INTRODUCTION TO RADIATION PROTECTION

Sources of ionizing radiationAtomic structure and radioactivityRadiation interaction with matterRadiation units and doseBiological effects

3/14/2018 1

Wilhelm C. Roentgen (1845-1923)In 1895, while working

with electrically-energized, sealed-glass “Crookes”tubes, he discovered that photographic plates kept near the tubes become darkened.

2

X-Ray Photography

Roentgen assumes previously unknown “X-RAYS” are escaping the tube.

Roentgen makes photo images with x-rays and shows they easily penetrate soft tissue.

3

Henri Becquerel(1852 – 1908)In 1896, discovered

other invisible rays coming from natural Uranium would also darken photo plates.

4

Ionizing Radiations(causing alteration of photo media) are generated by high energy natural or man-made processes occurring within the atom.

Roentgen and Becquerel had discovered IONIZING RADIATION

3/14/2018 5

Ionizing Radiation

Possess enough energy to remove electrons from atoms, creating ion pairs.

These ion pairs then go on to create highly reactive chemicals that can damage DNA and other important cellular molecules.

3/14/2018 6

We live in a sea of ionizing radiationTerrestrial Cosmic Human generated• Accelerators• Reactors• Medical procedures• Industrial (radiography, airports,

interrogation)

3/14/2018 7

Radiation Use

Availability and use of radioactive materials “exploded” after World War II.

Availability and use of radioactive materials “exploded” after World War II.3/14/2018 8

ResearchMedicine

Radiation in the Workplace

Nuclear Medicine

Radiation Therapy

IrradiationsLaboratory Use

3/14/2018 9

Radiation in the WorkplaceMeasure Thickness

Measure DensityIndustrial Radiography

Measurement and Quality Control

Static Control

3/14/2018 10

Baggage X-ray

Radiation in the Workplace

3/14/2018 11

Biomedical/Industrial wastes or byproducts

Lost sources

Radiation in the Environment

3/14/2018 12

Active Production or Processing Sites

Closed/Abandoned Production or

Processing Sites

Radiation in the Environment

3/14/2018 13

Nuclear Accidents

Radiation in the Environment

3/14/2018 14

Detecting Incoming Radioactive Materials

Seaports

Airports

Borders

3/14/2018 15

Where does it come from?

• Can be naturally occurring or man-made• Produce radiation at all times, but decays away

over time.• If unsealed and loose, it can be easily spread

around (contamination).

3/14/2018 16

3/14/2018 17

ISOTOPE ½ Life APPLICATIONS

Uranium billions of years

Natural uranium is comprised of several different isotopes. When enriched in the isotope of U-235, it’s used to power nuclear reactor or nuclear weapons.

Carbon-14 5730 y Found in nature from cosmic interactions, used to “carbon date” items and as radiolabel for detection of tumors.

Cesium-137 30.2 y Blood irradiators, tumor treatment through external exposure. Also used for industrial radiography.

Hydrogen-3 12.3 y Labeling biological tracers.Iridium-192 74 d Implants or "seeds" for treatment of cancer. Also

used for industrial radiography.Molybdenum-99 66 h Parent for Tc-99m generator.

Technicium-99m 6 h Brain, heart, liver (gastroenterology), lungs, bones, thyroid, and kidney imaging, regional cerebral blood flow, etc..

Machine ProducedWhere does it come from?

• X-ray Machines, cyclotrons, accelerators, etc.• Most produce x-rays but particles also possible.• Only produce radiation when energized.• High energy machines can activate materials to

create radioactive materials.

3/14/2018 18

Atomic Structure and RadioactivityNuclear notationTerminologyDecay modesX-raysHalf life

3/14/2018 19

Nuclear notation

3/14/2018 20

Li-7Not actual sizeNot to scale

TerminologyRadioactivity – processRadiation - energyActivity – “quantity”Contamination – materialHalf life - time

3/14/2018 21

RadioactivityThe process by which an energetically unstable

nucleus spontaneously transforms to a more stable energy state and in the process emits radiation.

Radiation means matter or energy moving outward from a point of origin.

3/14/2018 23

Radiation from a point source decreases as a function of the square of the distance (1/R2)

Five basic types of radiation

3/14/2018 24

From the nucleus

From the electron shells

Electromagnetic Radiation

• No Mass• No Charge• Very Penetrating

3/14/2018 25

X-ray/Gamma Same except for originPhoton Can be stopped by layers of lead or concreteHazardous to tissues and organs Common photon emitters: Tc-99m, I-125Characteristic x-rays and gamma are essentially

monoenergetic Bremsstrahlung x-rays can be a spectrum

Characteristic X-rays

3/14/2018 27

Characteristic X-rays are emitted when outer-shell electrons fill a vacancy in the inner shell of an atom, releasing X-rays in a pattern that is "characteristic" to each element.

