1 00:00:04,733 --> 00:00:05,833 - RADIOACTIVITY. 2 00:00:05,833 --> 00:00:07,433 THERE ARE LOTS OF THINGS THAT CAN GIVE OFF 3 00:00:07,433 --> 00:00:10,500 SMALL OR LARGE AMOUNTS OF ENERGY AND PARTICLES 4 00:00:10,500 --> 00:00:13,500 THAT WE REFER TO AS BEING RADIOACTIVE, 5 00:00:13,500 --> 00:00:15,833 INCLUDING MINERALS THAT COME OUT OF THE EARTH 6 00:00:15,833 --> 00:00:18,166 AND HELPFUL MEDICAL TECHNOLOGIES. 7 00:00:18,166 --> 00:00:20,000 EVEN BANANAS AND YOUR OWN BONES 8 00:00:20,000 --> 00:00:23,500 CONTAIN SUBSTANCES THAT ARE SLIGHTLY RADIOACTIVE. 9 00:00:23,500 --> 00:00:26,000 IN 1898, MADAME MARIE CURIE 10 00:00:26,000 --> 00:00:28,166 FIRST USED THE WORD "RADIOACTIVITY" 11 00:00:28,166 --> 00:00:30,666 TO DESCRIBE THE ABILITY OF CERTAIN ELEMENTS 12 00:00:30,666 --> 00:00:32,833 TO GIVE OFF INVISIBLE ENERGY. 13 00:00:32,833 --> 00:00:35,000 BUT DID YOU KNOW THIS TYPE OF ENERGY 14 00:00:35,000 --> 00:00:37,500 CAN BE USED TO EXPLORE THE SOLAR SYSTEM? 15 00:00:37,500 --> 00:00:40,600 FIND OUT HOW, NEXT ON "REAL WORLD." 16 00:00:47,566 --> 00:00:49,833 WHEN MOST PEOPLE HEAR THE WORD "RADIOACTIVITY" 17 00:00:49,833 --> 00:00:52,500 THEY THINK OF MYSTERIOUS GLOWING SUBSTANCES, 18 00:00:52,500 --> 00:00:55,000 NUCLEAR POWER PLANTS, OR WEAPONS. 19 00:00:55,000 --> 00:00:57,500 BUT YOU MIGHT NOT BE AWARE OF THE VAST DIFFERENCES 20 00:00:57,500 --> 00:01:00,433 BETWEEN THE DIFFERENT RADIOACTIVE SUBSTANCES. 21 00:01:00,433 --> 00:01:01,833 THESE DIFFERENT SUBSTANCES 22 00:01:01,833 --> 00:01:04,000 GIVE OFF DIFFERENT AMOUNTS OF ENERGY 23 00:01:04,000 --> 00:01:06,433 AND HAVE ALL KINDS OF PRACTICAL USES 24 00:01:06,433 --> 00:01:07,966 FROM BONE IMAGING 25 00:01:07,966 --> 00:01:09,300 TO SMOKE DETECTORS; 26 00:01:09,300 --> 00:01:10,600 ARCHAEOLOGICAL DATING 27 00:01:10,600 --> 00:01:12,033 TO FOOD PROCESSING. 28 00:01:12,033 --> 00:01:15,233 BUT WHAT MAKES A MATERIAL RADIOACTIVE TO BEGIN WITH? 29 00:01:15,233 --> 00:01:17,000 LET'S START WITH SOME BASICS. 30 00:01:17,000 --> 00:01:20,166 ALL MATTER IS MADE UP OF PARTICLES CALLED ATOMS. 31 00:01:20,166 --> 00:01:22,666 AND ATOMS ARE MADE UP OF SMALLER PARTICLES-- 32 00:01:22,666 --> 00:01:25,433 PROTONS, NEUTRONS, AND ELECTRONS. 33 00:01:25,433 --> 00:01:27,333 ATOMS OF A GIVEN ELEMENT 34 00:01:27,333 --> 00:01:29,333 ALL HAVE THE SAME NUMBER OF PROTONS, 35 00:01:29,333 --> 00:01:32,000 BUT THE NUMBER OF NEUTRONS CAN VARY. 36 00:01:32,000 --> 00:01:33,400 ATOMS OF THE SAME ELEMENT 37 00:01:33,400 --> 00:01:35,166 WITH A DIFFERENT NUMBER OF NEUTRONS 38 00:01:35,166 --> 00:01:37,833 ARE KNOWN AS ISOTOPES OF THAT ELEMENT. 39 00:01:37,833 --> 00:01:40,333 NOW, SOME ISOTOPES ARE STABLE, 40 00:01:40,333 --> 00:01:42,200 MEANING THEY DO NOT CHANGE OVER TIME; 41 00:01:42,200 --> 00:01:44,433 OTHERS ARE UNSTABLE. 