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Originally Posted by janetdoe
(Post 16695700)
As far as I can tell, every useful number is blacked out in the documents they released to EPIC. :rolleyes: But I have seen several third-party sources that confirm a 20-30 keV beam, e.g., http://www.diagnosticimaging.com/saf...113619/1521147.
The best clue, however, are the Rapiscan patents: http://www.google.com/patents?id=9tM...%2C1295&edge=0 What do these three charts tell us? |
Originally Posted by Bart
(Post 16691017)
Sorry, folks, but I don't feel obligated to provide you any further information. It simply comes down to this: the AIT is safe for use. You are exposed to much higher doses of ionizing radiation during your commercial flight than you are during a six second AIT scan. There are many other common use items that expose you to higher doses of ionizing radiation.
If you don't feel comfortable with the AIT scan, then by all means opt-out. You will be patted down instead. From my perspective, I don't care which option you choose. You're going to get screened one way or the other. You're supposed to be the smart ones. Figure it out. :rolleyes: |
Originally Posted by Bart
(Post 16691017)
Sorry, folks, but I don't feel obligated to provide you any further information. It simply comes down to this: the AIT is safe for use. You are exposed to much higher doses of ionizing radiation during your commercial flight than you are during a six second AIT scan. There are many other common use items that expose you to higher doses of ionizing radiation.
If you don't feel comfortable with the AIT scan, then by all means opt-out. You will be patted down instead. From my perspective, I don't care which option you choose. You're going to get screened one way or the other. You're supposed to be the smart ones. Figure it out. |
Originally Posted by Boggie Dog
(Post 16696190)
What do these three charts tell us?
Once we know what energy of the photons, we can compute their penetrating properties, which are the subject of this thread. |
Originally Posted by N965VJ
(Post 16684649)
Get your manufacturers brochure with sample images here.
The first item on the list of applications is: • Civil Security: airports, seaports, railways, bus stations Great first pass at getting the govt used to it, waiting for "the" incident on a airline. Sorry, I don't buy it, and wouldn't go thru it....ever. (And actually moving the person thru it on a "slide" is a pretty poor method,any person motion would blur the image.) |
Originally Posted by G_Wolf
(Post 16696240)
The AIT machines are safe because Bart says they are! That should be a good enough reason!!!
|
Originally Posted by BearX220
(Post 16698323)
What's ironic is this big parade of smart people with relevant medical and technical expertise, reasoning it all out and by extension explaining it to us laymen... versus Bart stating flatly that AIT is "safe," with no data or documentation for backup, and implying that we're not that smart for questioning him. Ho ho.
The if you just want low res, as Bart claims, the decision to dump the known safe tech of MMW machines in favor of ionizing radiation backscatter is particularly criminal. Clearly, this type of move shows a desire on TSA's part to move toward the securepass type machines that see completely through the body. They really want this. The only thing backing them off is the political opposition. They are just waiting for the right moment. |
Originally Posted by nachtnebel
(Post 16698883)
Bart is saying that there is no evidence that they are unsafe.
Originally Posted by Bart
(Post 16691017)
It simply comes down to this: the AIT is safe for use.
Originally Posted by Bart
You're supposed to be the smart ones. Figure it out.
|
Originally Posted by BearX220
(Post 16698928)
Oh, I think we are. Looks like a poor career choice to me, unless you are a self-hater or a masochist. |
Originally Posted by nachtnebel
(Post 16699052)
Looks like a poor career choice to me, unless you are a self-hater or a masochist. |
Originally Posted by Bart
(Post 16689566)
The radiation you're exposed to in an AIT during a 6 second scan is miniscule c
Oh wait. You stand next to these all day. So you ARE betting your life on it. That's ok with me and its your choice. If I'm wrong, I'm getting groped unnecessarily. If your wrong, you'll die prematurely of cancer after a long and painful period of suffering |
Originally Posted by tkey75
(Post 16699594)
...or narcissist, sadist, sociopathic...
|
Originally Posted by WillCAD
(Post 16694863)
I have another question for the resident TSOs:
Have any of you ever considered putting a dosimeter badge in your pocket while you work the AIT? Yes, yes, I know you're not allowed to wear them, it would disturb the uniform, but I bet money there is no rule or reg prohibiting you from carrying one in your pocket during your shift. Bart - I especially challenge you to put your money where your mouth is - get a dosimeter and check your dosage. |
Originally Posted by Bart
(Post 16689499)
I didn't realize there were so many medical experts on this board.
Originally Posted by BearX220
(Post 16689538)
It's not expertise you're seeing, it's healthy, intelligent skepticism. If I were you I'd wear a big lead smock to work.
Originally Posted by LeapingFrogs
(Post 16690118)
The onus is on your organization to provide the 3rd party unbiased testing. They haven't done that. Don't quote Johns Hopkins. We know how they feel about your agency. They are very publically unhappy with your bosses.
