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Radiation Radiation: The process of emitting energy in the form of waves or particles.

Where does radiation come from? Radiation is generally produced when particles interact or decay. A large contribution of the radiation on earth is from the sun (solar) or from radioactive isotopes of the elements (terrestrial). Radiation is going through you at this very moment!

Discovery of Radioactivity Antoine Henri Becquerel ( ) –Noticed the fogging of photographic plate by uranium crystals Pierre Curie ( ), Marie Curie ( ) –Further studies of uranium and discovery of polonium and radium. Marie received two Nobel prizes. She died from the effects of radiation doses received during her experiments Discovery Discovery 2 Discovery 3

Ernest Rutherford ( ) –His understanding of atomic structure helped us understand the role of the nucleus. He defined many of the terms used to discuss radioactivity today Discovery of Radioactivity

Radioactivity is the spontaneous disintegration of atomic nuclei. The nucleus emits α particles, ß particles, or electromagnetic rays during this process. Radioactivity is the spontaneous disintegration of atomic nuclei. The nucleus emits α particles, ß particles, or electromagnetic rays during this process. After decaying, radioactive atoms “change” into other atoms Clip

Why does the atom do this? –t–the nucleus of an atom attempts to become more stable In some instances, a new element is formed and in other cases, a new form of the original element, called an isotope, appears. –t–this process of change is often referred to as the decay of atoms. The rate of Radioactive decay is described in h hh half-lives.

Energy is released during radioactive decay

Biological Effects of Radiation: Ionizing radiation causes physical damage to cells and DNA. Radiation can excite DNA and result in the destruction on the DNA backbone. At high doses of radiation (10, ,000 rads), death occurs in a few hours because of neurological and cardiovascular breakdown (Central Nervous Syndrome).

Biological Effects of Radiation: Medium doses, rads, causes death to occur in a few days because of the destruction of the gastrointestinal mucosa. Lower doses, rads, causes death to occur after several weeks due to damage of the blood forming organs (hematopoietic syndrome).

Medicine For example, radiation and r rr radioactive tracers are used to diagnose and treat medical problems. A radioactive tracer is a radioactive isotope that is added to a substance so that the substance can be detected later. Radioactive tracers are used to locate tumors, to study the functioning of a particular organ, or to monitor the flow of blood. For example, radioactive iodine-131 is used to diagnose thyroid problems. Radiation therapy used to treat cancer may involve the use of implanted radioactive isotopes such as gold-198 or iridium-192. Radiation is used positively in a variety of ways

Industry Manufacturers can also use radiation to check the thickness of metal containers by measuring the amount of radiation that passes through. Small amounts of radioactive isotopes, like magnesium-28, can be introduced in a water source to determine the flow of underground water or to determine if an underground water system is leaking. Radioactive isotopes are even used in s ss smoke alarms.

Generate electrical power Nuclear fission is used to generate electricity as an alternative energy source. Dating Even the age of fossils or rocks can be determined by using radioactive isotopes.

Particles found in the nucleus of an atom –neutrons –protons Atomic Number (A) – number of protons in the nucleus Mass Number (Z) – sum of the number of protons and neutrons A Review of Atomic Terms

Radioactive Decay Radioactivity – the spontaneous decomposition of a nucleus forming a different nucleus and producing one or more additional particles Nuclear Forces – strong nuclear force holds neutrons and protons together to form a nucleus (counters electromagnetic repulsion). Weak nuclear force operates within individual particles and gives rise to some kinds of radioactivity

Isotopes What ’ s an isotope? Two or more varieties of an element having the same number of protons but different number of neutrons. Certain isotopes are “ unstable ” and decay to lighter isotopes or elements. A prime example is Uranium 238, or just 238 U.

Radioactivity By the end of the 1800s, it was known that certain isotopes emit penetrating rays. Three types of radiation were known: 1)Alpha particles (  ) 2)Beta particles (  ) 3)Gamma-rays (  ) By the end of the 1800s, it was known that certain isotopes emit penetrating rays. Three types of radiation were known: 1)Alpha particles (  ) 2)Beta particles (  ) 3)Gamma-rays (  )

Where do these particles come from ? These particles generally come from the nuclei of atomic isotopes which are not stable. The decay chain of Uranium produces all three of these forms of radiation.

Types of Nuclear Radiation When an unstable nucleus decays, particles and energy are given off from the decaying nucleus. α and β radiation is in the form of particles γ radiation is in the form of waves-kind of like light but higher frequency

Alpha Particles (  ) Radium R protons 138 neutrons Radon Rn 222 Note: This is the atomic weight, which is the number of protons plus neutrons 86 protons 136 neutrons + n n p p   He) 2 protons 2 neutrons The alpha-particle  is a Helium nucleus. It ’ s the same as the element Helium, with the electrons stripped off !

two protonstwo neutronsAlpha particles consist of two protons and two neutrons, identical to the nucleus of a helium atom. A sheet of paper or a person ’ s surface layer of skin will stop them. Alpha particles are only considered hazardous to a person ’ s health if they are ingested or inhaled and thus come into contact with sensitive cells such as in the lungs, liver and bones.