42 00:01:44,433 --> 00:01:48,500 WE CALL THESE UNSTABLE ISOTOPES "RADIOISOTOPES" 43 00:01:48,500 --> 00:01:50,333 BECAUSE, TO BECOME MORE STABLE, 44 00:01:50,333 --> 00:01:52,666 THEY RADIATE, OR GIVE OFF ENERGY, 45 00:01:52,666 --> 00:01:55,466 USUALLY MOVING PARTICLES PLUS HEAT. 46 00:01:55,466 --> 00:01:58,833 AND THIS PROCESS IS CALLED RADIOACTIVE DECAY. 47 00:01:58,833 --> 00:02:01,666 - RADIOACTIVE DECAY IS WHAT HAPPENS 48 00:02:01,666 --> 00:02:03,833 WHEN AN ATOM IS TRYING TO GET TO A STABLE STATE, 49 00:02:03,833 --> 00:02:05,633 THAT IS, A BALANCED STATE. 50 00:02:05,633 --> 00:02:07,833 - YOU HAVE A VERY UNSTABLE ATOM 51 00:02:07,833 --> 00:02:09,500 THAT LIKES TO EMIT THINGS 52 00:02:09,500 --> 00:02:14,333 FROM ALPHA PARTICLES TO BETA PARTICLES 53 00:02:14,333 --> 00:02:16,666 TO SOMETIMES GAMMA RAYS. 54 00:02:16,666 --> 00:02:17,833 BUT WHAT IT'S DOING IS, 55 00:02:17,833 --> 00:02:20,166 IT'S TAKING AN UNSTABLE ATOM 56 00:02:20,166 --> 00:02:22,333 AND GOING TO A MORE STABLE STATE 57 00:02:22,333 --> 00:02:24,666 AND RELEASING ENERGY DURING THE PROCESS. 58 00:02:24,666 --> 00:02:26,666 - ONE OF THE MOST IMPORTANT THINGS TO KNOW 59 00:02:26,666 --> 00:02:28,166 ABOUT THIS WHOLE PROCESS 60 00:02:28,166 --> 00:02:31,333 IS THAT THE RATE AT WHICH ANY RADIOISOTOPE DECAYS 61 00:02:31,333 --> 00:02:32,700 IS PREDICTABLE. 62 00:02:32,700 --> 00:02:34,000 UNDER THE SAME CONDITIONS, 63 00:02:34,000 --> 00:02:36,433 YOU CAN COUNT ON IT TO HAPPEN THE SAME WAY 64 00:02:36,433 --> 00:02:38,000 OVER AND OVER. 65 00:02:38,000 --> 00:02:39,833 NOW, FOR UNSTABLE ATOMS, 66 00:02:39,833 --> 00:02:43,333 THERE'S NO WAY OF TELLING WHEN AN INDIVIDUAL ATOM WILL DECAY, 67 00:02:43,333 --> 00:02:45,000 BUT THROUGH CAREFUL MEASUREMENT, 68 00:02:45,000 --> 00:02:47,833 IT IS POSSIBLE TO PREDICT HOW LONG IT WILL TAKE 69 00:02:47,833 --> 00:02:49,666 FOR A LARGE NUMBER OF THEM, 70 00:02:49,666 --> 00:02:53,800 SAY HALF OF THE ATOMS IN A GIVEN SAMPLE, TO DECAY. 71 00:02:53,800 --> 00:02:55,000 AS THE ATOMS DECAY, 72 00:02:55,000 --> 00:02:57,566 THEY CHANGE FROM ONE ELEMENT INTO ANOTHER. 73 00:02:57,566 --> 00:02:58,666 THE TIME IT TAKES 74 00:02:58,666 --> 00:03:00,833 FOR HALF AN AMOUNT OF ANY RADIOISOTOPE 75 00:03:00,833 --> 00:03:03,166 TO DECAY INTO ANOTHER TYPE OF ELEMENT 76 00:03:03,166 --> 00:03:05,500 IS CALLED ITS HALF-LIFE. 77 00:03:05,500 --> 00:03:10,000 - HALF-LIFE IS THE AMOUNT OF TIME IT TAKES 78 00:03:10,000 --> 00:03:15,033 FOR HALF OF THE RADIOISOTOPES TO DECAY 79 00:03:15,033 --> 00:03:19,000 FROM A MORE UNSTABLE STATE TO A MORE STABLE STATE. 80 00:03:19,000 --> 00:03:23,066 AND ATOMS OF DIFFERENT TYPES HAVE DIFFERENT WAYS OF DECAYING 81 00:03:23,066 --> 00:03:27,300 FROM THIS MORE UNSTABLE STATE TO THE MORE STABLE STATE. 