Radiation

[benparry]

ah ok cool thanks Jay. Tim informs me he has created an account so hopefully he can throw his two penneth in soon.

[bknight]

ah ok cool thanks Jay. Tim informs me he has created an account so hopefully he can throw his two penneth in soon.

It should be interesting whether or not he accepts the valid understanding of the radiation he speaks or just hand waves it away, because it doesn't look right to him.

[benparry]

I've been having a chat with him on FB but it would be interesting to hear your guys views. does it generally take a long time to approve new accounts

[benparry]

just while tim's account is activated he has posed a question. with the Mars rover mission he states that the radiation equipment measured the radiation that man would have been exposed to daily. he states that this is much higher than the Apollo missions showing that radiation levels in space are higher than we are being told. he uses this link as evidence.

https://arxiv.org/pdf/1503.06631.pdf

[Jason Thompson]

I see a nice graph there showing RAD levels in uGy/day which seem to be hovering between 300-600uGy/day. That's not actually 'much higher' than any of the doses listed on the Apollo data, which are given in mGy/day and range from 0.12-1.27mGy/day. Units are critical. Since 1mGy/day = 1000uGy/day, the Apollo data range from 120-1270uGy/day, so the Mars data sit comfortably in the middle of that range.

[benparry]

lol thanks Jason. it never amazes me how simple the answer always is

[jfb]

So, wait...

Is the claim that the radiation levels for the Apollo missions that were posted on the first page are unrealistically low?  That they should be much higher than that?  Is it possible that, like the Mars data, he's confusing units (milli- vs. micro-)?

Another thing to remember is that absorbed dose (rad or gray) is not the same as effective dose (rem or sievert):

Radiation type	Absorbed dose (mGy)	Effective dose (mSv)
Alpha	1	20
Beta	1	1
Gamma	1	1
Neutron	1	10

Source

The alpha effective dose is significantly higher than anything else, but it's only really dangerous if you inhale or ingest an alpha emitter like polonium.  Most alpha particles are slow and heavy and can be blocked by little more than a sheet of paper. 

The average American's effective radiation dosage from both natural and artificial sources of background radiation is on the order of 6 mSv/year (source), or about .016 mSv/day.  Given that 1 mGy translates to at least 1 mSv, then yeah, the Apollo astronauts absorbed at least one order of magnitude more radiation than someone standing at sea level per day for the durations of those missions.  The Apollo 14 astronauts absorbed considerably more than that.

Was it a big deal? 

Here's a chart of radiation amounts and effects in Sieverts.



The annual maximum dose for radiation workers is 50 mSv.  100 mSv is the lowest one-year dose clearly linked to increased cancer risk.  400 mSv is the dose where symptoms of radiation poisoning appear. 

Assuming the worst possible case scenario where the Apollo 14 astronauts were exclusively exposed to alpha radiation inside their bodies, they absorbed an effective dose of 228 mSv.  Significantly increased risk of cancer, but short of the dose necessary for acute radiation poisoning. 

Assuming a more reasonable scenario of mostly beta and gamma radiation, you're looking at 11.4 mSv on top of their annual background dosage (which, being pilots, would be a couple of mSv higher than the rest of us), which is well below the max annual dosage for a radiation worker. 

For the remaining missions, you're looking at an additional couple of mSv on top of the annual background dosage.  You're looking at a small increase in cancer risk. 

[benparry]

Hi JFB

i suspect my conversation with Tim has ended after reading Jasons explanation above. he started with the why have we not gone back and if there is a way to get past the VAB why are we still exploring ways to do it etc

many thanks for everybodies replies

Ben

[benparry]

Hi everyone Tim has indeed posed another question regarding neutron radiation on the moon. How was this defended against by the Apollo astranauts while they were on the moon

[Jason Thompson]

The first question is not how, it is whether any specific defence was necessary. What are the levels of neutron radiation in the cislunar environment, how penetrating is neutron radiation, and how long does a person have to be exposed under those levels for it to be an issue? Particle radiation is generally not very penetrating, as compared to EM radiation. With several layers of different materials going into a spacesuit and spacecraft, that may easily be enough protection for a short duration lunar mission.

