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Physics A Level OCR A > Module Six > Flashcards

Module Six Flashcards

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1
Q

Describe the basic structure of an X-ray tube

A

A high voltage supply connecting a cathode (hot filament) and anode (Metal target) with a vacuum between the two. It is surrounded in a lead case with a small window.

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2
Q

Describe how X-ray photons are produced

A
  • The high voltage causes electrons to be emitted from the cathode by thermionic emission.
  • They are then accelerated towards the anode
  • The anode is made of a metal target (e.g. tungsten), and is called the target metal.
  • X-ray photons are produced when the electrons are decelerated by hitting the anode.
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3
Q

Describe how X-ray tubes have been modified to make them more effective

A
  • Tube lined with lead to shield any X-rays being emmited in unwanted directions
  • Small window to allow X-rays of certain wavelength to exit and in a desired direction
  • Angled target metal to allow X-rays to be emitted in a certain direction
  • Oil is circulated to cool the anode
  • Anode is rotated to spread the heat over a larger surface area
  • Target metal has a high melting point so it won’t melt due to the heat of the tube
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4
Q

Describe the X-ray attenuation mechanism ‘Simple Scatter’

A

Energy: 1-20keV

  • X-ray photon interacts with an electron atom/absorbed by an electron
  • Does not have enough required to remove the electron
  • X-ray photons are scattered/re-admittted by the electron in a different direction, without change to its energy
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5
Q

Describe the X-ray attenuation mechanism ‘Photoelectric effect’

A

Energy less than 100keV

  • X-ray photon is absorbed by an electron
  • The electron uses this energy to escape from the atom
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6
Q

Describe the X-ray attenuation mechanism ‘Compton Scattering’

A

Energy between 0.5MeV and 5.0MeV

  • X-ray photon is absorbed by an electron
  • Electron uses some of this energy to escape the atom
  • X-ray photon is re-admitted by the electron with a lower energy and in a different direction
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7
Q

Describe the X-ray attenuation mechanism ‘Pair Production’

A

Energy ≥ 1.02 MeV

  • The X-ray photon interacts near the nucleus
  • The X-ray photon then disappears into an electron-positron pair.

This needs to by the nucleus so momentum is conserved

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8
Q

Describe the relationship between the initial intensity of an X-ray and the final intensity of an X-ray

A

Related by exponential decay: ln I and ln I0 are directly proportional where K = -µx, where x is the thickness of the material and µ is the attenuation coefficient

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9
Q

Give two examples of a contrast medium in X-rays

A
  • Barium
  • Iodine
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10
Q

Explain the use of contrast mediums in X-ray imaging

A

Help improve the visability of soft tissues and their internal structures.

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11
Q

Describe how a contrast medium helps to add detail to an X-ray image

A
  • Contrast medium is injested/injected into the patient (Organic compound of Iodine for liquids and Barium Sulfate for digestive systems)
  • The contrast medium passes through the desired areas.
  • As µ ∝ Z3, and the average atomic number of soft tissue is seven, and iodine 53 and Barium 56, there attenuation coefficients are much higher, so add high amounts of contrast.
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12
Q

Describe the process of a CAT (Computerised Axial Tomography) scan

A
  • X-ray tubes produce a thin fan-shapped beam of X-rays
  • They are detected by a set of detectors
  • The Tube and Detectors rotate around, giving a full 360° view of that slice
  • The patient is then moved out slightly, and the process continues
  • All of the slices are then put together to form a 3D computerised image.
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13
Q

Descrive the Advantages and Disadvantages of a CAT scan over a typical X-ray scan

A
  • Advantages:
    • 3D image
    • Better distinction between tissues of similar attenuation coefficients
    • Does not give a superimposed image
  • Disadvantages:
    • More Expensive
    • Can expose people to the equivalent background raditiation of several years
    • Patients have to remain very still, or a blurred image is given
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14
Q

Define medical tracer

A

A radioisotope which has been chemically combine with elements that will target the desired tissues to make a radiopharmaceutical (medical tracer)

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15
Q

Descrive the use and decay of and into Technetium-99m, and explain what the ‘m’ means

A

Tc-99m has a half life of six hours and used as a gamma emitter when using a gamma camera.

It is formed naturally by the beta- decay of molybenum-99 (Mo-99) which has a half life of 67 hours. It decays into Tc-99 by gamma decay, and Tc-99 has a half life of 210000 years.

