Neutron Detection Pager
Posted: Mon Dec 10, 2007 2:04 am
At HEAS this past year (2007), I brought a radiation detector made by NeutronRAE. The (CsI) detector is incredibly sensitive to gammas above around 60 KeV and a second detector using a Li6I crystal is sensitive to neutrons from thermal to about 14 MeV.
I have run this unit with my fusor and get counts of between 1 and 2 uSv/hr. Being the proud owner of such a compact unit I took it to Richard's to show it off. Unfortunately when Richard fired up his fusor, my NeutronRAE did not count any neutrons. It did "ping" a few times in the lab but even when Carl held it against the shell of Richards fusor, it was silent. There were some comments that the detector would not count fast neutrons and even though I thought otherwise, I was in favor of a test within a moderator in contact with Richard's fusor. Still nothing. My bubble was burst or at least wounded but I was not yet convinced of a problem with my pager detector.
Armed with the data from my personal fusor and the suspicion that my counts MIGHT be from noise, I decided on a high altitude test. On my recent East Coast to West Coast flight, I took my detector and my GPS. What I found was that the gammas were at a minum at around 3,000 ft ASL and increased rapidly above 20K feet. I attributed this to decreasing ground radiation at higher elevations but more cosmic radiation. This would only be true in air travel since on a mountain, the ground would still be there to contribute to background.
The neutron counts were <1 uSv/hr below 25,000 ft. At 35,000 ft the NeutronRAE read approximately 2.5 uSv/hr and at 40,000 ft was indicating 3.5 uSv/hr. These numbers were very consistant throughout the flight and were similar a week later on the return flight.
During my visit at Jon Rosenstiel's, we positioned the neutron detector on Jon's fusor and also behind a lead plate around 0.3 meters away to eliminate the possibility that high levels of gammas may be causing a false positive neutron reading.
On a run correlated with Jon's instrumentation and a bubble detector, the pager neutron detector agreed with Jon's. Attached is a photo of the pager behind the lead shield on a run of 3.5 E 5 neutrons/second. It is reading 4 uSv.
My three major conclusions from these experiments are:
1. The NeutronRAE is a good neutron detector for thermal and high energy neutrons.
2. RF noise in fusors can fool even the best detectors and can contribute to counts on electronic insturmentation.
3. High altitude flights have ~300 times the the gamma flux and even greater neutron flux than at sea level.
The neutron flux at 40,000 ft. is sufficient enough to activate metals such as silver. In a future flight I am going try a beta only detector and a piece of silver to try activation at altitude. In the mean time, I do not think I will travel with any coins in my pockets when I fly. The human body is a good moderator and activated silver is a fairly hot emitter.
Frank S.
I have run this unit with my fusor and get counts of between 1 and 2 uSv/hr. Being the proud owner of such a compact unit I took it to Richard's to show it off. Unfortunately when Richard fired up his fusor, my NeutronRAE did not count any neutrons. It did "ping" a few times in the lab but even when Carl held it against the shell of Richards fusor, it was silent. There were some comments that the detector would not count fast neutrons and even though I thought otherwise, I was in favor of a test within a moderator in contact with Richard's fusor. Still nothing. My bubble was burst or at least wounded but I was not yet convinced of a problem with my pager detector.
Armed with the data from my personal fusor and the suspicion that my counts MIGHT be from noise, I decided on a high altitude test. On my recent East Coast to West Coast flight, I took my detector and my GPS. What I found was that the gammas were at a minum at around 3,000 ft ASL and increased rapidly above 20K feet. I attributed this to decreasing ground radiation at higher elevations but more cosmic radiation. This would only be true in air travel since on a mountain, the ground would still be there to contribute to background.
The neutron counts were <1 uSv/hr below 25,000 ft. At 35,000 ft the NeutronRAE read approximately 2.5 uSv/hr and at 40,000 ft was indicating 3.5 uSv/hr. These numbers were very consistant throughout the flight and were similar a week later on the return flight.
During my visit at Jon Rosenstiel's, we positioned the neutron detector on Jon's fusor and also behind a lead plate around 0.3 meters away to eliminate the possibility that high levels of gammas may be causing a false positive neutron reading.
On a run correlated with Jon's instrumentation and a bubble detector, the pager neutron detector agreed with Jon's. Attached is a photo of the pager behind the lead shield on a run of 3.5 E 5 neutrons/second. It is reading 4 uSv.
My three major conclusions from these experiments are:
1. The NeutronRAE is a good neutron detector for thermal and high energy neutrons.
2. RF noise in fusors can fool even the best detectors and can contribute to counts on electronic insturmentation.
3. High altitude flights have ~300 times the the gamma flux and even greater neutron flux than at sea level.
The neutron flux at 40,000 ft. is sufficient enough to activate metals such as silver. In a future flight I am going try a beta only detector and a piece of silver to try activation at altitude. In the mean time, I do not think I will travel with any coins in my pockets when I fly. The human body is a good moderator and activated silver is a fairly hot emitter.
Frank S.