Bremstrahlung x-rays

3/14/2018 28

Alpha αMade up of 2 neutrons and 2 protons

(nucleus of the Helium atom) Travel short distances, stopped by paper and

dead layer of skin Mainly an internal hazard in the bodyCommon Alpha emitters: Uranium, Thorium,

Radon and radon daughtersCharacteristically mono energetic

Beta βEnergetic electronCan be stopped by 1 cm of plasticHazard to skin and eyes and when taken internallyCommon Beta emitters: Phosphorus, Tritium,

Carbon, SulfurSpectrum of energies are emitted (βmax)Most beta emitters are also gamma emitters

Neutron

Has no chargeRange in air is very far. Easily can go several

hundred feet. High penetrating power due to lack of charge

Can be a hazard to whole bodyCommon neutron emitter: Cf-252

After Time

Pure SampleFull Activity

Decayed SampleLower Activity

Radioactive Decay

3/14/2018 32

Half lifeThe radioactive half-life for a given radioisotope

is the time for half the radioactive nuclei in any sample to undergo radioactive decay.

Simple Half-Life Calculation

Activity decreases over time by a rate defined as the half-life

Where n is the number of half lives:

A = Ao/2n

3/14/2018 34

Thus after one half-life the nuclide will be half of its original activity, after two half-lives, one quarter, and etc.After 7 half lives less than 1% of the original activity remains

Activity

“Activity” describes how much radioactive material is present at any given time

Curie (Ci): 37 Billion transformations per secondUsually expressed as milli (10-3) or micro (10-6)

Bequerel (Bq): 1 transformation per secondUsually expressed in Mega (106) or Giga (109)

3/14/2018 35

Interaction of ionizing radiation with matter

Alpha and Beta – energy is lost by transfer of energy to electrons via electrostatic interaction

Photons – all or part of its energy is transferred to an orbital electron via collision

Neutron – energy and material dependent (Z#)• <0.5 MeV - elastic scattering with nucleus• >0.5 MeV - inelastic scattering with nucleus• Thermal – absorption in the nucleus

3/14/2018 36

Interaction of ionizing radiation with matter

3/14/2018 37

Penetration ability of some radiations

3/14/2018 38

Radiation Absorbed Dose (rad)Rad- A measure of energy deposition per unit mass

irradiated1 Rad = 100 ergs per gram of materialSI Unit is Gray 1Gy = 1 joule per kilogram (J kg –1)1 Gy = 100 rad

Dose equivalent (rem)rem: absorbed dose (D) modified by a radiation

weighting factor (wR ) or quality factor (Q) which accounts for the different biological effects of different types of radiation

rem = rad x QIn the SI system of units, it is replaced by the special

name sievert (Sv) where Sv = Gy x wR

1 Sv = 100 rem

Quality Factor (10CFR20)Type of radiation Quality

FactorX-, gamma, or beta radiation 1

Alpha particles, multiple-charged particles, fission fragments and heavy particles of unknown charge

20

Neutrons of unknown energy 10

High-energy protons 10

3/14/2018 41

Average dose equivalent = 620 mrem/yr

3/14/2018 43

Typical medical dosesChest X-ray = 2 mremMammogram = 13 mremAbdomen CT = 1000 mrem (1 rem)Heart stress test = 585 mrem

Terrestrial Radiation Levels

3/14/2018 45

Cosmic Radiation Levels

3/14/2018 46

Health physics nerd funWhat is the radiation dose equivalent for flying

across the United States?Seattle WA - Washington DC:• 37, 000 ft; 4.1hours• 0.0192 mSv (which is how many millirem?)

Reference: DOT/FAA/AM-03/16 Office of Aerospace Medicine Washington, DC 20591 “What Aircrews Should Know About Their Occupational Exposure to Ionizing Radiation”

3/14/2018 47

Could be partial or whole body.

Usuallymuch greater at entrance than exit.

May come from inhalation, ingestion, injection, absorption, or injury

Often concentrates in particular organs.

Radiation Hazards

External vs. Internal

3/14/2018 48

Biological Effects

3/14/2018 49

Acute effectsChronic effects Linear non-threshold modelBasis for regulatory limits

Biological EffectsMany groups and individuals exposed to

ionizing radiation at high levels resulted in adverse effects

Somatic effects– Prompt - skin burns and cataracts– Delayed - cancer

Genetic effectsTeratogenetic effects

Biological EffectsBiological effects are caused by chemical

changes in the cell brought about by the conversion of kinetic energy to chemical energy

Direct effects – caused by initial ionizationIndirect effects – free radicals and ions (mostly

from water) interact with cell material

Fate of Early Radiologists

3/14/2018 52

Radiologist Fingers

3/14/2018 53

1898 Photograph shows severe chest burn on a United States soldier in the Spanish-American War, caused by repeated exposure to X rays.

