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HSC ChemistryModule 1- Production

of Materials

Nuclear Chemistry

NOTE

Remove the word “chemical” from dot point 5.2.6

Should read.....explain their use in terms of theirproperties

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OUTCOMES explain the stability of the nucleus write equations for nuclear decay processes describe how transuranic elements and

commercial radioisotopes are produced identify processes and instruments used to

detect radioactivity describe some industrial and medical

applications of nuclear chemistry analyse benefits and problems associated with

the use of radioactive isotopes

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Radiation

energy traveling through space invisible except for light transmitted as waves OR as energetic particles

detected by changes caused in substances around it

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Radioactivity

the spontaneous and uncontrollable decay of an atomic nucleus resulting in the emission of this radiation

a natural process throughout the Universe and part of the inherent properties of many elements

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The Nucleus

The mass of an atom is concentrated in a tiny nucleus

force required to hold positively charged protonstogether is enormous

nuclear electrostaticforce force protons - neutrons electrons - nucleus

>>

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Identifying the nucleus

XAZ

a nuclide is a particular species of nucleus

Z = number of protons

N = number of neutronsmass number A = Z + N

nucleons are protons and neutrons

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Stability of the nucleus

depends on the ratio of protons to neutrons

radioisotopes are radioactive because they have unstable nuclei

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Band of stability

along the black band isotopes are stable

above and below isotopes are unstable

all isotopes above Z=83 (Bi) are radioactive

Stability of the nucleus10

nuclei whose n/p ratios lie outside the stable region undergo spontaneous radioactive decay by emitting one or more particles and/or electromagnetic radiation

atomic number > 83 most forms of radioactive decay cause a

change in the atomic number producing a new element a TRANSMUTATION

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Nuclei above the band of stability

have too high a n/p ratio decay to DECREASE the ratio most commonly by beta emission

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Beta decay (b)unstable nuclide is proton deficient (stable) C12

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transforms a neutron to a proton

high energy electron emitted (b particle)

resultant nuclide: A the same - Z increases by 1

eNC 01

147

146

epn01

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10

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Nuclei below the band of stability

have too low a n/p ratio increase this ratio usually by positron emission

or electron capture (k-capture) a positron has the mass of an electron but a

positive charge – forms when a proton is converted to a neutron

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Positron emissionunstable nuclide is proton rich (stable) C12

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transforms a proton to a neutron

high energy positron emitted

resultant nuclide: A the same - Z decreases by 1

eBC 01

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116

enp01

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Electron capture/K-capture

an electron from the first shell (K shell) is captured by the nucleus and combines with a proton to form a neutron

resultant nuclide: A the same - Z decreases by 1

a 23191

01

23192 PeU

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Nuclei with Z > 83Alpha decay

When Z > 83 an particle (4He2+) may be emitted

Z decreases by 2 particle emitted

A decreases by 4

He hT U 42

23490

23892

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Gamma Radiation (g)

high-energy electromagnetic radiation has no mass and no charge usually accompanies the emission of and b

particles when the product nucleus must lose excess energy to become stable

alone cannot cause a transmutation

Complete the equation below

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35 016 1S e ?

??

How much radiation is safe?

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5.2.2 describe how transuranic elements are produced

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5.2.3 describe how commercial radioisotopes are produced

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Synthesis of radioisotopes

Particle Accelerators target nuclei are bombarded with high energy particles

like protons in cyclotrons to induce nuclear reactions produce neutron deficient radioisotopes

nCpB 10

116

11

115

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Positron emission tomography important diagnostic technique uses positron emitters

e.g. 11C (t½20.3 min) or 15O (t½124 s)

incorporated into a molecule like glucose and injected into the body

can study blood flow, glucose metabolism by monitoring the positron emission

must be generated on-site as short t1/2

Synthesis of radioisotopes

Nuclear Reactors source of neutrons from the fission of the fuel e.g. U-235 radioisotopes may be products of fission of U-235

e.g. Mo-99, Cs-137 produces neutron rich radioisotopes

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g MonMo 9942

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9842

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Nuclear fissionWhen 235U is bombarded with neutrons the nuclei split into smaller nuclei, release some neutrons and energyAnother way of producing Mo-99 g Tc-99m

Synthesis of new elements

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Nuclear Reactors neutron bombardment of U-238 produced the first

transuranic element Np-239

g UnU 23992

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23892

eNpU 01

23993

23992

Synthesis of new elementsParticle Accelerators high energy projectile ions are fired at target nuclei

Ununbium 112 now Copernicium Discovered on 9th Feb 1996 at GSI in Darmstadt,

Germany. produced by firing accelerated zinc nuclei at lead

nuclei

Very short ½ life: 240 microseconds Undergoes alpha decay

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nCnCnZnPb 10

277112

278112

7030

20882

Uses of Radioisotopes27

There are 3 main uses of ionising radiation in medicine:Treatment

Diagnosis

Sterilisation

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Radiotherapy TreatmentIrradiation Using High Energy Gamma Rays Gamma rays are emitted

from a Cobalt-60 source The cobalt source is kept

within a thick, heavy metal container.

