Conversions from MeV to Rad or Gy

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In summary, the conversation was about converting MeV to Rad or Gy and the difficulty in finding a helpful solution. The question was raised in the context of potential global problems that could arise from a catastrophic event. The desired outcome was to determine the necessary depth of a bunker to protect from gamma radiation emitted from a solar flare with a median energy of 3.5 trillion electron-volts. While there is no direct conversion between these units, a formula for exposure was provided which takes into account the number of gammas emitted and the average gamma energy. It was also noted that gamma rays are not completely stopped, but can be reduced to near zero with a thick enough barrier.
  • #1
comasic
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I am seeking some light hearted assistance with a conversion from MeV to Rad or Gy.
Im a little new to these units and can't find any helpfull pointers on how to convert them.

This was the real world question that was raised after a conversation about global problems
that could be encountered in a http://www.mondovista.com/endtime2x.html" type event.


Question:
How deep would you have to dig a bunker, to reduce the radiation from a super solar flare if
the flare emitted gamma rays that had a median energy of 3.5 trillion electron-volts, or 3500
times the mass-energy of a proton.

Given that proton mass energy equivelent is 938.272 013 MeV
and that every layer of 3.6 inches or 9 cm of packed soil will reduce gamma radiation by half.

The final safe radiation level in the underground bunker should be zero.
Also note thet there is no need to take into consideration air or cloud cover above the bunker.

humm... sounds simple?

if i knew what 1 Rad or 1 Gy was in Mev i would be laughing...
but i could not google anything about the methods of conversion.
Any assistance would be appreciated.

P.S
I can dig the hole myself but calculating how deep it should be is the problem ;-)
 
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  • #3
Thank you for pointing out the basic units and pointing me in the right direction.
Im sure a conversion to a common unit is possible at some point but after days
of google and searching i have
found that some people have spent years researching and calculating radiation
from killer solar flares and still find it hard to explain how its calculated.

So I guess i was dreaming of finding a quick solution.

I did however find another topic that explains why the question was asked.
https://www.physicsforums.com/showthread.php?t=194860"

Thank you for your input.
 
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  • #4
One thing to also note is that since gamma rays are not charged particles, they are attenuated, not stopped completely. This means that theoretically you need an infinitely thick barrier to reduce exposure to zero. You can, however, reduce to near zero so as to be practically harmless. Also, the mass-energy of the proton is irrelevant for this problem, since it's asking about gammas, not charged particles.

As for a conversion from MeV to Rad, again, there is no standard formula, but you can use the formula

Exposure (in Roetgen) = 1.829E-8 x Number of Gammas x Average Gamma Energy (in MeV) x the mass energy absorption coefficient (in square cm per gram, and this is a function of the gamma energy and the temperature/pressure of the air).

This shows that you also need to know how many gammas are emitted, even if you do have air at STP (the coefficient at this energy is somewhere around 1E-2). A single photon is practically harmless, but a trillion of them would be fatal (around 600 R acute exposure). A non-stochastic safe level would be around 100 R. Of course, your risk of cancer would still go up at 100 R, but you wouldn't die from it.
 

1. What is the difference between MeV, Rad, and Gy?

MeV (Megaelectronvolt) is a unit of energy commonly used in particle physics, nuclear medicine, and radiation therapy. Rad (Radiation Absorbed Dose) is a unit of measurement for the amount of energy deposited by ionizing radiation in a medium. Gy (Gray) is a unit of measurement for the absorbed dose of ionizing radiation, taking into account the type and energy of the radiation.

2. Why are conversions from MeV to Rad or Gy necessary?

Conversions from MeV to Rad or Gy are necessary because they represent different units of measurement for radiation. MeV measures the energy of the radiation, while Rad and Gy measure the amount of energy deposited in a medium. Converting between these units allows for accurate and consistent measurements in different fields of radiation science.

3. How can I convert from MeV to Rad?

To convert from MeV to Rad, you can use the formula: 1 MeV = 10,000 Rad. This means that 1 MeV of energy is equivalent to 10,000 Rads of energy deposited in a medium.

4. How can I convert from MeV to Gy?

To convert from MeV to Gy, you can use the formula: 1 MeV = 0.01 Gy. This means that 1 MeV of energy is equivalent to 0.01 Grays of energy deposited in a medium.

5. What factors can affect the conversion from MeV to Rad or Gy?

The conversion from MeV to Rad or Gy can be affected by various factors such as the type of radiation, the energy of the radiation, and the material or medium through which the radiation is passing. These factors can affect the amount of energy deposited in the medium and thus impact the conversion. It is important to consider these factors when converting between units of radiation measurement.

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