Beta Particles (  ) Carbon C 14 6 protons 8 neutrons Nitrogen N 14 7 protons 7 neutrons + e-e- electron (beta-particle) We see that one of the neutrons from the C 14 nucleus “ converted ” into a proton, and an electron was ejected. The remaining nucleus contains 7p and 7n, which is a nitrogen nucleus.

Beta particles are electrons emitted from the nuclei of many fission products.Beta particles are electrons emitted from the nuclei of many fission products. They can travel a few feet in air but can usually be stopped by clothing or a few centimeters of wood. They are considered hazardous mainly if ingested or inhaled, but can cause radiation damage to the skin if the exposure is large enough. Unstable Neutron decays into a proton.

Gamma particles (  ) In much the same way that electrons in atoms can be in an excited state, so can a nucleus. Neon Ne protons 10 neutrons (in excited state) 10 protons 10 neutrons (lowest energy state) + gamma Neon Ne 20 A gamma is a high energy light particle. It is NOT visible by your naked eye. A gamma is a high energy light particle. It is NOT visible by your naked eye.

Gamma rays are a form of electromagnetic radiation (like light, radio, and television) that come from the nucleus of a radioactive atom. –O–Occurs when an unstable nucleus emits electromagnetic radiation. The radiation has no mass, and so its emission does not change the element. –T–They penetrate matter easily and are best stopped by water or thick layers of lead or concrete. –G–Gamma radiation is hazardous to people inside and outside of the body. However, gamma radiation often accompanies alpha and beta emission, which do change the element's identity. Gamma rays have the lowest ionizing power, but the highest penetrating power.

How do these particles differ ? Particle Mass* (AMU) Charge Gamma (  ) 00 Beta (  ) ~1/1836 Alpha (  ) ~4+2

Nuclear Decay Neutron decays into a proton 2 protons & 2 neutrons

Rate of Decay  Beyond knowing the types of particles which are emitted when an isotope decays, we also are interested in how frequently one of the atoms emits this radiation.  A very important point here is that we cannot predict when a particular entity will decay.  We do know though, that if we had a large sample of a radioactive substance, some number will decay after a given amount of time.  Some radioactive substances have a very high “ rate of decay ”, while others have a very low decay rate.  To differentiate different radioactive substances, we look to quantify this idea of “ decay rate ”

Half-Life  The “ half-life ” (h) is the time it takes for half the atoms of a radioactive substance to decay.  For example, suppose we had 20,000 atoms of a radioactive substance. If the half-life is 1 hour, how many atoms of that substance would be left after: 10,000 (50%) 5,000 (25%) 2,500 (12.5%) 1 hour (one lifetime) ? 2 hours (two lifetimes) ? 3 hours (three lifetimes) ? Time #atoms remaining % of atoms remaining

Half Life is the amount of time it takes for half of the nuclei in a sample to decay Mass (kg)

Decay of a Radioactive Element Half of the radioactive parent atoms decay after one half-life. Half of the remainder decay after another half-life and so on…….. Half-life activity

25g The half life of 14 C is 5,730 years. If a sample originally contained 100 g, how much would be left after 11,460 years? 50g

Older Dating Methods The isotopes 235 U and 238 U can be used to date objects billions of years old. 235 U has a half life of 704 million years. 238 U has a half life of 4.5 billion years. Mainly used for rocks.

Geiger Counter Used to measure radiation. The more intense the radiation the more “ clicks ”.

Fission and Fusion FissionFusion Splitting a nucleus Combining of two nuclei.

Nuclear power can come from the fission of uranium, plutonium or thorium or the fusion of hydrogen into helium. Today it is almost all uranium. The fission of an atom of uranium produces 10 million times the energy produced by the combustion of an atom of carbon from coal.

Issues for Fission Power Plants disposalNeed for a spent fuel disposal facility and a decommissioning plan Use of large amounts of water for cooling purposes (if wet cooling towers are used) –thermal pollution Biological impactsBiological impacts on the ocean due to thermal discharge (if seawater cooling is used) safetyPublic safety concerns Clip

FUSION A fusion reaction occurs when nuclei of light elements, specifically hydrogen and its isotopes (deuterium, or "heavy water," and tritium), are forced together at extremely h hh high temperatures and densities until they fuse into nuclei of heavier elements and release enormous amounts of energy.

heated temperature If fusion is to yield net energy, the fuel must be heated in the form of plasma (a highly ionized gas) to a very high temperature and the plasma must then be held together for a sufficiently long time such that the number of fusion reactions occurring releases more energy than was required to heat the fuel.