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Conceptual questions

Explain why the fission of heavy nuclei releases energy. Similarly, why is it that energy input is required to fission light nuclei?

Explain, in terms of conservation of momentum and energy, why collisions of neutrons with protons will thermalize neutrons better than collisions with oxygen.

The ruins of the Chernobyl reactor are enclosed in a huge concrete structure built around it after the accident. Some rain penetrates the building in winter, and radioactivity from the building increases. What does this imply is happening inside?

Since the uranium or plutonium nucleus fissions into several fission fragments whose mass distribution covers a wide range of pieces, would you expect more residual radioactivity from fission than fusion? Explain.

The core of a nuclear reactor generates a large amount of thermal energy from the decay of fission products, even when the power-producing fission chain reaction is turned off. Would this residual heat be greatest after the reactor has run for a long time or short time? What if the reactor has been shut down for months?

How can a nuclear reactor contain many critical masses and not go supercritical? What methods are used to control the fission in the reactor?

Why can heavy nuclei with odd numbers of neutrons be induced to fission with thermal neutrons, whereas those with even numbers of neutrons require more energy input to induce fission?

Why is a conventional fission nuclear reactor not able to explode as a bomb?

Problem exercises

(a) Calculate the energy released in the neutron-induced fission (similar to the spontaneous fission in [link] )

n + 238 U 96 Sr + 140 Xe + 3 n,

given m ( 96 Sr ) = 95.921750 u and m ( 140 Xe ) = 139.92164 . (b) This result is about 6 MeV greater than the result for spontaneous fission. Why? (c) Confirm that the total number of nucleons and total charge are conserved in this reaction.

(a) 177.1 MeV

(b) Because the gain of an external neutron yields about 6 MeV, which is the average BE/ A for heavy nuclei.

(c) A = 1 + 238 = 96 + 140 + 1 + 1 + 1, Z = 92 = 38 + 53 , efn = 0 = 0 size 12{A=1+"238"="96"+"140"+1+1+1,`Z="92"="38"+"53",`"efn"=0=0} {}

(a) Calculate the energy released in the neutron-induced fission reaction

n + 235 U 92 Kr + 142 Ba + 2 n,

given m ( 92 Kr ) = 91 . 926269 u and m ( 142 Ba ) = 141 . 916361 u .

(b) Confirm that the total number of nucleons and total charge are conserved in this reaction.

(a) Calculate the energy released in the neutron-induced fission reaction

n + 239 Pu 96 Sr + 140 Ba + 4 n ,

given m ( 96 Sr ) = 95 . 921750 u and m ( 140 Ba ) = 139 . 910581 u size 12{m \( "" lSup { size 8{"140"} } "Ba" \) ="139" "." "910581"`u} {} .

(b) Confirm that the total number of nucleons and total charge are conserved in this reaction.

(a) 180.6 MeV

(b) A = 1 + 239 = 96 + 140 + 1 + 1 + 1 + 1, Z = 94 = 38 + 56 , efn = 0 = 0 size 12{A=1+"239"="96"+"140"+1+1+1+1,`Z="94"="38"+"56",`"efn"=0=0} {}

Confirm that each of the reactions listed for plutonium breeding just following [link] conserves the total number of nucleons, the total charge, and electron family number.

Breeding plutonium produces energy even before any plutonium is fissioned. (The primary purpose of the four nuclear reactors at Chernobyl was breeding plutonium for weapons. Electrical power was a by-product used by the civilian population.) Calculate the energy produced in each of the reactions listed for plutonium breeding just following [link] . The pertinent masses are m ( 239 U ) = 239.054289 u , m ( 239 Np ) = 239.052932 u , and m ( 239 Pu ) = 239.052157 u .

238 U + n 239 U + γ 4.81 MeV

239 U 239 Np + β + v e 0.753 MeV

239 Np 239 Pu + β + v e size 12{"" lSup { size 8{"239"} } "Np" rightarrow "" lSup { size 8{"239"} } "Pu"+β rSup { size 8{ - {}} } +v rSub { size 8{e} } } {} 0.211 MeV

The naturally occurring radioactive isotope 232 Th size 12{"" lSup { size 8{"232"} } "Th"} {} does not make good fission fuel, because it has an even number of neutrons; however, it can be bred into a suitable fuel (much as 238 U size 12{"" lSup { size 8{"238"} } U} {} is bred into 239 P size 12{"" lSup { size 8{"239"} } P} {} ).

(a) What are Z size 12{Z} {} and N size 12{N} {} for 232 Th size 12{"" lSup { size 8{"232"} } "Th"} {} ?

(b) Write the reaction equation for neutron captured by 232 Th and identify the nuclide A X produced in n + 232 Th A X + γ .

(c) The product nucleus β size 12{β rSup { size 8{ - {}} } } {} decays, as does its daughter. Write the decay equations for each, and identify the final nucleus.

(d) Confirm that the final nucleus has an odd number of neutrons, making it a better fission fuel.

(e) Look up the half-life of the final nucleus to see if it lives long enough to be a useful fuel.

The electrical power output of a large nuclear reactor facility is 900 MW. It has a 35.0% efficiency in converting nuclear power to electrical.

(a) What is the thermal nuclear power output in megawatts?

(b) How many 235 U size 12{"" lSup { size 8{"235"} } U} {} nuclei fission each second, assuming the average fission produces 200 MeV?

(c) What mass of 235 U size 12{"" lSup { size 8{"235"} } U} {} is fissioned in one year of full-power operation?

(a) 2 . 57 × 10 3 MW size 12{2 "." "57" times "10" rSup { size 8{3} } `"MW"} {}

(b) 8.03 × 10 19 fission/s size 12{8 "." "04" times "10" rSup { size 8{"19"} } `"fission/s"} {}

(c) 991 kg

A large power reactor that has been in operation for some months is turned off, but residual activity in the core still produces 150 MW of power. If the average energy per decay of the fission products is 1.00 MeV, what is the core activity in curies?

Questions & Answers

what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
yes that's correct
I think
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Practice Key Terms 9

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Source:  OpenStax, Physics for the modern world. OpenStax CNX. Sep 16, 2015 Download for free at http://legacy.cnx.org/content/col11865/1.3
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