Freefall 3351 - 3360 (D)
Freefall 3351

Life problems in low gravity

I take it, you want to know more about types of radiation that are hazardous.
Yes, please.
Keep it short and accurate. Make it entertaining so my attention doesn't wander. And no math.
Do I need to change my voice to illustrate different wavelengths?
Entirely optional. I don't want to make this difficult by imposing too many conditions.

Color by George Peterson

Freefall 3352

Life problems in low gravity

Dangerous radiation refers to particles or high energy photons that can cause ionization. That's when an atom acquires a charge by gaining or losing electrons.
BOHR model user for simplicity.
When ionization occurs in a living cell, it can alter how the cellular machinery works.
That's how radiation gives you superpowers!
I suppose from an individual cell's point of view, cancer is a superpower.
Then forget it. I don't want my cells to have powers if they're going to be super villains.

Color by George Peterson

Freefall 3353

Life problems in low gravity

DNA is a section of the cell we really don't want to be damaged. Radiation can cause three types of damage to DNA. Single-strand break, dual strand break, and mutation.
Single-strand break
Dual-strand break
Dual-strand breaks and mutations usually can't be repaired. Given time, a cell can often fix a single-strand break.
The key is time. The faster a cell reproduces, the more vulnerable it is to radiation.
Product opportunity. Atomic-level duct tape for molecular repair. The tricky part will be finding someone with fingers small enough to apply it.

Color by George Peterson

Freefall 3354

Life problems in low gravity

If a cell is damaged by radiation, there are five ways it can go.
Cell repairs itself, divides into healthy daughter cells.
Mutated cell divides into mutant daughter cells that live.
Mutated cell divides into mutant daughter cells that die.
Reproductive death. Cell functions. No longer divides.
Cell death.
You left off “Cell vaporizes”.
If you're in a radiation field that strong, you won't need to worry about long-term health effects.
And technically, vaporization is covered under cell death.

Color by George Peterson

Freefall 3355

Life problems in low gravity

We don't know how sqids respond to radiation, so we're going to keep your exposure as low as practical.
A sievert is the biological equivalent of one joule of radiation energy per kilogram of matter. We want to keep your exposure less than .05 sieverts total dose for the entire year.
As low as practical. Not low as possible?
As low as possible would be not letting you off the planet.
Ah, yes. Hard to be a daring space captain if you're not allowed in space.

Color by George Peterson

Freefall 3356

Life problems in low gravity

There are two types of doses. Chronic is when you get the dose over a long period of time. Acute is when you get the same dose in a short time and is more harmful.
For humans, an acute dose of .3 sieverts will cause blood changes, one sievert will cause radiation sickness, two will cause half the cells to undergo reproductive death, four will kill half the people exposed and ten will kill everyone.
Of course, you won't be getting anywhere near that.
Florence, if I don't need to know the scary numbers, please don't tell me the scary numbers.

Color by George Peterson

Freefall 3357

Life problems in low gravity

Ship, how much radiation are we getting?
Outside dose from the current radiation field is .021 millisieverts an hour, or .5 millisieverts per day.
So to reach my limit, that would take…
100 days if you were on my hull.
You're shielding me.
I am shielding humans. Protecting you is an unfortunate side effect.

Color by George Peterson

Freefall 3358

Life problems in low gravity

How much shielding do we have?
Well, shielding is a little complicated. Higher energy gamma rays have more penetrating power. The thumb rule is 5 cm of lead, 10 cm of steel, or 120 cm of water is one ten-thickness.
A ten-thickness is the amount of material needed to reduce the radiation level to one tenth of the unshielded value.
100 gray, 6 MeV source
5 cm of lead
Radiation level: 10 gray
5 cm of lead
Radiation level: 1 gray
Wow. That much material wrapped around a spaceship would be heavy… and expensive to accelerate… and we don't have much shielding, do we?

Color by George Peterson

Freefall 3359

Life problems in low gravity

We have two other sources of radiation. Cosmic rays and solar energetic particles. These are mostly high speed protons and helium. They do direct damage and can produce secondary radiation.
They're best shielded by light materials. Hydrogen is good.
Oh. On this trip, every now and then, you're going to see a bright flash of light. That's a cosmic ray interacting with your eye or a visual neuron.
Light flashes. Got it. An unfriendly reminder from the universe that it's messing with my brain.

Color by George Peterson

Freefall 3360

Life problems in low gravity

When it comes to cosmic rays, our primary shielding is the solar wind. Plasma ejected by the sun.
The heliosphere blocks about 70 to 90 percent of the cosmic rays from getting to us.
It's another case where empty space isn't quite empty, and when you have billions of kilometers of not quite empty, it adds up.
Bow Shock
Termination Shock
Heliosphere (Not very spherical)

Color by George Peterson

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