Radiation basics presentation (Jeffrey Mahn)

Radiation Basics Energy Deposition in Matter Jeffrey A. Mahn Nuclear Engineer (Retired) Albuquerque, NM USA jamahn47@gmail.com

Ionizing & Non-Ionizing Radiation • Ionizing Radiation: Energy transmitted as particles or electromagnetic waves and having sufficient energy to dislodge orbital electrons in atoms, thereby producing ions.  Examples: alpha, beta, gamma, and x-ray • Non-Ionizing Radiation: Electromagnetic waves that do not have sufficient energy to dislodge orbital electrons in atoms; produces a heating effect in body tissue.  Examples: visible light, infrared, microwaves, radio waves, and radar

Ionizing Radiation • Alpha particle • Beta particle • Gamma ray

Types of Radiation • Alpha Particle – a – Helium nucleus (2 protons & 2 neutrons)

• Beta Particle – b

– Energetic electron emitted from atomic nucleus when a neutron converts to a proton and an electron

• Gamma Rays – g

– High energy electromagnetic wave emitted when nucleus of atom transitions from higher to lower energy state

Radioactive Decay The process by which an unstable atomic nucleus becomes more stable by emitting energy in the form of particles or ionizing electromagnetic waves

Unstable Atomic Nuclei What makes some atoms radioactive?

The ratio of neutrons to protons in the atomic nucleus is either too large or too small, causing the nucleus to be unstable. β- (electron) emission – occurs when a neutron in the nucleus converts to a proton β+ (positron) emission – occurs when a proton in the nucleus converts to a neutron

Alpha & Beta Decay • Original nucleus called parent nucleus

• Nucleus resulting from radioactive decay called daughter nucleus • Alpha and beta emission change original atomic element (parent) into a different atomic element (daughter) – Daughter nucleus has different number of protons than parent nucleus and therefore is different element

Alpha Particle Radiation

Daughter Nucleus Parent Nucleus



 a 

Alpha Particle (Helium Nucleus)

Beta Particle Radiation 



Antineutrino

Daughter Nucleus

Parent Nucleus



 b

Beta Particle

Gamma Radiation • Gamma radiation oftentimes accompanies alpha and beta radioactive decay processes in atoms – Has no effect on number of protons or neutrons in daughter nucleus produced from particle decay – Gamma-ray emission changes energy state of daughter nucleus from higher energy state to lower energy state or to ground energy state  When transition is immediate, gamma-ray is associated with parent alpha or beta decay  Metastable isotopes (e.g., Tc-99m) decay by gamma-ray emission and have associated decay half-lives – known as isomeric transition (IT)

Gamma-Ray Radiation 

β

_

Beta Particle

Gamma Rays Parent Nucleus

Daughter Nucleus

Decay Scheme for Cobalt-60

Radioactive Material Half-Life

1200 1000 800 Activity 600 400 200 0 New

The time required for the amount of radioactive material to decrease by one-half

1 2 3 4 Half- Half- Half- HalfLife Lives Lives Lives

Cosmic

Inhaled Radon

Bodies

Plants

Radioactive Elements K-40, Uranium, Radium

We live in a sea of radiation‌ Rocks

Quantifying Radioactivity • Decay rate of radioactive material is λN, where – λ is decay constant for particular radioisotope (usually expressed as disintegrations per second) – N is number of radioisotope atoms present in radioactive material

• Quantity λN known as activity of radioisotope – Activity expressed in units of Becquerel (Bq) or Curie (Ci) – 1 Bq = 1 atomic disintegration per second (dis/sec), 1 Ci = 3.7x1010 dis/sec

Quantifying Radioactivity (cont.)

• Decay constant of radioactive isotope can be calculated from its half-life (λ = 0.693/t1/2) – Radioisotope half-life is experimentally observed quantity – The smaller the half-life, the larger the decay constant – Radioisotope activity (i.e., decay rate) directly proportional to decay constant (e.g., large λ → large activity)

• Radioisotope activity can be converted to dose rate for calculating radiation exposure

Average Annual Radiation Exposure • Natural background (cosmic & terrestrial, including radon) varies around the world U.S. Average -- 350 mrem/y (3.5 mSv/y) Cosmic 30 mrem/y (0.3 mSv/y) Terrestrial 30 mrem/y (0.3 mSv/y) Internal (K-40) 40 mrem/y (0.4 mSv/y) Inhaled (Radon) 200 mrem/y (2.0 mSv/y) Medical/Etc. 50 mrem/y (0.5 mSv/y)

Terrestrial Sources of Radiation Isotope

Half-life (yrs)

Radiation α, γ

Ra-226

1622

U-238

4.5 x 109

α

Th-232

1.4 x 1010

α, γ

K-40

1.3 x 109

β, γ

Rb-87

4.7 x 1010

β

In-115

6 x 1014

β

La-138

1.1 x 1011

β, γ

Sm-147

1.2 x 1011

α

Lu-176

2.1 x 1010

β, γ

Typical Radioactivity in Common Building Materials Material Granite Sandstone Cement Limestone concrete Sandstone concrete Dry wallboard By-product gypsum Natural gypsum Wood Clay Brick

U-238 (pCi/g) 1.7 0.2 1.2 0.8 0.3 0.4 5.0 0.4 3

Th-232 (pCi/g) 0.22 0.19 0.57 0.23 0.23 0.32 1.8 0.2 1.2

K-40 (pCi/g) 32 11 6.4 2.4 10 2.4 0.2 4 90 18

Estimates of concentrations of uranium, thorium and potassium in in building materials (NCRP 94, 1987)

