1. Applications in biology
Part-XI
Applications in biology

2. Optical readout:
similar to spark counters,
but using CCD
and
special gas mixtures to obtain
intense light emission from
avalanches

3. Application in biology

4. Fig. (a) Images of the tritiated rat-kidney slice obtained with a gaseous detector : 256 grey level window centred at three different levels, in order to display details of very different intensity. Details of the renal ducts of about 50 µm are visible. Top right is the intensity distribution along the oblique line in the top- left picture, with a screen pixel width of 40 µm in the plane of the sample.
(b) Autoradiography. Image of the rat kidney slice, adjacent to the preceding one, to which aphotographic emulsion was apposed during 3 months.

5. Image of an electrophoresis gel with compounds labelled with 35S
Image of an electrophoresis gel with compounds labelled with 35S. Portion of a two-dimensional gel, with the intensity distribution along the oblique line.

6. Activity distribution in brain slices of female (above) and male (below) rats labelled with tritiated vasopressin (the real size is about 10 by 5 mm2).

7. Commercial devices

11. Application in Micro -nanodosimetry
While current dosimetric techniques are limited to measuring global or integral radiation effects, contemporary radiobiological concepts advocate the differential measurements. Indeed, because of the highly fluctuating stochastic nature of the energy deposits, it is important to measure not only the deposited energy by an event, within a given tissue-equivalent volume, but also the spatial distribution of the ionization pattern. Most signifcant damage occurs at the sub-cell level, more precisely to the DNA molecules.
It is currently established that irreversible radiation damage to a living cell occurs when its DNA is considerably upset. This occurs when a signifcant energy quantum is deposited within a small DNA segment, typically 30 bases long, causing multiple breaks in both DNA strands. In such events the cellular repair mechanism fails to correctly repair the damage, which results in cell mutations or death.

12. Images of ionizing particle track patterns recorded in an optical avalanche microdosimeter, on a tissue-equivalent scale shown in the figure. The 5MeV protons and 19MeV alpha particles traverse a gas volume at a pressure of 20 Torr. The potentially lethal to the DNA track spots are that of high local ionization, like the endpoints of the delta-electron trails, clearly observed in the figure.

13. MWPC in biology
(electronic readout)

14. Regional uptake of deoxyglucose under effort
Regional uptake of deoxyglucose under effort. The activity distribution in slices of a dog's heart is recorded following repeated stimulation of specific cardio- pulmonary nerves after injection of triziated deoxyglucose.