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Chapter 28

Nuclear Radiation

Adapted from notes by Stephen L. Cotton ©

Section 28.1 – Nuclear Radiation

Objectives:Discuss the processes of radioactivity and radioactive decayCharacterize alpha, beta, and gamma radiation in terms of composition and penetrating power

RadioactivityRadioisotopes – nuclei of isotopes that go through nuclear reactions in an attempt to gain .Radioactivity – process by which materials “give off” or mass and/or energy… when the nucleus “spits” stuff out.Radiation – penetrating and/or emitted by the . of a radioisotope.Radioactive decay – process by which a radioisotope emits energy and/or particles in an attempt to stabilize its .Radioactive decay is totally…

Types of Radiation

Name Symbol Comp.Relativemass

PenetrationBlockage

Alpha Radiation

The nucleus of an unstable radioisotope “throws out” or an .Loss of and Write the nuclear equation for the alpha decay of U-238.

Beta Radiation

The nucleus of an unstable radioisotope “throws out” or a .A neutron decays into a (which stays in the nucleus) and a that is ejected from the nucleus.This is WHY the atomic # , the number of nø , and the mass # .Write the nuclear equation for the beta decay of Th-230.

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Gamma RadiationGamma is the high-energy radiation or by a radioisotope.γ-rays are often (but not always) emitted along with α or β radiation from nuclei of .

.X-rays are “like” γ-rays, but X-rays can be produced by energizing the electrons of certain metals when the metals “relax” they emit X-rays.Write the nuclear equation for the beta decay of Th-230.

Electron Capture

Too few relative to p+… a p+ is converted to a .HOW?... an is captured by the nucleus and combined with a Write the nuclear equation for the electron capture by a Ni-59 nucleus.

Positron Emission

The nucleus of an unstable radioisotope “throws out” or a positron particle.Similar to a beta particle, but with an atomic# of .A proton changes to a neutron, “throwing out” or its positive charge.Write the nuclear equation for the positron emission of O-15.

Section 28.2 PART I.Nuclear Transformations

Objectives:Understand how and why radioisotopes go through radioactive decay.Use half-life information to determine the amount of radioisotope remaining at a given time.Give examples of equations for the synthesis of transuranium elements by transmutation.

What Holds the Nucleus Together?

Ex: Li-6Has p+ and nø

p+ and nø attract due to a force similar to gravity… known as .Neutrons are the of the nucleus.p+ and p+ due to like charges.

Why Does Radiation Occur?

Begins with an of some .

Unstable because of too few or too many . relative to the number of Too many p+ leads to too many .Too many nø leads to … too many particles and not enough space in the

, nucleus.

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Nuclear Stability and DecayNuclear stability depends on its ratio.Determine the nø/p+ ratio for the following:He-4N-14O-16Pb-206U-235Radiation generally occurs in all elements after element # …WHY?Too many

Mass DefectIs the difference between the sums of the mass of individual . in an atom compared to the of the same atom reported in the periodic table.The “actual” mass is always than the experimental mass whenever the nucleus contains more than one particle.This difference in mass is converted into that holds the nucleus together and can be released in reactions.Energy is when the nucleus “throws out” or radiates Is why matter is in nuclear reactions.Mass–Energy equivalence: the concept that any has an associated and vice versa, where

Band of StabilityF.28.6 pg.845. nuclei are stable with nø/p+ ratio of ≤

Up to atomic , a ratio of 1 : 1 works.For larger atoms (atomic# ), a ratio of 1 : 1.5 is needed…need more nø “glue” to hold nucleus together.

nø/p+ ratio > 1.5 results in .Determine the nø/p+ ratio for the following:C-12C-14Tc-101

Example 1

Where is C-14 relative to C-12 on the band of stability?

HINT: Is C-14 located above, within, or below the B.O.S.?ANSWER:

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Example 2The band of stability is above the line on the graph that has a slope of 1. What does this indicate about the number of protons and neutrons in the majority of elements?

HINT: Compare the B.O.S. to the line with slope = 1ANSWER:

Example 3

What type of decay would stabilize an atom of U-238?

HINT: Need to get rid of some of the 92 p+’s

in the Uranium nucleus to get to atomic #82 (STABLE). ANSWER:

Example 4A nuclide has 90 neutrons and 60 protons. What type of decay will this nuclide undergo?

HINT: What is the proton/neutron ratio?ANSWER:

Example 5Some radioisotope X has 60 protons and 60 neutrons. What type of radioactive decay would it most likely undergo?

HINT: 60/60 = 1.0… Big atom above atomic #20!!!ANSWER:

Example 6

Identify the region of the graph associated with beta emission.

HINT: Too many neutron to proton ratio = high nø/p+ ratio.ANSWER:

Example 7

Identify the region of the graph associated with the emission of alpha particles.

HINT: Need to get rid of p+.ANSWER:

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Example 8Identify the region of the graph associated with electron capture ORpositron emission.