82 00:03:27,300 --> 00:03:30,000 - IT IS JUST THE NATURE OF THE ELEMENT 83 00:03:30,000 --> 00:03:32,000 AND OF THE ISOTOPE OF THAT ELEMENT 84 00:03:32,000 --> 00:03:34,333 HOW LONG THAT HALF-LIFE IS. 85 00:03:34,333 --> 00:03:37,166 AND IT'S A NATURE OF HOW-- 86 00:03:37,166 --> 00:03:38,833 WHAT KIND OF ENERGY IT'S RELEASING, 87 00:03:38,833 --> 00:03:41,500 WHETHER IT'S GAMMA RAYS, WHETHER IT'S HEAT, 88 00:03:41,500 --> 00:03:43,333 WHETHER IT'S OTHER PARTICLES. 89 00:03:43,333 --> 00:03:45,000 - HALF-LIVES VARY GREATLY-- 90 00:03:45,000 --> 00:03:47,666 FROM MILLISECONDS TO BILLIONS OF YEARS-- 91 00:03:47,666 --> 00:03:51,466 BUT EACH RADIOISOTOPE HAS ITS OWN RATE OF DECAY. 92 00:03:51,466 --> 00:03:54,000 FOR EXAMPLE, IODINE-131 93 00:03:54,000 --> 00:03:56,500 HAS A HALF-LIFE OF ONLY EIGHT DAYS, 94 00:03:56,500 --> 00:03:58,333 WHILE CHLORINE-36 95 00:03:58,333 --> 00:04:02,066 HAS A HALF-LIFE OF 300,000 YEARS. 96 00:04:02,066 --> 00:04:05,166 SUPPOSE YOU HAVE 32 GRAMS OF SODIUM-24, 97 00:04:05,166 --> 00:04:07,833 WHICH HAS A HALF-LIFE OF 15 HOURS 98 00:04:07,833 --> 00:04:10,566 AND DECAYS INTO MAGNESIUM-24, 99 00:04:10,566 --> 00:04:12,800 A STABLE FORM OF MAGNESIUM. 100 00:04:12,800 --> 00:04:15,500 AN UNDERSTANDING OF HALF-LIFE AND SOME SIMPLE MATH 101 00:04:15,500 --> 00:04:16,666 CAN HELP YOU DETERMINE 102 00:04:16,666 --> 00:04:19,000 HOW MUCH OF THE ORIGINAL MATERIAL EXISTS 103 00:04:19,000 --> 00:04:21,633 AFTER A GIVEN PERIOD OF TIME. 104 00:04:21,633 --> 00:04:23,166 AFTER 15 HOURS, 105 00:04:23,166 --> 00:04:24,666 HALF OF THE SODIUM-24 106 00:04:24,666 --> 00:04:27,166 WOULD HAVE DECAYED INTO MAGNESIUM-24, 107 00:04:27,166 --> 00:04:30,333 LEAVING 16 GRAMS OF THE ORIGINAL ISOTOPE. 108 00:04:30,333 --> 00:04:31,833 AFTER 30 HOURS, 109 00:04:31,833 --> 00:04:34,666 THERE WOULD ONLY BE 8 GRAMS OF SODIUM-24 LEFT, 110 00:04:34,666 --> 00:04:36,000 AND SO ON, 111 00:04:36,000 --> 00:04:39,000 UNTIL THERE'S NOT ENOUGH SODIUM-24 LEFT IN THE SAMPLE 112 00:04:39,000 --> 00:04:41,166 TO DETECT ITS RADIOACTIVITY. 113 00:04:41,166 --> 00:04:44,333 SO NOW THAT YOU KNOW MORE ABOUT RADIOACTIVITY AND HALF-LIFE, 114 00:04:44,333 --> 00:04:47,833 HOW DOES NASA USE MADAME CURIE'S "INVISIBLE ENERGY" 115 00:04:47,833 --> 00:04:50,000 TO EXPLORE THE SOLAR SYSTEM? 116 00:04:50,000 --> 00:04:52,333 WELL, SINCE HALF-LIFE IS PREDICTABLE, 117 00:04:52,333 --> 00:04:55,000 SCIENTISTS AND ENGINEERS CAN USE THIS KNOWLEDGE 118 00:04:55,000 --> 00:04:56,500 TO CREATE POWER SOURCES 119 00:04:56,500 --> 00:04:58,500 THAT RELY ON THE PREDICTABLE HEAT 120 00:04:58,500 --> 00:05:01,666 GIVEN OFF BY RADIOISOTOPES AS THEY DECAY. 121 00:05:01,666 --> 00:05:04,333 NASA'S RADIOISOTOPE-POWERED SPACECRAFT 122 00:05:04,333 --> 00:05:08,333 USE A UNIQUE ISOTOPE CALLED PLUTONIUM-238, 123 00:05:08,333 --> 00:05:11,166 WHICH IS PROVIDED BY THE DEPARTMENT OF ENERGY. 