Radioactive Sealed Sources

Working safely with radioactive sealed sources at UCLA

Radiation Safety ProgramUCLA Office of Environment, Health & Safetywww.ehs.ucla.edu

• Identify different types of radiation and their applications as sealed sources.

• Classify the different types of sealed sources typically found at UCLA.

• Recognize sealed source regulations set by the NRC.

• Identify safe work practices for sealed sources.

Objectives

What is Radiation?Radiation is the emission of energy as either electromagnetic X-rays & gamma waves or as alpha, beta or neutron particles.

An unstable atom, in an effort to achieve stability, emits radiation through a process called radioactive decay.

Alpha particleNeutron

Electromagnetic Gamma/X-Rays

waves

Beta electron

The electromagnetic (EM) spectrum consists of photons of varying energies and frequencies, categorized as either Non-ionizing radiation or Ionizing radiation.

The diagram below provides examples of various types of radioactive waves and devices associated with each.

Electromagnetic Spectrum

• The EM spectrum can be split into two categories: ionizing and non-ionizing radiation.

• X-rays and gamma-rays are types of EM radiation that have enough energy to ionize (remove or excite electrons) atoms.

• For the purposes of this module, when we refer to radiation, we are referring only to ionizing.

Ionizing vs. Non-ionizing

Radioactivity is a measure of how much radiation is being emitted from a sample.

Radioactivity is expressed as the number of decays or disintegrations a sample is undergoing per unit time.

Quantifying Radiation

Unit of Measure Disintegrations per Second (dps)

Curie (Ci), Customarily used in the U.S. 3.7 x 1010

Becquerel (Bq), Scientifically expressed unit 1

The radioactivity of a sample decays over time. The time required for a radioactive substance to lose 50 percent of its activity by radioactive decay is called the half-life (T1/2). The chart below illustrates the change in half-life over time.

What is Half-Life?

Beginning with 1,000,000 radioactive atoms.

half-life (T1/2)

After two half lives, the number drops down to 250,000 atoms.

This process will continue indefinitely.

After one half life, the source size reduced to 500,000 atoms.

The half life is specific to a radionuclide and remains constant over time. Listed below are common sealed source radionuclides and their half lives.

The Half Life of Common Sealed Sources

Nuclide Half Life (T1/2)

C-14 5,730 years

Am-241 432 years

Na-22 2.60 years

Co-57 271 days

Sealed sources can emit one or more of the following types of radiation:

• Alpha• Beta• Gamma• X-rays• Neutron

By knowing how each type of radiation interacts with matter, you can better protect yourself against the hazards and safely use radioactive materials.

Types of Radiation

• An alpha particle is emitted by the decay of heavier radioactive nuclei.

Alpha Radiation

• The alpha particle is made up of two protons and two neutrons (this is essentially the nucleus of a helium atom and carries two positive charges).

• These particles are emitted with a large amount of energy. Due to its double charge, it readily interacts with matter and loses all of its energy over a relatively short distance (a few centimeters in air).

• Most alpha emitters are transuranics and deposit heavily in the nucleus of cells.

Beta Radiation• When an atom has greater neutrons than protons or protons

than neutrons, it will undergo radioactive decay by emission of a beta particle to reach stability.

• When an atom has greater neutrons than protons or protons than neutrons, it will undergo radioactive decay by emission of a beta particle to reach stability.

• The beta particle can carry either a negative or positive charge.

• When a beta decay is negative (β−), it is essentially emitting a normal electron, or negatron.

• When a beta decay is positive (β+), it is emitting a positive electron, also known as a positron.

Anti-ElectronPositron!

• The positron is the anti-particle of the electron. When a positron is emitted from an unstable radioactive atom and interacts with an electron, they will annihilate each other.

• This reaction releases two gamma rays in opposite directions.

• These gamma rays are the main safety concern and not the positron itself.

Gamma Radiation

Gamma radiation is the release of a photon from the nucleus of an atom. Gamma radiation occurs when the nucleus of an atom has too much energy and needs to release it.

X-Ray Radiation

X-Ray radiation is the release of a photon from the electron orbital of an atom. With sealed sources, X-ray radiation would occur during the Bremsstrahlung effect.

Neutron Radiation• Neutrons possess no electric charge and only

interact through collisions• These particles are emitted from either fissile

nuclear material or from Alpha-Beryllium interactions.

Question 1: What do you think?

What types of radiation are commonly related to sealed sources?

A. Just Alpha RadiationB. Alpha & Beta RadiationC. Alpha, Beta, Gamma and Neutron Radiation

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correct

answer…

Question 1: What do you think?

What types of radiation are commonly related to sealed sources?