Tc-99m is most commonly used in gamma cameras

‘m’ stands for metastable, meaning it stays in a higher energy state for longer than expected.

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16
Q

Descrive how a gamma camera works

A
  • The gamma photons from medical tracer are emitted
  • The photons travel through a colimator
  • The photons hit the scintillator, which turn the gamma photons into light photons
  • The light photons travel into a photomultiplier tube which causes the light to be turned into an electrical signal, allowing it to be detected by a computer and a high quality image is constructed
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17
Q

Descrive the use of a collimator in a gamma camera

A

A collimator allows only gamma photons travelling parallel to it to pass through, so the source of the gamma photons can be detected. Collimators are made of lead tubes, so the photons not travelling parallel are aborbed by it the tubes

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18
Q

Describe how a scintilator works in a gamma cammera

A

The scintillator material is a crystal, often sodium iodide, and a single gamma photon produces thousands of light photons when it reaches a scintiallator

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19
Q

Describe how a photomultiplier tube works in a gammer camera

A

These tubes are arranged in a hexagonal pattern, and it converts the light entering the tube into an electrical signal

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20
Q

Describe the use of Flourine-18 (F-18) as a medical tracer and its decay.

A

F-18 decays by beta+ decay, producing a positron and F-18 has a half life of around 110 minutes.

F-18 is used during PET scans, as it produces positrons which annihilate to form two gamma rays of equal magnitude, but moving in opposite directions.

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21
Q

Describe how a PET (Positron emission tomography) scan works

A
  • The patient is injected with a medical tracer
  • The gamma detectors detect the gamma photons from anhilated positrons
  • As the photons travel in opposite directions (to conserve momentum) with the same amount of energy, the computer can determine the point of annihilation from the difference in arrival times, and this allows the computer to form a slice image showing the different concentrations of the tracer.
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22
Q

Describe the advantages and disadvantages of a PET scan

A
  • Advantages
    • Non-invasive
    • Plan for complex surgery
    • Diagnose different types of cancer
    • Diagnose different types of brain disorders
    • Assess the effect of new medicines and drugs on organs
  • Disadvantages
    • Extremely expensive, so only patients with complex health problems are recommened for PET scans
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23
Q

Define Ultrasound

A

A longitudinal wave with frequency above 20kHz (human hearing)

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24
Q

Describe the piezoelectric effect

A

When a piezoelectric crystal has an e.m.f. applied to it, it causes it to compress and stretch, and this causes a pulse of ultrasound to be emitted

When a piezoelectric crystal has a force applied to it, it causes it to compress and stretch, inducing and e.m.f. in the crystal

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25
Q

Describe the use of an ultrasound transducer

A

An ultrasound transducer emits pulses of ultrasounds and receives them, using a piezoelectric crystal.

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26
Q

Describe what an A-scan is and explain its uses.

A

An A-scan uses a single transducer to record along a straight line within a patient, and can be used to determine the thickness of bone or the distance between the lens and retinca in the eye, and gives a graph of voltage against time.

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27
Q

Describe how ultrasound works in medical imaging

A
  • A pulse of ultra sound is send from a transducer
  • Each pulse is partially transmitted and partly reflected at each medium boundary
  • The reflected pulse is received by the transducer, and the intensity and time taken to return can be used to determine an image
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28
Q

Describe what a B-scan is and explain how it works

A

A B-Scan (Brightness Scan) gives a 2D image of the patient, in a cone shape.

  • Transducer is moved over patient’s skin
  • Output of the transducer is conncted to a high speed computer
  • Each position of the transducer produces a row of dots on the screen, which corresponds to a boundary between two tissues
  • The brightness of the dot is proportional to the intensity of the relfected ultrasound pulse
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29
Q

Define Acoustic Impedance

A

The product of the density of the substance and the speed of ultrasound in that substance. Units: kg m-2 s-1

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30
Q

Explain the use of coupling gel in an ultrasound scan

A

As the air skin boundary would reflect almost all of the incident ultrasound, a coupling gel is used with a similar impedance similar to that of skin. This fills the air gaps between the transducer and the skin, meaning that very little reflection occurs at this boundary

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31
Q

Define Impedance/acoustic matching

A

When two substances have similar values of acoustic impedance

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32
Q

Explain the Doppler effect

A

When the bunching up/spreading out of a wave from a moving object changes its frequency

