Proceedings of Topical Meeting on Optoinformatics (pdf-format, 1.21 ...

SAINT-PETERSBURG, October 17 – 20, 2005 27
ESTIMATION OF INFLUENCE OF STATISTICAL ERRORS ON AN
ACURACY OF CALIBRATION OF THE SPACE SOLAR PATROL
INSTRUMENTATION AT A SYNCHROTRON RADIATION SOURCE
Afanas’ev I.M., S.I. Vavilov State Optical Institute, Tuchkov lane, 1; St. Petersburg,
199034, Russia; e-mail: afanasy@rambler.ru
In the article the values <strong>of</strong> statistical errors, dealt with random character both
emitting <strong>of</strong> synchrotron radiation (SR) in a storage ring, and registration <strong>of</strong> a
SR by a receiving tract <strong>of</strong> the Space Solar patrol (SSP) instrumentation, are
evaluated.
The SSP instrumentation has been created to monitor the ionizing radiation from the
Sun in the spectral range 0,14 – 198 nm from space apparatus. It consists <strong>of</strong> a Radiometer
with 20 filters and two grating spectrometers [1] . The absolute spectral calibration <strong>of</strong> the
SSP instrumentation in the spectral range from 0,25 up to 122 nm (5000 - 10 eV) has been
preparing by the special metrological stations at the SR sources <strong>of</strong> the storage rings
VEPP-3 and VEPP-4 (at the G.I. Budker Institute <strong>of</strong> Nuclear Physics, Novosibirsk,
Russia) [2] . All SSP measuring channels have "solar-blind" detectors – open secondaryelectron
multipliers (SEM), which have high sensitivity to radiation below 160 nm [1] . The
registration <strong>of</strong> radiation by the SSP instrumentation is realized with SEM in pulse mode.
The aleatory variable <strong>of</strong> fluctuation <strong>of</strong> counting rate f (which is the SSP output
signal [3] ) is taken into account by the apparatus error σ app , which is distributed accordingly
normal law. It is stipulated by random character both SR beam intensity I, and losses in the
SSP registering channel η. [3] In the given calculation, the losses are admitted to the
constant value η=τ⋅γ=10 -4 electron/photon (thus, not taking into account their spectral
character), where τ - effective transmission <strong>of</strong> the SSP channel (mainly, filters for the
Radiometer and a polychromator for spectrometers; for both cases τ is about 10 -2 ) [4] , and γ
- quantum efficiency <strong>of</strong> the SEM photocathode (average value is about 10 -2 ) [4] . Thus, the
signal <strong>of</strong> counting rate will amount to f=I⋅η=10 4 pulses/sec, at the SR beam intensity I=10 8
photon/sec (see, table). The root-mean-square deviation f from the expected aleatory
variable f is "noise" <strong>of</strong> the SSP output signal, which hinders the measured signal the more,
the lower value <strong>of</strong> a counting rate (i.e. the lower level a loading <strong>of</strong> a SSP registering
channel).
For unambiguous explanation <strong>of</strong> calibration results it must be used the one-electron
mode at measurements. The two-electron event is considered as a certain hindering factor -
"noise". It should be noticed, that the multi-electron events at the given estimation are not
considered. As a matter <strong>of</strong> fact, the ratio <strong>of</strong> probabilities <strong>of</strong> one and two-electron events
P(1)/P(2) is the "signal-to-noise merit", inverse value <strong>of</strong> which is the statistical error σ stat .
It is supposed, that probability distribution <strong>of</strong> aleatory variable <strong>of</strong> appearing <strong>of</strong> one,
m −λ
two, etc. photoelectron events at experiment is described by the Poisson law: λ ⋅e
P(
m)
= ;
m!
where λ - expectation, which is the multiplication <strong>of</strong> the SR beam intensity I
(including its modulation with frequency <strong>of</strong> circulation <strong>of</strong> electron beam f VEPP-4 at the
VEPP-4 storage ring about 1 MHz) [3] by attenuation losses at the registering tract η;
m – value <strong>of</strong> acts <strong>of</strong> photoelectron emission from the SEM photocathode (i.e.
appearance <strong>of</strong> one-electron event (OEE) if m=1, two-electron event (TEE) if m=2, etc).