Your friend needs to understand that radiation damage is cumulative. If he's looking at data from Mars missions, noting that the scientists are considering it a problem or a concern, and assuming it was therefore a concern for Apollo, then he's making a flawed leap of logic. Mars missions are going to be months or years long. In that case a sustained exposure to a low radiation level is a problem that has to be solved. In the case of Apollo the solution was simply time. Two weeks of exposure under those conditions was not enough to be concerned about.

An everyday analogy I use is walking in the rain without an umbrella. I can run across the street to my neighbour's house in a torrential downpour and get a little bit wet, just needing to take off my coat and let it dry for a minute and maybe run a towel through my hair and I'm fine. Alternatively, I can walk ten miles in a light drizzle and end up soaked to the skin and freezing cold, needing to take off all my clothes and leave them hanging to dry for a few hours, wrap myself in a warm towel and have a cup of tea to even be comfortably warm again an hour after getting in. The point is, just as you can't look out of a window and conclude 'it's raining' means you will be soaked whatever you do outside, you can't look at radiation and conclude all space missions are deadly because of it. There are too many variables that you have to take into account.

[benparry]

do we know what level of neutron radiation was present on the moon Jason. and of so was this level dangerous

[Jason Thompson]

I don't know, but that is the question your friend needs to be asking before he asks about protection from it. Putting it bluntly, we get this from hoax believers a lot, and we will not do the legwork for them. If he wants to ask questions like this he needs to show he's done some basic research. If he wants to ask about shielding against neutron radiation then he needs to bring the data to the discussion that makes him think it's necessary.

[benparry]

fair enough Jason can't argue with that. I have actually just found a couple of links on this i'll share them below

https://history.nasa.gov/SP-368/s2ch3.htm

https://astrowright.wordpress.com/2013/02/13/surviving-radiation-in-space/

[JayUtah]

Neutron exposure on the lunar surface is not markedly different than in low Earth orbit, primarily for the reason that the Van Allen belts do very little to attenuate it.  Neutrons are -- as the name suggests -- neutral in charge and thus not affected by Earth's magnetic field.  Low Earth orbit is actually going to be slightly more dangerous than the lunar surface simply because you're slightly farther away from a nearby bulk in orbit than you are on the surface.  There are slightly more directions in LEO that radiation can come from.  It's Earth's atmosphere, actually, that attenuates solar neutrons so as to keep us safe on the surface.

People expect particle radiation to be expressible as a single number.  It isn't.  It's a two-dimensional quantity at its simplest.  One dimension is energy, the other is flux.  Energy for a particle is simply how fast it's moving.  Slow moving particles have small energy.  It's measured in electron-volts, or rather in thousands (keV), millions (MeV), or billions (GeV) of electron-volts.  A single electron-volt is a miniscule quantity.  Flux is the number of particles per second that pass through a square-centimeter window at a fixed position and orientation.  If the number differs depending on which way the window is facing, the flux is considered anisotropic, and you have to introduce additional dimensions to the measurement to codify that.  The important relationship is between energy and flux.  As it happens, the higher the energy the lower the flux.  The much lower the flux.  The vast majority of the neutron flux in any given point in the solar system is taken up by particles of largely inconsequential energy.  We generally break up the energy spectrum into discrete bands (e.g., >10 MeV in one category, 1-10 MeV in another, and so forth down the line).  In the 10+ MeV band, flux peaks around 30-40 MeV.  The quiescent flux in that band at Earth distance from the Sun is 3x10^-3 cm^-2s^-1.  That's 0.003 particles per square centimeter per second, or rather it means you have to wait about five minutes for even just one particle at that energy to hit your window.

Low-energy neutrons are easily attenuated by spacecraft structure, spacesuits, and so forth.  You may have seen pictures of open-pool nuclear reactors where the water completely attenuates the neutron radiation, but you can still look down into it from the observation deck.  High-energy neutrons require more elaborate shielding -- generally 7-15 mm of aluminum -- if the exposure is to be indefinite (such as for comm satellites with lifespans of 10-15 years).  For a two-week lunar mission, exposure to high-energy neutrons is really not much to worry about simply because the flux is so very low.

The point here is not to be swayed by people who want to simplify the concept down to scary scalar comparisons.  Those will be misleading.

[benparry]

its's quite interesting Jay but Tim's final try on this was to share with me a page from Moon fakers website.

it quoted the 1400 flares detected and i knew i had seen that on your website. i shared that with Tim while politely pointing out that Moon Faker is the work of Jarrah lol