Instrumentation

Question 1

____ is sensed by detecting the ionizations of gas molecules produced by deposition of energy during radiation’s passage. (Gas Filled Detectors)

Answer 1

Radiation

Question 2

_____ radiation interacts with the e- structure of an atom

Answer 2

Ionization

Question 3

______ the energy required to knock e- out of its orbit ( the energy of the radiation must be greater than the binding energy of the e-)

Answer 3

Ionization energy

Question 4

____ positive charged gas molecule and an e- that are produced as a result of ionization.

Answer 4

Ion pair

Question 5

A gas filled detector contains 2 electrodes

Answer 5

-Positive electrodes(anode)
-Negative (cathode)

Question 6

A gas filled detector is filled with what gases?

Answer 6

He,Ne,Ar,H or air

Question 7

Why are noble gases used instead of of air

Answer 7

They are more dense- it gives them a greater probability of interaction better efficiency

Question 8

The atmosphere of the gas is usually increased to ______

Answer 8

5 to 12 times more gas within the detectors

Question 9

Voltage source does what to the electrodes

Answer 9

Applies a voltage

Question 10

Current measuring device:

Answer 10

Measures current coming from the electrodes

Question 11

How does a gas detector work ? Steps

Answer 11

1. Radiation enters the chamber and causes an ion pair
2. Ion pair is produced from the interaction of radiation with an e- from the gas
3. Due to the voltage placed on the electrodes an positive gas molecule is attracted to the cathode
4. E- is attracted to the anode
5. When the e- and gas molecule reach the perspective electrodes a charge is produced
6. The charges produce a current( amps)
7. The current is being measured
8. The amount of current measured is proportional to the strength of the radiation (stronger radiation means higher current)

Question 12

There are 3 types of gas filled detectors that we use:

Answer 12

1. Ionization chambers
2. Proportional chambers
3. GM Detectors
   The voltage applied to the gas filled doctor determines the one we use

Question 13

What does the voltage curve shows:

Answer 13

As you increase voltage what happens to the number of ion pairs produced(more are produced)

Question 14

Each type of radiation has an amount of ionizing force a higher amount of ionizing force produces more

Answer 14

Ion pairs

Question 15

Alpha has a higher ionizing force than

Answer 15

Beta( alpha produced 100 time more ion pairs than beta)

Question 16

Beta has a higher ionizing force than

Answer 16

Gamma( Beta produces 100 time more ion pairs than gamma)

Question 17

The curve shows the difference in ion airs produced

Answer 17

For each type of radiation

Question 18

Voltage curve (region I) Recombination region ranges from ?

Answer 18

0-100 volts

Question 19

In the recombination region what happens?

Answer 19

Radiation enters the chamber an ion pair is formed but the migration of the ions to their perspective electrodes depends on the voltage if 0 volts are applied the gas ions recombine and because they recombined they are not detected.

Question 20

Voltage curve ( Region II) Ionization region volts ?

Answer 20

100-400 volts

Question 21

Region II the radiation

Answer 21

1. Enters the chamber
2. An ion pair is formed
3. The increase in the voltage allows all ion pairs produced to be collected
4. A plateau occurs in respect to voltage vs # of ion pairs( increasing the voltage doesn’t produce more ion pairs)
5. The plateau is called the saturaton voltage

Question 22

For region 2 if increasing the voltage doesn’t increase the number of ions collected what voltage should we operate at ?

Answer 22

150 volts over 150 volts only make ions migrate to the electrodes faster and will waste battery

Question 23

Equipment used in the region is called ____?

Answer 23

Ionization chambers

Question 24

Dose rate meters and dose meters

Answer 24

Are ionization chambers the current measured by an ionization chamber is direct measurement of the # of ions collected( good for measuring high radiation areas)

Question 25

What measures intensity of radiation

Answer 25

Dose rate meters = radiation/unit time mrem/hr is an example Cutie pie and ionization dose rate meters

Question 26

Dose rate measures only the amount of radiation present like

Answer 26

Ci or Bq with dose calibrators and pocket dosimeter

Question 27

Dose rate measures only the amount of radiation present like

Answer 27

Ci or Bq with dose calibrators and pocket dosimeter

Question 28

Voltage curve region III is called what region

Answer 28

Proportional region

Question 29

How many volts are in the region III (proportional)

Answer 29

400-800 volts

Question 30

What happens in the III region

Answer 30

1. Radiation enters the chamber 2. An ion pair is formed 3. The increased voltage increases the speed of migration of the ion pairs 4.The increase voltage will increase e- acceleration and kinetic energy 5.Because the e- are going faster they can cause further ionizations this is called gas amplification which causes more ion pairs to -e produced and collected. 6. A primary ion starts the reaction and the secondary ions are produced 7. If the secondary ions create more ions, an avalanche occurs the voltage allows all ions to be collected 8. The current will represent,ore radiation than actually entered the chamber

Question 31

The actual amount of radiation that entered the chamber is called?(region III)

Answer 31

A factor of the current detected Ex. 500 volts could have a factor of 1000 for every ion pairs that is created, 1000 more will be produced from the original

Question 32

The instrument used in the region(III)

Answer 32

Proportional counter which measure alpha and beta particles which is not used in nuclear medicine

Question 33

Region III measuring factor example

Answer 33

Your current device reads 5,000,000 and the factor used for this proportional counter is 5000. If we are detecting beta particles, how many do we actually have? 5,000,000/5000=1000 beta particles

Question 34

Region IV is called what region

Answer 34

Nonproportional which ranges from 800-1000 volts

Question 35

In the fourth region what happens

Answer 35

More ions are produced from the primary ion pairs the amount of radiation entering the chamber is not proportional to to the current measuring device and the actual amount of radiation entering the chamber can not be determined and no equipment is used in this region

Question 36

Voltage curve Region V or 5 is the what region?

Answer 36

The Geiger muller region ranges from 1000-1500

Question 37

Region 5 or the Geiger muller range what happens

Answer 37

Max gas amplification the most amplification that can occurs which increasing voltage doesn’t increase amplification we have reached saturation point this region can’t tell the difference between alpha,beta and gamma

Question 38

What is quenching?

Answer 38

Starting in the GM region you can have continues discharge of e- The positive gas molecule is accelerated toward the cathode but when it reaches the cathode it combines with an e- due to the higher velocity more energy is released on the combination of the e- and gas molecule the energy will act in the form of an x-ray and the X-ray acts as radiation and more ionization and this produces more avalanches which can result in a false high result

Question 39

Quenching can prevent x-rays from causing ionizations in the

Answer 39

GM tube