioactive decay is when radiation coming out from them so it is the process when a new an unstable nucleus remember Nuclear Physics is about the studying of nucleus so and when an unstable nucleus give out radiation it will be then become more stable and why is it why will it become unstable at the first place it could be due to they have too many protons and or that they have too many electrons so radioactive decay is a random process means you can't really manipulate it it just happens nucleus just undergo the Decay and then you cannot affect its rate of Decay by increasing temperature and so on and so forth so when after a nucleus undergo Decay it will release one of these three elements it can be a combination too but these are the three elements that it will release and these three elements are also what we call the radiation first one is alpha particle beta particles and Gamma particles and I have created a table to show their differences this is how they look like and they are symbols for alpha particles we have learned in last video they have two protons and two neutrons beta particles basically and electrons gamma rays is just an electromagnetic radiation remember the electromagnetic spectrum and the charge is positive because they have two protons and verbena is negative and Gamma is neutral so what happens after nucleus emits these particles is that they will become another elements remember the equation that we learned so what happened is that um if they alpha particles the element will change as I will show in the next few slides so another way we can compare the three different radiation is from the penetrating power so if you look at how this picture elastic perfectly how different radioactive substance they have different penetrating power alpha particle is the weakest they can only travel past paper beta can travel until aluminum and get radioactive gamma ray can pass through let so for alpha particles they'll absorbed most most easily therefore they have very little penetrating power they cannot penetrate through our skin and as for beta they can travel through error and paper can be absorbed by metal like like this aluminum and for gamma arrays most penetrating that's why we use it for cancer treatment it takes several centimeter of dense method like let to absorb it so if you were to rank the penetrating power gamma will be the first beta second alphared so that's when how when we compare the penetrating power another thing we can compare is the ionization power so before that let's look at their speed you can see that gamma ray is the fastest and alpha particles is the slowest and the math because they have more um there's more nucleons will be mass time proton times four and electrons mass of electrons gamma ray has no Mass the charge is depend on the number of protons they have so for ionization we've learned from the last slide that alphabetical is the least penetrating that's because they are the most strongly ionizing they can be most easily absorbed and they can they are able to ionize something easily because of the protons that they have all right so that's that's the description and beta particle is less ionizing as competitive alphabeticals because it's just an electrons right and they can travel further in air without getting absorbed that's why they can travel past this paper and as for gamma ray it is uncharged it is also a lease ionizing because it just can't ionize it it travels too fast and then it penetrates through something very quickly very easily so here I just want to show you two presets which involve the release of Outback particles and beta particles start of alpha decay so you can see that one example is the element uses called amerism so once it undergoes alpha decay it turns to uranium plus the helium particles with some energy that's when I say it when the particle when an element undergo rate alpha decay or beta Decay they turns to another element because of the extra particles that they produce and again you can compare the difference between the nucleon and also the proton number they are the same before and after the reaction so as for beta Decay is from let's say carbon and turn to another element plus electrons plus energy so this is the beta particle at this point you might ask hey I noticed that the number of protons increases after the reaction and where does this proton and where does this electron come from so um that's because in this reaction one of the new Neutron one of the neutron they are being split into one proton and also one electrons and that's the equation for that process and this proton here contributed to the extra proton in the element and then electrons and surfacial and that explains how beta decay occurs and also its equation and that's this part of the graph it is the beta particle so radiation may knock electrons out of atom this means the ions are formed this is process called ionization because once you knock this electron off now proton will have a higher you'll have higher proton number in the element so be positively charged that's called ionization making some making an iron so as radiation emitted by the nuclei of the radioactive substance causes ionization it is also known as ionizing nuclear radiation meaning the radiation process cause ionization so there is another way we can tell let's say you are carrying out an experiment you don't know which one is which there are two experiments that we can carry out to identify whether this is an alpha particle beta particles or electromagnetic radiation so if you look at this plate here we have electrically charged plate one is positive and negative so because opposite charges attract a charger so without seeing looking at the label we know that the radiation substance that is attracted to the positive slate will be the beta array because beta array is negatively charged it is attracted to the positive plate whereas the other plates here that is attracted to the negatively charged plate will be the alphabetical because alphabetical is positively charged and for the electromagnetic I mean the gamma array since it's not charged therefore it's not going to be attracted and the other way we can tell is to put a magnetic in between them so what happened is that we have magnetic field and then this uh Alpha and beta particles they are they have electric charge so in other words we have magnetic field electric charge we can then deduce the motion of where