Some notes on x-ray backscatter imaging

TJ Radcliffe Web Page ^ | 11/16/2010 | TJ Radcliffe

[Greysard]

This open letter from a group of scientists [...] is entirely to the point, in my view as a radiation transport physicist who is intimately familiar with the processes by which x-rays deposit energy in tissue. [...]

As it stands, these machines are a pure act of state-sponsored violence against anyone who is mislead into one. I would certainly not allow myself to be scanned by one of these machines, nor allow one of my minor children to be scanned by one. [...]

Based on a back of the envelope calculation with a 50 KVp Bremsstrahlung spectrum and the standard mass absorption coefficients for soft tissue, X-ray backscatter machines will, if widely deployed, almost certainly kill far more people than the terrorists they are supposed to protect us from.

[spokeshave]

...yeah...remember those “foot in shoe” X-Ray boxes in shoe stores.....all withdrawn for excessive radiation.

[Right Wing Assault]

http://www.npr.org/assets/news/2010/05/17/concern.pdf

Letter of concern sent to Holdren.

[Right Wing Assault]

those “foot in shoe” X-Ray boxes in shoe stores

I spent a lot of time with my feet in those things, but so far no cancer of the toes! I wonder if they have caused a problem.

[Recovering Ex-hippie]

PLUS....who is certifying and monitoring these machines? HA...no one.

[mad_as_he$$]

OSHA rules do not apply to Federal workers. If the TSA was privatized OSHA would shut them down.

http://www.osha.gov/OshDoc/data_General_Facts/federal-employee-factsheet.pdf

Read carefully between the lines.

[zeugma]

BFL

[bvw]

I commented there as follows:

Thanks for the warning on x-rays.

Some models show that terahertz scanners will unzip DNA. See http://www.technologyreview.com/blog/arxiv/24331/

How convenient for the cosmic ray dosing that follows in the same few hours when one is flying eight miles high.

We do not have much health data on either tech yet, it seems to me, extrapolations from this and that model. As you suggest it is utterly reckless to gain the health effects data by massive population exposures to novel energy spectrum exposures.

[bvw]

FYI

[DBrow]

Thanks for the ping!

According to the data at the original article, the Rapiscan dose to people is 1.55 microREM per scan, and the author feels that this could cause skin cancer because he’s modeled the skin dose.

Since that’s much less than the natural background (about 20 uREM/Hr), I can conclude that without flying, we are all doomed, and if we fly and get over 200 uREM/hour on a good day, anyone who flies is surely a goner. As I’ve mentioned before, the airline dose is comprised of heavy particles as well as a mix of photons.

Also note that he did his 50KVp Brems transport without considering the aluminum shield used in the Rapiscan, this required filter knocks out the low-energy photons that cause an unacceptable skin dose (he made the problem appear to be much worse by not modeling the actual system). Every xray used on people must have the shield, and he’s linked an article that mentions this and gives the thickness, so he could have included it.

You can see the effects of the Al filter by playing with the numbers here:

http://www.radprocalculator.com/XRay.aspx

Here is a “risk calculator” for medical xrays. I used the 1.55 uREM dose for a number of these procedures:

http://www.xrayrisk.com/calculator/calculator.php

And just sitting around for an hour exposes us to the equivalent of 13 (Thirteen!) Rapiscan doses, that surely cannot be good for us.

Dose or not these scanners are useless as a general screening tool.

[bvw]

Thanks for the info about the aluminum shield. You already know what I think of REM “measurements”, they are malarky, too coarse and too mixing of different things. A beta particle is not an x-ray, and a high energy cosmic thingee does damage according to what kind of thingee it is.

[dixiechick2000]

“Grammie has spoken. :)”

Then, all has been said. ;o)

[dixiechick2000]

“I have...from the start....”

Well...see...I...uh...have been...uh...absent for a while.

You get ‘em, Gramma! lol

[Brad’s Gramma]

YOU are an absolute nut. I love you.....

Have a WONDERFUL Thanksgiving, kiddo...if I don’t catch up w/ya before then!

May the BEST turkey...lose. May his life be...wait. Never mind. That sounds SOOOOOOOOOO wrong.

:)

[Greysard]

Consider the following sequence of numbers: "1, 1, 1, 10, 1" -- The “average” is nearly 3."

I just read your post again, after linking the whole thread here, and thought of another funny example:

The average voltage in a common house outlet is zero. But try to stick your fingers into it :-)

Hint: the AC voltage is positive half of the time, and negative other half of the time. The average is zero. But the peaks will kill you.

[dixiechick2000]

I love you, too, Gramma!

I hope you and yours have a very Happy Thanksgiving Day...and that the blessed turkey helps you be able to take a nap. ;o)