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Detector Shields

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CosmicGuard™ – Cosmic Veto Background Reduction System

CosmicGuard™ – Cosmic Veto Background Reduction System

Description

CANBERRA’s CosmicGuard is a simple add-on to any new or existing High Purity Germanium (HPGe) counting system that includes a Lynx Digital Signal Analyzer and Genie 2000 or Apex-Gamma spectroscopy software. The fully self-contained guard detector/electronics module either mounts directly onto a lead shield with a solid 50.8 or 55.9 cm (20 or 22 in.) diameter circular lid or via a lift mechanism that clamps to the shield table for top-opening or non-circular shields. The system connects directly to the HPGe detector’s Lynx DSA and a controlling Genie or Apex® computer – no NIM or other electronics is needed.

Why is cosmic background reduction important?

Background in gamma spectroscopy systems comes from three main sources: Terrestrial Radiation, Internal Radiation and Cosmic Radiation.

Terrestrial Radiation is driven by K-40, Uranium, and Thorium decay products and is greatly reduced by passive lead shielding.

Internal Radiation can come from the HPGe detector components or from the sample itself due to incomplete energy deposition in the detector (scattering) and from some of the detector/shield components themselves. In many counting systems, the scattering component will be present, although Compton suppression solutions can be applied in some instances to reduce this form of background. CANBERRA detectors are already built using selected materials to minimize the detector’s contribution to the radiation background. To further reduce this background component CANBERRA offers cryostat options like Remote Detector Chamber (RDC) or Ultra-Low Background (ULB) materials.

Cosmic Radiation consists of high energy charged particles (such as muons) originating from extraterrestrial sources. This form of background radiation cannot be significantly reduced by passive lead shielding. It is omnidirectional, but primarily vertically oriented. Therefore, a guard detector placed over an HPGe detector’s shield and equipped with anti-coincidence logic can eliminate much of the cosmic contribution to background. In this case, radiation detected in both the guard detector and HPGe detector at the same time can cause those counts from the HPGe detector to be discarded, thus reducing the cosmic background contribution.

Background reduction achieved by the CosmicGuard system ranges from 15 to 40 percent. In fact, a higher background reduction ratio is seen on HPGe detector systems that already have shielding, especially those that include ULB cryostat configurations and shields (like CANBERRA’s 777). With other sources of background minimized, the cosmic component of the remaining background can only be reduced with a guard detector-type set-up.

Features

  • Performs Cosmic background reduction that can’t be done with lead shielding alone
  • Typical background reduction by 15–40% resulting in lower MDA’s and count times
  • Turnkey solution that can be added to new or existing HPGe detector/shield configurations
  • Compatible with most standard HPGe Lead Shields – split or solid top
  • Electronics for Veto Guard Detector built into detector module – no NIM modules or other additional signal processing electronics required
  • Single cable connection to the acquisition PC or network hub
  • Simple software interface for set-up
  • Requires Lynx® Digital Signal Analyzer and Genie™ 2000 or Apex-Gamma™ software of current firmware/software versions

CosmicGuard™ – Cosmic Veto Background Reduction System

Model 767 Front Opening Split-Top Shield

Model 767 Front Opening Split-Top Shield

Description

The 767 is a full-size and full-featured lead shield for use with germanium detectors having a vertical orientation. It has several unique design features and is built with a great deal of attention to fit and finish. The 767 features 10 cm (4 in.) lead thickness and is jacketed by a 9.5 mm (3/8 in.) steel outer housing. The graded liner consists of a tin layer of 1 mm (0.040 in.) thickness and a copper layer of 1.5 mm (0.062 in.) thickness. There is no exposed lead in the 767 with or without the doors closed. The inside dimensions are 28 cm (11 in.) diameter by 40.6 cm (16 in.) high.

The top doors of the 767 are linked so they open and close together regardless of which is actuated. The front door opens to the right on precision adjustable hinges and provides full shield access.

Top doors are linked - so they open and close together - Front door provides full-area access

A novel latch secures both the front and top doors and provides a means to lock the shield with a user-supplied padlock.

The shield table is equipped with leveling legs and with braces which allow the assembled shield to be moved with a simple pallet truck.

The 767 is finished outside with an attractive textured light gray epoxy paint. The copper interior has a brush grain finish with a clear polyurethane coating to retard tarnishing.

