Radiation Interaction with Matter: What happens when radiation hits us (or a detector)? General: Matter = Atoms (small positively charged nucleus orbited by negatively charged electrons, electron orbits about factor 105 larger than nuclear radius)

In radiation interaction with matter:

- Energy is transferred from the radiation to the absorbing medium (which can be us) - Results usually in ionization and excitation of atoms or molecules in the absorber. (This can cause dissociation of the molecule.)

- Transferred energy is eventually dissipated as heat.

Radiation Safety

1 Radiation Safety

Alpha particles α = 42He2++

Interactions between the electric field of an alpha and orbital electrons cause ionization and excitation. Alpha particles lose their energy over a relatively short range. One α-particle will cause tens of thousands of ionizations per centimeter in air. Path is relatively straight as α-particle much heavier than the collision partners (electrons). Range in air: for 5-8 MeV alphas ~ 8-10 cm (less in denser materials, shielding by a piece of paper) α-sources are usually open (handled only by instructor)

Types of radiations (I)

2 Radiation Safety

Beta particles: β+, β- Energy transfer through collisions with atomic electrons leading to ionization and excitation. Due to its much lower mass a β-particle has a much higher velocity than α-particles of comparable energy. As the collision partners (atomic electrons) have the same rest mass, large deflection can occur resulting in many path changes. Additionally:

- Bremsstrahlung (X-rays) is produced when β-particle passes near the atomic nucleus - Positrons are antimatter and annihilate with atomic electrons to produce gamma radiation (511 keV)

For shielding use low Z-material to avoid X-ray production

Types of radiations (II)

3 Radiation Safety

Gamma (γ) X-Ray 10-100 KeV, Gamma-Ray higher energies Both are photons photons, electromagnetic radiation energy range keV – tens of MeV Zero rest mass photons traveling at the speed of light. They are basically distortions in the electromagnetic field of space and interact thus electrically with atoms even though they have no net electrical charge. While alphas and betas have a finite maximum range and can therefore be completely stopped with a sufficiently thick absorber, photons interact in a probabilistic manner. This means that an individual photon has no definite maximum range. However, the total fraction of photons passing through an absorber decreases exponentially with the thickness of the absorber. Energy transfer mechanisms:

- Photoelectric effect - Compton effect (elastic scattering) - Pair production (Matter – Antimatter production)

Shielding with high electron density materials = Lead (Pb)

Types of radiations (III) 4 Radiation Safety

BIOLOGICAL EFFECTS OF RADIATION

DNA double helix

• At the molecular level, the energy carried by the incident radiation is transferred to the DNA, leading damages in the DNA structure. • The energy transfer has direct and indirect pathways, in the latter the energy is transferred to water first to produce free radicals. The highly reactive free radicals then diffuses to DNA and causes damages.

Activity: is the rate of decay (disintegrations/time) of a given amount of radioactive material. 1 Bequerel (Bq) = 1 disintegration/second Old unit: 1 Curie (Ci) = 3.7 1010 Bq Exposure: is a measure of the ionizations produced in air by x-rays or gamma radiation. 1 Roentgen (R) = quantity of radiation that causes ionization = 2.58 10-4 C/kg

Activity & Exposure

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Dose: is 1- A measure of energy deposited by radiation in a material (absorbed dose) 2- A measure of the relative biological damage produced by that amount of energy given the nature of the radiation (dose equivalent) Absorbed dose: 1 Gray (Gy) = 1 Joule/kg Old unit: 1 rad = 1/100 Gy (1 R exposure ~ 0.87 rad dose) Dose equivalent: includes the biological effectiveness (for cell damage) multiplication with quality factor Q: Gammas, X-rays = 1 Beta particles = 1 Alpha particles = 20 (because of ionization power) 1 Sievert (Sv) = Q * absorbed dose (Gy) Old unit: 1 rem = Q * absorbed dose (rad) (1 Sv = 100 rem) Still most important in the US.

