Cf252 runs with HPGe

Detector efficiency measurements using a Cf-252 source.

Cf-252 source description

Serial Number: FTC-CFZ-431 Z=98 Mass:A document indicates that on 03/19/1993 the Cf-252 mass was 4.2[math]\mu g[/math]. ( [math]1\mu g[/math] is expected to emit [math]2.3 \times 10^6 n/s[/math])

Half Life= 2.652 years

Neutron fluence:A document indicates that on 03/19/1993 the Cf-252 the neutron rate was measured(?) to be [math]10^{7} n/s[/math]. Based on the mass one would expect [math]4 \times (2.3 \times 10^6 n/s) = 9.2 \times 10^6 n/s[/math].

Neutron energy spectrum (from A.B.Smith et.al, Physics. Rev. Vol 108 #2 pg 411-414, 1957 File:PhysRev108p411957.pdf):

Decay: Cf-252 undergoes alpha decay to Curium (cm-248) 96.9% of the time. The rest of the time it will undergo spontaneous Fission emitting 3.7 neutrons on average per fission.

The Fission Fragment Yield as a function Fission fragment Atomic Number ([math]Z[/math]) and Atomic Mass Number ([math]A[/math]) from Wahl, A., At. Data and Nuc. Data Tab., vol. 39, (1988) .

most likely observable isotopes:

40<Z<45 and 53<Z<58

Previously measured Gamma spec

Fragments to try and observe:

[math]{A \atop Z} X_N[/math] = Ac-228

[math]{214 \atop 83} Bi_{131}[/math] Bi-214

Tl-208

HpGe distribution

Test Run 5603 may be seeing Bi-214 line 1145 keV

HpGe Neutron Damage

I made a page discussing neutron damage to the HPGe detector (Fast_neutron_damage_to_HPGe_Detector) as a function of the total amount of fast neutrons per [math]cm^2[/math] irradiated on the detector face. [math]5 \times 10^6 n/cm^2[/math] is a factor of 10 below the point where damage was first observed in an experiment.

RunPlan

Object: Determine if an HpGe detector can be using to tag neutrons and identify the isotope species parent of the neutron

HpGe Singles measurement

Measure the energy distribution observed by the HpGe detector

Determine optimal neutron shielding between HpGe detector and Cf-252 source

Small Scintillator position

Determine how close the small scintillator can be positioned without having detected neutrons overwhelm detector photons. Want to be sure the small scintillator is detecting photons most of the time

Determine timing resolution of HpGe Detector

Below is a time difference plot of coincidence 511 keV photons from Na-22. The Na-22 source is 3" from both the timing scintillator and the HPGe detector. The following photon energy cut is applied: 508 < erg < 514. All coincidence events disappear if the source is removed, so there are virtually no accidentals. (run 5736).

search for fission fragment gammas

I completed a run with the CF252 source where all events were 3-fold coinc between the HPGe detector, a small timing scintillator nearby the source, and a hit in at least one neutron detector (run 5743). Neutrons were then discriminated in software by ToF, which is made possible by means of the timing scintillator.

I compared the photon energies of events with a neutron hit, to energies from a non-coincidence background subtracted CF252 spectrum (runs 5775 & 5773). I made a histogram for both cases and normalized the integrals to unity in oder to allow me to search for gammas that occur overwhelmingly when a neutron is coincident. I failed to see any pronounced energies occurring only when in coincidence with a neutron.

Runlist

12/29/16

No poly was used to shield the HPGe detector.

Run #	RunTime [sec]	distance[cm]	n flux [math][\frac{n}{cm^2}][/math] [math]=\frac{n_{rate}t}{4\pi d^2}[/math] (Cf252 rates)	Integral n flux [math][\frac{n}{cm^2}] [/math]	configuration	notes
5609	4060	30	6850	6850	Cf252 in. Coincidence between HPGe and timing PMT	A ToF spectrum exists but is very hectic. Problem may be that the TDC stop is determined by a widened timing PMT pulse in coinc. with a HPGe pulse that has high timing jitter.
none	1250	26	2800	9655	Not taking data during this time.
5611	2509	30	4230	13885	Cf252 in. Coincidence between HPGe and timing PMT. TDC stop was changed to always be 1200 ns after PMT timing pulse, otherwise same setup as 5609.	ToF looks good. Neutron rate approx. 3 Hz for detector 90.
5613	10025	15	0	13885	Na-22 source. Coincidence between HPGe and timing PMT	Calibration
5614	654	15	0	13885	Co-60 source. Coincidence between HPGe and timing PMT	Calibration
Total n flux: 13885 n/cm^2

01/01/17

CF-252 source is kept at a fixed distance while the thickness of poly between src and HPGe is increased by increments of 2".

Run #	RunTime [sec]	distance[cm]	n flux [math][\frac{n}{cm^2}][/math] [math]=\frac{n_{rate}t}{4\pi d^2}[/math] (Cf252 rates)	Integral n flux [math][\frac{n}{cm^2}] [/math]	configuration	num events	notes
5633	372	49	235	235	No poly.	303,929
5634	371		235	470	2" poly.	250,495
5635	371		235	705	4" poly.	202,942
5637	397		256	956	6" poly.	181,667
5638	371		235	1190	8" poly.	147,801
5639	371		235	1425	10" poly.	134,095
5641	110	-	-	-	--		CO-60 + Na-22 cal. run
5642	291	-	-	-	--		background run

01/12/17 - 01/18/17

Discriminator threshold for timing PMT, neutron PMT's, and HPGE are 50, 35, & 70 mV, respectively. When calculating neutron flux I reduced the result by factor of 4 because of the 4" of poly shielding the HPGe detector.

Run #	RunTime [sec]	distance[cm]	n flux [math][\frac{n}{cm^2}][/math] [math]=\frac{n_{rate}t}{4\pi d^2}[/math] (Cf252 rates)	Integral n flux [math][\frac{n}{cm^2}] [/math]	configuration	notes
5743	57515	10	218000	218000	CF252 src. 4" Poly. 3-fold coincidence between timing scint., HPGe, and at least one neutron PMT.	-
5766	1546		6000	224000	CF252 src. 4" Poly. 2-fold coincidence between timing scint and HPGe	-
5773	780		3000	227000	CF252 src. 4" Poly. no coincidence	-
5775	780	N/A	0	227000	No src. 4" Poly. no coincidence	Background run
5769	21097	10			Na-22. 4" Poly. 2-fold coincidence between timing scint and HPGe	Na-22 calibration run
5770	1211				C0-60. 4" Poly. 2-fold coincidence between timing scint and HPGe	Co-22 calibration run

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