Features

  • Four-inch low background lead
  • Graded tin and copper liner
  • Fully clad - no exposed lead
  • Full area front door
  • Synchronized split top door
  • Lockable door latch
  • Textured epoxy finish

Model 767 Front Opening Split-Top Shield

Model 747 and 747E Lead Shield

Model 747 and 747E Lead Shield

Description

The Model 747 CANBERRA Lead Shield is intended for use with Germanium detectors. It will prevent high background counts due to external sources, thus reducing counting times and improving the lower limit of detection. This shield is compact and easy to use with only 0.4 m2 (4 ft2) of floor space required. The shield may be set up so that the door opens right or left without need for clearance to the rear. A convenient lever-actuated door lift allows the door to be placed firmly on the shield to prevent direct path radiation from entering.

The 1 mm (0.040 in.) tin and 1.6 mm (0.062 in.) copper graded liner prevents interference by lead x rays. The exterior is attractively finished with light grey textured paint, the interior is coated with clear polyurethane to prevent oxidation and facilitate cleaning. The floor of the shield has a 12.1 cm (4.75 in.) diameter hole which will accommodate either flanged or slimline cryostats.

The 747E model is 10 cm (4 in.) shorter than the standard 747 and does not have a door lift mechanism.

A number of options are available.Four-inch long, clamp-on cold finger extensions are available for most cryostats. Preamp hardware Option PHW (for CANBERRA Preamp) is also required to ensure that flanged cryostats fit within the 28 cm (11 in.) shield diameter. Adjustable foot pads provide a convenient means for leveling. Optional annular lead plugs are available to minimize the streaming path through the hole in the shield floor. A detector lift and taller table are available to accommodate installation of other cryostat types, such as the Cryo-Pulse® 5 Plus, MAC's and 7500SL-RDC. See option list on back for details.

Features

  • 4-inch thick low-background lead
  • Easy-to-use lever-actuated door
  • Compact – 2 foot by 2 foot floor space
  • Graded tin and copper liner
  • Adjustable foot pads

Model 747 and 747E Lead Shield

Model 777 Ultra Low-Background Shield

Model 777 Ultra Low-Background Shield

Description

The CANBERRA 777 is an ultra low-background lead shield for germanium gamma-ray detectors. It features 50% greater lead thickness than that of typical lead shields and is constructed from materials carefully selected for low background. The 777 is available in three versions which complement CANBERRA ultra low-background cryostats. The 777 (pictured right) can accommodate either a vertical dipstick slimline cryostat or a U-style cryostat. The 777A accommodates vertical dipstick cryostats only such as the 7500SL with a remote detector chamber (Model RDC-6). The 777B accommodates only U-style cryostats. All versions of the 777 are equipped with a swing-top door for sample chamber access and a door lift mechanism which allows the door to fit tightly against the shield body.

Background radiation from lead is dominated by 210Pb because other elements are chemically separated fairly effectively in the refining process. 210Pb decays with the emission of a 46.5 keV gamma ray. This gamma ray is generally absorbed by the tin-copper liner and may be below the energy range of the detector so it is of little concern. The 210Bi daughter of 210Pb, however, is of concern. It is an energetic beta emitter and bremsstrahlung from this beta gives rise to a continuum of background counts ranging up to 500 keV. For this reason, the 777 is constructed with layered bulk lead. The outer five inches is ordinary low-background lead while the innermost one inch is selected for 210Pb content of about 20 Bq/kg. This thickness of lead will stop the bremsstrahlung from the outer lead volume.

The 777 has a graded liner to stop the lead K-shell x rays in the energy range of 75-85 keV. Liner materials are low background tin with a thickness of 1 mm (0.040 in.) and high purity copper with a thickness of 1.5 mm (0.060 in.).

The 777 is equipped with a gas port for the introduction of gas (bottled air or nitrogen) to flush the shield interior and reduce background from radon and radon daughters. Boil-off nitrogen from the LN2 cryostat is a free source of gas but care must be taken to prevent liquid nitrogen from entering the shield and freezing the cryostat seals. An N2 purge kit is available from CANBERRA for most cryostat types.

The 777A (see illustration in PDF) is supplied with a table which supports the shield above the LN2 Dewar. This shield has an opening in the floor and a split annular back shield which surrounds the cryostat RDC neck. The 777B (see illustration in PDF) is attached to a steel plate which normally sits on the floor. The 777B has a side port which accommodates the horizontal arm of a U-style cryostat and a rectangular plug which is withdrawn vertically to provide access to the port. An optional cryostat stand (Model 777-5) is available to support the cryostat.