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33
Q

Explain how Doppler imaging works

A
  • The ultrasound transducer is pressed lightly over the skin above the blood vessel at an angle
  • The transducer sends pulses of ultrasound and receives relflected pulses from inside the patient.
  • The frequency shift is measured and this is used to determine the speed and direction of the blood moving in the patient.
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34
Q

Describe the Alpha-Scattering experiment

A
  • A nattow beam of alpha particles, all of the same kinetic energy, were targeted at a thin piece of gold foil, which was only a few atoms thick
  • Alpha particles were scattered by the foil and detected on a screen mounted in front of a microscope
  • Each alpha particle hitting this screen produced a tiny speck of light
  • The microscope was moved around in order to see the number alpha partices per minute was being scattered in each region around the foil.
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35
Q

Explain the effect the Alpha-Scattering experiment had on model of the atom

A
  • Most atoms passed straight through - most of the atom was empty space, with the mass concentrated in a small region
  • A few of the alpha particles where scattered more than 90° - the nucleus had a positive charge overall, for it repelled the few alpha particles which came near it
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36
Q

Describe the basic structure of the nuclear model

A

A nucleus made up of protons and neutrons with electrons arranged in energy levels around the nucleus

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37
Q

Describe the the relationship between the radius of a nucleus and its nucleon number

A

R ∝ A1/3

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38
Q

Describe the nature of the strong nuclear force

A

It acts between all nucleons and its a very short range force of attraction. The force is attractive to about 3 fm and repulsive below about 0.5 fm

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39
Q

Describe the relationship between particles and antiparticles

A

Particles and antiparticles have the same mass, but everything else is opposite (e.g. electrons and positrons both have the same mass, but have opposite charges and lepton number) and will annihilate each other when they meet.

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40
Q

Describe what a hadron is

A

A hadron is a particle or antiparticle which is affected by the strong nuclear fource, and decay by the weak nuclear force

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41
Q

Describe what a lepton is

A

A lepton is a particle or antiparticle which is not affected by the strong nuclear force.

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42
Q

Give three examples of quarks

A

Up, Down and Strange (and there respective anti-quarks)

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43
Q

Describe the quark model of a proton

A

UUD (Up, Up, Down)

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44
Q

Describe the quark model of a neutron

A

UDD (Up, Down, Down)

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45
Q

Explain the difference between a baryon and a meson

A
  • Both are hadrons:
  • Baryons are made up of three quarks
  • Mesons are made up of a combination of a quark and an anti-quark
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46
Q

Describe what β- decay is, and include the quark model

A

Type of radioactive decay which emitts a high speed electron

n → p+ + e- + -νe

d → u + e- + -νe

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47
Q

Describe what β+ decay is, and include the quark model

A

Type of radioactive decay which emitts a high speed positron

p+ → n + e+ + νe

u → d + e+ + νe

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48
Q

What four things need to be conserved in a nuclear decay?

A
  • Momentum
  • Baryon Number
  • Lepton Number
  • Charge

As mass and energy can change, they are not conserved individually, but conserved together.

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49
Q

Define radioactive decay

A

The spontaneous and random decay of a nucleus, which gives off ionisation radiation.

50
Q

Describe how ionising radiation can be observed

A

A cloud chamber can be used.

It contains air saturated with vapour at very low temperatures, and when the air molecules are ionised, liquid condenses onto the ions to leave tracks of droplets marking the path of the radiation

51
Q

Describe the nature of alpha radiation

A

Consists of a helium nucleus and has a charge of +2e. This radiation is the least penetrating and the most ionising, and can be stopped by a few sheets of paper, or a few cm of air.

52
Q

Describe the nature of beta radiation

A

Consists of a fast moving electron/positron with a charge of -e/+e. It is neither the least nor most ionisating or penatrating radiation, and is stopped by a few mm of aluminium.

53
Q

Describe the nature of gamma radiation

A

An electromagnetic wave consisting of high-energy photons with wavelengths less than about 10-13 m. They travel at the speed of light and have no charge. They are the most penetrating, but the least ionising and are mainly absorbed by a few cm of lead.

54
Q

Describe how all types of radiation can easily be distinguised from one another

A

When placed in a uniform electric/magnetic field, the amounts of deflection can determine which is which radiation.

