Radiation Safety Course - Curtin Universityhealthandsafety.curtin.edu.au/local/docs/Radiation_safety_course.pdf · S.Siddiqui-Radiation Safety Notes 2 Learning Objectives On completion

S.Siddiqui-Radiation Safety Notes 1

Radiation Safety Course

Dr Salim Siddiqui

Radiation Safety Officer

Room 301.212A

Tel: 9266 7193

Curtin University of Technology


Learning Objectives On completion of this course, you should be able to

demonstrate the knowledge of:

1. Sources of Radiation (Man-made and Natural)

2. Types of Radiation (Ionizing and Non Ionizing Radiation)

3. General Characteristics of Radiation

4. Radioactivity

5. Quantification of Radiation (Units)

6. Radiation Exposure Measurement

7. ICRP Recommendations for Dose Limits (Permissible Dose)

8. Radiation Hazards (External and Internal)

9. Biological Effects of Radiation (Deterministic and Stochastic)

10. International Commission on Radiological Protection.

11. Radiation Safety Act and Regulations

12. Role of RSO

13. Role of Health and Safety

http://healthandsafety.curtin.edu.au/


1. Sources of Radiation

(a) Man-made sources: x-rays, radioisotopes.

Used in various industries, eg. Radiography,

radiotherapy, nuclear medicine, mining etc.

(b) Natural sources:

(i) External: cosmic and terrestrial, uranium, thorium in

soil, water.

(ii) Internal: Radionuclide within our body, e.g. C-14, K-40

and also other radionuclides that are ingested and

inhaled.

e.g. 222Rn gas.


2. Types of Radiation

(a) Ionizing Radiation

Radiation having sufficient energy to cause ionization in

matter. e.g. x-rays, gamma rays, charged particles

neutrons. (NHMRC p r-34)

(b) Non-ionizing Radiation

Visible light, UV radiation, microwaves, laser, Infrared,

Ultrasound


3. General Characteristics of Radiations

Particulate Radiation: Sub-atomic particles

with mass and charge. e.g. alpha, beta,

protons, electrons, neutrons

EM Radiation: Electromagnetic waves with

no mass and charge. e. g. X-rays, gamma

rays.


Characteristics of Radiations

Alpha particles

Generally emitted by heavy radioisotopes

It is a helium nucleus with two protons and two

neutrons in the nucleus.

Typical energy range (4 – 8 MeV)

Low range (<10 cm in air, 60 μm in tissue)

Can be stopped by a sheet of paper

He42

He Rn Ra 42

22286

22688

Example

He+ Np Am 42

23793241

95


Beta particles

There are two types of beta decay

1. Negative beta decay

In this process a neutron in the nucleus transforms into a proton resulting in the emission of an electron and an anti-neutrino.

2. Positive beta decay

In this process a proton in the nucleus transforms into a neutron resulting in the emission of a positron and a neutrino.

Typical energy range is several keV to few MeV. Unlike alpha particle beta particle has continuous energy range.

Low range (a few mm in tissue)


_

_

_A1+Z

AZ

+ + Y Sr

+ S P

+ + Y X

9039

9038

3216

3215

+ + Ne Na

+ + Y X

2210

A-1Z

AZ

2211

Example of negative beta decay

Example of positive beta decay


Gamma rays -are electromagnet waves, that travel with the speed of light in vacuum (roughly air).

-have no charge

- are emitted from the excited nucleus following alpha or beta decay as tiny packets of energy called photons.

There are very few isotopes that are pure beta emitters and do not emit gamma rays.

e.g. H-3, C-14, P-32


X-rays -are electromagnetic waves, that travel with the speed of light in vacuum (roughly air).

-have no charge

-x-rays are generated when fast moving electrons are decelerated in a high Z target. The emitted spectrum is continuous in energy (Bremsstrahlung spectrum).

-characteristic x-rays are produced when an excited orbital electron drops back to a lower energy orbit. The difference between the two energy levels is emitted as an x-ray photon which appears as a line spectrum

-x-rays are used in medical, research and other industries


Neutrons These are neutral particles with no charge

There are no naturally occurring nuclei* which emit neutrons (* Except Californium-252)

Neutron sources used in industry and research are produced through nuclear reactions.

Emitted neutrons are not mono-energetic

Typically, En = 0.1 – 13 MeV


In general neutrons are produced by three main

methods as follows:

i) Nuclear reaction induced by alpha or gamma

emitting isotopes

ii) Nuclear reaction induced by charged particles from

accelerator

iii) Research reactors

n+ C Be He 10

126

42 9

4

Example

Ra - Be neutron source or Am-Be neutron source


Plastic Lead Concrete Paper

Alpha radiation

Beta radiation

X and radiation

Neutron

Penetrating abilities of various radiation

Quiz: Which of these radiation can cause internal and

external hazard?

