Intensity of the background neutron radiation

[Garlic]

Hello everyone,
What is the average intensity of the background neutron radiation?

 

[mfb]

That will depend on your experiment.

 

[Garlic]

That will depend on your experiment.

Sorry, but I don't understand what do you mean by that. Why should the intensity change depending on my experiment?

 

[mathman]

Neutron background
Most of the natural neutron background is a product of cosmic rays interacting with the atmosphere. The neutron energy peaks at around 1 MeV and rapidly drops above. At sea level, the production of neutrons is about 20 neutrons per second per kilogram of material interacting with the cosmic rays (or, about 100-300 neutrons per square meter per second). The flux is dependent on geomagnetic latitude, with a maximum at about 45 degrees. At solar minimums, due to lower solar magnetic field shielding, the flux is about twice as high vs the solar maximum. It also dramatically increases during solar flares. In the vicinity of larger heavier objects, e.g. buildings or ships, the neutron flux measures higher; this is known as "cosmic ray induced neutron signature", or "ship effect" as it was first detected with ships at sea.[11]

Above from Wikipedia

 

[mfb]

Sorry, but I don't understand what do you mean by that. Why should the intensity change depending on my experiment?

Every piece of material in your experiment will (a) interact with high-energetic particles passing through (e.g. cosmic radiation) and release neutrons, and (b) absorb some neutrons. In addition, your experiment will have some shielding from the atmosphere above (depends on its height above sea level) and maybe from rock above (for unterground experiment).
And that is just the influence on the raw neutron spectrum, the influence on your measurement devices is more complicated.

How can the background of anything not depend on your experiment?

 

[gleem]

I take it that your question is in regards to your earlier post regarding the measurement of low activity fast neutron sources. Since the energy of the background neutron flux peaks at 1 MeV. and may decrease rapidly above that I would still investigate the possibility of the need of a shield consisting of a high content hydrogen material as polyethylene or paraffin to thermalize those neutrons and reduce their possible interference with your subject radiation. Your source you say is 0.1 Bq so even small background radiation will be of concern in order to achieve data with good accuracy.

 

[Garlic]

Thank you for your replies, I understand it better.