Alpha particles are deflected less than beta particles due to their mass, and beta +&- create mirror images of each other. Gamma photons are not reflected.

55
Q

Explain why radioactive decay is random

A
  • We cannot predict when a particular nucleus in a sample will decay, or which will decay next
  • Each nucleus within a sample has the sam chance of decaying per unit time.
56
Q

Explain why radioactive decay is spontaneous

A

It is not affected by:

  • Presence of other nuclei in the sample
  • External factors, such as pressure and temperature
57
Q

Define half life of an isotope.

A

The average time it takes for half the number of active nuclei in a sample to decay (t1/2 = ln(2)/𝜆)

58
Q

Define activity of a source

A

The rate at which nuclei decay or disintergrate

59
Q

Define the decay constant of an isotope

A

The probability of decay of an individual nuceus per unit time

60
Q

Describe the relationship between the initial activity/number of nucleons with final activity/number of nucleons

A

Exponential decay:

ln(A) = ln(A0) * -𝜆t

61
Q

Describe how the half life of an isotope such as protactinium can be determined

A

An isotope with a short life can easily have its half life measured, and this is the procedure with protactinium-234:

  • A sealed plastic bottle containing and organic solvent and solution of uranyl(VI) nitrate in water is used to separate the protactinium from its parent ion thorium-238.
  • The mixture is then shaken, and the lighter organic layer with only the protactinium-234 rises to the top and the count rate can be counted by using a GM tube.
  • The count rate is then recorded against time, and a graph is plotted which can be used to determine the half life.
62
Q

Describe how carbon-dating can be used to date an object

A
  • The ratio of carbon-14 to carbon-12 is know and is almost constant.
  • When an organism dies, it stops taking in carbon from the atmosphere.
  • The carbon-14 present continues to decay
  • Measure the new ratio of carbon-14 to carbon-12, and compare this to the known the ratio
  • Using the half life of carbon-14, and estimated age can be worked out.
63
Q

Describe the limitations of carbon-dating

A
  • Assumes that the ratio of carbon-14 atoms to carbon-12 atoms has remained constant over time, as increased carbon dioxide emissions due to buring fossil fuels may have reduced this ration, as would natural events such as volcanic eruptions, or solar flares from the sun, or the testing of nuclear bombs
  • The amounts of carbon-14 present in organisms is very small, so the activities are very small, so can be hard to have a comparable count rate.
64
Q

Describe the dating of rocks

A
  • The decay of rubidium-87 is used
  • Rubidium has an extremely long half life and is a beta minus emitter
  • |t can be compared to the amount of stable strontium-87 which it has formed.
65
Q

Describe the conservation of mass and energy

A

In a reaction, mass and energy individually are not always conserved.

Sometimes, mass is converted into energy (or vice versa) using the relationship ∆E=∆mc2

66
Q

Explain how mass and energy are conserved in simple nuclear reactions

A
  • In a nuclear decay, energy is released, so mass must slightly decrease
  • In nuclear fission and fusion, the mass on both sides of the reaction are not the same, so energy must be taken in/given out
67
Q

Describe how the conservation of mass and energy explains the annihilation and creation of matter/antimatter

A
  • When they annihilate, their mass is converted into energy
  • When they create, surrounding energy is converted into mass
68
Q

Define mass defect

A

The difference between the mass of the completely separated nucleons and the mass of the nucleus

69
Q

Define binding energy

A

The minimum energy required to completely separate a nucleus into its constituent protons and neutrons

70
Q

Explain the use of binding energy per nucleon of nuclei and state how this can be more useful to know than the binding energy of a nuclei

A

The binding energy per nucleon can tell us how tightly bound the nucleons are within the nucleus, and can be used to determine whether a reaction will a nuclear fission or fusion.