Ans.


4. Radioactivity

Spontaneous emission of radiation from unstable nuclei

t oeNN

N t

N

constantdecay a is Where

t N N

Radioactive decay law

If N is the number of nuclei present and ΔN decay in

time Δ t, we find that

t

No

Parents

remaining


2lnT

e2

1

eN2

N

2

1

1/2T

t o

o

t oeNN

No/8

No/4

No/2

No

T/2 2T/2 3T/2

Half-Life Time taken for half the radioactive nuclei to decay. It

varies, according to the isotope, from less than a few

micro seconds to more than a billion years.


5. Quantification of Radiation (Units)

Activity: Determines the strength of a radioactive source.

The number of disintegration occurring per unit of time is

called the activity.

Curie: it is the activity of that quantity of radioactive

material in which 3.71010 atoms are disintegrating per

second.

Old unit: 1 Curie = 3.7x1010 dps

SI unit: 1 Bq = 1 dps

Quiz. Which source has a higher activity, 1 gram of 238U

or 1 gram of 234Th?


Exposure: measure of the amount of ionization produced

in air by x or gamma radiation.

Old unit: 1 R = 2.58 x 10-4 C/kg

SI unit: 1 X unit = 1 C/kg

Conversion: 1 X unit = 3881 R

Q. But how much energy is absorbed in matter?

1 coulomb of charge produced

in 1 kilogram of air

+ + + + + + +

- - - - - - -

1 X unit of x

or radiation

Roentgen: Amount of x or gamma radiation that will

liberate a charge of 2.58 10-4 C in I kg of dry air at STP.


Radiation Absorbed Dose – (rad)

Energy deposited by any type of radiation in any material

(air, water, biological tissue etc) per unit mass.

Old unit: 1 rad = 10 mJ/kg

SI unit: 1 Gy = 1 J/kg

Conversion: 1 Gy = 100 rad

1 Joule of energy

deposited

1 kilogram of any

material

1 Gray of any

radiation


Quiz. Which will deposit more energy in tissue,

1 rad of x-rays or 1 rad of ?

Ans. Since particles travel slower than x or of the same

energy. Therefore, it can produce more ionization within a

small volume of the tissue, thus depositing more energy.

X-rays

Tissue

+ + + +

- - - -

Low density ionization

particle

Tissue

+ + + + + + + +

- - - - - - - -

High density ionization


Ans. Since alpha particle deposits more energy, hence

can cause more damage.

So the chance of damage to tissue depends not only on

the absorbed dose, but also on the:

i) type and energy of radiation.

ii) type of irradiated tissue

Quiz. Which will cause more damage to tissue?


The modified unit taking into account the type and

energy of radiation is called the „Equivalent Dose‟

Equivalent Dose = Absorbed Dose wR

Unit of equivalent dose is Sievert.

(R. Sievert, Swedish radiologist)

Some values of wR are given in the following table

Type of Radiation

Radiation Weighting

Factor, wR

x, , or

1.0

10 - 20

proton

10

neutron

5 - 20


However different tissues show different radiological

sensitivities as shown in the table on next page:

Effective Dose = Equivalent Dose wT

SI unit: Sievert

Old unit = “rem”

The modified unit taking into account the radiological

sensitivities of radiation is called the „Effective Dose‟

Effective Dose = Absorbed Dose wR wT


Tissue or organ Tissue weighting factor

Gonads 0.20

Bone marrow (red) 0.12

Colon 0.12

Lung 0.12

Stomach 0.12

Bladder 0.05

Breast 0.05

Liver 0.05

Oesophagus 0.05

Thyroid 0.05

Skin 0.01

Bone surface 0.01

Remainder 0.05

Total 1.00


Ans.

Quiz. Which will cause more damage to tissue 1 rem

of x-rays or 1 rem of ?

This unit of Effective dose is used only in radiation

protection.

Personal monitoring devices such as film badge are

designed to record dose in Sievert.


