Barry K James, NuclearScienceRevB.ppt CANNOCK CHASE U3A SCIENCE & TECHNOLOGY GROUP. Nuclear Science: What s all this isotope stuff?

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1 Barry K James, NuclearScienceRevB.ppt CANNOCK CHASE U3A SCIENCE & TECHNOLOGY GROUP Nuclear Science: What s all this isotope stuff? October 2016

2 ATOMS.ALL MATTER e Electrons e e Everything around us is made of atoms. Atoms are very small. The diameter of an average atom is a ten-billionth of a metre (or m). 10 million atoms would fit between a millimetre division on a ruler.

3 ATOMS & ELEMENTS There are just 118 different types of atom that have been observed. These are known as chemical elements and of those 118, only about 90 occur naturally. The image above was produced with a type of microscope that enables us to distinguish individual gold atoms (Au). Each element is represented by a chemical symbol, consisting of one or two letters, for example, H is for hydrogen and He is helium.

4 THE TABLE OF ELEMENTS Neodymium Magnetic material used in motors

5 SUB-ATOMIC PARTICLES e e Protons & Neutrons e The nucleus itself made up of smaller particles called protons and neutrons. The number of protons in the nucleus is known its atomic number. This determines the chemical element. The remainder comprises orbital electrons. Electrons are negatively charged, balancing out the positive charge of the nucleus. The number of electrons is always the same as the number of protons in its nucleus, making a neutral atom. All the matter in each atom is concentrated in this tiny volume and so nuclei are super dense and packed with energy

6 THE ROLE NEUTRONS PLAY FORCES WITHIN THE NUCLEUS o There is a repulsive electromagnetic force within the nucleus that acts between protons. o There is an attractive strong force within the nucleus that acts between both protons and neutrons. o Neutrons are necessary to hold the nucleus together for stability. o In the table below, notice that as nuclei get larger the ratio of neutrons to protons increases. o The uranium nucleus needs significantly more neutrons than protons to hold together. The number of protons and neutrons within isotopes Element Symbol Number of protons carbon 12 6 C 6 6 calcium Ca zinc Zn iodine I uranium U Number of neutrons

7 RADIOACTIVE ATOMS..ISOTOPES An element can have different forms where the atoms have the usual number of protons but a different number of neutrons than in the normal atom. These different forms are called isotopes. So, a normal Carbon atom is represented as 12 6C and an atom of an isotope, as 14 6C. Carbon-12 is stable while Carbon-14 is unstable and radioactive (2 more neutrons). Element numbering: 14 6 C Mass no. (A) = protons + neutrons Atomic no. = protons Element

8 STABLE OR UNSTABLE ISOTOPES? In most atoms, the nucleus forces reach an equilibrium. These are able to hold together and are said to be stable. In other nuclei the interaction between the forces can make the nuclei unstable. To gain stability, the unstable nucleus will emit particles and energy (either neutrons and protons bonded together or ejected electrons), and such nuclei are called radioactive. Ejected electrons turn the neutral atoms or molecules into charged ions and hence the emitted particles are sometimes called ionising radiation or Radioactivity. Ionising radiation can be Alpha, Beta or Gamma particles. When it emits a particle, the nucleus is said to decay. Each radioactive element has a half-life decay period.

9 ALPHA, BETA AND GAMMA PARTICLES Unstable nuclei can lead to radiation of 3 types, α, β and γ. All three types of radiation can damage human cells and this damage can lead to cancers developing in the area affected. Alpha particles (two protons and two neutrons) can be stopped by paper. Beta particles (ejected electrons) can be absorbed by water or aluminium. Gamma particles (EM radiation photons) are the highest energy and can only be absorbed by dense materials such as lead or concrete. β γ α

10 TRANSFORMATION Emission of particles transforms the element to a different element. Uranium 238 becomes Thorium 234. Radioactivity isn t new. It has always been part of the environment. Radioactive decay provides the majority of the Earth s internal heat that causes volcanoes to erupt and drives plate tectonics. Radioactive materials are all around you!

11 DISCOVERY OF RADIOACTIVITY Uranium was discovered by M. Klaproth in Radioactivity was discovered in 1896 by Becquerel. His uranium salts emitted particles that reacted with photographic plates and found ultraviolet light made uranium crystals glow. Marie and Pierre Curie, and Ernest Rutherford worked on identifying the different emissions called uranic rays. Marie Curie was working with a uranium ore called pitchblende. Within the pitchblende she discovered polonium and radium (luminous paint) in 1898, we now know to be radioactive.

12 Marie Curie died of exposure to radiation, not understanding the dangers. But still the World went mad about radium

13 THE MADNESS OF RADIUM The world fell in love with radium, assuming its invisible energy must be good for you. The French slapped on radium face powder. The Germans used radium toothpaste & ate radium chocolate. In 1900 s, the Americans sold spa sessions with radium. In 1912 the Americans sold crock pots with radium in to purify water. The Americans even wore radiumbranded condoms. And for sagging men.

