Regarding bremsstrahlung, there is an article on astrobiology.net which suggests that around one metre of ice is sufficient to shield from bremsstrahlung on Europa and Ganymede.
"The ions from the belt can penetrate about a millimeter into the ice. Electrons reach roughly a centimeter down, but they also emit high-energy photons that can go as far as a meter deep. Regardless of the type of radiation, these high-energy particles will rip electrons off of molecules, thereby "oxidizing" everything on the surface"
http://www.astrobio.net/news-exclusive/hiding-from-jupiters-radiation/
"Indications are that beyond a shield thickness of about 25 cm of aluminium, the radiation dose at Europa tends to stick at around 500 rads per month. For heavier materials (e.g. lead) this thickness can be greater before the Bremsstrahlung radiation becomes important."
I thought Bremsstrahlung increased with the square of Atomic Number. Surely lead should be a worse shield than aluminium?
Eamon
Sent from my iPad
On 20 Aug 2014, at 08:55, " [Traveller_TNE]" <> wrote:
> RE: point 2 - radiation won't be a problem if the base is underground or shielded. Here's something I wrote up for a discussion about Transhuman Space many many years ago on the subject:
> I've tracked down some radiation levels at the surfaces of each of the Galilean satellites, so we can get an idea of habitability of their surfaces. This is further to my impression that Ganymede's magnetic field could serve to shield the surface somewhat from radiation...
>
> Numbers are from "Energetic Ion and Electron Irradiation of the Icy Galilean Satellites" by John F. Cooper et al in the January 2001 "Icarus" (Vol. 149, pg. 133-59), which is is full of very detailed analysis of the radiation doses of different parts of the surfaces of the three icy Galileans. Usefully, it provides a graph showing the radiation in MegaRads per month (28 days presumably).
>
> Important things to note: even under a centimetre of water ice, the radiation levels drop dramatically compared to what they're at exactly on the surface. Behind sturdier shielding (eg metals) this protection could be even more significant.
>
> Below a surface layer of one hundred-thousandth of a gram per square cm of water ice (that is, virtually on the surface), Europa gets about 1500 megarads per month; Ganymede's polar caps 350 megarads; Ganymede's equator 150 megarads; and Callisto 30 megarads. But beneath only a 1-cm layer of solid water ice, the doses plummet to only 300,000 rads for Europa, 6000 rads for Ganymede's polar caps, and a mere 100 rads per month for Callisto and for Ganymede's equator.
>
> Figures are unclear for Io, but it seems a value of between 15 and 60 times that of Europa is appropriate. So let's assume 30 times Europa - 45000 megarads/month for the surface, 9 megarads/month under 1 cm of ice. (well, OK, it's not ice, but just to be consistent in this table we'll assume it is). (NB. 1 megarad = 10E8 ergs/cubic centimetre).
>
> Translated into rads/sec:
>
> Satellite Surface under 1 cm of ice
> ----------------------------------------------------------
> Io 18600 rad/sec 3.72 rad/sec
> Europa 620 rad/sec 0.124 rad/sec
> Ganymede Poles 145 rad/sec 0.0025 rad/sec
> Ganymede Equator 62 rad/sec 0.00004 rad/sec
> Callisto 12.5 rad/sec 0.00004 rad/sec
>
>
> So it seems the safest places to be are in the equatorial regions of Ganymede and on Callisto (under some shielding, that is!). Under 1 cm of ice shielding, at the levels quoted above, a person will suffer a dose of 0.144 rads/hour or 3.456 rads/day. However, thicker shielding will provide more protection UP TO A POINT.
>
> Thanks to the Bremsstrahlung radiation (X-rays and gamma rays) produced within the material of a shield itself as it stops high-energy charged particles, there's a point beyond which even very thick shielding sharply loses its ability to reduce radiation dosage at Jupiter. Indications are that beyond a shield thickness of about 25 cm of aluminium, the radiation dose at Europa tends to stick at around 500 rads per month.