Dose 8 Radiation Safety

Radiation and Doses • A number of units are used to describe radiation and its

effects on biological material

Common Unit SI Unit Description Application

1 Curie (C) 3.7x1010 decays

1Becquerel (Bq) 1 decay

Activity Describe amount of material ie 1 μC of 137Cs

Rad 0.01 Joule/Kg

Gray (G) 1Joule/Kg

Absorbed Dose How much Energy is absorbed

REM Rad x RBE

Equivalent Dose Absorbed x Relative Biological Effectiveness (RBE)

Biological Damage RBE 10-20 Alpha 1-2 Beta 1 Gamma

9 Radiation Safety

Radioactive decay law: Activity: A(t) = A(0)*exp(-λt) = A(0)*exp(- 0.693 t/T1/2) with: T1/2 Half-life of specific nucleus (tabulated) (time required for one half of a collection of atoms of that nuclide to decay) Example: 32P: T1/2 = 14.3 days Original activity (January 10): 10µCi I use the same source on February 6: ∆T = 27 days A (Feb 6) = A(Jan10)*exp(-0.693*27/14.3) = 2.7 µCi

Calculations of Activities

ln 2

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Calculation of exposure rates (rules of thumb – Rad) for γ’s and X-rays 6 . Ci . n . E Rad/hour at 30 cm (1 foot)

Source strength (in Curie) Fraction of decays

resulting in photons with energy E

Energy of the emitted photon in MeV

Radiation Protection, A guide for Scientists, Regulators, and Physicians, Jacob Shapiro, La Editorial, UPR, 2002 ISBN 0674007409, 9780674007406

Calculation of exposure rates (rules of thumb – Rad) for γ’s and X-rays 6 . Ci . n . E Rad/hour at 30 cm (1 foot)

Source strength (in Curie) Fraction of decays

resulting in photons with energy E

Energy of the emitted photon in MeV

Example from this lab: 1µCi 137Cs, n=1, E=0.663 MeV 6 . 1.10-6 . 1 . 0.663 R/hr at 30cm 3.10-6 Rad/hr at 30 cm with quality factor Q=1 3.10-6 rem/hour at 30 cm

Exposure Rate (II)

For 1µCi 137Cs source 3.10-6 rem/hr @ 30 cm Dose Equivalent 6 hour lab course 2.10-5 rem = 0.02 mrem (millirem) per lab session To be compared to: Chest X-ray ~ 10 mrem Cosmic Rays + Other Natural Activity ~ 100 – 200 mrem/year Cosmic rays @ sea level ~ 26 mrem/year Denver ~ 50 mrem/year smoking ~ 50-200 mrem/year ! We also have a 5 mCi source Shielded with lead (Pb)…

13 Radiation Safety

Radiation Safety 14

Sources in your pocket = BAD !!! 1/r2 law applies in pocket: d = 1 cm factor (30)2 = 900 >18 mrem / lab session !

6 . Ci . n . E Roentgen/hour at 30 cm (1 foot)

Factors which influence biological effects

• Type of Radiation

• Energy

• Time of exposure

• External / Internal

• Selective uptake

• Organ sensitivity

• Chemical characteristics

• Biological half-life (how long it takes for the body to get rid of half of it)

• Physical characteristics

15 Radiation Safety

BACKGROUND RADIATION DOSE

BACKGROUND RADIATION DOSE • We all live in an environment of

radiation.

• The sources of background radiation include cosmic rays, natural radioactive elements in earth, medical treatments, and consumer products.

• On average, each member of general public receives 620 mrem of radiation dose per year from the background (NCRP Report 160, 2006).

MEDICAL X-RAY DOSE

Type of Exam Patient Dose Per Exam

Background Equivalent

Pelvic CT 400 - 1200 mrem 1- 2 years

Spine 130-270 mrem 2-6 months

Mammogram 45 mrem 4 weeks

Dental 10 mrem 1 week

Chest 5 - 8 mrem 4 days

DEXA hip or spine 1 - 6 mrem < 4 days

DEXA wrist, heel <1 mrem < 1 day

OCCUPATIONAL DOSE LIMITS • The governmental agency regulating

occupational use of radiation is the Nuclear Regulatory Commission (NRC).

• NRC Dose limits: – Adult workers: 5,000 mrem/yr whole

body; 50,000 mrem/yr to any organs – Pregnant workers: 500 mrem during the

gestation period – Minors: 10% of adult’s limit – General public: 100 mrem/yr and not to

exceed 2 merm in any single hour.

Protection Against External Exposure • Time

• Distance

• Shielding

Principle for exposure planning ALARA: As Low As Reasonably Achievable

Internal exposure is usually a more serious threat to health… (time = depends of the physical and/or biological half-life, Distance = 0, Shielding = 0) ex: Plutonium (Pu), α-emitter, T1/2 = 24400 y, when inhaled, the body cannot get rid of it.

