Document Details


Title:
A NEW TYPE OF STANDARD FREE-AIR CHAMBER FOR HIGH QUANTUM ENERGIES
Author(s):
Subject Terms:
DOSIMETRY; MEASURING INSTRUMENTS; ENERGY; MEASURING METHODS; IONIZATION; DATA; PHOTOGRAPHS
Document Location:
Location - NNSA/NSO Nuclear Testing Archive Address - P.O. Box 98521 City - Las Vegas State - NV Zip - 89193-8521 Phone - (702)794-5106 Fax - (702)862-4240 Email - CIC@NV.DOE.GOV
Document Type:
REPORT
Publication Date:
1977 Dec 09
Declassification Status:
Never classified
Document Pages:
0008
Accession Number:
NV0062689
Document Number(s):
IAEASM2221
OpenNet Entry Date:
1994 Aug 26
Description/Abstract:
THE CONVENTIONAL FREE-AIR CHAMBER IS EMPLOYED FOR THE EXPOSURE STANDAR DIZATION OF X-RAYS GENERATED AT POTENTIALS UP TO A FEW HUNDRED KILOVOL TS, IE. FOR SECONDARY ELECTRON RANGES BELOW 1 M. TWO METHODS TO ATTAI N TO HIGHER ENERGIES HAVE BEEN PUBLISHED: SUPPRESSING ELECTRON RANGES BY OPERATING THE CHAMBER UNDER A HIGH PRESSURE, AND FORCING ELECTRON TRAJECTORIES INTO SPIRALS BY A MAGNETIC FIELD PARALLEL TO THE PHOTON B EAM. THE FIRST METHOD LEADS TO INCREASED ION RECOMBINATION CAUSING AD DITIONAL INACCURACY, THE SECOND LEAVES THE REQUIRED CHAMBER LENGTH UNC HANGED. THE SECONDARY ELECTRON TRAJECTORIES CAN ALSO BE CONFINED BY A MAGNETIC FIELD ORTHOGONAL TO THE PHOTON BEAM. THIS IS ACHIEVED BY ME ANS OF A TOROID WINDING, WHICH IS INTERSECTED BY THE BEAM PARALLEL TO THE TOROID SYMMETRY AXIS Z. THE FREE-AIR CHAMBER INSIDE THE TORUS CON SISTS OF TWO CYLINDERS (HIGH VOLTAGE ELECTRODE AND COLLECTOR-GUARD ELE CTRODE ASSEMBLY) AND TWO END PLATES (GUARD STRIP ASSEMBLIES). THE MAG NETIC FLUX DENSITY IS INVERSELY PROPORTIONAL TO THE DISTANCE R FROM TH E AXIS, THE LINES OF INDUCTION BEING AROUND IT. THE REQUIRED CHAMBER CROSS-SECTION IS DEFINED BY THE SECONDARY ELECTRON TRAJECTORIES IN THE RZ-PLANE. THESE ARE PERIODIC LOOPS WITH A NET DRIFT ALONG Z, AND CAN BE EXPRESSED IN TERMS OF BESSEL FUNCTIONS. THE PRODUCT, MASS OF THE WINDING MULTIPLIED BY POWER DISSIPATION IN IT DEPENDS ON THE MAXIMUM E NERGY T OF SECONDARY ELECTRONS BUT NOT SIGNIFICANTLY ON OTHER DESIGN P ARAMETERS. FOR COPPER A VALUE BELOW 10E07.(T/MEV)E04 KGW CAN BE ACHIE VED. THUS THIS METHOD IS FEASIBLE FOR EG. THE COBALT-60 QUANTUM ENERG IES (T=1.1 MEV). AN EXPERIMENTAL CHAMBER FOR X-RAYS IS DESCRIBED. TH E CHAMBER LENGTH IS 250 MM AND THE ELECTRODE RADII ARE 85 AND 195 MM. THE DESIGN ALLOWS SELECTION AMONG EIGHT COLLECTOR ELECTRODES AND AN A DJUSTABLE BEAM TO AXIS DISTANCE. THE WINDING CONSISTS OF 36 TURNS OF WATER COOLED COPPER TUBING, CARRYING A CURRENT OF 833 A MAXIMUM. MEAS UREMENTS OF THE IONIZATION AS A FUNCTION OF THE MAGNETIC INDUCTION ARE REPORTED.


<< Return to Search Results