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1) True or false

a) Half-wave rectification yields one x-ray pulse per cycle.

b) 99 42Mo decays to 99m 43 Tc by  β decay.

c) A K characteristic photon can occur when the electron jumps from the K-shell to ll an orbital vacancy in the L-shell.

d) A 100 keV photon has a smaller wavelength than a 1 MeV photon.

e) A semiconductor is characterized as having a conduction band and valence band.

f) The maximum possible number of electrons in any orbit is given by 2n2, where n is the principle orbit quantum number.

g) An antineutrino accompanies a β particle in   decays.

h) When a photon of 100 keV and another of 1 MeV are Compton scattered at an angle of 90° , the 1 MeV photon looses less energy.

i) The threshold energy of an incoming photon for pair production to occur is 2 X the rest energy of an electron.

j) In linacs, the flattening filter is used to generate a more uniform photon fluence at the patient surface.

2) SELECT (circle) THE CORRECT ANSWER

a. The concept of electronic equilibrium is significant in regards

i. to the generation of x rays in the anode.
ii. to the measurement of exposure with ionization chambers.
iii. to the generation of characteristic photons.

b. Consider two mono energetic photon beams with the similar photon fluences. In one beam the photons are 100 keV and in the other they are1 MeV. Select the most suitable relation among both exposures (X):

i. X(100keV) = 12 X(1MeV)
ii. X(1MeV) = 12 X(100keV)
iii. X(1MeV) = 1000 X(100keV)

c. Electrons with kinetic energy of 1.0 MeV have a specific ionization in air of 6000 IP/m while alpha particles of 2.0 MeV have an LET in air of 0.175 keV/ m. What following value is closest to the ratio LET(alphas)/LET(electrons) in air:

i. 860
ii. 4000
iii. 0.05

d. A α particle is

i. used in positron emission tomography (PET) imaging.
ii. a singly ionized helium atom with an LET greater than x rays.
iii. a helium nucleus with an LET greater than x rays.

e. The inherent filtration in x-ray tubes causes a beam to be harder by

i. absorbing more low energy photons than higher energy ones.
ii. absorbing more high energy photons that lower energy ones.
iii. filtering the electrons incident on the anode.

f. An ionization chamber is used on Tuesday (T=22°C, P=760mmHg) and then on Wednesday (T=25°C,P=740 mmHg) to monitor the output from an x-ray tube. If the output from the tube is identical on both days, then the chamber reading on Wednesday would be

i. higher than the reading on Tuesday.
ii. lower than the reading on Tuesday.
iii. the same as the reading on Tuesday.

g. The bending magnet within a linac is used to

i. bend the photon beam through a appropriate angle.
ii. Bend the electron beam through a appropriate angle.
iii. Bend the microwave beam through a appropriate angle.

h. A condenser-type pocket ionization chamber is filled with air at STP. The chamber volume is 2cm3. The capacitance of the chamber is 5 pF. The voltage across the chamber before exposure to radiation is 180 V. The voltage across the chamber after the exposure is 160 V. What value is closest to the radiation exposure?

i. 153 mR.
ii. 153 Gy.
iii. 0.153 C/kg.

i. One x-ray tube has a Mo anode and is operated at 4mA, 30 kV. Which of the following parameters for a tungsten anode tube would give a bremmstrahlung radiated power output that is 10 times bigger than the Mo (4mA, 30 kV) radiated power.

i. 2.1 mA, 100 kV.
ii. 5.1 mA, 80 kV.
iii. 501 mA, 100 kV.

j. A free air ionization chamber is

i. used to calibrate thimble ionization chambers.
ii. is used to measure capacitance.
iii. used to measure characteristic x rays.
iv. all of the above.

3) Exposure

a) A 2 mm diameter parallel beam of photons each with energy of 100 keV is incident on a water phantom of thickness 15 cm. If the exit exposure is 2 mR (caused by primary photons), find out the number of photons incident on the water phantom.

b) What will be your answer in (a) if the beam diameter was twice as big?

4) Nomenclature/Quantum

a) A point source of 60Co emits equal numbers of photons of 1.17 and 1.33 MeV giving a ux density (i.e. uence rate) of 5.7 109 photon cm-2 s-1 at a specified location. What is the energy uxdensity (i.e. energy uence rate) expressed in MeV cm-2 s-1?

b) Give the quantum numbers of all electrons in a silicon (Z=14) atom.

5) Photon Interactions

a) Consider a Si detector of 1 mm thickness. 106 photons each with energy of 100 keV are incident on the detector. Find the number of coherent, Compton, and photoelectric absorption interactions.

b) What are the mean energy transferred and mean energy absorbed in the 1 mm thick Si detector in (a)?

6) Activity

a) A certain radioactive material emits gamma rays with energy 1 MeV. Another sample of radioactive material emits gamma rays with energy 10 keV. If both of these emit the same amount of energy per unit time, compare their activities.

b) A source of 198Au with a half-life of 2.69 days has an initial activity of 5 Ci. find out the activity after 4.0 days. Express this activity in Bq.

7) Production of X Rays

a) Consider an x-ray machine with a step-up transformer consisting of a primary coil of 100 turns and a secondary one with 50000 turns. If the voltage applied across the primary coil is 100 volts, find the minimum wavelength of a bremsstrahlung photon emitted by the x-ray tube, the frequency of the photon, and the energy of the photon.

b) Identify (via circling and labelling) the anode, cathode, step-up transformer, step-down transformer, the primary and secondary windings of the transformers, and the diodes. Consider the depicted electron. What path would it take to get to the point labelled as a?

a) Identify the radioactive process pictured in this graph: (i) alpha emission, (ii) electron capture, (iii) beta emission, and (iv) gamma emission.

b) 614C is a pure beta emitter that decays to 147N. If the exact atomic masses of the parent and daughter are 14.003242 amu and 14.003074 amu, respectively, find out the energy of the most energetic beta particle.

9) Dose

a) How many ion pairs are produced in 1 cm3 of air during an exposure of 100 mR? The density of air at STP is ρ= 1:293kg m-3. What is the absorded dose to air?

b) An thin walled carbon-wall ionization chamber, whose volume is 2 cm3, is  lled with standard air at 0°C and 760 mmHg and is placed inside a tank of water to make a depth-dose measurement. A 25 MeV electron beam produces a current of 0.02 µA in the chamber. If the mass stopping power of water at the depth of measurement for 25 MeV electrons relative to air is 1.068, what is the dose?

• Category:- Physics
• Reference No.:- M9978

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