Editing Hal backscatter exposure (section)

== 2/1/2017 ==

No salesperson should every demonstrate the HBI-120 in an unsafe way: the HBI-120 is an x-ray instrument that produces ionizing radiation; therefore you shouldn't stand in front of it while taking a scan. Always follow the as low as reasonably achievable (ALARA) standards for any non-naturally occurring source of radiation. 

The acceptable dose limit for members of the general public â€” not only in the US, but in most countries â€” is 1.0 mSv (100 mREM) per year. 

The radiation dose from a typical mammogram is 3 mSv (300 mREM). The dose from eating a typical banana (from the ^40K radioisotope in the banana) is around 0.1 Î¼Sv (0.01 mREM). If you eat 1 banana per day, you will expose yourself to about 36.5 Î¼Sv (3.65 mREM) per year of radiation. The radiation exposure from a single round-trip flight to and from Boston to Hong Kong is around 250 to 300 Î¼Sv (25 to 30 mREM). 

We have published data on the radiation output of the HBI-120. The maximum in-beam dose produced by the HBI-120 directly in front of the center of the unit at a distance of 30 cm (~11.8 inches) in air is 9.5 mSv/hour (950 mREM/hour); that's 2.64 Î¼SV/second (264 Î¼REM/second). Directly in front of the center of the unit at a distance of 1 m (~3 ft, 3 inches), the maximum in-beam dose is 855 Î¼Sv/hour (85.5 mREM/hour); that's 0.238 Î¼Sv/second (23.8 Î¼REM/second) â€” that's about the equivalent of eating 2.38 bananas (banana-equivalent doses) for every second of exposure 1 m (~3 ft, 3 inches) from the front of the HBI-120 at the point of maximum radiation with nothing between you and the instrument. Note: a typical scan with the HBI-120 takes 5 to 10 seconds.

Practically speaking, at a distance of 1 m (~3 ft, 3 inches), the radiation exposure is lower, because the in-beam radiation falls off rapidly as you move away from the center line of the instrument. 25 degrees to the left or right of the center line of the HBI-120 at a distance of 1 m (~3 ft, 3 inches) in air, the in-beam dose is 63 Î¼Sv/hour (6.3 mREM/hour), or 0.0175 Î¼Sv/second (1.75 Î¼REM/second). 40 degrees to the left or right of the center of the HBI-120 there is no measurable direct radiation from the instrument.

Obviously your radiation exposure behind a door from the front of the HBI-120 with the instrument in use is far less than the radiation exposure at the same distance with only air between you and the instrument; the amount of exposure would depend on what the door was made of and how thick the door was. The same would apply for radiation exposure behind a wall. In practice all of the above means that the HBI-120 is safe for incidental exposure, including repeated incidental exposures, but always follow ALARA standards. 

Following up from my earlier email:

The radiation dose from a typical mammogram is 3 milliSieverts = 300 milliREM.

The radiation dose from eating a typical banana is around 100 nanoSieverts = 10 microREM = 0.01 milliREM. If you eat 1 banana per day, you will expose yourself to about 36.5 microSieverts = 3.65 milliREM per year.

The radiation exposure from a single round-trip flight to and from Boston and Hong Kong is around 250 to 300 microSieverts (25 to 30 milliREM).

Total body exposure for a typical person from a 10 second direct scan of the torso with the HBI-120 (which of course is not permitted), for a top to bottom scan centered on the center of the torso, at a distance of 30 centimeters (just under 1 ft), would be slightly more than 1 microSievert (0.1 milliREM), a little more radiation than you'd receive from eating 10 bananas. You could be subjected to one such 10 second HBI-120 scan from 30 cm away every workday over the course of a year, and you would receive about the same radiation from one round-trip flight to and from Boston and Hong Kong. 

An HBI-120 body scan at a distance of only 10 cm, would produce 9 times the peak radiation on the person's body, but close to 20 times the average body radiation, since a much higher percentage of the body would be exposed to the higher levels of radiation produced near the centerline of HBI-120. Even this radiation exposure though would be less than your exposure from one round-trip flight to and from Boston and Hong Kong.