No heavy-ion residues (e.g. Hf) recorded in USDRAW with icode = 300 for low-energy neutron-induced reactions on W

Scoring
1

Dear FLUKA experts,

I am investigating the heavy residues produced by low-energy (eV–keV) neutron bombardment of a thick tungsten target.

In mgdraw.f I activate the USDRAW entry and filter on icode = 300 (heavy ion in the bank). The heavy-ion properties are read from the fheavy.inc include file.
pka.flair (4.8 KB)
mgdraw_empty.f (10.2 KB)

Despite the well-known fact that neutron capture on W followed by β-decay chains populates nuclides such as ¹⁷⁸Hf, ¹⁸¹Ta, etc., the only heavy-ion entries I obtain are excited or ground-state W isotopes (A = 182–186, Z = 74). No fragments with Z < 74 are ever present in the particle bank.

Could you please clarify:

  1. Does FLUKA transport the β-decay daughters (Hf, Ta, …) as heavy ions in the same event, or are they only accounted for in the off-line activation module (RESNUCLIDE, DCYSCORE) and therefore absent from the bank filled at icode = 300?

  2. Is icode = 300 restricted to primary heavy ions and direct reaction fragments, so that decay products are either not banked or tracked separately?

  3. If so, what is the recommended way to extract, on an event-by-event basis, the identity, momentum and space-time coordinates of every heavy residue including those originating from radioactive decay?

Any guidance or reference to the relevant manual sections would be highly appreciated.

Best regards,
Yingming

2

As written in the USDRAW header, radioactive decay products can be found with ICODE=110, provided that radioactive decay has been enabled (on-line, not off-line) by RADDECAY.

3

Dear Francesco,

But the spectrum I’m dealing with involves low-energy neutrons; theoretically, shouldn’t I only use codes of the ICODE=3× type? Is it permissible to use code with ICODE=110 instead?

Thank you in advance.

Best regards

4

Dear Yingming,

not instead, rather in addition: with ICODE=300, you intercept the products of the nuclear interaction induced by a low-energy neutron, then the subsequent radioactive decay of the residual nucleus is an independent process - triggered by RADDECAY - that is no longer linked to the original neutron and that you can intercept with ICODE=110.