AQA A2 Physics P27 Nuclear Energy Kerboodle Answers

Banner 1

C27.1 Energy and mass AQA A2 Physics P27 Nuclear Energy Kerboodle Answers : Page No. 474

1a} 10kg object when it is raised through a height of 2.0m.

2.18x 10¹⁵ kg

b an electron when it is accelerated from rest through a pd of

i 5000V,

8.89 X 10^-33 kg

ii 5MV

8.89 x 10^-30 kg

2 ]

a Write down an equation to represent this process and calculate the energy released.

27.2 Binding energy AQA A2 Physics P27 Nuclear Energy Kerboodle Answers  : Page No. 477

1a ]

Nuclear binding energy is the energy required to split a nucleus of an atom into its component parts: protons and neutrons, or, collectively, the nucleons. The binding energy of nuclei is always a positive number, since all nuclei require net energy to separate them into individual protons and neutrons.

b Sketch a curve to show how the binding energy per nucleon Of a nucleus varies with its rnass number A, showing the approximate scale cri each axis.

 

2

m (5626Fe) = 55.934939u

tomic mass of (⁵⁶₂₆Fe), m_Fe = 55.934939 u

(⁵⁶₂₆Fe) nucleus has 26 protons and (56 − 26) = 30 neutrons

Hence, the mass defect of the nucleus, ∆m = ((26 × m_H) + (30 × m_n)– m_Fe)

Where,

Mass of a proton, m_H = 1.007825 u

Mass of a neutron, m_n = 1.008665 u

∆m = ((26 × 1.007825 + 30 × 1.008665) − 55.934939)

= (26.20345 + 30.25995 − 55.934939)

= 0.528461 u

But 1 u = 931.5 MeV/c²

Therefore, ∆m = 0.528461 × 931.5 MeV/c²

The binding energy of this nucleus is given as:

E_b1 = ∆mc²

Where, c =Speed of light

E_b1 = 0.528461 × 931.5(MeV/c²)/c²

= 492.26 MeV

Average binding energy per nucleon= (492.26/56)=8.76 MeV

3 a Calculate the binding energy per nucleon, in MeV per nucleon, of

i an particle.

ii a 3He nucleus.

Mass of an o, particle 4.00150 u; mass of a 3 He nucleus 3.014 93 u

b Use the results Of your calculations in a to explain whg an (X particle rather than a SHe nucleus is emitted by a large unstable nucleus.

27.3 Fission and fusion AQA A2 Physics P27 Nuclear Energy Kerboodle Answers  : Page No. 480

1 a There is some repulsion due to electromagnetic charge, but there is another force called the strong nuclear force holding them together.

b

Nuclei are made up of protons and neutron, but the mass of a nucleus is always less than the sum of the individual masses of the protons and neutrons which constitute it. The difference is a measure of the nuclear binding energy which holds the nucleus together. This binding energy can be calculated from the Einstein relationship:

Nuclear binding energy = Δmc²

2 Nuclear fission is the process in which a large nucleus splits into two smaller nuclei with the release of energy. In other words, fission the process in which a nucleus is divided into two or more fragments, and neutrons and energy are released.

3 a Nuclear fusion is an atomic reaction in which multiple atom s combine to create a single, more massive atom. The resulting atom has a slightly smaller mass than the sum of the masses of the original atoms. The difference in mass is released in the form of energy during the reaction, according to the Einstein formula E = mc 2 , where E is the energy in joule s, m is the mass difference in kilogram s, and c is the speed of light (approximately 300,000,000 or 3 x 10 8 meters per second).

27.4 The thermal nuclear reactor AQA A2 Physics P27 Nuclear Energy Kerboodle Answers  : Page No. 484

1 What is meant by induced fission ?

Induced fission is where a stable atom has the nucleus absorb a neutron. The previously stable atom becomes unstable due to the extra neutron and fissions into two lighter elements.

i Control rods are used in nuclear reactors to control the fission rate of uranium and plutonium. They are composed of chemical elements such as boron, silver, indium and cadmium that are capable of absorbing many neutrons without themselves fissioning.

ii

The control rods are made of materials having a large absorption cross-section for slow/thermal neutrons. Some of these materials are Cadmium, Boron, Hafnium, Gadolinium.

iii

The control rods are inserted and removed from the core, as needed, to absorb neutrons and keep the reactor in a critical state. For the power output to remain steady, only one neutron from each fission should trigger an additional fission. If more than one fission neutron triggers an additional fission the reactor becomes supercritical and risks meltdown. If less than one fission neutron triggers an additional fission the reactor becomes subcritical and the chain reaction could die altogether.

