Refresher Training for Users of Radiation Producing Devices

Elayna MellasRadiation Safety Officer

Environmental Health & Safety ManagerClarkson UniversityDowntown Snell 155

Tel: 315-268-6640emellas@clarkson.edu

This training course has been partially adaptedfrom slides provided by Steve Backurz, RadiationSafety Officer of The University of New Hampshire

Introduction• Radiation is a valuable tool used in research

at Clarkson– Electron microscopes– X-ray fluorescence spectrometry– X-ray diffraction analysis of samples for

chemistry and engineering research• Radioactive materials and X-ray machines

are very safe if used properly and simple precautions are followed

The Basics: Definitions• Radioactivity: The spontaneous disintegration or decay of an

unstable atom, resulting in the release of energy (radiation).

• Radiation: Energy in the form of particles or waves

• Radioactive material: Any material that is composed of (or contains) radioactive atoms.

• Ion: Any atom or molecule with an imbalance in electrical charge. Ions are very unstable and will seek electrical neutrality by reacting with other atoms or molecules

• Activity: The number of disintegrations (decays) occurring per unit of time.

• Half Life: The time it takes for an amount of radioactive material to lose half (50%) of its activity because of decay.

The Particles• ALPHA PARTICLE (): A high energy particle emitted

from the nucleus during the decay of an atom.

– Travel a few centimeters in air

– Stopped by a sheet of paper or layer of skin

– Not an external hazard; ingestion or inhalation concern

• BETA PARTICLE (): A high energy particle emitted from the nucleus during the decay of an atom

– Travel 10 to 20 feet in air

– Stopped by a book

– Shielding high energy betas with lead can generate more radiation due to Bremsstrahlung x-rays

• GAMMA RADIATION (): Electromagnetic radiation emitted from the nucleus during decay

– No mass, no charge

– Travel many feet in air

The Electromagnetic SpectrumRadiation Wavelength in Angstrom Units

Photon Energy in Million Electron Volts (MeV)

108 106 104 102 1 10-2 10-4 10-6

X-RaysRadio Infrared Visible

Ultra-VioletLight

Gamma Rays

Cosmic Rays

10-10 10-8 10-6 10-4 10-2 1 10222 4 10

X-Rays Wave type of radiation - non-particulate Photons originating from the electron cloud Same properties as gamma rays relative to mass,

charge, distance traveled, and shielding Characteristic X-rays are generated when electrons fall

from higher to lower energy electron shells Discrete energy depending on the shell energy level

of the atom Bremsstrahlung X-rays are created when electrons or

beta particles slow down in the vicinity of a nucleus Produced in a broad spectrum of energies Reason you shield betas with low density material

Bremsstrahlung Radiation

Energy is lost by the incoming charged particle through a radiative mechanism

Beta Particle

-Bremsstrahlung Photon

+ +

Nucleus

X-Ray Machine Components

High Voltage

Power Supply

Tungsten Filament

Target

Glass Envelope

Tube Housing

CathodeAnode

Current

X-Ray Machine Basics

kVp - how penetrating the X-rays are Mammography - 20 - 30 kVp Dental - 70 - 90 kVp Chest - 110 - 120 kVp

mA - how much radiation is producedTime - how long the machine is on Combination of the above determines exposure

Ionization

Ionization by a Beta particle:

-

-

-

-

The neutral absorber atom acquires a positive charge

Beta Particle

-

CollidingCoulombic Fields

ejected electron

Gamma Interactions

Gamma interactions differ from charged particle Interactions

Interactions called "cataclysmic" - infrequent but when they occur lot of energy transferred

Three possibilities: May pass through - no interaction May interact, lose energy & change

direction (Compton effect) May transfer all its energy & disappear

(photoelectric effect)

Compton Effect An incident photon interacts with an orbital electron

to produce a recoil electron and a scattered photon of energy less than the incident photon

Before interaction After interaction

-

--

Incoming photonCollides with electron

--

--

Electron is ejected from atom

-

Scattered Photon

Biological Effects

Acute Exposure Large Doses Received in a

Short Time Period Accidents Nuclear War Cancer Therapy

Short Term Effects (Acute Radiation Syndrome 150 to 350 rad Whole Body)Anorexia Nausea Erythema Fatigue

Vomiting Hemorrhage Epilation Diarrhea

Mortality

Effects of Acute Whole Body Exposure on Man

Absorbed Dose (rads)

