FAQ - Flux to Dose Rate Conversions for Neutrons and Photons

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Liam David
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FAQ - Flux to Dose Rate Conversions for Neutrons and Photons

Post by Liam David »

In my research I found it useful to have neutron and photon flux to dose rate conversion factors on hand. The below graphs are derived from data in ICRP Publication 116 Conversion Coefficients for Radiological Protection Quantities for External Radiation Exposures, which is linked and attached below. Antero-posterior is the dose received if you're facing the source and differs from other orientations (e.g. isotropic) due to the positions of organs within the body. In the neutron plot I labeled the values for 2.45MeV neutrons.


Equivalent to ICRP 116 figure 4.20, pg. 89
neutron dose rate 1.png

Equivalent to ICRP 116 figure 4.4, pg. 71
photon dose rate 1.png


https://www.icrp.org/publication.asp?id ... tion%20116
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Rich Gorski
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Re: FAQ - Flux to Dose Rate Conversions for Neutrons and Photons

Post by Rich Gorski »

So, to put this in regard to fusors…

Assume we have a fusor that magically emits an isotropic neutron rate of 1 million n/s. 10^6 tier (or Tien). Then a person sitting 1 meter from the fusor (no moderator material) would experience a 2.5MeV neutron flux of 1^6/4*Pi*100^2 = 8 n/cm2/s . Then based on the isotropic curve presented that person sitting there for one hour would receive a dose of …

0.8(uSv/hr/n/cm2/s) * 8 (n/cm2/s) = 6.4 uSv isotropic or about equivalent to 1 dental X-ray. (or antero/posterior of 1.55*8 = 12.4uSv)

And if that person decided to submerge the fusor in a pool of water (neutrons fully thermalized) and again sat 1 meter away with a snorkel then according to the chart that person would receive a antero/posterior dose of about (1/100)*8 = 0.08 uSv.

I guess we’re safe unless we run the fusor at the 1M n/s tier, sit 1 meter away for an hour and do this every day for a year. A chest X-ray every day.

Interesting.

Rich G.

Ps. Did I do that right?
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Richard Hull
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Re: FAQ - Flux to Dose Rate Conversions for Neutrons and Photons

Post by Richard Hull »

I shield only for X-rays and have never run at a full mega mark non-isotropic, sitting at the controls about 1.5 meters from the fusor for more than 4 minutes at a time. This is repeated maybe for another 3 mega runs of similar run time during a session, (single day). I typically do only 4 sessions, (days), per year! Zero effective net exposure to neutrons. No need for a neutron shield.

Still, an excellent FAQ in the proper forum with good solid information. Had this been a normal post and not a FAQ it would have joined thousands of other useful older posts buried deep in the forums.

The responding post putting things in perspective for others here, was also right on point.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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