Quantity

Measure of Traditional Unit SI Unit

Activity

Decay rate Curie Bq

Exposure

Ionization in air Roentgen C/kg

Absorbed

dose

Energy

absorption

rad Gray

Effective

Dose

Biological

effectiveness

rem Sv

Summary

Quantities and Units of Radiation


Summary

Activity: 1 Curie = 3.7x1010 dps

1 Bq = 1 dps

Exposure: 1 R = 2.58 x 10-4 C/kg

1 X unit = 1 C/kg

1 X unit = 3881 R

Absorbed dose: 1 rad = 10 mJ/kg

1 Gy = 1 J/kg

1 Gy = 100 rad

Equivalent Dose: Sievert = Gray wR

1 Sv = 100 rem

Effective Dose: Sievert = Gray wR wT


6. Radiation Exposure Measurement

The standard detector is an ionization chamber

The current trough a resistor is a measure of

exposure = C/kg/s = Gy/s

Personal Monitoring

- Film badges

- TLD (Thermo-luminescent dosimeter) (LiF: Mg, Ti)

- OSL* (Optically stimulated luminescence) (Al2O3: C)

- Curtin uses Luxel dosimeter (Sensitivity 0.01 mSv)


Personal Radiation Monitoring

Badges are issued by the RSO upon request

Badges are issued and collected quarterly

Badges are to be worn all the time when working with

radiation

Badges should not be tempered or misused (Safety

Regulation)

Inform your supervisor of any spills or unusual exposure

to radiation


7. ICRP Recommendations for Dose Limits

Occupational exposures: 20 mSv/year

(averaged over 5 consecutive years, and should not exceed 50 mSv in any single year)

General public: 1 mSv/year (averaged over 5 years)

Pregnancy: 1 mSv/y to the abdominal surface

Note: These limits do not include, Natural background

and Medical diagnosis and therapy dose

The Effective Dose limits are as follows:


Equivalent Dose Limits

The eye lens:150 mSv/y

The skin: 500 mSv/y (over any 1 cm2 of skin)

The hands and feet: 500 mSv/y

Note: For general public, the limits are 1/10th of the

above values.


8. Radiation Hazard

Two types of radiation hazard are involved when working

with radioactive materials

i) External radiation hazard

ii) Internal contamination hazard

(i) External Hazard

Associated with high activity sources that emit x, , neutron

and high energy . These radiations can penetrate the body

and result in a high absorbed dose.


STDA Rule to Reduce the External Hazard

SHIELDING: Keep suitable shielding between user and source

eg. use Pb, concrete Al, perspex shielding

TIME: Minimize handling time

Dose = Dose rate x Time

DISTANCE: Maximize the distance between user and Source.

Dose rate 1/r2

ACTIVITY: Minimize activity of the source.

Doe rate Activity


don't touch any material

cordon off the area and place warning signs

stay at a safe distance from the accident site

don't leave the site unless you are checked of

contamination

don't eat drink or smoke at the accident site

call the Radiation safety supervisor of your

area or Radiation safety officer

In case of accident


ii) Internal Hazards

Radionuclides emitting , taken internally into the

human body can deposit their energy in the host tissue, thus causing damage.

Ingestion

from surface contamination. Eating drinking in workplace

Inhalation

from contaminated air, due to airborne dust, vapours

Absorption

either directly through the skin or through cuts and wounds

The routes of entry into the body may be:


9. Biological Effects

When radiation traverses through the tissue, following may happen:

(i) no damage to the cells

(ii) cell is damaged, but is repaired

(iii) cell survives but with permanent damage.

This is called mutation. Such cells multiply with deformity and are thought to eventuate in cancer.

(iv) cell is totally damaged.

(death of many cells causes Radiation sickness)


Categories of Biological Effects

Somatic

cancer in exposed person

Genetic

mutation in off springs

1. Stochastic

at low doses

2. Deterministic

at high doses

radiation sickness, cataracts,

skin damage etc


Categories of Biological Effects

Biological effects may be divided into two categories:

(i) Stochastic

(ii) Deterministic

(i) Stochastic effects

Stochastic means chance or random effect in an exposed

person.

"An effect known to occur sometimes as a consequence

to radiation, but which may or may not be expressed in a

particular exposed person" (NHMRC, 1995, p r-36)


The probability of the effect is proportional to the dose,

with out any dose threshold.

This occur when the cell that has been irradiated is

modified rather than killed.

This may lead to cancer in the exposed person, or

mutation in the off springs.


The stochastic effects are further classified as:

Somatic: When the effects appear in the exposed person.

eg. cancer

Genetic: When effects appear in the off springs of the

exposed person, eg. mutation. This happens if the damage

is incurred to the reproductive cells of the exposed person.


(ii) Deterministic effects

Which can cause " partial loss of function of an organ or

tissue (NHMRC, 1995, pr-32)

These are caused when the dose is above the threshold

value.

The severity of the effect varies with the dose.

