Download TROUBLESHOOTING NUCLEAR INSTRUMENTS

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Chapter 4
4.
Check whether pulses are coincident with the
fluorescent lamps.
5.
Or with starting or running
parking.
6.
Unproperly filtered AC.
flickering
of
motorbikes and cars on an outside
Other origins of spurious counts may be:
7.
E l e c t r o s t a t i c discharges, especially in very dry laboratories.
8.
HV sparking due to dust or humidity or parts starting to fail.
9.
N e a r b y switching thyristors or triacs.
10.
When there are nearby radio or TV receivers, check whether the
instrument
is properly grounded. Try different points, and
check connections and coaxial cables. •
11.
E l e c t r i c a l discharge
humid ity.
12.
Loose cable c o n t a c t s .
ics in PM tube.
4.9
on
surface
of
components, due to high
Cable-movement-caused noise, raicrophon-
THE SPREAD IN THE NUMBER OF COUNTS IS LARGER THAN MAY BE
EXPECTED ACCORDING TO STATISTICAL FLUCTUATIONS WHEN
M E A S U R E M E N T S OF THE SAME SOURCE IN FIXED GEOMETRICAL
POSITIONS ARE DONE EACH DAY
Possible causes may be:
1.
An irreproducible source positioning.
2.
The use of different source holders or test tubes.
3.
Changes in the absorbing medium:
4.
The timer uses (the f l u c t u a t i n g ) AC frequency as time base.
5.
The setting of the HV is irreproducible or the HV is unstable.
6.
I r r e p r o d u c i b l e settings of the amplifier and/or SCA.
7.
Large temperature
ins t rumen t .
8.
Spurious counts.
9.
Large AC fluctuations.
10.
Unstable LV power supplies.
11.
Bad earthing.
dust or dirt in factories.
changes, or too short warming-up times
of
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