Radiation Detection

1. Radiation Detection
STSN 1132 # 3
Nuclear Instrumentation
2019/2020
1

2. QUIZ1
1. Describe Ionizing radiation (2 marks)
2. Describe Non-Ionizing radiation (2 marks)
3. What is the suitable shielding material to
attenuate gamma radiation? Why? (2 marks)
4. Describe ALLtypes of ionizing radiation. (2 marks)
5. List 2 application of ionizing radiation in daily life.
( 2marks)

3. Outlines..
• Introduction
•The detector
• The NIM concept
• The High Voltage Power Supply
• The Preamplifier
• The Amplifier
•The oscilloscope
•The Discriminator or Single Channel Analyzer (SCA)
• The Scaler
•The Timer
•The Multichannel Analyzer

4. INTRODUCTION
• Counting systems are classified into two types,
according to the method of operation:
i. Pulse-type systems. The output consists of
voltage pulses, one pulse per particle detected.
ii. Current-type systems. Theoutput is an average
value, resulting from the detection of many
particles.

5. INTRODUCTION
Abasicdiagram for radiation detection system

6. THEDETECTOR
What isthe function of the detector???
• The function of the detector is to produce a
signal for every particle entering into it. Every
detector works by using some interaction of
particles with matter.

7. THEDETECTOR
Typesof common detector:
1. Gas-filled counters (ionization, proportional, Geiger-
Muller counters)
2. Scintillation detectors
3. Semiconductor detectors
4. Spark chambers
5. Bubble chambers (used with high energy particles)
6. Photographic emulsions
7. Thermoluminescent dosimeters (TLDs)
8. Cerenkov counters
9. Self-powered neutron detectors

8. THEDETECTOR
• The signal at the output of most detectors is avoltage
pulse.
• For others, the signal may be achange in colour
(emulsions) or some trace that can be photographed
(bubble or spark chambers)

9. THEDETECTOR
• The ideal pulse-type counter should satisfy the
following requirements:
i. Every particle entering the detector should produce a
pulse at the exit of the counter, which is higher than
the electronic noise.
ii. The duration of the pulse should be short, so that
particles coming in one after the other in quick
succession produce separate pulses. The duration of
the pulse is a measure of the dead time of the counter
and may result in loss of counts in the caseof high
counting rates.

10. THEDETECTOR
iii. If the energy of the particle is to be measured, the
height of the pulse should have some known fixed
relationship to the energy of the particle. it is
important that the size of the counter is such that the
particle deposits all its energy (or a known fraction) in
it.
iv.If two or more particles deposit the same energy in the
detector, the corresponding pulses should have the
same height. energy resolution

11. Goodand bad energy resolution

12. Varioussizeof Detector
(in Nuclear Science Program, UKM)

13. THENIM CONCEPT
• Nuclear Instrument Modules (NIM) – is the most
commercially available instruments that are used in
radiation measurements conform to the standards.
design of
physically
• The objective of the NIM standard is the
commercial modules that are interchangeable
and electrically.
• The electrical interchangeability is confined to the supply of
power to the modules and in general does not cover the
design of the internal circuits.

14. NIM Bin
(in Nuclear Science Program, UKM)

15. THEHIGHVOLTAGEPOWERSUPPL
Y(HV)
• The high-voltage power supply (HV) provides a positive or negative
voltage necessary for the operation of the detector. Most detectors
need positive high voltage (HV).
HighVoltage Needed for Certain CommonDetectors
Detector Highvoltage (V)
Ionization counters HV<1000
Proportional counters 500 <HV<1500
GM counters 500 <HV<1500
Semiconductor detectors
•Surface-barrier
•Lidrifted
HV<100
100 <HV<3000

16. HVPower Supply
(in Nuclear Science Program, UKM)

17. Voltageknob – to set the
voltage
ON/OFF button –
indicator light
Polarity– the output is
positive or negative
Voltagedisplay panel – show
the voltage for the system

18. THEPREAMPLIFIER
• The primary purpose of the preamplifier is
to provide an optimized coupling between the output of the
detector and the rest of the counting system.
• The preamplifier is also necessary to minimize any sources of noise
that may change the signal.
• Thesignal that comes out of the detector is very weak, in the millivolt
(mV) range. Before it can be recorded, it will have to be amplified by
afactor of athousand or more.
• The signal will have to be transmitted through a cable to the next
instrument of the counting system, which is the amplifier.
• Transmission of any signal through acable attenuates it to a certain
extent. might be lost in the electronic noise.

19. THEPREAMPLIFIER
• This is avoided by placing the preamplifier asclose to the detector as
possible.
The preamplifier shapes the signal and reduces its attenuation by
matching the impedance of the detector with that of the
amplifier. After going through the preamplifier, the signal may be
safely transmitted to the amplifier, which may be located at a
considerable distance away. Although some preamplifiers amplify
the signal slightly, their primary function is that of providing
electronic matching between the output of the detector and the
input of the amplifier.

20. Preamplifier
(in Nuclear Science Program, UKM)
Front view of preamplifier Above view of preamplifier

21. Amp connector
HVconnector
TESTconnector
Signaloutput

22. THEAMPLIFIER
• Themain amplification unit is the amplifier. increases
the signal by asmany as1000 times or more.
• In addition to signal amplification, an equally
important function of the amplifier is to convert the
signal at the output of the preamplifier into aform
suitable for the measurement desired.
• Commercial amplifiers have two dials for adjusting the
amplification:
a. Coarse gain - This dial adjusts the amplification in
steps.
b. Fine gain - This dial adjusts the amplification continuously
within each step of the coarse gain.