> For heavier materials (e.g. lead) this thickness can be greater before the Bremsstrahlung radiation becomes important.
>
"The ions from the belt can penetrate about a millimeter into the ice. Electrons reach roughly a centimeter down, but they also emit high-energy photons that can go as far as a meter deep. Regardless of the type of radiation, these high-energy particles will rip electrons off of molecules, thereby "oxidizing" everything on the surface"
http://www.astrobio.net/news-exclusive/hiding-from-jupiters-radiation/
"Indications are that beyond a shield thickness of about 25 cm of aluminium, the radiation dose at Europa tends to stick at around 500 rads per month. For heavier materials (e.g. lead) this thickness can be greater before the Bremsstrahlung radiation becomes important."
I thought Bremsstrahlung increased with the square of Atomic Number. Surely lead should be a worse shield than aluminium?
Eamon
Sent from my iPad
On 20 Aug 2014, at 08:55, " [Traveller_TNE]" <> wrote:
> RE: point 2 - radiation won't be a problem if the base is underground or shielded. Here's something I wrote up for a discussion about Transhuman Space many many years ago on the subject:
> I've tracked down some radiation levels at the surfaces of each of the Galilean satellites, so we can get an idea of habitability of their surfaces. This is further to my impression that Ganymede's magnetic field could serve to shield the surface somewhat from radiation...
>
> Numbers are from "Energetic Ion and Electron Irradiation of the Icy Galilean Satellites" by John F. Cooper et al in the January 2001 "Icarus" (Vol. 149, pg. 133-59), which is is full of very detailed analysis of the radiation doses of different parts of the surfaces of the three icy Galileans. Usefully, it provides a graph showing the radiation in MegaRads per month (28 days presumably).
>
> Important things to note: even under a centimetre of water ice, the radiation levels drop dramatically compared to what they're at exactly on the surface. Behind sturdier shielding (eg metals) this protection could be even more significant.
>
> Below a surface layer of one hundred-thousandth of a gram per square cm of water ice (that is, virtually on the surface), Europa gets about 1500 megarads per month; Ganymede's polar caps 350 megarads; Ganymede's equator 150 megarads; and Callisto 30 megarads. But beneath only a 1-cm layer of solid water ice, the doses plummet to only 300,000 rads for Europa, 6000 rads for Ganymede's polar caps, and a mere 100 rads per month for Callisto and for Ganymede's equator.
>
> Figures are unclear for Io, but it seems a value of between 15 and 60 times that of Europa is appropriate. So let's assume 30 times Europa - 45000 megarads/month for the surface, 9 megarads/month under 1 cm of ice. (well, OK, it's not ice, but just to be consistent in this table we'll assume it is). (NB. 1 megarad = 10E8 ergs/cubic centimetre).
>
> Translated into rads/sec:
>
> Satellite Surface under 1 cm of ice
> ----------------------------------------------------------
> Io 18600 rad/sec 3.72 rad/sec
> Europa 620 rad/sec 0.124 rad/sec
> Ganymede Poles 145 rad/sec 0.0025 rad/sec
> Ganymede Equator 62 rad/sec 0.00004 rad/sec
> Callisto 12.5 rad/sec 0.00004 rad/sec
>
>
> So it seems the safest places to be are in the equatorial regions of Ganymede and on Callisto (under some shielding, that is!). Under 1 cm of ice shielding, at the levels quoted above, a person will suffer a dose of 0.144 rads/hour or 3.456 rads/day. However, thicker shielding will provide more protection UP TO A POINT.
>
> Thanks to the Bremsstrahlung radiation (X-rays and gamma rays) produced within the material of a shield itself as it stops high-energy charged particles, there's a point beyond which even very thick shielding sharply loses its ability to reduce radiation dosage at Jupiter. Indications are that beyond a shield thickness of about 25 cm of aluminium, the radiation dose at Europa tends to stick at around 500 rads per month.
> For heavier materials (e.g. lead) this thickness can be greater before the Bremsstrahlung radiation becomes important.
>