Flags on the Moon

[Erasmus00]

In regards to protons.

 

They are more penetrating than gamma rays and not a lot less than neutrons.

 

Thats not true at all! Protons are FAR less penetrating than neutrons. Neutrons are (as the name implies) neutral, so short of nearly direct scattering off a nucleus they won't be effected. Protons are electrically charged, so electric fields from both electrons and protons can change their course from a distance!

-Will

[silverslith]

Now we have some meaningful data on radiation belt proto density I can do a reasonable dose estimate. In my next post I'll explain some of the basics of the magnetosphere that I've learnt. Please check my calculations, I'd hate to have made a major botch.

 

Radiation dose estimate for four hour transit of inner radiation belt out to 12000km altitude

 

Taking Proton average energy=50MeV (actually average energy over 100MeV)

Taking Proton density 100 per cubic cm (actually 100-1000 per cubic cm)

 

Proton density 100 / cubic cm

Energy proton = 50MeV

Energy / cubic cm=5000MeV

1 eV= 1.6e-19 joules

 

Velocity of 50 MeV proton:

50 MeV= 8e-12 joules

mass proton = 1/6.022e26kg

=1.66 e-27kg

V= sqrt(2xEk/m)= sqrt (2 x 8e-12 / 1.66e-27 )

=98 000 000 m/s

=9 800 000 000 cm/s

 

Energy per square cm per second = 9 800 000 000 cm/s x 5000MeV /cubic cm

=4.9 e13 MeV = 4.9e19 eV

=7.84 joules per square cm per second.

 

Human body 5000 sqcm = 39200 joules per second

Grays/second =39200/100kg = 392grays per second

 

1hr=3600 s

Grays per hr = 1411200grays

 

RBE protons =10

Sieverts per hr = grays x RBE = 14112000Sv

Sieverts 4 hrs = 56 448 000Sv

 

Edit: actually that RBE is inappropriate for protons above a few MeV. As faster Protons drop less energy per distance a smaller RBE is needed as they get faster than the speed that they are absorbed in a human body. It will be a fraction rather than a multiplier at energies that allow them to lose little of their energy passing through you.

 

Note: maximum survivable Sv dose is ~10 Sv (100% death in 4 weeks)

[silverslith]

In regards to protons.

 

 

 

Thats not true at all! Protons are FAR less penetrating than neutrons. Neutrons are (as the name implies) neutral, so short of nearly direct scattering off a nucleus they won't be effected. Protons are electrically charged, so electric fields from both electrons and protons can change their course from a distance!

-Will

 

Can you provide data on this? I'd like to see it. apparently over 30MeV they cannot be feasibly shielded with solid matter.

[Tormod]

We have all been fooled. Here is the proof:

 

Fake Moon Landings The moon landings are fake!

[freeztar]

We have all been fooled. Here is the proof:

 

Fake Moon Landings The moon landings are fake!

 

:shrug:

[Erasmus00]

Can you provide data on this? I'd like to see it. apparently over 30MeV they cannot be feasibly shielded with solid matter.

 

Compare the Rutherford cross section to a cross section for neutral particles of the same weight. Yes, high energy protons are going to be hard to shield, but high energy neutrons are much more difficult.

-Will

[CraigD]

Now we have some meaningful data on radiation belt proto density I can do a reasonable dose estimate. In my next post I'll explain some of the basics of the magnetosphere that I've learnt. Please check my calculations, I'd hate to have made a major botch.

…

7.84 joules per square cm per second.

 

Human body 5000 sqcm = 39200 joules per second

Grays/second =39200/100kg = 392grays per second

I repeated your calculations and get the same result. However, the remainder of you calculation assume that the target (the human body) absorbs all of the protons, which I don’t believe is true.

 

To calculate radiation dose given particle energy (50 MeV) and power density (7.84 J/cm^2/s), we must know the work done by a proton of a particular energy when it passes through a length of a medium (meat, in this case). A straightforward way to do this would be to measure the energy of a proton beam in an accelerator before and after placing a sample of the media (meat, and, because we’re also interested in shielding, materials such as aluminum and lead). Since, presumably, none of us have a proton accelerator, we’ll have to find, not generate, this data.