124 00:05:11,166 --> 00:05:13,700 IT HAS A HALF-LIFE OF 88 YEARS 125 00:05:13,700 --> 00:05:15,000 AND GIVES OFF HEAT 126 00:05:15,000 --> 00:05:18,133 PLUS LOW-ENERGY PARTICLES CALLED ALPHA PARTICLES. 127 00:05:18,133 --> 00:05:20,500 THE FACT THAT IT'S A LONG-LIVED SOURCE OF HEAT 128 00:05:20,500 --> 00:05:24,500 MAKES THIS ISOTOPE AN IDEAL FUEL FOR LONG-LIVED SPACE MISSIONS. 129 00:05:24,500 --> 00:05:27,833 - A RADIOISOTOPE POWER SYSTEM IS A SPECIAL SYSTEM 130 00:05:27,833 --> 00:05:30,666 THAT USES THE DECAY OF A RADIOISOTOPE, 131 00:05:30,666 --> 00:05:34,833 IN OUR CASE, PLUTONIUM-238, TO GENERATE HEAT. 132 00:05:34,833 --> 00:05:39,666 THAT HEAT THEN IS CONVERTED INTO POWER OR ELECTRICITY 133 00:05:39,666 --> 00:05:41,166 THAT WE USE ON SPACECRAFT. 134 00:05:41,166 --> 00:05:43,666 - THIS MAKES RADIOISOTOPE POWER SYSTEMS-- 135 00:05:43,666 --> 00:05:45,833 OR AN R.P.S. FOR SHORT-- 136 00:05:45,833 --> 00:05:47,833 IDEALLY SUITED FOR MISSIONS 137 00:05:47,833 --> 00:05:50,166 IN THE EXTREME ENVIRONMENTS OF SPACE 138 00:05:50,166 --> 00:05:52,166 OR ON PLANETARY SURFACES, 139 00:05:52,166 --> 00:05:54,666 LIKE SOME DESTINATIONS ON MARS. 140 00:05:54,666 --> 00:05:57,166 THE MARS SCIENCE LABORATORY ROVER, 141 00:05:57,166 --> 00:05:59,500 ALSO KNOWN AS CURIOSITY, 142 00:05:59,500 --> 00:06:02,666 HAS BEEN DESIGNED TO USE A RADIOISOTOPE POWER SYSTEM 143 00:06:02,666 --> 00:06:04,533 AS IT EXPLORES THE RED PLANET. 144 00:06:04,533 --> 00:06:07,166 THE R.P.S. CAN GENERATE ELECTRICITY NEEDED 145 00:06:07,166 --> 00:06:10,000 TO OPERATE THE ROVER AND ITS INSTRUMENTS, 146 00:06:10,000 --> 00:06:12,000 AND EXCESS HEAT FROM THE POWER SOURCE 147 00:06:12,000 --> 00:06:15,666 CAN KEEP THE ROVER WARM ON THIS COLD, DUSTY PLANET. 148 00:06:15,666 --> 00:06:18,500 THE STEADY AND RELIABLE OUTPUT OF ITS R.P.S. 149 00:06:18,500 --> 00:06:20,166 SHOULD ENABLE THE LARGE ROVER 150 00:06:20,166 --> 00:06:22,500 TO TRAVEL FARTHER, LAST LONGER, 151 00:06:22,500 --> 00:06:23,666 AND DO MORE SCIENCE 152 00:06:23,666 --> 00:06:26,766 THAN ANY PREVIOUS MOBILE MARTIAN EXPLORER. 153 00:06:26,766 --> 00:06:29,000 CURIOSITY IS DESIGNED TO ROAM MARS 154 00:06:29,000 --> 00:06:31,033 FOR A FULL MARTIAN YEAR-- 155 00:06:31,033 --> 00:06:32,900 THAT'S ABOUT TWO EARTH YEARS. 156 00:06:32,900 --> 00:06:35,833 WITH ITS RELIABLE, LONG- LASTING POWER SOURCE, 157 00:06:35,833 --> 00:06:38,066 THE MISSION COULD GO EVEN LONGER. 158 00:06:38,066 --> 00:06:39,400 AND THAT LONGEVITY 159 00:06:39,400 --> 00:06:42,833 IS THANKS TO OUR UNDERSTANDING OF RADIOACTIVE DECAY. 160 00:06:42,833 --> 00:06:44,500 SO HOW ABOUT THAT? 161 00:06:44,500 --> 00:06:48,033 FROM LABORATORIES ON EARTH TO ROVERS ON MARS, 162 00:06:48,033 --> 00:06:49,333 SCIENCE AND MATH 163 00:06:49,333 --> 00:06:52,000 CAN HARNESS THE POWER OF RADIOACTIVE DECAY 164 00:06:52,000 --> 00:06:56,000 TO HELP MAKE EXPLORATION TRULY A COSMIC ENDEAVOR.