A. Just Alpha RadiationB. Alpha & Beta RadiationC. Alpha, Beta, Gamma and Neutron Radiation

Correct! The most common types of radiations associated with a sealed source are Alpha, Beta, Gamma and Neutron radiation.

2. Indirect exposure, resulting in hydrolysis of water in your cells leading to the formation of free radicals

Biological Effects

1. Direct exposure, resulting in damage to DNA

There are two ways exposure to radiation can cause biological effects:

Direct Damage to DNA • Did you know that our everyday surroundings contains

substances (known as carcinogens) that cause damage to the DNA in our cells?

• DNA damage is extremely common. DNA in a single human cell gets damaged over 10,000 times every single day.

• Although our cells are very good at repairing this damage, errors can happen, creating a cancerous cell.

Indirect DNA Damage: Free Radicals

• As radiation hits our cells, majority of interactions will occur with water creating highly reactive free radicals that are chemically toxic.

• The free radicals H and OH may combine with like radicals, or they may react with other molecules.

• When alpha particles interact with water, the radicals are formed and can recombine with other radicals to create hydrogen peroxide.

• Hydrogen peroxide is a very powerful oxidizing agent and can affect molecules or cells that did not suffer radiation damage directly.

• Absorbed Dose is a measure of the amount of energy from ionizing radiation deposited in a material, such as human tissue.

• Effective dose takes into account the energy deposited (absorbed dose) as well as the type of radiation and affected tissues, etc. Therefore, dose equivalent is a more accurate measure of dose.

Measuring Radiation Doses

Absorbed Dose Effective Dose

US Customary Units rad rem

SI Units Gray (Gy) Sievert (Sv)

We are exposed to radiation on a daily basis. This image shows sources of typical radiation exposures.

Radiation is all around us!

National Council on Radiation Protection and Measurements (NCRP) Report 160 2006

To put into perspective, let’s

look at some common activities that might have some radiation

exposure and how much radiation someone could

receive from them.

Measuring Dose

www.Udigmining.com

Dose Limits

1

0 2500 5000

Radiation workers are limited to an annual radiation dose set by the Nuclear Regulator Commission (NRC). Even in occupations with more frequent exposure to radiation, average doses do not typically approach the conservative NRC limits.

Typical Average Annual Doses for Common Radiation Workers Based on Occupational Dose (mrem/year)

NRC Occupational Dose Limits

Adult Radiation Worker

Embryo-fetus of Declared Worker

Member of the Public

Dose (mrem/yr)

0 100 200 300

Airline Flight Crew Member

Nuclear Power Plant Worker

Medical Personnel

Average Annual Occupational Radiation Dose Received

NRC Annual Dose Limit

Risk ComparisonExpected Days of Life Lost by Activity A review of common activities illustrates the risk of radiation exposure compared to activities considered harmful to the human body. For example, smoking a pack of cigarettes daily potentially decreases life expectancy by 2190 days. In contrast, exposure to an annual dose of 1 rem of radiation throughout a lifetime decreases life expectancy by 51 days.

Home Accidents [207]

Occupational Dose [51]

Smoking Pack/Day [2190]

15 % Overweight [730]

NRC draft guide DG-8012

• maintain leak tightness under the conditions of use for which the source was designed

• contain the radioactive material under normal operating condition

• contain the radioactive material under foreseeable mishaps

What is a Sealed Source?

A sealed radioactive source is a container of encapsulated radioactive material. The capsule of a sealed source is strong enough to:

Know Your Sealed SourcesType of Sealed Source

Static Eliminator

Irradiator Brachytherapy seed

Inside Liquid

Scintillation Counter

Smoke Detector

Isotope Source

Polonium-210

Cobalt-60 Iodine-125 Cesium-137 Americium-241

Half-Life 138 days 5.3 years 60.1 days 30.1 years 432 years

Primary Radiation Type

Alpha (α)5,304 keV

Gamma (γ) 1,173 keV & 1,332 keV

Gamma (γ)27 keV &31 keV

Beta (β-)516 keV (max)

Alpha (α)5,486 keV

Secondary

Radiation Type

None Beta (β-)318 keV (max)

None Gamma (γ)662 keV

Gamma (γ)

60 keV

There are often multiple types of radiation emissions for any given sealed source. Review the table below to identify which types of radiation emissions a sealed source contains so that we may properly protect ourselves.

Question 2:What do you think?

What is a Sealed Source?A. Usually has high concentration of radioactive material in a small

volume.B. Capsule or material strong enough to maintain leak tightness.C. Designed to contain the radioactive material under normal

operating conditions.D. Designed to contain the radioactive material under foreseeable

mishaps.E. All of the above

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correct

answer…

Question 2:What do you think?What is a Sealed Source?

