Radiation - how dangerous is it really?

RobertDyck · 2015-11-28 14:25:43

Here is a paper from the RAD instrument on Mars Science Laboratory, known as the Curiosity rover. Published at the Eighth International Conference on Mars (2014).
CHARGED PARTICLE MEASUREMENTS WITH THE RADIATION ASSESSMENT DETECTOR ON BOARD THE MARS SCIENCE LABORATORY.

Below are charts from that paper; click for full resolution. According to the references, these charts are from "B. Ehresmann et al. (2014), Journal of Geophys. Res. Planets, 119"

Figure 1: Particle spectra measured with MSL/RAD from sols 13 to 173 (since landing). Shown are isotopes of ions with charges Z = 1 and 2.

Figure 2: Particle spectra measured with MSL/RAD from sols 13 to 173 (since landing). Shown are ions with charges Z = 3 to 26.

Another paper from that same conference.
NEW RESULTS FROM THE MSL-RAD EXPERIMENT ON THE CURIOSITY MARS ROVER

I had previously posted links to papers published by the team for the MARIE instrument on Mars Odyssey. They estimated surface radiation based on measurements from orbit. This provides "ground truth". The MARIE papers broke radiation down by protons, the first chart has protons, deuterons, and tritons. The MARIE papers had alpha, the first chart has He3 and He4. The MARIE papers had light ions, the second chart has Li,Be,B and C,N,O. The MARIE papers had medium ions, the second chart has Z=9-13. The MARIE papers had heavy ions, the second chart has Z=14-24, and Fe (Z>24). So they do relate, although the above charts break it down more finely. Note the flux scale is logarithmic.

We have an on-going problem that even members who post to this forum think a greenhouse must be buried underground. Overall results from the MARIE papers showed surface radiation on Mars was half that of ISS, and astronauts spend months at a time on ISS. Plants are much more hardy vs radiation than humans, so plants don't need radiation protection on Mars. I have said many times, the atmosphere of Mars blocks over 90% of heavy ion radiation. At low altitude locations such as where Curiosity is located, atmosphere blocks 95% to 98%. Heavy ions are extremely difficult to block with shielding, so the fact atmosphere does the job for us makes habitat design easy. Beta is high energy electrons; it's blocked by a single sheet of plastic film, such as a spacesuit or plastic film of a greenhouse. Spectrally selective coatings on windows and spacesuit visors block UV. There isn't much X-ray radiation in space, the metal coatings for UV protection also block what little X-rays are there. Alpha is helium ions, He3 and He4; it's blocked by a single sheet of aluminum foil, such as the aluminized Mylar of multilayer insulation of a spacesuit, or hull of a spacecraft or space station, or metal coatings for UV protection. Space doesn't have any neutron radiation, the only neutron radiation is secondary from solar radiation impacting Mars soil. This only leaves proton, ion, and gamma. These charts show what's there. Notice the dose chart is measured in µGy/day. That's micro Gray per day.

RobertDyck · 2015-11-28 15:11:40

I looked up the meaning for the Greek letter Phi (Φ). It has a couple dozen meanings, depending which field of study. For radiation it can mean magnetic flux, or radiant flux, so two meanings within the same field. I suspect they mean radiant flux, which is total energy per unit time.

SpaceNut · 2015-11-28 22:26:42

past topic quotes.... plus more...

http://www.newmars.com/forums/viewtopic … 91#p110691

http://www.newmars.com/forums/viewtopic … 01#p110701

RobertDyck · 2015-11-29 10:46:16

Veggie Plant Growth System Activated on International Space Station

Growing Plants and Vegetables in a Space Garden

NASA is growing crops on ISS. Radiation on the surface of Mars is half that of ISS. So fear of radiation on Mars is unfounded.

SpaceNut · 2015-11-29 16:22:05

I do agree that short term plant life is promising and that we may be exagerating that of radiation exposure but I do believe that long term exposure which we would be incurring for a mars trip and stay does pose issues for survival.

reposting plant grow into other topics

Antius · 2015-12-01 06:14:22

Averaging out the dose rate shown in the graph gives about 0.21mgray per day. That works out to 77mgray per year. The actual human dose depends upon the radiation weighting factor. Charged particle radiation is generally believed to do more damage to the human body than gamma rays. A deuteron moving at half the speed of light will leave a cone of dead cells in its wake. Rather like being hit by a microscopic bullet.