Features

  • 15 cm (6 in.) lead thickness
  • Ultra low-background materials
  • Versions for vertical or U-style cryostats
  • Purge port for radon expulsion
  • Graded tin-copper liner

 

Model 777 Ultra Low-Background Shield

Model 737 Lead Shield

Model 737 Lead Shield

Description

The Model 737 Lead Shield is designed to accommodate U-style cryostats which have a vertical detector chamber located at the end of a horizontal arm extending from the side of the Dewar. This detector/shield arrangement excludes the preamplifier and other hardware from the shield volume and eliminates all line-of-sight streaming paths to the detector element. These factors can contribute significantly to overall background reduction in the counting system.

Unlike most shields of this type, the 737 is designed for ease of detector installation with a narrow, stepped plug providing access for the horizontal arm of the detector. This plug is removed vertically, thus minimal space is required between the shield and the Dewar with attendant reduction in floor space required for the system.

Like the Model 747 Shield, the 737 has a graded copper-tin liner and is jacketed by 3/8 in. steel finished in an attractive light grey textured paint which matches other CANBERRA products. The exclusive CANBERRA door lift mechanism allows the shield door to close lightly against the shield body, reducing the streaming path to virtually nothing.

Lead Shield Model 737 - U-Style

Features

  • "No stream" design for U-style cryostat
  • Low center of gravity
  • Four-inch low background lead
  • Graded tin and copper liner
  • Easy detector installation
Lead Shield Model 707/707M - Slimline

Lead Shield Model 707/707M - Slimline

Model 707 Lead Shield

  • Economical and light weight
  • For Slimline cryostats
  • Construction: steel jacket, lead bulk, Sn/Cu liner
  • Dimensions:
  • 152 mm (6 in.) inside diameter
  • 254 mm (10 in.) inside depth
  • 51 mm (2 in.) lead thickness
  • Table included: 61 x 61 cm (24 x 24 in.) x 68-76 cm (27-30 in.) high
  • Shipping weight - 250 kg (550 lb)

Model 707 Lead Shield

Model 707M Modular Lead Shield

  • Modular construction
  • Maximum component weight- 227 kg (500 lb)
  • For Slimline cryostats
  • Construction: steel jacket, chevron lead rings, Sn/Cu liner
  • Dimensions:
  • 152 mm (6 in.) inside diameter
  • 254 mm (10 in.) inside depth
  • 102 mm (4 in.) shield thickness
  • Table included: 61 x 61 cm (24 x 24 in.) x 68-76 cm (27-30 in.) high
  • Shipping weight - 646 kg (1425 lb)

Model 707M Modular Lead Shield

Ge Detector Accessories

Ge Detector Accessories

Model 7413, 7413F Detector Tripod

  • For field measurements
  • Heavy duty construction
  • 7413 accommodates Slimline, MAC or Big MAC
  • 7413F accommodates Flanged, MAC or Big MAC
  • Detector element elevation (<30 cm to >120 cm)
  • Built-in level
  • Shipping weight - 9 kg (20 lb)

Model 757 Tungsten Shield/Collimator

  • High density (17 g/cc)
  • Compact
  • Requires special MAC
  • Specify collimator opening
  • Dimensions: 7.7 cm I.D. x 17.8 cm O.D. x 20.3 cm long (3.05 x 7.0 x 8.0 in.)
  • Shipping weight - 85 kg (187 lb)

Model 7415 Detector Lift

  • Accomodates MAC, Big MAC and Cryolectric II
  • Compatible with CANBERRA shields
  • Convenient and safe operation

Model 717 Portable Detector Shield

  • For MAC or Big MAC
  • 89 mm I.D. x 165 mm long (3.5 x 6.5 in.)
  • 25 mm (1.0 in.) thick lead
  • Brass lined-steel jacketed
  • Shipping weight - 34.5 kg (76 lb)

Model 7411 Detector Submarine

  • Accommodates single-port MAC
  • 6 m (20 ft) umbilical hose (longer available)
  • Ballast for fresh or salt water (specify)
  • Body Dimensions - 178 mm diameter x 591 mm long (7 x 23.25 in.)
  • Shipping weight - 20 kg (45 lb)

Model 7412 Annealing Kit

  • Fix radiation damage in situ
  • Includes:
  • Valve operator
  • Temperature controller (115 V ac only)
  • Heating tape or air heater (MAC)
  • Specify cryostat type
  • Shipping weight - 5 kg (11 lb)

Note: Controller subject to change with availability