Some of the examples are, radiation sickness, cataracts,

and skin damage


10. International Commission on Radiological

Protection (ICRP)

ICRP was formed in 1928. It is a fully independent

body, free of governments or nuclear industry

constraints.

The function of the ICRP is:

(ii) set dose limits for radiation workers.

these limits are set to prevent the occurrence of

deterministic effects by keeping doses below the

thresholds for individual tissue and also to reduce the

incidence of stochastic effects, to an acceptable level.

(iii) set dose limits for general public.


(i) Justification of a practice: No practice involving exposures to

radiation should be adopted unless it produces sufficient

benefit to the exposed individuals or to society to offset the

radiation detriment it causes.

(ii) Optimization of protection: In relation to any particular source

within a practice, the magnitude of individual doses, the

number of people exposed, and the likelihood of incurring

exposures where these are not certain to be received should

all be kept as low as reasonably achievable (ALARA

Principle) economic and social factors being taken into

account.

(iii) Dose limits: The exposures of individuals from the combination

of all the relevant practices should be subject to dose limits, or

to some control of risk in the case of potential exposures.

(ICRP Guidelines, 1991, from NHMRC 1995, p r-7)

Principles of Radiological Protection – ICRP 1977


National Health & Medical Research Council,

NHMRC

NHMRC was formed in 1936

The council is responsible for setting radiological

protection standards in occupational, medical and public,

in Australia.

NHMRC takes the recommendations of the ICRP as the

basis for its own recommendations and then " implement

legislation directed towards the effective control of

exposure of people to radiation" (NHMRC, 1995, p r-v).


Radiological Council of WA

The Radiological Council of WA is appointed under the Radiation Safety Act 1975. It is a statutory body responsible for the administration of the Radiation Safety Act through the Radiation Health Section of the Health Department of WA.

Its function is:

(i) advising the minister for health on hazards of radiation

(ii) implementing and enforcing the Act

(iii) inducting inquiry into alleged contravention

(iv) suspending or cancelling licence and registration

(v) investigating and prosecuting offences under the act.


11. Radiation Safety Act (1975) and Radiation Safety (General) Regulations (1983)

Under the State‟s Radiation Safety Act, all premises

holding x-ray equipment, radioactive substances

(including radiation gauges) and prescribed electronic

products ( including lasers and ultraviolet

transilluminators) are registered with the Radiological

Council of WA.

The registrant of the premises is responsible for the safe

use of radioactive substances and the radiation

generating equipments, and the safety of the users and

the public as described in the Radiation Safety (General)

Regulations (1983)


Radiation Safety Regulation

1. All premises involved with the radiation work are

registered.

2. All radioactive substances, x-ray equipment and

prescribed electronic products are registered.

3. All personnel involved in radiation work hold a valid

personal radiation licence, or work under the

supervision of a person holding a valid radiation

licence

4. All personnel involved in radiation work are registered

with the Radiation Safety Office.

5. All personnel involved in radiation work must wear

personal radiation monitoring device.


6. All Radiation monitoring equipment used in work

place are maintained and regularly calibrated.

7. Any acquisition or use of radioactive materials

must be reported to Radiation Safety Office.

8. Any project involving use of radiation or

radioactive materials must obtain clearance from

the Radiation Safety Office.

Safety Rules for All

When dealing with radiation work, each person is

responsible for his/her own safety and also for the safety

of people around.


12. Role of the RSO

Ensures site, equipment and personnel are licensed as

required by the RC.

Vetting students‟ projects involving radiation

Ensure students are supervised by a licencee

Project details (candidacy) must be submitted to the

RSO for approval.

Issue radiation approval number.

Issue radiation badges

Advise students to undergo radiation safety training. e.g.

UWA unsealed course.


13. Role of Health and Safety

Health and Safety is a specialist area within Curtin which provides professional advice and services in workplace health and safety, Workers‟ Compensation, and Injury Management. It has overarching responsibility for workplace health and safety matters within Curtin and maintains an informative website which includes a section on Radiation Safety.

Compliance with Radiation Safety requirements is overseen by a Radiation Safety Officer (RSO), and Radiation Safety Supervisors have been appointed in the main departments or locations that use radioactive materials or devices that generate radiation.

Projects are approved by the RSO through Health and Safety.

Incidents are reported to Health and Safety on-line.



http://healthandsafety.curtin.edu.au/event_and_hazard/index.cfm



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Radiation Safety Course - Curtin Universityhealthandsafety.curtin.edu.au/local/docs/Radiation_safety_course.pdf · S.Siddiqui-Radiation Safety Notes 2 Learning Objectives On completion