Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: Madidus_Scientia on 10/04/2011 11:09:45

Title: How many sieverts of radiation would an average sunburn be?
Post by: Madidus_Scientia on 10/04/2011 11:09:45

I'm going to refer to sunburns as radiation burns from now on, just since everybody seems to be terrified of the word radiation.

Title: How many sieverts of radiation would an average sunburn be?
Post by: Soul Surfer on 10/04/2011 12:20:03

Although the Sievert is a measure of biological damage caused by radiation this is specifically ionising radiation,  that is radiation powerful enough to cause ionisation in materials  this is related back to the basic doses of deposited energy the gray in joules per kilogram of material but weighted with a factor depending on the nature of the radiation.  Ultra violet light is not strictly ionising radiation and although it does cause damage by breaking chemical bonds it is not measured in sieverts so the question is not really a totally valid one.

It is possible to define the UV energy  received per hour by full sunlight but people differ vastly in how much they can stand before showing symptoms of damage.

Title: How many sieverts of radiation would an average sunburn be?
Post by: Bored chemist on 10/04/2011 12:58:44

"Ultra violet light is not strictly ionising radiation "
Oh yes it is.

Title: How many sieverts of radiation would an average sunburn be?
Post by: Madidus_Scientia on 11/04/2011 01:11:16

Ah, so the sievert system has no weighting for uv?

Title: How many sieverts of radiation would an average sunburn be?
Post by: Bored chemist on 11/04/2011 06:49:03

It has a weighting for photons.

Title: How many sieverts of radiation would an average sunburn be?
Post by: Madidus_Scientia on 11/04/2011 20:13:02

So we could figure out how much say, 2 hours worth of sunlight would be in sieverts?

Title: How many sieverts of radiation would an average sunburn be?
Post by: imatfaal on 13/04/2011 16:59:15

Quote from: Bored chemist on 11/04/2011 06:49:03

It has a weighting for photons.

The Sievert (dose equivalent) has  Q (quality factor weighting) for the different forms of radiation to allow the conversion from Grays (absorbed dose) - but references vary, even on a single wikipage, as to whether all photons having weighting of 1 or just Xray and Gamma.  I cannot find the actual definition anywhere -  but out of curiosity does anyone have a good reference? 

Title: How many sieverts of radiation would an average sunburn be?
Post by: wolfekeeper on 13/04/2011 17:54:46

Quote from: Bored chemist on 10/04/2011 12:58:44

"Ultra violet light is not strictly ionising radiation "
Oh yes it is.

Not the UV that we get from the Sun, on Earth.

Ionisation starts in the vacuum UV range, at about 200nm; but it's blocked by air.

Title: How many sieverts of radiation would an average sunburn be?
Post by: Geezer on 14/04/2011 00:25:52

Quote from: wolfekeeper on 13/04/2011 17:54:46

Quote from: Bored chemist on 10/04/2011 12:58:44

"Ultra violet light is not strictly ionising radiation "
Oh yes it is.

Not the UV that we get from the Sun, on Earth.

Ionisation starts in the vacuum UV range, at about 200nm; but it's blocked by air.

Perhaps our skin cells are unaware of that limitation?

Title: How many sieverts of radiation would an average sunburn be?
Post by: Madidus_Scientia on 14/04/2011 03:43:40

Yeah, how do explain sunburn then

Title: How many sieverts of radiation would an average sunburn be?
Post by: Bored chemist on 14/04/2011 06:54:03

Quote from: wolfekeeper on 13/04/2011 17:54:46

Quote from: Bored chemist on 10/04/2011 12:58:44

"Ultra violet light is not strictly ionising radiation "
Oh yes it is.

Not the UV that we get from the Sun, on Earth.

Ionisation starts in the vacuum UV range, at about 200nm; but it's blocked by air.

Bollocks
Ask Einstein, he did lots of work with vacuum photodiodes. You can ionise things with visible, or even IR light.
Incidentally, 200 nm isn't in the vacuum UV.