Effect

10,000 Death in a few hours

1,200 Death within days

600 Death within weeks

450 LD 50/30

100 Probable Recovery

50 No observable effect

25 Blood changes definite

5 1st blood changes observed

Biological Effects• Chronic Exposure

– Doses Received over Long Periods • Background Radiation Exposure• Occupational Radiation Exposure

– 50 rem acute vs 50 rem chronic• acute: no time for cell repair• chronic: time for cell repair

– Average US will receive 20 - 30 rem lifetime– Long Term Effects

• Increased Risk of Cancer• 0.07% per rem lifetime exposure• Normal Risk: 30% (cancer incidence)

Background Exposure Your exposure to radiation can never be zero because

background radiation is always present Natural Sources (Radon), Cosmic, Terrestrial, Medical

Diagnostic, Consumer Products, etc

Total US average dose equivalent = 360 mrem/year

Total exposure Man-made sources

Radon

Internal 11%

Cosmic 8%Terrestrial 6%

Man-Made 18%

55.0% Medical X-Rays

NuclearMedicine 4%

ConsumerProducts 3%

Other 1%11

Annual Dose from Background Radiation

• Occupational Limits (Researchers) 5 rem per year (total effective dose equivalent: TEDE) 50 rem per year (any single organ) 15 rem per year lens of the eye 50 rem per year skin dose

• Members of Public 100 mrem per year No more than 2 mrem in any one hour in unrestricted

areas from external sources• Declared Pregnant Females (Occupational)

500 mrem/term (evenly distributed) Declaration is voluntary and must be submitted to RSO in

writing (see form on website)

Standards for Rad Protection

Clarkson AnticipatedWorker Radiation Exposure

Anticipated Exposures: Less than the minimum detectable dose for film badges (10 mrem/month) - essentially zero

Average annual background exposure for U.S.

population = 360 mrem/year

State and Federal Exposure Limits = 5000 mrem/year

Uses of Radiation

Consumer Products

Building materials Tobacco (Po-210) Smoke detectors (Am-241) Welding rods (Th-222) Television (low levels of X-rays) watches & other luminescent products

(tritium or radium) Gas lantern mantles Fiesta ware (Ur-235) Jewelry

Research at ClarksonUsing Radiation Sources

Radioactive Materials (both open and sealed sources)

Gas Chromatographs (sealed sources) Liquid Scintillation Counters (sealed

sources for internal standards) X-ray Diffraction equipment Electron microscopes X-ray fluorescence spectrometer

MedicalDiagnostic

X-rays Nuclear Medicine (Tc-99m, Tl-201, I-123) Positron Emission Tomography (PET)

Therapeutic X-rays (Linear Accelerators) Radioisotopes

Brachytherapy (Cs-137, Ir-192, Ra-226)Teletherapy (Co-60)Radiopharmaceuticals (I-131, Sr-89, Sm-153)

The goal of radiation protection is to keep radiation doses As Low As Reasonably Achievable and eliminate any unnecessary dose to yourself, coworkers, and the public

Clarkson is committed to keeping radiation exposures to all personnel ALARA

What is reasonable? Includes:

State and cost of technologyCost vs. benefitSocietal & socioeconomic

considerations

A sL owA sR easonablyA chievable

Reducing Exposure

Practicing ALARA

Time: minimize the time that you are in contact with radioactive material to reduce exposure

Distance: keep your distance. If you double the distance the exposure rate drops by factor of 4

Shielding: place a barrier between you and the radioactive source Source Reduction: order and use the smallest amount of radioactive

materials as necessary Protective clothing: protects against contamination only - keeps

radioactive material off skin and clothes

Protect Yourself & Your Colleagues!

OPTIMIZE USE OF ALL PROTECTIVE MECHANISMS TO MINIMIZE DOSE.

Shielding Recommendations:• Betas (ex: 32P):

– Use material with low atomic number, such as:

• Plastic, lucite, acrylic• Wood, paper, cardboard

• Gammas (ex: 125I or 51Cr):– Use material with high

atomic number, such as:• Lead, concrete, bricks,

stainless steel, cast iron

External Radiation Inverse Square Law

Radiation levels decrease as the inverse square of the distance (i.e. move back by a factor of two, radiation levels drop to one fourth)

Applies to point sources (distance greater than 5 times the maximum source dimension)

where I = Intensity (exposure rate) at position 1 and 2 andR = distance from source for position 1 and 2

Position 1Position 2

(mrem/hr) (mrem/hr)