Natural Radioactivity in the Body Total Activity of Nuclide Nuclide in the Body Uranium 30 pCi Thorium 3 pCi Potassium 40 120,000 pCi Radium 226 30 pCi Carbon 14 400,000 pCi Tritium 600 pCi Polonium 1,000 pCi Estimated concentrations of radionuclides calculated for a 70 kilogram adult based on ICRP 30 data

Natural Radioactivity in Food Food

40K

(βγ) pCi/kg

226Ra

(α) pCi/kg

Brazil Nuts

5600

1000-7000

Lima Bean

4640

2-5

Banana

3520

1

White Potato

3400

1-2.5

Carrot

3400

0.6-2

Red Meat

3000

0.5

Low-sodium Salt

3000

---

Beer

390

---

---

0-0.17

Drinking Water

Natural Radiation Exposures • Radioactive content of earth’s crust responsible

for about 75% of natural radiation exposure

• Areas in the world where natural background radiation is much higher than in U.S. (360 mrem/yr avg.)  average annual dose in Araxa, Brazil is 2,500 mrem  annual dose in State of Kerala, India as high as 3,500 mrem  annual dose in Guarapari, Brazil as high as 17,500 mrem  annual dose in Ramsar, Iran as high as 26,000 mrem

Interaction With Matter -------------------------------------------------Relative Relative Radiation Range LET* -------------------------------------------------Alpha 1 10,000 Beta 100 100 Gamma 10,000 1 -------------------------------------------------* Linear Energy Transfer – energy deposition per unit of distance traveled

What Does This Mean?

Radiation

Range in Air

Alpha (4-5 MeV)a

1-2 inches

Beta – 0.1 MeV 1.0 MeVb 3.0 MeV

4 inches 12 feet 43 feet

Notes: a. Alpha energy associated with Uranium, Thorium, and Plutonium decay

b. Average maximum energy of beta particles from fission products is about 1.2 MeV

Penetrating Properties of Ionizing Radiation

Focus of Radiation Concerns Based on Penetrating Power Internal radiation hazards • result from inhalation or ingestion of alpha and beta sources • concern about skin and clothing contamination with alpha and beta sources is proximity to pathways for inhalation and ingestion

External radiation hazards – gamma- and xrays

Absorbed Dose • Radiation Absorbed Dose (rad) – Energy deposition per unit mass of material – Describes concentration and not amount of energy absorbed in exposed mass

International Standard – Gray [Gy] 1 Gy = 100 rad

Radiation Effects • Depend on absorbed dose and LET • Effect on biological systems quantified using relative biological effectiveness [RBE] Radiation X-rays Gamma radiation Beta particles Thermal neutrons Fast neutrons Alpha particles

RBE Factor 1 1 1 5 10 20

Equivalent Dose • Historical/conventional unit

Dose (rem) = RBE x Dose (rad) • Provides common reference and allows for additive doses • Represents POTENTIAL for biological effects

Equivalent Dose Units • International (SI) unit – Sievert [Sv] Dose (Sv) = RBE x Dose (Gy) 1 Sv = 100 rem

Radiation Terms and Units

Activity Absorbed Dose

Traditional

S.I.*

Curie (Ci) 3.7x1010 dis/sec

Becquerel (Bq) 1 dis/sec

Rad 100 ergs/gm

Gray (Gy) 1 joule/gm

Rem

Sievert (Sv)

Committed Effective Dose

* Abbreviation for International System of Units

Dose Factors • Acute Dose – Dose delivered over a short period of time

• Chronic Dose – Dose delivered over an extended period of time

• Dose Rate Effect – Acute dose generally more damaging than chronic dose of same magnitude because short term cell damage overwhelms body’s natural repair mechanisms

Nuclear Regulatory Commission Administrative Limits Subjects Exposed

Time Frame

Dose (mrem)

Nuclear Worker

1 year

5000

General Public (from nuclear facility)

1 year

100

9 months

500

Pregnant Woman

Radiation Damage • Biological Tissue – Dose & dose rate (acute or chronic) – Direct effects → break important molecular chains – Indirect effects → break less critical molecules into reactive parts

Radiation Damage (cont.)

• Hierarchy of susceptibility – – – – – –

Lymph nodes (most susceptible to damage) Blood Bone Nerve Brain Muscle (least susceptible to damage)

Human Response • LD 50/30: Lethal acute dose for 50 percent of exposed population within 30 days without medical attention (~ 450 rem)

• Threshold for detectable medical effects (red & white blood cell count): ~ 25 rem

Human Response (cont.)

• Potential delayed effects may include – Leukemia/Cancers – Cataracts – Genetic Effects

– Blood Disorders – Lifespan Shortening

Correcting a Radiation Exposure Misconception • Exposure to gamma radiation does not make

humans, animals, or food radioactive • Only way to make an atom radioactive is to change ratio of neutrons to protons in atomic nucleus • Gamma-rays only interact with atomic electrons and have no effect on numbers of neutrons and protons in atomic nucleus

Dose Reduction and Control • Basic principles – Restrict proximity TIME  Dose = Dose Rate x Time

– Increase DISTANCE from the source  Point source: “1-over-R-squared” reduction

– Use SHIELDING material

Radiation Basics Summary • Types of ionizing radiation – alpha, beta, gamma-ray, x-ray • Our radiation environment – cosmic, terrestrial, inhaled (radon), internal • Radiation health concerns based on penetrating power  External hazard – gamma-ray and x-ray  Internal hazard – alpha and beta

Radiation Basics Summary (cont.)

• Dose factors – biological effect of acute exposure more serious than chronic exposure of same magnitude • Radiation protection principles  Time – minimize exposure time  Distance – maximize distance from source  Shielding – insert appropriate shielding material between people and source

Contact Information Jeffrey A. Mahn Nuclear Engineer (Retired) Albuquerque, NM USA jamahn47@gmail.com