2 a the moderator.

Material in the core which slows down the neutrons released from fission so that they cause more fission. It is usually water, but may be heavy water or graphite.

b the coolant.

A fluid circulating through the core so as to transfer the heat from it. In light water reactors the water moderator functions also as primary coolant. Except in BWRs, there is secondary coolant circuit where the water becomes steam.

3 Explain why the mass of fissile fuel in a nuclear reactor must exceed a critical value in order for fission to be sustained in the reactor.

4 a

The uranium that is used in the reactors has a half-life of almost a billion years. When it fissions, it turns into elements that have a much shorter half-life, seconds to decades. A shorter half-life means more radioactive.

That may seem counter intuitive, but think of it this way. First note a thumb-rule that radioactive material is effectively gone after 10 half-lives.

If something has a half-life of a billion years, it will release all its radiation over the next ten billion years or so. That means very little will be released today. Thus we will measure few radioactive particles today. However, if it had a half-life of 2 hours, it will release all its radiation today. Thus it is more radioactive.

b Used nuclear fuel is very hot and radioactive. Handling and storing it safely can be done as long as it is cooled and plant workers are shielded from the radiation it produces by a dense material like concrete or steel, or by a few metres of water.

Water can conveniently provide both cooling and shielding, so a typical reactor will have its fuel removed underwater and transferred to a storage pool. After about five years it can be transferred into dry ventilated concrete containers, but otherwise it can safely remain in the pool indefinitely – usually for up to 50 years.

Banner 2

Practice questions: Page No. 485-487

1 (a) (i)

(ii)

β– particle(s)

Electron antineutrinos

(b)

For:

Natural uranium is 98% uranium-238 which would be otherwise unused.

• Plutonium-239 would not need to be stored long term as it would be used.
• World’s uranium reserves would last many more years.
• Carbon emissions would be reduced if a higher % of world’s energy was from nuclear power.

Against:

• More radioactive waste in the form of fission products would be produced.
• Plutonium-239 would need to be transported safely to these reactors.
• There would be major security issues about the transport of plutonium-239.
• Funding of a fast breeder program would be better used on proven renewables.
• Private companies more likely to fund proven renewables than unproven fast breeders.

2 (a) (i)

Binding energy is the energy released when a nucleus is formed from separate nucleons (or the energy required to break up a nucleus into separate nucleons).

• It is energy associated with the strong nuclear force.
• The strong force does work on the nucleons in bringing them together (or the potential energy of the nucleons decreases when they are attracted together).

(ii)

The mass of a nucleus is less than the total mass of its constituent nucleons.

• Mass difference = (total mass of nucleons) − (mass of nucleus)

(iii)

The binding energy is the energy equivalent of the mass difference, by E = mc²

(b)

(c)

The zinc nucleus is very stable because it has a high value of average binding energy per nucleon (or is near the maximum of the curve of average binding energy per nucleon against mass number).

3 (a) (i)

Two small (or light) nuclei combine.

• Electrostatic repulsion has to be overcome.
• Nuclei have to be given kinetic energy for them to meet.

(ii)

A large (or heavy) nucleus splits into two smaller nuclei.

• Neutrons are released.
• Fission is usually brought about by neutron bombardment.

(iii)

Binding energy per nucleon increases when light nuclei (e.g. Z < 10) combine.

• Binding energy per nucleon also increases when heavy nuclei split.

(b)

 

Mass difference Δm between parent nucleus and products

= 219.96410 − (215.95572 + 4.00150)

= 0.00688 u

Energy released = 0.00688 × 931.3

= 6.41 MeV

= 6.41 × 10⁶ × 1.6 × 10^-19

= 1.03 × 10^-12 J

4 (a) (i

Use of P = IV gives power output of panel

Pout = 2.4 × 20 = 48 W

(ii)

(b)

(i)

Energy emitted in each decay

= 5.1 × 10⁶ × 1.6 × 10^-19

= 8.16 × 10^-13 J

Energy emitted per second

= 1.1 × 10¹⁴× 8.16 × 10^-13 = 89.8 J (which is 90 J to 2 sig figs)

(ii)

(iii)

5

(i) Point marked S at maximum of curve.

