Radioactive decay based stable time or frequency reference signal source

• US 7,476,865 B2
• Filed: 05/11/2006
• Issued: 01/13/2009
• Est. Priority Date: 05/12/2005
• Status: Expired due to Fees

• Current Assignee: Cornell Research Foundation Incorporated (Cornell University)
• Original Assignee: Cornell Research Foundation Incorporated (Cornell University)
• Inventors: Lal, Amit, Li, Hui, Guo, Hang, Radhakrishnan, Shankar
• Primary Examiner(s): Porta; David P
• Assistant Examiner(s): Baker; David S
• Application Number:
  US11/431,506
• Publication Number:
  US 20060255281A1
• Time in Patent Office: 978 Days
• Field of Search: 250/370.11, 250/252.1, 368/155, 368/156
• US Class Current: 250/370.11
• CPC Class Codes: G01T 1/171 Compensation of dead-time counting losses see provisionally also G01T1/17
• CPC Class Codes: G04F 5/16 using pulses produced by radio-isotopes

Abstract

A signal source for use as a frequency source or time keeping signal source includes a radioactive emission source generating a substantially periodic signal corresponding to a radioactive material'"'"'s disintegration rate. A radioactive emission detector generates a radioactive emission detection signal and, to stabilize the detected periodic signal, a dead time controlling attenuator blanks or shuts off the radioactive emission detection signal for a selected dead time interval in response to each detected radioactive emission (i.e., a detected signal pulse or signal component) generated by the source. The dead time controlling attenuator output provides a long-term and short-term a stable periodic signal.

Claims

1. A signal source generating a stable periodic signal, for use as a frequency source or time keeping signal source, comprising:

a radioactive emission source generating a first signal corresponding to a selected radioactive material'"'"'s disintegration rate;

a detector responsive to said first signal, generating a radioactive emission detection signal in response to said first signal; and

a dead time controlling attenuator responsive to said radioactive emission detection signal, attenuating said radioactive emission detection signal for a selected dead time interval in response to a periodic radioactive emission detection signal component;

wherein said dead time controlling attenuator output comprises a stable radioactive emission periodic signal.

2. The signal source of claim 1, further comprising:

an adjustable oscillator generating a second signal, said second signal having a controllable period or frequency;

a comparison circuit responsive to said stable radioactive emission periodic signal and to said second signal, generating a control signal in response thereto; and

wherein said adjustable oscillator controls said second signal'"'"'s period or frequency in response to said comparison circuit'"'"'s control signal.

3. The signal source of claim 2, wherein said comparison circuit comprises:

a first counter responsive to said stable radioactive emission periodic signal and generating a first counter signal in response thereto; and

a second counter responsive to said adjustable oscillator'"'"'s second signal and generating a second counter signal in response thereto.

4. The signal source of claim 3, wherein said second counter signal is subtracted from said first counter signal to generate an error signal.

5. The signal source of claim 4, wherein said comparison circuit further comprises a feedback control circuit responsive to said error signal, generating said control signal in response thereto.

6. The signal source of claim 3, further comprising an up-down counter having an up-count input responsive to one of said first counter signal and second counter signal and having a down-count input responsive to the other of said first counter signal and second counter signal, said up-down counter generating an up-down error signal in response thereto.

7. The signal source of claim 6, wherein said comparison circuit further comprises a feedback control circuit responsive to said up-down error signal, generating said control signal in response thereto.

8. The signal source of claim 1, wherein said selected radioactive material comprises a beta emitter.

9. The signal source of claim 8, wherein said selected radioactive material comprises Ni⁶³.

10. The signal source of claim 9, wherein said selected radioactive material comprises a thin film of Ni⁶³ on a substrate.

11. The signal source of claim 9, wherein said selected radioactive material comprises a thin film of Ni⁶³ electroplated on a substrate to have activity approximating 25mCi/cm² of area.

12. The signal source of claim 8, wherein said selected radioactive material comprises Tritium.

13. The signal source of claim 1, wherein said a detector for generating said radioactive emission detection signal in response to said first signal comprises:

an avalanche photo detector biased to detect said emission source'"'"'s first signal and generating a beta decay signal in response thereto;

a charge sensitive amplifier responsive to said beta decay signal and generating an amplified signal in response thereto;

a shaping amplifier responsive to said amplified signal and generating a shaped signal in response thereto; and

a buffer stage responsive to said shaped signal and generating said radioactive emission detection signal in response thereto.

14. A reference signal source comprising a radioactive emission source generating a substantially periodic signal corresponding to a selected radioactive material'"'"'s disintegration or decay rate, and a detector responsive to said radioactive emission, said detector generating a stable periodic signal, for use as a frequency source or time keeping reference signal source;

and

further comprising a dead time controlling attenuator responsive to said radioactive emission, attenuating the detector'"'"'s signal for a selected dead time interval in response to a periodic radioactive emission detection signal;

wherein said dead time controlling attenuator output comprises a stable radioactive emission periodic signal.

15. The reference signal source of claim 14, further comprising a an adjustable oscillator generating a second signal, said second signal having a controllable period or frequency;

a comparison circuit responsive to said stable radioactive emission periodic signal and to said second signal, generating a control signal in response thereto; and

wherein said adjustable oscillator controls said second signal'"'"'s period or frequency in response to said comparison circuit'"'"'s control signal.

16. The reference signal source of claim 15, wherein said comparison circuit comprises:

a first counter responsive to said stable radioactive emission periodic signal and generating a first counter signal in response thereto; and

a second counter responsive to said adjustable oscillator'"'"'s second signal and generating a second counter signal in response thereto;

wherein said second counter signal is subtracted from said first counter signal to generate an error signal; and

wherein said comparison circuit further comprises a feedback control circuit responsive to said error signal, generating said control signal in response thereto.

17. A method for generating a stable periodic signal for use as a frequency source or time keeping signal source, comprising the method steps of:

(a) providing a radioactive emission source generating a first signal corresponding to a selected radioactive material'"'"'s disintegration rate;

(b) providing a detector responsive to said first signal. generating a radioactive emission detection signal in response to said first signal; and

(c) providing a dead time controlling attenuator responsive to said radioactive emission detection signal; and

(d) attenuating said radioactive emission detection signal for a selected dead time interval in response to a periodic radioactive emission detection signal component;

wherein said dead time controlling attenuator output comprises a stable radioactive emission periodic signal.