It is more useful as binding energy per nucleon can be used to compare different atoms

71
Q

Describe the process of induced fission

A
  • A thermal neutron is absorbed by the nucleus
  • The nucleus becomes unstable
  • The nucleus splits into two daughter nuclei of roughly equal size and some fast moving neutrons
  • Energy is released as mass has been converted kinetic energy
72
Q

Explain how induced fission can cause a chain reaction

A
  • The induced fission causes fast neutrons to be produced
  • These neutrons are then slowed to thermal neutrons
  • These new thermal neutrons can then cause another fission reaction
73
Q

State the main components of a fission reactor

A
  • Fuel Rods
  • Control Rods
  • Moderator
  • Coolant
  • Heat Exchanger
74
Q

Describe what the role of fuel rods are in a fission reactor

A

Contains enriched uranium, mainly U-238 with small amounts of U-235

The U-235 accepts thermal neutrons, causing a fission reaction

The U-238 absorbs excess neutrons to slow down the rate of reaction

75
Q

Describe what the role of the moderator is in a fission reactor

A
  • To slow down the fast neutrons produced into thermal neutrons
    • The fast moving electrons collide elastically with the moderator (often graphite or heavy (D2O) water
    • They trasfer significant kinetic energy and slow down
  • In many reactors, heavy water is used, for the D2O can act as the moderator and as the coolant (instead of light water and a graphite moderator)
76
Q

Describe what the role of the control rods are in a fission reactor

A

They are made of a material whose nuclei readily absorb neutrons, to slow down a nuclear reaction, and are controlled by a computer as to how much of the rods are inserted into the reactor at any one time.

77
Q

Discuss the environmental impacts of nuclear waste

A
  • The uranium-238, when absorbs an extra neutron, decays into plutonium-239, which is highly toxic, with a very long half life.
  • Daughter nuclei produced by a nuclear fission reaction is also often radioactive
  • They are often buried deep underground, and they need to be geologically stable, secure from attack and designed for saftey
78
Q

Describe the process of a nuclear fusion reaction

A
  • Nuclei are brought extremely close together
  • The strong nuclear force then causes them to fuse together, forming one nucleus
79
Q

Describe the limitations of conducting a nuclear fusion reaction on earth

A
  • Extremely high temperatures are required to force the nuclei together, for they have to overcome a huge electrostatic force of repulsion
  • Currenlty, reactors take in more energy to do the reaction then they can have as an output, not making them economically viable
80
Q

What causes a magnetic field

A

Due to either:

  • Moving charges
  • Permanent magnets
81
Q

Describe the magnetic field line patterns for a long straigh current-carrying conducter

A

Use right hand grip rule:

  • Thumb points in direction of conventional current
  • Your fingers curl around the wire, showing the direction of the magnetic field lines.
82
Q

Describe the magnetic field pattern for a flat coil

A

The lines come out from the end where the current comes out and go into the end which the current goes in

83
Q

Describe Fleming’s left hand rule

A

A way to show the relationship in the directions of current, magnetic field lines and the force applied

84
Q

Define magnetic flux density

A

The strength of the magnetic field, measured in teslas, hence:

The amount of force applied by unit current and unit length on an object in a magnetic field.

85
Q

State four factors which effect the magnitude of the force experienced by a wire in an external magnetic field

A
  • Current
  • Length of the wire in the magnetic field
  • Sin x, where x is the angle between the magnetic field and the current direction
  • Strength of the magnetic field.
86
Q

Explain how a charged particle can go travel in circular motion due to a magnetic field

A

If the force applied to the charged particle due to a magnetic field is at right angles to the particle’s velocity, the force acts as the centrapetal force on the object.

87
Q

Define a velocity selector

A

A velocity selector is a device that uses both electric and magnetic fields to select charged particles of specific velocity.

88
Q

Describe how a velocity selector works

A
  • Two parallel horizontal plates are connected to a power supply
  • They produce a uniform electric field
  • A uniform magnetic field is also applied perpendicular to the electric field
  • All particles enter the velocity selector through a narrow slit
  • In order to be undeflected, only particles with electric force which is equal to its magnetic force will leave through a second narror slit
  • The desired velocity is chosen by using v= E/B
89
Q

Define magnetic flux

A

The product of the component of the magnetic field density perpenicular to the area and the crossectinal area

90
Q

Define the unit weber

A

One weber is equal to 1 Tesla unit area (magnetic flux)

91
Q

What is magnetic flux linkage?

A

The product of the number of turns in the coil (N) and the magnetic flux

92
Q

What causes an e.m.f. to be induced in a circuit, when related to magnetism?