the radioactive substance will be going and we learned this in chapter 20 when we learn about flaming left hand rule so by using flaming left hand rule you can try that out just point your finger according to the magnetic field not to soft and then alpha particles electric current flow and then you'll find out that uh the force the direction of force that is exerted on the radioactive substance so that's when flaming left hand rule comes in so um now we have learned the three different types of radioactive particles let's look into how fast how do we quantify how fast the nucleus will decay and that's when we have the term called activity the rate at which a radioactive Source nuclei decay so the activity of the source decreases with time meaning um as time goes by it the case slower and slower as nuclei Decay and becomes stable they are more unstable nucleus so there are fewer decades per second so in order to explain this sentence just look into this yeah so imagine that um this is the element and that and their nucleus so what happened here is that asthma and more nucleus undergo Decay right um the rate of Decay will get slower because there's less nuclei remaining so that's basically what it means here um in fact I have a Decay graph you can see that the graph shows that the amount of radioactive substance decreases rapidly at first and then more and more slowly in fact the graph tears off slowly more emotionally we cannot see when the last atom will decay so different reactive substances they Decay at different rates so but then how do we quantify how fast it is we use the term half-life half-life of radioactive isotope is the average time taken for half of the atom in the sample to Decay or the time phase activity to occur into half so it doesn't mean that uh after two Half-Life every atom will have Decay and that's that's just not the case um I think the proper explanation would be like that imagine you have 16 atoms um what Half-Life means is that after a particular Half-Life half of this atom represented by the red color will have Decay and then on the other half uh live the remaining atom like one two three four five six seven eight so these are the remaining atoms that half of this atom will Decay so it will lead at four and then another Half-Life you left two then one so that's more like the concept of half-life great so let's do some work example strontium 90 has a housewife of 28 years so that means for 20 they only decaf to 28 years the count rate of a sample is 480. how long would it take for the country to drop to 30. so we know that initially they have a counter of um 480 remember Curry is how we'd identify the radioactive substance and after 28 years half of them will indicate meaning now I'll have 240 calorie um should be count per second yeah and another 28 year it will be 120 another 28 it will be 60. and it's only after another 28 years it will turn to 30. so you can see that we have undergo for 28 years so the answer should be 4 multiplied by 28. and that's how I show it um therefore the answer is that it takes 112 years for the country to drop to 30. great so um when doing this type of question do know that sometimes we also want to consider the background concrete remember radiation Source can come from the ground the house anywhere so we need to consider the background coverage so how we can get the corrected Cloud rate of the substances that whatever we measured we minus the current rate then we this is our exact corrected comrade so let's solve a question to understand it the current rate of radioactive material is measured and the reading is 88 the background is 40 meaning the actual count rate of the substance is 88 minus 40 which is 48. and the half-life of the radioactive substance is 12 hours what is the reading of the detector after 24. so we know that initially we didn't know that it's 48 so this is the substance that will undergo decay so after 12 hour it will be 24 another 12 hours since we are looking at 24 it will be 12. so for this substance is 12 countries per second but we of course what the geiger counter will show is they will include the background radiation so whatever we calculated here we need to plus back the 40 count rate from the natural radiation source so whatever it will show 42 on the guide 52 on the geiger counter all right so that's about it oh it's 12. but the correct answer should be 52. we need to plus 40 there's an arrow on my slide and that's about it great so let's look into some of the usages of radioisotopes I will just go through this because I think they are self-explanatory you can always read the slide of one usage of radioisotopes is smoke detector how it works is that the smoke detector contains America which emits alpha particles therefore this alpha particles will ionized air in a smoke detector so um if smokes comes in it detects it disrupts the iron flow then the alarm will get triggered so that's something that um Howard isotope is used second example would be thickness measurement we know that different elements have different penetrating power um first of almost alpha beta radiation is aimed at the paper the amount of radiation that passed through the vapor is detected all right measured by a sensor so if the paper here is too thick then it will absorb a lot of the better particles and the reading will then be different so the sensor will detect when there's an abnormal reading and then control the paper thickness accordingly so here they bit up radiation is used because alpha particles would have been absorbed by the paper here it won't be detected by sensor and then for gamma array it will just pass through without much effect even if this paper is very thick so beta particle is the right choice cancer treatment gamma ray is used to aim at the tumor and then so the technique ensure that other tissue receive only a minimum dose of radiation because gamer is very they just Target at the affected area so cancer treatment is one of the usage food evaluation um gamma ray can also kill micro probes so this results in Stereo food and that's this also ensures that the food is properly preserved sterilization of equipment like what I said similarly to what if the food example here they can be used to sterilize all the equipments and for medicine is this is interesting um they are used to identify a blockage in the kidney so the process involves injecting the patient with a radioactive chemical and the scanner