(ii)

Nucleon number A = 56 (54 to 58 allowed)

Binding energy per nucleon = 8.8 MeV

(iii) Calculate the total binding energy of this nuclide.

Binding energy of this nuclide

= 56 × 8.8 = 493 MeV

(b)

(i)

(ii)

Charge: +1 +1 → +1 +1 + 0 + 0

Baryon number: 1 + 1 → 2 + 0 + 0 + 0

Lepton number: 0 + 0 → 0 + (−1) + 1 + 0

(iii)

(c)

Fission involves the splitting of a large nucleus into two smaller nuclei.

• Fusion involves two small nuclei joining to form a slightly larger nucleus.
• Both processes cause an increase in the binding energy per nucleon.
• This energy is released as the kinetic energy of the products of the reaction.
• The increase in binding energy per nucleon is greater in a fusion reaction than in a fission reaction.
• The binding energy of a large nucleus is very much greater than that of a small nucleus, because the former contains many more nucleons.
• The net increase in binding energy during the fission of a large nucleus is therefore greater than that occurring during the fusion of two small nuclei.

6 (a

Energy is released because

• Fusion of two nuclei increases their binding energy per nucleon
• The fusion reaction produces an increase in the mass difference (or the nucleus formed is more stable than the two original nuclei).

Fusion is difficult to achieve because

• Each of the two original nuclei has a positive charge
• The electrostatic repulsion of these positive charges has to be overcome.

(b)

 (i)

Mass difference produced by fusion Δm

= (2 × 2.01355) − (3.01493 + 1.00867)

= 3.50 × 10^-3 u

(ii)

= 3.50 × 10−3 × 931.3 = 3.26 MeV

= 3.26 × 1.60 × 10^-13

= 5.22 × 10^-13 J

7 (a

Thermal neutrons

• have low kinetic energies e.g. 0.03 eV (or low speeds);

(ii) Induced fission is:

• The splitting of a large nucleus into two smaller nuclei
• That is brought about by bombardment by neutrons;

(iii) A self-sustaining chain reaction. (5 marks)

In a self-sustaining chain reaction

• The fission reaction gives out neutrons
• These neutrons cause further fissions
• The reaction is self-sustaining when one fission leads to at least one further fission.

(b) (i)

Moderation

• The neutrons from fission are fast (high energy) neutrons e.g. 2 MeV.
• The fission reaction is more favourable with thermal (low energy) neutrons.
• Moderation involves slowing down the neutrons…
• By collision with moderator atoms.
• A large number of collisions (e.g. 50) is required to do this.
• The collisions are elastic (or kinetic energy is passed to the atoms).
• The moderator atoms should have a (relatively) low mass.
• The moderator must not absorb neutrons.
• Suitable materials are graphite or water.

(ii)

Control

• Involves limiting the number of neutrons.
• Neutrons are absorbed by control rods…
• Which are inserted into the reactor to slow the reaction rate (or vice−versa).
• Boron and cadmium are suitable materials to absorb neutrons.

8 (a)

The amount of fissionable uranium-235 in the fuel rods decreases.

• Nuclei of some fission fragments can absorb neutrons.
• Nuclei of the fission fragments are radioactive.
• They emit β− and γ radiation.
• Some fission fragments have short half-lives (or high activities).

(b)

Rods are removed by remote control.

• Rods placed in cooling ponds.
• Kept in ponds for several months (or to allow short half-life isotopes to decay).
• Reference to transport precautions, such as impact resistant flasks.
• Uranium is separated from active wastes.
• High level waste is stored (as a liquid).
• Reference to storage precautions, for example shielded tanks, monitoring of emissions.
• Possibility of long−term storage by sealing active wastes in glass (vitrification) and storing the material at a geologically stable site.

Banner 2

DISCLAIMER

Disclaimer: I have tried by level best to provide the answers and video explanations to the best of my knowledge. All the answers and notes are written by me and if there is any similarity in the content then it is purely coincidental. But this is not an alternative to the textbook. You should cover the specification or the textbook thoroughly. This is the quick revision to help you cover the gist of everything. In case you spot any errors then do let us know and we will rectify it. References: BBC Bitesize AQA GCSE Science Kerboodle textbook Wikipedia Wikimedia Commons Join Our Free Facebook Group : Get A* in GCSE and A LEVEL Science and Maths by Mahima Laroyia: https://www.facebook.com/groups/expertguidance.co.uk/ For Free Tips, advice and Maths and Science Help