23. • Most commercial amplifiers provide at the output
two types of pulses, called unipolar and bipolar.
Thepulse at the output of the amplifier: (a) unipolar pulse and (b) bipolar pulse.
THEAMPLIFIER

24. Amplifier
(in Nuclear Science Program, UKM)

25. Coarsegainknob
Finegainknob
Shapingtime knob
Polarity switch
Coaxialcableknob

26. • The oscilloscope is an instrument that permits the
study of rapidly changing phenomena, such asa
sinusoidal voltage or the pulse of acounter.
• The phenomenon is observed on a fluorescent
screen. Thehorizontal axis of the screen measures
time. Thevertical axis gives volts.
• In radiation measurements the oscilloscope is used
to check the quality of the signal as well as the level
and type of the electronic noise.
It is always a good practice before any measurement is
attempted to examine the signal at the output of the
amplifier.
THEOSCILLOSCOPE

27. • Theexamples of good and bad pulses:
• (a) and (b) good pulses
• (c) bad pulses (probably because an electrical discharge)
• (d) bad pulses (high-frequency signalis "riding" on the output of the
preamplifier)
THEOSCILLOSCOPE

28. Oscilloscope
(in Nuclear Science Program, UKM)

31. • SCAis used to eliminate the electronic noise and, in
general, to reject unwanted pulses.
When a pulse is amplified, the electronic noise that is
always present in a circuit is also amplified.
If you count all the pulses present, the counting rate
may be exceedingly high.
But electronic noise is a nuisance and it should not be
counted.
THEDISCRIMINATOROR
SINGLECHANNELANAL
YZER(SCA)

32. • Let sayyou want to count only pulses above a
certain height, (i.e., particles with energy above
certain threshold energy) so the pulses lower than
that height should be rejected.
• In this case,we usethe discriminator or SCAto
select the desired pulses.
THEDISCRIMINATOROR
SINGLECHANNELANAL
YZER(SCA)

33. • There are two dials on the front panel of the unit.
 One is marked E,for energy, or LLD,for lower-level dial
 the other is marked ΔEor ULD/ ΔE,for upper-level
dial/ ΔE.
• There is also a two-position switch with INT (integral)
and DIFF(differential) positions.
• In the INTposition, only the Edial operates, and the
unit functions asadiscriminator.
• In the DIFFposition, both Eand ΔEoperate, and the
unit is then asingle-channel analyzer.
THEDISCRIMINATOROR
SINGLECHANNELANAL
YZER(SCA)

34. THEDISCRIMINATOROR
SINGLECHANNELANAL
YZER(SCA)
• The discriminator (switch position: INT)
Assume that the discriminator is set to E= 2.00 V
(the 2 V may also correspond to 2 MeV of
energy). Only pulses with height greater than 2V
will pass through the discriminator. Pulses lower
than 2Vwill be rejected.

35. Thepulse at the output of a discriminator.
THEDISCRIMINATOROR
SINGLECHANNELANAL
YZER(SCA)

36. THEDISCRIMINATOROR
SINGLECHANNELANAL
YZER(SCA)
• Thesingle-channelanalyzer (switch position: DIFF)
Both Eand ΔEdials operate. Only pulses with heights
between Eand E+ΔEare counted.
The two dials form a "channel"; hence the name single-
channel analyzer.
If the Edial is changed to E1, then pulses with heights
between E1 and E1 +ΔEwill be counted.
In other words, the width ΔE,or window, of the
channel is always added to E.

37. THEDISCRIMINATOROR
SINGLECHANNELANAL
YZER(SCA)
The operation of a single-channel analyzer

38. SCA
(in Nuclear Science Program, UKM)

39. UpperLevelDial (ΔE or ULD)
LowerLevel Dial (E or ULD)
ΔErange
SCAoutput

40. THESCALER
• The scaler is a recorder of pulses. For every pulse
entering the scaler, a count of 1 is added to the
previous total. At the end of the counting period,
the total number of pulses recorded is displayed.

41. THETIMER
• Thetimer is connected to the scaler, and its
purpose is to start and stop the scaler at desired
counting time intervals.
• Normally, the timer and scaler are combined in one
module.

42. TheScalerand Timer
(in Nuclear Science Program, UKM)

43. Timer display panel
Reset button
Preset button
Start button
Coaxial cable knob
Display select button

44. THEMULTI CHANNELANALYZER(MCA)
• The multichannel analyzer (MCA) records and stores
pulses according to their height. Eachstorage unit is called
a channel.
• The height of the pulse usually proportional to the
energy of the particle that enters into the detector.
• Eachpulse is in turn stored in aparticular channel
corresponding to a certain energy.
• The distribution of pulses in the channels is an image of the
distribution of the energies of the particles.
• At the end of a counting period, the spectrum that was
recorded may be displayed on the screen of the MCA

45. THEMULTICHANNELANAL
YZER(MCA)
Anenergy spectrum shownonthe screenof an MCA.

46. Multi Channel Analyzer (MCA)
(in Nuclear Science Program, UKM)
MCA module

47. Energyspectrums from Gamma SpectrometrySystem

48. Gamma SpectrometrySystem (with MCA) in NuclearScienceProgram

49. Gamma SpectrometrySystem (with MCA) in NuclearScienceProgram

50. Gamma SpectrometrySystem (with MCA) in NuclearScienceProgram

51. Gamma SpectrometrySystem (with SCA)in Nuclear ScienceProgram

52. THECOAXIALCABLE
• Coaxial cable is an electrical cable with an inner
conductor surrounded by aflexible, tubular
insulating layer, surrounded by a tubular conducting
shield.
• Theterm coaxial comes from the inner conductor
and the outer shield sharing the samegeometric
axis.

53. CoaxialCable

54. inner dielectric
insulator
woven copper
shield
outer plastic sheath
coppercore