A

When there is a change in the magnetic flux linking the circuit

93
Q

Define Faraday’s Law

A

The magnitude of the induced e.m.f is directly proportional to the rate of change of magnetic flux linkage

94
Q

Define Lenz’s Law

A

The direction of the induced e.m.f. or current is always such as to oppose the change producing it

95
Q

Describe how a simple A.C. works

A
  • A coil is turned in radical magnetic field
  • The change in magnetic flux linkage causes an e.m.f to be induced
  • As e.m.f. ∝ -∆ø, plotting a graph of magnetic flux linkage against time’s negative gradient will equal the e.m.f.
  • As the change in magnetic flux linkage varies with cos(x) where x is the angle made with the vertical, and the coil is turned at a constant speed, the rate of change of magnetic flux linkage changes in relation to a cos graph, so the gradient will give a sin graph, giving an alternating e.m.f., so an alternating current
96
Q

Define a transformer

A

An appliance which changes alternating voltages to higher or lower values

97
Q

Suggest why a transformer is made from a laminated soft iron core?

A
  • Soft Iron: can easily be magnitised and de-magnitised
  • Laminated: minimise currents in the core itself, so minimising loses due to heating
98
Q

Define Capacitance

A

The charge stored pur unit p.d. across it.

99
Q

What is a capacitor?

A

An electrical component in which charge is separated and stored

100
Q

Describe the charging and discharging of a capacitor

A
  • When connected to an e.m.f, electrons flow from the cell for a very short time
  • They cannot travel through the plates for they are insulated
  • This means electrons are removed from one plate of the capacitor and electrons are depsoited onto the other plate.
  • The first plate becomes deficient in electrons, and gets a positive charge, and the second plate vice versa.
  • As current is the same, charge must be conserved, so there is a potential difference across the plates
  • The current becomes zero in the circuit when the p.d. across the plates equals the e.m.f. of the circuit
101
Q

Define the unit Farad

A

One coulomb per volt

102
Q

What is the relationship between the capacitance of a circuit when the capacitors are in parallel?

A

C1 + C2 …. = CT

103
Q

What is the relationship between the voltage of two capacitors in parallel?

A

The p.d. across each capacitor is the same

104
Q

What is the relationship of the capacitance of capacitors in series?

A

1/C1 +1/C2 …… = 1/CT

105
Q

How is it possible to determine the energy stored by a capacitor graphically?

A

The area under a p.d./Q graph is equal to the energy stored

106
Q

What is the use of a capacitor?

A

Storage of energy, e.g:

  • Camera flash
  • Emergency power backup
  • Rectifier circuits

Or any other use which requies a short burst of energy.

107
Q

Why is a resistor used when discharging a capacitor?

A

As the resistor can be used to effect the time constant, so can be used to control the rate of discharge of a capacitor

108
Q

Describe the time constant of a capacitor-resistor circuit

A

Is roughtly the time which it takes the capacitor to decay to 37% of its original value (e-1)

109
Q

What causes an electric field?

A

Any object with a charge

110
Q

Define electric field strength

A

The force experienced per unit positive charge at that point

111
Q

Describe how an object with an electric field can be modelled

A

A uniformly charged sphere is often modelled as a point charge at its centre

112
Q

What is the use of electric field lines?

A

They are used to map electric fields and travel from positive to negative

113
Q

Define coulomb’s law

A

Any two point charges exert an electrostatic force on each other which is directly proportional to the product of their charges and inversely proportional to the square of the distance between them.

114
Q

Give the similarities between electric and gravitational fields

A
  • Both inversley proportional to the separation2
  • Both a point mass/charge which produces a radial field
  • Field strenght is both a force per unit of something
115
Q

Give the differences between electric fields and gravitational fields

A
  • Gravitational is always attractive, whilst electric can be both
  • Gravitational fields are related to masses, whilst electric fields are related to charge.
116
Q

Describe how the electric field strength of two parallel plates can be determined

A

The voltatge across the plates can be measured and divided by the distance between the plates in metres.

117
Q

Define electric potential

A

The work done per unit charge in bringing a positive charge from infinity to that point.

118
Q

What is the electric potential at infinity?

A

Zero

119
Q

Derive an equation for the capacitance of an isolated sphere

A

C=Q/V

Q=4πε0RV

Combining gives: C=4πε0RV/V

So C=4πε0R

120
Q

Describe how the work done for a point charge can be worked out

A

Calculate the area under the force-distance graph for that point charge

121
Q

Define electric potential energy

A

The work done on a particle to bring it from infinity to a certain point in an electric field

Physics A Level OCR A (4 decks)

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