PDF 4.2 Radiation Damage in Biological Systems

7/28/2019 PDF 4.2 Radiation Damage in Biological Systems

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A Look at NuclearScience and Technology

Larry Foulke

Radiation and Realism

4.2 Radiation Damage in Biological Systems


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Nuclear Engineering Program

All three radiation types are capable of ionizingtarget atoms in materials.

What were the three types of radiation?

Lets Review Ionization

Charged particles (protons, electrons, fissionproducts, alpha particles)

Electromagnetic radiation (gamma rays, X-rays)

Neutrons


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All three radiation types are capable of ionizing targetatoms in materials.

Ionization events are the root cause behindALL

observable effects of radiation. Ionization reactions damage materials by breaking chemical

bonds and disrupting normal chemical processes (materialembrittlement, biological damage, etc.).

The rate of ionization (damage) depends on the typeand energy of the radiation, as well as the constituentatoms in the target material.

Lets Review Ionization


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Ionizing Radiations Is radiation that contains enough energy to

remove one or more electrons from an atom ormolecule.

All charged particles are ionizing. Only photons with an energy greater than the ionization energy

of a given atom or molecule are considered ionizing.

Some molecules are affected by photons in the visible or UVrange, but typically only X-rays and gamma rays are considered

ionizing.photon

neutron

chargedparticle

Image Source: See Note 1


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Ionizing Radiations

Neutrons do not have a charge and do not interact withthe electron cloud so they are not able to directly causeionizations.

However, neutron interactions with atomic nuclei canproduce secondary particles that cause ionizations.

Elastic collisions with light (H, C, O, N) nuclei cause thepositively charged nucleus to recoil.

Inelastic collisions or nuclear absorptions produce ionizing rays.

Fission events produce positively charged fission fragments aswell as ionizing rays.


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The number of ionization events that a single particle ofradiation can produce is determined by the energy ofthe radiation.

The ionization density is determined by the LET.

----------------------------------------------------------Relative Relative

Radiation Range LET

----------------------------------------------------------Alpha 1 10,000Beta 100 100Gamma 10,000 1----------------------------------------------------------

Ionization Density


7/20Nuclear Engineering Program

Ionization DensityAverage Human Cell

neutron

gamma ray

x-ray

alpha particle

Separation of ion clusters relative to size of a human cell (conceptualized)




Review of Biology 101

An animal is an organized collection of organs, heldtogether by connective tissue, whose functions arecoordinated by a nervous system.

Cells are the basic building blocks of life

Cells are grouped together by specialization into tissues

Tissues work together to form organs, which perform

specific functions Adult humans have approximately 71013 total cells of

210 different types



Cell Functions

All cells perform certain basic tasks:

Metabolism Cells break down complex nutrient molecules to release energy

that is used to enable biochemical reactions within the cell.

Protein Synthesis Protein molecules take part in all biochemical processes in the

cell. Each cell builds proteins required to perform thespecialized tasks of the cell.

Reproduction Cells reproduce by division, referred to as mitosis in eukaryotic

cells.

Every cell contains specialized organelles, which areresponsible for performing these tasks.


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Cell Biology 101

Every cell is 70-90% water


1.Nucleolus

2.Nucleus

3. Ribosome

4. Vesicle

5. Rough endoplasmic

reticulum6. Golgi apparatus

7. Cytoskeleton

8. Smooth endoplasmic reticulum

9. Mitochondrion

10. Vacuole

11. Cytoplasm12. Lysosome

13. Centriole

Organelles


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Cell Damage

Ionization can disrupt any of the threemajor functions of cells: Metabolism

Cell may not produce the energy that it needs and dies.

Protein synthesis

Cell may not create protein needed for cell survival. -or-

Cell may not create protein required for its specialized task.

Cell is alive but useless. Reproduction

Cell may not reproduce, or may reproduce incorrectly. Cellremains alive and functioning, but is sterile.


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Cell Damage

Many ionizations within a single cell typically results inenough damage to disrupt metabolism or proteinsynthesis and immediately kill the cell.

