Survey Instruments (6)

Question 1

Types of Survey Meters

Answer 1

• Ionization Chamber

- Geiger Muller Detector

Question 2

How does an Ionization Chamber work?

Answer 2

• Cylindrical container filled with gas (air), two electrodes, a low voltage electrical field.
• Amplifier
• Readout device

Radioactive photons or particles enter the chamber interacting with gas to form ion pairs, producing (positive and negative ions) that migrate towards the oppositely charged electrode = momentary drop in circuit voltage.

• Current flow is measured via ammeter and amplified for low readings
• Low sensitivity, can measure high radiation fields
• used in industrial radiography

Question 3

Ionization Meter readings

Answer 3

• Top scale (high-intensity) 0.1 R/h - 10 R/h
• Lower Scale 1 - 100 mrem/h

reading settings:

• off
• Check (for battery)
• High (top scale)
• Low (lower scale)

Question 4

How does a Geiger Muller Detector work?

Answer 4

• Cylindrical container filled with gas (argon), two electrodes, a high voltage electrical field.
• Amplifier
• Readout device

Higher voltage causes negative ion production to be accelerated - more ionization of gas (gas multiplication/amplification), # of electrons collected at anode, depends on number of ion pairs originally produced from the radiation.

• Interacts with incoming ions instead of air (Ionization meter)
• Detect low levels of gamma, X-ray, beta or alpa
• high # of ions can saturate meter making it inoperable for some time.
• used in laboratories
• used for geological surveys
• Internal detector, external detector or both

Question 5

Geiger Muller Detector Readings

Answer 5

• one scale, four multiplication factors (settings)
• mR/h 0-10

settings:

• off
• x100 (0-100 mR/h or 10 R/h
• x10 (0-100 mR/h)
• x1 (0-10 mR/h)
• x 0.1 ( 0-1 mR/h)

separate button for battery check

Question 6

Digital Survey Meters

Answer 6

• provide an accurate reading
• read in either mR/h, µR/h, mSv/h
• record doses as low as 0.01mSv/h
• audible signal proportional to dose rate

Becoming more popular

Question 7

Contamination Detectors

Answer 7

detect contamination by determining activity in counts per minute (CPM)

• called “pancake detectors”
• measure alpha, beta, gamma
• do not indicate associated risk