 

NIST’s PSTAR database appears to be a good source for this data. It’s based on data from a model confirmed by experimental observation. Here’re some values calculated from this data:

Kinetic  |Total    |Total    |Total    |Total    |Total    |Total
Energy   |Stp. Pow.|Stp. Pow.|Stp. Pow.|Stp. Pow.|Stp. Pow.|Stp. Pow.
MeV      |MeV/cm   |MeV/cm   |MeV/cm   |MeV/cm   |MeV/cm   |MeV/cm   
        |ALUMINUM |MS20 TIS.|LEAD     |AIR,DRY  |GLASS,   |WATER
        |         |SUBST.   |         |         |(Pryex)  |
10       |91.114864|44.34    |201.9165 |.04826388|81.4173  |45.67
20       |53.141341|25.3     |126.666  |.02763788|47.1422  |26.07
30       |38.621259|18.21    |95.2946  |.01991517|34.1636  |18.76
40       |30.821438|14.44    |77.46375 |.01580684|27.206   |14.88
50       |25.893246|12.08    |65.8981  |.01324064|22.8352  |12.45
60       |22.492632|10.46    |57.7715  |.01146598|19.81355 |10.78
70       |19.993451|9.278    |51.7333  |.01017204|17.60139 |9.559
80       |18.077232|8.372    |47.06845 |.00918049|15.90436 |8.625
90       |16.557751|7.656    |43.34565 |.00839738|14.5619  |7.888
100      |15.324354|7.075    |40.3152  |.00776246|13.47143 |7.289
110      |14.301471|6.594    |37.78415 |.00723596|12.56605 |6.794
120      |13.437823|6.189    |35.65035 |.00679260|11.80562 |6.377
130      |12.698324|5.844    |33.81165 |.00641430|11.15446 |6.021
140      |12.061384|5.545    |32.2113  |.00608780|10.59027 |5.713
150      |11.502711|5.285    |30.8039  |.00580226|10.09967 |5.445
160      |11.011512|5.056    |29.56675 |.00555167|9.66705  |5.209
170      |10.574290|4.852    |28.4658  |.00532878|9.28126  |4.999
180      |10.185648|4.671    |27.467   |.00512999|8.93784  |4.812
190      |9.8347916|4.507    |26.5817  |.00495168|8.6301   |4.644
200      |9.5163214|4.36     |25.77585 |.00479024|8.35135  |4.492

Kinetic  |Total    |Required |Total    |Required
Energy   |Stp. Pow.|for full |Stp. Pow.|for full 
MeV      |MeV/cm   |shielding|MeV/cm   |shielding
        |ALUMINUM |cm       |MS20     |cm       
        |         |ALUMINUM |         |MS20     
10       |91.114864|.10975157|44.34    |.22552999
20       |53.141341|.37635482|25.3     |.79051383
30       |38.621259|.77677426|18.21    |1.6474464
40       |30.821438|1.2977979|14.44    |2.7700831
50       |25.893246|1.9310054|12.08    |4.1390728
60       |22.492632|2.6675401|10.46    |5.7361376
70       |19.993451|3.5011464|9.278    |7.5447294
80       |18.077232|4.4254562|8.372    |9.5556617
90       |16.557751|5.4355208|7.656    |11.755485
100      |15.324354|6.5255605|7.075    |14.134275
110      |14.301471|7.6915164|6.594    |16.681831
120      |13.437823|8.9300179|6.189    |19.389238
130      |12.698324|10.237571|5.844    |22.245037
140      |12.061384|11.607291|5.545    |25.247971
150      |11.502711|13.040404|5.285    |28.382213
160      |11.011512|14.530247|5.056    |31.645569
170      |10.574290|16.076729|4.852    |35.037098
180      |10.185648|17.671924|4.671    |38.535645
190      |9.8347916|19.319168|4.507    |42.156645
200      |9.5163214|21.016524|4.36     |45.871559

From this, and silverslith’s calculations, we can draw a few conclusions

• Human tissue has enough stopping power to absorb a lot of proton radiation. A naked human being exposed to the Van Allen proton belt for would quickly receive a fatally dose.
  
