Dear Researchers,
I have an arrangement of ultraviolet lamps placed on each of the four walls of an upright rectangular structure as shown in the attached pix. The purpose of the arrangement is to disinfect fruits and vegetables in water, as the lamp is designed to operate in water thus the upright rectangular structure will be filled with water to the effective lamp height, excluding the sealings. Samples to be treated is designed to be equidistant from all four walls and the base, giving the position coloured yellow at the centre in the pix attached.
My Concerns:
1) Considering the fact that the ultraviolet lamp will transmit its energy through the medium (water) to the sample at the center, Is it proper use the effective dose (intensity * time) supplied to the system (volume of water) or that supplied to the centre where the sample is situated?
2) Depending answer supplied to concern 1, How do I determine the intensity so I can multiply by resident time so I can obtain the dose. I have tried different approaches. I have kept all lamps switched on and read intensities at various spots (coloured circles in pix) and found the average. Also since radiometer can only read intensity in one direction, to determine intensity at the centre, I kept one lamp switched on at a time, take the readings in its direction and found the average.
Your suggestions and observations will be highly appreciated.
Best Regards
Jay.
In terms of your experimental conditions, radiometer does not provide accurate readings, as you mentioned. The best method to determine the fluence rate is actinometry, using KI/KIO3 or ferrioxalate, depeding on what kind of UV lamps you are using. More details could be found from relevant literature.
First off, ensure that the lamps are designed for water immersion. If it is a mercury vapor lamp, it will require a quartz sleeve so that the lamp is not over-cooled. Direct water contact with a mercury lamp will cause it to operate very poorly (mercury will not vaporize).
Is the fruit going to be stationary at the point in the middle of the box? If so, then you need only consider the fluence rate (flux) from the lamp that can "see" the surface of the fruit. UV from the other side won't penetrate the fruit, of course! A submersible radiometer pointed directly at the relevant lamp(s) would work.
It's not clear to me how the top and bottom of the fruit would be irradiated. You don't show a lamp above or below the point of interest.
If the fruit is going to be transported through the volume (by flow?), then things get complicated. Actinometry solutions (see Rahn and others) will give a flow-weighted fluence measurement, but that may not be relevant for the path that the fruit would take. Same for microsphere actinometry (see Blatchley) - the beads may not follow the relevant path. Same for biodosimetry (flowing a solution spiked with phage such as MS2) - the viruses may not follow the relevant path. In addition, these methods would all quantify fluence from any direction that reached the molecule, microsphere, or virus. Fruit, being opaque, will shield the radiation from one side to the other.
Good luck!
Dear Michael
Thank you for your observations and insight.
Yes the lamps are designed for water immersion. It is a mercury lamp with quartz sleeve. The fruit is designed to be stationary at the point in the middle of the box. The design could not incorporate a lamp below or above the point of interest due to lamp design. The lamps are not completely immersible in water. The sealing contains the wiring hence should be outside the water. Any configuration to place the lamp horizontally above or below the point of interest to irradiate the top and the bottom would mean complete immersion with the sealing (electrical part). This is taken care of by placing four lamps around the box, and ensuring that the fruit is placed at the centre along the vertical length of the lamp. The theory is that radiation from the middle segment upwards will take care of the top of the fruit, while radiation from the middle segment downwards will take care of the bottom of the fruit.
I cannot lay my hands on a submersible radiometer at the moment, but I had placed the lamp in the box without water and pointed a radiometer at the relevant lamps. For this I have four different readings for the four different lamps.
How do I get the effective or average intensity from these four readings. Is it just a simple average of the four readings or is there a special formula to calculate this?
Regards,
Jay
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