Beta-X Cooled Spectrometer

BETA-X Cooled Spectrometer betax.jpg (25947 bytes)

Excellent spectroscopy for up to 2-MeV electrons and 20-keV x rays
4-1/2-in. ConFlat^® flange permits insertion of a source or connection to a beam tube
Contains reliable 10-mm diameter, 5-mm thick Si(Li) device
Room temperature storage
High-voltage shutoff protection

When conversion electron spectroscopy or determination of a beta decay end point is the objective, room temperature silicon detectors are often unsatisfactory because of their relatively high noise level (an 80-mm² detector has about 7 keV FWHM noise). To minimize the noise, both the detector and the first stage of the preamplifier must be cooled. Considerable expertise is required to deal with the subtle technologies involved.

The problems are solved with ORTEC's cooled BETA-X Spectrometer. It contains a 10-mm diameter, 5-mm deep Si(Li) detector coupled to a noise-optimized cryogenic electronic front end. An easy-to-operate valve gives access to the cryostat vacuum. The front flange can be opened for connection to an experiment chamber or a beam tube. A beryllium window in the front flange makes the BETA-X Spectrometer a useful tool for x-ray spectroscopy (Fig. 1) and permits measuring noise and x-ray resolution without opening the front flange.

For electron spectroscopy at low to ultra-high counting rate energy products (up to 4,000 MeV/s) choose Model SLB-10490; however, only modest resolution is available when used for x rays.

Using the BETA-X Spectrometer requires familiarity with vacuum equipment. The vacuum system must be absolutely oil free (via a well trapped diffusion pump or a cryogenic pump) and should provide a vacuum of 10^–5 torr or better. Because the detector responds to light of any frequency, there must be no light leaks.

The electron energy resolution is limited, at low energies, by the thickness of the entrance contact on the Si(Li) detector (equivalent to approximately 2000 Å of silicon) and, at high energies, by the thickness and density of the material supporting the source and any source window thickness.

Beta and electron spectroscopy is feasible from 20 keV to 3 MeV.

Each model of the BETA-X is equipped with a pulsed optical feedback (POF) cryogenic streamline preamplifier and high-voltage filter combination optimized for the specific application. This includes high-voltage shutoff to protect the detector from FET failures.

REFERENCES

1. C.T. Prevo and J.L. Cate, "A Practical Solid State Beta Spectrometer," Nucl. Instrum. Methods 55, 173–176 (1967).

2. R.E. Wood, P. Venugapala Rao, O.H. Puckett, and J.M. Palms, "Si(Li) Spectrometers for Electrons and Low Energy Photons," Nucl. Instrum. Methods 94, 245–252 (1971).

3. I. Amad and F. Wagner, "A Simple Cooled Si(Li) Electron Spectrometer," Nucl. Instrum. Methods 116, 465–469 (1974).

ORDERING INFORMATION

Model		Description
SLB-10490		BETA-X Spectrometer
CFG-B-SH		Pumpable SH Cryostat with End Cap Flange
DWR-B-30		30-Liter Dewar

Table 1.
Radiation
Type	Energy (keV)	Warranted Energy Resolution (eV) FWHM	Max. Energy Rate (MeV/s)	Max. Single Pulse Energy (MeV)
⁵⁵Fe X-Ray	5.9	490	130,000	10
⁵⁷Co Conversion Electrons	115	1000	130,000	10
²⁰⁷Bi Conversion Electrons	976	3500*	130,000	10
* This figure was obtained with a source depostied on aluminum, causing peak broadening due to backscattering. It is expected that with an accelerator beam or with conversion electrons from a thin source, the energy resolution will be ~2 keV FWHM at 1 MeV.

betax_fig1.jpg (54737 bytes)

Fig. 1. Si(Li) Electron and X-Ray Spectrometer. Cryostat and Dewar dimensions are subject to change. If these specifications are critical to your application, please contact the factory.