An automatic gamma-ray spectrometer equipped with a micro-robot for sample changing has been developed and constructed. The facility is comprised of a commercially available micro-robot, sample changer for up to 36 samples, personal computer programmed in BASIC language, input/output devices, detector and multichannel analyzer. This paper describes the components, software and effective uses of the above facility.
Semiconductor particle detectors are ideal for alpha spectroscopy due to their compact size, low noise, and high resolution.
This paper describes the construction and testing of an automatic sample changer for use with such a detector. The changer
was constructed from locally available services and materials. It holds up to 24 samples of alpha emitting material deposited
on 22 mm stainless steel counting planchets. The vacuum chamber can be evacuated to less than 10 μm mercury in 10 to 15 minutes.
Once the chamber has been evacuated and detector bias has been applied, any sample in the chamber may be selected for analysis,
either automatically or manually. Continuous automatic analysis of up to 24 samples is possible. Variation in efficiency from
position to position was found to be 3.25% at the detector-sample spacing of 4.8 mm, and 2.31% at 27 mm. Shielding between
the adjacent samples not under analysis and the detector was acceptable.
The Budapest Research Reactor’s Prompt Gamma Activation Analysis (PGAA) and Neutron-Induced Prompt gamma Spectroscopy (NIPS)
facilities were significantly upgraded during the last few years. The higher neutron flux, achieved by the partial replacement
and realignment of the neutron guides, made feasible the automation and specialization of the two experimental stations. A
new neutron flux monitor, computer-controlled beam shutters and a low-level counting chamber have been put into operation
to assist with in-beam activation experiments. An automatic sample changer has been installed at the PGAA station, while the
NIPS station was redesigned and upgraded with a Compton suppressor to use for the non-destructive analysis of bulky samples.
In the near future the latter setup will be completed with a neutron tomograph and a moving table, to turn it into a Neutron
Radiography/Tomography-driven PGAA equipment.
A Microbot Alpha robot has been interfaced to a Nuclear Data Model 680 multichannel analyzer (MCA) and computer to allow unattended accumulation and storage of gamma-ray spectra. Software was written in DEC RT-11 system language to control the robot, MCA and dual floppy disk system from a DEC LSI-11 microcomputer. Typically, 8 spectra are accomulated for 3 hours each, providing 24 hours of unattended operation for one detector or 12 hours for two detectors. The system has proven to be highly reliable and has eliminated the need for operator intervention after working hours.
The effect of small geometric errors in positioning samples in front of gamma detectors during instrumental neutron activation
analysis is discussed and it is shown that, for example, a 0.2 mm repositioning discrepancy for a source to detector distance
of 10 mm can cause errors in measured activity of as much as 4 per cent. This calculation has been undertaken for a range
of sample-detector distances (5–50 mm) in order to emphasise the importance of sample counting geometry on the accuracy of
INAA calibrations. Criteria derived from this investigation have been used to design and construct a simple samplechanging
wheel suitable for the routine analysis of low activity geological samples. The effect of the choice of sample wheel size
on the magnitude of spectral interference between counting and non-counting samples mounted in the wheel has been considered.
sample to sample [ 14 , 18 , 20 ]. If the bulk morphology of sampleschanges with various thickness, considering the effective contact resistances at the solid–solid interfaces should improve the accuracy of thermal conductivity measurements. Camirand
An automated neutron activation analysis data acquisition system has been assembled from commercially available equipment.
The modifications of the components needed to make this into a working system are described in the text. The main components
of the data acquisition system are a sample changer, a Ge(Li) detector, a magnetic tape deck and a minicomputer based multichannel
analyzer. The sample changer has a 200-sample capacity and can handle both solid and liquid samples. Software for controlling
the data acquisition system is flexible, yet simple to use. The system has operated reliably for a year and has sharply reduced
the effort needed for data acquisition.
The measuring system described in this paper, developed for non-destructive neutron activation analysis, consists of a semiconductor
detector gamma-ray spectrometer and a sample changer coupled to a PDP-9 computer via a CAMAC interface system. CAMAC modules
implemented in this system are an ADC interface, a sample changer control, display unit, a timer and a time-of-the-year clock.
The spectra are accumulated in a section of the computer memory. The computer is further used for experiment control and for
the analysis and interpretation of the measured gamma-ray spectra.
The inherent advantage of anti-coincidence counting of low-level radioactivity is defined in terms of changes in the limits of decision, detection and determination. It appears that the advantage factor can be expressed in the experimentally observed reductions of peak area, compton continuum and natural background. For an array equipped with a sample changer the advantage factor for interference by the compton continuum is4, while that for interference by the natural background amounts to 3. By sacrificing the sample changer and closing its gap with a Nal-plug, additional factors of 1.5 and 2 can be obtained for compton and natural background respectively.
The inherent advantage of anti-Compton counting of low-level radioactivity is defined in terms of changes in the limits of decision, detection and determination. It appears that the advantage factor can be expressed in the experimentally observed reductions of peak area, compton continuum and natural background. For an array equipped with a sample changer, the advantage factor for interference by the compton continuum is 4, while that for interference by the natural background amounts to 3. By sacrificing the sample changer and closing its gap with NaI-plug, additional factors of 1.5 and 2 can be obtained for compton and natural background, respectively.