4-86
The curves show the series resonance resistance, RS, vs. time following a
4 x 104 rad pulse.  Resonators made of swept quartz show no change in RS from the earliest measurement time (1 ms) after exposure, at room temperature.  Large increases in RS (i.e., large decrease in the Q) will stop the oscillation.
Text Box: RS in Ohms
RS in Ohms
14
13
12
11
10
9
8
7
6
5
80
70
60
50
40
30
0.001
0.01
0.1
1.0
10
100
1000
Text Box: Value of Q-1 x 106
Value of Q-1 x 106
Time following exposure (seconds)
32 MHz AT-cut resonators
Preirradiation value RS
(S-26)
(S-25)
C-22
C-7
N-4
N-4   (Natural)                        4.5 x 104 R
C-7   (Unswept synthetic)    4 x 104 R
C-22 (Unswept synthetic)    3.5 x 104 R
S-25   Swept synthetic)        4 x 104 R
S-26   Swept synthetic)        4 x 104 R
Effects of Flash X-rays on RS
   Ionizing radiation changes a crystal oscillator's frequency primarily because of changes the radiation produces in the crystal unit (also see chapter 5).  Under certain conditions, the radiation will also produce an increase in the crystal unit's equivalent series resistance. The resistance increase can be large enough to stop the oscillation when the oscillator is not radiation hardened.
   A high level pulse of ionizing radiation will produce photocurrents in the circuit which result in a momentary cessation of oscillation, independent of the type of quartz used in the resonator.  In oscillators using properly designed oscillator circuitry and resonators made of swept quartz, the oscillator recovers within 15 µs after exposure.
   The energy band gap of quartz is ~9 eV; it is an insulator, however, a pulse of ionizing radiation (x-rays, -rays, high energy particles) creates electrons and holes, and these result in a momentary conductivity that lasts ~5 to 30 ns after the pulse.  In addition, the radiation induced electrons and holes lead to a freeing of interstitial H+, Li+ and Na+ which results in additional conductivity.  The conductivity results in losses, i.e., a drop in the resonator’s Q.


J. C. King and H. H. Sander, "Transient Change in Q and Frequency of AT-Cut Quartz Resonators Following Exposure to Pulse X-Rays," IEEE Trans. Nucl. Sci., NS-20, pp. 117-125, 1973.

R. E. Paradysz, and W. L. Smith, “Crystal Controlled Oscillators for Radiation Environments,” Proc. 27th Ann. Symp. Frequency Control, pp. 120-123, NTIS Accession No. AD-771042, 1973.