Early Radiation Injury

3/14/2018 54

Internal DoseCaused by radioactive material inside the bodyRoutes of entry:

– Inhalation– Ingestion– Absorbtion– Injection

Organs can concentrate based on chemical affinity (e.g. thyroid, bone, kidneys)

3/14/2018 55

Radiation Health EffectsHigh-level radiation effects are acute effects

which are manifested shortly after (hours, days, weeks) a large exposure (1 Sv or 100 rem+).

Low-level radiation effects are described as• latent effects, appearing many years after a

“non-lethal” acute dose, or• chronic effects after many years of small

doses (like radiation workers).

3/14/2018 56

High Level Radiation Effects

• Acute Radiation Syndrome• Bone Marrow Injury (over 1 Sv or 100 rem)– may

cause death if injury is severe.• GI Tract Injury (over 6 Sv or 600 rem) – causes

death in days or weeks. • Central Nervous System Injury (over 50 Sv or 5000

rem) – causes death in hours or days.• Radiation Burns (over 2 Sv or 200 rem) – local or whole

body • Cataracts (over 1.5 Sv or 150 rem)

3/14/2018 57

Dose (Rads*) Effects

25-50First sign of physical effects(drop in white blood cell count)

100 Threshold for vomiting (within a few hours of exposure)

320 - 360~ 50% die within 60 days (with minimal supportive care)

480 - 540~50 % die within 60 days(with supportive medical care)

1,000 ~ 100% die within 30 days

X-Ray Burns

5,000+ rad

500+ rad

CancerRadiation can damage cells through two

methods;– Production of free radicals and– Direct damage to the DNA

Risk factor for radiation dose:– 4% increase in risk of dying of cancer for

every 100 rem of dose.– Normal cancer risk is 20%.

Low Level Radiation Health Effects

Cancer – 0.1 Sv (10 rem) given to 100 people in U.S. population would be expected to cause about 1 extra cancer over a lifetime. About 42 of these people would be expected to get cancer from natural causes.

BIER VII Report

3/14/2018 61

0 10 20 30 40 50 60 70Committed Lifetime Dose (rem)

0.00

0.01

0.02

0.03

Risk

ofde

ath

f rom

can c

e r

Dose Response Relationship

Predictable EffectsRisk Is not

Predictablebelow 20 rem

Effect is Detrimentalrisk level is uncertain

Low Level Radiation Health Effects

Genetic mutations – has not been observed in humans, but has been observed in experimental animal populations

Teratogenesis - abnormalities induced in an exposed fetus – depends on dose and period of pregnancy.The risk of abnormality is considered negligible at

5 rad or less when compared to the other risks of pregnancy. (NCRP Report 54)

3/14/2018 63

Relative hazard summary1 rem received in a short period or over a long period is

safe—we don’t expect observable health effects.10 rem received in a short period or over a long period is

safe—we don’t expect immediate observable health effects, although your chances of getting cancer might be very slightly increased.

100 rem received in a short time can cause observable health effects from which your body will likely recover, and 100 rem received in a short time or over many years will increase your chances of getting cancer.

1,000 rem in a short or long period of time will cause immediately observable health effects and is likely to cause death

Health physics nerd funHow much energy is absorbed in the body for

an LD 100/30 day whole body acute dose of gamma radiation?

• LD 100/30 day dose is 1000 rads; person = 87kg (160lb)• 1000 rads x (100 ergs/gm/rad) x (87kg) = 8.7e+6 ergs• 8.3 BTU to raise 1 gallon (3.76 kg) of water 1°F = 8.8e+10erg • (1 BTU = 1.06e+10 erg)• (87kg/3.76kg) x 8.8e+10 erg = 2e+12erg to raise the body 1°F• 8.7e+6erg/2e+12 erg per 1°F= 4.3e-6 °F

3/14/2018 65

Health physics nerd fun

Compute your radiation dose exercise– https://www.epa.gov/radiation/calculate-

your-radiation-dose– http://www.ans.org/pi/resources/dosechart/

3/14/2018 66

Information sources• Health Physics Society – www.hps.org• National Council on Radiation Protection -

http://ncrponline.org/• Nuclear Regulatory Commission –

www.nrc.gov• American Nuclear Society – www.ans.org• Radiation Answers -

http://www.radiationanswers.org/

3/14/2018 67