A. Usually has high concentration of radioactive material in a small volume.

B. Capsule or material strong enough to maintain leak tightness.C. Designed to contain the radioactive material under normal

operating conditions.D. Designed to contain the radioactive material under foreseeable

mishaps.E. All of the above

If you said E, All of the Above, You are Correct!

Regulatory ClassificationsThe Nuclear Regulator Commission (NRC) regulates sealed sources in different ways, depending on which categories they fall in.NRC Source Categories Conditions

Leak-Test Required Requires a license to possess these sources. Leak-tests must be performed every 6 months.

Leak-Test ExemptExempt from 6 month leak test requirements under certain conditions

Generally Licensed

Sources are licensed directly to the individual. Those who possess generally licensed sources are responsible for all requirements set by the manufacturer.

Protecting You: NRC-Required Leak Tests

The NRC requires the testing of most sealed sources for leakage every 6 months.

If a leaking sealed source is found, you can expect the source to be removed from use for additional testing and repair.

*Exemptions to this required testing are:• Hydrogen-3 (tritium) sources• Sources containing material with a half-life of

30 days or less• Sealed sources containing material in gaseous

form• Sources of beta- or gamma-emitting

radioactive material with an activity of 3.7 MBq (100 microCuries) or less

• Sources of alpha- or neutron-emitting radioactive material with an activity of 0.37 MBq (10 microCuries) or less.

*

Conducting the Required Leak TestsThe Radiation Safety Program performs annual leak tests to ensure the safety of equipment. How?1. This is done by conducting a swipe test of the

sealed source (using alcohol and a wet swab) and measuring for any removable contamination.

2. If the source is not immediately accessible without exposing the source, the nearest accessible area where contamination may accumulate can be swiped. This swipe is then analyzed by liquid scintillation counting.

Results?If a swipe test results in an activity of over 185 Bq [5 nanoCuries] of removable radioactive material, the sealed source is considered to be leaking and:3. The machine will be removed from service immediately and the lab

notified.4. A supplementary survey of the equipment/lab will be conducted.5. EH&S will work with the lab on disposal of the leaking source.

Generally Licensed Sources

Such devices usually consists of radioactive material contained in a sealed source within a shielded device. Some chemical compounds may also meet this criteria. Other examples include:

Static Eliminator

Generally licensed devices and materials, such as exit signs, are designed with safety features for safe use for the general public with no radiation training or experience.

• Static eliminators Electron capture detectors (gas chromatograph units)

• Calibration standards installed in liquid scintillation counters

Responsibilities of the General Licensee: Important Safety Instructions

The instructions and Safety Data Sheet (SDS) must be read thoroughly to ensure proper use and disposal.

Some of these requirements may include but are not limited to:

1. Security of the device/material 2. Proper handling and use and appropriate personal

protective equipment3. Routine maintenance of the device/material 4. Semi-annual leak testing 5. Return to vendor, or disposal of as radioactive waste,

after the source is no longer useful

The generally licensed item will arrive with labeled instructions affixed prominently on the equipment. For unsealed generally licensed materials, an SDS will be provided.

Notify EH&S upon receipt of Generally Licensed Material

The most efficient way to do this is to complete the Laboratory Hazard Assessment Tool (LHAT) on an annual basis, or whenever inventory changes occur.

1.

2.

The NRC requires recipients of Generally Licensed Materials to notify EH&S if the material was purchased directly from a vendor and not received through the EH&S Radiation Safety Office.

NEVER dispose of generally licensed material or devices as regular trash. EH&S is able to assist with the shipment of unwanted sources to the original manufacturer or may be able to collect the device for proper disposal through an approved disposal facility.

Question 3:What do you think?

The Nuclear Regulator Commission (NRC) regulates sealed sources in different ways. What 3 categories can a sealed source be categorizes under?A. Leak-Test Required, Leak-Test Exempt or Generally

Licensed.B. Hazardous, Dangerous, or DestructiveC. Flammable, Inflammable, or IgnitableD. Small, Medium, or Large

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correct

answer…

Question 3:What do you think?

The Nuclear Regulator Commission (NRC) regulates sealed sources in different ways. What 3 categories can a sealed source be categorizes under?A. Leak-Test Required, Leak-Test Exempt or Generally

Licensed.B. Hazardous, Dangerous, or DestructiveC. Flammable, Inflammable, or IgnitableD. Small, Medium, or Large

Correct! The 3 categories of sealed sources as defined by the NRC are Leak-Test Required, Leak-Test Exempt, and Generally

Licensed.

Radiation ProtectionThe ALARA safety principle uses all reasonable

methods to achieve the lowest dose as reasonably achievable.

A.L.A.R.A.As Low As Reasonably Achievable

Time, Distance, ShieldingFollowing the Time, Distance and Shielding techniques

will help achieve the ALARA principal.