Source

222

211 RIRI

R1

R2 I2

I1

Gamma Ray Constant

Gamma Ray Constant to determine exposure rate

(mSv/hr)/MBq at 1 meterHint: multiply (mSv/hr)/MBq by 3.7 to get (mrem/hr)/uCi

Exposure Rate Calculation, X (mrem/hr) at one meter:

X =Where, A = Activity (Ci)

Gamma Ray Constant(mSv/hr)/Mbq 3.7 is the conversion factor

Sample Calculation

• 5 Curie Cs-137 Source• Calculate Exposure Rate at 1 meter

= 1.032 E-4 mSv/hr/MBq @ 1 meter

X = 1.032 E-4 * 3.7 * 5 Ci * 1000 mCi/Ci * 1000 uCi/mCi

X = 1909 mrem/hour

X = 1.91 rem/hour

Survey Meters are portable instruments that can be used to detect most spots of contamination - except for 3H.

Wipe Testing must always be done for 3H and lower activities (100 µCi or less) of 35S and 14C.

Detecting Contamination

Detecting Common Isotopes

Sodium Iodide (NaI)

Probe

Survey Meter

Geiger- Mueller

(GM) Probe

3H Liquid Scintillation Counter

14C

GM Probe with

Survey Meter32P

33P

35S

51Cr GM or NaI Probe w/ Survey Meter

125I NaI Probe w/ Survey Meter

Liquid Scintillation Counter

• Check calibration date (not older than 12

months)• Batteries must be fresh / good• Background count rate• Detector/instrument must be responsive• Miscellaneous conditions…?

•Check Physical Condition•Cables, Connections, Damage•Select Proper Scale•Response Time (Fast or Slow?)•Audio (On or Off)

Survey Meter Operability

Each USER must verify that the survey instrument is in good working order before each use.

CPM & DPM

A radiation detector will not detect every disintegration from a source (i.e., they are not 100% efficient)

Counts per minute (cpm) is the number of disintegrations that a detector “sees”

The efficiency of a detector is determined by the following:

Efficiency = net cpm / dpm= gross cpm – background cpm /

dpm

Each detector will have its own background level.

1st check the background level - use it as a baseline. Observed:

Background:

Zero:

Any reading higher than the background level means the item is radioactive.

Remember that background is radiation coming from the environment, and it cannot be prevented or eliminated.

Survey Meter “Background” Levels

• U. S. Nuclear Regulatory Commission Regulates the nuclear industry pursuant to the

Atomic Energy Act Regulatory guides published to describe

methods for complying with regulations• Agreement States

Some states have entered into an agreement with the NRC to regulate by-product material (and small quantities of source and special nuclear material)

Currently, 30 states are agreement states including New York

Regulatory Agencies

Radiation at ClarksonActivities are licensed by the State of New YorkRadiation Safety Committee has responsibility

to review, approve, and oversee activitiesRadiation Safety Officer (RSO) runs programClarkson is required to:

Train individuals that use sources of radiation

Train non-radiation workers that work in the vicinity of radiation sources

Monitor and control radiation exposures Maintain signs, labels, postings

Posting & Labeling Notices Posting

New York Notice to employees form Caution Radiation Producing Devices or X-

Rays

Employee Rightsand Responsibilities

Right to report any radiation protection problem to state without repercussions

Responsibility to comply with the Radiation Protection Program and the RSO's instructions pertaining to radiation protection

Right to request inspectionin writinggrounds for noticesigned

Responsibility to cooperate with NY State inspectors during inspections and RSO during internal lab audits

• Inspections NY shall be afforded opportunity to inspect at

all reasonable times Records shall be made available Inspector may consult with workers privately Worker may bring matters to inspector

privately Workers can request inspection

• Must be in writing • Name is not revealed

Inspections

• Internal audits by Clarkson RSO are performed in all labs on campus

• Looking for same things as state inspector Security of radiation producing devices Proper procedures in use Postings, dosimetry, survey meters,

calibrations, records of surveys, etc.

Internal Audits

Your Rolein Radiation Protection

Report anything that looks out of the ordinary or if you are uncertain about what to do, where to go, requirements, exposures:

Call the people on the emergency list

Ask the Radiation Safety Officer (RSO)Elayna Mellas268-6640emellas@clarkson.edu

Acknowledgements

This training course has been adapted from slides provided by Steve Backurz, Radiation Safety Officer of The University of New Hampshire and Eric Andersen, Radiation Safety Officer at the Dana-Farber Cancer Institute.