RADIATION POLYMERIZATION DOSIMETRY

Technical Report · Fri Oct 31 04:00:00 EST 1958

OSTI ID:4305895

Hoecker, F E; Brown, D Q; Han, J T

Quantitative studies of the high energy radiation photo sensitivity of certain liquid monomer-polymers have indicated a possible solution to the problem of high level dosimetry. Investigations of the relation between absorbed dose and factors which influence sensitivity have led to the development of a dependable system of radiation polymerization dosimetry. Changes in the composition of the liquid permit preparation of dosimeters which cover an x ray, gamma-ray dose range from 7.5 x 10/sup 4/ to 10/sup 7/ rads. Pre-irradication permits increase of sensitivity which is predictable when radical decny with time is taken into account. Experimental data are obtained by the use of dosimeter cells each consisting of a No. 000 gelatin capsule containing approximately one ml of dosimetric liquid, an air bubble and a 3 mm diameter lead sphere. Gel phase polymerlzation, a sudden transition from liquid to gel which occurs within a dose increment of 5% of the total dose, is taken as thae end-point index and is indicated by the movement of the sphere to the boundary between gel and liquid upon inversion of the cell after irradication. Exposure of the cell to isotropic radiation results in uniform polymerization and failure of the sphere to move after exposure to the design dose. Exposure of the cell witha its axis vertical and parallel to the intensity gradient ia directional beams of x- or gamma-rays or high energy electrons yields quantitatlve data when the axial exteat of gelation in m.m. in calibrated in terms of delivered dose. Most of the studies use a styrene-polyester as the dosimetric liquid in which radiation absorption produces radicals eventuating in long chain and crosslinked macromolecules. Radiation sensitivity depends upon the composition which may be varied in a number of ways. Elemental iodine used as an inhibitor to reduce the sensitivity, acts as a radical scavenger to give a linear relation between dose and iodine conceatration which yields a G value of approximately 7. The sensitivity of the basic dosimetric liquid remains stable for several months after a 5.5% increase in sensitivity during the first four days after preparation. Self terminntion of the cross-linkage and chain formation is insured by a process interpreted as radical decay revealed by fractionation of exposure with increasing time between fractions. The data lead to an approximately exponential decay curve but the offect appears to be complex possibly due to competition between chain formation and degradation with different time constants. Sensitivity dependence on dose rate dees net appear significant between 10/sup 2/ rads/min and 10/sup 5/ rads/min for x rays and for gamma rays from spent fuel elements. A factor of approximately 2 between doses required for 250 kv x rays at 5000 rads/min and 2 Mev eleetrons at 10/sup 6/ rads/min may be due to lower values of linear energy transfer for the high energy electrons although dose rate drpendence clearly appears at 10/sup 7/ rads/min for electrons. Evaluation of radiation polymerization as a dosimetric system involves the consideration that it is based on physico-chemical processes similar to those which occur in food preservation and drug product sterilization by radiation. It suggests the possibility of radiation measurement by processes similar to those it is intended to monitor. The dosimeter is small in size, expendable, self contained and readable without auxiliary equipment by untrained personnel. (auth)

• Research Organization: Kansas. Univ., Lawrence
• NSA Number: NSA-12-014933
• OSTI ID: 4305895
• Report Number(s): A/CONF.15/P/2009
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

ABSORPTION
COLLOIDS
CONFIGURATION
DECAY
DOSEMETERS
ELECTRONS
FUEL ELEMENTS
GAMMA RADIATION
IODINE
LEAD
LIQUIDS
MOLECULES
MONITORING
PHYSICS
POLYESTERS
POLYMERS
RADIATION DOSES
SENSITIVITY
STABILITY
STANDARDS
STERILIZATION
STYRENE
X RADIATION