This container has a slit in it to allow a narrow beam of gamma rays to emerge.

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Radiation TherapyBrachytherapy

A radiation source is placed inside or next to the area requiring treatment.Can be used to treat the following cancers:

Uterus Cervix Prostate Intraocular Skin Thyroid Bone

“Seeds" - small radioactive rods implanted directly into the tumour. e.g. prostate cancer

Brachytherapy30

Radionuclide Type Half-life Energy

Caesium-137 (137Cs) γ-ray 30.17 years 0.662 MeV

Cobalt-60 (60Co) γ-rays 5.26 years 1.17, 1.33 MeV

Iridium-192 (192Ir) γ-ray 74.0 days 0.38 MeV (mean)

Ruthenium-106 (106Ru) β-particles 1.02 years 3.54 MeV

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Sterilisation Radiation not only kills cells, it can also kill

germs or bacteria. Medical instruments (e.g. syringes) are

prepacked and then irradiated using an intense gamma ray source.

This kills any germs or bacteria but does not damage the syringe, nor make it radioactive.

Technetium-99m most significant radioisotope used in medical diagnosis t1/2 = 6 h – long enough to get a good scan, but decays

quickly to reduce exposure of patient decays by release of gamma rays

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chemically versatile as it can be bound to a variety of compounds to target many areas of the body

can be economically produced in large quantities used to image – brain, thyroid, lungs, liver, spleen,

kidney, gall bladder, skeleton, bone marrow, heart

g TcTcm 9943

9943

Technetium-99m decay product of Mo-99 which has a t1/2 = 66h Mo-99 produced in nuclear reactor at Lucas

Heights in Sydney and transported around country

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b TcMo m9943

9942

Industrial radioisotopeCesium-137 half-life of 30 years decays by emission of a beta particle and

gamma rays to Ba-137m one of the most common used in industry

thickness gauges – sheet metal, paper, plastic film levelling gauges to detect liquid flow in pipes and

tanks densitometer to check roads

one of the products of the fission of uranium when U-235 absorbs neutrons in a nuclear reactor

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5.2.4 Identify instruments and processes that can be used to detect radiation

Ionisation removal of an electron from an atom to form a

positive ion Excitation

moving an electron to a higher energy level emits photon of light when returns to ground state

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Excitation

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Instruments to detect radiation Ionisation

Photographic film (Radiation badge) Geiger-Muller tube (Geiger counter) Cloud chamber

Excitation and ionisation Scintillation counter (gamma camera)

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Cloud Chamberhttp://www.yteach.com/page.php/resources/view_all?id=affect_radiation_live_organism_scintillation_counter_Geiger_Muller_Wilson_cloud_absorbed_dose_equivalent_source_t_page_2&from=search

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Nuclear fission

when uncontrolled enormous amounts of energy released chain reaction atomic bomb

when controlled a rich source of power nuclear power reactors radioactive waste likelihood of catastrophic accidents

Nuclear Fission Animated

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Controlled and Uncontrolled Fission

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Nuclear fusion

union of two light nuclei to form a heavier nucleus

produces much more energy than nuclear fission and should be a rich source of “clean” power

nHeHH 10

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Nuclear Fusion Animation

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Half-life t1/2 a radioisotope decays at a fixed fractional rate in each second a constant fraction of the total

amount present decays t1/2 is the time for half of the atoms of a

radioisotope to decay the half-life for a given radioisotope is

always the same the longer the half-life the more stable the

radioisotope

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Half-life

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A radioactive decay curve

1 gof U-235

0.5 gof U-235

0.5 gof Pb-207

0.75 gof Pb-207

0.25 gof U-235

0.875 gof Pb-207

0.125 gof U-235

713 million years 713 million

years713 million years

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Measuring radiation Film badges

radiation darkens the photographic emulsion degree of darkening quantity of radiation

Scintillation counter crystal of NaCl “doped” with Tl+ ions pulse of light emitted on absorbing b particles or g rays photomultiplier tube detects and counts the pulses

Geiger counter cylindrical tube containing argon and ethanol vapour tube is –ve electrode, wire down middle +ve electrode measures current caused by electrons and positive

ions produced by high energy radiation (better for b)