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Scale of Effects

Over 5000 rem Death within 1-2 days 1000 – 5000 rem Death within 1-2 weeks 1000 rem 80-90% death rate 500 rem 50% death rate 100 rem Detectable damage to bone marrow 5 rem Annual Occupational Dose Limit .01 rem Chest X-ray

INC

REA

SIN

G D

OSE

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1945 Japan

Two Categories of Health Effect PROBABILISTIC:

• Dose – Response in a large population

• Cancer, Genetic Defects

DETERMINISTIC:

• Dose – Response in a single individual

• Reddening of Skin, Cataracts, Hair Loss Theory of Dose Limits:

• Limit the chances of probabilistic effects • Prevent the occurrence of deterministic effects

Res

pons

e

Dose

Res

pons

e

Dose

Thre

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23 Radiation Safety

The Radium Girls 24 Radiation Safety

Radiation Safety 25

What makes the numbers Glow? And How?

Radiation Safety 26

How does Radium (or other radioactive isotopes) make the dials glow all the time?

Radiation Safety 27

How does Radium (or other radioactive isotopes) make the dials glow all the time?

The electrons emitted (via beta decay) excite atoms in fluorescent material in the paint. Electrons in these atoms transition to higher energy states. When they drop back to lower energy states, visible light is emitted. Sustain fluorescence emission

The Radium Girls

In the early 1920s, about 70 women were hired at the radium factory in New Jersey where they worked as dial painters and used luminescent paint. They assumed they were not using anything poisonous. Even though some women thought it was strange that when a few of them blew their nose the handkerchief glowed in the dark, they thought the stuff was harmless. Some women even painted their nails and their teeth to surprise their boyfriends when the lights went out. At work, the women were painting glow-in-the-dark radium compounds on the dials of watches and clocks. The women sat at long tables row after row. Dials waiting to be painted sat nearby. Each day they would mix up glue, water and radium powder (a mixture of radium salts and zinc sulfide, ZnS) into a glowing greenish-white paint. With care they would then apply it with camel hair brush to dial numbers. As the brush lost its shape, the paint couldn't be applied accurately, so the women would put the brush in their mouth and use the lips to make a point. The paint has no taste, and the women didn't know it was harmful. In those days most people thought radium was a scientific miracle for curing cancer and other medical problems. Unfortunately, for many of these women it did just the opposite. After several years of working as a dial painter, some women's teeth started falling out and their jaws developed a painful abscess. (…) The glow effect that was seen with the dial painters was the result of ionization of atmospheric gases, producing a blue glow. The blue glow can be enhanced in luminescent paints by the addition of zinc sulfide (ZnS). As the alpha particles strike the ZnS, visible light is emitted in response to the ionizing radiation. By the end of the 1920s, many of the dial painters died from symptoms associated with radium poisoning.

From: www.unco.edu/chemist/Bulletin/Chem101/radium.htm

28 Radiation Safety

Question: Why is ingesting Radium (Ra) so harmful?

Why is ingesting Radium (Ra) so harmful?

Why is ingesting Radium (Ra) so harmful?

Radium is especially dangerous because the configuration of its outer electrons are similar to that of Calcium. So it can form chemical bonds in the same way that Calcium does. Calcium is one of the elements in bone. Ingested Radium can replace Calcium in bone to become a long lasting internal radiation source. Leukemia and other cancers can result. 222Ra t1/2 = 1601 years

Why is ingesting Radium (Ra) so harmful?

“FITRITE RADIUM OUTFIT NOTE!!!!!NOTE!!!!! This is a radium outfit used to put luminous material on watch hands and/or dials. The box says it is easily applied and dries quickly. The directions are on the box, which is original. There are 2 cans of material, one light and one dark and they have been used. There is a metal tool for application.” (Description posted)

From E-Bay Nov. 29th 2010

The 1987 Goiania (Brazil) event (I) (from APS News, March 2004)

An example of massive exposure (2nd largest nuclear incident after Chernobyl): - Two scrap metal scavengers find an abandoned (!) radiotherapy source of

137Cs Chloride 1,375 Ci (!) in soluble form removed from its protective housing. The 2 men start vomiting because, they assumed, of bad food !

- 5 days later: hole made in the source, the radioactive powder leaks - Sold to a junkyard the same day, who notices the glowing blue color - Brings the capsule home to show it off !!!! - People sprinkle and rub the powder on their body like carnival glitter - Few days later, people start to develop acute radiation sickness - During the same time, two operators disassemble the whole assembly !

Both of them die.