Why the TSA of course! It's cute and so innocent that he has such faith in his employers. The rest of us know better.
Originally Posted by janetdoe
(Post 16690200)
It only takes some basic physics knowledge to determine the penetration depth of X-rays into soft tissue and bone. . .
The majority of the x-rays will penetrate the body, but they will not have enough energy to escape (backscatter). Instead, they are mostly dissipated within your tissues, generally through the photoelectric effect or Compton scattering. Both of these mechanisms involve knocking an electron out of an atom, i.e. they are ionizing. There is general lack of knowledge on the biological impact of these low energy x-rays, but preliminary findings seem to indicate that a dose of low-energy x-rays can be 2x or 4x as damaging as the same dose of high-energy x-rays or gamma rays. (Discussed in previous threads.)
Originally Posted by janetdoe
(Post 16695700)
As far as I can tell, every useful number is blacked out in the documents they released to EPIC. :rolleyes: But I have seen several third-party sources that confirm a 20-30 keV beam, e.g., http://www.diagnosticimaging.com/saf...113619/1521147.
The best clue, however, are the Rapiscan patents: http://www.google.com/patents?id=9tM...%2C1295&edge=0 Sorry Bart, but other important information in radiobiology and physics is well known and long published: Johns and Cunningham's classic Textbook, Eric Hall's Radiobiology for the Radiobiologist now in at least its 4th or 5th edition, and Faiz Khan's Physics of Radiation Therapy. Examining the graphs, the highest contrast energies are in the 35-50 kVp range. At these ranges, the dose to bone is around 4.6 times higher than the dose to soft tissue. When I first saw those pseudo-images the TSA published, my first thought and I remarked in an earlier FT thread on this, that if the bones are visible, they are absorbing dose. My best guess at the time was the energy was between 25 kVp and 75 kVp, based on earlier research friends of mine did with soft x-ray imaging in Ann Arbor. What this means is that bone exposed to your x-rays absorbs 4.6 times the dose of skin. Examining the radiation spectrum in flight at FL400, the predominant energy is from cosmic radiation, and having passed through the atmosphere, the bulk of the lower energy radiation has scattered or attenuated, leaving only the higher energy radiation which does not have a differential dose in bone (at 1.25 MeV) the bone dosimetry factor is 0.94 - 0.96 depending on whose text you use. Therefore the shin biologically effective dose is lower in flight than it appears with your machines. Next, consider the physics of cancer induction. Cancer induction is a stochastic process. It only takes one hit in the right place to start the ball rolling. Dose is, per se, relevant to carcinogenesis only to the extent that the higher the dose the higher the number of ionizing events, and the more likely a critical event will occur. This is why radiation safety experts use the "linear no-safe-threshold" model in designing radiation protection requirements. While it can be debated that this theory is not 100% accurate, there is little debate concerning the stochastic effects of ionizing radiation, as janetdoe has so eloquently identified. Finally consider the types of secondary cancers most often seen with ionizing radiation exposure and the areas they are seen. In cancer patients treated with very high doses, the most commonly seen secondary cancers, although very rare, are in the penumbra of the primary treatment field. This is in the area where the dose drops rapidly from very high to very, very low. What types of secondary malignancies? Sarcomas. And guess what types of primary bone cancers are most common: sarcomas. |
I admit that I have no technical expertise in radiation and its effect on the body. I am not a radiologist or even a technician. My experience is a few dozen medical and dental x-rays and a Red Goose machine many, many years ago. What I have to do is take the knowledge presented here, judge its veracity based on what I know and can look up, and make my decision based on the information at hand.
Presented first is the it is no more dangerous that the rest of my life argument:
Originally Posted by Bart
(Post 16685444)
Swore up and down? I'm not so sure about that. However, it is true that portions of the shin bone are barely visible on the AIT. That's because there is very little tissue in that part of the body between the bone and skin surface. But the AIT does not penetrate the body in a manner that it's a skeletal image like you might have seen in True Lies, Total Recall or any other sci-fi movie, as the title of your thread seems to indicate.