If radiation weighting factor is 1, then unprotected dose would be 77mSv per year (7.7 rads). That's not too bad. If an astronaut/colonist spends 25% of time outside of the habitat (which is shielded) then dose would be <20mSv per year. There are people on Earth that take background doses higher than that. An extra risk of fatal cancer of 0.1% for each year exposed, if you believe the LNT model. If weighting factors are 20, which is what tends to be used for fast charged particle radiation, things are a lot more scary.

SpaceNut · 2015-12-01 21:35:06

Here is what direction nasa thinks for Orion: http://www.nasa.gov/sites/default/files … andout.pdf

Four Primary Types of Ionizing Radiation

Antius · 2015-12-02 06:03:30

SpaceNut wrote:

Here is what direction nasa thinks for Orion: http://www.nasa.gov/sites/default/files … andout.pdf
Four Primary Types of Ionizing Radiation

Your link gives a quality factor of 10 for protons. On that basis, absorbed dose would be 770mSv per year unshielded and 193mSv per year at 25% exposure. If correct, then living on Mars for 1 year at 25% exposure would increase cancer probability by ~1%. A lifetime of that would see cancer frequency increase by 50%. Not good at all. There are dietary countermeasures that may be effective at counteracting this, such as low sugar diets and periodic fasting, but these would be permanent life changes.

RobertDyck · 2015-12-02 07:29:40

I started this thread when members repeatedly advocated burying a greenhouse. My point is that crops do not need radiation shielding. Life support on Mars must have multiple backups. You can't evacuate back to Earth. Launch opportunity could be months away, and transit would be about 6 months. I have listed life support systems before, using multiple different systems, and ensuring components can be mixed-and-matched in new ways co create even more options. However, every life support system has a single point of failure: power. If power goes, you're dead. There is only one exception: ambient light greenhouse. Plants produce oxygen using only sunlight for power. And sewage from the toilet can be processed to produce grey water, sufficiently clean to water crops. Plants will transpire water through their leaves; that humidity will condense on cold windows of the greenhouse. A trough/gutter at the bottom of each window can collect that water, producing drinking water. I'm told water produced this way tastes better than the best filtration system NASA has devised. And power to recycle water this way is sunlight, and the cold of Mars. Not sure what it would take to produce grey water, but going from grey water to drinking water can be done without power.

So one reason I'm so passionate about an ambient light greenhouse for Mars is life support.

As for humans, we ran a quick calculation during the Mars Homestead Project, Phase 1. One member suggested keeping annual exposure down to the level of a US nuclear reactor worker: 5 REM per year. To do that would require radiation shielding for the habitat. Again, this is for a permanent settlement, not a science mission. We designed a habitat with a bachelor/studio apartment for each crew member, and atrium common space. Assume a minimum of 2 metres of regolith piled on the roof of the habitat, and where the regolith is relatively thin (only 2 metres deep) we could soak the regolith in water, and let it freeze. The hillside settlement buried the common spaces deep within a hillside, but the apartments were on the hill edge with a large window at one end. So apartments would have layers of frozen mud. Soak regolith with water, let it freeze, repeat until you have 2 metre depth on the roof. This creates permafrost.

To keep radiation exposure to that of a US nuclear reactor worker, time outside in a spacesuit would have to be limited to 40 hours per week. That's a work week, so I don't think anyone would object. Radiation shielding for an ambient light, plastic film greenhouse would be equivalent to a spacesuit, so time in the greenhouse would count.

The atrium common space of our hillside settlement included a number of plants, including trees. So if you want to hang out in green space, you can do so there. The atrium was buried deep within the hillside, so several metres of regolith overhead. With mirrors on top of the hill reflecting sunlight into light pipes, that direct light to diffusers in the ceiling of the atrium. So natural sunlight, but filtered through glass.

