Capintec CRC-712MX, Руководство пользователя, Страница: 54 / 68

CAPINTEC, INC. CRC
®
-712MX
The collection voltage across the chamber sets up an electric field. The positive ions will drift
towards the negative electrode and the electron (and negative ions if they are formed) will
drift towards the positive electrode, thus producing a current. The electronic circuitry then
measures either the current or the total charge produced during the period of interest.
The number of ions produced in the chamber is directly related to the energy deposited in the
chamber by the radiation.
DETERMINING CALIBRATION SETTING NUMBERS
A method of determining a calibration setting number is described in this section.
1
RESPONSE and Sensitivity
It is very convenient to express the response of the detector to a radioisotope, A, relative to
that of a standard reference material, e.g. Co60.
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
≡
Co60 SRM of Activity Certified
Co60 SRM to due Output Detector
A Sample of Activity
A Sample to due Output Detector
R
A
(1)
The sensitivity of the detector for a photon of energy E
i
is defined as:
60 - Co of Curie one to due Output Dtector
E of Photons 10 3.7 to due Output Detector
i
10
i
×
≡
S
(2)
The detector response and the sensitivity have the following relation:
(3)
∑
≡
i
i i
S I
i
R
Where I
i
is the intensity of the photon whose energy is E
i
.
The procedure is to measure the response of the detector to all the available primary
standard samples and to establish the sensitivity of the detector as a function of photon
energy so as to satisfy equation (3) for all standards.
Once the sensitivity curve has been determined, the response of the detector to any
radioisotope may be calculated using equation (3), provided that the decay data are known.
1 See Suzuki, A., Suzuki M.N., and Weis A.M.: Analysis of a Radioisotope Calibrator; Journal of Nuclear Medicine Technology,
Dec. 1976 for more detailed discussions.
A1 - 6 APPENDIX I January 08