[ RadSafe ] RadSafe Digest, Vol 1945, Issue 1 regarding backscatter x-ray

[Bob May]

NCRP Commentary 20, Radiation Protection and Measurements Issues Related to Cargo Scanning With Accelerator Technology discusses how to apply decades of knowledge amassed by accelerator physicists, engineers, and safety professionals during the design and operation of cargo interrogation systems using accelerators. It may be of some interest. http://www.ncrponline.org/Publications/Commentaries/Comm20press.html
Bob
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Message: 2
Date: Wed, 28 Oct 2015 14:04:31 +0000
From: "Bradt, Clayton (HEALTH)" <clayton.bradt at health.ny.gov>
To: "bradkeck at mac.com" <bradkeck at mac.com>, RADSAFE
	<radsafe at health.phys.iit.edu>
Subject: [ RadSafe ] Z-Backscatter technology
Message-ID:
	<BN1PR09MB0226C9F04647CDB1AA050AB8A2210 at BN1PR09MB0226.namprd09.prod.outlook.com>
	
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Thanks, Brad. You confirm some of my conjectures about how this works, but I never considered that the side of the van itself was the detector. Others have recently suggested that the dark regions that appear to be lung cavities are actually artifacts of the imaging software. This may well be the case. However, I reason that  x-rays from the interrogating beam able to penetrate the sides of the scanned vehicle AND produce Compton backscatter able to penetrate the same vehicle on the way back to the detector would have to be of reasonably high energy so that the return signal is not swallowed up by attenuation.  This means that the device must employ x-ray energies that are sufficiently penetrating to produce density information from the chest cavity and result in those dark regions in the image.  Now I hate having to rely upon conjecture and wish someone would be able to give me an authoritative explanation of how this technology works.  After all, someone must have evaluated
 
  and approved the use of these devices -right? I hope that whoever did so reads RADSAFE and will respond in due time.  Now, here's the kicker:  In most states, including New York, the intentional application of ionizing radiation to humans requires a physician's order, and the presence of a licensed, registered radiological technician.  There are no law enforcement or "national security" exceptions in the code.  How on earth can NYPD be legally scanning occupied vehicles?



Clayton Bradt

Principal Radiophysicist

NYS Dept. of Health





******************************

From: Brad Keck <bradkeck at mac.com<mailto:bradkeck at mac.com>>



Clayton,



If i understand the Z-backscatter physics correctly, then the dark images of the lungs result from a lesser backscatter signal being generated in the lung cavity versus the thicker surrounding tissues.



Unlike an airport scanner, which does not need to penetrate the side of a truck, the cargo scan uses a higher energy (and intensity, i would think)  x-ray source which penetrates humans more than the energies used in airport scans.  The detector array - basically the side panel of the truck - is then used to measure the intensity of the x-rays corresponding to those scattered by low-Z material so you build an image of the low-Z materials in the first few centimeters lying along the side of the truck, including humans, drugs, explosives, cantaloupes, etc?.   Interestingly, both air and high-Z materials would give a ?dark? image, where any organic or low-Z materials would give a ?bright? image under the acquisition parameters used.



There are numerous dose estimates on the internet for the airport scanners, but I have not seen estimates for the cargo scans where a human might inadvertently be present.



Hope this helps,



Brad

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Message: 4
Date: Wed, 28 Oct 2015 16:22:49 +0000
From: "Dixon, John E. (CDC/ONDIEH/NCEH)" <gyf7 at cdc.gov>
To: "The International Radiation Protection (Health Physics) Mailing
	List"	<radsafe at health.phys.iit.edu>
Subject: Re: [ RadSafe ] Z-Backscatter technology
Message-ID:
	<27EC09363DB1C14BB68D7360DE2E9F674834AE28 at EMBX-CHAM4.cdc.gov>
Content-Type: text/plain; charset="utf-8"

All,
Here is a good link to this device: 

http://as-e.com/products-solutions/cargo-vehicle-inspection/mobile/product/zbv/

If you pull down the safety tab you will find this:

"Dose to Cargo: Less than 0.1 microSievert (?Sv) per scan (equivalent to 10 microRem (?rem)), at an average speed of 5 km/h (3 mph) at a scan distance of 1.5 m (5 ft). Should a stowaway accidentally be scanned, the effective dose is well below the ANSI specified limit for accidental exposure and is equivalent to flying two minutes at altitude."

1 mrem maximum for a scan of a stowaway (aka- the cargo) isn't all bad. No health risk here...

Regards,
John Dixon

-----Original Message-----
From: radsafe-bounces at health.phys.iit.edu [mailto:radsafe-bounces at health.phys.iit.edu] On Behalf Of Brad Keck
Sent: Tuesday, October 27, 2015 11:02 AM
To: The International Radiation Protection (Health Physics) Mailing List <radsafe at health.phys.iit.edu>
Subject: Re: [ RadSafe ] Z-Backscatter technology

Clayton,

If i understand the Z-backscatter physics correctly, then the dark images of the lungs result from a lesser backscatter signal being generated in the lung cavity versus the thicker surrounding tissues.  

Unlike an airport scanner, which does not need to penetrate the side of a truck, the cargo scan uses a higher energy (and intensity, i would think)  x-ray source which penetrates humans more than the energies used in airport scans.  The detector array - basically the side panel of the truck - is then used to measure the intensity of the x-rays corresponding to those scattered by low-Z material so you build an image of the low-Z materials in the first few centimeters lying along the side of the truck, including humans, drugs, explosives, cantaloupes, etc?.   Interestingly, both air and high-Z materials would give a ?dark? image, where any organic or low-Z materials would give a ?bright? image under the acquisition parameters used.

There are numerous dose estimates on the internet for the airport scanners, but I have not seen estimates for the cargo scans where a human might inadvertently be present.  

Hope this helps,

Brad


> On Oct 22, 2015, at 11:13 AM, Bradt, Clayton (HEALTH) <clayton.bradt at health.ny.gov> wrote:
> 
> 
> Does anyone know how I might get ahold of technical information on the Z-Backscatter technology as used for example by the AE&S vans mentioned in the above article? I am especially curious as to how the image of the contents of a vehicle is not obscured by backscatter off of the sides of the van and of the vehicle being scanned. Both the beam and scattered x-rays must pass through both vehicles on the way out and back. Also I'm curious about the density information presented in the images of people within a trailer. They appear to show the individuals lungs as dark regions within the thoracic cavities. I would not expect this from a backscatter image.
> 
> Clayton Bradt
> Principal Radiophysicist
> NYS Dept. of Health
> 518-474-1993
>