Answer to Question #8622 Submitted to "Ask the Experts"

Is there an inherently different albedo effect as experienced by the genders?

Dosimetry is to be worn on the upper front of the torso, which places it in the vicinity of the female breasts. Due to the geometry of the reflective/absorbent tissue (the breast may envelope the dosimetry), is the albedo effect more pronounced for females than males?

Some background: We had some painters who were doing paint prep/painting in containment (pressurized water reactor) at power. The painters (one female, one male) made repeated entries into containment, worked at the same location, took breaks (allowing the paint to dry) in the same area, and otherwise had identical entries.

The female consistently had higher measured (by the Siemens electronic neutron dosimeter) neutron absorbed dose (each exit indicated a 10-fold difference in their dose albeit the doses were minimal: hers was 11 µSv neutron dose and his was 1.0 µSv. The next exit indicated 9 µSv neutron dose for her and 1.0 for him).

Gender may be less an issue than size as she is a normal/slightly larger-than-normal woman but he is quite a small man. A significant detail, however, is that she has large breasts that provide better geometry (with respect to the relative location of breast tissue to the dosimeter) for the albedo effect to take place.

Is breast size (therefore gender) a legitimate issue in neutron (albedo effect) dose measurement?
 

This brings an entirely new perspective to the subject of "breast enhancement." Your inferences about the possible consequences of variations in tissue geometry with respect to neutron albedo effects are consistent with physics of neutron interactions and actual observations—i.e., the extent of neutron albedo has been shown to vary with thickness and lateral extent of soft tissue equivalent material. It has also been demonstrated that many albedo dosimeters show noticeably decreasing response as the distance of the dosimeter from the surface of the body increases.

I believe the Siemens electronic neutron dosimeter is primarily sensitive to low-energy neutrons for which the albedo effect is most dominant. Thus, I believe it is not surprising that such a dosimeter nestled in the valley of multiple reflections afforded by your buxom painter might well yield an enhanced response compared to that experienced by her less-than-Hulk-like partner. A factor of 10 difference in response does seem somewhat exaggerated, but the fact that the female's dosimeter reads higher seems consistent with the described different anatomies. I assume that both of the dosimeters in question were properly calibrated and that they exhibited similar responses under fixed conditions when irradiated on an appropriate phantom.

Small differences in the physical features of the diodes and any radiators or attenuators used, as well as variations in the electronic thresholds set for the diodes, can have marked effects on response. The latter determines the sizes of pulses that contribute to the response and, depending on algorithms used, can influence the extent to which gamma-induced pulses might contribute to neutron readings. This is relatively more important when neutron doses are low and gamma doses are considerably higher, as might be the situation in your case. Have you made any independent gamma and neutron dose measurements with portable instruments in the areas where the painters have been involved? These could assist you in judging the validity of the electronic personal dosimeter measurements.

We should also note that most albedo dosimeters, including TLDs (thermoluminescent dosimeters) and, I believe, the Siemens electronic dosimeter, show an extreme neutron energy-dependent response. If actual exposure conditions, especially neutron energy, differ from the calibration conditions, interpreted doses may be off by well more than an order of magnitude; this holds for both men and women. Also, albedo devices are sensitive to the directionality of neutrons, and differences in the physical characteristics of men and women might yield increased differences in the doses interpreted from the dosimeters exposed in such fields.

I do not know of any studies that have been done to investigate the differential responses of albedo dosimeter devices worn by men and women. There may be some anecdotal evidence of gender-dependent responses, but I am not aware of such. The fact that the electronic dosimeters have high sensitivity for low-energy neutrons, being able to measure less than a mrem of dose, does allow for observations, such as yours, that might have been missed by dosimetrists involved with the use of TLD albedo devices, which have been much more common than the relatively recent electronic neutron dosimeters.

In closing, insofar as neutron albedo is concerned, your observations may provide yet one more affirmation of author John Gray's claim that Men Are from Mars, Women Are from Venus.

Thanks for a fun question.

George Chabot, PhD, CHP