Ionising Radiation: Measurements And Standards

Question 1

Who is the father of radiology

Answer 1

Wilhelm Conrad Rontgen

Question 2

We cannot detect ionizing radiation ______

Answer 2

Directly

Question 3

What are 2 methods commonly used to detect ionizing radiation

Answer 3

Film
Electroscope

Question 4

In order to detect ionizing radiation

Answer 4

The radiation must interact with something else

Question 5

We need to know the dose rate asap because

Answer 5

We can calculate the accumulated dose faster in time to give a warning if the dose rate is very high

Question 6

What is an instrument that measures ionizing radiation

Answer 6

Dosimeter, it measures the amount of radiation you’ve been exposed to

Question 7

Monitoring equipment are often calibrated in terms of

Answer 7

Question 8

Dose rate can also be measured using an

Answer 8

Ionization chamber

Question 9

Dose rate is

Answer 9

The dosage absorbed per unit time

Question 10

Ionization chamber advantages

Answer 10

• more accurate
• less affected by radiation
• can measure high dose rates which would saturate pother monitors

Question 11

Name 2 instruments to monitor dose/ dose rate that can be worn on the body

Answer 11

Pocket dosimeters
G-M tube instruments with a dose rate alarm

Question 12

The cheapest and most commonly used personal monitors use

Answer 12

Thermoluminescent dosimetry (TLD)

Question 13

4 Advantages of film dosimeters

Answer 13

• film badge are simple and inexpensive
• provides a permanent record
• very reliable
• measures and records radiation exposure due to gamma rays, X-rays and beta particles

Question 14

3 Disadvantages box film dosimeters

Answer 14

• cannot be read on site instead they have to be send away for developing
• one time use only
• exposures less than 0.2 mSv (20 milligram) of gamma radiation are not measured accurately

Question 15

4 advantages of TLDs dosimeters

Answer 15

• measure a greater range of doses in comparison with film badges
• doses are easily obtained
• can be read on the spot
• easily reusable

Question 16

2 disadvantages of TLDs

Answer 16

• each dose cannot be read out more than once
• the readout process effectively “zeroes” the tld

Question 17

What are electronic personal dosimeters?

Answer 17

They are high range, alarming, active dosimeters, designed for occupational radiation workers in planned exposure sites.

• displays does AND dose rate
• high level of radiation sensitivity

Question 18

An electric current is simply a flow of

Answer 18

Electrons or ions

Question 19

Electricity cannot flow through air because there are no free electrons or ions to carry the current, however;

Answer 19

If some of the atoms in the are are IONIZED, then free electrons are produced and an electric current can flow

Ionized atoms = free electrons
Free electrons = electrical current flow

Question 20

Inside an ionization chamber, the _____ radiation ____ electrons into the air

Answer 20

Ionizing, frees

Question 21

The nose free electrons fill the chamber and allow

Answer 21

A current to flow

Question 22

The chamber may be ___ or _____ to the atmosphere

Answer 22

Sealed or open

Question 23

When the chamber is exposed to ionizing radiation what happens besides the freeing of electrons

Answer 23

Positive and negative ions are produced.

Question 24

The positively charged ions are attracted to the

Answer 24

Negative plate

Question 25

The negative ions are attracted to the

Answer 25

Positive plate.

THE IONS ATTRACTIONS TO THE OPPOSITELY CHARGED PLATES IS WHAT ALLOWS A CURRENT TO FLOWW THROUGH THE CHAMBER.

Question 26

The current flow in an ionizing chamber is measured by a

Answer 26

Sensitive ammeter

Question 27

The current is measured at

Answer 27

10^-9 A (6 x 10^9 electrons per second)

Question 28

Ionization chambers are used to

Answer 28

• Measure the ionizing radiation output of therapeutic and diagnostic ionizing radiation generators
• make accurate measurements of patient radiation dose

Question 29

What is the very sensitive form of ionization chamber

Answer 29

The G-M tube “Geiger muller tube. SO SENSITIVE THAT IT CAN DETECT SINGLE IONIZING PARTICLES WHICH ENTER THE TUBE.

Question 30

How does the G-M type differ from the ionisation chamber

Answer 30

It’s filled with gas such as argon or neon rather than air

Question 31

The gas in an ionization chamber is about ____- of atmospheric pressure

Answer 31

One-fifth

Question 32

How does the G-M tube work

Answer 32

• incident ionizing radiation will produce free electrons within the tube
• the free electrons will be attracted to the central electrode which is held at positive potential (larger potential than in the ionization chamber)
• the electrons attracted to the central anode are accelerated by the potential
• they therefore gain a lot of energy to cause further ionization = a chain reaction occurs
• when all electrons produced hit the central anode they can cause photons (visible light or ultraviolet radiation) to be emitted
• these photons cause more ionization in the gas of the chamber
• the original ionizing radiation can produce 10^5 electrons in the chamber (a pulse of current)
• the tube takes long to recover from the recorded pulse because of the positive ions in the tube “dead time”

The dead time limits the number of events which can be recorded each second

Question 33

A G-M tube is used for the detection and measurement of all types of radiation like

Answer 33

Alpha, beta and gamma radiation

Question 34

The use of G-M is not recommended for

Answer 34

diagnostic radiology

Question 35

G-M counters are designed to detect

Answer 35

Isotope emissions

Question 36

The two main difficulties in diagnostic radiology for the GM counters are

Answer 36

• response time of several seconds
• strong energy dependence at low photon energies

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