is used to trace the path of the chemical the technique allowed for the detection of abnormal areas of growth aiding in the diagnosis of disease because we can't see through what is inside our organisms so they inject this radioactive chemical so for kidney blockage they inject this specific element and then if the kidney is blocked the Tracer will not pass through indicating the presence of a blockage and because why this is this is because they have very short half-life meaning they will Decay very quickly it won't stay in the body for too long so they are used in this example and another one is engineering it's very much like the tracing example for engineering here they just inject some radioactive materials into the pipe and if there's a blockage in the pipe there um means that this radioactive elements will not pass through it all right so again again they allow them to track the flow of water and identify any pathway that could lead to contamination of local water supply I'm just reading it because I think I couldn't explain much here it will make the video very lengthy so if you want to revise the subject using this slide you can always purchase it on my website all right so another example usage of radioactive isotope is Radio carbon dating it's not like a dating thing but it's a technique that helps us to identify how long has you know this object has been like a radioactive like the dinosaur Stone so how it works is that because carbon is present in all living organism so when some an organism die the carbon 14 will begin to Decay so by looking at how much carbon 14 is inside a particular organism we we will know um how long has this organism died because um we we know how the half-life of this substance right so that basically help us to identify how long a living organism has passed away like a dinosaur right so you can read it so um of course there are some safety precautions when it comes to using this elements because there are three ways that radiation can damage living cell they can kill us all they could also cause cancer by mutating um by the DNA mutation because if you learn biology radiation could cause uncontrollable mitosis right they also change your Gene which leads to um very a different generation so yeah yeah so the change DNA will affect your offspring wait so the alpha particles here they said it is less likely to harm us but then if it enters us our body then we will probably um it will probably lead to the development of lung cancer it kind of hurt us on the outside because it's not very penetrating so some safety precautions for workers working in a area that has a lot of radioactive elements just wear a suit put in label to remind people and then photographic film don't match like for badges they track how much radiation someone is exposed to so if the value get too high then probably you have to walk away record keeping right that's pretty um straightforward remote operated thing of scanners so calculate the distance between them and the radiation Source storage box for sauces so that um radiation won't leak out of the box so let's try to solve some passive question all right a student carried out an experiment to find out the half-life of radioactive substance their results are shown in the table share what is the half-life of this substance so remember Half-Life is the amount of time for this element to decrease by half so we need to try go at what point it reaches half of the original country which is for 150 so you can see that it takes 40 seconds therefore the half-life is 40. B second question we have look at this diagram later already X it can only pass through b you can't even pass through paper therefore it will be alpha particles C and D are incorrect and for y it can pass through everything therefore y should be a gamma array and for that it can only pass through aluminum so it should be beta particles my answer should be a so that's oops sorry yeah I make a mistake here should be the Y here should be beta um gamma array So my answer should be B right y great next one which statement is not a method used to minimize the risk so store the sources in the light LED line box that's correct proper storage minimize the amount of time spent handling yeah that's correct keep the sauce cool that's not correct because we know that radioactive decay the process cannot be manipulated by temperature So my answer is C great so next one radioactive sources are used in manufacturing process the diagrams shows how radiation used to measure the thickness okay so um for this one we know that um the answer is beta particles that's something that we learned because um for Elf gamma ray it will just pass through it it will make no difference to to whether the aluminum is stick or not and alphabetical would just be absorbed so that it will not be suitable so next one a nucleus of uranium undergo an amid an alpha particles which equation correctly describe this process it's already mentioned in when we compare the three radioactive particles right so initially it's uranium turn to the helium I mean no not helium but alpha particles for this in order to know what is the correct answer we just need to look into the element it doesn't for Uranium this is confirmed not correct because they are the same this is the same element this is not what we want and then for Uranium Decay they also do not need to be combined with in alphabeticals that's also incorrect and for the fourth answer is either the number four or D or a if you look at d right the number of protons does not when they add up 2 plus 88 will be equal to 90 and it doesn't match 92. so the correct answer should be a in which the proton number before and after the reaction matches um left and right hand side so a so next one the last question a radioactive substance has a half-life of four days it emits 8 000 particles per minute how many particles will you only per minute after 12 days so it has a half-life of four days meaning after four days it'll be four thousand after eight days another four day will be two thousand since we are looking at 12 day just do another one 1000 so the answer should be C and that's it and that's about it for this chapter so in this video we have companion contrast the different radioactive substance alpha beta and gamma and let me know if you have any question in the comment section and I will try my best to help you thank you so much for watching see you in the next video