HINT: Electron capture ANDpositron emission both happen to “make” more nø’s

ANSWER:

Section 28.2 PART II.Half-Life (t1/2) & Transmutation

There is a characteristic rate of of the nucleus in every radioisotope.t1/2 is the time required for of the nuclei of a radioisotope sample to decay to products.1st t1/2 = 2nd t1/2 = 3rd t1/2 = 4th t1/2 = 5th t1/2 =

Example 1

C-14 has a t1/2 of 5730 years. If a medical anthropologist determines that a sample of human bone has only 25% of its original C-14 remaining, how old would the human bone be (approximately)?ANSWER:

Example 2

Tc-104 has a t1/2 of 18 minutes. If a sample originally contained 1.00g of Tc-104, how many grams would remain after 1 ½ hours?ANSWER:

t1/2 Used for

C-14 t1/2 =

Tc-104 t1/2 =

U-238 t1/2 =

Transmutation Reactions

. the and/or of the nucleus of one element into the nucleus of another element.By nuclear OR forced of the nucleus… such as Fermi National Accelerator Lab or the Hadron Collider!!!Rutherford transmutated N-14 into F-18 by bombarding it with an , which quickly decomposed into the more stable O-17 and a proton.Write the nuclear equation for the above!

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Transuranium Elements

Means Uranium and man-made.Most use as the building block.Example: U-238 is bombarded with a neutron; the product is unstable and goes through beta decay; this product is unstable and goes through beta decay as well; finally a “somewhat” stable element results… what element is it?

Section 28.3 – Fission and Fusion of Atomic Nuclei

Objectives:Compare nuclear fission and nuclear fusion, and comment on their potential as sources of energy.Describe the methods used in nuclear power plants to produce and control fission reactions

Nuclear Fission

The of the nuclei of radioisotopes into smaller fragments when bombarded with neutrons.U-235 and Pu-239 are two most common . radioisotopes.F.28.11 pg.853Neutron gun (fires nø’s) fissionable U-235 unstable U-238 , Kr-91, Ba-142, more neutrons U-235… CHAIN RXN!!!

Nuclear Powerplants

F.28.12, pg.854 KNOW & UNDERSTAND THE DIAGRAM!!!Neutron Moderation – down the neutrons so that they may be absorbed by the nucleus of a radioisotope… H2O or C.

Neutron Absorption – neutrons…control rods of Cd.

Nuclear Regulatory Commission (NRC)Nuclear Regulatory Commission (NRC)

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Nuclear FusionThe of the nuclei of two light isotopes to produce a nucleus of greater mass + ENERGY.Requires tremendous and .H-2 (Deuterium) + H-3 (Tritium) + FORCE + HEAT

He-5 (Unstable Intermediate) He-4 + neutron + Thermonuclear fusion occurs in the … provides energy to the Earth.Fusion not yet possible on Earth If used, 1 gal. of sea water contains enough H-isotopes to equal the energy released by the combustion of

gal. of gasoline.

Section 28.4 – Radiation in Your Life

Objectives:Describe three methods of detecting radiation.List some applications of radioisotopes in research and medicine.

Detecting Radiation

Ionizing Radiation – has enough energy to knock electrons off atoms to produce … (β)Geiger Counter – F.28.15, pg. 857.Scintillation Counter – phosphor screen produces flashes of when hit by radiation… (β)Film Badge – uses “camera film” that turns dark upon exposure to … (detects all types and strength)

Other Implications of Radiation

Neutron Activation Analysis firing nø’s at samples activates radioactive elements present… used in .Tracers study reactions, biological processes/food ingestion, , water seepage.Medical Diagnosis Cancer Treatment Nuclear Weapons Radon Poisoning result of decaying

Positron Emission Tomography (PET)using fluorodeoxyglucose (FDG) tracer

Scintillation Material & Photomultipliers

Wikipedia

PET brain image using FDG

Wikipedia

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Wikipedia Wikipedia - http://en.wikipedia.org/wiki/Atomic_bombings_of_Hiroshima_and_Nagasaki

•First nuclear test, “Trinity” in New Mexico, 16 July 1945•First nuclear weapon used by the U.S. on Hiroshima, 6 August 1945 - ~140,000 dead•Second nuclear weapon used by the U.S. on Nagasaki, 9 August 1945 - ~74,000 dead•At least 4 major false alarms of nuclear weapon release since then, most recent 1995.•~29,000 nuclear weapons held by 8 countries.

Figure 4. One major means by which fallout and nuclear debris are transferred through the atmosphere to people is via the production and consumption of dairy products. Fallout descends onto vegetation, which is eaten by dairy animals. The fallout passes into the animals' milk, which is prepared for human consumption. This pathway is the single largest means by which people in the U.S. were exposed to iodine-131 from fallout generated by nuclear weapons testing. Figure adapted from the National Cancer Institute; illustration by Barbara Aulicino

American Scientist Online - http://www.americanscientist.org/template/AssetDetail/assetid/48543?fulltext=true&print=yes#48751