14 BUT THE REALISATION Curie, Becquerel and others had no idea of the dangers, nor the public in products of the 1900 s. But the magic faded when doctors realised that far from boosting health, it triggered cancers.

15 TEA ANYONE?

16 NOW WE CAN MEASURE RADIATION THE GEIGER COUNTER Radioactive material emissions can heard by a Geiger counter Wristwatch has radioactive paint on the face contains radium and shows 8 cps. Used to detect Radon gas, a source from the ground (under some houses). A Geiger counter consists of a Geiger-Müller tube, the sensing element which detects the radiation, and the processing electronics, which displays the result. The Geiger-Müller tube is filled with an inert gas such as helium, neon, or argon at low pressure, to which 400 volts is applied between conductor and case. The tube briefly conducts electrical charge when a particle or photon of incident radiation makes the gas conductive by ionization. This charge causes a pulse or count to occur.

17 WHERE IS THIS RADIATION? Radiation dose is expressed in micro-sieverts/hour (µsv/hr). It s cumulative. Some medical procedures involve the use of radiation Flying increases your exposure to cosmic rays. Particles are in the air that you breathe. The food that you eat In the materials with which we build our houses. The rocks in the ground. What are the worst exposures to radiation over a year?

18 THE ANSWERS:

19 EXAMPLE RADIATION DOSE LEVELS The personal annual dose from background radiation in the UK is 2,700 µsv/year (microsieverts). A typical house may have a natural radiation level of about 0.12 µsv/hour, totally harmless, less than 3 µsv per day. A dental X-ray gives a dose of 800 µsv (but in around 1 second). A chest CT scan is about 7000 µsieverts of exposure. A 100,000 µsievert dose is associated with a small but measurable increase in cancer.

20 CAN ISOTOPES BE USEFUL? Americium-241 Americium-241 is an alpha emitter. The alpha particles ionise the air molecules in a chamber open to the air and carry a charge. The charged ions allow a tiny current to flow. If smoke particles enter the chamber this current is disrupted and the alarm sounds. Technetium-99 Iodine-131 Carbon-14 Carbon dating Thyroid cancer therapy Blood tracer, brain and infections

21 CAN URANIUM BE USEFUL? Yes really, really useful: Uranium powers such processes as plate tectonics and the maintenance of the Earth s molten core. It is likely that without the energy released by radioactive decay, the Earth would have cooled long ago causing it to have a Mars-like environment. Without uranium it is probable that there would be no life on Earth. The core would have cooled to a point where the Earth s magnetic field would have collapsed, allowing the solar wind to strip away the atmosphere and the oceans. And for nuclear Fission, generating electricity.

22 FISSION & FUSION Fission (energy from nuclear reactors) Splitting of nuclei of unstable elements, such as Uranium & Plutonium. Splits into two stable elements (nuclear waste). Energy is released by the splitting (power generation). Usually uranium 235 is used in the nuclear industry. Fusion (the sun) Forcing atoms to collide at huge temperature and speed to bind them together. Releases energy [JET ITER experiments] One day may become our energy source. As reliable as the Sun.

23 FISSION HEAT & POWER GENERATION It s all to do with the Neutron Bombarding Uranium with neutrons Cs-140 Unstable Rb-92 The neutrons must be going at the right speed Too fast, they bounce off the Uranium. Releasing binding force causes energy release They must be absorbed to give the right speed & mass. Speed of neutrons controlled by absorber controls. Reaction can run-away if not controlled (critical mass)

24 WHERE DO THESE NEUTRONS COME FROM? A Neutron start-up source is required: Californium-252, a heavy synthetic element that has a significant spontaneous fission (SF) mode of decay emitting neutrons. Or, antimony-beryllium neutron source activated during previous reactor operation. Then we can create lots of energy...

25 USE OF FISSION IN NUCLEAR POWER STATIONS

26 NUCLEAR POWER STATION CORE 300 deg Celcius core 40,000 tonnes pressure Tubes of zirconium Filled with Uranium dioxide (UO 2 ) pellets Fuel rods can last for 3-6 years in use Process starts with free neutrons Neutron control is essential Neutrons must be at the right speed Neutrons can be slowed down or absorbed by control rods of hydrogen, deutirium, carbon graphite, or water. When absorbed by the uranium, the transformation process starts, generating heat.

27 THE INSIDES This Zwentondorf reactor was designed as a boiling water reactor (BWR). The reactor was built but never used; it was prevented by a vote within a referendum on the issue. Since 1978 Austria has banned using fission as an energy source in power stations. Reactor core Steam turbine

28 ANOTHER TIME? What can go wrong with nuclear Safety of nuclear power Accidents in nuclear Long term effects World nuclear power stations Half life What about nuclear waste? Running the National Grid Nuclear Fusion advantages