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We took some high-quality images of Echinacea achenes for our q2 experiment this fall; an example is below. Notice how easy it is to distinguish empty achenes from those with embryos. By darkening the room and removing the opaque film, we were able to use lower levels of xrays for a shorter duration than we have previously. This plate was exposed to 12kV x-rays for 4s. We used long, thin glassine envelopes to facilitate counting. Notice also that the laser-printed labels reveal the packet IDs. xrayimage648.1.png
X-ray image of 30 packets of achenes from
Echinacea angustifolia. Click on thumbnail to enlarge.
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What is a typical radiation dose experienced by an Echinacea seed when we x-ray Echinacea fruits to assess seed set?

We usually put the seeds on the bottom tray and the setting 10 s @ 18 kV. According to the documentation on dosage for our x-ray machine 18 kV outputs 292.6 R/h when the dosimeter probe is 57.2 cm away (that's the shelf with 1:1 magnification). The dose unit quote here R is Roetngen.

A little arithmetic can tell us total Roentgens for a ten second exposure:

\( 10 s \frac{1 h}{60 min} \frac{1 min}{60 s} 292.6 \frac{R}{h} \)

In R code, that's

10 * 1/60 * 1/60 * 292.6
## [1] 0.8128

0.8128 R (Roentgen)

We may put the seeds on a higher shelf for more magnification, maybe 1:1.5 or the 1:2. We can enter dosages from each shelf from the documenation on exposure levels by shelf to estimate how much higher the dose is.

lvl <- c(1, 1.5, 2, 3, 4, 5)
RPM <- c(7.815, 20.55, 42.55, 115.45, 232, 397)
data.frame(shelf = lvl, dose = RPM)
##   shelf    dose
## 1   1.0   7.815
## 2   1.5  20.550
## 3   2.0  42.550
## 4   3.0 115.450
## 5   4.0 232.000
## 6   5.0 397.000

The dose on the 2x magnification shelf is RPM[3]/RPM[1] = 5.4447 times greater than the dose on the 1:1 shelf. Doubling the magnification generally should increase the dose by a factor of 5.4. Let's check: the dose on the 4x shelf is RPM[5]/RPM[3] = 5.4524 times greater than the dose on the 2x shelf. Also, the dose on the 3x shelf is RPM[4]/RPM[2] = 5.618 times greater than the dose on the 1.5x shelf. Close.

The expected dose at the stadard settings is 0.82 R on the bottom shelf and 0.8128 * 5.5 = 4.4704, or about 4.5 R on the 2x shelf.

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Here is Sebastian Di Clemente's final report on the main project of his internship:

X-ray Radiation Effects on
Germination and Growth of Echinacea angustifolia


DiClementeReport2012-06-01.pdf

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