Firma:              Canberra-Packard

Modell:                         Cobra 5002

Kommentar:     Dokumente engl.

Figure 1-1. Cobra 5000 Series Single Detector Gamma Counting System.

SYSTEM DESCRIPTION

The Cobra 5000 series automated, single detector gamma counting system is designed for the detection and quantitative measurement of gamma radiation. It can be configured as a 2 inch (Model 5002) or 3 inch (Model 5003) crystal unit. The system is controlled by an IBMO-compatible computer (Figure 1-1).

Physical Dimensions

Height:         28 inches (71 cm)

Width:          27 inches (69 cm)

Depth:         32 inches (81 cm)

Weight:        400 lbs (181 kg), Model 5002

                   500 lbs (226 kg), Model 5003

IBM is a registered trademark of International Business Machines Corp.

Electrical Requirements

100 to 122 VAC ±10% at 50/60 Hz or

200 to 244 VAC ±10% at 50/60 Hz

350 VA maximum

The System must be connected to a stable power source. The system provides automatic restart after a power failure.

Environmental Requirements

Operating Temperature:         60 to 95 degrees Fahrenheit (°F)

                                               15 to 35 degrees Celsius (°C)

Relative Humidity:                   30 to 85 percent noncondensing

The instrument should be located away from all sources of radiation (X-ray machines, radiation storage vaults, etc.).

Detector

The detector consists of a 2" or 3" thallium-activated, sodium iodide crystal of the through-hole design. The crystal is optically coupled to a photomultiplier tube (PMT). The detector is surrounded by a minimum of 2" of lead (for a 2" detector) or 3" of lead (for a 3" detector).

Sample Changer

The automatic, unidirectional (clockwise) sample changer consists of paired fabric belts which move sample cassettes along the deck to and from the detector. The sample is positioned under the detector by chain-driven pins which engage the sample cassette as it moves against the detector assembly wall. The sample is loaded into the detector by an elevator which pushes the tube up into the detector. A counterweight helps to guide the sample in and out of the detector. An optical tube sensor monitors the cassette, and bypasses missing tubes.

System Control

The system is controlled by an IBM-compatible computer which is configured with one 720kb, 3.5" floppy disk drive and one 20Mb hard drive. The computer contains 640kb of RAM memory, a serial RS-232 communication port, a parallel printer port and a color graphics adapter (CGA) for the video output. The video signal is displayed on a 12" amber screen monitor. The printouts are produced by a dot matrix printer. The keyboard is an "AT" style with ten function keys on the extreme left side. These function keys provide the user with the means to control the instrument.

The analysis of samples (counting and data reduction) is controlled by 60 user-defined protocols. These numbered protocols are automatically called by Speed-Pro clips which attach to the sample cassettes. This provides the user with the "walk away" concept of sample analysis. To analyze samples, the user needs only to define a protocol, load the samples in a cassette with the appropriate protocol clip and start the instrument. The samples are counted, the data are reduced and printed without any additional user intervention.

INSTRUMENT SPECIFICATIONS

The specifications for the Cobra 5000 series gamma counter are described as confirmed by Packard reference methods at Downers Grove, Illinois. These specifications apply to the Cobra Model 5002 and Model 5003.

PHYSICAL DIMENSIONS

Height:              28 inches (71 cm)

Width:              27 inches (69 cm)

Depth:              32 inches (81 cm)

Weight:            400 lbs (181 kg) for Model 5002

                        500 lbs (226 kg) for Model 5003

ELECTRICAL REQUIREMENTS

100 to 122 VAC ± 10% at 50/60 Hz or

200 to 244 VAC ± 10% at 50/60 Hz

350 VA maximum

The system must be connected to a stable power source.

ENVIRONMENTAL REQUIREMENTS

Operating Temperature:         60 to 95 degrees Fahrenheit (°F)

                                               15 to 35 degrees Centrigrade (°C)

Relative Humidity:                   30 to 85 percent (noncondensing)

The instrument should be located away from all sources of radiation (X-ray equipment, radiation storage vaults, etc.).

DETECTOR

The detector consists of a 2” or 3" thallium-activated, sodium iodide crystal of the through-hole design. The crystal is optically coupled to a photomultiplier tube (PMT).

Shielding

The detector is surrounded by a minimum of 2 inches (Model 5002) or 3 inches (Model 5003) of lead shielding.

Energy Range

¹²⁵ I Preset Region:       15 to 75 keV

⁵⁷ Co Preset Region:     75 to 165 keV

⁵¹ Cr Preset Region:      240 to 400 keV

⁶⁰ Co Preset Region      1050 to 1550 keV

⁷⁵ Se Preset Region:     60 to 467 keV

¹³¹ I Preset Region:       260 to 470 keV

⁵⁹ Fe Preset Region:     940 to 1400 keV

²² Na Preset Region:     433 to 1417 keV

Manual Region:              15 to 2000 keV (adjustable)

When counting high energy radionuclides, sample changer deck-to-detector crosstalk may occur.

Efficiency

The following efficiencies were determined using 12x75 mm polypropylene plastic tubes.

NOTE

Use of glass tubes may lower the efficiencies to the point where an efficiency failure message may be reported.

As counted in preset region:

For 2" detector            ¹²⁵ I:         > 72%

For 3"" detector            ¹²⁵ I:        > 74%

Resolution

For 2" detector            ¹²⁵ I:         ≤ 32%

For 3" detector            ¹³⁷ Cs:    ≤ 12%

Background

As counted in preset regions (empty tube in the counting chamber, at Downers Grove, Il. facility):

For 2" detector             ¹²⁵ I:         < 50 CPM

For 3" detector             ¹²⁵ I:        < 50 CPM

Spilldown

⁵⁷ Co into ¹²⁵ I preset region (at elevator position 1): < 3%

SAMPLE CHANGER

The automatic sample changer consists of paired fabric belts which move the sample cassettes along the deck to and from the detector. The sample is positioned under the detector by chain driven pins which engage the sample cassette as it moves against the detector assembly wall. The sample is loaded into the detector by an elevator which pushes the tube up into the detector. A counter weight helps to guide the sample in and out of the detector. An optical sensor monitors the cassette, and bypasses missing tubes.

Sample Cassettes

Length:       10.48"

Width:         0.90"

Height:        2.875"

Sample Tubes

                   DIAMETER (mm)                        HEIGHT (mm)                        

                            12mm                        75-87mm (Including cap)

Caps for sample tubes are not to exceed the outside diameter of the tubes. If caps are used, no more than two capped tubes can be in adjacent cassette positions.

SYSTEM CONTROL

The system is controlled by an IBM-compatible computer which is configured with one 720kb (3.5") floppy disk drive and a 20 Mb hard drive. The computer contains 640kb of RAM memory, a serial RS-232 communication port, a parallel printer port and a color graphics adapter (CGA) for the video output. The video signal is displayed on a 12" amber screen monitor. The printouts are produced by a dot matrix printer. The keyboard is an "AT" style with ten function keys on the extreme left side.