For radiation damage, this requires a lot of energy to be

deposited within a single cell: Direct radiation damage

High LET charged particles ionize biological molecules directly.

Indirect radiation damage

High-energy rays produce strongly oxidizing free-radicals byradiolysis. The free radicals then travel through the cell destroyingmolecules. Because cells are mostly water, indirect damage due toradiolysis of water is the most common mechanism.


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Radiolysis of Water

ray

Oxygen

Hydrogen

Electron

Before ReactionPossible

Recombination Products

Free electron

(Charged particle)

H, H- or H+

(Free radical, andcharged particles)

Hydroxyl

(Free radical)

Hydrogen peroxide

(Free radical)

BAD

Other (neutral) products: H2, O

2, H

2O

Hydroperoxyl

(Free radical)



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Traumatic Cell Death Cells have redundant features and many types of repairmechanisms to handle biochemical disruptions(otherwise we would never survive!).

Cell death typically requires hundreds of ionizations oroxidations within a single cell.

However, cell reproduction is much more sensitive toionization / oxidation events. One or two events can

disrupt the normal cell cycle.


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What about radiation and DNA? Cells have redundant features and many types of repair

mechanisms to handle biochemical disruptions (otherwise wewould never survive!).

Cell death typically requires hundreds of ionizations or oxidations

within a single cell.

In the human body, approximately 500,000 radioactivedisintegrations occur every minute. (Luckey,Radiation Hormesis,1991)

Every hour on the average, every cell in the human body undergoesapproximately 8000 DNA-modifying events, independentofradiation. (Abelson, P.H.;Science, Vol. 265, 9 September 1994, p.1507)


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DNA DNA is organized into a double-helix shape,

with nucleotide base-pairs between 2phosphate backbones.

The DNA sequence is arranged into bands

called genes. Each gene carries the recipe forone protein.

Humans have 23 pairs of chromosomes (oneset from mom, one from dad).

Pollycove: The body has about 100 trillioncells.

Pollycove: Each cell undergoes about 25,000DNA alternations daily.



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Radiation Dose Effects

The amount of energy deposited in amaterial is referred to as radiation dose.

Chronic Dose Dose delivered over an extended period of time.

Acute Dose

Dose delivered over a short period of time.

An acute dose is generally more damaging than a chronic doseof the same size, because the bodys repair mechanisms haveless opportunity to act.


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Short-Term Radiation Effects

Immediate Effects (hours to days) Skin reddening, inflammation

Immune suppression

Sterility

Blood chemistry changes

Loss of hair

Gastrointestinal syndromes

Central nervous system syndromes

IncreasingDose


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Long-Term Radiation Effects

Long term effects (months to years)

Cancer / leukemia

Cataracts

Genetic defects

Blood disorders

Lifespan shortening

Scientific consensus on high dose effects.

Lack of consensus on low dose effects.


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1. Reprinted with permission from DavidGriesheimer, University of Pittsburgh.

2. Public domain:

http://commons.wikimedia.org/wiki/File:Diagram_human_cell_nucleus_no_text.png

3. Public domain:http://en.wikipedia.org/wiki/File:Animal_Ce

ll.svg4. Public domain:http://en.wikipedia.org/wiki/Dna

Image Source Notes
http://commons.wikimedia.org/wiki/File:Diagram_human_cell_nucleus_no_text.pnghttp://commons.wikimedia.org/wiki/File:Diagram_human_cell_nucleus_no_text.pnghttp://en.wikipedia.org/wiki/File:Animal_Cell.svghttp://en.wikipedia.org/wiki/File:Animal_Cell.svghttp://en.wikipedia.org/wiki/Dnahttp://en.wikipedia.org/wiki/Dnahttp://en.wikipedia.org/wiki/File:Animal_Cell.svghttp://en.wikipedia.org/wiki/File:Animal_Cell.svghttp://commons.wikimedia.org/wiki/File:Diagram_human_cell_nucleus_no_text.pnghttp://commons.wikimedia.org/wiki/File:Diagram_human_cell_nucleus_no_text.png

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