Artificial Radioactivity by Miriam and Jonah
What is Artificial Radioactivity? ●
Artificial radioactivity or _____________ radioactivity was discovered by Irene Curie and F. Joliot in 1934
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This is also known as manmade radioactivity
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It is the phenomenon by which even light __________ are made radioactive by artificial or induced methods
Background ●
Curie and Joliot showed that when _____________ elements, such as boron and aluminum were bombarded with αlpha-particles (a helium nucleus emitted by some radioactive substances, originally regarded as a ray), there was a continuous ________________ of radioactive radiations, even after the α−source had been removed
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They showed that the radiation was due to the emission of a particle carrying one unit positive charge with a mass equal to that of an ____________
Background ●
This particle is known as a _____________ and the reaction is: 10 4 13 1 B + He → N + n 5 2 7 0
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The nitrogen atom is radioactive and decays with a half life of about 10.1 minutes into a stable isotope of carbon with the emission of a positron: 13 13 0 N → C + e 7 6 1
Reminder ●
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mass numbers of the reactants ___________ the mass numbers of the products atomic numbers of the reactants equal the atomic number of the products BUT the total mass for both sides will be different, due to the _________________________________ of mass-energy.
Bombardment Reactions Nuclear bombardment reactions generally involve 4 particles: ● ● ● ●
Target Nucleus is the stable isotope that is bombarded. Projectile Particle (bullet) is the particle fired at the ____________ nucleus. Product Nucleus is the isotope _______________ in the reaction. Ejected Particle is the lighter nucleus or particle emitted from the reaction.
Aluminum-27
Alpha Particle
Phosphorus-30
Neutron
Target Nucleus
Projectile Particle
Product Nucleus
Ejected Particle
Bombardment Reaction Example Nobelium (No) can be produced by bombarding Curium (Cm) with projectile nuclei of a light element. That element can be identified by completing the following equation: 246 96
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Cm + ?
254 102
No + 410n
Remember: The sum of the top numbers on the left is equal to the sum of the top numbers on the right and the sum of the bottom numbers on the left is equal to the sum of the bottom numbers on the right.
Answer Top (mass):
Bottom (atomic #):
Which element has a mass of 12 and
an 246 + x = 254 + 4(1)
96 + x = 102 + 0
246 + x = 258
x = 102 - 96
x = 258 - 246
x=6
atomic number of 6? Carbon
x = 12
246
12 Cm + C 96 6
254
1 No + 4 n 102 0
Nuclear Fission vs Nuclear Fusion These are two forms of reactions where energy is _______________ from atomic bonds between particles in the nucleus. Nuclear Fission is the separation of a large atom into two or more smaller atoms. This reaction does not normally occur _______________. Nuclear Fusion is the fusion between two or more smaller atoms to create a larger atom (the reverse of the fission process). This occurs naturally in the ___________.
Nuclear Fission vs Nuclear Fusion An easy way to remember the difference between these is: When things fizz or break down (fission), you start with a larger object and finish with ____________ objects. When things fuse (fusion), you start with smaller objects and build larger objects.