Antius · 2015-12-03 05:48:26

An attractive concept, though it does appear to require a lot of digging.

When calculating radiation dose, did you account for radiation quality/weighting factors? Whilst there is some disagreement on what the weighting factors should be, it is generally agreed that charged particles and neutrons have a more significant biological effect (per gray absorbed) than gamma rays. So you cannot simply equate absorbed energy to dose without applying a weighting factor.

Antius · 2015-12-03 10:00:25

The flux appears to be dominated by protons in the 10-100MeV range. According to ICRP and RBE of 2 is appropriate for this type of radiation. Other heavier ions have an RBE up to 20 but fluxes are about 2 orders of magnitude lower. So an approximate average RBE for Mars radiation would appear to be about 2.1. On this basis, unshielded equivelent dose would be 16.2rem per year for a background rate of 77mgray per year.

Terraformer · 2015-12-03 11:09:44

If you're using light pipes, why not put the greenhouse underground as well and pipe in the light from the surface? You might want to put some sort of cover (inflated?) over the collectors to keep dust off.

RobertDyck · 2015-12-03 11:58:33

We used data from papers published by the MARIE instrument team, from Mars Odyssey.
RADIATION CLIMATE MAP FOR ANALYZING RISKS TO ASTRONAUTS ON THE MARS SURFACE FROM GALACTIC COSMIC RAYS - 1,262 KB
RADIATION CLIMATE MAP FOR ANALYZING RISKS TO ASTRONAUTS ON THE MARS SURFACE FROM GALACTIC COSMIC RAYS - 979 KB
MODEL PREDICTIONS AND VISUALIZATION OF THE PARTICLE FLUX ON THE SURFACE OF MARS - 174 KB
VISUALIZATION OF PARTICLE FLUX IN THE HUMAN BODY ON THE SURFACE OF MARS - 183 KB

I'm not sure what the difference is between the first two papers, they have the same title and abstract, but size is different. They also have the same charts at the end. Figure 6 shows radiation flux for the area with frozen pack ice is 22; the label on the chart says REM/yr but the caption beneath that figure says cSv/yr. That is centiSievert/year. Most of the radiation discussed in the paper is charged particles. The paper discusses effect on biological organisms (humans), so I used their results rather than trying to second guess them. They already have required calculations for biological effects, I didn't think a computer programmer with aspirations for aerospace engineering was qualified to second guess a team of individuals with Ph.D.s in the exact field of radiation. If you want details then you can read their papers.

RobertDyck · 2015-12-03 12:00:23

Terraformer wrote:

You might want to put some sort of cover (inflated?) over the collectors to keep dust off.

The side cut-away shows the reflector on the hill does have that.

Antius · 2015-12-03 12:03:04

Terraformer wrote:

If you're using light pipes, why not put the greenhouse underground as well and pipe in the light from the surface? You might want to put some sort of cover (inflated?) over the collectors to keep dust off.

You could do that, like everything else it would be based on cost-benefit analysis. How much are you prepared to pay to avoid a risk? The figures show that it may not be neccesary in order to avoid radiation. An 8hour working day, 5 days a week, 46 weeks a year, would reduce work-time equivelent dose to 3.4rem per year.

That's heavy by Earth standards but not unprecedented for background radiation. To keep dose down, you would want to time major construction projects for solar maximum. It is much easier to shield out solar storm protons than 50MeV cosmic ray protons. And the atmosphere is a much more efficient shield against lower energy solar particles.

It does narrow down the options for where you are likely to build the first base. To maintain good agriculture and reasonable day-time temperature year round, you would want to be close to the equator. But for radiation shielding you clearly want as much atmosphere above as possible. That chaotic terrain at the edge of Valles Marinaris looks good.

SpaceNut · 2015-12-03 20:40:26

I have not had the time to go through the links but is there a day to night side change in the levels received?

If so do the majority of the work at night to lower the levels received.

RobertDyck · 2015-12-04 01:16:17

SpaceNut wrote:

I have not had the time to go through the links but is there a day to night side change in the levels received?
If so do the majority of the work at night to lower the levels received.