34 Radiation Safety

The 1987 Goiania (Brazil) event (II) An example of massive exposure: - a 6-year old girl plays with the colorful source powder, painted it on her body, and ate a sandwich while her hands were contaminated - When problem discovered: the brazilian authorities monitored over 112,000 people in the city’s stadium for radiation exposure and sickness 249 people contaminated ! - 151 people both externally and internally Internally exposed = Radioactive ! - 49 people admitted to the hospital, 20 received doses from 100 to 800 rads. - At the end: 5 dead, including the little girl The little girl: consumed (with her sandwich) about (only) 27 mCi dead within a month; Dose: 600 Rad ; LD50 ~ 300 Rad Reading: http://www.aps.org/apsnews/0304/030415.cfm

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Nov. 2006: The Litvinenko Case Polonium 210 poisoning

Alpha emitter, half-life 138 days First known case of fatal polonium poisoning

http://nuclearweaponarchive.org/News/Litvinenko.html

http://www.msnbc.msn.com/id/17332541/

Known for attempting to make a fast-breeder reactor in his backyard at age 17

David Hahn “The Radioactive Boyscout” 1976-

36 Radiation Safety

X-RAYS

Characteristic X-ray • electrons jump from higher energy orbitals to lower energy orbitals • extra energy is release as X-rays • this type of X-rays has discrete energy spectrum

e−

e-

X-ray

Cathode(-) Anode (+) Man-made X-rays

Voltage potential

• electrons are accelerated by high voltage, then stopped by high-density target at the anode

• energy of electrons is converted to X-rays

• energy of X-rays has a continuous spectrum

X-ray

HISTORY “When the X-Ray came up, I made the first fluoroscope, using tungstate of calcium…… I started in to make a number of these lamps, but I soon found that the x-ray had affected poisonously my assistant, Mr. Dally, so that his hair came out and his flesh commenced to ulcerate. I then concluded it would not do, and that it would not be a very popular kind of light; so I dropped it.” – Thomas Edison

RADIATION PROTECTION PRINCIPLES

• There are three basic principles in radiation protection: time, distance and shielding.

• Use theses principles in addition to proper contamination controls to make dose ALARA

Question:

Rank particle types in order of amount of material required to stop them

(less to more) 1: beta,gamma,alpha 2: beta,alpha,gamma 3: gama,beta,alpha 4: alpha,beta,gamma

Question:

Rank particle types in order of amount of material required to stop them

(less to more) 1: beta,gamma,alpha 2: beta,alpha,gamma 3: gama,beta,alpha 4: alpha,beta,gamma

Question – Which factors will all reduce exposure to external Radiation? 1. More Shielding, Less Time, Less Distance

2. Less Shielding, Less Time, More Distance

3. More Shielding, More Time, Less Distance

4. More Shielding, Less Time, More Distance

Question – Which factors will all reduce exposure to external Radiation? 1. More Shielding, Less Time, Less Distance

2. Less Shielding, Less Time, More Distance

3. More Shielding, More Time, Less Distance

4. More Shielding, Less Time, More Distance

For Discussion. In this course we work with radiation from 6 types of sources. gamma (137 Cs, 60 CO) – 1-5 uC gamma (137 Cs) 5 mC gamma (X-Ray source) Alpha polonium 0.001 uC Alpha Curium ~5 uC Cosmic Rays

discuss and rank in terms radiation safety risk (lowest to highest)

Radiation Safety 44

For Discussion. In this course we work with radiation from 6 types of sources. Cosmic Rays Alpha polonium 0.001 uC gamma (137 Cs, 60 CO) – 1-5 uC gamma (X-Ray source) gamma (137 Cs) 5 mC Alpha Curium ~5 uC

rank in terms radiation safety risk (lowest to highest)

Radiation Safety 45

Important points Radiation Safety 46

• Only the TA’s and Instructors handle the sources. • Make sure the instructor/TA puts them away.

• We need to use the sources for the next lab too.

• Do not eat them. Do not put them in your pockets

• Be especially careful when bolting and unbolting the vacuum system in lab 4. Do not let the alpha source assembly fall on the floor. Yes, this happened once.

• When working with the 137Cs source (Compton Scattering Lab), Block the access port with a lead brick temporarily before moving the detector arm. Stand behind the source when you do this.

• Do not power on the X-Ray apparatus until the instructor has checked everything and reviewed safety procedure with you

• Think about ALARA when setting up your apparatus

• If you have questions or something doesn’t look right – ASK!