------ Intelligent skepticism? OK. If you say so. By the way, how long have you been sitting in front of your computer (assuming it's a PC or desktop)? The radiation you're exposed to in an AIT during a 6 second scan is miniscule compared to sitting in front of a computer, even far less than in front of a TV. Do you wear a smock at the computer? When watching TV? Sorry, the lot of your comments comes across as fear and superstition. No intelligence involved at all. --------- Sorry, folks, but I don't feel obligated to provide you any further information. It simply comes down to this: the AIT is safe for use. You are exposed to much higher doses of ionizing radiation during your commercial flight than you are during a six second AIT scan. There are many other common use items that expose you to higher doses of ionizing radiation. If you don't feel comfortable with the AIT scan, then by all means opt-out. You will be patted down instead. From my perspective, I don't care which option you choose. You're going to get screened one way or the other. You're supposed to be the smart ones. Figure it out. On the other side we have the it can be really, really bad argument:
Originally Posted by janetdoe
(Post 16690200)
High-energy medical x-rays mostly pass through the body, and end up hitting the detector or film behind you. Backscatter works differently. The x-rays hit you and some percentage bounce backwards to hit the detector in front of you. This means that the bones that you see on the pictures do NOT indicate the total depth of x-ray penetration. The things you see in the picture are things that the X-rays hit and still have at least 50% of their original energy to reflect back to the detector. As a rough rule of thumb, at least 50% of the initial x-rays penetrate to the deepest levels you see in the image. 25% of the x-rays make it to double that depth. 12.5% make it to triple that depth... and on and on. The majority of the x-rays will penetrate the body, but they will not have enough energy to escape (backscatter). Instead, they are mostly dissipated within your tissues, generally through the photoelectric effect or Compton scattering. Both of these mechanisms involve knocking an electron out of an atom, i.e. they are ionizing. There is general lack of knowledge on the biological impact of these low energy x-rays, but preliminary findings seem to indicate that a dose of low-energy x-rays can be 2x or 4x as damaging as the same dose of high-energy x-rays or gamma rays. (Discussed in previous threads.)
Originally Posted by greentips
(Post 16701510)
Haven't been reading that carefully?
No, There's expertise here, as janetdoe has considerable expertise in this area, if indeed she is not a qualified expert within the meaning of 10CFR35, as she appears to be quite knowledgable, and I am such an expert as well. ----- Precisely. In addition, there are no daily output checks on these units that have been publicly announced: at a minimum they should have daily beam energy calibrations and/or checks, and detector sensitivity checks. Why? Because beam energy is important, it is a description of a.) the depth of penetration and b.) the nature of ionization events that take place as the beam transits tissue. [Snip] Wow, I missed that one when I was looking. If I ever need a another physicist, I'll be calling you. I guessed the energy range was in the Superficial (30-70 kVp) range, and speculated it could be has high as 125 kVp. We do not know the beam currents, nor the detector sensitivity thresholds. That is why calibration is essential, especially if these machines have auto-intensifier corrections. If the detectors get noisy, the machines, in some designs could compensate for that noise by boosting beam current to obtain better contrast, thus increasing the dose. I'll have a look at those patents in detail when I get a chance. Sorry Bart, but other important information in radiobiology and physics is well known and long published: Johns and Cunningham's classic Textbook, Eric Hall's Radiobiology for the Radiobiologist now in at least its 4th or 5th edition, and Faiz Khan's Physics of Radiation Therapy. Examining the graphs, the highest contrast energies are in the 35-50 kVp range. At these ranges, the dose to bone is around 4.6 times higher than the dose to soft tissue. When I first saw those pseudo-images the TSA published, my first thought and I remarked in an earlier FT thread on this, that if the bones are visible, they are absorbing dose. My best guess at the time was the energy was between 25 kVp and 75 kVp, based on earlier research friends of mine did with soft x-ray imaging in Ann Arbor. What this means is that bone exposed to your x-rays absorbs 4.6 times the dose of skin. Examining the radiation spectrum in flight at FL400, the predominant energy is from cosmic radiation, and having passed through the atmosphere, the bulk of the lower energy radiation has scattered or attenuated, leaving only the higher energy radiation which does not have a differential dose in bone (at 1.25 MeV) the bone dosimetry factor is 0.94 - 0.96 depending on whose text you use. Therefore the shin biologically effective dose is lower in flight than it appears with your machines. Next, consider the physics of cancer induction. Cancer induction is a stochastic process. It only takes one hit in the right place to start the ball rolling. Dose is, per se, relevant to carcinogenesis only to the extent that the higher the dose the higher the number of ionizing events, and the more likely a critical event will occur. This is why radiation safety experts use the "linear no-safe-threshold" model in designing radiation protection requirements. While it can be debated that this theory is not 100% accurate, there is little debate concerning the stochastic effects of ionizing radiation, as janetdoe has so eloquently identified. Finally consider the types of secondary cancers most often seen with ionizing radiation exposure and the areas they are seen. In cancer patients treated with very high doses, the most commonly seen secondary cancers, although very rare, are in the penumbra of the primary treatment field. This is in the area where the dose drops rapidly from very high to very, very low. What types of secondary malignancies? Sarcomas. And guess what types of primary bone cancers are most common: sarcomas. I can be convinced to change my mind. Is there independent study and scientific analysis from experts, even anonymous ones, that supports the "it is safe" side of the argument? Where is it? |
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