Keep some distance

Place a barrier between you and

the radiation source

Spend less time around radiation

Time

For example, the longer a person stays at the beach out in the sun (a radiation source), the greater chance of receiving a sunburn.

The less time someone spends around radiation the less exposure they will receive.

Ouch! I’ve been out here

too long!

Distance

Adding distance between the radiation source and the human body greatly reduces exposure.

A radioactive source emits radiation at a relatively constant rate in all directions and follows the inverse square law, which states that the intensity of the radiation is reduced by 1/distance^2 as someone moves further away from the radiation source.

For example, if a person moves from 1 feet to 3 feet away from the source, they have reduced their exposure by 1/9th or 11% of the original valve.

ShieldingPlacing a physical barrier between you and the radiation source can block some or all of the radiation. Choose the shielding material appropriate for the type of radiation being emitted from the source.

PaperPlexiglass

Water or concreteLead

Question 4:What do you think?

When working with radiation, what method(s) should be used to achieve the ALARA principal?A. Minimizing the time spent around a radiation sourceB. Increasing the distance between the radiation source

and yourselfC. Placing an shield of appropriate material between the

source and yourself.D. All of the above

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correct

answer…

Question 4:What do you think?

When working with radiation, what method(s) should be used to achieve the ALARA principal?A. Minimizing the time spent around a radiation sourceB. Increasing the distance between the radiation source

and yourselfC. Placing an shield of appropriate material between the

source and yourself.D. All of the above

If you said D, All of the Above, You are Correct!

Monitoring Radiation Exposure

Exposure monitoring is required to prevent users from exceeding the NRC-established exposure limits.

The most common ways to measure radiation exposure are:

• Geiger-Muller (GM) detection instruments

• Dosimetry personal monitoring devices

Geiger-Muller (GM) Detectors

A Geiger-Muller (GM) detector is a simple to operate gas-filled detector used to detect alpha, beta and gamma radiation.GM detectors count individual radiation events as a pulse and provide readings in counts per minute (CPM). These detectors can not distinguish between radiation types nor can it distinguish between different energies of a single type of radiation.

Disadvantages

Cannot distinguish between alpha, gamma or beta radiation.

Does not provide an overall exposure rate, just a count of what's happening at that moment.

Advantages

Good for locating spots of radiation.

Detects alpha, gamma, and limited beta radiation but not low energy beta radiation.

Dosimetry - Personnel Monitoring

External radiation exposure can be measured by personnel monitoring devices called dosimeters, providing a permanent, legal record of an individual's occupational exposure to radiation.

What is Used for Monitoring?

Optical-Stimulated Luminescence dosimeters (OSL’s) Badges and Thermo luminescent Dosimeters (TLD’s) rings are the most common types of dosimeters used at UCLA.

OSL badges measures whole body, lens of the eyes and shallow

skin doses

TLD rings are used to assess extremity

doses

Disadvantages

TLDs and OSLs require processing in order for dose information to be obtained.

Advantages

Keep a permanent record of your dose

When is Monitoring Required?

If an individual can likely exceed 10% of the occupational dose limits associated by a particular source, dosimeter usage will be required when during handling.

Proper use of Personnel Dosimeters

Do’

s Don

’ts

• Never share your dosimetry badge or wear someone else’s

• Do not intentionally expose dosimeters to radiation

• Do not wear your dosimetry badge for non-occupational exposures

• Do not use your badge at an institution other than UCLA

• Store your dosimetry badge in a non-radiation location when not in use

• Exchange your badge when requested by the Departmental Badge Coordinator

• Keep your badge at work. Don’t take it home

• Wear your dosimetry badge: • whenever using

radiation-producing machines or radioactive materials that present an external hazard

• for the current monitoring period

• in the correct location on the body

• If you are pregnant and wish to begin fetal monitoring, it is your responsibility to declare your pregnancy in writing to the RSP

Sealed Source Disposal: Contact Radiation Safety

Like most radioactive materials, sealed sources cannot be disposed of as regular trash. In fact, most sealed sources require special disposal due to their high concentration and small size.

As a result, all sealed sources must be given to the Radiation Safety Program for appropriate disposal. Yes, even leak-test exempt and generally licensed sealed sources ordered directly by the lab will most likely need special treatment.

Congratulations!Next step, Recording Completion of Your Annual Refresher Training

Now that you have read through this annual refresher training

module, be sure to record it on your

laboratory’s Principal Radiation Worker

Training Record Form. Beside your name,

mark the “OL” box for online, date, and initial

the form.

For more information

Questions about the annual refresher training or need a copy of your lab group’s training form?

Contact your responsible health physicist or the Radiation Safety Training Manager at

ext. 4-1876 or eesparza@ehs.ucla.edu

Questions about topics discussed in this module? Contact the Sealed Source Program Manager at mlabron@ehs.ucla.edu