Nuclear Fission ●
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Nuclear fission takes place when a large, somewhat _______________ isotope (atoms with the same number of protons but different number of neutrons) is bombarded by high-speed particles, usually neutrons These neutrons are accelerated and then slammed into the unstable isotope, causing it to fission, or break into _____________ particles During the process, a neutron is accelerated and strikes the target nucleus, which in the majority of nuclear power reactors today is Uranium-235 This splits the target nucleus and breaks it down into two smaller isotopes (the fission products), three high-speed neutrons, and a large amount of _____________
Nuclear Fission ●
The sum of the masses of these fragments is less than the _____________ mass
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This 'missing' mass (about 0.1 percent of the original mass) has been converted into energy according to Einstein's equation
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Fission can occur when a nucleus of a ______________ atom captures a neutron, or it can happen spontaneously
Nuclear Fission - Chain Reactions
U235 + n → fission + 2 or 3 n + 200 MeV
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A chain reaction refers to a process in which neutrons released in fission produce an additional fission in at least one further nucleus
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This nucleus produces ______________ and the process repeats
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The process may be controlled (nuclear power) or uncontrolled (nuclear weapons)
Nuclear Fission - Critical Mass ● ● ● ●
Although 2-3 neutrons are produced for every fission, not all of these neutrons are available for continuing the fission reaction If the neutrons are lost at a faster rate than they are formed by _____________, the chain reaction will not be self-sustaining At the point where the chain reaction can become self-sustaining, this is referred to as critical mass The amount of a fissionable material's critical mass depends on several factors; the shape of the material, its composition and density, and the level of ______________
Nuclear Fission - Controlled ● ● ● ● ● ● ● ●
To maintain a sustained controlled nuclear reaction, for every 2 or 3 neutrons released, only one must be allowed to strike another uranium _____________ If this ratio is less than one then the reaction will die out; if it is greater than one it will grow uncontrolled (an atomic explosion) A neutron _____________________ element must be present to control the amount of free neutrons in the reaction space Most reactors are controlled by means of control rods that are made of a strongly neutron-absorbent material such as boron or cadmium In addition to the need to capture neutrons, the neutrons often have too much ________________ energy These fast neutrons are slowed through the use of a moderator such as heavy water and ordinary water Some reactors use graphite as a moderator, but this design has several problems Once the fast neutrons have been slowed, they are more likely to produce further nuclear fissions or be ___________________ by the control rod
Why Uranium and Plutonium? ● ● ● ● ● ● ●
Scientists knew that the most common isotope, uranium 238, was not ________________ for a nuclear weapon There is a fairly high probability that an incident neutron would be captured to form U-239 instead of causing a fission. However, U-235 has a high fission probability Of natural uranium, only 0.7% is U-235. This meant that a large amount of uranium was needed to obtain the necessary quantities of U-235 Also, U-235 cannot be separated chemically from U-238, since the isotopes are chemically similar Alternative methods had to be developed to separate the isotopes Research had also predicted that plutonium 239 would have a high fission ___________ However, Pu-239 is not a naturally occurring element and would have to be made
Nuclear Fission Reactor https://www.youtube.com/watch?v=D91T-B-PVE0
Nuclear Fusion ●
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Fusion is the process of two small atomic nuclei coming together to make a larger nucleus which is stable The simplest nuclei to use are deuterium and tritium (isotopes of hydrogen) Scientists find deuterium in the ________________
Nuclear Fusion - In The Sky ● ● ● ● ● ●
The fusion reactions in many stars are different from the reactions we are trying to develop on Earth Scientists call the fusion process on a star the proton-proton chain reaction Two protons ______________ with each other and form a deuteron A third proton then collides with the deuteron to create a helium isotope Helium isotopes then fuse to make beryllium, which then breaks down When the beryllium breaks down, two protons are ________________ and the reaction can start again
Nuclear Fusion - Making It A Reality ● ● ● ● ● ● ● ●
Fusion reactions need very ________ environments to occur Temperatures hit millions of degrees, like the temperature of the Sun When you heat a gas, you create plasma The problem is that we can't create a container that can make plasma hot enough to let a fusion reaction occur To make sure that the plasma doesn't really touch the container, scientists use magnetic fields to hold the plasma in place The plasma is just floating, not touching anything The best container is in the shape of a torus Compared to a fission reaction, there is very little radioactivity released when a fusion reaction is complete
Nuclear Fusion Reactor https://www.youtube.com/watch?v=mZsaaturR6E
Conclusion ● ● ●
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Both fission and fusion are nuclear reactions that produce _______________, but the applications are not the same Fission is the splitting of a heavy, unstable nucleus into two lighter nuclei, and fusion is the process where two light nuclei ________________ together releasing vast amounts of energy Fission is used in nuclear power reactors since it can be controlled, while fusion is not utilized to produce power since the reaction is not easily controlled and is expensive to create the needed conditions for a fusion reaction Research continues into ways to better harness the power of fusion, but research is in experimental stages While different, the two processes have an important role in the past, present and future of energy ________________
Sources http://www.readorrefer.in/article/Artificial-radioactivity_2961/ https://www.thoughtco.com/nuclear-fission-definition-and-examples-4065372 http://www.physics4kids.com/files/mod_fusion.html http://www.physics4kids.com/files/mod_fission.html
