226
Problem
26. “In a proportional counter, a pulse height analyzer can be used to determine the
energy of α-particles as well as E max for β-particles”. Explain.
27. What is the dead time of a counter and from where does it originate? Why
does the G.M. counter have a dead time of the order of 200 ms, whereas the
proportional counter has 1–10 ms? Explain.
28. Explain the working principle of a Geiger–Müller counter. G.M. (end-window)
counter can be used to detect β-particles and γ -rays and not α-particles. Why?
Explain.
29. What is a plateau of an ionization counter? What information do you derive out
of the current–voltage characteristics of an ionization counter?
30. Semiconductor detectors are sensitive to detect α-particles efficiently and the
level of background activity recorded by such counter is very low. Why? Explain.
31. A Geiger–Müller counter can be made of any shape and size, whereas there is
some restriction to the design of proportional counter. Is it a correct statement?
Discuss.
32. What are the advantages of a halogen quenched Geiger–Müller counter over the
organic quenched G.M. counter? Explain the mechanism of quenching spurious
pulses with this type of counter.
33. How will you determine the dead time of a liquid G.M. counter? Would it differ
from one counter to another? If so, why? Explain. What is the best method for
correcting the dead time of a G.M. counter? Explain.
34. Explain the principle of scintillation counter and explain with the block diagram, a scintillation counter for determining the γ -rays spectrum of a radioactive
source.
35. Why is NaI(Tl) used for counting high energetic-β-particles and γ -rays and
not for α-particles, whereas organic scintillators are used for β-particles and
α-particles but not vice versa?
36. How will you find out the best operating conditions for obtaining an energy
spectrum of γ -rays by the scintillation counter? How does this differ from the
operating conditions for counting β-particles?
37. The identification of a γ -emitting source and its characterization can be done
accurately with the scintillation counter and not with a proportional counter.
Discuss.
38. Explain the use of a pulse height analyzer in the scintillation counter to identify
a γ -source.
39. Discuss the application of standard deviation calculation in radioactive measurements and explain why a mean count rate of 100 obtained from a population of
count rates of range 80–120 will have 30% error? What procedure would you
adopt to decrease this percentage of the error to less than 1%, and what are the
factors you would need to consider for achieving this accuracy of counting?
40. Which counter would you use to detect the isotope after considering the decay
scheme of a Cesium-137 isotope? Explain the reasons for your selection.
41. (a) Explain the principle of a scintillation counter and discuss its application in
the determination of the energy of γ -rays.
Problem
26. “In a proportional counter, a pulse height analyzer can be used to determine the
energy of α-particles as well as E max for β-particles”. Explain.
27. What is the dead time of a counter and from where does it originate? Why
does the G.M. counter have a dead time of the order of 200 ms, whereas the
proportional counter has 1–10 ms? Explain.
28. Explain the working principle of a Geiger–Müller counter. G.M. (end-window)
counter can be used to detect β-particles and γ -rays and not α-particles. Why?
Explain.
29. What is a plateau of an ionization counter? What information do you derive out
of the current–voltage characteristics of an ionization counter?
30. Semiconductor detectors are sensitive to detect α-particles efficiently and the
level of background activity recorded by such counter is very low. Why? Explain.
31. A Geiger–Müller counter can be made of any shape and size, whereas there is
some restriction to the design of proportional counter. Is it a correct statement?
Discuss.
32. What are the advantages of a halogen quenched Geiger–Müller counter over the
organic quenched G.M. counter? Explain the mechanism of quenching spurious
pulses with this type of counter.
33. How will you determine the dead time of a liquid G.M. counter? Would it differ
from one counter to another? If so, why? Explain. What is the best method for
correcting the dead time of a G.M. counter? Explain.
34. Explain the principle of scintillation counter and explain with the block diagram, a scintillation counter for determining the γ -rays spectrum of a radioactive
source.
35. Why is NaI(Tl) used for counting high energetic-β-particles and γ -rays and
not for α-particles, whereas organic scintillators are used for β-particles and
α-particles but not vice versa?
36. How will you find out the best operating conditions for obtaining an energy
spectrum of γ -rays by the scintillation counter? How does this differ from the
operating conditions for counting β-particles?
37. The identification of a γ -emitting source and its characterization can be done
accurately with the scintillation counter and not with a proportional counter.
Discuss.
38. Explain the use of a pulse height analyzer in the scintillation counter to identify
a γ -source.
39. Discuss the application of standard deviation calculation in radioactive measurements and explain why a mean count rate of 100 obtained from a population of
count rates of range 80–120 will have 30% error? What procedure would you
adopt to decrease this percentage of the error to less than 1%, and what are the
factors you would need to consider for achieving this accuracy of counting?
40. Which counter would you use to detect the isotope after considering the decay
scheme of a Cesium-137 isotope? Explain the reasons for your selection.
41. (a) Explain the principle of a scintillation counter and discuss its application in
the determination of the energy of γ -rays.