That has two problems: dark and cold. It's dark at night. Same as a cloudless night on Earth, with no moon. And it's cold at night; really really cold. Here is a chart I captured from the Mars Weather Widget. It shows air temperature recorded by Curiosity, average daily high and low for most of a Mars year.

And here is top mast temperature measured by Mars Pathfinder, a little over a single solar day.

It's in Kelvin, subtract 273.15 to convert Kelvin to Celsius.
260°K = -13.15°C
240°K = -33.15°C
220°K = -53.15°C
200°K = -73.15°C
I suspect temperature is "noisy" during the day because direct sunlight is warm, but air is cold. You don't want to be outside handling rocks (collecting samples) when temperature is below -33.15°C (or there about). Trust me, I live in Winnipeg, it gets that cold here on the coldest nights of winter. You don't want to have to handle lug nuts and replace a tire when it's -36°C; I have.

Antius · 2015-12-04 09:14:36

I don't see how day-night temperature variation would make a difference to radiation levels, unless there are big changes to the column density of the atmosphere.

The fact that temperature does not rise above freezing for the whole year could be a real problem for agriculture. I wonder if we would need supplentary heating in the greenhouses? Heat pumps perhaps. On the other side of things, these sorts of day-night temperature variations are perfect for CO2 heat engines working on day-night temperature difference. The CO2 would liquefy at night temperatures and boil at day temperature. Cheap power.

RobertDyck · 2015-12-04 15:37:13

Oh. SpaceNut asked about night because the vast majority of proton radiation comes from the Sun. At night you have the bulk of the planet as radiation shielding. That doesn't help with galactic cosmic radiation, but does with solar wind. But as I said, the problem with that is dark and cold.

SpaceNut · 2015-12-04 22:16:51

Thanks RobertDyck, I read an article about a universities research on a design that had a central hub with 4 tubes like spokes on the ground capped with regolith that had a 30 meter length ending with a glass surface greenhouse that had a demension of 5.5 meters in length and was 2 meters in diameter. The information in the article indicated hydroponic food growth and was sized for a single crew mens useage for not only the garden but the living quarters as described. I looked for the link again once home as I had read it during lunch break but no luck. Sorry.

RobertDyck · 2017-06-01 12:48:36

Radiation keeps coming up. Above I posted papers published by the team for the radiation instrument on the Mars Odyssey orbiter. More recently the Curiosity rover has measured radiation on the surface. This provides "ground truth" for surface estimates from the Odyssey team. A couple papers have been published, but they require a paid subscription to access them. I used to subscribe to the journal Science, which includes free access to their online papers. But I've been unemployed for a number of years now, can't afford it. Does someone have access to either of these papers? Could I get a copy?

Measurements of Energetic Particle Radiation in Transit to Mars on the Mars Science Laboratory

Mars’ Surface Radiation Environment Measured with the Mars Science Laboratory’s Curiosity Rover

::Edit:: Opps. Never mind. I have the second one. Will read (I guess again) and get back to you.

Last edited by RobertDyck (2017-06-01 12:55:53)

Antius · 2017-06-01 15:52:51

The average surface dose rate measured by curiosity is 22.5 microsieverts per hour.

http://www.mars-one.com/faq/health-and- … exposed-to

For an 1800 hour working year in a greenhouse, total dose would be 40.5mSv. Over a 20 year career, total dose would be 0.81Sv. That is enough to increase fatal cancer risk later in life from 20% to 24%. All else being equal, it would knock about a year off the average life expectancy.

Then again, we can all reduce our cancer risk by at least half just by fasting two days a week. Combine that with a diet heavy in micronutrients and risk goes down further. This is why the Victorians rarely suffered from cancer, whereas today we drop like flies because of it.

Last edited by Antius (2017-06-01 15:58:48)

RobertDyck · 2017-06-01 18:24:05

Thanks. Trying to compare with the papers from the team for the MARIE instrument on Odyssey is a challenge. Too many different units.

Table 2: cruise during transit Curiosity received 0.464 mGy/day (milli-Gray per day), which the paper says is a dose equivalent rate of 1.84 mSv/day (milli-Sievert per day). On Mars surface during 2012-2013 Curiosity received 0.210 mGy/day, 0.64 mSv/day.