• Aluminum, glass, and other spacecraft materials have even greater stopping power. Fairly thin layers of these materials can absorb all of the protons
  

Comparing these values to the construction of an Apollo spacecraft, there appears to be about enough aluminum and phenolic to effectively shield against Van Allen belt radiation – but just barely. I assume this is because its designers had access to the same data we do, and designed the spacecraft to provide just enough shielding.

 

A more detailed analysis requires precise data about the distribution of proton energies in the Van Allen belt, and detailed Apollo spacecraft engineering data. However, based on the research and analysis we’ve collaboratively done in this thread, I’m now confident that

• Radiation shielding is required for a human being to survive passing through though the Van Allen belts at typical spacecraft speeds
  
• Effective radiation shielding is technically feasible, and was included in the Apollo spacecraft
  

[TheBigDog]

Good work Craig. Case closed.

[silverslith]

Aspects of the Magnetosphere.

 

Earlier in the thread I misunderestimated the quantity of solar wind protons that enter the magnetosphere. The assumption that they are energetic enough to penetrate the magnetopause (the transition point between solar and earth magnetic field) is largely not correct. While the more energetic of solar protons may do this, most are slowed to subsonic speed by the bowshock, a sonic shockwave formed by the buildup of solar plasma against the front of the magnetopause. This slows the incoming solar wind to subsonic speed and forms a region of plasma called the magnetosheath over 1000 times denser than the solar wind in empty space.

The magnetosheath is still carrying the solar magnetic field and this cannot directly penetrate the earth’s field. It is hot and turbulent though and two mechanisms allow particles to cross the magnetopause into the magnetosphere. At the polar Cusps the magnetic field lines of the earth are at right angles to the field and particles can drop down into the earths upper atmosphere where they cause the aurora.

Along the magnetopause boundary which is drawn into a long teardrop stream behind the earth for millions of kilometers called the magnetail, diffusion of particles from the higher pressure magnetosheath occurs. These particles drift into the centre of the magnetail where no orbital rotation means they are accelerated for millions of kilometers towards the earth by gravity in a stream called the Plasmasheet. This pours into the the Radiation belt, with Protons turned towards the west and electrons to the east by the more parallel to the earths surface field lines as they near the earth. This forms the ring current. Many resources claim that “electrons are found throughout the radiation belts but protons are found in two separate regions the inner and outer Van Allen belts” It turns out that the reverse is true. Electrons are found in two belts with peak densities at 14000km and 40000km altitude above equator of ~100000 per cubic cm and a “slot” at 24000km altitude above equator density ~10000 percubic cm.

Protons are at peak density at 14000km of ~1000 per cubic cm and taper to ~100 per cubic cm at 2000km and 40000km.

The proton energy’s are highest at the inner edge up to 3000MeV, 100MeV at their peak density at 14000km alt above equator, 1MeV at 40000 km. This is due to higher field strength as you get closer to earth.

As you move away from the equator the polewise velocity of the particles is slowed and reversed by the converging field lines. The belts are also compressed as field strength increases. Higher velocity particles generally can penetrate further south and north before being reversed.

These factors mean that the areas of the radiation belts away from the equator are higher in density and energy than the more diffuse zone at the equator.

Spacecraft launch trajectories to achieve geo-synchronous orbits or escape from earth must either:

Leave via the polar holes.

If their electronics are hardened enough for short exposure at equatorial latitudes (millions of rads lifespan), by steep fast trajectories to 20000 km altitude where proton energies are low enough to physically shield. Shielding higher than 30MeV Protons is detrimental because Protons lose more energy per distance as they slow down. This means that high energy protons are best left to drill electronics or people undisturbed because the energy they offload is less than if they have lost some previously drilling a thick shield.

 

The Tsoline Mikaelian paper used by MIT seems extremely well referenced and says that Protons above 30MeV cannot be shielded and thats for little boxes of electronics.