Table 3: Mars subsurface radiation estimates (scaled to RAD surface measurements)
Mars surface (RAD): 232 mSv/year
-10 cm: 295
-1 m: 81
-2 m: 15
-3 m: 2.9
Interesting that 10 cm (4") below surface is actually worse. That must be due to secondary radiation cause by interaction of radiation with regolith. However, 1 m (39.370") shows significant reduction.

The papers from the Odyssey team produced a radiation map. Curiosity is at Gale Crater, in a dried up river delta on the shore of the ancient ocean basin. The map shows 26 REM/year on "dry land" surrounding the ocean basin, or 22 REM/year on the ocean basin floor. The river delta will be lower than the surrounding land, but higher than the ocean floor, so lets say about 24 REM/year. It also states an equivalence of 1 REM = 1 cSv (centi-Sievert). Metric prefix means 1 centi = 10 milli, so data published in the Curiosity paper states 232 mSv/year = 23.2 cSv/year, the Odyssey paper estimated less than 26 but higher than 22 cSv/year, so that's within the range. Closer comparison would require pinning the Odyssey map to the specific location of Gale Crater.

Curiosity paper Figure 4: Radiation dose-equivalent comparison
180-day transit: 330 mSv
500-day on Mars: 320 mSv
6 months on ISS (average): 70 mSv
DOE radiation worker annual limit: 20 mSv
Abdominal CT scan: 7 mSv
US Annual Average, All Sources: 2.7 mSv
Annual Cosmic Radiation (sea level): 0.2 mSv
The bar graph has a logarithmic scale, the numbers are my read.

During the Mars Homestead Project, Joe Palaia told me the limit for DOE radiation worker was 5 REM = 5 cSv. This paper says it's 20 mSv = 2 cSv. I assume that's due to a regulation change. Joe said a little more than 2 metre deep regolith was required. Robert Zubrin said 2.4 metre depth; that's a little more than 2. That depth would reduce radiation to DOE radiation worker limit.

So Curiosity data has confirmed what we learned from Odyssey. Ground truth is always good.

Last edited by RobertDyck (2017-06-02 00:59:25)

kbd512 · 2017-06-01 18:56:37

Rob,

Thanks for posting the data.

RobertDyck · 2017-06-02 01:39:13

Antius wrote:

Then again, we can all reduce our cancer risk by at least half just by fasting two days a week. Combine that with a diet heavy in micronutrients and risk goes down further. This is why the Victorians rarely suffered from cancer, whereas today we drop like flies because of it.

I've never heard of Victorians fasting two days per week. Catholics did eat fish on Friday instead of meat. Found this...
Why Do Christians Eat Fish on Friday and During Lent?

But Victorians did eat a lot of fruits and vegetables rich in micronutrients.
Victorian life expectancy and diet

Interesting. So yeast is good for you. I make home made beer from a kit. The kit is a can of malt plus a packet of yeast. I use a hose to siphon beer into bottles, leaving yeast at the bottom of the fermentation vat. Actually, I double ferment beer, using the same procedure as wine. That is a primary fermentation is "open" in a food grade bucket covered by a plastic sheet held with string which is kept taught by a rubber band. That keeps flies and dust out. Then it's transferred to a glass carboy with a fermentation lock. The fermentation lock allows CO2 to get out by bubbling through a little water. The water is kept clean with sulphite. The water prevents air from getting in, so the secondary fermentation is anaerobic. A little sugar is added to each bottle, allowing that much fermentation in the beer bottle to carbonate it. No filter, and no CO2 canister.

I also make wine from grapes I grow in my back yard. Similar procedure, but secondary fermentation is longer (3 months instead of 3 weeks) and no sugar added when bottling.

Should add some yeast to my diet. Yea, that's why I do it. Yea, that's the ticket!

I also have a bread machine, but honestly don't use it often. You can get a kitchen flour mill. Of course that will produce whole wheat flour. Would doing that on Mars satisfy you?

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Radiation - how dangerous is it really?

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