Looking at those figures I'm not at all sure that 10cm of aluminium was on the apollo craft as shielding. I'll have to go and look at the apollo capsule we have at MOTAT in Auckland next time I'm there. Actually you'd need a lot more than that with many of them in the lower belt up to 3000MeV

[silverslith]

If the phenolic and aluminium was absorbing all the energy then we are looking at peaks of well over 80kw per square meter of heat absorbed. That scares the daylights out of me.:)

[Tormod]

The Tsoline Mikaelian paper used by MIT seems extremely well referenced and says that Protons above 30MeV cannot be shielded and thats for little boxes of electronics.

 

Then how do you explain the abundance of (working) satellites that orbit the Earth outwards of 500 km? They are well within the proton band. According to you they cannot be shielded and thus cannot work.

 

Looking at those figures I'm not at all sure that 10cm of aluminium was on the apollo craft as shielding. I'll have to go and look at the apollo capsule we have at MOTAT in Auckland next time I'm there. Actually you'd need a lot more than that with many of them in the lower belt up to 3000MeV

 

Do not confuse the landing capsule with the entire Apollo craft. It is a complex piece of kit, but only the landing capsule ever returned.

[silverslith]

specific heat capacity aluminium 900J/(kg.kelvin)

1sqmeter aluminium 10 cm thick= 270kg

 

tempchangealuminium= energy/(900 x 270kg)

per sec = 80000/(900x270)= 0.329K per second

per minute = 19.75K

per 30min = 592K + ambient = melted

 

Phenolic would be a lot worse.

[Boerseun]

I fail to see the problem, here.

 

Voyagers 1 & 2 cruised through the intense radiation fields wrapping Jupiter, and they worked fine during and after the event. And that was with crappy 70's radiation shielding technology.

 

Slith, the guys went to the moon. It happened.

 

(Btw - wasn't the one lander photographed by some moon probe last year?)

[Tormod]

(Btw - wasn't the one lander photographed by some moon probe last year?)

 

No, AFAIK only the relevant areas have been mapped. No resolved photographs yet.

[silverslith]

guys,

If you shield them they are cooked.

if you don't they are nuked

voyager has megaRad hardened electronics, and did not go into the radiation belts close to jupiter.

You need to lower the dose by billions to get what they had on their badges.

Case closed

[Tormod]

guys,

If you shield them they are cooked.

if you don't they are nuked

voyager has megaRad hardened electronics, and did not go into the radiation belts close to jupiter.

You need to lower the dose by billions to get what they had on their badges.

Case closed

 

:) You are either a very good humored fellow who is pulling our leg, or you completely ignore anything we write. These options do not exclude each other, of course.

[silverslith]

I have just logged online to find an infraction for something I have not had an opportunity to respond to.

 

No I cannot confirm that voyager stayed out of the most energetic radiation belt of jupiter close above its atmosphere. That is speculation.

I have seen on documentaries that the electronics was hardened to the maximum that technology allowed and they were still not sure it would hack it.

If you shield them they are cooked.

if you don't they are nuked.

You need to lower the dose by billions to get what they had on their badges.

I have provided conservative calculations that demonstrate why these statements are so. Note that 10cm of aluminium is not enough to reduce the dose by a useful amount according to the great proton penetration data Craig has provided and would weigh 5 tonnes in a 2mx2m capped cylinder.

 

I have finished my work here but for one thing:

 

Above I made a mistake in quoting the boston U resource on the reason for the auroras. They are not caused by the solar wind falling down the cusp's. That would cause a small spot aurora at the magnetic pole. Any charged particles falling from the cusps into the magnetic field are injected into the radiation belt.

The Auroras are more likely caused by the ends of the radiation belt contacting the upper atmosphere and the particles with most polewise velocity/lateral velocity entering it between 61 and 71 degrees south. When solar maximum and flare activity occurs the proton density reduces (1) as more receive enough extra polewise energy to burn out in the atmosphere enhancing the Aurora. When solar minimum occurs, the proton density increases (1)

 

(1). Tsoline Mikaelian.